Street Touring / Track Day Tire FAQ - UTQG 140+ by Hollis

[jev61]

I read this on Andy Hollis' Facebook page and thought many would find it helpful or at least interesting. If I've violated a site rule repeating someone else's words, let me know and I'll delete this. Joe


Street Touring and Track Day Tire FAQ - UTQG 140+
by Hollis Racing on Saturday, March 10, 2012 at 2:19pm •
http://www.facebook.com/notes/hollis-ra ... 8598916447

[This note brings together information that we are constantly asked about, and will hopefully serve as an FAQ that we can simply link to going forward. Let us know if you find anything in error, or if there are questions. We'll do our best to answer.]

Who cares about street tires?
A key part of the popularity of the Street Touring category in autocross has been the requirement that tires be designed for normal highway street use, with a UTQG tread wear rating of at least 140. This requirement has also been adopted by some track day groups (e.g. One Lap of America) to delineate from r-comps. This typically lowers the per-event cost of competing, which also makes for more cost-effective practice and development testing. In addition to increasing the fun factor, this allows for more highly developed cars and deeper fields, as resources can be spent in other places.. One final benefit, is that the lower grip levels afforded by these tires versus the typical r-comps and slicks, makes driving on them more of a challenge.

The downside of street tires is that the marketplace is constantly evolving, since these are consumer-oriented products, not bespoke racing tires. So it becomes difficult to know the traits of all the best tires without constant testing, which is a never-ending challenge and costs a lot of time and money. You also have to be aware of what's on the horizon, and there's always something new coming.

Why do my ST tires overheat/need heat? Why can't I get the size I need?
Contrary to popular belief, autocrossers are not a large enough market to support development of tires exclusively for our sport (outside of r-comps made by low volume, specialty tire makers). That said, tires are often marketed using reference to autocross and successes therein, but this is mostly a "win on Sunday, sell on Monday" approach. The design engineers are focused on real street use. As a result, the tires we find to be the most competitive often have a variety of side-effects when used outside their intended design parameters. Some will overheat easily, while others don't grip all that much until they get heat in them. Some have squishy sidewalls that allow them to be run at large slip angles with progressive breakaway, while others are stiff and responsive, yet also edgy.

Another key ingredient in choosing a street tire for autocross is fitment. Since tire makers are targeting these products for specific vehicle applications, not all tire models have good sizes to fit all vehicles. You may have to sacrifice gearing to get width or vice versa. In addition, within a specific model, variations in belt packages and even tread compounding are common. Indications of this are many times found in speed/load ratings, and also the sidewall belt listings. Also, compounds and constructions may undergo running changes, so what holds true for a tire today, may not for future batches. Learning to read build dates is important, as well as keeping your ear to the ground for the rumor mill.

Tests and Other Resources
Before we get into our current recommendations, here's some background reading we find interesting. Some of it is testing we've done while some is from friends of ours (Tire Rack and GRM). These are in reverse chronological order within each grouping.

Grassroots Motorsports Tire Testing articles
GRM Project MX5 dry/wet tire test of Dunlop Z1, Hankook R-S3, Bridgestone RE-11, Kumho XS, Yokohama AD08 & Toyo R1R.
Summary (Dry): R-S3 (55.7) > AD08 (56.1) > R1R (56.2) > RE-11 (56.2) > Z1 (56.6) > XS 56.8
Summary (Wet): Z1 (62.3) > AD08 (62.5) > R1R (63.2) > R-S3 (63.4) > XS (63.5) > RE-11 (62.9)

Splish-Splash
http://grassrootsmotorsports.com/articl ... sh-splash/" onclick="window.open(this.href);return false;
Wet weather testing on the GRM Project MX5 by the Tire Rack.
Summary: Conti DW > Toyo R1R > Dunlop Z1

Top Tires
http://grassrootsmotorsports.com/articles/top-tires/" onclick="window.open(this.href);return false;
Dry autocross and track testing of shaved Hankook R-S3, Kumho XS, Falken RT-615K, Dunlop Z1
Summary: R-S3 > XS > Z1 > RT615K

**Non-published extra: Since we had already previously tested the R1R (205/50-15), GRM did not wish to include the 195 R1R in this test. Same with the AD08's we had remaining. Still, as competitors we were curious...so we tested them anyway, and did not publish the data...until now.

The AD08 served as our warm-up tire to get the hang of the course and we put down a 43.308 best and 43.387 average. After the magazine test was complete, including the re-test of the XS, we put on the R1R and laid down a best lap of 42.672 and average of 42.898. Since that was better than the R-S3 that had "won" the magazine test, we wanted to verify back-to-back: we put the R-S3 back on and got 42.747 best with 42.869 average. So the two were similar on average, though the R1R could lay down a single flyer. Finally, to bracket the whole day we put the AD08 on and turned 42.799 best and 42.831 average.

Bottom line...none of these tires is bad. They all have different strengths and weaknesses. But the R-S3 and R1R were a tad stronger than the rest...shaved, on concrete, on a light car, on a temperate day.

Texas Toasted Tires: Part 1
http://grassrootsmotorsports.com/articl ... es-part-1/" onclick="window.open(this.href);return false;
Spring day test of top tires, shaved and mostly in 205/50-15 on very grippy track. Falken RT-615, Kumho XS, Dunlop Z1 (195), Toyo R1R, Bridgestone RE-01R (195) and RE11.

Summary: XS > RE-01R > RE-11 > R1R > Z1 > RT-615. Note: Knowing what we know today, shaving definitely hurt the R1R and probably the Z1.

Texas Toasted Tires: Part 2
http://grassrootsmotorsports.com/articl ... es-part-2/" onclick="window.open(this.href);return false;
Similar to Part 1, but compares 205/50-15 XS & RE-11 to new Yokohama AD08 and new size of R1R (225/45-15)
Summary: AD08 = XS > RE11 = R1R

Tire Rack Testing
For these, ignore the subjective evaluations and go straight to the objective track test results, particularly Lap Times, but also Slalom and Average Cornering.

Clash of the Titans
http://www.tirerack.com/tires/tests/tes ... p?ttid=148" onclick="window.open(this.href);return false;
Max Performance Summer tires including the Michelin PSS, Continental DW, Bridgestone S-04 & Pirelli P-Zero: Conditions: Dry was done on 85-90 degree day, wet was 60-70
Summary: Dry...PSS > P-0 > DW > S-04 ; Wet: PSS > DW > S-04 > P-0

Testing the New Extremes
http://www.tirerack.com/tires/tests/tes ... p?ttid=118" onclick="window.open(this.href);return false;
Extreme Performance Summer tires with the Bridgestone RE-11, Yokohama AD08, Kumho XS, and Dunlop Z1
Summary: Dry....AD08 > XS > Z1 > RE11...all very close; Wet: 3-way tie, except XS much slower

Other tests
High-Performance Tires Buying Guide
http://www.eurotuner.com/techarticles/e ... ewall.html" onclick="window.open(this.href);return false;

Note: The tests done at the Tire Rack typically use "Manufacturer's Recommended Tire Pressures" for the test vehicle... same pressure for every tire. This may or may not deliver optimal performance in an autocross or track setting for every tire being tested, so the relative performances will be affected. The GRM tests we have done use skid pad testing (see below) to develop specific pressures for each tire on the testing vehicles.

What's "The Best" ST tire for me?
Sorry to say, but there is no one right answer. It really depends on what sort of usage the tire will see. Weather (temp and rain), surface type (asphalt versus concrete), course content (transitions versus sweepers), weight of vehicle and drivetrain layout all have major impacts on the decision. That's why you need as much data as possible to help make an optimal decision. It's also why you may wish to consider multiple sets of tires if trying to run at the pointy end of the field. The good news is that there are really no "bad" tires in the bunch. So you can't make the wrong decision, just maybe one that isn't quite as optimal for your situation.

Toyo Proxes R1R - Let's go right to the jugular with this controversial tire. In a way, it is like the Falken RT-215 that catapulted the ST category to extreme popularity a decade ago. Easy to drive, forgiving, works in a wide variety of temps -- especially cooler ones -- and fits well on the smaller cars that formed the original basis for ST. It is also inexpensive...sorta. The downsides are that the extremely progressive breakaway makes it a challenge to find where the grip level starts to drop off. As a result, the large slip angles developed by overly aggressive driving will literally grind the rubber off the tire. This can be observed as an extreme "graining" pattern across the tread face, eventually wearing out the tire prematurely. In addition, if the vehicle has poor camber control, that wear can be quite uneven, further reducing tire life. All of this leads to debate over validity of the UTQG rating, as some competitors have extreme issues, while others have none.

Another element of the debate is the apparent variation among tire sizes in the depth to which the surface compound extends (relative to the tread voids), versus the underlying support layer of rubber that encases the belt package and sidewalls. The support layer's purpose is to hold together the tire's infrastructure, not grip the road, so when tread wears down to its level, grip drops off significantly. Most people have seen the joint where this underlay meets the surface compound right at the sidewall junction. That same "joint" exists between the two layers deep within the surface of the tire tread. Within the R1R model line, there is anecdotal evidence that the 195/50-15 size has the "good stuff" all the way to the bottom of the tread voids, while other commonly used sizes do not. In the latter sizes, the tires lose grip somewhere in the vicinity of 3-4/32nds of remaining void. This has led to the "magic size" moniker often applied to the 195 R1R. That said, it is quite possible that more sizes feature the "good to the last drop" feature of the 195/50, but they aren't sizes that optimally fit the vehicles at the tops of the ST classes so nobody has any data. As mentioned earlier, looking carefully at the variance in speed ratings across the line may give hints.

The variance in the depth of the underlay is most likely due to the varying load requirements of the application vehicles each tire size is designed for. Tire performance is not linear, so a tire that is twice as big does not deliver twice the load capability. Variances within a tire model are sometimes made in both construction and compound to support this. Some tire models even have two versions of a tire with two separate load/speed ratings in the exact same size. As mentioned earlier in this note, these are tires made for the street and the tiremakers design considerations don't always align with best use for autocrossing. Street tires are considered by their manufacturers to be "worn out" when the tread reaches the a depth of 3-4/32nds, so changes to tread rubber at those depths should have no adverse effect for the tire's intended street use. The fact that some tires still work well until the tread disappears is simply a bonus, not a requirement.

As an aside, some tiremakers use dual compounds for exactly the opposite situation. As rubber ages, the vulcanization process continues which makes the tire grip less. Bridgestone uses a dual compound to expose fresh rubber that is softer as the tire wears so as to give more consistent performance across the tire's life time. They call this technology UNI-T.

But back to the R1R...This tire shines in cooler weather, but can easily overheat if not cooled off between runs on warmer days. In the 195/50 size, this can be moderated through shaving to 3/32nds or so. Other sizes are limited to starting at full-tread and watching for a performance drop-off as the tire nears the 4/32nds level. Given the temperature profile, this makes for a great wet weather tire, as the water will continually cool the tire to optimal levels. At full tread, the tread design is sufficient to channel water very well, but can't handle really deep puddling. These tires like low pressures and we run cold pressures of around 25 psi for optimal grip. The tire may feel better at higher pressures, but it doesn't grip as well.

Edit: Here's another thought on the wear issue:
As mentioned earlier, tire designs are not linear in performance across a model's size range, especially the compounding. A tire that is 30% wider doesn't give 30% more grip or support 30% more load. So when a heavier car is put on larger tires, they are less efficient and having to work harder. Thus, tire wear is worse on a relative basis. You get some of that back by dividing the extra load across more tire, but not all of it. It's a lot like weight transfer where the inefficiency of the load transfer is why you avoid it. Given that the R1R was originally only available in smaller sizes, it seems to have been designed around lighter cars initially. So that is where it is most efficient, both in performance and longevity.

Hankook Ventus R-S3 is the other big heavy hitter. This one is the polar opposite of the R1R. It has a stiffer sidewall for responsive handling and much more heat tolerant compounding. In fact, it needs significant heat to develop optimal grip. This can be a challenge on a cool day, or for a car that loads the tires hard on only one end of the vehicle. It also means that the cooling effect of rain water limits its foul weather performance. This tire has limited available sizing, though one key size is the 225/45-15 that is a 23" tall tire with a 225 section width. That is perfect for many cars in STF, and STC, and STS. In addition to a stellar autocrosser on bigger cars, the tire's heat profile makes it ideal for track day use.

Optimal tire pressure on this one depends a lot on the rim/tire combo. For example, when the 225/45-15 is put on a 9" rim, you can effectively run pressures between 28-32 psi for best performance. But on a 7.5" rim, you need upwards of 40 lbs or the tire is slower. On 8's, we run 33.

Dunlop Direzza Z1 Star Spec has one of the largest ranges of available sizes, including some 14". It is the "jack of all trades" tire, producing performance near the top in almost all conditions. It tolerates heat well with only slight loss of performance as it gets hot. It also works well in cooler temps, needing little heat for optimal grip. Combine this with a V-shaped tread design and full-tread examples work well in the rain. In short, if you need one tire to do it all, this could be the one. Reports are that the Dunlop exhibits the same dual compound grip loss as the R1R once you get to the 3-4 32nds level, so keep that in mind if considering shaving. This one seems to like more air and we found 40 psi was best.

Yokohama's AD08 is another solid performer that comes in a wide range of sizes. Like the R-S3, it tolerates heat well enough to be strong on the track but needs some warming up to work well on an autocross course. The carcass is remarkably responsive and the tire transitions better than any other we've driven since the venerable Falken RT-215. Given the heat profile, grip is a little lacking in the wet, but the tire is still better there than the R-S3. Also, the responsiveness makes it less confidence-inspiring once the rains come. This is another really good track day tire, especially if your size is not available in the R-S3. This tire has a wide range of pressures across which it delivers similar performance (28-36 psi)

Bridgestone's Potenza RE-11 was once the top dog, but has been surpassed. Like the Dunlop, it is a great all-around tire, though a bit softer than the Z1. As such, it isn't the best choice for track days in warm weather, but is a great all-around tire for autocross and street use. This one likes more air, and our tests showed 42-50 gave similar performance, with a sweet spot at 46.

Falken has been a player in this category since the beginning. Its latest tire, the RT-615K is a lot like the R1R in its temperature profile, operating well in cooler temps. It does overheat quite easily, but doesn't fall off quite as much as the R1R when it does. Even more air is needed here than the others. 44 was our pressure number.

Kumho XS is a great choice for warm, dry weather. Like the R-S3, it does need some heat to build grip, but delivers responsive performance. Given that, it works realyl well on the track during the summer months. We use these on the front of our track CRX during the hot Texas summers. 36 psi is a good starting cold pressure, warming to 39.

Wet/cool weather tires
All of the above are in the industry's Extreme Performance Summer tire category. The next category down in performance (theoretically) is Max Performance Summer tires. These are a bit more of a compromise, giving up a little in warm/dry performance to provide a more versatile tire. In particular, the tread designs have larger circumferential voids for channeling deep water, and the compounds work well in a wider range of temps. That makes them typically better in the wet and cold than the Extreme tires listed above. Two tires of note are listed below.

Continental has wet performance figured out and continues to deliver great foul-weather performance tires. The ExtremeContact DW is their latest and greatest, delivering amazing performance in cooler temps and/or wet weather, while working at the 90% level in the warm/dry. We use these on our track car (OneLapCRX.com) for cool and/or wet days, and also as street daily drivers. In one test, we found them to be the equal of the R-S3 on a 45-degree day at the track, and only a second or two slower at the same ambients in the rain (Barber Motorsports Park). On a warm 60-70 degree day, however, they were 1.7 seconds slower than the R-S3. Due to availability, the sizes used in this testing were 205/45-16 on 7.5" rims and 225/45-15 R-S3 on 9" rims. In another wet test we did (45 degrees, rain Harris Hill ROad), the DW was 2 seconds a lap faster than a 205/50-15 Dunlop on an 8" rim. By comparison, the R-S3 was virtually undriveable in those conditions.

The new Max Performance schnizzle is the Michelin Pilot Super Sport. The successor to the PS2, this tire shines in similar circumstances to the DW, but at a higher performance level. Unfortunately, it is only available in larger sizes, so small cars will have to look elsewhere. This tire has become the one to have for One Lap of America competition, taking the top spots for both wet and dry skid pad competition, as well as top performance on the track. In short, it is a great all-around tire for both street and track use...assuming they fit.

The future:
Looking back on this category, a new top dog seems to emerge every 3-4 years, sometimes sooner. Over the past decade the following progression has been seen: Michelin Pilot MXXV=>Falken RT-215=>Falken RT-615=>Bridgestone RE-01R=>Bridgestone RE-11/Dunlop Z1=>Toyo R1R/Hankook R-S3. Given that the status quo has remained for a solid 4 years, we are on the cusp of a refresh for several of the top dogs. We have solid knowledge of two of these, and rumors of another. In short, expect 2013 to be the beginning of the next wave of hot new street tires. Everything appears to be poised for a major upheaval. Hang on!

What do you guys run?
On our ST Civic, we used to run both the R-S3 and R1R on the front, swapping depending on how hot of a day it was, with R1R always on the rear. But that became a PITA, and Hankook never delivered on their promised contingency program. So we went with Toyos all around. We'll be doing the same for our STF Mazda 2 we are working on

For track use (OneLapCRX), we mostly use the R-S3 in the warm and dry, which is pretty much most of the year here in central Texas. On colder days, we'll stick a pair of R1R's or Falken RT-615K's on the rear of the car since they need no heat to work. And if it's really cold, we'll run the Conti DW all around.

For the wet, we are running Toyos autocross. Why? Contingency. And consistency. It is rare to have all three runs at a big event in exactly the same sort of wet condition. At least one of them is usually drier than the others. And I'd rather switch between full and shaved tires that are the same. The Toyo is hard enough to drive at the limit as it is.

For the track in the wet, we use the DW for much the same reason. As it gets drier, that tire still works whereas the R1R turns to mush. Plus, the R1R is not nearly as good at track speeds in active rain since it doesn't evacuate water that well. Hydroplaning is related to speed.

Where's the best place to buy, shave?
If you are buying full-tread tires, you can pretty much shop based on price (including shipping), service, and availability. We also buy based on loyalty.

Tirerack.com (Hankook, Yokohama, Bridgestone, Dunlop, Continental, Michelin) Tire Rack supports motorsports, so we support the Tire Rack...and we list them first. Their shaving is also first-rate, though they will typically not go below 4/32nds. We love the ability to check stock at all locations for best shipping time and cost.

DiscountTireDirect.com (Hankook, Yokohama, Bridgestone, Dunlop, Continental, Michelin) Great pricing and service. But they'll charge you sales tax if there is a Discount store in your area. Beat the system by taking the DTD price to your local store and have them match it (usually they will).

Treadzone.com (Hankook, Toyo) These guys have long been the go-to folks for the Spec Miata crowd, so they really know how to shave tires. Also, Joe keeps a lot of R1R's in stock, so your tires get sent quicker than with other outlets. Their shipping prices are on the high side, though.

Tiresdirect.net (Toyo) These guys are internet darlings due to pricing. Nobody will sell for less, especially when yo consider shipping. And now they will shave, as well. That said, we personally do not like their shaving on the R1R, as they do it too square (thick at the sides) and the tire gets mushier than it needs to be. Also, they tend not to stock some of the more popular R1R sizes in large quantity, so you often have to wait a week before they even get shipped.

Vilven - These guys will sell you tires, but mostly we use them for shaving and they do a killer job. They've been shaving tires for decades and have it down to a science. Rates are good and service is quick.

Why doesn't Tire Rack carry the entire Toyo line?
The Tire Rack is a great supporter of SCCA Solo, BMWCCA, and the One Lap of America so we like to do business with them. But the only Toyo products they sell are OE replacement fitments, which seems really odd when Toyo makes so many tire models used heavily in motorsports.

The answer has to do with Toyo's old school distribution/retail system. They still do it with territories and since Tire Rack sells everywhere, they'd be in someone else's playground almost all the time. And even that wouldn't be so bad except for Les Schwab which is big and bad ass out west. They are the 500-lb gorilla that keeps TR out of the aftermarket Toyo business.

That said, the competition tire portion of Toyo's business is a little less strict. Otherwise, places like Treadzone wouldn't be able to do business via mail order. But it's more of a "look the other way" thing on Toyo's part. Mostly because normal retail outlets don't stock competition tires. The R1R model straddles the line and can usually be bought from either type of outlet.

Why does the Hankook R-S3 seem to go on backorder so often?
Hankook uses an antiquated system for ordering and shipping from overseas to the US. They pretty much build the tires, stick them in a container and when they arrive and make it through customs, their local warehouse guys look and see what they received. Orders are then filled from that stock. But nobody really knows for sure what's in each container so the US retailers can't be very definitive when they give expected shipment dates, unless they have tires in stock. Also, Hankook builds in big batches, so tires will be plentiful for awhile and then dry up all of a sudden. The big retailers like Tire Rack are typically first in line for new stock, and have developed a decent sense of what tends to come in each container, but it's still just guesswork.

Optimal wheel size
Many folks entering the ST category are refugees from Stock looking to make some performance upgrades to their car and/or reduce their tire budget. Unfortunately, they carry with them some baggage on concepts that may work well in Stock, but not in ST. One of these is optimal wheel/tire fitment.

Since Stock limits you to the OE wheel sizing, astute competitors have learned how to stuff increasingly wider tires onto those skinny rims. And tire makers have been happy to make wider and wider tires, likewise charging more and more money. But, is wider better? In Stock, the answer is often "yes". The sidewalls on these DOT-approved "Not for Highway Use" R-comps are super stiff and allow for "overtiring" much in the way that a cantilever style slick works to get around wheel width limitations for formula cars.

In ST, drivers in most classes have limits on both wheel width and tire section width, both of which are much wider than OE. The tendency is to cram the widest legal tire on the widest legal rim that will fit and go for it. But that is not always the optimal solution, as street tires do not have the same super-stiff sidewalls as do the best R-comps. Sometimes it makes sense to run a narrower tire for a given rim fitment. From the testing we've done, we find that a good rule of thumb is that the optimal rim is the same size (rounded up to the nearest half-inch or so) as the tread width (not section width!). So a 205/50-15 tire with a typical tread width of 7.5" is best on 7.5" rim. An 8" rim will work, too, but it will be majorly stretched on a 9. Likewise, it will lose some performance on a 7, and will lose a LOT going down to a 6 or 6.5. Similarly, a 225/45-15 with an 8.2" tread width works best on at least an 8.5" rim and loses a fair bit on a 7.5".

A practical example of this is in STC, STF and STS where the rim limitation of 7.5" keeps the 195/50-15 Toyo R1R at the top despite it not being the widest allowed tire size. The 225/45-15 R-S3 mounted on that same 7.5" rim is not quite as fast. But put that same R-S3 on an 8 and it comes alive. And it's even better on something a bit bigger. So in STR, where wider rims are allowed, the common 225 R-S3 on 9's is a faster combo than the 195 R1R on a 7.5 (assuming nominal weather). And putting the 195 on an 8 or wider does nothing to enhance performance and close the gap.

Non-Square setups
As you've seen, each tire model has strengths and weaknesses. Now look at your car, is the front the same as the rear? For RWD, the front steers and the rear has to put power down. So a responsive tire on the front would be good, and one with good longitudinal grip would do well on the rear. Are you one of the few whose car has a 50/50 weight distribution? If so, your tires will likely heat up at the same rate. For the rest of you, one end will warm up faster than the other. Now, think about the various available tires and you can see how the balance of the car would change dynamically as each end gained (or lost) grip at a different rate.

So then, why does everyone run the same tire model at all four corners? Contingency programs are one reason, and that's why we've done it the past couple of years. Ability to rotate is another, but that can even itself out over time.

As you can see from the section about on our personal usage, we are huge fans of different tires at each end of the car. Of course, that pretty much quadruples the testing needed if you want to try out all combinations, so there is that one small drawback. Still, some combinations should be obvious just by the subjective test data listed above (words, not numbers). The turning point for God's Chariot (88-91 CRX and Civic Si) in performance relative to others classes came when the Toyo R1R came out. And not because of the front of the car, but because of the rear. Here you had a tire that would work immediately, so the car could be setup with a lot of roll stiffness to the rear, making it a slalom-eating machine, and adding better corner exit power-down. The Falken RT-615K is very similar in its ability to do so. And for cars that are heavy on the nose, the Kumho XS and Hankook R-S3 love the heat the extra weight generates. And the Yokohama AD08 is the most responsive tire out there. Lots to consider here.

We'd like to see some RWD folks try out combos. In particular, an MX5 with R1R's on the rear and R-S3's on the front might just be the killer combination to get better gearing, better and more progressive power-down, but nice directional control and heat tolerance on the nose.

Size is yet another way to make a non-square setup work. On colder days, a narrow tire will heat up faster. And if less weight is on that end of the car, less tire width is needed. Finally, tread depth can also be staggered with more on the light end of the car to even out temperature gain during a lap. Deeper tread also tends to launch better...we've done one tenth faster 60-foot times with 4/32nd R1Rs versus 2/32nds.

Soft versus Sticky
Softer is better, right? Not always.

Tires develop grip through several mechanisms. One of them is softness, which allows for some level of mechanical interlock with the racing surface at the molecular level. But there is also adhesive grip, which is the trademark "stickiness" of an r-comp or racing slick, which usually increases as the tire gets warm and gooey. This is one of the key differences between street tires and r-comps. And finally, there is grip that comes from abrasion or tearing/wear. This is what creates the marbles that are typically seen outside of the racing line on a track. Paul Haney's book, "The Racing and High Performance Tire" describes these mechanisms.

Tire compounding is as much black art as it is science. Compounders are like composers, and skilled/successful ones are recruited heavily by tiremakers. And while new technology trends affect the entire industry, what mix each compounder puts into their tires varies quite a bit. Some tires do rely on softness for grip. But increasingly, new materials are allowing for both higher mileage and better stick. The R1R and R-S3 are a study in contrasts on this very point. Likewise, soft isn't always fast. The softest tire we've ever measured was an inexpensive Pep Boys private label tire that we put on our daughter's college beater. Didn't last long, and didn't grip all that well, either. But it sure was soft.

Durometers
When a tire is made, the curing of the rubber is done under extremes of heat and pressure. Much like a steak coming off the grill, this vulcanization process continues even after the tire is removed from the pressure cooker. It does slow down over time, but continues throughout the life of the tire. As such, tires have a shelf life. Tire also have a "born on" date stamped right into the sidewall that can be read to understand how old the rubber is. But other external factors also have an impact on the continued vulcanization, so how a tire is stored makes a difference (bagging a tire is common). And finally, the continued working of the rubber (heat-cycling) will also change the tire permanently.

One tool we've used extensively is a hardness meter known as a durometer. This small handheld device allows you to monitor the rubber's changes over the life of the tire. And on a relative basis, for the same tire, softer usually is better. But hardness readings are incredibly temperature sensitive, so comparison readings must always be taken with tires at the same temperature. We keep tires in a climate controlled public storage facility, which makes it easy. Alternatively, always comparing your "current" set to a fresh set allows the test to be done anywhere, so long as both sets are together.

Technique with the durometer is also important for consistency. It is easy to fool yourself if you don't stick each tire the same way, and multiple times. We've also noticed that shorter tread depths tend to produce harder readings as the plunger of the durometer can't push down as easily when there is little tread depth left.

Despite these challenges, a well-used durometer can be a lifesaver in explaining why you are suddenly moving backwards relative to your competition. It can also be useful in understanding how a particular tire is affected by heat and cold.

Story time: A great example of all this is the ubiquitous 195 R1R. This was the first size of the tire that came out and Toyo must have made a ton of them as the 2007 build dates were still being sold well into 2010. All other sizes were being seen in 2008-2010 dates by then. Finally, mid-year in 2010 the cry went out that the 2007's were all gone and the 2010's were the only thing available. So, was there a difference and if so, was it good or bad? The durometer showed the new tires to be softer than the 3-year old ones. Not surprising, but was this better? Early testing showed that the new tires "went off" earlier in a run and were slower. But this testing was being done in the heat of the summer...would it hold true for cooler temps?

At the Solo Nats in Lincoln that year, we brought sets of both with us, initially running the 2007 tires at the Pro Finale based on our testing. Things weren't going well on the first day, though, so we checked date codes in impound and noticed that everyone in front of us after Saturday's competition was on the 2010's. We put those on for Sunday, moved to within a tenth of the class leader, then did well enough in the Challenge to win the Pro Solo Overall title. For the short duration Pro Solo runs, the newer tire was better. And for the Solo Nats itself, we ran as a single driver in an early heat so tire temp was a non-issue. As a result, two more championships were won that year on those tires. Most in the grid had no idea of the aging differences. We still have some of those 2007's and use them on hot days with repeated runs (e.g. summer testing) where they are faster and more consistent. For all other conditions we use the fresher tires.

Aren't UTQG treadwear ratings totally arbitrary anyway?
No, not totally. But there is some fudge.

UTQG treadwear comes from a real-live scientific test using a real car and a "100" standard tire as a comparable (some old Cooper design they still have to make just for the test). Testing is done in South Texas and tire makers contract to have it done, not the Feds. And they don't have to test every size. Just enough to feel confident about the rating based on their engineering. That's the first piece of latitude.

The bigger issue comes from the fact that the test is only for 7200 miles. Back in the day, that was plenty to wear out a tire...today, not so much. And since a tire does not wear at the same rate during the second half of its life as the first, you have to extrapolate in a non-linear fashion. There is no scientific formula for this so each manufacturer does it differently. That's the "fudge" you hear about.

Marketing forces often will push the fudge a little one way or the other. For example, Bridgestone makes some OE fitments that are treadwear rated at 140-160. To performance-oriented people, that signifies "sticky" and can be used to market the car on a positive note for that audience. OTOH, for an economy tire, the numbers might be pushed as far the other direction as you feel comfortable, based on the test results.That signifies long life to a value-oriented consumer.

R-comps likewise have very low treadwears to distinguish them from real street tires. This gives the tiremaker a leg-up in court to defend against liability if the tires is misused. And it more clearly delineates the tire's intended use so customers know what to expect. Whether that number is "0" or "50" is pretty immaterial, as the tire is designed only to stick...just not for all that long.

If you look at tire categorization within the industry, the "best" high performance street tires are in the Extreme Performance Summer category. No tire there is under 140, though there is no hard and fast rule. And all r-comps are well less than that.

Could a tire maker "cheat" the system? Sure. But they'd be open to huge liability issues should something bad happen when one of those tires was involved in an accident on the street. The tire industry has had enough failure lawsuits in the past decade. This is a powerful disincentive to play games with the small group of folks who autocross.

The Tire Rack has a great write-up on UTQG ratings:
http://www.tirerack.com/tires/tiretech/ ... ?techid=48" onclick="window.open(this.href);return false;

How to determine best pressures
There are a variety of methods used by folks to determine the optimal pressure for competition use for a given tire. The most common method to "ask the experts" on the Internet. And while this can certainly get you in the ballpark, it is fraught with issues. Optimal pressure depends a lot on how your car is setup, the surfaces you run on and the weather. In particular, if you don't have optimal camber settings for your suspension, you'll need more air. Likewise, if yo are running on a smaller rim width or if your car is heavier, you'll need more air. So take everything you hear with a grain of salt and do your own testing.

Here's how we do it on a FWD car: skid pad. Set up a skid pad with a radius that is similar to the types of turns you typically run at your events and a timer. Set a starting pressure on the front tires that is higher than you think is optimal and get the tires up to temp with a couple of laps in each direction. Take note of the warm pressure and do some timed laps in only one direction. Make sure you are right at the limit of adhesion, consistently the same distance away from the cones. We do three in a row and add up the times. Now, check the pressure again after those laps, write that down alongside the elapsed time. Subtract 3 lbs. Spray down the tires. Repeat. Keep doing this until performance drops off. You will most likely find that the tire delivers similar performance across a fairly wide range of pressures, with a sweet spot somewhere. Go back to that sweet spot on pressure and retest to verify that it is indeed sweet.

Now, pack up your gear, let the tires cool and check the pressure again later on. That's your cool starting pressure to achieve the optimal warm pressure you tested for. This pressure can then be tweaked on the other end of the car to get the balance you want. When needed, we like to go up in rear pressure to reduce grip and increase spring rate at the same time, but you can also go below optimal pressures to get a similar result. Breakaway is different with each method.

[Loren]

Good stuff, Joe!

Since it would be an understatement to say that Andy is a "friend of the sport", he posted it publicly, and you were clear about both the author and the source... I can't think of a reason for it not to be here.

(Where do my 175/70 all-season tires fit in this mix?)

[twistedwankel]

(Where do my 175/70 all-season tires fit in this mix?)

Dead last.

Dear Avis,

You way too much. Drive more, read less, PLEASE.

Hertz

[Loren]

You way too much. Drive more, read less, PLEASE.

Hey, Doug, there were some great tips on tire pressure in that article.

[twistedwankel]

You way too much. Drive more, read less, PLEASE.

Hey, Doug, there were some great tips on tire pressure in that article.

Okay that's funny. Ask me how I learned that my "calibrated" tire pressure gage was off -10psi when my rims were nearly grinding on the pavement.

+1 for Loren = lick the sky and jump high

[snookwheel]

Need Cliff notes..

Ok, now I have something to read over coffee tomorrow. Thanks, Joe!

[Jamie]

Good stuff, Joe!

Since it would be an understatement to say that Andy is a "friend of the sport", he posted it publicly, and you were clear about both the author and the source... I can't think of a reason for it not to be here.

Know that he's continuing to add to it, so maybe post the link as well.

(Where do my 175/70 all-season tires fit in this mix?)

You have to ask?

[blacksheep-1]

I think that the excuse of "we're going to run a "spec" tire of any type and justifying it by the reason of cost is total complete and utter BS...



While it may work for a small club like ours the fact is the real serious guys will be firing new "over 140 UTQC" tires at the car as fast as they would race only tires. The fastest the tire will ever be, regardless of type, is the first 5 minutes of operating time (the first heat cycle). You can extend the life of the tire by breaking them in with controlled heat cycles and they will stick less, but have a longer life. If you need traction, it's all gonna be in the first heat cycle, then it will not last as long. So invest in some of this....

http://www.tsracing.com/store/showdetl. ... 50&CATID=3" onclick="window.open(this.href);return false;

Also, while I'm thinking about it, Bridgestone has in the past (but why stop there) had no problem stamping whatever tires with whatever tire markings that will make them competitive. IMO they are the main reason that kart racers now have the entire "spec" tire supply of a given race dumped in parc ferme, then you pick them out, mount them and they never leave parc ferme except to go on the track. I'm sure they aren't the only one with questionable scruples.

[Jamie]

They already do -- in national competition, people shave street tires, bring multiple sets, rains, you name it. It's racing....

[blacksheep-1]

I just go completely berserk when I hear that old line about how "Spec tires save money".

[Loren]

I was about to dive into this discussion about spec tire, but I'm not.

That's not the point of this thread. It's here to provide a great deal of FAQ info about currently available street tires. Let's leave it at that.