195/60 14 Star specs on Daisies or lesser tire on 16x7 rim

[rab]

OK here is my predicament.
I ran November's Autocross in my Miata for the first time on 5 year old BFGoodrich g-Force Sport 205/45ZR16's. These are running on a nice set of ATS Planets.

To me it felt kinda felt like I was running on ball bearings.

So, I was going to replace them.

Looking at Tire Rack I see there is very little selection in performance tires in that size. RE11's appear to be the best solution, but at $180.00 per tire, I kinda blanch at the thought. So I am left with either The G-force Sports or perhaps a set of S-drives. Both are in the $90.00 range.

Now here is the question and post title. Would I be better off with my Daisies running 195/60 14 Star Spec's with more side wall compliance and smaller foot print or going with a new set of 205/45 16 G-Force or S-Drives on my ATS'?

[Jeremy]

205/50R16 Star specs on the 16 x 7 wheel. $126 each.

Daisies are like 5.5 wide or something, forget that.

[rab]

Will I have clearance problems on the 205/50's? Acceleration issues? Anyone running them on NA Miata's?

[Jeremy]

http://forum.miata.net/vb/showpost.php? ... ostcount=5" onclick="window.open(this.href);return false;

I believe that guy is a well known autocrosser.
Guess it depends on the offset. Google says the wheels may be +38 which sounds pretty conservative. So I am guessing they will fit fine.

I am not a miata person though, so maybe one of them will chime in.

[Jeremy]

Here is a video of him running them, it says on 16 x 7 rota grids which are +40mm offset.

http://www.youtube.com/watch?v=0Xx9n6yFIa4" onclick="window.open(this.href);return false;

So assuming yours are +38, you'll be good to go.

[Loren]

The difference in width isn't that much. 10mm isn't going to make or break you. I could really go either way on this... but I just might lean toward the 14" option.

Consider that you're in a Miata that weighs barely 2250 pounds WITH you in it. It has something like 116 hp, and an equivalent amount of torque (that is: not much). Now, consider the weight of your 16" wheel/tire combo and the weight of the 14" setup. I'm gonna bet that your 16's weigh at least 16 pounds and the tires weigh 20-21 pounds... 36 pounds total. The daisies weigh 12 pounds and the 195/14's should weigh about 19 pounds... 31 pounds total. That's 5 pounds of rotational mass, and that's HUGE on a Miata!

[Jeremy]

195 on a 5.5 inch wheel vs. a 205 on a 7 inch wheel.
They could be chrome plated steel wheels and I would still run the 205's.

According to Grassroots motorsports, wheel weights don't do anything for autocross lap times.

[Native]

Pick the cheaper option. Run it until you decide you don't like it or wear out the tires. Then see where you are and go from there.

[rab]

Loren, would I see any compliance issues with the 195/50-14's? would that be noticeable on slaloms?

You brought up a major issue with unsprung weight. The 205/50-16's would even add more weight to the package. So if I get this right, the 16 inch solution would give me less acceleration due to less mechanical reduction and then additional inertia. Now combine that with additional weight on the suspension, causing it to be less responsive to irregularities, (would the V-max's help this?), I might have overall performance issues that would slow the car down more in a typical autocross than a reduction of tire patch and and increase in compliance in the slaloms.

Jeremy, I find it very interesting re grassroots findings. Did they develop these findings with a Miata? At full throttle in the last autocross I was not shifting into 2nd until after the first gate. Seems like I already have an acceleration disadvantage.

Native, you have a great point there...

Edit ***

of course as a true Knob much will be obtained just improving driving style...
Just thought I would say this before someone else did...

Edit***

[Jeremy]

Jeremy, I find it very interesting re grassroots findings. Did they develop these findings with a Miata? At full throttle in the last autocross I was not shifting into 2nd until after the first gate. Seems like I already have an acceleration disadvantage.

I think so, they've done it twice on a miata. The last time was June 2011 if you know anyone that has a copy.

[Loren]

Decisions, decisions.

A pound of rotational mass is usually regarded as being equivalent to at least 4 pounds of sprung weight (some say as much as 8 or 10 pounds, even). So, 5 pounds per corner = 80 pounds off the car. Assuming the total weight of the car with driver is 2250, that's equivalent to 3.5% weight reduction.

Or... an increase in tire width from 195 to 205 is an increase of 5.1%, which could potentially raise max sustainable G load from something like .95 G to .998 G. (assuming a direct relationship between tread width and lateral G load)

What's going to make more difference? It depends on the car. It depends on the course. It depends on the driver.

For a relatively novice autocrosser, it won't make much difference either way, but they might feel the difference in acceleration more readily than the 5% increase in grip out there beyond where they're capable of consistently driving in the first place.

For an experienced driver who knows how to drive on the ragged edge of whatever traction they have available... more grip would surely be more beneficial in most cases. (and GRM's tests surely used experienced drivers, hence their results)

But, ultimately, I think Steve nailed it. To learn on, you don't need "the best", though clearly what you have is probably a bit too frustrating to have any fun while you're learning. Get what's affordable and makes the most sense to you.

BTW, Rick, did you get a good alignment yet? That can make almost as much difference as tires.

[Jeremy]

Or... an increase in tire width from 195 to 205 is an increase of 5.1%

I think it's more significant than that. According to tirerack 195mm has a range of 5.5-7" wheel. 205mm has a range of 5.5-7.5"
Being that the 195 is at the very bottom of the range, there might be a little ballooning and the 205 is going to have a much a larger contact patch. Maybe even double your original estimate of 10mm?

But, ultimately, I think Steve nailed it.

Yep, go with the cheapest option and save up for 15 x 8's and 225's!!!

[rab]

Thanks guy's!
You have given me much food for thought.
I will probably go with the 14's but I will think on this a little bit more.

Loren, I got an alignment using FM's spec's when I put on the V-Max coil overs form the Goodyear shop in front of my office... But I don't really like the results. The car is very very darty on uneven roads. Are you still doing your string alignments?

[Loren]

Thanks guy's!
You have given me much food for thought.
I will probably go with the 14's but I will think on this a little bit more.

Loren, I got an alignment using FM's spec's when I put on the V-Max coil overs form the Goodyear shop in front of my office... But I don't really like the results. The car is very very darty on uneven roads. Are you still doing your string alignments?

Yeah, I can do a garage alignment and work with you to come up with something that works for you. Probably just needs a toe adjustment rather than a full alignment. PM me, we can discuss.

[jev61]

OK here is my predicament.
I ran November's Autocross in my Miata for the first time on 5 year old BFGoodrich g-Force Sport 205/45ZR16's. These are running on a nice set of ATS Planets.

To me it felt kinda felt like I was running on ball bearings.

So, I was going to replace them.

Looking at Tire Rack I see there is very little selection in performance tires in that size. RE11's appear to be the best solution, but at $180.00 per tire, I kinda blanch at the thought. So I am left with either The G-force Sports or perhaps a set of S-drives. Both are in the $90.00 range.

Now here is the question and post title. Would I be better off with my Daisies running 195/60 14 Star Spec's with more side wall compliance and smaller foot print or going with a new set of 205/45 16 G-Force or S-Drives on my ATS'?

Rick, I suggest 215/35R16 or 215/40R16 Yokohoma S.drives' from TireRack.

Your car would have had 185/60R14 tires that are 22.7" tall and weigh 18lb. The 215/35R16 tires are 21.9" tall and weigh 19lb each. The 215/40R16 tires are 22.7" tall and weigh 19lb.

You trade one pound of weight for a shorter sidewall, wider width and faster acceleration with the 215/35R16.

You like your 16" wheels, so use them. Put the shortest, softest and widest rubber on them you can afford.

BTW, I insulated the cockpit of my car the way you did yours. Thanks for the write up.

Joe

Just my two cents worth, Joe

[rab]

OK... weighing all of the options I think I will go with new S-drives on the 16's. Replacing the tires needs to be done anyway.

Joe I used the MintyLamb.co "Wheel & Tyre Compare-o-rama" that 76-TR6 recommended. The 215/40-16's will give me a reduction in rolling circumference of 2.16% over the existing 205/45-16's. This will help but still not be too far off for the speedo. Loren, I you are correct in your G force estimation I should get fairly good response with this size. But since I have to replace tires anyway no harm no foul if I need to go another way after I improve.

One question, will this extra width cause scrubbing with the 38mm offset on an early NA Miata? I don't want to role the fenders. Note, I have put on the FM NA to NB suspension conversion kit.

Joe, have you seen any difference in sound and heat with the insulation?

[Loren]

Loren, I you are correct in your G force estimation I should get fairly good response with this size. But since I have to replace tires anyway no harm no foul if I need to go another way after I improve.

That's a negative. You're no longer comparing Apples (Star Specs) to Apples (Star Specs). I firmly believe that a 195 Star Spec of any diameter on damn near any wheel is going to out-perform a 215 S-Drive. Like a lot of tires, the S-Drive is a good street tires and an "okay" autocross tire... but there's a reason nobody mentions S-Drive when they're talking about Star Specs and Hankook S3's and Kumho XS and the other "really good" streetable autocross tires.

Will the S-Drives be better than what you have? Probably, but not as much as you might think. (talk to Bill Flowers, he had a set of S-Drives on his S2000, I believe)

[rab]

Well bummer... now back to square 1!
Bill you out there?

[Jeremy]

I am on my 2nd or 3rd set of s.drives for daily tires. I would rather stay at home than autocross on them. But I am weird like that. I ran them once in the rain at Lakeland. It sucked but it very well could have been the gravelly course.

I think the s.drives are going to be at least 1 sec slower than dunlop, toyo, hankook, etc.

And after more research I change my original recommendation. the 205/50/16's are too tall. Seems that everyone is running 15's. So get the 14's for now and start saving up for 15's would be my advice.

[jev61]

OK... weighing all of the options I think I will go with new S-drives on the 16's. Replacing the tires needs to be done anyway.

Joe I used the MintyLamb.co "Wheel & Tyre Compare-o-rama" that 76-TR6 recommended. The 215/40-16's will give me a reduction in rolling circumference of 2.16% over the existing 205/45-16's. This will help but still not be too far off for the speedo. Loren, I you are correct in your G force estimation I should get fairly good response with this size. But since I have to replace tires anyway no harm no foul if I need to go another way after I improve.

One question, will this extra width cause scrubbing with the 38mm offset on an early NA Miata? I don't want to role the fenders. Note, I have put on the FM NA to NB suspension conversion kit.

Joe, have you seen any difference in sound and heat with the insulation?

Yes, the cockpit is cooler and quieter. And I didn't mean to suggest S drives would be the best autocross tires, only they fit better.

Joe