Page 1 of 1

Wheel choice for an S4 Miata?

Posted: Mon Jul 10, 2017 9:34 am
by jaball77
When I had my tires flipped I found out that one of my stock Miata wheels is pretty badly bent. Bad enough that it won't balance properly and causes a pretty severe shimmy at 35 and 65 mph. This is the reason I will be giving the wife for buying a new set of wheels. :grin:

When these tires are done (6 more months maybe?) I'm going to replace the wheels with an aftermarket set or 15x7 or 15x8. I don't plan on rolling the fenders so I'll be sticking with a 205 tire and I'm not sure how much I'd gain from using an 8" wide wheel.

I was looking at the bronze (gold) 6UL 15x8 +36. Reasonably priced, light, nice design, and I think gold on black looks fantastic.

But then I see that Tire Rack has some old school Kosei K1 in 15x7 +30 for $104/wheel. Super cheap, one of my favorite wheel designs of all time, but heavier and narrower. Not sure if this is a temporary deal or a permanent price, but even the "full price" K1s are $150 a set cheaper than the 6ULs.

If price was no object I'd go with the 15x8 RPF1s but that's just not in the budget, heh.

So what do you think?

Wheel choice for an S4 Miata?

Posted: Mon Jul 10, 2017 10:23 am
by Loren
Get the Kosei's. 15x7 is plenty for a stock Miata running 205's. I'm even okay with 225's on a 15x7. (but, 225's will tend to rub a little without some fender rolling)

Wheel choice for an S4 Miata?

Posted: Mon Jul 10, 2017 11:17 am
by Carracer
I ran a 15X8 with 205s last season, the extra width is noticeable and worth enough time to sneak out a win but that's compared to a 6 inch rim. I would bet 7 vs 8 wouldn't be worth mentioning and at that price my vote would be the Kosei K1.

Wheel choice for an S4 Miata?

Posted: Wed Jul 12, 2017 4:07 pm
by jaball77
Huh, it looks like the cheap +30 K1 is HUBCENTRIC for Miatas. The others come with centering rings, but the cheap +30 ones don't.

Interesting.

Wheel choice for an S4 Miata?

Posted: Wed Jul 12, 2017 4:40 pm
by Loren
They're lug centric, anyway. I've run LOTS of different aftermarket wheels on Miatas without centering rings. The rings make it easier to install the wheel, that's all.

Wheel choice for an S4 Miata?

Posted: Wed Jul 12, 2017 5:16 pm
by jev61
I will re-post some info from Andy Hollis' Facebook page that he posted way back in 2012. You will notice the specific tires mentioned are out of date, but the general rule of thumb for tire width and rim width is still worthwhile. Keith Tanner has written about tire and rim widths in his book about Miata performance, his advice is the same as Andy Hollis for absolute performance.

https://www.facebook.com/notes/hollis-r ... 598916447/

Street Touring and Track Day Tire FAQ - UTQG 140+

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.

Wheel choice for an S4 Miata?

Posted: Wed Jul 12, 2017 8:18 pm
by Loren
While I don't doubt anything that Andy Hollis says for a second. What's missing from that write-up is data. If a 205/50 is "best on a 7.5", and "an 8 will work", and you "lose some performance on a 7". What are the relative numbers? I'm betting it's on the order of 3-4 tenths. It's enough that a driver like Andy can readily quantify it and say "the 7.5 is better". But, for a driver like ME (and most of the people that I know), I'm not consistent enough to pin down less than half a second. Sure, if I was prepping a car for Nationals and had the money, I'd "chase" those tenths of a second. But, for local competition? I'm gonna take the cheap 7" wheels and be happy.

Wheel choice for an S4 Miata?

Posted: Thu Jul 13, 2017 11:35 am
by jmdoc66
I'm with Loren.

Wheel choice for an S4 Miata?

Posted: Thu Jul 13, 2017 3:27 pm
by jev61
How often has S4 been determined by less than 2 tenths of a second?

Wheel choice for an S4 Miata?

Posted: Thu Jul 13, 2017 8:14 pm
by Loren
I can't answer that, but I can tell you that anytime *I* lose by 2/10ths of a second, I'm not blaming my wheels, or even my tires. 2/10ths is something that I should be able to overcome as a driver. Some days I have it, some days I don't. When I get to where I have "it" every day, then I'll worry about trying to make the car perfect.

Wheel choice for an S4 Miata?

Posted: Thu Jul 13, 2017 9:29 pm
by Jamie
jev61 wrote:How often has S4 been determined by less than 2 tenths of a second?
More often than you think. Multiple times, we've been into the hundredths. But not consistently enough to credit car setup.

Wheel choice for an S4 Miata?

Posted: Thu Jul 13, 2017 9:53 pm
by Carracer
Jamie wrote:
jev61 wrote:How often has S4 been determined by less than 2 tenths of a second?
More often than you think. Multiple times, we've been into the hundredths. But not consistently enough to credit car setup.
Many times is right, at least 6+ in the hundredths for S4 in the past 2 years. And also this event:
http://drivefast.org/wp/Results/2016/20 ... _Class.pdf

1T 31 Jamie Sculerati 2001 Miata 52.658
2T 94 Kevin Bonitz 2002 Miata 52.667 +0.009
3T 321 Philip Petrie 1996 Miata 52.747 +0.080