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Another tire question?


espog
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I have a sub #2000 miata with 8 in rims. In the past we have run 205/50/15 rivals(non s) and been happy with them. I was thinking of maybe going with something different like the re71's in a 205 or the rs4's in a 225. They dont make the rs4 in a 205. Thoughts? 

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15 hours ago, espog said:

I have a sub #2000 miata with 8 in rims. In the past we have run 205/50/15 rivals(non s) and been happy with them. I was thinking of maybe going with something different like the re71's in a 205 or the rs4's in a 225. They dont make the rs4 in a 205. Thoughts? 

The 225 rs4’s will work pretty well on an 8 inch wheel. A little better on a 9.  It’s a great tire for grip and wear. 

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17 minutes ago, Alchemy Autosport said:

sub 2000lbs?  You might be just fine on a 205 and not want a larger tire.  Are you running aero?  We are 2100lbs, with big aero and run the 225 RS4 and are extremely pleased with them

No aero. We have always been happy with a 205, but we have never run a 225. So we dont really know what we are missing out on.  Car weighs around #1940 dry. My theory was that we are small/light enough that 205s were fine and we might not generate enough heat for a 225. Just a theory.

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1 hour ago, espog said:

No aero. We have always been happy with a 205, but we have never run a 225. So we dont really know what we are missing out on.  Car weighs around #1940 dry. My theory was that we are small/light enough that 205s were fine and we might not generate enough heat for a 225. Just a theory.

If you gave the budget, get a set and try.  I think they are just under $600/set shipped.  Or you can try and get a used set from another team running them, like us.  But someone closer.  

 

Do you have any blistering or chunking of the 205s?  I would use a tire pyrometer to see where you are for tire temps and figure out of you need the tire or just want it, i suspect you wil be just fine on tire temps but the extra grip could be worth it.

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1 hour ago, Alchemy Autosport said:

 

 

Do you have any blistering or chunking of the 205s?  I would use a tire pyrometer to see where you are for tire temps and figure out of you need the tire or just want it, i suspect you wil be just fine on tire temps but the extra grip could be worth it.

We have no problem with blistering or chunking.  Just wanted to try something different.

1 hour ago, wvumtnbkr said:

The extra tire life will probably be worth it.

 

I don't think you will see a 1 lap improvement.  You should see slightly lower temps and longer life.

Right now we can get at least 1.5-2 full race weekends on a set.

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The contact patch size isn't gonna change.  If you aren't getting them hot, and your tire life is good, why change?

 

I don't think you are gonna see improved grip that is gonna be seconds per lap better.

 

I've been wrong before.

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21 minutes ago, wvumtnbkr said:

The contact patch size isn't gonna change.  If you aren't getting them hot, and your tire life is good, why change?

 

I don't think you are gonna see improved grip that is gonna be seconds per lap better.

 

I've been wrong before.

I was just trying to see if i could get a second or so a lap with new tires.

Thanks

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This is a cut and paste from another thread, but thought you might find it useful:

 

We tested this on an admittedly outlier car for Champ (close to 10lb/hp), and found that on two very different courses we got similar results when comparing 225/50/16 on 8j vs 255/40/17 on 9.5j - the 255's are significantly (roughly ~1.5 to 2s per lap) faster. On a really bumpy track with somewhat rough braking zones in a couple of spots, we expected the much lighter 16 inch setup to be closer or faster, but it wasn't. The lighter smaller 16 inch wheels felt smoother and tracked better on the bumpy track, but lap times were still worse as the 17 inch setup provided more lateral grip in all the turns, acceleration should have been better on the 16's but it is very very subtle to the point of not being able to see it easily in the accelerometer data..

 

Given the ability to fit and afford 12j wheels it would be fascinating to test 305/335 to see if the lap times and wear improved further, but packaging and budget aren't going to allow that (at least for us). The larger 17" wheels/tires grip better, and last much longer, our testing has pointed to the larger setup in every quantitative measure, subjectively, some things are better on 16s, but for racing, there is no question for our application. Interestingly because of the wear rate of the 225s, the larger tires are cheaper to run in 16/24 hour events because we can get a full event from them, where we can't expect same from 16's.

 

I am not at all sure that on a Miata you will see the same results as wheelspin and braking are not as big of a factor in tire wear on a <200lb car, and any hit on acceleration will be more noticeable (maybe - I was wrong about being able to see a difference in our tests on that). 

 

Based on our tests and articles on the topic, I would be inclined to think a 225 on a 9" rim would go ~1 sec/lap (245 on a 10 even more so) faster, but not sure if you will see much benefit on an 8" rim. Probably lose some steering feel and the peak grip would likely have less steep approach and drop off. 225 on an 8" for us felt smooth and a little less connected / it muted the (lower) peak grip vs the 255 on 9.5.

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