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What rim width size for 245 40 15


MIata Tom
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A couple years back, Will G. from GWR racing, a front running E30 team, did a whole write up on their testing of wide tires and different width rims. His findings showed that these tires perform best with a bit of stretch on the sidewalls to provide maximum grip and to keep the 'rollover' effect from happening.

 

I recall the GWR on track test results showed 10" was optimal for 245/40/15 Hankooks. You'll see a lot of guys on 245's running 9's and 10's. Some folks opt for 9's due to packaging and weight issues with 10's on small cars. A rule of thumb to follow is to avoid running a rim width that is narrower than the tire's advertised tread width.

 

edit 2: I found the post I referenced...

 

Edited by mcoppola
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We run both 9s and 10s.  We had to mix 9s and 10s at Road Atlanta as we debeaded one tire in the first stint and curbed another in the second to last stint(both me as the driver).  There was no noticeable difference between the 9s and 10s that any of us could tell, to our surprise, however we were having issues getting heat into them.  We will be testing them at Road America for lap time we will also have the carousel which will be a great litmus test.  

 

I do know that we were very hard on our 9s at Sebring, including cracking one, but the tire kept air and the rim didn't bend enough to get out of balance.  We were very impressed.

 

At Road Atlanta, both incidents we felt the rim could have done much better.

 

Our current hypothesis is that the 9" is actually a much more durable combination that might might be worth it to go narrower if the speed difference is small.

 

 

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So here is my dilemma.  I have 12 15 x 7 rims and ran the Dunlop ZII StarSpec - 205/50-15 last year and I liked them. From what I am reading the Hankook R S4 are the tires to have or this their a better tire than I can run with 15x7 rims?

 

Tom M

Sweetwater Racing 

91 Miata 

WGI  46 and 36 

Thompson 5th

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We’ve always run 205s on 15x6s.  Not stretched like a lot of people run, but they fit good.  225 on your 15x7 should fit fine.  Probably won’t get you the maximum performance, but not far off.  Or you could try to sell some of your 3 full sets of wheels to fund a new set of 15x8s.

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2 hours ago, MIata Tom said:

So here is my dilemma.  I have 12 15 x 7 rims and ran the Dunlop ZII StarSpec - 205/50-15 last year and I liked them. From what I am reading the Hankook R S4 are the tires to have or this their a better tire than I can run with 15x7 rims?

 

Tom M

Sweetwater Racing 

91 Miata 

WGI  46 and 36 

Thompson 5th

We bit the bullet last year and went to 15 x 9s with 225/45-15 R-S4s on our '95 Civic. The justification was mainly to have longer tire life than we got from the Z3s and RE-71Rs.

 

Some internet searching showed a test of another Civic that was slightly faster on the 15 x 8/225 R-S4 combo than it was on the 15 x 8/205 RE-71R combo.

https://ham-ind.com/2017/04/25/hankook-rs-4-vs-bridgestone-re71r/

 

We didn't quite get the opportunity to test that last year but the numbers said that the cost of the new tire and rim combo would be the same as the two sets of 205/50-15 RE-71Rs that we'd need to last as long as the larger 225/45-15 R-S4s. I went with the 9" rims in case we wanted to try the 245s but there were some tests showing that the 225s were about a second quicker on 9" than on 8" rims so no downside going with the 9" that I can see. :) 

 

Anecdotal tire life for the RE-71Rs showed about 6 hours vs up to 20 from the R-S4s; not purely scientific but I considered that a reasonable indication.

 

I would say that 205/50-15s are as wide as you should go with a 7" rim. If you want to go to a 225 or 245, I suggest that you sell your 15 x 7 rims or keep them as spares and step up to the wider rims. 

Edited by mender
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On 2/24/2019 at 9:03 PM, MIata Tom said:

So here is my dilemma.  I have 12 15 x 7 rims and ran the Dunlop ZII StarSpec - 205/50-15 last year and I liked them. From what I am reading the Hankook R S4 are the tires to have or this their a better tire than I can run with 15x7 rims?

 

Tom M

Sweetwater Racing 

91 Miata 

WGI  46 and 36 

Thompson 5th

 

I have the same question-ish.

 

I was racing in chump ~3 years ago but our car had gotten tired and the motor blew.  Blah Blah, I am almost done full rebuild and looking to get back into the game this spring.

 

Back in the day we ran 205 Direzza's and they were great, predictable but most importantly we would get like 40-50 hours out of those bad boys.

 

So, is it a lot of forum hype that every team is running 245s now?  Because you can get 225 Direzzas in a 16" wheel (if you want 245s you have to get 17" wheels, ick) but for 245s on a 16 I would have to go into rivals and hancooks... which I just don't have any experience with.  It just isn't in my budget to put new tires on every weekend, let alone 2 sets in one weekend. 

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45 minutes ago, Alex3000 said:

 

I have the same question-ish.

 

I was racing in chump ~3 years ago but our car had gotten tired and the motor blew.  Blah Blah, I am almost done full rebuild and looking to get back into the game this spring.

 

Back in the day we ran 205 Direzza's and they were great, predictable but most importantly we would get like 40-50 hours out of those bad boys.

 

So, is it a lot of forum hype that every team is running 245s now?  Because you can get 225 Direzzas in a 16" wheel (if you want 245s you have to get 17" wheels, ick) but for 245s on a 16 I would have to go into rivals and hancooks... which I just don't have any experience with.  It just isn't in my budget to put new tires on every weekend, let alone 2 sets in one weekend. 

We ran the new Z3s at Portland last summer, and they performed quite well though not as good as RE-71Rs.

 

They also didn't like the heat. After 4.5 hours on Saturday, the tires looked to have more than enough wear left to run on Sunday. However, the temps went up to 95 F from the low '80s the day before, and during a red flag stop I noticed the tires were wearing quickly. We traded out the left side tires for a pair of heat-cycled but still usable RE-71Rs. When I got in the car I could feel the difference left to right, with the RE-71Rs having more grip. 

 

I think the total amount of time we got out of the Z3s was about 15 hours and there's not much left. 

 

Z3s and RE-71R = cooler track and short life; R-S4s and Rivals = hot track and good life. You can change tire width to move either group towards the middle ground. 

Edited by mender
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On 2/24/2019 at 7:03 PM, MIata Tom said:

So here is my dilemma.  I have 12 15 x 7 rims and ran the Dunlop ZII StarSpec - 205/50-15 last year and I liked them. From what I am reading the Hankook R S4 are the tires to have or this their a better tire than I can run with 15x7 rims?

 

Tom M

Sweetwater Racing 

91 Miata 

WGI  46 and 36 

Thompson 5th

All I used to use were the Star Specs on 15X7 205s.  They were good tires but I was lucky to get through a weekend on a set, sometimes just one race and practice was all that was left.  Moving to the 245s and changing to the RS4s, I believe they are slightly faster tires and seeming never run out.  I'll be tossing eight of them that are still at least 1/2 tread but heat-cycled out.  They are 1.5 years old and had more to give but I didn't do a good job bagging them and taking care of them.  I know the RE71s are faster, but to switch to them means going back to 205s, and buying literally 4 times the number of tires.  For me that's not worth it.  I'll stick with the RS4s.  

 

Edit: if you move to 15s and 245s, you will have to redo the suspension up front for sure, even in the rear.  Just an FYI.  

Edited by Jer
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There is a risk of not getting the tires to temp with a light car.

 

Our Civic is a light car so I went with 225 R-S4s. If I had a lot of money I would consider the Rival 1.5s in a 245, should have lots of grip but still reasonable tread life. Considering Jer is tossing a couple of sets with half the tread left, maybe a tire that wears 50% faster but is still usable all the way to the cords might be a better plan. 

 

Hmmm ... let's see, cost per hour of R-S4s at half tread depth vs used up Rival 1.5s ...

Edited by mender
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16 hours ago, wvumtnbkr said:

Well, you have a 1st gen.  It's light.  You could probably get away with 225.  

 

However, 245 is where it's currently at.  

 

Last I weighed our car it was ~2,150# with a 3/4 tank of gas, which I was pretty pleased with. It just seems hard to believe that going full tilt for 8-12 hours that any street tire wouldn't heat up, but people do seem to be be reporting that so what do I know.

 

I think I may have been convinced to do R-S4s.

 

It's a gamble though because my father races with me and if I switch tires and they don't last he'll give me the old "I'm not mad, just disappointed" face. I hate that face.

 

/end threadjack.

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43 minutes ago, Alex3000 said:

 

Last I weighed our car it was ~2,150# with a 3/4 tank of gas, which I was pretty pleased with. It just seems hard to believe that going full tilt for 8-12 hours that any street tire wouldn't heat up, but people do seem to be be reporting that so what do I know.

 

I think I may have been convinced to do R-S4s.

 

It's a gamble though because my father races with me and if I switch tires and they don't last he'll give me the old "I'm not mad, just disappointed" face. I hate that face.

 

/end threadjack.

Damn!  They better last more than 8 to 12 hours.  Tyler did 24 hours on his RS4 at Nelson ledges.  He changed 1 tire just to be on the safe side.

 

What tires are you running now?  Im gonna bet that you get longer run time out of the RS4 than what ever you are running now.

 

Make sure you make the tires happy.  Get them a heat cycle before the race (or order them heat cycled).  Also, make sure your tire temps are fairly even.  Align the car to tire temps.  Set pressures based on tire temps.

 

your tires will thank you.  I am gonna guess you will need to start at about 27 psi cold for that car.

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