New Street class Tire sizes on OEM wheels
12-17-2013, 04:33 PM
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Thoughts on overtiring like Hoosiers in Stock versus something more appropriate for the wheel width?
I've driven Nick's car and it's certainly not slow with a 245/40 on a 7" wheel. Andy Hollis' testing as well as comments I've read on various forums point to a narrower tire, so maybe something like the OEM-sized 215/45. Then again, all of this comes from cars setup for ST with more setup and alignment options than Stock/Street. Here's the section quoted for those without FB:
I've driven Nick's car and it's certainly not slow with a 245/40 on a 7" wheel. Andy Hollis' testing as well as comments I've read on various forums point to a narrower tire, so maybe something like the OEM-sized 215/45. Then again, all of this comes from cars setup for ST with more setup and alignment options than Stock/Street. Here's the section quoted for those without FB:
Originally Posted by Andy Hollis
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.
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.
12-17-2013, 04:51 PM
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Originally Posted by recnelis
Thoughts on overtiring like Hoosiers in Stock versus something more appropriate for the wheel width? I've driven Nick's car and it's certainly not slow with a 245/40 on a 7" wheel. Andy Hollis' testing as well as comments I've read on various forums point to a narrower tire, so maybe something like the OEM-sized 215/45. Then again, all of this comes from cars setup for ST with more setup and alignment options than Stock/Street. Here's the section quoted for those without FB:
To my understanding the bigger sway bar helps the over steer and transitions but in order not to lift the inside rear tire you need to compensate with larger front tires. Again this is all based off or what I have read. And in stock, soon to be street, the balance is between how hard of bar, with the harder the bar the bigger the front tires needed and the softer the bar the more oversteer and tire lifting issues. If anyone else can way in on this with more expired please way in.
Thanks
12-17-2013, 07:36 PM
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If you've been following the STR threads floating around here, the allowances are very similar as both are classes within the Street Touring category. You are allowed to change both sway bars, install "coilovers", camber plates (for strut cars), and change wheels (max 7.5" wide for STS, 9" for STR) among other things.
12-17-2013, 09:11 PM
#14
when i first put my 245s on the front i had the stock front sway. I spun out EVERY RUN!
Put a comptech front sway on for the next weekend on full stiff and it was back to normal.
I found I had to run more psi in the front(up from 34psi hot to 38psi with 245s) to get rid of the tire wiggle i felt
I ran -2.8 up front, max caster was about 6 degrees with 0 toe. On the rear i ran -2.5 with 1/8 toe in
Put a comptech front sway on for the next weekend on full stiff and it was back to normal.
I found I had to run more psi in the front(up from 34psi hot to 38psi with 245s) to get rid of the tire wiggle i felt
I ran -2.8 up front, max caster was about 6 degrees with 0 toe. On the rear i ran -2.5 with 1/8 toe in
12-18-2013, 04:28 AM
#15
Thanks iamxpL,
I read through your build and it was very informative and almost exactly the path I have planned for the next few years. I guess all my forum research has helped, but I love that you have all ready done everything and listed it in one place.
I do have one question for you, or anyone. What kind of an alignment would be a good Base for the 245/255 ZII setup?
I read through your build and it was very informative and almost exactly the path I have planned for the next few years. I guess all my forum research has helped, but I love that you have all ready done everything and listed it in one place.
I do have one question for you, or anyone. What kind of an alignment would be a good Base for the 245/255 ZII setup?
thanks
i am continually updating the thread so that others like you and me would have an easier time. feel free to PM me with any questions you may have. ill dig up my alignment sheet later and scan it. 
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