LargeOrangeFont

iTrader: (7)

Then don't bring up a rediculous test of shoving a 285 on an 8 inch wheel

Anyway in general I agree, but no one is saying shove the biggest tire you can on regardless of rim width either.

What ZDan and I are saying is run the widest tire that you can fit under the car with the wheels you are running. And use common sense, some thought, and a tire company's recommendations when picking the size.

I've had instance on my FC where a wider tire rear tire was slower, but it was slower because it was taller. Now that the car has actual power, I am trying to cram as much tire as I can under it with the rims I have, and run a 255/40/17 on a 9 inch wheel all around.

ZDan

This I agree with, if maximum cornering is the goal and ride quality and protection against curbing are not considerations (or personal tastes regarding the look of stretchy vs. poochy fitments).

What I disagree with is the suggestion that a 235/40-18 or 245/35-18 is inherently better on an 18x9.5" wheel than a 255/35-18 or 265/35-18 (or, given enough power to overcome the gearing and weight disadvantages, 275/35-18).

LargeOrangeFont

iTrader: (7)

Agreed.

silverTRD

iTrader: (37)

This was my thinking as well, I couldn't understand how a 235 would be better than a 265 on a 9.5 " wheel.

Flyweight

iTrader: (1)

Zdan is spot on here. Anyone who believes that a 235 on a 9.5 is faster than a 255 or 265 is just plain wrong.

People need to understand that my original recommendations were given 3.5 years ago and were designed for people who want relatively stock rolled but not pulled fenders.

I think that the TurboII's 18x11 +45 fitment is fantastic. Thank you for providing so much information on how you made it fit. People need to understand what is involved. I have no doubt that the 295/30 on a 18x11 is very quick!

lOOkatme

iTrader: (19)

I am glad we have all used BRO science to ensure you are right. I know for a fact that you are wrong and I am right. Look at race cars, ANY race car and they ALL stretch the tires onto their wheels. I mean race cars, ones with engineers, tire manufacturers working together designing the fastest car possible for $$$$$ or sponserships on the line. Not back yard racers who don't test their stuff.

Find me one picture of a high dollar car, limited rules or restricted wheel widths that have a tread width WIDER than the wheel width.

You won't find it because its slower. I am not 100% sure that a 235 or 245 on a 9.5" wheel will provide more grip than that of a 255/265 width, what I do know is a 235/245 is FASTER than a 255/265 on a 9.5" because it handles better and provides better feedback, and also easier to drive at the limit. Much easier. Wheel width, (not tire width), is where speed is obtained regardless of the weight penelty of going wider. You want to run the widest wheel possible and fit the tire with a slight stretch on it because of the way the tire behaves at the limits. Race cars do this.

And its shown that you guys obviously haven't tried what I am talking about. It completly changes the way the car handles. It's leagues better stretching it some. Hell, check out go kart wheels, they do the same thing. The slip and catch of the tire when stretched is a beauty. The wider tread width than wheel width is the snap oversteer, grip grip grip, let go scenario. The stretch tires is a slide progressively let go re-grip scenario. so much better and more predictable.


So if you still don't believe me. How about you read what the Michelin tire engineers have to say about the data they collected on the porsche race cars and fitting tires onto wheels.

Check out slide 34 and on. They talk about fitting smaller tires onto the wheel than fitting a wide tire for the wheel. exactly what we are talking about here.

www.cb-racing.com/PilotCup_Presentation.​PPT



FYI
I run a 18x11.5 +42MM wheel on my set up with a 285/30/18 tire (11" tread width).


from a go kart racing website.
Setting is also easier is the rim width is changed. Overall stiffness is changed uniformly as inflation pressure is varied but by changing the rim width, lateral and vertical stiffness, especially lateral stiffness, can be greatly varied. Furthermore, since the contact area does not change appreciably as it does with a alteration in inflation pressure, grip remains the same but fine changes can be made in maneuverability (steering response, smooth slides, true following of the rear tires). For example, if the rear slide is not smooth, a wider rim than standard is called for. However, the range in which rim width can be varied is within ± 0.5 inches (approx. 13mm).


Most people on this website are going about it all wrong. wider tires MAY not give you more forward/rearward traction. they give better left to right traction, but when going wide on skinny wheels will make the car handle worse because now your have a muffin top shape and a tire that will fold on you, not giving you the progressive slide you want. It's more of a snap oversteer response. Speedjunkie is well aware of this with his 11.5" tread width AD08 on a 10.5" wide wheel. The car did a perfect 360 spin around a corner when his car just "let go". Wider tires do provide more traction if you can heat them up and lower the PSI. that is why a 16" wheel would be better in the rear for drag racing an rx7, and why faster rx7's run 16's, because you can lower the PSI of the tire gaining longitudinal grip. Wide tires on 18" wheels are great for handling, not straight line speed.

My 265/35/18 on a 10" wheel (9.6" tread width) never behaved in that manner ever. I could hit it hard and the car would predictibly slide and progressively let go.

Our racer in the group got faster times going to a wider wheel with the same tire width, he also went faster on his old wheels and a skinnier tire, same model/manufacturer of tire.

Anyway from tirerack

As a general rule, Tire Rack recommends mounting Track & Competition DOT tires on the widest rim widths approved by the tire manufacturer (up to the widest permitted by the competition class rules).

http://www.tirerack.com/tires/tirete...jsp?techid=233

LargeOrangeFont

iTrader: (7)

No one is arguing with you from the standpoint of running the widest rim you can, but the logic does not always work and can't always be applied in practice. Also race cars use spec tires and wheel sizes typically. The Grand Am GS cars run 275 width tires on 10 inch wheels for instance.

You are running a wheel that is outside the recommendations of the tire manufacturer. There is a reason for those guidelines and a reason the OEMs don't stretch tires like that even on performance cars. Show me a race car or successful track car running 285s on an 11.5 inch wheel (or some other stupid configuration that is outside of the manufacturers recommendations.) Im sure that advice is given by all the race and tire engineers right?

Also you are running DOT street tires I imagine, not race tires. There is a difference.

Here is an example of it not working on my FC. I run 9 inch wheels. The car is much faster with 255 tires than it is with 235s, period. I've ran both, I have GPS data for both. It is easier to drive with the 255s as well. They are more forgiving and have more grip.

I don't have an easy option of running 9.5 inch wheels at the moment so I am optimizing what I have and 235s are not optimal on a car with 400+ WHP.

Flyweight

iTrader: (1)

lOOKatme...None of us are arguing that wider wheels = slower. In fact ALL of us are arguing wider wheels = faster.

Tires widths/sizes/compounds are regulated in professional racing. Consider this when looking at your evidence.

Like everything in life, this is a balance. Is a 195/50 17 on a 17x10 faster than a 255/40 on a 17x10? No! This does not require contemplation. Your example of a 235 on a 9.5in wheel is bordering on this.

Is a 255/40 faster than a 275/40 on a 17x10?...well this does require our contemplation...

What did you need to do to be able to fit your 18x11.5 +42? I would hazard a serious fender pull. While I am sure this is a quick setup this may not be for everyone and people should be aware of what is necessary to fit the wheels you are running.

LargeOrangeFont

iTrader: (7)

Exactly!!! And blindly saying the 275 is slower than the 255 without any other knowledge is rediculous.

lOOkatme

iTrader: (19)

some more data from racers.

Anyway. Here are some guys from autoX that have tested different widths and their opinions.


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.


S2000 and miata guys

In the Miata community, 225 width tires work best on 9" width wheels. In the S2000 community, 255 width tires work best on 10" width wheels. The width of the tires is basically equivalent to the width of the wheel.

225/25.4 ~ 9", likewise, 255/25.4 ~ 10"

Anymore stretch than that is overkill and does not function as well as what I mentioned earlier. Most people will run whatever is recommended on the spec sheet, for example, 255 tires on 9" width wheels, 245 tires on 8.5" tires, 235 tires can be either on 8.5" or 8" wheels, etc.

For stock power, 215 width tires are good enough for the BRZ/FRS. We ran 215s on 8" width wheels to start off with on the track. This extra "stretch" helped improve some sidewall stiffness, but the car needed serious camber to fix most of our wear problems!

Autocross guys have to use the OEM wheel sizes for certain classes and will stuff as wide of a tire as possible. That's because those specific tires have super stiff sidewalls and at slower speeds, more tire equates to more grip for the given course. I'm not much of an autocross guy, so some autocross guys have to chime in on that idea.

Hope this helps out!

s2000 racer
On track, having a 255 on a 10" width wheel is only a couple tenths faster on a consistent basis. How the S2k Challenge base their point system is through the testing on Buttonwillow Raceway. There is sufficient data to support the 255 on 10" vs the 255 on 9". The difference is approximately 0.25 seconds on a 2.68 mile track, hence the 0.25 point penalty. The key is consistency at this point. Also, I'd like to point out the S2k guys run either NT01s (R-comps) or Hankook RS3s/Dunlop Z1SS. Everything else is too expensive and unproven to go faster that those setups thus far.

lOOkatme

iTrader: (19)

Just wanted to remember that a lot of people are focused on the 235/255 width number,

there are really wide 235 and 245 tires, and very skinny 255 wide tires.

you want the wheel width to be wider than the tread width.

Just for sakes

a 255/35/18 RE-11 tread width is 9.4" (9.5") the 265/35/18 is 9.6" (10") and the 285/30/18 is 11".

a 255/35/18 AD08 is 9.9" (10" wheel) and the 265/35/18 is 10.3" and would work great on a 10.5" wheel.

Flyweight

iTrader: (1)

What did you need to do to be able to fit your 18x11.5 +42? I would hazard a serious fender pull. While I am sure this is a quick setup this may not be for everyone and people should be aware of what is necessary to fit the wheels you are running.

LargeOrangeFont

iTrader: (7)

That's nice and everything.. But that is AutoX. An AutoX setup and a open track setup are completely different. And BRZs, Miatas, and S2000s in those classes are slow, and do not need wide tires, so yes stretching the tire is probably better. You will not see any of the Mustangs or Camaros in the faster classes doing that.

As far as the S2k challenge data.. We are all in agreement. But a 255 is designed to work on a 10 inch wheel. I'd run 10s all around on my FC if I could.

lOOkatme

iTrader: (19)

I have a fender roll front and rear. no pull. I have -2 degrees camber front and -1.3 degrees camber rear.


The rear has plenty of room and the front is a little tighter fit but has some wiggle room.

I went with an 18x11.5" wheel to be able to step up to a 295/30/18 all around if wanted. the tread width is 11.5" on the AD08R tire. the R888 is 11.2" tread width. The 285/30/18 gives more room because of the shorter tire diameter and more leeway for the front wheels being about to turn, and more room with a 25" front ride height I have. so I opted for a wider 285/30/18 up front RE-11. The AD08R would also be a good candidate for tire to run with an 11" wide tread width.


I am talking in generalities here. I am trying to help people set up their car for the most driveable fastest set up. The wider wheels sure make the car feel more planted, and the slight stretch gives you the feedback and confidence, also the steering input is crisp and precise.


Now I know everyone is up in arms about my statement of a 235/245 wide tire being faster on a 9.5" wheel than a 255/35/18.

I focus on the extreme sports tires class for myself, R1R, RE-11, ZII, AD08R, XS etc. These tires run pretty wide, so in general I try to make a recommendation that I know will work. You need to be careful and look at the tread widths and size the tire to the wheel you already have, or find a tire you want and see if the wheel will fit, if not, perhaps go less wide or choose a different tire.

The slight stretch approach is to maximize grip/ handling/feel/turn in response/ease of driving/etc. It's the best of all worlds to go wide and stretch the tire. It will yield very fast times on fast tracks. The slower speeds in AutoX probably won't be as advantageous, its those long sweepers and fast tight turns at 30-60mph where this set up is great. where the limits are high and the consequences bad when you crash or spin out.

a kumho XS 245/35/18 tread width is 9.2", I would run it on a 9.5" wheel, and it also gives plenty of room to move around up front with a tire diameter of 24.7". The kumho XS 265/35/18 had a tread width of 9.75" or so, I run it on a 18x10" wheel. the RE-11 265/35/18 is about 9.6 to 9.7" and I am going to run it on my 10" wheel.

When I was looking at tires, the michelin PS2 285/30/18 has a tread width of 10.6" and the 295/30/18 has a tread width of 11.5". miles apart, yet the same tire mfr/model and only 10mm wider. I would run the ps2 in 295 on a 11.5" or 12" wide wheel.

fit the tires with a slight stretch and I am willing to bet you will be smiling all day long.

lOOkatme

iTrader: (19)

Funny, the fastest autoX guys are danny popp and Brian Hobaugh.

Danny runs a 18x11.5 F and 18x12.5" rear. tires slightly stretched.

Brian runs a square 18x12" set up and 315's with a slight stretch on his azenis sport tires.

they run the same set ups on track. I do agree set ups are different.

BLUE TII

iTrader: (9)

You will not see any of the Mustangs or Camaros in the faster classes doing that.

This brings up another very important point. We cannot compare wheel/tire sizing regarding performance across platforms.

Live axle rear and strut front end cars will perform better with a whole different set up than multi link rear and SA/LA double wishbone front end cars.

I noticed on my strut front FC that a tall, soft, rounded sidewall is fast because-

it allows the contact patch to conform to the road surface and provide better braking with all the static negative camber you have to run to counter the effects of body roll.

it creates a tire with a rounded tread profile that presents a larger average contact patch over the widely varying upright angles of the wheel/tire during cornering.

it absorbs minor impacts that the high spring rate on strut front end (required to limit its camber loss) cannot- keeping the tire in contact with the track instead of bouncing the vehicle up.

This same tall, soft, rounded sidewall tire is exactly what the FD doesn't need!

When you put rounded profile race tires the FD wears them to a nice square profile as it has a very good camber gain curve and can run much less static camber.

LargeOrangeFont

iTrader: (7)

Those are normal tire sizes to run with those wheels, and are not outside of the manufacturers guidelines.

lOOkatme

iTrader: (19)

actually the 315/30/18 on the falken website says to run it on a max of 11.5" width, Brian went .5" wider than the spec.

Also, danny is a 1/2" wider on the front and rear of his car than the tire mfg spec.

Porsche, yes the manufacturer, runs 1/2" size wider than the specified spec of the manufacturer on some of their cars.

if you measure the tire bead width and go the next .5" higher than it, you will be fine.

The re-11 285/30/18 has a tire bead width from the manufacturer of 11.1". I put it on a wheel width of 11.5" wide.

My 265 is a 10.1" wide tire bead width and they recommend a 10.5" wide wheel width as the max. for some reason I think the wider tire widths are messed up on tirerack. They have some super wide tires and the wheel widths don't correlate well.

Skeeg

iTrader: (1)

Feed front and rear fenders..... looking for a square setup, was thinking of getting some enki NT03+ in 18x10.5 +30 and running 285/30 tire?

this is track/street setup and i suck at sizing.

manana

lOOkatme

iTrader: (19)

they should fit fine.....plus you will run a little camber for handling to make it an easier fit, might need spacers to bring them out in the rear to be flush. up to you.

Skeeg

iTrader: (1)

okay awesome, from what ive been reading a 20-25mm spacer will bring the back flush. thanks for the help!

ZDan

You are making an argument against a point that NO ONE IS MAKING. No one here is suggesting that same-width tires will perform better on narrower wheels. NO ONE!

You can't make such a broad statement. You don't *know* that 235/245 is categorically always FASTER than 255/265 on a 9.5" wheel because there are other HUGE factors involved (car weight, power, alignment, etc. etc. etc.).

No one is saying it's not *generally* "better" from a pure performance/handling standpoint to run tires on the max allowed wheel width.. NO ONE. Although "leagues better" might be "stretching" the point a bit (har har har).

What I am saying is that a 235/245 recommendation on a 9.5" wheel is NOT necessarily going to give better performance than a 255/265/275 on the same wheel and in many cases is likely give inferior performance.

Well, from my experience on 275/40-17 rears on 17x9.5" over the weekend at NHMS, I can say that inevitable powerslides (525ish hp, worn-out Nittos) were incredibly progressive in nature. I don't think I would have been better off on 235s...

Again, no one is saying otherwise.

But it is NOT THE SAME THING to suggest that running the skinniest tires allowed on a given wheel width is necessarily superior to running a wider tire on the same wheel.

Pietro931

I'm looking to get 18x9.5 +45 for both and front, will these fit stock the set up? I don't want to roll fenders or do anything to the car nor add spacers. If they will fit, will they rub or hit anything if the car hits a bump or a pothole?

lOOkatme

iTrader: (19)

the wheel is just as important as tire selection. what tire width are you wanting to run? I know a 245/35/18 will fit, 255/35/18 will most likely fit.

I would avoid anyhting else larger because the tire diameter is too large and the width too wide.

I would search to ensure the 255/35/18 will clear in the front just to double check.

Rxmfn7

iTrader: (4)

^ A 255/35r18 would fit fine on a stock body and 9.5+45 wheels. I ran the same size/offset wheels with 265/35r18s with no issues for a while.