What am I missing with all the ultra-wide wheels & tires?
 

Is everyone who gets 9"+ wheels & 245+ tires tracking a lot? I've been spending the last several weeks deciding how best to spend $2k on a new set of wheels. The wide ones definitely look better, but they weigh (and cost) soooo much more!

Due to the weight, I'm leaning on buying some lightweight wheels that are only 7.5" wide and putting Michelin PSSs on them in stock size of 215/45R17. They won't look as cool, but I feel like I'll actually notice a little bit better acceleration. Yeah, I'd get more traction with wider tires, but getting grippier tires in the stock size seems like it will be sufficient in 98% of cases.

So with my 2 cents out of the way, if you got super wide tires, what was your reasoning behind it? Do you really need the extra traction at the expense of weight & speed? Or was it just because they look cooler?

My money is on "wider is better".

Very easy to over tire the 86. I went 17x8 with a 225. Weight, and rotating unsprung mass is evil, in my race car designing mind...even though I don't track the car.

If you don't track or autocross the car, you are just doing cosmetics. If you are tracking/autocrossing your car, then class rules and testing/comparing setups will quickly yield the optimum combinations.

There are a bunch of racers and a lot of hard parkers. The racers are almost all on 17" wheels (tires are much cheaper and the wheels are usually lighter), the show and shine guys like the 18"+ wheels.

A bunch of the autox/time trial classes make a 9" wide wheel the max for the twins.

You and I agree, Vdub. My ideal setup is an 8" wheel with 225/45-17 high-end tires. it's what I use for winter, summer and track. I also prefer a wheel with a significantly lower offset than stock, which is tough to find. I am very happy with my Kosei K4Rs.

225/50-16 on a 7" wheel and +40 ET. Yeah, a 7 is a bit narrow for a 225, but man, they're light. And the car stays fun to drive. :)

When people change their wheels, they change also the tires to stickier ones. So, they see they are faster but not so much because of the size. You can check a test made some time ago:

http://www.roadandtrack.com/car-cult...ransformation/

Most of the gains can be obtained by just changing the rubber and keeping the size same. In fact, the car was a bit slower with the bigger tires!

Where size matters is on the better heat energy dissipation. If you don't track at all, or track up to 5 laps per time then it doesn't really matter.

I am 17x9 245/40 to stay in my autocross class(STX), but my dailies are also 17x9 cause they are pretty. If it rains i just use my dailies to run, so they are at least somewhat competitive.

also the road and track article sums it up pretty good. The wide stuff is better for lateral G's and autocross is all about low speed high G.

I've put a set of 225/45/17 Michelin PSSs on the Stock PP wheels and they have been serving me great! They are only ~1lb difference between the 215s and you get 0.5" (6%) more contact patch and 225 is a better fit to the 7.5" wide wheel.

**Also food for thought since you are shopping the PSS: Contact patch gain vs rotational weight gains

size weight tread width
215/45 21 lbs 7.7"
225/45 22 lbs +1lb 8.2" +.5"
235/45 22 lbs +1lb 8.2" +.5"
245/40 23 lbs +2lb 8.5" +.8"
245/45 23 lbs +2lb 8.0" +.3"

Lateral G is bit better, but the difference is small: +0.02 g. Another note is that the wider tires have a higher load index (91 vs. 87). This means a bit stiffer sidewalls that give an advantage in cornering and slalom. Overall, not the difference someone might expect from a 235 tire.

Spending all that money and going with pss? Lol
Get a better tire. Unless you pay under $120 for each you are clearly getting ripped off.
For some odd reason people still think just because it's an oem brand it has to be better right? Wrong. That's just the sales rep pulling a fast on.

For auto-x, wider is better because you can add cornering grip without going fast enough to worry about drag/aero. STX is limited to 245 on 17x9 so it's the standard setup.

For track, you need to weigh the gains in cornering grip against the losses from drag/aero. Will be course-dependent but 225 on 17x8 is a good starting point.

For street, I don't think it really matters unless you're really concerned about fuel economy. I'd run the stock setup on cheap tires (215 on 17x7) just to have fun, but wide tires/wheels do look nice aesthetically.

STX allows up to 265, if you are 2wd, only the AWD guys in STX are limited to 245. most of the guys in my club run 255/40

Ah ok I stand corrected!

I don't think there is enough time to overheat a tire in auto-x. A narrower tire with same compound should provide almost same grip. Maybe you have better results because the axle track is a bit bigger and the suspension geometry is altered.

from Texas, we can 100% overheat tires. single driver maybe on your 5th run if its hot(100+) out, have a co-driver and spraying them down after each run you will get 3-4 runs each before they go.

My 17x9's w/245's (RPF1) weigh less than my OE set of wheel/tires, Tirerack will ship 'em to you mounted and balanced for <$2k, other vendors can beat Tirerack's pricing on the wheels and they pop up used all the time.

As above it's an autocross setup.

Like mentioned elsewhere in this thread, for a general performance setup on an NA 86 7.5" and 8" wheels are going to do you good but I'd only do that if you wanted to run a 225 tire, 215 fits great on a 7" wheel and it doesn't need to be stretched imo and you can save more money by sticking to a lightweight 7" (I'm doubled down on that opinion after seeing a new BRZ with 7.5" wheels and stretched OE 215 Michelins, I drive another car with 225's on 7.5). I'm sure some will disagree on that.

Also as above MPSS are good street tires that hold up to abuse better than most but they're not some magic transformative thing that'll turn your car into a Lotus level corner carver. Pretty much no tire above 200TW is.

What are you actually going to do with your car OP? The tl;dr is yes, the wider wheels/tires are bought by people who want the traction for track/autocross OR for looks, totally unnecessary for just driving around. (As a tip, it's pretty easy to tell based on the tire they're running, Bridgestone RE71R, BF Goodrich Rival-S for autoxers, Dunlop Z2SS, RS3/RS4, RE11, Rival (non-S), Nitto, etc. etc. for track. Anything with lots of little tread blocks: just for looks)



Based on the questions I think you're overthinking it, just grab something that looks good to your eye, <20 lbs, if you go with 7" stick with OE tire sizing, 7.5 and 8 jump up to 225's, and don't put 225's on 7" wide wheels and you'll be a happy camper (caveat being for competitive autox 225 w/ 7" is worth losing the steering feel).

Also, don't go staggered (wider in the back)

If the course is big enough and it's warm out you can totally overheat 200TW tires, and fade street pads/OE fluids. Did both on Saturday, on a tiny course, with a cold breeze, in a different car :bonk:

I can see it being the case that it's hard to get up to temp (I struggled for awhile getting heat in my Bridgestones last year) especially in colder regions and with short <40s courses, but that's definitely not universal, tire sprayers are common at competitive events out here for people to cool off tires between runs.

Hey I DD 245/40 RE71R!

But I'm also a moron.

Hey if you can use 'em up within a year at least you're posing hard.

If you're still running 'em next year and they're not bald you should be exiled to the old man car meets next to the Cadillacs with original whitewalls.

You're forgetting one extremely important fact: the sidewall height. For example a 235/45 is significantly taller than stock and that elongates your gear ratio, so you accelerate slower and therefore feel very noticeably heavier. 245/45 would be awful.
I run a 235/40 (can't get PSS in that size tho unfortunately) for this reason: light, wide, and a better rear end gear ratio. The car felt instantly lighter going to them from 225/45/17 PSS despite the combo actually weighing .5-1 pound more.

Some people do it because they plan to go forced induction in the future and in some states in Australia having a wider wheel and tyre for the increased torque and power makes it easier to get the car engineer certified so you can drive it without having to worry about getting pulled over by the local police and slapped with an unroadworthy certificate.

I went with 18x9 wheels with 255/35 tires for my daily setup. I did that because I loved the look of the 18s in black (I think lighter colored wheels look too big in 18s on our cars, personally.) I went with a 9" width because they didn't offer anything narrower, and I'd heard good things about how much grip you could get out of some 255s. That setup "only" weighs 3.9 lb more than the OEM setup, despite being significantly larger, but I'm okay with that for my DD setup.

For autocross, I have a set of 17x9s with 245/40 tires. That was the "best" width for autocross according to just about everyone I talked to, and everything I read. That setup is also quite a bit larger than stock, but weighs only 0.4 lb more than stock because of the lighter wheels.

I don't understand why people think wider is better. I run 225's (nitto NT0'1s mind you) and can put down 300whp no problem.

Straight-line power delivery isn't the only thing wider tires are good for.

What?

No idea what I am talking about I am drunk apparently lmao!!!

Surprised the question about the larger contact patch hasn't come up....is it larger, or just a different shape with the wider tire?

/pot stirred

If you lower the pressure, it is larger. Otherwise, it just changes shape.
( I guess there might be some slight differences at very high lateral g's).

I've seen lots of internet/bench racers argue the patch gets larger, even on equal air pressure, and tire carcass.

Wait... WTF? That's a thing!?!? I guess it is similar to inspections in the US, but tire width vs power checks?

:threadjacked:

In other news...
As for contact patch, in general I would think you would need to run lower pressure to prevent uneven wear and other problems associated with too high tire pressures. Which has the results previously described.

Physics >>> internet/bench racers......:paddle:

i think they have done tests to show it actually does grow contact patch some. i think due to the fact that it isnt just gas pressure keeping the car off the ground. the reason 9 inch wheels are nice is because they are faster and they can fit the bbks.

Static contact patches do not change area - that is the physics. They can change shape, but all else being equal, they are the same area.
If someone goes around changing multiple parameters, yes, area can change some, but it can shrink as well as grow under multiple changes. If you consistently want a larger contact patch, you must reduce tire pressure - but even that within limits.

"Physics" assumes a tire is a perfectly deformable air vessel that allows the pressurized air in the tire to react perfectly to the normal force on that corner of the car. The fact is that tires have structural rigidity, especially in the sidewalls, and this affects the contact patch. Assuming that you properly set up the suspension to account for the new width of tire and new wheel offset, you absolutely do get a larger contact patch from a wider tire. That is not debatable.


What is debatable is how much of an effect this change has on the vehicle's ability to accelerate and brake, as well as its cornering stiffness. This is mainly debatable because it in fact, has yet to be fully understood. To get close, you need equations like this, and a whole lot of experimental data from your vehicle in order to fill in all of the constants: https://en.wikipedia.org/wiki/Hans_B._Pacejka
Since I doubt any of the people on this forum have plugged through this with any of their setups, let alone a large number of different ones, I leave you with this advice:
Get ahold of your local 86 club and if the owners are so kind as to let you, try as many different setups as you can so that you know how they feel to you. The theoretical fastest is not always the fastest in reality. Race car drivers make their engineers make changes to "less ideal" setups all the time, and then end up running faster simply because they are able to work better with the new setup.
Also, look at what autocrossers and road racers are saying. I wouldn't take their lap time input as gospel because there is a lot of margin for error with different skill levels but trends can still be noticed in terms of wider vs. narrower, and also things like tire size in relation to wheel diameter and width. For example, we all hate on stretch and camber for obvious reasons but the absolute widest tire that you can squeeze onto a wheel is also not the ideal setup. If you can find information about the same driver running two different setups and comparing them, that would be particularly useful. The classing that your setup fits into is also important if you are going to be doing anything where that matters.


Use the information that you have collected to make an informed purchase based what you prefer and what you want to do with the car.

As noted before, if you change more than one thing, results may differ. Given the same ID and OD and sidewall, the contact patch stays the same. Change it and your contact patch may change, but not necessarily larger.
The original point was to not automatically assume a wider tire yields a larger contact. As you noted, there are different conditions that benefit from a change in tire width, and there is a "better" tire width for each condition. There are also worse tire widths!!

My post probably focused too much on the effect of width given the same tire pressure and carcass (in the later quoted post).

As you noted, unless I find a test of the conditions I am interested in, or am willing to spend the money to test various combinations, I will not assume wider is better or worse.

I have not read all the posts here, but perhaps there are some that describe enough measured data to make a good decision. I know I use a wider tire (on my Supra) because of other benefits related to road racing because I did find significant data indicating wider was better due to the other aspects not related to size of contact patch. YMMV!

Carry on.

There are other unspoken benefits to a wider tire as well.

I would expect a wider tire to wear longer, as the load is distributed over a larger area, and it also does better on crappy roads, as small potholes and cracks are less likely to suck the entire wheel in.

Of course, there are also downsides, such as higher cost, and arguably a higher propensity to hydroplane, though I've done 80 in torrential rain on my 255s without any issue (Michelin PSS FTW!!!)

It's also harder to get enough heat for wider tire, if it's compound grips best only starting from specific temp range. Just like it's harder to bed pads on some of biggest BBKs, when pads of very same compound are easy to bed on smaller stockers. Same story of much more heat needed. And it's not just standing water "aquaplaning" matters at. Throw in liquid dirt or snow slush, and that difference rises quickly. Everything is compromise, and for most uses imho very wide tire cons outweight pros.

I've tried out a couple of combinations on the track and at autox, I have 2 sets of wheels: 17x9 with 245 RE71r and 17x8 with 225 RE71r both of which weigh the exact same (the wider wheels are slightly lighter but tires are heavier and the combos come out the exact same weight).

The wider tires are consistently faster at both autox and on the track for me (1-2s). I run at MSR Cresson, which is a 1.7mi track that has few long straights and a healthy amount of low speed elements.

I thought the skinnier tires might be faster after reading a few of the threads; however, I believe that since my two setups are the same weight I am only getting the wider tire benefit and not seeing any pickup on the smaller setup. My experience leads me to the conclusion that the smaller setup is only going to be as fast or faster with lighter weight.

I know that the R-comp tires all run much wider than street tire equivalents (a 225 Hoosier is as wide as a 245 street tire), and I didn't see any benefits trying a 255 over a 245 street tire for autox (the 255 cost more and didn't seem any faster and didn't show any additional grip under analysis).

I started reading this in the hope that it may shed some light on what I should be running for a DD and the occasional track day, but nope...even more confused now.


Running a supercharger, I want to figure out how I can get better speed through the corners on standard OEM wheels. I have 215 Continental DWS right now and I am very disappointed in their performance. I don't think anyone has mentioned spacers...or is that considered a no-no for the track. Driving in the wet, I might as well have been driving on ice, but the pressures might have been too high at around 35 psi. Nothing's simple is it? :)