Robby

I've got 17" Cup 2's on a Turbo S- 255/40/17 on 17X9 rear & a 225/45/17 on the front 17X7. The 968 had these as an option, but the front wheel was 7.5" wide instead of 7". The Club Sport on Turbo S was 16X7 & wore a 225, so I knew I'd be ok w/the 17X7 w/225... It seems to be fine & I've had it this way a year & half or so, but am still keeping my eyes open for factory 17x7.5 Cup 2's.... Wouldn't be worth the money for me to remount tires, etc, for them, but if I could time it right, when buying new tires anyway, I could do it then & then sell my 17X7's. Well, what I'm wondering is- what affect would it would have, me backing up my 225's w/an extra half inch of wheel...??? More understeer, oversteer, or what...? Would I even really notice on a street car? I understand that race cars ususally fill more tire up w/rim whereas street cars usuall try to squeeze more tire on for better looks- i'm just wondering how the change would make my car handle differently...?


thanks
Robby

ninefiveone

negligible effect.. i wouldn't bother

Dave in Chicago

Yup, negligible.

When you buy tires, there are always specs for "recommended rim widths". This is the part to watch as various sizes of tire, various models of tire, and various manufactures will have different specs.

I've always stayed within the rim width recommendation for THAT specific tire that I was mounting.

KuHL 951

I doubt if you would notice the wider front wheels/tires. I run 9"(F) and 10.5"(R) after 7.5" and 9". The biggest improvement I found was getting better tires. Now the car has much better high stability and grip at the limit but my turn-in suffered a bit compared to the smaller earlier combo. Much better gains can be had from tweaking the supension with sways, springs, and shocks plus getting a slightly more agressive alignment.

Robby

Hey guys, thanks for the input, but, I already knew it wasn't worth doing- I mean, the only way I'd do it is AFTER my tires are worn out & I'm ready to buy new ones, assuming I'd found a deal on the wheels- I would spend the money to dismount the current Pilot sports & then remount them, etc- all the money & effort- BUT- if timed correctly, it wouldn't be much work OR any more money really, after having sold the 7's....

Anyway, I knew it wouldn't do much... I want to know what it would do though, no matter how slight....??? It HAS to do something.... Let's say that I went from 6's wearing 225's to 8's wearing 225's... what would the effects be then? OR, from 7's to 9's....? I'm just wanting to know what adding that half inch to my wheel w/the given 225 front tire size would cause- oversteer, understeer, faster turn-in, slower turn-in, better stability, more tramling, or less, etc...? By the same token, I GUESS I could ask what the effect would be if I went down to a 6.5" from the 7"...? Obvoiusly, not something I'd ever do, especially since 7's seem to be at the bottom of the rim width range for 225's... Any input here would be greatly appreciated...


thanks again,
Robby

Oddjob

Regardless of application (street/track/auto-x), you will not notice the difference in handling at all with a 1/2" wheel width increase. You will not increase the tire contact patch by any significant amount and you will not feel any difference.

You may have some slightly different tire wear characteristics (moreso with track use), since the wider wheel will not buldge the sidewall as much so the shoulder wear will be a little better with a 225 on a 7.5 vs a 7, but it will only be very slight.

If you went from a 7" with a 225 tire to an 8" (or greater) with a 245 tire, everything else being equal - you would get more grip up front = better turn-in and less understeer.

Z-man

I dunno about that...

I have done back to back comparions of the following two setups:

Setup one: Front: 225-50/16 on 7Jx16, Rear: 245-45/16 on 8Jx16

Setup two: Front and rear all: 245-45/16 on 8Jx16.

Car: 944S2, Tire: Toyo Proxes RA-1's, Track: Lime Rock Park (and some autocrosses)

With setup two, there is a noticable improvment in turn in, and some of the inherent understeer are cars have is dialed out.

I think the key to seeing improvement in handling when it comes to our cars and wheels is to increase the contact patch in the front to match the rear width. If that can't be done (some people run steam roller-tires in the back), then narrow the gap between the two.

-Z-man.

Oddjob

Your setup 2 sounds an awful lot like the last comment of my previous post...

>>>If you went from a 7" with a 225 tire to an 8" (or greater) with a 245 tire, everything else being equal - you would get more grip up front = better turn-in and less understeer.<<<<

Sure if you upgrade both wheel width and TIRE width you will notice something. But that is not what Robby was asking.

Using the same tire size and only increasing the wheel width by a 1/2" - you will not notice any real difference. I can nearly guarantee that if the driver was not told which wheels were on the car, there is no way he would notice a 225 on a 7" versus a 225 on a 7.5".

Z-man

Note to self: remember to read the FULL posts before posting your opinions...

IE: Yeah, what he (Oddjob) said.

-Z.

Robby

Yes, I know it would be minimal at best, but there has to be some sort of change & I want to know which direction it would go...? I mean, running smaller wheel w/given tire size up front vs running larger wheel w/given tire size up front...??? I mean, does backing up the front tire w/slightly more wheel actually allow a greater contact patch for the same given tire size- is that what you guys are saying??? therefore, IF I decided to go to a 6" wheel & cram the same 225 tire on there, I would be limiting some of the contact patch??? Completely hypothetical- I would never do this... Then, there has to be some point where any extra wheel behind the given tire size would be pointless, such as putting 225's on 10" wide rims- you'd just be adding rotational & unsprung weight.... Anyway, does this make more sense....? I'm really just curious to know...

Also, what would most people here run if sticking w/the same 225/45/17 & 255/40/17 combo...?? The 9" seems perfect w/the 255, but the 225 is really 30mm less than the 255, obviously- this means that the 225 would be closest match to an 8" wide wheel.... I know the 17" Cup 2's come in 7, 7.5, 8, & 9, but the 8's are a dif offset, from what I understand- not to mention that even if I could get them, bew, they cost about what Fikses, etc do- cup 2's are some of the lightest factory wheels made, but even still, Fikses are slightly even lighter...

Thanks...

ninefiveone

Alright alright... since you won't accept the truthful answers of collective wisdom...lets beat it to death.

A tire fits or doesn't fit. If you fit a tire onto a rim that's within the manufacturer's suggested range, and inflate the tire to the appropriate pressure... it'll perform as expected. Sidewall flex is such a dynamic thing based on how hard you're cornering, what the temperature of the road is, the temperature of the tire, the air pressure in the tire, whether there's a bump in the road right there, what kind of bump, whether it's wet out, what the lunar cycle is, whether you're wearing blue that day...

You get the idea. wheel width is not going to be a deciding or even significant factor in this.

Also, tire widths vary widely amongst manufacturers and models within manufacturers. A 225 Bridgestone S03 is not the same width as a 225 Michelin Pilot Sport Cup. So one needs to accept that this is not an exact science where measurements are precise.

If you're going to someday go through the effort of buying wheels in various sizes, what you really want to consider is what size tire you're going to ultimately want to run and that will be based entirely on what you intend to do with the car.

If you plan on sticking to the street, I would stick to the 225 and 255 that the factory runs. The steering will be most responsive with this setup. Actually it'll be even more responsive with light 205's but I think that's just too thin for the weight of the car. I've driven everything from 205's to 255's on the front of the car and while the grip goes up with the tire width as you'd expect, steering feel also gets heavier and the car will have a greater tendency to follow grooves.

So with that setup, I would run 7.5's and 9's as the factory does. It's the easiest setup to obtain and it'll feel exactly the way it should.

If you're going to run at the track a lot, then I would run the same size all around and i would run 17X9's or 17X10's. 245/40/17 or 255/40/17 are common sizes and easy to find in performance tires.

For the money, unless you get a great deal Cup2's and Fikses prob aren't the greatest value out there. You can pick up boxster rims in the appropriate sizes all day long for quite cheap and it's within a lb or so of cup2's or fikses in the same size. Or you can go CCW, forgeline, etc.... it's a long list.

If you love the Cup2 look...then by all means go ahead but don't make it harder on yourself for zero benefit. Get the easiest sizes to obtain. You're not going to get any benefit out of an extra .5 inches of rim width.

Robby

Hey, thanks for the input, but I think my point has been missed here... I already have 17x7 fronts- MUCH easier (& cheaper?) to obtain than 17X7.5's- I've seen that most lists recommend at LEAST 7.5" for 225's & some even 8"- this is what I'm wondering-> what am I missing? what effects would the extra 1/2" OR whole 1" have? It HAS to be SOMETHING! there's no way it's nothing, although, I'm SURE that the argument of "you wont notice a difference" is dead-on, as I'm sure the dif is MINIMAL at best.... Therefore, I'm not looking to buy new 7.5's unless I find a hell of a deal & still wont mount them until I buy new tires all-around anyway... As for dif tire sizes, I'm sticking to 225's- unless I win the lottery (which I dont even play)- in that case, I'll be going for 18x8 w/235/40/18 & 18x10 w/275/35/18 OR 18x8.5 w/245/40/18 & 18x10(?) w/285/35/18 (IF it would fit)....

So alas, my question- quite simply, forget the rears- we'll deal w/225mm fronts- what would the handling dif's be b/t me running these 225's w/7" vs 8" rims??? There are enough track junkies here, I would think, who would have an idea... if I leaned toward the small wheel for a 225 vs a large wheel for a 225, what would be the differences I could expect? Would braking be helped in any way by using a larger wheel? What about turn-in, OR, is braking or turn-in, etc, ONLY enhanced by using dif sized tires? I mean, I assume 7" is about the smallest most would mount a 225 too, so I'm now at the low end... I'm wondering what I could expect, even if minimal at best, if I ran 7.5's or even 8's?

thanks...

bleucamaro

That turn in feel is more likely from a change in scrub radius than an effect of larger overall width.