Wheel width front to rear and Handling

[BuddyP]

I know I've seen a topic on this but can't seem to find it. I'm curious about the handling differences with having a car with say 8" wide wheels in front and 12" in back vs having 9" in front and 10" in back. I know suspension, track width, wheel offests all play into this as well but curious to hear from the experts which is better on the track.



As I see it the wider rear and narrower car would cause a understeer condition causing the need for rear sway bar??? whereas the 9" offering more front grip and 10" offering less causing a little more oversteer? And would the narrower rear cause issues with traction on say a 500 ish hp car coming out of a turn huring what you gained coming into the turn with a 9" front?

[Paul Huryk]

I'm a small volume wheel manufacturer and will put in my 2 cents... The wheels I produce are for 3rd generation F-Bodies (82 to 92) at this point.

The issue comes down to balance with a front engined RWD car, most of these vehicles have 55% to 60% of the weight on the front wheels. The optimal way to balance a FE RWD car is to have a square tire setup all around (same size on all 4 corners), so you might have a 245-45-17 in all 4 corners, or a 275-35-18. Each tire has the same contact patch and should be able to keep a more neutral handling consistency, depending on the suspension design and tuning (of course). In some very front biased cars, having a wider front tire may actually help, much the same as having a rear engine/mid engined car with wider rear tires to balance the handling.

As I mentioned above, I make wheels for the 82 to 92 f-bodies; cars that came with relatively wide tires (245-50-16 in some cases) from the factory (compared to older cars) - they all used square tire fitments and handled pretty neutral, regardless of suspension tuning. Unfortunately the 245-50-16 size is almost extinct and people are fitting 17" and larger wheels where tires are available. Problem is that people are running into major balance issues with staggered tire setups, say a 245 on the front and a 275 on the rear - in a front heavy car the rear tires can give more cornering force than the fronts, leading to heavy understeer, even with additional tuning. It can be even worse if you go with different diameter wheels and tires too - say a 245-45-17 on the front and a 275-35-18 on the rear. Our wheels are 17" x 9.5" and allow a 275-40-17 on all 4 corners, providing the square setup while simultaneously allowing the maximum width 17" tire in front (you can fit larger in the rear still) - handling is neutral and predictable. Even cars like 3 series BMWs with a 50:50 bias can benefit from a square setup, even though some sport suspensions on those cars were staggered from the factory (typically a 225/255 fitment).

Now I have a buddy who has a 3rd gen with a 245/335 staggered setup on his car - very unbalanced and hard to drive fast (and it has a lot of power too) - would probably be a handful and not turn very good times on a road course. I've also driven the cars with a 275/315 stagger and they are a lot better balanced and would probably be tunable through the suspension (only a 40mm difference in tires, not 90mm).

On the track, the square or close to square setups would probably be the fastest with a FE RWD car and the close stagger would be right up there in terms of times. You mention 9"/10", which would allow a 255/275 stagger on a car (assuming no tire contact), which would probably work very well. Keep in mind that sway bars can be used to tune, but won't necessarily correct large problems.

I'm not an expert, but this is what I have found out over the years; not to mention many expert sources have published similar findings.

[LS1-IROC]

On my 3rd gen I run a 265/335 and it is somewhat unbalanced. My old 255/295 felt a little more predictable in the turns...however the 295's could not provide the straight line grip I needed. I wish I could fit a 295 in front with the 335's in back. I think I need to change up my sway bars in order to get it better balanced.

[icemanrd19]

ive always been told to run no more than a 40mm difference I went with a 315/30/18 and 275/35/18 setup. Perfect in my opinion between looks and traction

[Paul Huryk]

On my 3rd gen I run a 265/335 and it is somewhat unbalanced. My old 255/295 felt a little more predictable in the turns...however the 295's could not provide the straight line grip I needed. I wish I could fit a 295 in front with the 335's in back. I think I need to change up my sway bars in order to get it better balanced.

70mm is a huge difference from front to rear on these cars - not surprised the older combo felt more predictable.

Question - why 265 and not 275 or 285 width on the front?

You can fit a 295-35-18 in the front - as long as you have the right BS on a 10.5" wheel, know a few people who have that on their rides.

Changing the sway bars will probably help, but with that large of a difference front to rear, you may need to change your springs too. Bars are easy enough to try out.

One thing I have always suggested is to build the car's suspension around it's primary purpose and not try to make it do 1 or 2 other things also. For example, on a street car, you would want to run a moderate spring rate and quality, but decent in the rain and somewhat long lasting tires. If you want to hit the 1/4 mile, you have another pair of wheels with drag radials and if you want to hit the road course, a set of road race tires on a set of wheels. Obviously thinking ahead when building helps - adjustable shocks might cover 80% of the applications you might run into with a twist of the knob...

[TheJDMan]

I'm running 275/35R-18 on 10" wheels front and 335/30R-18 on 12" wheels rear and the car will push if I don't set the front end properly before entering a corner. Next time I need tires I will likely go to 285 on the front.

[LS1-IROC]

70mm is a huge difference from front to rear on these cars - not surprised the older combo felt more predictable.

Question - why 265 and not 275 or 285 width on the front?

You can fit a 295-35-18 in the front - as long as you have the right BS on a 10.5" wheel, know a few people who have that on their rides.

Changing the sway bars will probably help, but with that large of a difference front to rear, you may need to change your springs too. Bars are easy enough to try out.

One thing I have always suggested is to build the car's suspension around it's primary purpose and not try to make it do 1 or 2 other things also. For example, on a street car, you would want to run a moderate spring rate and quality, but decent in the rain and somewhat long lasting tires. If you want to hit the 1/4 mile, you have another pair of wheels with drag radials and if you want to hit the road course, a set of road race tires on a set of wheels. Obviously thinking ahead when building helps - adjustable shocks might cover 80% of the applications you might run into with a twist of the knob...

The car was built as a compromise of many things. The car is 99% street driven. It was built to have fun driving back and forth to work with an occasional trip to the track both 1/4 mile and autoX. That being said, I expected it to be way more unbalanced than what it actually is. I think with the R888's it helps overcome some of the problems.

[Paul Huryk]

The car was built as a compromise of many things. The car is 99% street driven. It was built to have fun driving back and forth to work with an occasional trip to the track both 1/4 mile and autoX. That being said, I expected it to be way more unbalanced than what it actually is. I think with the R888's it helps overcome some of the problems.

If you car is lightened on the front end also - that helps a lot. My Camaro has been lightened about 100lbs from stock on the nose (hood, heads, brakes, no A/C) and you can definitely feel it push less.

[XLexusTech]

Doesn't offset play a big part as well? Scrub?

[Paul Huryk]

Doesn't offset play a big part as well? Scrub?

Offset (or backspacing) has a huge amount of impact on the fitment of wheels and tires. Pick the right offset and you can fit larger tires and never have a problem, pick the wrong one and you rub like crazy.

[LS1-IROC]

If you car is lightened on the front end also - that helps a lot. My Camaro has been lightened about 100lbs from stock on the nose (hood, heads, brakes, no A/C) and you can definitely feel it push less.

Interesting you say that. I noticed a huge difference when I put the LS1 in and then again when I put the heavy 9" rear in as well.

[GeoffP]

Weight bias definitely matters. I also think offset variation can make a decent difference. IMHO, GM had different offsets (wider track width in the front) on the IROC for a reason. I noticed a fairly significant change in the balance of my IROC when I changed the factory wheels to matched offset Centerline 16x8's. It wasn't a big deal to me because I drove the car on the street 99% of the time.

Also, it's been suggested to me by more experienced guys to put matched tires on my 68 to balance the car better and help me learn how to drive with a more predictable vehicle. 275/35-18's on all 4 corners vs a 245/45-17 to 275/40-17 stagger. The car pushed terribly with the old combo. It took next to nothing to oversteer the car and have it keep going forward. I slid over many cones over the last 2-3 years thanks to this. I hope the new tires/wheels along with my new suspension setup provides some significant improvements.

[SLO_Z28]

As someone thats been there, a square tire is a MUST. The car will push with smaller tires on the front.

[SkinsandJrfan]

I have a 68 camaro with a heidts Pro G subframe. I currently have a 245/40/18 front and 275/35/20 rear. Whats the widest tire I can run up front to try to square this thing up. I'm running a 383 stroker engine.

[GeoffP]

Brian - I suggest calling Heidts tomorrow and ask. I bet your car would really benefit from a 275/35-18 on the front. We'll know for sure what the difference is in just a few weeks on my car.

Hey I did a search and came up with a 265/35-18 as the largest tire the Heidts frame can accommodate - look here: http://www.hotrod.com/techarticles/c.../photo_02.html

[SkinsandJrfan]

Damn. Thanks Geoff. 265 would be awesome. Much closer to square.

[SkinsandJrfan]

So would I be best served ya think, running the 265 fronts and keeping the 275 rears? I might be able to fit a 285 in the rear. I want to go wider in the rear due to straight line grip but don't know what's best at this point.

[GeoffP]

It'd be my guess that there isn't a significant enough difference in a 265 and 285 to make a lot of difference in the front to rear bias plus having a 20" wheel may remove some of the "bite" of that wider tire. Your car may end up being more evenly matched front to rear than you'd think going on width alone. Hopefully someone with more experience with this will chime in.

[Paul Huryk]

Weight bias definitely matters. I also think offset variation can make a decent difference. IMHO, GM had different offsets (wider track width in the front) on the IROC for a reason. I noticed a fairly significant change in the balance of my IROC when I changed the factory wheels to matched offset Centerline 16x8's. It wasn't a big deal to me because I drove the car on the street 99% of the time.

Also, it's been suggested to me by more experienced guys to put matched tires on my 68 to balance the car better and help me learn how to drive with a more predictable vehicle. 275/35-18's on all 4 corners vs a 245/45-17 to 275/40-17 stagger. The car pushed terribly with the old combo. It took next to nothing to oversteer the car and have it keep going forward. I slid over many cones over the last 2-3 years thanks to this. I hope the new tires/wheels along with my new suspension setup provides some significant improvements.

I have no idea why GM used different offsets on the front and rear of the 3rd gen cars in 16" - maybe only to make it harder to rotate tires. By putting 2 fronts on all 4 corners, you can improve handling (and confidence) by widening the rear track to the same dimensions as the front.

The same size is going to be a lot more predictable all around - assuming you can fit them (some cars have very limited in front sizes as we all know). Your friends in the know are correct, although a 275-40-17 may actually be faster on a track vs the 275-35-18 due to more sidewall buffer.

I shed (barely) a tear every time a fellow 3rd genner puts a 245/275 stagger on their cars for looks and then complain the car pushes too much - even though folks like me try to talk them into a square setup.

[Paul Huryk]

I have a 68 camaro with a heidts Pro G subframe. I currently have a 245/40/18 front and 275/35/20 rear. Whats the widest tire I can run up front to try to square this thing up. I'm running a 383 stroker engine.

Brian, keep in mind that square means the same size tire on all 4 corners (not necessarily wheel width though). If you were to go 275-35-18 in front and keep your 275-35-20 in the rear, it would not be balanced right. This is due to the 20" tire having a 2" larger circumference and that means about 8% more tire on the road with the same width - so you are running a stagger in effect. Now if you were to go 275-35-18 all around, then that would be optimal in terms of balance.