Currently I've got a set of 18x9.5 5 Zigens on my BSP car. I know several people run different setups and was wondering if anyone has tested the two?

Showcase cars run 18x10 frt and 18x9.5 rr
Daddio runs 18x10 frt and 18x9.5 rr
Evolutionary runs 18x10 frt and rr
from Prosolo finale and Nationals pics:
Berry ran 18x9.5 frt and rr at Prosolo finale...
...then 18x10 frt and 18x9.5 rr

Does the extra 1/2" make a real difference?

I would assume benefits are:
More mechanical support on the tire
Wider track by 1"
Wider contact patch

Detractions might be:
Extra weight
Inability to rotate frt to rr (applies to staggered only)
Extra rear track width/grip not necessary on a pushy car (18x10 frt and rr)

I might as well add the Hoosier vs Kumho debate to this as well. Anyone test back to back or have any real data?

 

John,
I'm not an expert by any strech of the word and have not ran that particular staggered set up( 18x10 frt with 18x9.5rr) you are inquiring about.
However, I have ran 17x9.5 all around and later opted for a staggered 17x9.5 frt and 17x 8 RR which totally changed (positively) the balance of the car.
With all else being equal, the flatter and squarish footprint in the front combatting the push and and the rounder rear promoting earlier break away and rotation transformed the car from understeer monster to a nicer balanced and easier to drive car .
To me the evo has tons of rear grip and the front needs more attention as it has:
1) a weeker geometry loosing substantial camber with roll (lesser footprint the more it leans)
2) More work to do because of the weight bias, having to do the turning and at the same time put down a bigger percentage of the available power.
My own conclusion is that the car feels better the more it's treated as a FWD and more front mechanical support for tires and even more front rubber will help with balance, driver confidence and time.

 

John,

Given the number of events we do, and the very heavy front tire wear the Evo can generate, I would choose an 18x10 setup all the way around - so you can rotate the tires.

Especially if you have a co-driver next year as you mentioned, tire wear is going to be critical. Take this from a guy who has 50+ events in the Evo with a codriver, hahaha. Chris Carris would be another expert on AWD tire wear!

That is my view from a practicality standpoint. In addition, I've never been a subscriber to the "make the car faster by removing rear grip" theory. I would adjust rotation through alignment and tire pressure rather than through tire/wheel size. A balanced approach, IMO is key. I don't think there will be a significant change in grip levels on a 285 V710 on a 18x9.5 wheel vs an 18x10 either - within the realm of measurement error and other variables, like wheel weights. But as you know, I'm no expert; my car is still faster than the nut behind the wheel.

I did see your post on Perry's board. Gimme a holler when you're ready to sell. Did you end up picking up the Ohlins that were for sale on the SCCA Forums board?

 

Staggering fitments has its benefits, no doubt....

But staggering fitments is no replacement for a careful, well chosen suspension setup.

In this case, I would say 18x10 all the way around. Figure on using tires at least 265mm wide, which will fit on an 18x10 fine if I am not mistaken, but an 18x10 will also package all the way up to a 315, again, if I am not mistaken.

 

I would go with the 18x10 all around as well if you are going to do 18x10 for the ability to rotate the tires unless you have the money to put new fronts on them every couple of events...but me personally I would stick to 18x9.5s all around...

 

Tire wear is not a great concern. I don't overdrive the car enough to ruin tires and my car is certainly not camber challenged (like Chris Carris AS Sti). If you look at my V710's now which have about 15 events this year they still look great. There is no abnormal outside wear and there is minimal inside wear from the front wheelspin. This is with rotation front to rear throughout the season, which is why I really like the idea of 18x9.5 or 18x10 all around.

Tire temps don't indicate any real problem either.

I won't be running a staggered setup (beyond the 18x10 and 18x9.5 setup) in the rear. The balance is very close to good and there is no reason to reduce rear grip. I am no longer a subscriber to that theory anyway.

In speaking with Mark he had no wear issues with his setup all year. I believe he ran the same set of tires up until Nationals.

The key metric I'm looking to improve here is time. Does the 1/2" of rim width make a noticeable/measureable difference?

Ok here's the one tidbit that has me curious about this in the 1st place. I have video of the front outside tire deflecting ALOT. I will make up a short vid and post it in a day or two. My guess is that this leads to deformation of the contact patch under high loads and is therefore limiting ultimate grip of the tire.

 

What about different offsets for F and R? Wider track in the front but same wheel and/or tire width all around? Though rotating the tires would be a bit of a biatch.

 

Thats what I have already. The wheels/tires are the same and you run a spacer up front for clearance and extra track width.

 

I would say yes it does make a difference.

changing the width of the rim for a given tire size affects the aspect ratio of the contact patch.

here is a good link on how the shape of the contact patch affects overall tire performance.
http://www.toyojapan.com/tires/pdf/TTT_08.pdf

draw your own conclusions, YMMV

 

Think of it this way, you are not removing rear grip as you are already running
285's on 18x9.5 wheel and staying that way.
The problem is that it's not optimal and you are cramming as much tire possible for that specific wheel size (makes sense on wheel size limited classes but not BSP).

By going to 18x10 frt on the same 285 tire you will be increasing available front grip wich in my case (275 on 17x9.5 frt and 275 on 17x8 rr) gave better feel and balance and improved times.

As for the questionable extra 1/2 '' not being enough to provide substantial gain, it does in theory and also did when I tried it, but others with more credentials than me who have tried it can testify (Daddio comes in mind) .

 

Chrisw great link! You just added to my wish list! Really interesting as the small radius tire looks alot like a drag tire with a long contact patch. The large radius tire has super long shoulders and a wider patch, yet the overall contact patch area is very similar.

Max,

Thanks for clarifying your point. The 10" wheel is a very tight fit on the stock fenders and they tend to get expensive. That is why I ran the 9.5's for the last 2 yrs.

So is a 10.5" wheel with 295 hoosiers and flares the next hot setup?

 

That's what i'm going with in my XP build for next season.

The problem now is that with 4 doors and limited room between fenders and doors it's not as easy to fit flares like it is on a two door .

The rear can be done with some minor work but the front is harder, oh well that's why it's called a build.
There's a XP thread that recently started and I'll post pictures of my flares when I'm done (soon).

 

Hadnt even thought about the spacers-thats a great idea...

Run spacers up front, you'd be set with a wider track. But like I said, Im not fully sure there is benefit to wider rubber and wider rims, as the hassles far outweigh the benefits. But if you can afford a set of wider rims and a set of narrower rims, it'd be a sweet deal....

 

I was under the impression that some are already running 10.5's up front with the 285's.

Having run 10/9.5 and 9.5's all around the difference is pretty subtle. the ability to rotate tires with out having to dismount is nice (and certainly cheaper). We will typically run the 10's up front at important events based on the principle that they should work better. Even doing back to back testing, the lap time variance between wheels is similar to Tom's driving variance and is tough to measure. New tires on the 9.5 fronts will out perform used tires on 10's so for long events we'll switch in the middle. We usually have 3 drivers in an event so the tire wear is quite amazing.

 

Thanks for the input.

We have one guy in SM running 10.5 fronts, but he has front fenders to boot. I don't think the 10.5 would fit a stock fender based on the look of 10's I've seen.

What kind of wear are you guys seeing? I would guess with 3 drivers you're at a minimum of 36 runs for a Pro + challenge runs. I can get alot of runs (50-60 with good grip) out of 710's and I know Mark got quite a few out of his A6's.

I'm contemplating the switch to Hoosiers next year, but now that Kumho is tweaking the 710 formula I might wait and see.

John