Hello all, I was wondering if the road race people (Manny, H. Coleman, etc) as well as the auto-cross guru's (Max Cooper, Damon B, Montego, etc ) as well as everyone else, can you please give your professional input on equal tire sizes front and rear, i.e. 255/40/17, vs the custom wheel set ups that have 255 up front and 285 rears, etc? I ask this, as I am about to put my foot in the door to the autocross world (2 weeks to be exact), and after that, the road racing world. I know that equal tire sizes helps the car rotate better, and give it a nuetral feeling, and the wider rears give considerably better grip, but at the expense of understeer being that the grip wheels are smaller than the drive wheels.

Is this all driver prefference when it comes to tire size? I really only see show cars that have the huge tires in the rear, but all the track cars, set ups posted by road racers, and even professional race teams and time attackers have equal tire sizes when they pull the best laps. Does it all depend on driver style?

Or, is my understanding all mixed up, and I have everything wrong? I am here to learn, so please post links to sites, threads, even book titles (Yea, i'll actually go search it out in hopes it will better my understanding, skill and knowledge) that would help me better understand this, as well as your input.

Thanks in advance,
Chris

 

My opinion is this. It's never a BAD thing to have equal size front/rear tires, but i would not subordinate rear tire size for the front.... in other words:

If you were to mount 265-section front tires on the 9.0" CE28's in your sig, which would be about as large as i'd go on that wheel, I wouldn't feel any pressure to mount a matching tire on the rear wheel, because you could go wider... go for a 275-295 section tire.

Then again, if you are going to purchase track-specific wheels, and the choices in your price range include fitments suitable for running front tires as wide as the widest rears, go for it.

I currently run a 255/275 combo, and would consider the car ballanced on everything but very low-speed turn-in, or on long, low-speed exits where they'll start to plow a little, and heat up the outside front wheel. On the street, and on most other corners, i'd call it perfect.

 

If you are just getting started, like me, I would go with the same size all around for rotating purposes. Performance will come after more seat time and then you could look at staggered verses same at that point.

Until you get the seat time down, your personal performance will be more of a hindrance than your tire setup.

 

Refer to my review of the Enkei/Toyo for my opinions on this topic....

https://www.rx7club.com/showthread.p...ighlight=enkei

 

I agree with Mahjik. Get the seat time in, and develop your skills to the point of turning consistently quick laptimes (with 0.1 seconds each lap).

My opinion for staggered vs symmetrical fr/rr widths is mixed:

I've driven with both setups, and have turned quick laptimes with either setup.

Admittedly, the staggered setup allowed me to push harder with confidence, knowing that if I exceed maximum cornering grip, all I need to do is let off of the gas, to get the front tires to bite again.

With the symmetrical setup, I find myself sawing at the steering wheel, and feathering the gas pedal at the absolute limit of tire stick--and this is certainly more entertaining than just letting off of the gas pedal to regain tire stick

It will come down to your preference as a driver.

Personally, I prefer the symmetrical, but that's due to logistical considerations. I don't trailer my FD to track events, so getting a flat tire en route to a track venue really sucks. With a symmetrical setup, you can carry a full size spare in the car, and not worry about ruining your weekend, if you get a flat--the full size spare can go at any wheel position on the car. With a staggered setup, you'll need to carry a fr and rr wheel/tire--space is limited in the FD!

 

Another thing to consider is the class you want to race in. If you plan on racing in a stock autocross class, you must use stock size wheels, with a stock (or nearly stock) offset. Bigger wheels will put you into a street prepared class. I'm not familiar with the road racing rules, but I suggest that you check them out before upgrading. I don't know if stock is an option for you, as I don't know your mods.

If you are a beginner, I suggest that you go with what you have. Get a feel for the car. Spend some time learning to drive it as is. You will find that it does pretty well in its stock form.

Lastly, do some research on alignment settings, and then get it aligned to your specifications. The stock alignment is geared toward good tire wear rather than performance.

 

Some manufacturers set up the suspesion and the steering ratio on the vehicle to perform specifically with a staggered tire and wheel set up like the newer model BMW M3's, Porsche 911, Acura NSX and the list goes on. Having the staggered fitment will certaily increase the way you accelerate and in some small ways assist in braking but you are also going to increase the amount of understeer on your car. When your auto crossing understeer normally will take away from your times. where as staggered fitments can help with road racing where you have longer straight runs.
It comes down to how your specific vehicle is set up, the type of racing you want to do, and how aggressively you want to get into it. i have to agree with the other guys and say the best advice would be to drive the car for awhile and see how it handles and then make the changes and you see fit for that car and the tracks you are driving on.

 

My E36 M3 4-door understeers with the stock aymmetric fitment (225/45-17 on 7.5 wides front; 245/40-17 on 8.5 wides rear). Most of the BMW CCA E36 M3 club racers I know run 9 x 17 (SSR Comps) all around with 245/40-17s to dial in more neutral handling.

Off/topic for Connor, how do you explain the price reduction for the Pireli P-Zero Corsas in 255/40-17? I'm not complaining, but the price dropped $100/tire??

 

Quick question then, does the difference in tread width account for MUCH greater understeer? Would the general rule of thumb for tire widths be the same as difference in offset width (i remember reading on one of the 7 sites that if you go over 20mm difference in offset, it hinders performance greatly)? If going with a staggered setup, should i try to keep it somewhat symmetrical (i.e. 265 fr and 275 fr) or is that old addage "wider is better" true for this case? For now, I would be autocrossing (for the most part of 2005) and I would eventually like to end up road racing.

I appreciate all of the information that everyone has given me! That's the thing I love about this board, everyone's willingness to help others that are just getting into autocross and the likes, unlike other places that shun beginners and what not (afraid of the future competition?).

 

I realize my last post was. . . .. . cluttered. Was in a rush to type it as I was out the door evacuating for the hurricane, and thought I could get a post in, and check it later when i got to the hotel. Anyhow what i meant to ask was: At what point does the staggered setup become a huge hinderance in performance (i.e. 20mm difference in rim offset), or is there a limit at all when it comes to the tires?

thanks,
Chris-

 

SleepR1,

I tried to order the 255/40/17's today and was told they were on national backorder and no new date.

What did they drop to? I was quoted $155 per tire.

 

Yes, they are on backorder. The Tire Rack has $160/tire for 255/40-17 P-Zero Corsa, so you get a $5 discount? I wonder if that's our Rx7 Owner's Club discount LOL Before the price decrease, I saw $250 each for 255/40-17?

 

Greater than 1.5 inch wider in back relative to front, and you get probably too much understeer. Although if you ask Peter Hahn, who had 8.5 wide x 17 front, 10 wide x 17 rear Fikse FM-10s, he'd say that 1.5-inch width difference fr/rr was neglible. My old SSR Comps were 8.5 wide fr x 17, and 9.5 rr x 17, so 1-inch difference. That was plenty of "push" for me LOL

 

You guys act like tire size is the only thing effecting over/understeer... there are so many variables. Since we are operating in gross generalizations, if you have enough power(a stock FD for example), you can easily counteract the small amount of understeer encountered with the small amounts of stagger you are all talking about. I guess nobody here has access to an alignment, sway bars, coilovers, or a tire pressure gauge LOL. Larger rear tires will allow you to accelerate, and brake better (on anything but extremely underpowered vehicals where unsprung weight is a signifigant issue). now, if you are already running 335s all around, you don't have much choice, but short of that, for most of us running the largest tires you can front and rear will usally be the best choice for performance. Carl

 

Carl, you bring up excellent points. I think our responses were in the context of the original question regarding how an FD handles with either symmetrical or asymmetrical wheel/tire widths. No doubt you can dial in/out handling characteristics with sway bar settings, spring rates, tire pressures etc.

 

Carl, I definately agree with your points. To me the FD to its limits (with my personal experience; your driving techinique probably is years better than mine) tends to oversteer. One thing I remember reading, that always stuck with me was, "everything on the car is designed to make the tires work better." In that sense, I was wondering what the different tire set-up's yielded, how different set-up's handled, etc. More or less food for thought for myself, as I can't afford to buy new tires if an idea of mine doesnt work out or if i go too wide and extreme understeer happens bc of that "bigger is better" theory, etc (as funds are limited this year bc of all the hurricanes. . . .. that and im poor ).

Thanks for the input tho!

 

I thought you just got a sponsorship for a big brake kit? Weren't you selling a set of Volk CE28Ns?

https://www.rx7club.com/showthread.php?t=339117

 

Thanks for the reminder, I sold the Volks and need to update that. Tires are expensive now-a-days, Haha. Don't gotta be rich to be sponsored (if you can't tell, im quite modest..or at least try to be).

But on a more serious note, with the rest of this year going as it is (hurricane popping up every week now as it seems this hurricane season) I wont be able to get to as many autocrosses to try out different suspension settings, different tires, etc., since i've already evacuated twice in less than 3 weeks

 

Roger that! I think b/c we're not rich is why we need sponsorship LOL Good luck!

 

I'll jump on Carl's bandwagon

...unless you find yourself constantly having to feather the gas at corner exit to keep the rearend from breaking loose you have no need for more rubber in the rear. Even so I would adjust the chassis first before going staggered as if the tire sizes are the same on all 4 corners you can rotate tires.

I find the FD pretty neutral. Any RWD car with horsepower can swap ends if you get on the throttle too hard and break the tires loose...

I no longer have "forgiving" as my setup goal, just "fast"

 

Go Damon, Go Damon

 

One thing to keep in mind when reading about staggered setups on 911's, NSX's, Enzo's etc, is that they have the majority of the weight over the rear wheels, so they need more tire there. The car company's lawers also like cars to understeer alot for liablility purposes, as it's easier to control and recover from. That motivates some of the staggered setups on stock performance cars.

 

Hee hee hee,

This is why the Suspension/Wheels/Tires/Brakes has become my favorite sub forum....lots and lots and lots of knowledge poping up ALL the time from very knowledgable and reputable members!