I've autocrossed my '08 Bullitt a few times this year. So far it's completely stock down to the 235/50/18 BFG KDWS's. I've been curious how much better it would do with just a change to some good Summer tires. The best local FS driver/car is a '98 Z28 that the guy has had since new and is set up for autocross. This summer I ran against him 3 times and on 45-50 second tracks he's been beating me by about 1.5-2 seconds. I always seem to feel like I leave enough on the course that just a driver mod would get me faster than him. I'm curious if some of you experienced people think that a switch to summer tires would get me in the ballpark, or would it take autocross tires and/or a better driver (you won't hurt my feelings) to be competitive. It'll be a while until I need new tires, but what size would you suggest - assuming I keep the stock 18x8.5 rim size?

Is there ANYTHING you can do to the rear suspension to decrease wheel hop and keep it FS legal? I enjoy drag racing, too, so I don't want to break stuff with wheel hop, but I'd like to keep it FS legal if I can.

Thanks for any input.

 

I would say that tires are the single biggest improvement that you can make for the handling of the car, more than any single suspension part. you look at the cars that handle the best from the factory and they never have the crappy tires that our cars came with stock. Porsches, M series BMW's, Lotus Elise's all come with R compound tires for a reason

my last two cars I ran R compound street legal race tires all the time even though they were street cars. the added traction for launches and grip for handling was awesome and once you get used to it you can't go back people will argue that they don't last long, which is true to a point, but if you're driving hard stock tires won't last long either. if your tire life is going to be limited you might as well have grip

the R compound tires I used to use would last 8000-10000 on the drive tires and 14000-16000 on the non-drive tires. I used Advan A048's and they're great but noisy. I also used Kumho VictoRacers and those grip awesome and are quiet, very good tires.

here's Michelin's brochure on their Pilot Sport Cups, lots of good tire info in there, worth the quick read. if you just want a race set of wheels and tires then you can get the tires heat cycled and shaved. Michelin says those two things are good for 0.6 to 1 second off your time in a 40 second autocross lap, that's on top of the gains just from switching to that tire in the first place. shaving kills about half your usable tire tread so it's up to you whether it's worth it or not. you might want to try it full depth first, they'll end up at half depth eventually anyway

http://www.tirerack.com/tires/tirete...nd_Feeding.pdf

there's some good info on tire pressures and general camber stuff in there too.

 

just re-reading your post that's a lot of weight on a 235 tire. I would look into a set of wider wheels so you could run something like a 275 up front and a 305 rear, the extra tread will help a lot on it's own. I've seen some guys that don't run staggered tire sizes but that's a preference and it kinda depends on how you set up the suspension and want the car to handle. I personally would rather have the rear planted so I would run the staggered size. but if the car under steers a lot on the small auto-x course then running a non-staggered setup would probably help.

 

+1 on the comment re tires making the biggest difference you can make to the car.

The biggest overall difference is due to driver improvement so the more track time you can get, with instruction if available, the faster you will go.

Here is a recent thread that discusses tire choices for our cars

https://mustangforums.com/forum/s197...-rankings.html

 

On a 45-50 second course, R-Comps are going to be good for almost 2 seconds better then any street tire. They are also a whole different animal to drive on, meaning they can cover up bad driving. It is good that you didn't race on R-Comps right out of the gate but once you do get a set you want to run on anything else If you are going to an 18" tire better tires can start to get expensive but that is up to you and how competitive you want to be compared to others. I run on 17x8s with 275-40/17 which by comparison are a little lower cost.

Well if you are going to stay in F-Stock with the car the wheel hop isn't going to go completely away. But a good set of dampers will help that a lot, I have Koni's in my car. Call up Sam Strano, www.stranoparts.com. He can definitely give you some suggestions, all the parts in my car I bought from him. He has been the F-Stock national champion for the last 3 years.

 

Yeah, I've always been told to start out on street tires and once I consistently reach a limit, then try swapping over to r-comps if I want a better experience. But nobody is able to stress enough how much of a difference a good tire makes. I'm pretty sure my nt555s are holding me back on the track - I want to try something a little more aggressive like the nt05s. Eventually I'll make the transition to nt01s though...

Even Billy Johnson, co-driver of the Jack Roush Jr. Koni Challenge Mustang, told me to stick with street tires for a while, and that kid knows too much for his own good!!!

 

I've heard that it's good to learn on normal tires and not R comps but nobody ever has given me a real explanation as to why. the biggest argument for the stock type tires I hear is that when they start to slip you hear the tires slipping. well if you don't feel the tires slipping at the limit then yeah, stick with the ones you can hear slipping for a while longer

I think the only real reason is that the less grip you have the slower you'll be going and the safer it'll be if you go off the track. if you're brand new to racing then slower is safer for you and everyone around you

 

Thanks for the replies and all of the info. This is kind of gives me an idea where I'm at. I'm the kind of person that would rather get the most out of a slower car than to have a fast car and be slow with it. Someday I'd like to get to the point of saying "this is what a stock Bullitt will do", but the nut behind the wheel needs to be modified first. I'll never forget when I first started autocrossing a guy brought a completely stock Probe GT (down to the Gatorbacks) and proceeded to kick everybody's butt - even the so called "fast guys". Turns out he had won a national event the week before and happened to be in town.

I've had 4 different cars that I've autocrossed (and drag raced) through the years and this is definitely the best one. I don't really have a lot of experience - probably 15 events in the last 15 years, but I really enjoy it. I went from an '87 GT to a '98 Cobra convertible to an '06 Civic Si and now my '08 Bullitt (don't ask about the Honda - won't ever do that again). My experience says Ford made a lot of progress through the years with Mustangs.

My BFG's still have quite a bit of tread on them, so it'll probably be a while until I get tires for it. I really like the look of the stock rims, so I'll probably stick with them (18x8.5's). At some point I may get some slicks for it, but that's a different story.

I actually haven't had any wheel hop except for on the drag strip. It even hopped when I hit 3rd gear one time. I calmed it down a bit with lowering the air pressure, but I still had to leave pretty easy. I'll definitely look at getting Koni's sometime down the road.

Thanks again for your replies. Nice to know there's some pretty experienced people on this site.

 

It's really easy to (wrongly) teach yourself to be too abrupt or jerky with the controls. The only comparison that most folks have is their street driving, which isn't even in the same league with autocross driving, NO MATTER HOW HARD YOU DRIVE ON THE STREET. There's so much more grip available with R-comps than what you're accustomed to asking your street tires to give that you can end up expecting it to always be there for you. This applies, if perhaps to a slightly lesser extent, to tires in the Street Touring category (typically 140 - 200-ish treadwear competition tires, think Azenis, NT05's, Star-Specs, etc.).

R-comps have a finite lifespan before the best of their grip goes away due to heat cycling. Abusing them with heavy, plowing understeer because you came into a turn too hot, or by smoking an inside rear tire on corner exit because the limited slip diff isn't quite as "posi" as it used to be simply uses up that life that much faster. A little experience with what the various feedback sensations mean will help keep you from getting into such situations. During early stages of the autocross learning curve, there's enough to process just to stay on course, keep looking ahead and do things sort of right, without also trying to learn how R-comps differ from street tires.

The handling balance (understeer/oversteer) also shifts when you move up to R-comps from street tires. In nearly all cases, the car's ultimate handling balance goes more understeerish as tire grip improves.

By way of example, I'm past the useful life of the set of tires I use on my autocross car, and it's getting noticeably "loose" as a result - understand that this is happening in a FWD car where you'd expect understeer, always. Not as tail-happy as the same car was with old street tires and OE shocks, but it's sending clear signals. I'm guessing that I've given up about a second on a 40-second run, making them only a tiny bit better than really good street tires Enough to cost me 1st place yesterday (and a shot at a donated set of tires ). One more event and they may not even be that "good".


Norm

 

From my ancient experience autocrossing a then-new 1985 MR2, after switching from OE street tires to R-compund Yokohamas, I gained about 2 seconds a lap on 45-50 sec autocross courses. Do yourself a favor though and mount them on a separate set of wheels so you can use them exclusively for auto-X - otherwise they'll wear out quickly. In the long run, though, more seat time will help the most.