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So, I just got the first set of 225/50 BFGs mounted on the Civic Si. That are on RPF1s with 41mm offset. They clear everything with no rub, but they are Very close to the rear trailing arms, probably less than 1/8 in. I know the tires deform a lot under load. Does anyone have any experience with tires rubbing under load or have an idea of what is unacceptable clearance.
Thanks.
1/2 in or more at 90* to the contact patch often will show signs of rub. I paint parts that are close with orange paint to monitor interference.
1/8 will have some rub to it. You can reduce the rub by increasing tire pressure. , add spacer etc.
Run 205 on the rear.
225s on my Integra slightly rub the trailing arm. Doesn't seem to cause any problems.
I used to run 205s on the rear, but it just makes for easier tire management to run all four corners the same (old fronts go to the rear). And I had to keep a unique spare tire just for the rear. Then again, when I did run 205s in back, I never had to touch them all season...just kept flipping fronts.
Thanks Greg. Was that with 41mm offset?
Smaller rears tires = faster car . Why leave speed on the table?
It makes absolutely no difference in speed, all other factors being the same. And yes, that's in direct back-to-back testing with data acquisition.Quote:
Originally Posted by Flyinglizard
I ended up with big Hohos in front and little Khumos in the rear, full tread. I don't know if it was faster than 4x Hoosiers (I strongly suspect it was), but it certainly worked better.Quote:
Originally Posted by Greg Amy
First, it saved bringing so many tires with me. Drive in on the "rains" (Khumos) and only switch 2 tires max.
Second, the car was SO much easier to drive; where it was near impossible to get the Hoosier rears up to temp, especially at the start of a race, the Khumos got on board quickly and the balance was great out the gate and stayed that way.
I think it helps to look at FWD from the perspective of a Formula Ford-driven backwards!
I've been tempted to run A-compound in the rear to get them up to temp. However, I'm not really at the point where I'm trying to add grip to the rear...hell, I've thought about A in front and R in the rear...
To clarify my test on the rear tire sizes, both were well-cycled-out R-compounds, with new(er) tires up front. I was not able to tell the difference in either handling or lap times solely based on size difference. Thus, I'm choosing to run the same tires on all four corners just for ease of tire inventory management (once they wear/cycle out in front, they get tossed on the rear).
GA
Interesting back to back testing Greg. I do currently run a smaller size on the rear primarily because my fronts are corded faster than they heat cycle out while the narrower rears last 2-3 times as long. Of course I also used to like the balance with the narrower rears but with changes I made to the front last year I seem to find myself a little short of rear grip so it may be time to move back to wider rears. If my wear rate wasn't so high on the front I would see the advantage of only dealing with a single tire size.
It's funny that this thread has swung in this direction. I have considered the benefits of smaller rears and thought about a post to that affect to get opinions. Good info.
Anyone have age any old BFG R1 s in a 205/15 they want to part with?
Smaller tires= less weight= goes faster. I doubt that Greg will argue physics with me. There may be changes needed to realize the value. Maybe less spring rate to add grip. more or less bar. etc.
Each time I have reduced rear rolling drag, the cars go faster. Amazing .
Some drag reduction points of interest; Higher pressure ,like 41# , lowering spring rate to gain some grip back.
Zero scrub alignment ; using lower rear camber and some toe out for a zero scrub rear axle. IE if you have 2 * camber you need about 3-5mm of toe out so that the tires dont push against each other. Do a search for camber thrust, for a much better description. yada yada
Smaller rear tires may also lower the windshield angle , guess what? goes faster.. yes, the rear roll center may also lower and the car may need a balance trim.
Most of the time , I can take a VW race car, swap small rear tires onto the rear, up the pressures to about 40 hot and the car will go faster.
etc.
HTH, MM