SCCA F-Street Setup. What's Everyone Done so Far?

[NightmareMoon]

For the guys running front bars, what stiffness setting are you liking? I've been using a rear bar but am going to try the switch.

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[jpaulson]

For the guys running front bars, what stiffness setting are you liking? I've been using a rear bar but am going to try the switch.

I run a modified oem front bar. I drilled a hole 1 1/2inches forward of existing hole.

I did some rough measurements and I think it is pretty close to most aftermarkert bars on the softest setting.

 

[NightmareMoon]

For those running a 34/35mm front bar, what adjustment hole are you guys using?

 

[Whiskey11]

For those running a 34/35mm front bar, what adjustment hole are you guys using?

Softest. It didn't need much more front bar IMO, just enough to settle the rear of the car a little bit. I run the BMR front bar there and have ran it in all three places and the other two just made the car a smidge too pushy in steadstate for my codriver and I's driving style.

 

[Brazos609]

What about running a 265/40R19 RE-71R front and rear on PP spec 9" front and 9.5" rear rims?

 

[kz]

What about running a 265/40R19 RE-71R front and rear on PP spec 9" front and 9.5" rear rims?

You can do it, but why ? Fir tiny gain on the max speed in 2nd gear ?

 

[Brazos609]

You can do it, but why ? Fir tiny gain on the max speed in 2nd gear ?

For me the speedometer should be dead on with the 265/40R19, with the stock 275/40R19 it actually reads slow. I thought the would work well on both the 9" front and 9.5" rear. The 265/40R19 is 2lbs lighter and $48 cheaper than the 275/35R19. Wouldn't the 275/35R19 only be a tiny gain in traction over the 265/40R19 given the same tire and tread compound?

 

[jpaulson]

For me the speedometer should be dead on with the 265/40R19, with the stock 275/40R19 it actually reads fast. I thought the would work well on both the 9" front and 9.5" rear. The 265/40R19 is 2lbs lighter and $48 cheaper than the 275/35R19. Wouldn't the 275/35R19 only be a tiny gain in traction over the 265/40R19 given the same tire and tread compound?

IIRC, tire rack measured the tread width to be substantially narrower. Almost an inch I think it was.

 

[Norm Peterson]

For me the speedometer should be dead on with the 265/40R19, with the stock 275/40R19 it actually reads fast.

Why would speedometer accuracy matter at autocross?

If a 275/40-19 causes the speedometer to "read fast" - displaying more mph than actual, going to a 265/40-19 would only exaggerate the inaccuracy.


Norm

 

[Brazos609]

I should have said slow, GPS and radar put me at 77 at an indicated 75. The real question was one tire to fit well on the 9"/9.5" combo and not go to a smaller overall diameter if possible.

 

[johnson.ba]

I should have said slow, GPS and radar put me at 77 at an indicated 75. The real question was one tire to fit well on the 9"/9.5" combo and not go to a smaller overall diameter if possible.

I run 275s on all 4. I should be running a 5mm spacer up front but I haven't been to the auto parts store to get one.

 

[DickR]

Why would speedometer accuracy matter at autocross?

If a 275/40-19 causes the speedometer to "read fast" - displaying more mph than actual, going to a 265/40-19 would only exaggerate the inaccuracy.


Norm

It doesn't at the autocross but most of us these days drive to/from the event, sometimes hundreds of miles each way, and around town in the autocross season on our autocross RE-71R's.

FYI on a heavy car like the Mustang the wider 35 series tires are better than the narrower 40 series tires. More rubber on the road for corners and better response.

 

[qtrracer]

There are trade-offs everywhere. Run the 40 and get a little more MPH. Run the 35 and get a little more grip. And it's all theoretical anyway. I run the 40s - 265/285 MPSS.

 

[Norm Peterson]

It doesn't at the autocross but most of us these days drive to/from the event, sometimes hundreds of miles each way, and around town in the autocross season on our autocross RE-71R's.

Actually, I'm in much the same situation when I've got multiple events within a small time frame with 285/35-18 (25.9" tall) "track tires" vs ~27" tall OE's. These days, even my "strictly street use set" tires are only 26.3" tall (265/40-18's). For only a couple mph @ highway speeds I don't ever worry about whether the speedometer/odometer is off, which way it might be off, or by exactly how much. Probably won't ever go back to a 27" tall size. A couple mph of speedometer error isn't something I'd ever worry about.

Norm

 

[NightmareMoon]

Tire rack specs for the RE71R

265/40R19 27.4” diameter, tread width 9.3, section width 10.7 on a 9.5” wheel
275/35R19 26.6” dia, tread 10.0, section 10.9 on a 9.5” wheel
285/35R19 26.8” dia, tread 10.1 section 11.4 on a 10” wheel

Keep in mind the section width is highly dependent on the wheel width, which explains the entirety of the difference between the tested section widths between the 275 and 285 tires.

According to those stats, the 265 is ~0.8” (-8%) narrower tread than the 285 for only 2.2% more diameter. I’m keeping the 285s

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