STX Rules and Setup Questions

[BR-ZED]

So with my 255/40, approximately 1.1 to 1.25" lower than stock in the rear, and a 9k spring, should I rub? Wheels are 17x9 +35 RPF1.

saw some rubbing marks, but they may have been from before when the car was slightly lower. Given my setup I didn't think i would have to worry about rubbing but maybe I'm wrong?

Could this level of rubbing (see pic) cause significant damage to the tire in an autocross? Or is it just the fender lining that will wear down over time?

[cjd]

Originally Posted by BR-ZED

So with my 255/40, approximately 1.1 to 1.25" lower than stock in the rear, and a 9k spring, should I rub? Wheels are 17x9 +35 RPF1.

saw some rubbing marks, but they may have been from before when the car was slightly lower. Given my setup I didn't think i would have to worry about rubbing but maybe I'm wrong?

Could this level of rubbing (see pic) cause significant damage to the tire in an autocross? Or is it just the fender lining that will wear down over time?

Any rubbing on the fender is not a good thing and might fail tech. It may be worth taking the time to verify exactly where it's rubbing and be sure it's never on metal.



I did not have issues on a 255/40 and 17x9+35 - I was on 10/12k, a bit lower, and -3.5°/-2.8° camber. You'll almost surely be fully compressed under the highest cornering load - how low you are won't play a role in this I think. I haven't run 255's on the new suspension yet, just 245's.



The only rubbing I've ever noticed is on the fender liner, and happened at full lock. I don't think it's any of my race tires doing this.

[BR-ZED]

Does anyone here roll their rear fenders? I searched the whole thread but couldn't find anyone mentioning it.

I probably will have to bring it back to the shop to see if its the same marks he noticed before aligning the car. He raised that corner about 3/8" of an inch during corner balance, so I'm really hoping the marks are just from before. I didn't really pay attention to the tire when I picked it up at the shop so the guy at the shop is the only one who can say if it was before or after the alignment :-/

I guess worst case I have them roll the fenders, didn't really want to do that but I guess better to be safe than sorry.

[justinco]

There is not really much to roll on the fenders. Clearance should be fine with your wheels/tires. Most people that I know with similar setups are not rolling the fenders. I didn't roll fenders on my FRS or my BRZ and it's a non issue.

[BR-ZED]

Originally Posted by justinco

There is not really much to roll on the fenders. Clearance should be fine with your wheels/tires. Most people that I know with similar setups are not rolling the fenders. I didn't roll fenders on my FRS or my BRZ and it's a non issue.

Hey Justin, good to see you on here (I met you briefly in CO but I moved back to MD shortly after that).

Yeah. It seems like a small lip... but where else would those marks be coming from?

[justinco]

Originally Posted by BR-ZED

Hey Justin, good to see you on here (I met you briefly in CO but I moved back to MD shortly after that).

Yeah. It seems like a small lip... but where else would those marks be coming from?

Ah nice.

The tire mark does look like it is from the lip or outer part of the liner. I've seen that on my tires but usually only when the car was really low or bottomed on something. I have the same rear camber and have had the same sized wheels/tires and never had any catastrophic issues. I wouldn't worry about it too much.

[BR-ZED]

Thanks again. Guy from the shop said the rubbing looked the same as before the alignment which is why he raised it for me. Looks like I'm ready to go.

[BR-ZED]

And on another note - what is a good starting point for hankook rs4 in 255/40? I was reading 38, but that seemed high (especially because I ran 32/30 on my 225/45/17 RE71Rs in CS/DS).

[NJ10]

I ran 30/28(same as RE71), car felt compliant. ymmv

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[Lincoln Logs]

Originally Posted by BR-ZED

And on another note - what is a good starting point for hankook rs4 in 255/40? I was reading 38, but that seemed high (especially because I ran 32/30 on my 225/45/17 RE71Rs in CS/DS).

Use a pryometer! That is the only way to really know the right tire pressure.

[BR-ZED]

Originally Posted by Lincoln Logs

Use a pryometer! That is the only way to really know the right tire pressure.

How? I can see why you would use a pyrometer to determine if you have too much or too little camber, but how can you use it to determine tire pressure?

Edit: Ah, found this informative article.
https://949racing.com/using-a-tire-p...49-Racing.aspx

Too bad I bought a laser pyrometer already to monitor camber. Oh well, better than nothing i guess?

[Lincoln Logs]

Originally Posted by BR-ZED

How? I can see why you would use a pyrometer to determine if you have too much or too little camber, but how can you use it to determine tire pressure?

Edit: Ah, found this informative article.
https://949racing.com/using-a-tire-p...49-Racing.aspx

Too bad I bought a laser pyrometer already to monitor camber. Oh well, better than nothing i guess?

That is the exact guide I was going to link you, but you found it already. The laser pyrometer won't work for this because the surface temp changes too fast. The probe types tell you the actual temp of the rubber.

I use an inexpensive economy pyrometer, the Joe's Racing brand.

[jbailey8748]

Does the brz ts fit in stx, with all the plastic body kit gurney flap, under trays side kirts and front lip. If not where does it fall?

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[tony_r]

Originally Posted by jbailey8748

Does the brz ts fit in stx, with all the plastic body kit gurney flap, under trays side kirts and front lip. If not where does it fall?

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It's not classed at the moment. I dont see a problem with classing it in STX but others might due to the aero bits. If it doesnt fall in STX then I don't see a reason to class it.