Dallas J

iTrader: (1)

The conversation would be too long to type up my feelings on things but its not really "do this" sort of thing. But here are some notes...

• Make the rear work harder, more tire will let that happen but also needs more spring.
• To much rear tire wont heat up in the first run except the hottest days, I want my first run to be 80% up to grip. Changing conditions run to run makes it hard to find the magic on course and you'll likely underdrive the potential of a hot tire.
• Square to rotate is best for tire life, but if you can run more front tire than the rear because fit and dont care about dealing with OPR after the event, that will probably be faster.
  • I would run 335 front 315 rear if it weren't for OPR, but 315s are already hard enough to get warm in the back.
• Tires and Aero set the potential, Spring balance the weight transfer. But don't forget about effects of toe and damping. An oversteering car is probably not over sprung but over damped.
• STU is no where near the limit of tire vs weight vs heat, run as much as you can then keep running more rear spring till mid corner its too playfull, add toe-in or adjust shocks to get it happy other places.
• Even in the rain, the rear 1450s in my car are not too much, in the dry they are not enough. That may be too much for street tires, but 50-100% more rear spring is still the right direction outside of high aero cars.

Butt Dyno

iTrader: (10)

1450 as in lb/in?

Back in.. 2014? 2015? I went from 600/800 to 700/900 because while my car was great on asphalt it was harder to get it to rotate on concrete. So this ^ is reassuring that with 285s I probably don't have too much spring. My worry was that with a "real" rear diff, I wouldn't need as much spring to get the car to rotate.. but I wasn't thinking as much about the balance implications of running square 285s.

LV///R

iTrader: (36)

Thanks as always Dallas. With that being said, I feel like I'd still like to try the 295/11" and 255 or 265/10" route for ****s and giggles. I'm just wondering if it's going to be TOO big of a difference from front to rear. Only way to know is to try I guess!

I'm sure he's referring to lb/in.

For STU this year I was running 800/1000lb springs for the JRZ's. Still streetable to be honest - my car isn't trailered when I make the trek to Lincoln.

I ran on 285's in the past (RE71R's and Hoosier A7's) with a Cusco rear diff on asphalt locally and on Lincoln's concrete. While it helped with rotation, I still am a firm believer that a 1000+ rear will be optimal if you are going the square 285mm route.

LV///R

iTrader: (36)

As stated earlier, my biggest concern about going the 285 square route is production is stopped for the RE71R. What if the successor to this tire doesn't come in a 285mm size? A052/Rival1.5S/660 and the possible newcomer to the stage, assuming they make more sizes, the Nankang CR-1 don't come in 285mm sizes.


I am going to mount a shelled out 295mm A052 on my 18x10 just to see what it looks like out back for test fitting purposes. Maybe try a 11" 295 front, 10" 295 rear combo? I have my doubts, but I gotta see what that tire looks like on the 10" wheel...

heel2toe

iTrader: (41)

Does pinching a tire provide any fitment benefits short of the wheel physically hitting something? Meaning, when you go into a corner and the tire squirms it would make sense that there is more movement on a pinched tire relative to a stretched tire. So while the static fitment might be fine, dynamic fitment might be even worse. Any truth to that?

LV///R

iTrader: (36)

I'd assume in this case, running a 295 on a 10" wheel isn't going to be much benefit if any, over the 265. Next year, assuming these changes actually take place, I could try and do some testing between the 265 vs 295 rear (assuming that even fits). I'm guessing the 295 tire is going to be all up in the rear trailing arm's business for it to even work.

LetsGetThisDone

iTrader: (1)

265/35r18 on 18x9.5 +35 rubs the stock trailing arm a bit. Not way a 295 fits without pushing it outboard and past the fender.

Terror Rising

iTrader: (26)

Once again paraphrasing Mr. Dallas J, don't bother with the 295 A052 unless you have a 10.5"+ width wheel as they squirm and don't like that much pinch. Remember you're also going to have to balance tire height F&R to keep your diffs from hating you. The 295/30 is 25.1", 265/35 is 25.4".

LV///R

iTrader: (36)

That is true...I forget that the A052 doesn't love life when pinched. Scrap that idea.

So the 255/35/18 has a OD of 25.1"

Begs the question, is the difference from the 295 / 265 combo too much for the drivetrain from loving life? I'd obviously only be driving on this combo for autox only...

Construct

iTrader: (4)

I didn't have any rubbing with 265/35R18 on 18x10 +33. I think the wider wheel reduces tire squirm enough to keep it off the trailing arm.

I still ground down the small bracket just in case.

I agree that 285/295 isn't happening in the rear under strict STU fender rules.

Dallas J

iTrader: (1)

Rotating off throttle and on throttle are two very different things. Off throttle, diff is irrelevant and you need rear rate to get rear slip angle. On throttle you want to put all the power down and not rotate. The less throttle rotation you have the earlier you can get on power and pull through things.

I can show you what A052 295 on a 10.5" wheel looks like and its pinched. It really wants an 11. But this season its worked well enough to still be competitive with the XSA index changing tires only. The XSA index only gives me a 0.5/60 sec benefit over SM running 315 A7s, so should give you reference.

LetsGetThisDone

iTrader: (1)

I had marks from the wheel touching..

Dallas J

iTrader: (1)

295s with stock trailing arms requires some aggressive fender messaging. Like super duper aggressive. I think 265 is about all you're going to get.

Construct

iTrader: (4)

Toed in?

LetsGetThisDone

iTrader: (1)

Zero or just smidgen of toe in per side (like .05*), depending on what I was doing with it.