I would think you'd have enough room, dependent upon how much toe in you may run. If worse came to worse - you could probably get by with a 2/3/5mm spacer in the rear and still be fine, assuming you aren't slammed in the rear. The 285 RE71R vs 265 A052 in the rear on a 10 look VERY different, but both work while keeping the rear quarters in tact (no pull).

Yeah the difference on turn in from the 1st turn was absolutely noticeable when I took it on the street last night. I'll probably end up hitting a lot of cones because of this alone (will have to slow the hands down even more). Acceleration was absolutely noticeable too as mentioned. My lightweight brake rotors (girodisc ultralites) were a noticable difference, but this is a step above the difference felt. Obviously because most of the weight savings with the wheels/tires is on the outer most circumference as opposed to the rotors.... The car literally feels like 200-300lbs were shed, quite eye opening to say the least! Whether this attributes to it being faster for autox though, is still to be determined.

I threw up a poll on our local autox forum to see who thought the car would be faster/slower with these smaller wheels. The club is about 50/50 split currently in thinking this new setup would be faster than the old. I think there are too many variables at play to give a definitive answer, even after this weekend. Outside temp, surface temp, course design, course length, driving style will all come into play.

I plan to do more testing in Lincoln - but that may not be until next year.

I also plan on running these 255's at the upcoming Gridlife Event in Heartland Park of Topeka - assuming other things work out! I know this car will be under-classed severely, but just dipping the feet and I really don't want to have to make changes between SCCA SOLO and Gridlife.

 

ooof your spring rates might be an issue going over crests

 

Valid concern. However I did take my '05 evo there once and was running similar rates, just maybe a 100lbs softer in the rear. I also endurance raced a couple times in a miata there. The crests/curbs are quite gentle there from what I recall. Worse comes to worse - I can stay off them. But I recall most of them being a non-issue.

 

Cool. i just put my rear swaybar at full-soft and skip wet sessions Hoping to finally try the Shaftworks soon! hopeful that its a big improvement

 

A bunch of us have dataloggers. I only have 17x9 + 245 Indy500s / 18x10 + 265 A052s, so not directly comparable, but one could test this on the street at autocross speeds (a bunch of 20-60 mph pulls) to see if there was a measurable difference.

 

First, I don't believe that tire width would produce such noticeably different acceleration numbers.

One of the culprits is an OID and that would definitely make a difference! 265/35/18 is about half an inch taller than 255/40/17 (according to the TireRack. for RE71RS, difference is 0.4"), and should affect acceleration numbers. If would be interesting to do the same test between 255/40/17 and 285/30/18 in which case wider tire is slightly shorter.

Another thing that could contribute here is having a different rotational mass. I am wondering how much of a difference there is between the two tire/wheel combos and how much of acceleration difference that would actually create...

 

This is fun to play with

http://hpwizard.com/rotational-inertia.html

 

WOW!

That is a great site! Tons of info there!!
Thanks for sharing Marshall

 

Thanks, Marshall!


On a semi negative note - our events were cancelled this weekend so I have no data. Currently in the process of prepping the car for Gridlife in less than 2 weeks! Throwing on stock rotors, putting in stainless lines, nut and bolting. I do plan on running both the 18x10 / 255 A052 (70% life left) as well as throwing on the 17x9.5 / 255 A052 for comparison there. Curious to see if there's any sort of difference once I get settled in on track again.

A few years back when I had my mild prep ASP Evo - I took it for a SCCA Track night in America event. Worse track day I've had... lost the brakes coming into turn "0". Also snapped the top of my Ohlins shafts (the threaded part). I'm really hoping that things won't go as bad as that weekend.

 

What a weekend! I absolutely had a blast attending my first Gridlife Time Attack event at Heartland Motorsports Park. It has been about 4 years since I've last been on a road course, either doing a HPDE or Endurance races with WRL. Dust definitely needed to be knocked off!

Heartland park has two definite areas that are high risk, high reward. Turns 0 - 2 as well as the series of 8 - 9. Specifically turns 0-2 are a bit intimidating initially (especially when you don't trust your brakes fully) as you are coming over a hill blindly into a series of higher speed turns. Either way, I'm thrilled that in each session (I didn't run in the last one) I knocked off time consistently and dropped down to my goal of a 1:45 - running a 1:45.9 specifically. I also brought the car home in one piece!

As mentioned before, I had issues with the ST43 pads and overheating them after 4-6 laps. Charles Miller was nice enough to take some time to help assist with his input in regards to ducting/titanium shims/moving to an even better pad.

For those who know, my car is prepped for SCCA SOLO - STU. The only things I changed were to use a set of 255mm A052s and dial up the front sway bar a notch. I feel like my 800lb/1100lb springs were probably a bit much.

The level of prep of the top Street Class cars in Gridlife is mind boggling compared to where my car currently sits. Ended up in 6th place out of 16 drivers in Street. I'm content with that as I really never fully trusted the car in the series of turns mentioned previously. I definitely left some time not going into 5th on the back straight as well. I also had one lap in my 6th session that I had to shut down early due to traffic - could have been a good one!

I learned a lot, met some great individuals and really look forward to hopefully attending events next year if possible!

Video link below!

 

^^^Nice run & well done! Representing the Evo community well & giving that center seater spec car a real run!

You running a hard compound tire? (tire squeal)

 

Thanks! I appreciate it! Haha yeah - kinda surprised he was running times similar to I was at the time!

I was running the 255mm A052. 18x10" as well as 17x9.5". You should hear the noise they make when you REALLY exceed limits on track. It almost becomes a low growl sound.

 

Were you overheating the pads? Or the fluid? In my setup even the high temperature fluids give out before the ST43s on the stock calipers.

What pads are you moving to?

 

And, what kind of fluid you use?

 

So I keep going back and forth whether it was the fluid or pads.

Full disclosure - I took my '05 evo to this same track almost 4 years ago and experienced the same situation. I was on the ST43, however I was running Motul brake fluid at the time. The current IX RS is running Endless 650 fluid.

Timeline:

1st session - obviously I was on the brakes longer in zones that I should have been, which probably generated extra heat. After about lap # 4 - I noticed when I hit the brakes, that I was having to push it in further than normal - felt like an extra half inch or so. That should have been my first warning. However I kept going and the next turn(s) the pedal went to the floor and BARELY slowed the car. Limped it back to the pits. Got it on stands - bled the brakes with like 2 very small bubbles of air.

2nd session. Same thing - approximately 4-5 laps. Pedal to the floor - limped it in. Let the car sit - once cooled down - brake pedal felt totally fine.

3rd session - same.

Every other session - I tried not touching the brakes on the out lap. Ended each one after 4 laps - as a precautionary measure prior to the pedal getting soft. This gave me more confidence to trust the brakes since I practically knew it would happen after so many laps out there.

I'm open to ideas. Granted it won't be until next year until I get back on a roadcourse again, but it was a bit frustrating since I only got about half of the laps that I should have over the course of the event.

I was looking at the Performance Friction PF01, PF08 and/or PF15 (I believe if my memory serves me correctly). Maybe the ST47 up front? Was looking to try Castrol, titanium shims and/or ducting too.