Stage 5: M240iR
End track-hours: ~120
End Laguna Seca time: 1:44.0
End parts/specs:
M235iR fender flares from Flossman
Calipers: Brembo Club Race F, Brembo GT R
Rotors: 355x35 mm F, 345x28 mm R
Pads: RaceTechnologies RE10
Wheels: Apex FL-5 / SM-10 18x10" ET25
12 -> 15 -> 20 mm spacer front
Tires: RE71-r 285/30/18 square
occasional "drift setup": Hankook RS4 285/35 R only
Springs: 90 N/m 200 mm F, 150 N/m 200mm R
-3 camber, 1/16 toe out F, -2.2 camber 2/16 toe in R
many alignment variations between (-3;-3.5) F, (-2; -2.5) R
All the braking issues I described earlier made me realize the difference between a car that can do a few "hero" laps on track, and a sorted racecar with consistent performance every day. There's a massive step in between and the F22 weight isn't exactly helping it. Add in all the issues from damaging the bodywork and it seemed like the right time to try and step in the latter category. This would mean at the very least bumping up tires and brakes to match the car's weight.
Like many folks here, I'd salivated over the few bodykits for our chassis. I was leaning toward Manhart, but then I saw a set of cup car flares from a shop in Germany for what looked like a good price, so I jumped in. In hindsight, it was definitely not worth the trouble -- after taxes, duties, freight shipping, and a customs broker fee the cost was pretty much the same as getting them from Bimmerworld. Oh well, now I know...
I knew that the cup cars run 265/660 slicks at VLN. In the DOT sizes we're used to, that's about 285/35. There aren't that many sticky tires in 285/35/18, so I was choosing between 275/35 (very popular, many compounds) and the rare 285/30 (pretty much just RE71-r and Hoosiers). Decided to go for the 285/30 so I can still use the RE71-rs I was used to (I'd later find out that 275/35 actually needs a fair bit more work to fit in the well). A 10" wheel seems about right for that, with as low offset as possible -- there should be plenty of room to push them out with the flares and I was expecting the biggest problem would be clearing the suspension at the front.
I was already overwhelming the brakes with 245 tires -- adding this much more grip without better brakes wouldn't be smart. At that point I was thinking a Stoptech BBK with some ducting, similar to what I've been mocking out at home. Also, a big bump in grip under braking would probably need stiffer springs too -- my previous setup was already diving a lot in braking zones. Problem is, I had no idea what the effective rate of the progressive spring in my KW V3 was. I cursed the shop that sold me the V3 again for good measure (not that I'm holding a grudge or anything), and figured 90 N/m might be a good starting point (based on the Clubsport rates).
With that, I felt like I'd done enough of my homework to start talking to the race shop that was actually doing the work. The plan changed a bit after talking to them -- they'd spec out a brake kit with Brembo (Club Race calipers front and GT calipers rear) and ditch the brake ducts (unless we really need them). I still don't trailer the car and drive it to the track and back -- brake ducts would probably get destroyed in that process. Plus, they had had very good experience competing with the Brembo brakes (including in the 25 hours of Thunderhill), so it was a known solid piece of kit to go with. There isn't that much choice in race pads for this caliper shape -- I'd rather not use a sprint compound on a car that still sees the street, which left us with the enduro RE10. On some other (admittedly much lighter) cars, they'd lasted more than half-distance in the 25-hours, which sounded pretty promising.
Fitting the fender flares went without much trouble. Of course, we needed to trim the original fender lips -- that's the whole purpose of doing this. The front flares have a convenient lip on the inside with mounting holes, so we could just bolt them in. The big rear panels actually had bolts laid into the fiber and sticking out, but we ended up not using them -- that would've required taking out all the interior panels (that was probably a mistake -- I should've just gutted the interior and stopped pretending this is a street car any more). Instead we riveted them. Also riveted the front bumper extensions. The point was never to optimize for looks, so rivets didn't bother me -- plus a livery would mostly cover them anyway. For the most part the new panels fit ok -- the front bumper extensions needed a tiny trim to clear my air dam, and the driver-side rear panel had a bit of a kink near the tail light, but really nothing major.
Here's a few closeups on fitment (for
Dylan86 ).
No problems with fitting the wheels and tires at the rear, there's plenty of space there -- if I had to guess probably enough even to fit a 305 tire on a 11" wheel. The front, on the other hand... much more painful. To clear the suspension, we started with a 12mm spacer. It was still a pretty tight fit -- maybe 2-3 mm clearance from the spring perch. The low-profile 285/30 tires barely brushed the fender liners (which we kept, because why not) once you add a lot of steering lock -- both at the front and at the back of the wheel well. Not enough to cause trouble yet, but it meant that pushing the wheel out even more would start rubbing harder (and at less steering lock). It would also mean running /35 tires would be much harder without more drastic changes.
All that said and done, it was time to start testing. First, the good. The increase in front-end grip is pretty drastic. The car actually wants to rotate on entry now instead of only pushing, so I had to unlearn some of my deep trailbraking habits. Also, braking distances are way shorter now. In fact, the first thing anyone notices riding along on track is "Holy cow, these brakes!". Even after ~30 hours with this config, I'm still not completely used to it and tend to overbrake into corners. They seem to cool adequately without brake ducts too -- for now at least, I'd be curious to see if that's still the case during the summer. The spring rates we ended up with actually turned out OK too -- I was worried they might bring back some snappy behaviors, but slides are still very predictable.
The bad -- these 285/30 tires. First test day out with this setup, the inside sidewall of the loaded tire caught the suspension and tore. I didn't think too much of it -- there was barely 2-3 mm clearance, the tires expand a bit when you push them, plus the sidewall can flex a little. So, I just swapped the 12mm spacers with 15mm and decided to live with a little more fender liner rubbing for the time being.
A couple of days later, similar story. Inside sidewall of the loaded tire caught the suspension again and tore. More worried now, but went to a 20mm spacer with heaps of suspension clearance (and a pretty bad rub in the frame once you add steering lock). More testing (and more failed tires) revealed the root cause of the issue -- the sidewall was failing and buldging out
and only then catching the suspension (
example). Kinda like runflats against potholes -- but I wouldn't expect that from stiff sidewall tires like the RE71-r. Over the next few test days, I tried out many theories about what could be causing this -- too much camber, too much toe out, pushing too hard on cold tires, etc. None of them seemed to pan out. After 7 tires failing this way (as if the running costs of this car weren't already absurd) and trying to make the /30 tire work, I decided I've had enough and the simplest explanation was probably enough -- just too little sidewall to support the car's (massive) weight when leaning in a corner. Which would mean making even more changes to try and fit a /35-profile tire.
