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Even WI(L)DER: BMW 135i Track Wheel Fitment Test, Round 2

Previously, with some dumb luck, and a bit of (okay, entirely too much time wasted doing) research, I was able to select a track wheel and tire setup for the 135i. It was good. Lap times dropped, and I began to throw down times at autocross that could be considered vaguely competitive, much in the same way that former Top Gear guests in the Star in a Reasonably Priced Car segments were vaguely competitive with the Stig. I’ll take what I can get here.

After a while, I had become antsy. I made that fit, and I wanted more. As far as the course for future modifications, everything looked pretty straight forward. The car has a big front sway bar, good coilovers with camber plates, a Torsen diff, and likely more power than any car in it’s class (SCCA - Street Touring Ultra). However, it also had an abundance of mass, that my competitors did not have. With me in the car, and everything ready to go, the car weighed in at 3409lb/1550kg, yet the car’s footprint wasn’t that large, relative to it’s mass, with 17x8.5″ wheels and 255/40R17 tires. Consider that most of competitors are working with between 200-500 lbs less mass, AND more tire, and the 1-series proclivity for understeer, and we have a vehicle that is inherently non-competitive. Gotta love a challenge.

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This is the current front wheel setup on the car, 17x8.5 ET40 with a 255/40 Hankook RS3. Outer clearance could be described as tight, and the strut clearance (inside) isn’t much better.

While the tire size is about right for an STU car, the 255/40R17 as seen in the Hankook RS3, Dunlop Direzza ZII Star Spec, and many others are actually wider that their printed size suggests. By pinching that much tire onto a narrow 8.5″ wheel, the sidewall response is diminished, and the actual footprint of the tire is compromised. Competitors with E36M3 and the like are commonly running 17x9.5″ on the same 255 tire, and the footprint is visibly different. Every inch counts, and with the fun-series’ tricky wheel fitment, it was going to be tough finding a solution towards getting more tire under the car. Gotta love a challenge.

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After a lovely autocross at the Autoclub Speedway, I had found a local seller, who had listed a pair of 17x9 ET40 wheels for sale at a reasonable rate. He lived in the area, we agreed to a price, and since I was already up here (about 50 miles from home), we agreed to meet at a Chase bank so I could hit up the ATM and we could trade cash for wheels. These wheels are the now discontinued TireRack Motorsports MT1-R wheels, made by Enkei, utilizing the same M.A.T. flow forming process as seen with the RPF-1 wheel.

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These wheels are super light, at 16 pounds, and are decently strong, given their price point. Lucky me, my seller had left his track tires on the wheels, 255/40 Hankook RS3, the same size and compound that I currently run, and wanted to continue using. Lucky day.

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Sidebar: Well, I did intend for these to be a front fitment, but I figured, that while I had the car in the air, I may as well try them on the rear axle. The 1-series requires a very high offset (wheel clearance is all in-board) wheel for the rear, and is notorious for not accepting even medium offset wheels, if they are wide at all.

It’s still worth a shot.

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Yeah, not happening. Plenty of inside clearance though!

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At ride height, it actually doesn’t look bad:

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This angle starts to show the problem. Every if I rolled the rear wheel opening lips flat and did some cutting, fitment would be tricky with the fat tires.

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Here is the rear suspension at full compression with the OEM wheels and 255/35R18 RS3:

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Easily clears the quarter panel edge by 5 or so millimeters. Here is the same level of compression with the 17x9 ET40 wheels and 255/40R17 RS3:

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Not so much. I like a challenge as much as the next guy, but this would take more heating, cutting, and “massaging” then I would feel comfortable with on a still relatively young, low mileage vehicle.

Since the car was in the air, I had both a front and rear wheel off. This gave room to some documentation about wheel and tire sizes. Check out these pictures!

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On the left is my current front wheel fitment, 17x8.5 ET40. On the far right is an OEM 18″ rear wheel that I have been using for a budget track wheel setup, it is 18x8.5 ET52 (note the higher offset to tuck the wheel further inboard). In the center is the new hotness, the 17x9 ET40 TRM wheel. All three of these wheels are 255 section width, and despite one of them being an 18″ wheel, they retain the same total height (note the aspect ratio).

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Despite the fact that they are all 255 Hankook RS3 tires, note the ACTUAL difference in width between the three:

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My notes are tagged on the image. Despite all three of these being labelled as 255 section width tires, the more common track size of 255/40R17 is noticeably wider than the less common 255/35R18, despite the overall height being the same (meaning, that they should look identical). Further, the same 255 tire has a much broader fitment when “stretched” (using that one loosely) over a 9″ wheel versus an 8.5″ wheel. Every 1/10″ counts in this rat race.

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With the rear fitment considered, and tire variables addressed and noted, it was time to resume out original goal of fitting the new wheels to the front axle. It’s time to play the Internet Stance Kid’s favorite game, “Will It Fit?”

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The wheel bolted up without any fuss, and the -3* of camber looked to be sucking the wheels right into the wheel well. Excellent. Of note is that these wheels are not particularly “big brake” friendly. The stock 6-piston Brembo calipers just squeeze by in here.

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We are talking millimeters here. The “lip” and barrel design of the TRM wheels limits brake clearance as compared the APEX ARC-8 wheels. Cutting it close.

Speaking of close, I did say that the wheels bolted up to the car, which they did, but after trying to spin the wheel on the hub, it was clear that we had gotten a little too close.

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One 5mm spacer later, and here’s what we’ve got:

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If you listen closely, you do hear some rubbing, but that was an accessory bracket that had loosened, and was rubbing the tire. We are clearing the strut by about 3mm.

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Here is the end result:

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It fits! A tentative drive down the block, putting full lock in the steering, and no catastrophic sounds of despair have emanated from the fenders. I do want to get a proper fender roll done on the car, just so I don’t cut a tire, or blow out a fender if these fatty tires snag the fender lip.

Final spec is 17x9 ET35 (including 5mm spacer), 255/40R17 RS3. For a street tire, the RS3 are fat, almost Nitto NT01 status. A comparable Bridgestone RE71R or Dunlop ZII Star Spec should fit even more cleanly. With this done, I can safely say that there is no way to get more rubber under the front end as per SCCA Street Touring rules. If we were to chop up the bumper and fenders, I could see a 17x9.5 fitting, but for now, I think we’re good.

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