Quote:
Originally Posted by ApexRaceParts
Thanks for the question, sounds like a killer build! We run AP Essex Brakes on several of our own track/race cars, including the 6 pot 372mm CP9668 BBK on our E92 M3. Fantastic brakes. Our 18” EC-7, SM-10 and FL-5 flow formed wheels, as well as our new ARC-8R and EC-7R forged wheels for the E9X M3 will all clear those brakes no problem.
In regards to your Moton suspension, can you tell us what front spring configuration you are running? Ex. 5” main 2.25” ID springs with helper springs. Stack height and the overall suspension silhouette matters when it comes to running wide wheel and tire configurations like 10.5” or 11” square.
What tire compound will you be running, and have you taken into consideration the endurance class wheel & tire rules that you are building the car to compete in?
305/680-18 is going to be too tall with a diameter of 26.8”, and would result in serious clearance issues up front. These tall tires are commonly used on Mustangs and Camaros. If your goal is to run 305 square, then 305/645-18 is more appropriate for the E9X chassis.
OEM Benchmark
F) 245/40-18 → 25.7”
R) 265/40-18 → 26.3”
Square tire configurations that work for a track/race E9X M3:
275/35-18 → 25.6”
285/30-18 → 24.7” (short, but they work)
285/35-18 → 25.9” (About as tall as you can go up front without major modifications)
295/30-18 → 25”
305/645-18 → 25.4”
305/660-18 → 26” (Tall. Works on an F8X & might be possible on E9X M3)
315/30-18 → 25.4”
In terms of aggressive 18” wheel fitments to support the compounds listed above, we have two good options. Which is best for you will depend on a number of things like your suspension configuration, which tire size and compound you choose, and how the rest of the car is developed.
Option 1: 18x10.5” ET22 / ET27 square - Available in all APEX designs
This is the most common rotatable square setup for more serious E9X M3 track/race cars, as the 10.5” wheels provide superior sidewall support over the 10” wheels commonly found on street/weekend warrior HPDE cars. Most drivers pair these 10.5” wheels with either 275/35-18 tires to maximize sidewall support, or 295/30-18 depending on desired compound (not every tire comes in every size), driver experience, class rules, etc.
Our original ARC-8 and EC-7 flow formed designs are 18x10.5” ET27 which will require spacers up front to clear the struts, however, our newer SM-10 and FL-5 flow formed designs as well as our brand new EC-7R and ARC-8R forged designs are offered in 18x10.5” ET22 which were engineered specifically for the E9X M3.
Since ET22 is the optimal offset for a 10.5” wheel, you can run up to 295’s without the need for spacers as long as the spring stack height is appropriate (shorter 5” main springs). This wheel fitment will require negative camber up front, but these are track/race cars so that is par for the course. You can also run the 305/645-18’s on these 10.5” wheels with added negative camber, but I think most drivers would prefer running 11” wheels for proper sidewall support, especially since slicks run quite wide.
Option 2: 18x11” ET25 square - Available in EC-7 design only
This setup is typically reserved for hard core race cars and W2W racers planning to run 295, 305 or 315 compounds where maximum sidewall support is desired. Naturally, the fitment requires a little more love in the form of very aggressive camber specifications, rear fender rolling/pulling and possibly some inner clearancing work with the liners, etc. Up front, even the slimmest of suspension designs paired with short 5” springs will need spacers to clear the struts due to the sheer width of the wheel, and the spacer thickness you’ll need will depend on contributing factors like spring stack height and tire size/model (ballpark 10mm - 15mm spacers will be needed).
I hope this was helpful. Please let me know if you have any other questions!
-Tom & the BMW team
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Tom
Thanks for the quick and detailed reply, you made a lot of sense, I have 2.25 5" springs on the front, no helper springs right now, but probably need them. I have been running an AIX mustang that uses the 305/680 tires so I was trying to use some of those up but not if it doesn't make sense. I am hoping to eventually run slick tires but may not have that option early in this build, will start out running ST3/E0 NASA classes. I need to digest this a little bit but will be in touch, trying to race in the 6 hour at Utah in AUG but got a lot to do.
Thanks