You’ve heard me complain numerous times in my posts and videos about the terrible tires that I’ve been racing on this season. Thanks to a generous gift (let’s call it a sponsorship), I was able to finally get the tires for my BMW E36 that it deserves! I ordered a new set of Bridgestone Potenza RE-71R tires and had them installed on my current wheels. All in the quest for just a few more seconds in reduced run times! Let’s look into the research that I performed when deciding on these tires and how they fit on the E36.
Just looking at the picture of the Bridgestone Potenza RE-71R tire, you can see how aggressive the tread design is. There are only two circumferential grooves and not that many sipes (cuts) in the tread to interrupt the large rubber contact patch. Couple that with the 200 treadwear rating (meaning they won’t last long but they give it their all in their short life) and these tires should perform on the track. I know that they’re a very popular tire for everyone in my local SCCA club and are run on many different types of cars.
Being an engineer, I’m definitely one to look for well documented research in order to make an informed decision. Luckily, Tire Rack had just completed an autocross tire comparison test in late June of this year. You can see some of their test results above for both dry and wet testing. As you’ve seen with my autocross event conditions lately, driving in the wet is a normal occurrence in the Seattle area (I know, a surprise for sure!). I was impressed by the Bridgestone Potenza RE-71R’s wet performance given the little siping present. So far, the Bridgestone has the clear lead over the competition in the testing!
Then the Tire Rack crew put the tires onto a new 2017 BMW 430i Coupe and took them to the track. As you can see above, the tire’s subjective performance ratings correlated to the fastest slalom and lap times (both in the dry and the wet). Why choose anything else, especially when the Bridgestones are similarly priced or cheaper than the competition?
The Tire Rack wrapped it up when they said, “The Bridgestone Potenza RE-71R presents an amazing package on track, with huge grip in every direction, wonderful balance and steering precision that is second to none. Ride and noise comfort were obviously low on the priority list during the tire’s development, and it may no longer be the overdog it once was in terms of outright lap times in the dry, but it is definitely a go-to choice for any enthusiast with track or autocross time in their future.”
After a little more research on various BMW forums, I decided that a tire size of 245/40R17 would provide the most grip with the least amount of possible fitment issues. I could’ve potentially stepped up to 255 section width but others spoke of possible rubbing on the rear inner fender of an E36 (which would require fender rolling). It wasn’t worth the risk to me at this time so I went with 245s at all four corners.
Having the new tires installed also gave me the opportunity to weigh a few things. I wanted to see how heavy my aluminum wheels are to see if it potentially makes sense in the future to get lighter weight ones. Turns out my current wheels are 23.6 lbs each which isn’t so terrible but I could maybe lose around 5 lbs per corner switching to lower weight units in the future. For reference, the Bridgestones are 24.0 lbs each.
Another thing that my research turned up is that I would probably need wheel spacers on the front corners. Wheel spacers push the wheels out farther away from the suspension so the tires won’t rub on the Eibach springs. I determined that 12.5mm thickness would probably be the right size and ordered a set of Renn Motorsport units.
After removing the front dust caps, they fit perfectly flush as they should. No issues at all.
The picture above shows how the tires are now nearly flush with the wheel opening but are just barely contained within the fender. That means that they don’t rub during full compression and give me maximum track width for cornering prowess.
Here’s a picture of the rear showing how the tires are just inside the fenders. Without the -2 degrees of camber it probably wouldn’t work though. No wheel spacers were used on the rear. I honestly can’t believe how well everything came together!
Shortly it’ll be time to put them to the real test when I run them at the last timed event of the summer! Expectations are high!