Wider Proves to be Faster

So, now that we have tires and wheels installed, it’s time to find out how much quicker around our test track this combination is versus the O.E. tires and wheels. To simulate the total lap time of a typical national level autocross event, we combined 2 flying laps of our standard test course.

First setting a baseline reference with the factory 205/45R17 Bridgestone Potenza RE050A tire/O.E. wheel package, we then bolted on the 255/40R17 Dunlop Direzza Sport Z1 Star Spec  tires on 17x9.0 TRMotorsports C3 wheels and ran a few comparison laps. With nothing else done to the car, and no real tuning done Project STR testing tiresto optimize tire performance, we went well over 2 seconds a lap faster, on a 55-second course. Steady state lateral g-forces were improved, too.

We’re looking forward to installing the coil-over suspension, so we can better control the performance of the Dunlop tires.


Friday, April 9, 2010 by Dave

How do we isolate where the improvement came, from Z1 Star Spec or the size? Has the OEM size 204/45R17 been tested using the Star Spec (if available) or the 255/40R17 using the OEM model tire?
Friday, April 9, 2010 by Tire Rack Motorsports

Dave: Good question. For this project, we opted to make the jump to the maximum width tire and wheel package dimensions allowed by the SCCA rules, recognizing that the net improvement in performance comes from both the tire choice, and the change in size when mounted on the wider wheel. We know from our regular tire test program that the Dunlop Direzza Sport Z1 Star Spec is focused on activity like we will be competing in (and similar to Tire Rack's standard test course design), and brings a performance advantage over the Potenza RE050A. So, how much is the tire, how much is the change in size, and how much is due to the wider wheel? We can't say. But we know that all together, it's a significant jump over the OE tire and wheel package. And for this project, that's exactly what we're trying to accomplish.
Wednesday, May 5, 2010 by Kevin

DO you need to roll the fenders to fit the 255 tires? How much is the car lowered ? Thanks.
Wednesday, May 5, 2010 by Tire Rack Motorsports

Kevin: it does take a little persuasion to get the wide 255s to fit. We had to work on both front and rear. The baseline KW Variant 3 Coil-Over install lowered the car 1" front and rear. Ride height may change somewhat as we continue to tune the car set up.

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