Turning a new corner?
Senior Road Test Editor, Josh Jacquot, piloting the 2007 Porsche 911 GT3
Tomorrow at 3 PM PDT, I am scheduled to meet with the Editorial Director of Edmunds.com to discuss the Vehicle Testing Assistant position I applied for. God’s will be done!
I’m going to answer Jasper’s comment here for anyone else who may be interested.
good read on the track day. what mpg do you get on that 100 oct? do you go through a tank per track day? looking at your pictures, do you think a lower offset on your wheels would improve handling by having a wider stance? what suspension mods have you done so far? is it even worth changing from stock setup?
- I’m not running on full 100 octane at the track since I had some 91 octane already in the tank. With the amount of 100 octane fuel I put in, I’m guessing I was running anywhere between 93 to 96 octane. The car will average a little over 8 miles per gallon when it’s on running on the track. I try to run with a little over half a tank (9-10 gal., tank capacity is 15.9 gal.) for hour of track usage. Running with a full tank is undesirable due to the weight penalty it would produce (5.8 to 6.5 lbs./gal. – http://www.santacruzpl.org/readyref/files/g-l/gasoline.shtml).
- 50 minutes to an hour of track day use will usually consume half a tank.
- Wheel offset isn’t nearly as important as the size of the contact patch of the tires with the track surface. Going to a wider tire definitely doesn’t hurt when running on the track. My wheels are only 7″ wide; a 225 mm wide tire is the fattest/widest tire I can put on the wheels I use on the track. 225 mm is the widest a 7′ wide wheel can handle. The 2004 Subaru Impreza WRX STi has 17″ x 7.5″ BBS wheels with 225 mm wide tires. The 2005 and later STi/STIs have wider wheels (8″ wide) with the same width tires from the factory. On an eight inch wide wheel, I believe 245 mm is probably the widest tire that can be put without having to roll the fenders.
- The suspension mods I’ve done so far consist of Prodrive (manufactured by Eibach) springs and STI Group N strut tops. The latter are much stiffer than the stock ones as they are used in Group N rally competition.
- Yes, it’s worth changing from the stock setup for the WRX. This does not apply universally to all vehicles. The WRX has a tremendous amount of wheel travel for a sports car and a pretty soft suspension which makes for a lot of body roll-something unwanted when handling at the limit. Stiffer springs, in my case I’m guessing they’re 15-25% stiffer than stock (Prodrive spring rates are unpublished), reduce some of the body roll. The springs on the car aren’t so stiff that the car’s ride is completely bone-jarring by any means. I imagine my car handles a little bit better than the 2003 Prodrive Subaru Impreza WRX that Motor Trend tested (http://www.santacruzpl.org/readyref/files/g-l/gasoline.shtml). I say slightly better because I can vouch for the Bridgestone Potenza RE-01R tires having better grip than Potenza S-03 tires.
COBB AccessPORT Stage 1
OEM STi short throw shifter
Prodrive round tip muffler (axle back only)
Prodrive silicone intercooler hose
Wheels & Tires
Prodrive P1 Gold 17″ x 7″
Bridgestone Potenza RE-01R P225/45R17
Prodrive WRX springs (2004-on)
STI Group N strut tops (2004-on)
Whiteline steering rack bushings
Subaru 4-pot front/2-pot rear brakes (red)
Goodridge stainless steel brake lines
Motul RBF 600 brake fluid
OEM painted sideskirts
2006 STI rear diffuser
OEM turbo boost gauge
MOMO shift knob
STI 5-speed shift pattern emblem
Rear dual cupholder from a Subaru Forester
Update: Below is a response to part of banilla777’s comment
Understeer really isn’t a problem for me. In my opinion, people who complain about understeer are usually trying to enter a turn faster than the car is capable of turning. I just get the car slowed down more for the turn and all is well. “Slow in. Fast out.” Naturally, “Fast in. Fast out,” is even better. But if you’re overcooking your “Fast in,” you’re going to have a “Slow out,” which hurts exponentially on the following straightaways the longer the straights are.
On a road course, a wider tire should never hurt your lap time if the vehicle is set up properly. Increasing the size of the contact patch is never a bad thing on a road course or in situations where handling is of the utmost importance (e.g., autocrossing). On a drag strip, it would increase the drag (rolling friction) of the tire and thus, slow it down (marginally in most cases).