Footage from a 2008 Porsche GT3 Cup car, on Michelin slicks, splitter, wing, etc Race weight around 2600 pounds (and this driver is maybe 160 soaking wet). And he's a good driver, a multi-time SCCA Solo National Champion, like me. Footage taken using the same Chase Cam w/data that I use (hence the comparison). http://vimeo.com/19751331

Some footage that you've likely seen before, of me in the Shelby GT.... Car is 3436 pounds, and I'm heavier @ about 290. Also I'm not on slicks, but Hoosier A6 tires which while not street tires, are actually still DOT approved and on 18x8.5" wheels And of course solid axle, no aero devices, etc.
http://www.stranoparts.com/videos.php?VideoID=1

And for another comparison, my 2011 GT @ Nationals this year. Surface is not as grippy, and it's a little bumpy... Again, this is a very, very stock (Koni's and a front bar change, alignment and Hoosier's vs. stock is about it) car. Again consider the differences in cars here--and look what a Mustang can do--and remember we can make it much better!!!
http://www.stranoparts.com/videos.php?VideoID=8

Take particular note of lateral g numbers. Porsche with 1000 less pounds, slicks, aerodynamic help @ Sebring. Mustangs are competing @ over 1000 pounds more, without all those other tricky things and still able to pull some pretty good numbers.

The Mustang footage comes from two cars setup or stock class. For this year I'll be moving up with my 2011 to a class that allows a lot more goodies, which makes the car even better. Stay tuned for that comparison down the road!

 

Nice!

 

Oh no. They IRS to handle at all. Just ask all the internet racers.

 

Thanks for setting up your G meter properly. It makes me sick when the bars go the wrong direction. Nice driving.

 

I can't lie, on occasion it's been put in backwards. We've since marked it "front" so we don't do that anymore.

 

Hey Sam, what size tires do you run on the 8.5" and track pack wheels (are 9 or 9.5"??)

I have older GT500 takeoff wheels (9.5") and am trying to decide if I should try the 285/35-18s that the NT01s, Ventus R-S3s, and NT 555Rs are available in, or do the 275/40-18s that are the correct 27" outer diameter height. They'd be track-only wheels/tires at that point of course. 285 is max width on a 9.5", generally. Thinking the reduced diameter might give a bit better torque as well....

 

Hey Vapor, going from a 275/40R18 to a 285/35R18 will produce about a 4-5% increase in torque, but its interesting to note that a 285/35R18 on a 10" wide rim measures 11.22" wide and a 285/40R18 measures 11.40" on a 10" rim (a 275/40R18 measures 10.91" on a 9.5" rim) putting a 285/35R18 on a 9.5" rim will reduce the section width by .20" as will mounting a 285/40R18 on a 9.5" wheel.

With a 285/35R18 @ 25.85" dia vs a 275/40R18 @ 26.66" dia on the same 9.5" rim there might not be any real gain in the contact patch since the section width is within spitting distance of each other; 11.02 for the 285/35 and 10.91 for the 275/40, but you've lost nearly an inch on overall diameter for a small gain in road force.

This all depends on how you feel about contact patch though ( height x width = contact patch or weight x pressure = contact patch) In either instance (height x width) the contact patch may be less or (weight x pressure) the bias of the patch will favor the width making it longer (width) but narrower (length).

 

Hey Bob

I understand what you're saying, might not mean much in terms of lateral grip for the same compound/tread, but maybe the increased torque will help a bit (I lose so much at 5000+ft in the first place, can use any that I can reclaim; course, lighter wheels would help even more, these GT500 ones are heavy).

What tire/manufacturer data you using on those calculations and info? I know a lot of the Kumho tend to run narrow, and the makers all seem to measure differently and not be consistent on the same tire size from Kumho to Nitto to Hoosier, etc (even different tire series within the same maker). I figure the max I can get on these 9.5" rim is the 275 or 285, and there's not much price difference for the same tire, but many more DOT R compounds in the 285/35 size (like Sam's Hoosiers, I'd get the R6 though), so will likely go that route, then experiment with different tires over the years. Swapping around sizes just introduces another variable...

Any one know if that change in diameter will affect the ABS enough to pose a problem?
Would it be something worth flashing with my SCT before each track weekend to change the outer diameter setting?

Thanks guys!

Josh

 

I ran 295's on both the Shelby 8.5" wheels and my Brembo car's 9" wheels. That's the fastest setup for me and that's what matters. Wear wise, a tire more appropriately matched to wheel size would be recommended.

 

Whoa! I'm assuming the 295/30-18?? On a 8.5" wide wheel? Much wider than I expected. Obviously works for you though, can't argue with results!

I think I'm gonna go for the 285/35-18 when I get around to buying them, though with y 9.5" wide wheel could probably do a 305 or more based on this!

I'm hoping to do NASA time trials in a few years, so the series rules will also come into play, I think over 275 or 285 bumps you into one of the top classes regardless.

Thanks Sam!

 

Nitto for the width, and I just calced the tire dia, IIRC both BFG and Nitto rounded those OD numbers. The section width difference should apply across any radial tire using standard construction.