On a completely non-turbo related subject...
I had a hell of a time in Harrisburg this past weekend, taken quite literally.
The car was slipping and sliding around all over the place (decidedly NOT the
behaviour you want in a high-speed slalom), driver confidence plummeted, and I
never did put together a run that was anything near competitive.
Once the red mist had cleared, I went looking for what could be the cause, as I
had had similar problems in Virginia, and quite possibly Peru too.
On impulse, I had stuck a pyrometer into the tires once I had cruised back to
the pits, and found that, even after 4 runs (and taking into account the cooling
effect of my trip back) the tires were still pretty cold - 120 front, 100 rear -
on tires that want to be somewhere up around 160-200.
I also overheard a few fellow wide-tire g-force drivers bitching about how their
tires never got up to temperature and so slid around, and it suddenly fell into
place. When hot, the g-forces are phenomenal, but cold, they frankly suck. The
evidence is there - a car nearly identical to mine, running much narrower "old
R1s" didn't seem to have nearly the grip problems that I did.
My g-forces have been wearing really well, I have nearly 60 runs on them, and I
expect to see about 20 more, but it's getting near time to buy tires. I have a
choice to make:
1) Stick with the g-force, but drop down a size, to 255-40R17
2) Switch to Kumho, at 275-40R17
3) Both, a Kumho 255-40R17
That's right, the Dark Side of the Force, the K-tire, is beckoning me from the
shadows.
Here's the relevant data:
Section Tread Diameter
g-force 275-40R17 10.6 10.1 25.6
g-force 255-40R17 9.9 9.7 24.7
Kumho 275-40R17 11.18 10.39 25.35
Kumho 255-40R17 10.63 9.72 24.80
Interestingly enough, the big K-tire is both wider and shorter than the big BFG.
The Kumhos are also much more "bulbous" than the BFGs - you get less tread for
the section width.
But here's the $10,000 question - how good are the K-tires, both hot and cold? I
understand that a hot g-force is a better tire than a hot Kumho, but is a cold
Kumho better than a cold g-force? Or is it better to stick with the BFGs, but
move down a size (and so get a lower car and better gearing, but less grip when
hot?)
Any thoughts?
DG
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