by Audi1 » Wed Sep 02, 2015 3:44 am
I recently did a front-motored Alfa TZ2 and, so far, it's doing well in the IPS proxy. I think that most front motored cars can benefit from some weight just in front of the rear axle; I used about 5 gms and it seemed to help.
A good set of trued XPGs will also help. I recently trued a pair and finished them off with 2000 grit sandpaper (your method, Harry). After running them in on my skid pad, they were so sticky that the rear of the car wouldn't slide on my SCC set-up plate! Now, that's sticky!
Separately..........and I don't mean to hijack this tread................ :text-threadjacked:
I did some testing on PGT and XPG tires recently; after talking to Paul about the two of them. In our discussion, he said that PGTs get their maximum bite at a lower slip angle, whereas the XPGs get their maximum bite at a higher slip angle. I understood this, but couldn't really envision it until I ran the two tires on identical wheels on my skid pad. Then it was clear. Here are the results of that testing, which I sent on to Paul:
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Hi Paul,
I finally got a demonstration of what you're talking about when you talk about different slip angles for PGT and XPG tires
I had a car on my skid pad and tested it first with PGT rears, then with XPG rears.
I put the car on the skid pad and ran it in both directions, slowly increasing the voltage until one of two things happened:
1. the inside rear tire moved into the area of the inside braid, or
2. the car was about to de-slot.
Both of those measurements turned out to be important.
For the PGT rears, the inside rear wheel moved into the inside braid at 5.2V run counterclockwise and at 5.3V run clockwise. It was on the verge of de-slotting at 5.7V run counterclockwise and 5.8V run clockwise
For the XPG rears, the inside rear wheel moved into the inside braid at 4.8V run counterclockwise and at 5.0V run clockwise. It was on the verge of de-slotting at 6.7V run counterclockwise and 6.8V run clockwise.
So, the PGT rears stayed on track at a higher voltage than the XPG; which gybes with your statement that they get their maximum bite at a lower slip angle. On the other hand, the car was on the verge of a de-slot at a lower voltage when running the PGT rears than it was when running the XPG rears, which gybes with your statement that the XPG's have their maximum bite at a higher slip angle.
To my observation, it took longer for the PGT rears to drift out of their original line, but the XPG's kept their line and stayed on the track longer.
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So, for proxy racing, where you experience drivers with different driving styles, the XPGs seem to be the way to go. Although, if I was building a car for a local series race held on a twisty track, I might go with the PGT compound, just because it can hold a tight line a little longer.
I also wanted to add, that, for me, the difference between truing PGT and XPG tires using a mediuim grit sandpaper, like 220 grit, for example, and truing them (or finishing off the truing) with fine 2000 grit, followed by some "polishing" at the track, is night and day. I think it's definitely worth the time to do as Harry does and finish off your truing with the fine grit paper. By the way, you will find that truing the harder compound PGTs is much easier than truing the XPGs on finer sandpaper, but they both come out well.
End of thread hijack :text-threadjacked:
And now, back to your front motored L88 car thread..........................................
Allan
