Autocrossing your chevy truck....who wants to?

[N2TRUX]

Originally Posted by 68Stepbed

.....Can anyone give me some info on Treadwear ratings. I've seen where alot of AC events require a minimum of either 180 or 200 TWR. My tires have a 420 TWR. Would I still be able to AC? Or are they basically saying you can't use a real sticky race tire?

Another good Pro Touring forum is http://www.lateral-g.net and they have a truck section. Its not as active, but lots of good info there.

Take a look at the info Rob posted in the "Make it handle" thread in our Suspension forum- LINK

Originally Posted by robnolimit

Remember in "Days of Thunder" when Harry said "it's all about tires, tires win races" well, he was right. To understand about suspension tuning, you have to understand TIRES. All tires are different, and each will deliver a certain amount of traction. The amount of traction varies with the amount of LOAD on the tires. Yes, traction increases with load, BUT, the tires efficiency falls with increased loads. Tire manufacturures will post a "Tire performance chart", but they are to come by, as most in the business have never heard of such a thing. The chart will show a graph, with a curve showing traction in relation to verticle load (weight). Here is some info from a chart for a 245/40/18 KDW Goodrich.
LOAD TRACTION EFFICIENCY
250lbs 490lbs 1.96
500lbs 700lbs 1.4
750lbs 890lbs 1.18
1000lbs 1000lbs 1.0
1250lbs 1125lbs .9
1500lbs 1260lbs .84
1750lbs 1365lbs .78

This willgive you an idea of how the tire LOOSES traction as it GAINS load. The efficiency is in "G" forces (this is the simplified approach) and is simply Traction divided by Load. If you had the perfect set up, to get the max contact patch, you can chart out the max traction available. So, heres an example. The average C-10 weighs in about 4000 lbs. and scaling it would look like this:
LOAD LF 1195 RF 1160 58%

LR 860 RR 830 42%

Total wieght = 4045

Notice the 58% nose weight? thats pretty common, and it's not good for handling. '47-'59 guys just subtract 100lbs from each corner. If we apply the Traction Curve, we can chart the avail traction. It looks like this:

TRACTION LF 1075 RF 1055 52%

LR 963 RR 938 48%

Total traction = 4031

You can see that the front has 58% of the weight, but only 52% of the available traction. And, at this point, were rolling dead straight, with no accel, brake, or turn. This is the best it will ever be for this set up. At first, you might think that dividing total Traction by total Weight would give you the max G avail ( 4031/4045 = .99G) Looks great! - ahh, no. You know the whole 'weakest link of the chain' thing? Apply the efficiency to each tire:

Max G LF .899 G RF .909 G

LR 1.12 G RR 1.13 G

The LF will loose traction first, at .899 G, and then it's over, thats the best the truck can do. So, can our example truck pull .89 G? - no. We haven't added any cornering forces yet. OK, give this some thought. What does your truck do when you turn hard into a corner? If it's normal, it will PUSH (understeer) going into, and throught the turn, and then transition and get LOOSE (oversteer) as you throttle out of the turn. I'll add to this later. Just think on this a bit.