Posted by Paul Cook on March 20, 2000 at 11:03:14:
In Reply to: COMBAT RIMS?TIRES: Are they balanceable???? posted by dave on March 20, 2000 at 07:53:36:
I bought a WC-52 restored by Tim Peterson (originator of disc brake conversion) and it was in excellent condition. The combat rims had been balanced and there was no sense of tire/wheel inbalance.
You described shimmy which is different from inbalance. Shimmy almost always starts at the same speed on the same type road, usually pavement. If the front end is tight, it rarely occurs on dirt roads. I experienced front end shimmy at 35 - 38 mph. Tim had installed a steering stabilizer (shock absorber between tie rod and axle housing) which did not eliminate the shimmy. The immediate fix was a jab on the brakes and drive 3 mph below the speed where the shimmy started.
Military NDT's are not happy with longitudinal pavement imperfections. The vehicle tread width (measured at the tire centerlines) does not match the width of the slight depressions in the pavement caused by heavy trucks. Because of the NDT tire design, they try to climb out of the depressions. This momentarily overrides the toe-in and shimmy occurs - even with a tight front end.
The cure is to inflate the tires to 35 psi. If you don't carry a real load, the tires look inflated with 15 psi. This is great for certain off road driving, but is a NO GO on pavement at higher than parade speeds. 9.00 x 16 NDT's are at least C rated with a maximum inflation of 50 psi. Most are D rated with a max inflation of 65 psi. The Army standard inflation for a 9.00 x 16 has always been 35 psi.
Increasing the inflation is not always a total cure because of the nature of the NDT tire tread. It may only raise the speed where shimmy starts so you can drive those extra 4 or 5 mph faster.