Learning how to build Lotus Seven replicas...together!
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 Post subject: Squirm
PostPosted: October 5, 2015, 9:57 am 

Joined: February 28, 2009, 11:09 pm
Posts: 1305
Location: Connersville, Indiana
As I get the older the Alpine gets harder to maneuver at low speeds. It was wearing Cooper CS4 185 tires with 5.75" tread. I decided to go to the narrowest 175 tire I could find. That turned out to be General Altimax RT43, 5.0" tread width. Got them mounted, drove down the street, turned the corner and all hell broke loose.

Damn near drove up onto the sidewalk. Steering return was nil. Steering response was "Oh, so you want to THAT way? No problem. Zoom." Slight road irregularities would send it half way across the lane. Lowered tire pressure from 32 to 28 psi. Helped. Increased caster from about 3 degrees to 6. That helped a lot. Steering return got better, but it was spooky enough to make me slow down and alert with both hands on the wheel.

Things improved gradually as the miles accumulated. As mileage approached 2,500, I noticed the car was becoming almost civilized. We now have 3,000 miles on the tires and am able to drive it at speed on county roads. They are very bumpy with deep depressions which would send the car off into the wild. Sort of like bump steer, but delayed and unpredictable.

This is my first experience with this phenomenon. Always before the new tire strangeness would be gone within a very few miles.

I post this mainly to warn guys that build a car, take them out for a trial run on new tires to see how it drives. If they happen to have squirmy tires, those first miles mean NOTHING.

Oh yes, it steers much easier and I'm leaving caster at 6 degrees.


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