quote:Originally posted by ParaPantera:
Kelly, I have no answer for you discrepancy at speed (tire diameter difference?), but all Pantera speedos stay at 10 MPH at rest. If you look closly, there is a very small pin sticking out of the speedo face that stops the needle at that location.
I'll have to take another look but at least in my mind it was resting above the pin. It registers 70 mph in 5th at 3krpm. I have the stock 4.22 ring and pinion but have 345/30/19 rears. If you do the math that’s a 27.14” diameter wheel. They measure accordingly, slightly under with weight on wheel but I'd say rolling diameter is pretty close. A stock wheel was supposedly 26.5”. If I do the math through the gears I get I should be 81 mph at 3krpm with this tire. The speed calculator at Mike Dailey’s site predicts the same. The larger tire only accounts for 2 mph increase as 79 mph is predicted for a 26.5” tall tire.
I’d time it over distance but the snow is flying.
I’ve had the car back on the road for a couple months now and just noticed it. Don't pay much attention to the speedo. Eyes are on the tach and the country road ahead. If it’s really reading 10 mph slow at 70 my top end smile just got wider.
I suppose my tach could be off but I have a 6200 rpm chip in my rev limiter and have verified (repeatedly) that it’s right on the money as I’m bouncing off the rev limiter.
So good people of the PI Forum, my questions are:
- What was stock tire diameter?
What’s your rpm at 70 mph?
Are the speedometers easily rebuildable or able to be calibrated?
Anyone done it or have a reference procedure?
Figure I’ll brighten up the instrument lights while I’m in there this winter. I found some good posts on that.
Kelly