Jon_Purdy

Hello everyone. I think my speedometer might be off a bit. Not sure how it got that way. The attached Excel document says with stock 3.55 gears, at 2200 rpm I should be going 74.23 mph, but the speedo says I'm going 70. I assume the dealership can fix that but how? Or is it something that I can fix with my tuner?

Jon

2kanchoo

If you haven't changed the gears it should be correct. You're tune could have changed it. If you have a 93 octane tune I'm assuming you have a tuner. Plug it in and change the axle ratio to 3:55 yourself.

Edit: your speedo will be out if you have a different size rear wheel as well. (outer diameter bigger or smaller than 27", if so find the rotations per mile of that tire and you can enter that yourself with the tuner aswell)

Glenn

everyones speedo is off from what I have read here at TMS. There are several threads about it. My speedo does not set at zero when I am at a complete stop. Its at 2 mph.

Five Oh Brian

In addition to selecting the right gear ratio with your tuner, you can set the number of tire rotations per mile to fine tune the odometer and speedometer (at least with a Predator like I have). I believe with the factory 235/50/18 tires I have it set at 758 revolutions per mile? When I put on the shorter 275/40/17 drag radials for race days I have to reset it to 806 (shorter tire turns more per mile).

I double checked via the freeway mileage markers for accuracy, going 10 miles and making sure the odometer went exactly 10 miles, as well.

uberPony

What kind of handheld tuner do you have?
Have you looked at that to correct this?

Glenn

use a portable gsp to get it right. Doesn't get much better than that

steevr

Exact same thing with mine. I compared it to my Garmin C330 GPS and the speedo reads 1-2 mph high. The odometer is dead on with the GPS.

I can compensate for the speedo reading a bit high, but I'd be ticked if the odo was racking up extra miles over time.

zaghloul

The needle is about a 1/4 inch away from the dial, and therefore the position of your head will change the reading a bit. Try this, just sit in the car at 0mph and move your head up and down, closer and further, and you'll notice the difference. This might not explain it entirely, but atleast that's part of the issue.