revs per mile not being corrected with turner. 4.10 Gears?

[gismik531]

I thought I had this problem fixed with the 02 Mustang GT. At first it seemed to work, and I got the revs per mile tech info from Discount tires who sells the Nitto tires. I have the 275/40/ZR 17 98W Nitto NT 555 Extreme Performance tires. The revs per mile is listed as 711 from the manufacturer. I am not sure now what to do, because it is still about 20 mph faster than it should be. Could it be that someone put 4.10 gears in it, would that make sense that the gears have been changed? I would have thought if the gears were 4.10's it would slow the speedo, not make it faster. Correct me if I am wrong, and advice on what needs to be done to correct this? Thanks Mike

[mikel]

Well, yes, you need to know what gears are in it to set it correctly.

If you restore the stock tune, how far off is it?

If its more than 2-3 MPH off, you have non stock gears....

[gismik531]

It has been like over 21-22 mph on the speedo since I bought the car, 91-92 mph to equal 70 mph . One of the main reasons I bought the Turner was to set the revs per mile. Stock tune loaded back up reads the same, regardless. I tried that this morning, it was originally set at 895 revs per mile, and like I said the dealer has it listed as 711 revs per mile. Reads the same at bot settings. So any suggestions as to what to try?

[mikel]

you need to figure out what gears are in it and set the axle ratio correctly.

[MesaRec]

The Revs/Mile for 275/40/17's should be set at 813. This is the rounded figure and obtained via Ford's formula.

Revs per mile = 20850 / { (2 * 275 * 40) / 2540] + 17 } = 812.504 which rounds up to 813.

Once you have that dialed in, don't change the revs per mile on the tires, and adjust the gear ratio until your dead on. It shouldn't be difficult to get it right since each gear will vary the MPH significantly.

Good luck.

[RobD]

If you have a Mustang that has the original gears from factory there should be 2 toe tags on the rear end cover it will say your gear ratio on it .There might be a L or a LS in between the ratio #'s . Example 3.73 Gear ratio might say 373 or 3L73. Hope that Helps.