Speedometer Error

[94MustangGT5.0]

I got my 4.10's put on this weekend and changed my speedo gear out as well. I knew going into the install that because I have an automatic, no speedo gear will calibrate the speedometer perfectly. Anyways, I put my 23 tooth gear in and then got out my portable GPS unit and wanted to calculate how far off my speedo was. Not knowing for sure that if my car was dead on to begin with (white face gauge installation with removal of needles and 275/40's out back), I found that I have about 4-5 percent error. At 100 mph on the speedo, the GPS unit reported a speed of 96.2 mph, and at 60 on my speedo, the GPS said 57. Anyways, I just wondered if others found there was a similar error when they did their gear swaps and what tire size (205, 245, 315) would make up for this error if that were possible to cancel out. I will make sure I post timeslips when I (hopefully) go to the track this weekend!

 

[5.0_GT_kid]

I believe the SpeedCal from Dallas Mustangs will solve this problem.

 

[Black95GTS]

The 23 tooth speedo gear will correct for 3.55, and even then it will be off. The 23 tooth gear is a chrysler part and does not mesh properly. It will have to be replaced regularly depending on how you drive it.

Our T-5s have an 8 tooth drive gear. If you want to correct for the 4.10s and not buy a speedcal, you would have to replace the drive gear and the speedo gear. A 6 tooth drive gear coupled with a 20 tooth speedo gear will yield accurate results

The best way to correct for this (IMHO) is a Dallas Mustang Speedcal. Simple install and dial in the gears.

http://www.partshopper.com/fordmustang/Items/DMP-9910.html

 

[CManT1914]

I found that my speedo was pretty much dead on with some taller tires than stock. How do I know? I got pulled over and the cop said he clocked me at 79, exactly how fast my needle said. I have also compared it with other vehicles, and those radar signs. I was running 255/45/17's then, now I have 315/35/17's out back, and it's pretty much the same.

 

[5.0_GT_kid]

I found that my speedo was pretty much dead on with some taller tires than stock. How do I know? I got pulled over and the cop said he clocked me at 79, exactly how fast my needle said. I have also compared it with other vehicles, and those radar signs. I was running 255/45/17's then, now I have 315/35/17's out back, and it's pretty much the same.

I wanna know if you got the ticket for that

 

[96darkhorse]

i recently put my 373s in and didint change any speedo gear....im running 295/35/18's...anybody know how much is my speedo off??? im gessing 15mph

 

[94MustangGT5.0]

I was under the impression that the Speed Cal only worked for 96+ Mustangs, I could be wrong though. I think for now I'll just live with the slightly off speedo and remember that when driving past cops.

 

[CManT1914]

I wanna know if you got the ticket for that

Heck yes I did!! But I was speeding, so I guess I deserved it.

I was under the impression that the Speed Cal only worked for 96+ Mustangs, I could be wrong though. I think for now I'll just live with the slightly off speedo and remember that when driving past cops.

I thought they only worked on 96+ as well.

 

[krahkin]

I run a SpeedCal on my '95. One of the best things Ive purchased for it.