Speedometer in the '07 - Page 2

89 Hoss · 06-29-2008, 08:58 AM

When I bought my tune I had to send ford the vin#, tire size I was currently running as well as the gear size. They processed the info. and sent it back for me to get installed.

redhorse · 06-30-2008, 07:50 AM

Lee, the stock tire may have been 55, I can't remember for sure. They were only on the car for 1 day before they were changed.

89 Hoss, I had to give the same info for my tune also. It would be interesting to see if your car is off as well.

NightHawk756 · 06-30-2008, 08:02 AM

Quote:

Originally Posted by QWKSNKE

That's just it. Ray is not running a larger tire combo. He is running a wider tire than stock but it is shorter than stock by over an inch which would make the speedo read faster than actual travel speed.

Yeah, but he went from a 17 to an 18. If the tire is 1" shorter, then it should be about perfect then since that would make up the 1" difference in wheel size right?

Italian LX · 06-30-2008, 09:28 AM

Quote:

Originally Posted by NightHawk756

Yeah, but he went from a 17 to an 18. If the tire is 1" shorter, then it should be about perfect then since that would make up the 1" difference in wheel size right?

Not with a 275/35 tire. Lee is right in the calculations.

(((275/25.4)*.35)*2)+18 = 25.578" tall tire/wheel combo

. . . which, as Lee already mentioned, is a lot shorter than the stock tire and therefore would register a faster speed.

NightHawk756 · 06-30-2008, 10:54 AM

Quote:

Originally Posted by Italian LX

Not with a 275/35 tire. Lee is right in the calculations.

(((275/25.4)*.35)*2)+18 = 25.578" tall tire/wheel combo

. . . which, as Lee already mentioned, is a lot shorter than the stock tire and therefore would register a faster speed.

Hmmmmm......interesting. That difference creates a 5-6 mph difference. Just seems like alot for what seems like a small difference in height.

For some reason I couldn't wrap my mind around the concept that going from a 17 to an 18 would be smaller. But thinking how tall the stock tires are on the new ones, it's starting to click now.

QWKSNKE · 06-30-2008, 03:07 PM

Quote:

Originally Posted by NightHawk756

Hmmmmm......interesting. That difference creates a 5-6 mph difference. Just seems like alot for what seems like a small difference in height.

For some reason I couldn't wrap my mind around the concept that going from a 17 to an 18 would be smaller. But thinking how tall the stock tires are on the new ones, it's starting to click now.

yeah its very important to figure out your overall diameter and maintain it as close as possible when stepping up wheel size. Hell its even important when you go to a wider tire.

It (1.5" shorter tire) actually should have created a larger difference in his speedometer than what he is showing. I am ass'uming that either the FRPP tune is either wrong or is limited in what tire size values you can input and they just a size that was close to what he has on the car.

Ray,
89 Hoss no longer has the car that he installed the FRPP tune in but I don't think he had any major speedo issues. He ran a 275/40/18 on his car

QWKSNKE · 06-30-2008, 03:08 PM

Quote:

Originally Posted by NightHawk756

Yeah, but he went from a 17 to an 18. If the tire is 1" shorter, then it should be about perfect then since that would make up the 1" difference in wheel size right?

yep 1" larger wheel but 2.5" or so shorter tire.

Also, the guy with the Razors should be running a 255/35/20 if he is running the same size at all 4 corners

89 Hoss · 06-30-2008, 04:24 PM

Quote:

Originally Posted by QWKSNKE

yeah its very important to figure out your overall diameter and maintain it as close as possible when stepping up wheel size. Hell its even important when you go to a wider tire.

It (1.5" shorter tire) actually should have created a larger difference in his speedometer than what he is showing. I am ass'uming that either the FRPP tune is either wrong or is limited in what tire size values you can input and they just a size that was close to what he has on the car.

Ray,
89 Hoss no longer has the car that he installed the FRPP tune in but I don't think he had any major speedo issues. He ran a 275/40/18 on his car

Correct ole great one! (future engineer!)

redhorse · 06-30-2008, 07:59 PM

Now the million dollar question: How to fix it without redoing the FRPP tune or changing wheel sizes?

QWKSNKE · 06-30-2008, 08:10 PM

Quote:

Originally Posted by redhorse

Now the million dollar question: How to fix it without redoing the FRPP tune or changing wheel sizes?

you can't. either modifying the tune or tire replacement will be required

06-29-2008, 08:58 AM	#11
89 Hoss Mustang Retailer Join Date: Oct 2005 Location: Anniston Posts: 986	When I bought my tune I had to send ford the vin#, tire size I was currently running as well as the gear size. They processed the info. and sent it back for me to get installed. __________________ 2007 SHELBY GT CSM073649 1992 Black on Black Vert lx 5.0 1985 Chevy c10 383 stroker 2000 Jeep Grand Cherokee 4.7 (daddy mobile)

06-30-2008, 07:50 AM	#12
redhorse Senior Member Join Date: Jul 2005 Location: Trussville, Al Posts: 819	Lee, the stock tire may have been 55, I can't remember for sure. They were only on the car for 1 day before they were changed. 89 Hoss, I had to give the same info for my tune also. It would be interesting to see if your car is off as well. __________________ Mean Little Man

06-30-2008, 07:59 PM	#19
redhorse Senior Member Join Date: Jul 2005 Location: Trussville, Al Posts: 819	Now the million dollar question: How to fix it without redoing the FRPP tune or changing wheel sizes? __________________ Mean Little Man