Speed odometer off

gmantheman

Member

Dec 30, 2007

483

1

16

Escondido, CA

May 17, 2008

#1

• May 17, 2008

• #1

When I purchased my 89tq tune from Doug, I had 3.55 gears and my tires were 255/50/17. Since then I changed my tires and gears. My tires are now 245/45/17 and I now have 4.10s. I modified my custom tune. I adjusted my tire revs to 785 per. min and gears to 4.09 (diablo doesn't have 4.10). When I compare my speed odometer to my GPS my speed odometer reads about 5mph than the GPS. When I modify my tune to 4.30 gears my speed odometer is off by only 2 mph. Does Doug need to re-send a new tune to reflect my new gears and tires?
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DarkFireGT

Playing with my wife's really makes me want one.

10 Year Member

May 23, 2004

692

10

89

East Moline, IL

May 17, 2008

#2

• May 17, 2008

• #2

What tires do you have? Due to manufacturer variances, your calculation of 785 revs per mile could be quite off. I'm assuming you used the Miata calculator. If you go to the tire manufacturer's website, you can find the true revs per mile.

Diablo doesn't have 4.10 in there? That's goofy. If everything else is dead on, I would email Doug.

 

gmantheman

Member

Dec 30, 2007

483

1

16

Escondido, CA

May 17, 2008

#3

• May 17, 2008

• #3

I used this formula (forgot where I found it) 20168/tire diameter. 20168/25.7 is approx 785

 

DarkFireGT

Playing with my wife's really makes me want one.

10 Year Member

May 23, 2004

692

10

89

East Moline, IL

May 17, 2008

#4

• May 17, 2008

• #4

Ok, but again, what make and model are the tires? Tires differ between companies. Trust me. My 325/45/18 M&H's are not as tall as my 295/45/18 Nitto's.

 

gmantheman

Member

Dec 30, 2007

483

1

16

Escondido, CA

May 17, 2008

#5

• May 17, 2008

• #5

BFG KDW

 

DarkFireGT

Playing with my wife's really makes me want one.

10 Year Member

May 23, 2004

692

10

89

East Moline, IL

May 17, 2008

#6

• May 17, 2008

• #6

The revs per mile for the KDW is 810 for a 245/45/17. Try plugging that in and see what happens.

 

gmantheman

Member

Dec 30, 2007

483

1

16

Escondido, CA

May 17, 2008

#7

• May 17, 2008

• #7

Thanks for the info. Just wondering, were did you get that information?

 

gmantheman

Member

Dec 30, 2007

483

1

16

Escondido, CA

May 17, 2008

#8

• May 17, 2008

• #8

Never mind, it's right on their website.

 

gmantheman

Member

Dec 30, 2007

483

1

16

Escondido, CA

May 18, 2008

#9

• May 18, 2008

• #9

I set the tire revs to 810, but still my speed odometer reads about 2 MPH. This is close enough for me. In fact aren't most speed odometers off by by -/+ 2-3 MPH?