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Old 01-04-2013, 07:28 PM   #1
Juspassinthru
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Question Does changing tire sizes affect speedo?

Im running a set of 215 70 15's . Not sure wha thesE trucks came with originally. Thx
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Old 01-04-2013, 07:37 PM   #2
PAPA KENT
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Re: Does changing tire sizes affect speedo?

i don't have a chart anymore but i believe a p215/75r15 is close to the originals.i run a 245/75r15 and mine is 5 mph off.some one here will have a chart for rotations per mile for each size.
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Old 01-04-2013, 07:51 PM   #3
Tshort1
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Re: Does changing tire sizes affect speedo?

Yes! you can Google tire size calculator.
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Old 01-04-2013, 08:33 PM   #4
61_FL_Apache
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Re: Does changing tire sizes affect speedo?

This is a calc I use.

http://www.miata.net/garage/tirecalc.html
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Old 01-04-2013, 08:53 PM   #5
jocko
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Re: Does changing tire sizes affect speedo?

agree with above - answer is yes, but the easiest way to figure it out is use/borrow a gps to see how far you're off from reality. keep in mind that in many of these oldies, the rear gears have been changed also, and that will much more significantly throw off the speedo. If you crosscheck displayed speed on speedo with a gps, you'll at least have a mental correction factor that covers all things that contribute to your speedo being off. Or, you'll discover that you're pretty darn close. agree with others, you're pretty close to factory tire outside diameter - that is what matters when it comes to tire changes.
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