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Old 09-13-2010
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spedomiter question.

so my friend is lookin into buyin a chevy 1500, it has a 7 inch fabtech kit on sum 35" km2s. the spedo is off 20 mph and has stock gearing...normal?
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Old 09-13-2010
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anytime you change tire size or gears, it will throw off the speedometer.
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Old 09-14-2010
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Originally Posted by drppdyllwrngr View Post
anytime you change tire size or gears, it will throw off the speedometer.
Ya I kno but that much?
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Old 09-14-2010
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Friends don't let friends buy Chevys!
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Old 09-14-2010
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Ya I kno but that much?
yes very much. I had 3.73s and 31s. swapped to 4.10s. My speedo reads about 10mph over at highway speed.
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Old 09-14-2010
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it wouldn't be off by a set MPH

it would be off by a percentage.....

i switched from 225/75/R14 to a 245/75/R16
its about an 10.5% difference
so i just do the math when driving down the road.... 60 mph X 1.10 = 66mph
so if my speedo says i'm doing 60 i'm actually doing 67
if it says i'm doing 65, i'm actually doing about 73

use a tire calculator online to figure out what percentage its off by, then just do the math on the fly
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Old 09-14-2010
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Quote:
Originally Posted by TheStig88 View Post
it wouldn't be off by a set MPH

it would be off by a percentage.....

i switched from 225/75/R14 to a 245/75/R16
its about an 10.5% difference
so i just do the math when driving down the road.... 60 mph X 1.10 = 66mph
so if my speedo says i'm doing 60 i'm actually doing 67
if it says i'm doing 65, i'm actually doing about 73

use a tire calculator online to figure out what percentage its off by, then just do the math on the fly
exactly! i just didnt want to get into all that crap. I believe mine is really 12% or so.
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