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post #1 of (permalink) Old 11-05-2000, 01:24 AM
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speedo with 31s?

I just bought my 31x10.5 bfg all terrains and will put them on the truck tomorrow.How much will the speedo be out?Right now it has 235s,the truck is a 91 blazer with digital dash.

1991 blazer 4 dr 4.3 headers,flowmaster,k&n,31x10.5x15 bfg allterrains
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post #2 of (permalink) Old 11-05-2000, 04:24 AM
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Re: speedo with 31s?

Try this link. http://4lo.com, after getting there click true MPH. If you had 235's befor you had 28" for 235/70/15 or 28.9 for 235/75/15.

1995 S10 Truck, 4X4, Ext. Cab, 4.3 Vortec V6, 31/10.5/15 BFG TA's, American Racing rims,3" Trailmaster Body Lift, Westin Side Bars.
Ryan Sharpe.......Denver, CO.
post #3 of (permalink) Old 11-05-2000, 12:34 PM
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Re: speedo with 31s?

The calculators only give a rough estimate. Mathmatically the speedo should be 6-7% off assuming 235/75.
A more accurate method would be to use a GPS or use a stopwatch and time how long it takes to cover one mile using the highway mile markers (gotta be level to maintain constant speed though). Or trail someone that has an accurate speedo. Using these methods I figure mine is actually 10% off.

Hit? Them tires rub. Rubbin's off roadin.
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post #4 of (permalink) Old 11-06-2000, 09:29 AM
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Re: speedo with 31s?

Just based on prior experience, your speedo should be off by about 4-6 mph. You'll read slower than actual.

I've always used a friend with a CB radio to show the actual speed he's going and compared.

J.R. [img]/wwwthreads_images/icons/cool.gif[/img]

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post #5 of (permalink) Old 11-06-2000, 05:22 PM
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Re: speedo with 31s?

Well I just got back from a small road trip with some friends. My speedo read exactly 80 and when we stopped for gas I asked my buddy who i was following what he was cruising at and he said 87 so what is that about a 8 or 9 percent increase, remeber dont look at it as a certain mph off it is a percentage of your speed.


-I shoulda been a cowboy-
post #6 of (permalink) Old 12-08-2000, 04:30 PM
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Re: speedo with 31s?

bla bla bla calculators and [censored]. When it says 50, you'll be doing 53

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