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post #1 of (permalink) Old 01-31-2000, 12:00 AM
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87 S-Blazer tire upgrade

i have an 87 Chevy S-10 Blazer with the 2.8 and 5-speed. i'd like to replace my worn 205/75/R15 tires with the 235/75/R15's i know they put on some of these trucks. could i correct the speedometer by replacing the speedo gear at the tranny? were 235's an option in 87? at any time in with the 2.8 and 5-speed? would it be a GM or aftermarket part? i didn't get much help from the service counter at my local Chevy dealership. any help would be greatly appreciated.

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post #2 of (permalink) Old 01-31-2000, 12:14 AM
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Re: 87 S-Blazer tire upgrade

It shouldn't be a really big deal. Your truck should have a gear driven speedo, so you can take it to a speedometer shop and have them do it for you. From what I know about it, it's not an exact science, but it will get you within 1-2% accuracy, I believe. Most of those corrections are with aftermarket parts, not GM.

Or, you can just find out what your real speed is vs. what you have on the odometer and go from there. The 235's shouldn't make that much of a difference in your speedometer reading. Maybe 3-5 mph difference. I have never had mine corrected, although I may do it this time when I get larger tires put on my '98 (which I think involves a computer reprogram in my case).

Hope that helps.

[img]/wwwthreads_images/icons/shocked.gif[/img]- <font color=purple>J.R.</font color=purple> -[img]/wwwthreads_images/icons/shocked.gif[/img]
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post #3 of (permalink) Old 01-31-2000, 12:23 AM
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Re: 87 S-Blazer tire upgrade

On my 85, there isn't that much of a difference in speedometer from stock tire size which I don't know positively, but the speedometer is within about 3mph of 55... Not much to worry about, I hardly think it'd be worth the effort to get the corrected speedometer gear, just make sure at time of sale (if you ever do sell your truck) that you tell the buyers that the mileage is a bit off... Check out the gear calculator here Gear Calculator You just need to punch in the diameter of the old tires, the diameter of the 235's, and your gear ratio and it'll tell you the change on the speedometer... But anyway, I'm rambling (like usual)... [img]/wwwthreads_images/icons/crazy.gif[/img]


[img]/wwwthreads_images/icons/cool.gif[/img] '79 Suburban 4x4 454, 6" lift, 35x12.5s & '85 GMC S15 4x4
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post #4 of (permalink) Old 01-31-2000, 01:01 AM
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Re: 87 S-Blazer tire upgrade

I've got 30-9.5/15's on my '87 pu,it made less than a 5% diffrence(check w/ a radar gun)

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post #5 of (permalink) Old 01-31-2000, 10:56 AM
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Re: 87 S-Blazer tire upgrade

Oh, I've been checked with a radar gun.[img]/wwwthreads_images/icons/wink.gif[/img][img]/wwwthreads_images/icons/smile.gif[/img]

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