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Old 07-08-2008, 10:39 PM   #1
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Bigger tires, do I need to change the speedo?

So I have an 06 Wrangler 6cyl, 3.07 gear, no lift. I just changed from 30x9.50 to 31x10.50s. Do I need to change anything else, so the mphs and odometer stay the same? Hope this makes sense, thanks guys.

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Old 07-08-2008, 10:45 PM   #2
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i got a 05, 4.56 gears, 35's, and my sppeometer is only off by like 7 mph, so personally it doesnt bother me, no bigger change than u made i dont imagin it would be off by much

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Old 07-08-2008, 10:45 PM   #3
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typo, sorry i got a 04
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Old 07-08-2008, 10:48 PM   #4
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Old 07-08-2008, 10:52 PM   #5
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WOW, that was a fast reply. Thanks, I didn't think it was a big deal, but why not get some input.

YES THEY DO!
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Old 07-09-2008, 06:20 AM   #6
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easy enough to check it against a gps
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Old 07-09-2008, 09:29 AM   #7
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Anyone know off hand how much my speedo might be off? D35/30 3:73's,2"BB,33x12.5's?
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Old 07-09-2008, 10:32 AM   #8
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should be about 5-7 MPH. That's what mine was with 33x12.50's when I was going about 50 MPH.
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Old 07-09-2008, 01:05 PM   #9
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it will be 33/29 so multiple what the speed is on the speedometer by 1.14 and thats the real speed
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Old 07-09-2008, 01:23 PM   #10
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Quote:
Originally Posted by 98TJSahara View Post
Anyone know off hand how much my speedo might be off? D35/30 3:73's,2"BB,33x12.5's?
Simply multiply your speed (on your speedometer now) by 1.14 and you have your real speed
1.14 from derek but it sounds about right.. what tires did you have before? 30s or 29s?

mine from 30s to 35s was 17% off and i was darn close. I measured distance with my jeep and then with my gfs car and i got 17% difference. Now i have corrected speedo gear and i'm getting the exact same distance as her
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Old 07-09-2008, 01:50 PM   #11
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Here's a chart of the right speedo gears for common tire sizes and axle ratios... it also gives instructions on how to change the speedometer gear which takes 5 minutes to do.
http://www.4x4xplor.com/speedo.html

Click on the speedo gear chart to make it large enough to view.
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Old 07-09-2008, 06:18 PM   #12
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I don't want to hijack this thread, but what speedo gear would be best for 34" tires? I found some TSL's that are 33.8", but listed as 34", so what speedo gear would you recommend?
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Old 07-09-2008, 07:34 PM   #13
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Originally Posted by Warpman89 View Post
I don't want to hijack this thread, but what speedo gear would be best for 34" tires? I found some TSL's that are 33.8", but listed as 34", so what speedo gear would you recommend?
Rubicons as you have don't use speedometer gears. Your only way to recalibrate your speedometer is to either have the dealer recalibrate it for likely an exhorbitant fee, or buy an electronic speedometer calibrator like a TrueSpeed. However, TrueSpeeds go for nearly $200 and there's another brand I can't think of that does the same thing for only $80 or so. I seem to recall seeing them advertised in the back of most Jeep and 4x4 oriented magazines.
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Old 07-09-2008, 11:04 PM   #14
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Quote:
Originally Posted by Warpman89 View Post
I don't want to hijack this thread, but what speedo gear would be best for 34" tires? I found some TSL's that are 33.8", but listed as 34", so what speedo gear would you recommend?
as Jerry said you're screwed however if you didnt have a rubi.. you would technically need a 30 tooth gear if you have 3.73 gears.

Also when replacing the speedo gear. MAKE SURE YOU DONT RIP THE ORING. I have a spare that i got from ace hardware for i think 40 cents vs 2-3 bucks from the rest of the stores specifically for jeeps.
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Old 10-24-2010, 09:31 AM   #15
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mighty helpful thread, i've got 32" tall tires and my speedo is out, and with all the average speed cameras we have to deal with here in the UK it's best i get it sorted ! Just hope my local dealer can get the speedo gear i need

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