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sms1688
12-27-2007, 08:13 AM
When you get larger tires does you speedo show higher then actual or lower. At 50 does it show 60 or at 50 does it show 40. Yeah I know I should know this but I am brain farting it.

TRLR8TDTJ
12-27-2007, 08:16 AM
It will indicate lower speed than you are going. What tire size, and gear ratio are you running.
Kyle

ArizonaXJ
12-27-2007, 08:51 AM
A good rule of thumb is this:
Take your speed and add 10% I.E. at 40 MPH you're 44, at 50 MPH you're doing 55, at 75 MPH you're doing 82.5 MPH....I clocked all my Jeeps with my GPS and this theory works out almost perfectly +/- .5 - 1 MPH.

sms1688
12-27-2007, 08:57 AM
I am running 35" tires and 4.88 gears.

Polka Dot
12-27-2007, 09:55 AM
http://www.stu-offroad.com/engine/speedo/speed1.htm

sms1688
12-27-2007, 10:00 AM
http://www.stu-offroad.com/engine/speedo/speed1.htm

Got more important things to buy for the jeep was just curious. My speedo has been off ever since I bought it. Was just curious if it was getting worst or better. Guess what it actually adjusted the correct way but still way off

OlneyJeeps
12-27-2007, 10:05 AM
several diff sites to compute difference
http://www.miata.net/garage/tirecalc.html

TRobertsRN
12-27-2007, 06:37 PM
Since I have never kept the same size tires for much more than 6 months and change vehicles every year or so and put bigger tires on what ever I get I no longer get the speedo adjusted.

I just use my GPS to give me an accurate speed.

Tom

AZXJ
12-27-2007, 09:54 PM
Paul,

The speedo gear is like 25 bucks.. Cheap and Easy.. :D

Fire Ball
12-27-2007, 10:43 PM
My speed is off around 20% or more :D

ademster
12-27-2007, 11:36 PM
speedometer?

Whats that hahahaha
I use GPS

sms1688
12-28-2007, 08:38 AM
Paul,

The speedo gear is like 25 bucks.. Cheap and Easy.. :D

Yeah I know how and where to do It But I aint cheap and easy.

I was makeing sure that the wobble I had at 90Mph(my speedo) was gone with the bigger tires and it wasnt because I was actually driveing slower. Oh and yes it is gone thanks DAVE

TRLR8TDTJ
12-28-2007, 08:41 AM
I am running 35" tires and 4.88 gears.

I thought I might have the right gear for you , but I only have 34, 35, 37.

Kyle

lancetkenyon
12-28-2007, 08:51 PM
A good rule of thumb is this:
Take your speed and add 10% I.E. at 40 MPH you're 44, at 50 MPH you're doing 55, at 75 MPH you're doing 82.5 MPH....I clocked all my Jeeps with my GPS and this theory works out almost perfectly +/- .5 - 1 MPH.

Depends on your tire size increase. If you go up 10%, like 30" to 33", then this is correct. but 30" to 37" is more like 23% off with stock gears. Gear ratios have the same effect, 3.73 to 4.10 is about 10%. 3.73 to 5.89 is around 40%. I run 37s on 5.89 gears, and mine are WAY off from stock, about 30% HIGHER reading than actual. If I am going 65 MPH, according to GPS,which I did in Moab and to the Coles Crazy Christmas sale, my speedo says around 90 MPH.

Mike M
12-28-2007, 09:50 PM
Not only will your speed be off, slower than actual, but your odometer will be off too. An easy way to determine your speed and milage is to set your trip odometer to zero as you pass a highway mile marker. Count off ten mile markers and note the miles on your trip odometer. For example, when I increased my tire size to 33's, ten actual miles by counting ten mile markers equaled 8.5 miles on my trip odometer. With this information, you can calculate your speed. For example, for my case, to determine 45 actual miles per hour, mutiply 45 by 8.5 and divide by 10 which equates to about 38 miles per hour on the speedometer. Or, multiply the speed you desire by 0.85 and this will give you the speed you need to set your speedometer to.