Speedometer Adjustment??

[85xtracab]

Is it true that if i regear to 5.29s and have bigger tires on my truck that the speedometer reading will be off and that i have to get a gear to sync it back up????

[robrocketanski]

the speedometer gets its reading off the back of the trans so if you change tire size then the truck will be traveling a different speed at a certain rpm causing your speedo to read wrong.

your speedo determines speed based on rpm of your rear driveshaft so if your tire is bigger then the distance traveled will be different at a certain revoltion speed of the shaft.

if you keep the relationship between tire and gear the same then your speedo will be right. a 5.29 would need something like a 38 or bigger to be correct. you will read faster than actual speed w/ a smaller than 38 tire. but it is not a big difference.

my runner has 30" bfg and i switched from stock 4.30 to 4.10 so the truck acts like a stock truck on 33's. my speedo is documented courtesy of MI state police as being about 10% off.

[Rescue]

5.29's and 35"s.... I am just 5 km/hr faster...

[Chad George]

5 29's and 33's reads 7 mph's fast

[cruiseroutfit]

There are speedo shops that do nothing but repair and calibrate your speedo. Not sure if your speedometer sending unit is mechanical (like early cruisers) or electronic (like later cruisers) but they have decent options for both.

[NavyDood]

35" Xterrains measure at 34.5" on a 10" rim running 4:88's read 2 mph slow. Me 63 mph, her 65 mph.

I used the precision measurement of me on my cell phone and my wife on her cell phone going down the highway. :D