Tire Size - Worth The Change?

This isn't the old days... If you have a ECM and you change tires sizes, then you need to recalibrate your ecm otherwise your asking for trouble. I learn this long ago when I bought a truck that the guy went from lo pro 22.5 to tall 24.5.... what a nightmare.

 

If you need tires I would change to 24.5 that way you match up to the trailer. It's always nice to have the same size tires on both so you can move tires to the trailer if you get irregular wear and also you only need one spare if you carry one. Plus 4.33 is pretty short gearing even for a old Cummins. The taller tires will help out a little there also.

 

Exactly, every little bit will help with 4:33's!

 

How does the ECM know what tire size and how does this cause trouble?

 

It's all in the programming. If you change tires sizes and don't reprogram the ECM then the speedo is incorrect.

 

The ECM has the tire size programmed in it to make your speedometer read correctly. Changing tire size, obviously, makes the speedometer read wrong. The ECM doesnt know you've changed tire sizes. Go to a dealer and have them change parameters in the ECM so your speedo is correct. About a 15 minute job if that...

 

my speedo already reads incorrectly. it's too fast.

and i'd never put the drive tires on the trailer. the drives are biter tires for traction in snow where as the trailer are simply trailing tires. no traction needed.

totally different tread patterns. the trailer matches the steers somewhat but doesn't match the drives.