Switching from 24.5lp tires to 22.5lp

Bigger tires to smaller tires, the speedometer will read faster than your actual speed...which makes a governed truck slower. Changing from smaller tires to larger tires causes the speedometer to read slower than actual speed.

Think about it. The "speed sensor" on the back of the transmission only counts the revolutions of the drive shaft. Anything you do that alters the distance traveled per revolution of the drive shaft is going to make your speedometer less-than-accurate one way or the other. Larger tires cover more distance per revolution of the axle than smaller tires...3.55 axle ratio turns the axles around more times per driveshaft revolution than a 4.10 axle ratio would.

In any case, more ground covered by the same number of revolutions of the drive shaft = faster speeds than the speedometer shows. Less ground covered = slower speeds.

 

Why would you switch?

 

First low-rider rig?

The simple explanation is that your speed is counted by revolutions of the tire or drive shaft. (Like PB said.). It's never based on how fast you're actually moving.

Take a quarter and nickle and color the edges with a marker. Run them across a sheet of paper for the same amount of revolutions. The nickle's trail will be much shorter than the quarter. It's the same principle with your tires. They'll be going the same speed according to your speedometer, but you'll covered distance.

Good way to prove your mechanic wrong!

tl;dr

The smaller the tire the slower you'll go.

 

Wont it throw the speedometer and odometer off if you change the wheel/tire size from factory or am I not understanding that correctly? I wouldn't want to do that even if I had a preference for one size wheel or another.

 

Youre correct, it'd throw the odometer as well.

 

Yeah, why would you want to go to a smaller size? Does it have anything to do with tire availability, cost,etc? myself I'm looking at doing the opposite. To answer the question the actual distance covered will be less than the odometer shows.

 

You just change the calibration so it's accurate. ECM parameter change that isn't hard.

 

There are some benefits to 22.5 LP tires as far as availability and core credits since that's what most of the big fleets run nowadays. That's what the guy at Loves tire shack told me when I was in there looking for a used LP 24.5 trailer tire.

I think 24.5's look cooler but I cant tell any difference in ride quality or performance like some guys claim to. Of course I've never switched from one to the other on the same truck so maybe I don't know what I'm talking about.

 

My speedometer had been off since I got the truck. When I originally got the truck the speedometer was off by 10 mph. So when I was doing 50, my speed was actually 60 mph. The boss then switched the tires from 11r22.5 to 11r24.5 and now when I am doing 45 mph on the speedometer, the actual speed is 60 mph. But you have to be careful about that. Mine changes with the raise in speed. For instance at 25 mph actual speed the speedometer reads 19 mph but at 60 mph the speedometer reads 45 mph. About 7 mph difference from top to bottom. I downloaded a free app and figured out all the ranges 25,30,35 etc.

When you switch from smaller to larger your speedometer will be slower than your actual speed. When going from larger to smaller the speedometer will read faster than your actual speed.