Switching from 24.5lp tires to 22.5lp

Just take the truck to someone with the software and plug in the new tire revolution per mile in the ECM and problem solved. Casing credits are pretty good right now. Lots of retreading going on. I got $150 a casing credit on my steer tires the last time I changed them.

 

Don't forget about the change in overall gearing!

That may well be more of an issue than speedometer/odometer inaccuracy. Changing tire sizes can (WILL) affect your engine RPM at any given speed. It can also make a good performing truck feel like a dog (usually when going from small to large). Moving the RPM out of the optimal range can have a big affect on your MPG and therefore an even greater affect on your bottom line than whatever you saved on the tires in the first place. This is exactly why there are so many different differential gear ratios! Changing tire size is no different than changing rear gears, or transmission gears. They all have an affect on usable engine power and the speed/engine RPM relationship.

Going from large tires to smaller tires will give you better acceleration but less top end speed as you will run out of acceptable engine RPM range.

Going from small tires to larger tires will give you less acceleration (Read this as "guts" or pull power.. Can make you think you need a lower gear than first to start off with heavy load/up hill..) but will allow you a higher top end speed before you run out of usable engine RPM. (Assuming you have enough "acceleration" to actually get you to that speed in the first place...)

Note that, "Acceptable RPM range" means either what is safe for the engine or what is best for MPG, whichever applies to you, (are you trying to save fuel or get there faster?)

 

bigger tires will also wear longer since they turn slower, so I guess longevity could be a plus side for big wheels and tall rubber. guys running 19.5 LP's on their car haul rigs or step deck trailers burn through them faster since they're turning much higher RPMS and getting hotter.

 

And bearings turn faster with smaller tires so they run hotter as well....

 

^^^ aren't synthetic lubes a wonderful thing!

 

One more plus...For all those megas running governed rigs, dropping a tire size will make you think you're actually running the speed limit for once! LMFAO

 

yep all true. thanks for saving me time to type it all.

 

Hello,
I have a 2009 volvo with 10 speed transmission. I change the tires to brand new on the drive. The driver is complaining that the mileage is off and not accurate.
Can you please help and guide me what needs to be changed in the ECM parameters in order to synchronized the odometer and actual miles. Do we need to change transmission parameters also?

 

Did you stay with the same size tires? Was the odometer accurate before putting the new tires on? If the answer to these questions is yes then what you are experiencing is going to happen every time you or new tires on.

A new tire has more tread, therefore a larger diameter than a worn out tire. It travels farther on each revolution so it throws off the speedo and odometer by a little bit. You will never get it 100% accurate all the time. You cos set it to match the new tire but then it's going to be off as the tire wears.