I need some help with changing a trucks factory set-up. The truck is a 2005 9900I Eagle, 475 CAT, 13 SPD OD and 3.73 rears. The truck is currently set on 22.5 Low Pro.

At 1450 RPMs the truck is running the following:

67.124 MPH on 24.5
64.159 MPH on 22.5
63.774 MPH on 24.5 LP
61.920 MPH on 22.5 LP

I have a light right foot and no real need to really stretch it out going down the road (tankers). I want to maintain resonable pulling power, as I am too old to have to get out of the truck and push to help it get to the top of a hill. :sad:

Question is, what will the overall affect of the change from 22.5 Low Pro to 24.5 be?

All thoughts, opinions and suggestions are greatly appreciated.

Why would you want to go with a taller tire? To go faster?

I would keep the 22.5's lo pros.

I have 3.73's and 13 spd OD on my truck, and currently have 24.5 lo pros. It feels sluggish at times. I want to switch to 22.5 lo pros.

3.73's with a 2005 cat? That's a weird spec. Usually they come with 3.36's.

You beat me to it Heavy. I cut out the text from that article.



Dear Tire Doctor,
Please explain the differences between 22.5 low profile and 24.5 low-profile tires. Does one get better wear over the other? Does one get better fuel economy over the over?

Thanks, Scott
^ back to top Dear Scott,

Thank you for this opportunity to be of assistance.

Many large fleets traditionally operate low profile (LP) 22.5" tires. Prior to January 2005, the Federal Excise Tax, or FET, was based on a tire's weight, and since 22.5" tires weigh less, the FET was lower, thus making them the popular choice. After the FET law changed, most of these fleets continued to operate the 22.5" tires to avoid duplicating inventories.

There are several small advantages for each size.

LP24.5" tires, according to tests performed to SAE standards by an independent testing laboratory, tend to have a slightly lower rolling resistance at a given weight and speed than do LP22.5" tires, and thus have the potential of a very slight fuel mileage advantage.

LP24.5" tires turn fewer RPM than LP22.5" tires and are credited with being able to deliver slightly higher removal mileages, although this may be disputed by some.

LP22.5" tires weigh less, which allow a slight increase in maximum payload.

LP22.5" tires have a lower center of gravity, promoting slightly better handling characteristics.

LP22.5" tires typically feature the latest technology.

LP22.5" tires are far more popular, which can influence availability and casing pricing.

Generally speaking, the differences are so slight, that it would not pay to change a current fleet from one size to the other due to duplicate inventory costs and problems.

Best regards, Tire Doctor

Allan,

Thanks for your response.

I will be pulling a tank. With that I will be running dual PTO's for product pump and compressor. I need clearance to protect this set up. Also the additional height helps with the unloading process and will help control the surge in smooth bore tanks. More an issue of what is most pratical for the work the truck will be doing.
As far as sluggish is concerned, if memory serves me correctly, I seem to recall that a tire size change (for example 22.5 Low Pro to 22.5) equals out to approximately 5-10 HP decrease, which would have an adverse affect on the trucks pulling ability.

Thanks again, I appreciate your suggestions.

Heavy,

Thanks for the link, lots of good information.

Steve,

Thanks for posting the article.

I appreciate your assistance.

You could always build up the 5th wheel.

All the more reason to keep the lo pro 22.5's.

I'd build up the 5th wheel, get some michelin XDA energies(most efficient conventional drive tire out there) and run at 60.

That will get you the best fuel mileage.

If you want MORE, you can always go for a gear change. Aim for 1325 rpms at whatever your cruising speed. But that will cost ~$4000.

22.5lp are not pratical when pulling tanks IMO,our owner would kill you if he saw a fifth wheel built up that much,I am switching over to tall 24.5's from 24.5lp's to help in getting some weight off my drives.I also am gonna get my 5th wheel raised up to about 51".

What's wrong with building up a 5th wheel?

The taller the legs on the fifth wheel the more leverage the trailer has to rip the fifth off the frame in a serious crash.

Graybeard, if you don't want to change wheels you can use tall 22.5's and get about the same circumference as a lo pro 24.5. I have measured the fifth wheels on our company trucks and they average about 50 - 51 inches so I would assume that's the height you need to get the trailer tandems right about 34k when grossed out.

You may loose some mileage with the tall tires but you do increase traction as they have a larger contact patch.