Switching from 11R 22.5 to 295/75R 22.5 Volvo VNL 670

I was able to change Volvo parameters with my Diesel Laptops unit, so I would think most independents could

 

Any shop should be able to do it if they have the software. Also on the fuel economy, It depends on what the sweet spot is on that engine. Slower will always get better MPG's once over 55 MPH. Pulling should not be much difference.

 

I will throw in my 2 cents since I just went through a bigger change in my drives. Wanted to get my 5th wheel lower and lower the truck some, so I went from lo pro 24's which are around 42" tires down to 255 70 22.5 tires which sit right around 37". I have 2.74 gearing and an 18 speed, so my thinking was yes my rpm will be different but with the 24's on I never got out of direct and could finally use my overdrives, I knew the truck loses power in overdrive (every truck does it is a moot point don't argue it) but figured that I was getting rid of about 400 lbs of unsprung weight and lowering my rolling resistance so it should offset that. I ran a ton of calculations before I did it and figured it would be close, or might get slightly worse MPG. Well my calculations were wrong, switching to the 37" tires put me at about the same rpm I would push with the 24's in 17th gear which is first overdrive it is a .86 gear. It basically turned my gearing into 3.26 gears. with 42-43" tires. So my truck is now sitting with the 24's back on it, my average fuel use went up about ten-15 gallons a night that is about 1mpg on average every night, where I really suffered was windy nights, which I am heading to North Dakota and back every night so its windy almost every #### night in the winter. My old record for fuel usage on an exceptionally windy night was 121 gallons, I broke that record multiple times (like 9 that I can remember) and the new record is 134, which I didn't even know if I had that much useable fuel in the tanks before that. In all of my experiment with small tires I can say the only way I picked up fuel mileage was when I bobtailed (which is not very often) but when you are pulling weight all that reduction in unsprung weight and lower rolling resistance doesn't matter to the truck one bit, all that matters is either staying in direct at the same rpm as overdrive, or lowering your speed and staying in direct (which was 55 mph for the same rpm I do 65 now) and dropping my speed by 10 mph to get any benefit from the lighter tires was not in the cards. SO if you ask me should you go smaller, I will tell you no do not do that, the other thing no one brought up was ride quality, ride quality from lo pros is awful, you feel everything in the road, I run tall 22's on my front end now and the ride qualty alone from the tall 22 steers is night and day ahead of any lo pro tire. I will also say when I get rid of the 24's I have right now (due to wear) I am not going to lo pro's again, I am going with tall 11r24.5 when I get new tires my direct gear will be 1450 rpm's at 70mph then which is right in the sweet spot for my fuel mileage

 

Be sure to update the ECM and/or odometer so your mileage and speedometer stay accurate. You're going to have to switch studs as mentioned earlier as well.

Once it's all said and done with your time involved factored in I don't believe you'll save enough to make it worth it to me in the long run.

It's a good idea to factor swappable parts on various pieces of equipment when considering adding something new to your fleet. Can save significantly over time.

 

What was the engine and spec's on the truck? I dont remember but sure you told me a while back ago. Can look it up and see what is the best cruise speed.