355 rears?

If the torque was applied at the edge of the tire OK but it isn't. it is applied at the gear set. The twisting force doesn't change at the pavement.

 

Torque is a distance/force value...foot/pounds. As such, it is directly affected in 2 ways: 1) You can alter the distance (ratchet handle length, tire size, etc...this is the distance from the object that is twisting to the object either creating the force (your hand on the ratchet) or generating the resistance (the road under your tire)). 2) You can alter the amount of force applied (push harder or softer on the ratchet handle, or change the gear ratio on the axle differential).

Either way, you're affecting the distance/pressure equation.

If you have 12 inch/pounds (1 ft/lb) of force turning the drive shaft passing through a 3.23:1 differential, it applies 38.76 inch/pounds of force to the axle shaft. With a 40" tire (20" radius), that reduces the torque applied to the ground down to 1.938 inch/pounds at the ground.

Same 12 inch/pounds at the drive shaft pass through a 3.55:1 differential. 42.6 inch/pounds are applied to the axle shaft. With a 44" tire (22" radius), there is 1.936 inch pounds of force applied at the ground.

The 1.938 inch/pounds of force applied to the ground with the 40" tires (LP22.5) and 3.23 gears is nearly identical to the 1.936 inch/pounds you have with the 44" tires (11R24.5) and 3.55 gears. That is per foot/pound of torque sent through the drive shaft. 2/1000 of an inch/pound per foot/pound at the back of the transmission. You aren't going to notice that at all.

Make sense now?

 

That was the point of going to smaller tires, to get the engine rpm into a better spot for the speed I drive. It was a generic truck spec’d for super-b train operations which I do. But set up to run 65 mph (105 kph) which I don’t do. I run 60 mph (98 kph) or less. But occasionally need to run 70 mph (110 kph) to get to an elevator before they close. But I’ve only done that three times in two years.

 

Not true in all manufacturers. Michelin tall rubber has better rolling resistance than lo pro.

 

Small tire equals less rolling resistance is not true in all manufacturers

 

Yes it does but probably not in the conventional way your thinking. Numerically the tire has a rating yes. However it is dead weight and with a smaller tire it weighs less. Which rotates easier. That makes the truck weigh less and we all know it takes less horsepower to move a lighter truck than heavy.

 

...but once rolling, it has more rotational mass which helps maintain speed the same way a heavy flywheel makes an engine feel smoother despite being slower to rev.

Considering you're only talking about 6 pounds per tire between a LP22.5 and an 11R22.5, and only 3 pounds difference in the LP22.5 and LP24.5, you aren't really adding THAT much weight...less than 8/100 of 1% of the total loaded weight. Even jumping all of the way from a load range G LP22.5 tire up to a load range H 11R24.5 is only 15 pounds per tire and makes up less than 2/10 of 1% of your total loaded weight (which could be made up and then some by swapping from steel wheels to aluminum if you've got steel 22.5's)...but you're gaining quite a bit in load rating. Not enough to be significant by any means. Most drivers could make up than difference by avoiding the buffet and walking a couple laps around the truck stop every night...especially if they only go up 1 tire size and keep the same load rating.

 

I’m only speaking on Michelin tires. They measure rolling resistance by compression of the tread in the contact patch. The taller rubber goes thru the contact patch less times per mile than the lo pro. Which gives the tall rubber a slight advantage. Notice when you buy a fuel efficient tire over a grip, the tread depth is not as much on fuel tire.

 

I'M not so sure of that. the contact patch is longer on the taller tire but I'm not doing the math.

 

No the revs per mile is less in tall rubber so less times thru contact patch.