355 rears?

I understand that part as far as lowering your rpm but there is other factors involved like increased sidewall flex and tire weight when going with a tall tire. One of those age old debates

 

You have it backwards, the greater the circumference the less rolling resistance and less RPM. For example try rolling a tennis ball across the floor, then a basketball. Then latter will roll with less effort and for a greater distance.

 

I see what your saying but the outer circumference doesn't necessarily pertain to tire rolling resistance, just means it will turn less revolutions. The taller the sidewall the more flex you will have when weight is applied.

 

Changes your RPM's, though. If you like that switch, you can buy new rims the next time and go LP24.5 which is the same size as an 11R22.5 to get whatever benefits you think there might be with the low profile tire while also taking advantage of the mimicked gear ratio change for not much more cost (or downtime) than it takes to replace tires which need to be replaced anyway. If you want to go a little farther, 11R24.5 will make your 3.55's feel like a 2.23 ratio.

Changing a gear ratio costs real money, takes the truck out of service for at least a couple days, and if you don't like it, it costs real money and a couple more days out of service to swap back. I wouldn't put out that level of commitment to a change unless you're 1000% certain that's what you want AND you're happy with the performance of the truck with those changes.

There is more to life than just fuel mileage. Will it pull a hill? Can it get out of it's own way? Is it going to put you right at a shift point at your cruising speed on some roads, where one gear feels like you're overrevving and the next gear feels like you're lugging? Things to think about before you invest a lot of time and money into the change.

Tire swaps are easy enough to swap back if you don't like the changes. If you DO like the changes and want to run the LP22.5's, THEN change the gear ratio and put the 22.5's back on the next time you're needing tires.

 

Idk I run 11R 24.5 holds all the weight I wanna haul and not look half flat!

 

Same here. 16 ply 11R24.5's on my truck. I'll have 35,500# on the drives and they'll squish less than the LP22.5 tires the company has on their trailer despite the fact they are only carrying 32,500#. Same psi in both. Makes it easier to hide a little extra weight without drawing the attention of the law rolling down the road.

 

I run tall rubber as well. That's what I prefer. I was simply stating the fact that just changing from lo pro to tall may not yield the same gain as actually changing gear ratio. Would I go through the trouble of doing that myself, probably not especially with 3.55s

 

You can run lopro 24.5 336 rears and run the same speed as tall 24.5 3:55 rears, same rpm

 

First the smaller the tire the less rolling resistance. They weigh less. Second if you don't have a boost gauge buy one and install it. Drive with the least amount of boost possible. If you like driving fast and hard, there is no way or product that will improve your mpg. Your right foot is the best way, Cruise control eats fuel. You will learn this from boost gauge. Now I run mostly lp 22.5 except one truck has lp 24.5 till next tire change. 11r 22.5 or 24.5 are useless unless its extreme weight or for ground clearence, the are heavy and have next to no trade in value. I run 40k on drives with little squat, 40k on trailer tandem at 90 psi. little squat. To many trucker myths about tires. Trying to gain mpg with bigger tires is one of them.

 

Changing tire size does NOT change gear ratio and is NOT the same thing. Yes it changes the roll out and the rpm vs actual speed [not the speedometer vs rpm ] so make sure you are measuring actual speed.

As alluded to previously on modern engines they are calibrated so changing ratio's or tire size 'could' require calibration.

What do the numbers mean eg 3.55 and how does changing tire size change that.