rear ends.

Train71 · Dec 28, 2017

melpromud said: ↑

Well the flat bed forum is the wrong forum for this subject but Ill try to explain anyhow. The number is how many times the drive shaft turns to one turn of your tire. 3.55:1 means the drive shat turns 3.55 times every time the tire turns once. 3.70:1 = 3.7 times. 3.90:1 =3.9 times. 4.10:1 = 4.1 times and so on. The more the drive shaft turns per tire revolution the higher the RPM of the engine at any given speed. The higher the number the lower the gear. 3.90:1 are lower (higher RPMS) than 3.70:1. Every engine has a given RPM that it makes peak torque at. Trucks should be geared so they run in their peak torque at highway speed. Trucks that run heavy or go off road are geared lower than highway trucks. Different size tires will require different gear ratios to have the same RPMs at the same speed. Usually a higher geared truck will get better fuel milage but wont pull as well getting up to speed or pulling up a hill though road conditions, driving style and the type and weight of a load may actually make a lower geared truck get better milage. 3.36:1, 3.42:1, and 3.55:1 are typical highway gears. 4.10:1, 4.30:1, and 4.56:1 are what log trucks, dump trucks, and low boy trucks will typically use. 3.70:1 and 3.90:1 are nice middle of the road gears for trucks that see some heavy haul or off road but also see some long highway miles.
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So what's a good size tire to run with a 3.9? 11r 22.5 or low pro?

snowman_w900 · Dec 28, 2017

Train71 said: ↑

So what's a good size tire to run with a 3.9? 11r 22.5 or low pro?
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It depends what you wanna do with the truck.

rank · Jan 3, 2018

Train71 said: ↑

So what's a good size tire to run with a 3.9? 11r 22.5 or low pro?
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Do you have height issues? Pulling a low deck trailer and tall freight? Do you have sliding winches on the top deck or are they bolted to the side? Low fifth wheel or regular? Full fenders over the drives?

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