Western Star

3:21 with 24.5 low profile and a 13 speed will give you 68 mph at 1300 rpm, I run a Western Star with a C13 Caterpillar, 430 hp 1750 fpt, I love the truck, hate the engine, gutless wonder, dies on the hills because there's no power. I would carry a spare blower motor with the tools to change it. I've driven a 2008 since August 6th 2007 and I've changed the cab blower motor four times. You can't get enough heat or A/C without it. The blower motors are about $98.00 each. Tat's been the biggest problem with the truck, I won't go into the BS with the C13 Caterpillar, as I type this I'm waiting overnight for parts to come in so I can get my truck repaired at Butler in Sioux Falls SD. I've been in so may Caterpillar shops with this truck I know most of the mechanics by name.
Our standing joke with my company is, "If the truck catches fire use the fire extinguisher to beat off anyone who tries to put the fire out."

 

You should chose the tire size you want, then gear the truck for the power and speed. I wouldn't own or drive a truck with short tires, I'm running Michelin Xone Super Singles, 455/55 22.5, which are the same hight as 24.5 low pro. some of our tractors and most of the trailers have 445/50 22.5 Singles and the tractors are too low. Super Singles are junk! they suck in the snow. If I owned a truck I'd have dual 24.5 drives, with 3:55 locking rears.

 

I have a 97 star and love the truck only problem I see is they weigh more than most. Also part availibilty is not very good. Most dealers do not stock many star parts.

 

I have a friend that has a 2001 W900 that is 800# heavier than my 2001 WS. His is 260" WB vs my 244". Somewhere you reach a point where reduced weight = reduced reliability and longivity.

 

I have PM'ed you the info you need to calculate engine RPM's at a chosen MPH. Tire sizes make a small change from 22.5lp to 24 tall there is about 100 rpm difference. 22.5lp are 41". 22.5 tall and 24.5lp are roughly the same height of 42". 24 Talls are 44". Of course manufacturers are going to differ some but within the same brand they will be about a 3 in. difference from shortest to tallest. Your biggest change comes in the transmission and rears you choose. The reason for 22.5lps is that they will typically give better milage due to less rolling resistance. The need for them with the taller rear gears is that the tires will give you back about 100rpm to put your motor in its tourqe range and not lug the motor. You want it speced so that the rpm's are no less than 1200rpm at 55mph in top gear. Once you start playing with the info I sent you it will all make more sense. I have not heard good things about the singles. Availability over the road and poor wear are what I have heard most. I don't know how tall the singles are but asumming they are equal to a 22.5lp you would need these specs to get best milage. .73 final ttrans, 3.36 rears and the 22.5lp at 41" 65mph = 1307rpm 70mph= 1407rpm. I think a 3.55 would be a better choice for mountain driving. .73 final, 3.55 rears, 22.5lp 65mph=1380 rpm 70mph= 1487rpm. You never mentioned what tranny you are considering which would be a determining factor depending on where you are going to be hauling. Personally there are only 2 choices for tranny's 13 and 18. Given a choice I'd go 18 for the most versatility but if you know you are going 53ft reefer then 13 would be fine.

 

Let me say I do not own a WS and never have. But, you are talking of gearing and tires. My 07 Volvo 780 runs the 24.5's, Super Single equivalent on the drives. 13 speed with 3:42 gears with power coming from a Cummins 530hp ISX.

She pulls great with this set up even grossed out in the hills. I rarely get stuck in the right lane while pulling a hill and can eat a Cat for lunch.

The fuel mileage right now pulling a van is roughly between 7-7.7 mpg, as long as I keep my foot out of it. Right now she is just breaking in at 130,000 miles on the odo.

And the tractor itself weighs, with full tanks, right at 21,500 lbs.

Mike