Expert
Posts: 3802
   
Location: Rocky Mount N.C. | What will your GCVW be? Weight of truck, trailer, horses, stuff, folks, etc? I would go with the 4.30's. That 4.88 will slow the truck on top end and keep the engine wound pretty tight at highway speeds, plus it will burn fuel like you wouldn't believe. |
Elite Veteran
Posts: 798
Location: Tenn/Ala. | Well, I always try to keep my cruising RPMs low for fuel economy. At 2,000 RPM I could do 55 with my 4:88, and about 60 with the 4:30. Same economy, but I gained 5MPH.
I've had all 3 brands, and they seem to go from sipping to gulping right at the 2K mark on the tach. |
Veteran
Posts: 188
Location: Ingalls, Ks | I'd do 4.3, when engine hp wasn't as high as todays powerplants you needed the lower ratio, but with todays tq. and hp there's no need to wind them that tight. I have a 4.88 in my 550 pulling a trailer like your talking and it does fine, but the RPM can get pretty high on the interstate. No I do not possess the discipline to slow down. |
Expert
Posts: 5870
Location: western PA | The best axle ratio is dependent on a few factors. The load you will be pulling, the amount of power you have available, and the type of service your rig will encounter. The loading and the power are a fixed and known amount. The type of service will be determined by where you live, and the terraine in which your rig will be used. If you live in the mountain states, high ratios and exhaust braking are very important. If you regularly travel flat, open roads, lower RPMs and higher cruising speeds are more important. If you travel within both environments, a compromise should be chosen. There is no one ratio that is best for everyone. That is the reason varying options are available. You must determine what type of usage you expect, and base your response on that knowledge. As it was mentioned, all of the newer diesels produce much more power, than they did even a few years ago. This means that the same amount of rear wheel HP and torque, can now be attained at a lower RPM. A higher RPM will eat up your fuel mileage. The lower the ratio you can run, will enhance the amount of MPG you can save. The newer automatic transmissions now have more available gearing, offering better lower and midrange pulling, with lower engine RPMs at cruising speeds. If you are using the experience of fellow truck owners to help determine your out come, make sure you are using the results of similarily aged and equipped trucks for the advice. Their operating terraine should be similar. If they are not significantly the same, you may not get an accurate answer. |
Which axel ratio do I need?
