How critical is axle ratio?
In the modern day of 10 speed automatics, how necessary are 'towing' gears? By 'towing' I mean anything over 4.xx. These new transmissions have such low first gears compared to just a decade ago, is ...
Forum Discussion
I think choosing the best gear ratio begins with having a good understanding of your engine’s powerband. Seeing a torque curve of the 7.3 would be very useful. A bsfc map would also be helpful. After getting a sense of your engine’s capabilities knowing the transmission’s gear ratios is essential. Finally knowing how the truck will be used needs to be considered.
I don’t know much about the 7.3 other than it has a long flat torque curve and I believe it makes 430 peak hp at 5500 rpm. It makes 425 lb ft of torque at 3250 rpm (263 hp). and 350 hp at 3900 rpm.
350 hp should be more than enough power to tow a 12000 lb rv up a 6% grade at 60 mph.
With 3.55 gears and the 10 speed 7 th gear would put you at 2150 rpm at 60 mph with 34 inch tires and 4th gear would put the engine at 3800 rpm at 60 mph.
Without giving it much more thought I’d agree with Shiners earlier post:
If your going to be running empty a fair bit get 3.55 gears and you’ll have the opportunity to get better fuel economy unloaded on the highway. While towing you can lock out the top gears and still have all the performance you need, seldom dropping below 4th gear in the hills.
If your primarily going to be towing with the truck you may as well get 4.30 gears to gain a little bit of grunt at the rear wheels to get your trailer moving in first gear. The odd time when your running empty down the highway you’ll be at 2060 rpm in 10 th gear at 75 mph…. which doesn’t sound too bad.
I don’t know much about the 7.3 other than it has a long flat torque curve and I believe it makes 430 peak hp at 5500 rpm. It makes 425 lb ft of torque at 3250 rpm (263 hp). and 350 hp at 3900 rpm.
350 hp should be more than enough power to tow a 12000 lb rv up a 6% grade at 60 mph.
With 3.55 gears and the 10 speed 7 th gear would put you at 2150 rpm at 60 mph with 34 inch tires and 4th gear would put the engine at 3800 rpm at 60 mph.
Without giving it much more thought I’d agree with Shiners earlier post:
If your going to be running empty a fair bit get 3.55 gears and you’ll have the opportunity to get better fuel economy unloaded on the highway. While towing you can lock out the top gears and still have all the performance you need, seldom dropping below 4th gear in the hills.
If your primarily going to be towing with the truck you may as well get 4.30 gears to gain a little bit of grunt at the rear wheels to get your trailer moving in first gear. The odd time when your running empty down the highway you’ll be at 2060 rpm in 10 th gear at 75 mph…. which doesn’t sound too bad.
