Hitch Height/Pin Height

[bmzero]

Just a cation about rear ratio's. Unlike a pickup there is a very wide variance on the numbers and what is appropriate. As an example, my Volvo 610 with auto shift, 400/1450 hp/torque had a 3.90 rear ratio. That was perfect for the hp/torque and trans gears I had. You CANNOT assume that a number that works well in one truck works well in another. There are far too many variable to make that assumption. There are simulator you can use to see what the effect is on a truck by changing gears. Having a lot of torque allows options that a lower torque truck does not have.

 

Agreed.

 

I plan to do my final selection based on the final drive RPM at 70MPH. Currently, I run a little less than 1500 at that speed (going by fuzzy memory). I would like to bring that down a couple hundred RPM to get it at the bottom of the sweet spot. My truck is a D16 pulling a light load, so I have plenty of "torques" and "horsepowers" to burn.

[The Few]

Just a cation about rear ratio's. Unlike a pickup there is a very wide variance on the numbers and what is appropriate. As an example, my Volvo 610 with auto shift, 400/1450 hp/torque had a 3.90 rear ratio. That was perfect for the hp/torque and trans gears I had. You CANNOT assume that a number that works well in one truck works well in another. There are far too many variable to make that assumption. There are simulator you can use to see what the effect is on a truck by changing gears. Having a lot of torque allows options that a lower torque truck does not have.

Now that makes a LOT of sense Jack!! I am only trying to mirror the fuel economy and work that I have seen ( for example) what Gregg Shields has done with a few HDT Rv's through his videos when he changed rear end ratio's for his customers.. The rig I plan to buy/ build will be no more diffrent in specs to what Gregg has displayed in his video, except that I plan to keep mine tandem.. I plan to have an engine that has at least 450 hp, and triple that in torque, so I am hopeful I can find a solution, because I am determined to make this work.. Do you have any suggestions Jack???

[Phil D]

My truck has a 3.18 gearset, which I feel makes a big difference in relation to some others. In the later model 630's, you can get 2.50's. At some point, I'm going to put a locker in my drive axle. At that time, I will swap to the 2.50 R&P if possible.

 

I'd recommend consulting Volvo before making such a drastic change. The engines in the trucks with the "super tall" gearing may be programmed entirely differently from yours, even if the displacement is the same, and you could end up with a combination of lousy drivability, gradeability, fuel economy, or a combination of any or all of those characteristics.

 

We can usually get away with re-gearing a step or two higher (numerically lower), given our relatively light weights (I re-geared mine one step higher when I singled, from 3.55 to 3.36, and that 0.19 difference is an uncharacteristically wide step), but too radical a change could drop your truck completely out of its engine's power band at normal speeds.

[bmzero]

 

I'd recommend consulting Volvo before making such a drastic change. The engines in the trucks with the "super tall" gearing may be programmed entirely differently from yours, even if the displacement is the same, and you could end up with a combination of lousy drivability, gradeability, fuel economy, or a combination of any or all of those characteristics.

 

We can usually get away with re-gearing a step or two higher (numerically lower), given our relatively light weights (I re-geared mine one step higher when I singled, from 3.55 to 3.36, and that 0.19 difference is an uncharacteristically wide step), but too radical a change could drop your truck completely out of its engine's power band at normal speeds.

 

I agree completely. I have a pretty good relationship with my local Volvo tech. I would definitely get his input before doing the switch, and would probably let them do the work.

[Nigel]

One other thing to keep in mind. Most ST trailer tires are rated for 65 mph. I know a lot of you have upgraded to LT and don't have that issue.

 

Nigel

[Mark and Dale Bruss]

One other thing to keep in mind. Most ST trailer tires are rated for 65 mph. I know a lot of you have upgraded to LT and don't have that issue.

 

Nigel

Most of the trailers in this HDT Forum are too heavy for LT tires. Not an appropriate option.

[Bob Cochran]

Something I don't think I heard mention yet is the transmission ratio's needs also be factored in. We all know this but thought would bring that up for the new-be. look forward to your arrival to the HDT and hearing from you as you plan getting here.

[The Few]

Something I don't think I heard mention yet is the transmission ratio's needs also be factored in. We all know this but thought would bring that up for the new-be. look forward to your arrival to the HDT and hearing from you as you plan getting here.

Thank you sir, much obliged!!! Looking forward to being "in the know" with the rest of you, but I am trying to be very smart and educate myself before "jumping off the cliff" of no return!!!