4x4ord wrote:
ShinerBock wrote:
Otrfun is correct. The lower the rear axle ratio, the more stress it puts on the driveline component between the engine and rear axle. This is regardless of trans gear.
Downspeeding has become a big deal in the medium/heavy duty industry in the past ten years due to the new fuel economy regulations for these class of trucks. What people thought they would save in fuel economy, they ended up spending on driveline components because the low rpm and gearing put a lot of torque stress on the driveline. They finally started making drivelines that can handle it, and many handled it great within their respective ratings. However, the drivelines of the taller rear gear still could not handle as much weight as the shorter geared trucks due to this driveline stress.
I have no qualms with using my 3.42 axle to tow 15k, but I would started looking at getting a truck with shorter gears if I towed more than that especially if it was on a regular basis.
Ive got very close to one million miles on my ‘07 Pete with a 15 litre Cat engine. It has fairly tall rear gears. I broke all 4 axles within about 20000 miles of each other which I thought might be more than coincidental. Anyway that is the only driveline components that have been touched on the truck. It is usually pulling foot to the floor about 12 to 1600 rpm. I think the newer heavy duties might be set up to run around 1000 to 1400 rpm under load. When you say the medium duty industry is running lower rpms to conserve fuel what engines and rpm are they running?
The downspeeding trend came in after 2010(when the new EPA requirements hit) when Cat exited the medium/heavy duty market so I am fairly certain that your truck is not one of them. Downspeeding is also not meant for every medium/heavy duty application and is only meant for long haul trucks that driver over relatively flat land. The ratios used in the trucks are around 2.20:1 and the rpms get as low as 1,000 today. They also use direct drive transmissions.
The Downspeeding Learning Curve
