Axle Ratio and tow rating

I'm just trying to call it what it is. The power doesn't change. You just swap rpm for torque.

That's how the 400hp turbo-diesel climbs the hill at 50mph in 4th while the 150hp hot water six in can only make 20 mph in 1st. Gearing down won't give the diesel more power, it would just slow it down.

Sport45 wrote:

Denny & Jami wrote:
You can talk this to the death but it all comes down to the HP/torque at the pavement and the lower the gears the more HP/torque you have at the pavement.

Denny

Leave the HP part out and I agree with you.

Whether the lower gear ratio is in the axle, transmission or auxiliary transmission (transfer case, underdrive, etc) makes no difference.

Call it whatever you want it's still the amount of power applied to the pavement and lower gears will give you more power to the pavement were it counts. Flywheel HP is a good for advertising but it's the final numbers at the ground that matter.

Denny

Not much mileage difference between gear ratios anymore IMO due to the newer 6 speed autos. They keep the rpms down pretty good even with 4.10 axles. With a gasser get as deep an axle as you can find to make up for the lack of torque compard to an oil burner if you toe significant loads.

Denny & Jami wrote:
You can talk this to the death but it all comes down to the HP/torque at the pavement and the lower the gears the more HP/torque you have at the pavement.

Denny

Leave the HP part out and I agree with you.

Whether the lower gear ratio is in the axle, transmission or auxiliary transmission (transfer case, underdrive, etc) makes no difference.

You can talk this to the death but it all comes down to the HP/torque at the pavement and the lower the gears the more HP/torque you have at the pavement.

Denny

TomG2 wrote:

wilber1 wrote:
Using a lower gear puts less stress on the rest of the driveline and allows components like thectransmission to handle more weight.

At full throttle and maximum rpm, the drivetrain is subjected to all the power the engine can produce regardless of the rear axle ratio. There might be a slight reduction when cruising empty in overdrive.

Related to my post above, subjecting the drivetrain to "power" is through a combination of force (torque) and speed (rpm). It depends upon which of those your drivetrain can better handle. The stress wilber1 was referring to is likely torque as it's usually the thing that breaks stuff and lower gears in the rearend does decrease that.

BenK wrote:
All gearing is either or both a change in direction or torque multiplication

Multiplication as in reducing power or increasing power

A 3.73 has the input shaft (drive shaft) turn 3.73 times to ONE axle turn

Meaning 3.73 times the drive shaft power at the axle shaft...minus losses
4.1 means 4.1 times the drive shaft power and 3.55 means 3.55 times...etc

This is regardless to the throttle setting. Just that multiplication factor.

Then toss in throttle setting and it too will be multiplied likewise by the
ratio.

Part throttle at 50% and say 50% torque will have it multiplied by the diff ratio
number

Full throttle will have that 100% torque multiplied by the diff ratio

All minus losses and other factors

Some times a higher numeric will have better economy because the throttle does
NOT need to be pressed as far. The ICE just turns more at a lower throttle setting vs a lower numeric which would require a higher throttle setting as there
isn't as much power multiplication

Not to nitpick but torque is changed through gearing while power is not (ignoring losses), but I think you already know that.

Gearing trades torque for RPM and vice versa, with constant power throughout. With a 4.10, you spin the driveshaft faster and with less torque applied than you do with a 3.73, given the same road speed and load.

All gearing is either or both a change in direction or torque multiplication

Multiplication as in reducing power or increasing power

A 3.73 has the input shaft (drive shaft) turn 3.73 times to ONE axle turn

Meaning 3.73 times the drive shaft power at the axle shaft...minus losses
4.1 means 4.1 times the drive shaft power and 3.55 means 3.55 times...etc

This is regardless to the throttle setting. Just that multiplication factor.

Then toss in throttle setting and it too will be multiplied likewise by the
ratio.

Part throttle at 50% and say 50% torque will have it multiplied by the diff ratio
number

Full throttle will have that 100% torque multiplied by the diff ratio

All minus losses and other factors

Some times a higher numeric will have better economy because the throttle does
NOT need to be pressed as far. The ICE just turns more at a lower throttle setting vs a lower numeric which would require a higher throttle setting as there
isn't as much power multiplication

Bedlam wrote:

TomG2 wrote:

wilber1 wrote:
Using a lower gear puts less stress on the rest of the driveline and allows components like the transmission to handle more weight.

At full throttle and maximum rpm, the drivetrain is subjected to all the power the engine can produce regardless of the rear axle ratio. There might be a slight reduction when cruising empty in overdrive.

My experience with off-road toys proves otherwise. When I ran too tall or aggressive tires (like towing a heavy load), the CVT would complain by shredding my drive belt. Luckily, the final drive to the wheels was chain driven and I was able change sprockets (kind of like changing your differential ratios) and was able to keep the CVT happy. Before doing this sprocket swap, I had to run shorter tires or tires that would slip more so the transmission would not stress.

I am sure you have a point, but I think there are different factors involved when off roading than in towing a trailer down the highway at sixty mph. Modern six speed transmissions have low enough first gears that they will not stall out at take-off speeds.

TomG2 wrote:

wilber1 wrote:
Using a lower gear puts less stress on the rest of the driveline and allows components like the transmission to handle more weight.

At full throttle and maximum rpm, the drivetrain is subjected to all the power the engine can produce regardless of the rear axle ratio. There might be a slight reduction when cruising empty in overdrive.

My experience with off-road toys proves otherwise. When I ran too tall or aggressive tires (like towing a heavy load), the CVT would complain by shredding my drive belt. Luckily, the final drive to the wheels was chain driven and I was able change sprockets (kind of like changing your differential ratios) and was able to keep the CVT happy. Before doing this sprocket swap, I had to run shorter tires or tires that would slip more so the transmission would not stress.