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scmil95eg · 07-10-2014, 05:42 PM

There are fixed drivetrain losses and variable drivetrain losses simultaneously occurring. Combined, they represent an overall percentage of drivetrain loss, which is definitely proportionate to power & speed.

To understand the big picture, you have to understand all the elements occurring on each "side" independently.

4 major elements on the "fixed" side of things are:
transmission gear tooth angles; more angle = more DT loss
final drive gear tooth angles; again more angle = more DT loss
[read: http://www.ehow.com/how_6513778_calc...cal-gear.html]
Trans ratios / FD ratio / tire size; less mechanical leverage = more DT loss
[dyno your car in 1st gear vs. 6th gear to see the effect of mech. leverage)
Rotating mass; more rotating mass requires more energy = more DT loss
[pick up something that weighs 1 lb, then pick up something that weighs 1000 lbs and decide which took more effort]

Gear tooth angles, weights, and ratios don't change over the course of any given RPM band (forget shifting gears) so you can consider these "fixed" or "constant" losses.

The "variable" side of DT loss changes in relation to power & speed:
Friction - input/output shaft bearings, diff bearings, wheel bearings, tire friction - all increase proportionately with speed. Low RPM = lower DT losses / High RPM = higher DT losses

You also have friction between the trans gears and FD gears. And it shouldn't be too hard to understand that the friction between two gears in a 200 HP car will be less than the friction between two gears in a 400 HP car. DT loss will be proportionate to the difference in power. Simply put; the gears are transferring more power, more power = more friction = more DT loss

RPM/Speed goes hand-in-hand with this. Higher speed = more gear tooth engagements within a given period of time = more DT loss. Again, the loss will be proportionate to speed.

There's also centrifugal losses and torque converter losses and one could write a doctorate thesis on the topic as a whole. But I just wanted to give some food for thought because DT loss isn't a fixed value. And you really need some qualifiers before you can say it's just a fixed percentage as well.

07-10-2014, 05:42 PM	#89
scmil95eg Member Join Date: Jul 2013 Drives: '95 delSol, '13 EvoX, '14 Leaf Location: miserable mitten Posts: 59 Thanks: 0 Thanked 48 Times in 26 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	There are fixed drivetrain losses and variable drivetrain losses simultaneously occurring. Combined, they represent an overall percentage of drivetrain loss, which is definitely proportionate to power & speed. To understand the big picture, you have to understand all the elements occurring on each "side" independently. 4 major elements on the "fixed" side of things are: transmission gear tooth angles; more angle = more DT loss final drive gear tooth angles; again more angle = more DT loss [read: http://www.ehow.com/how_6513778_calc...cal-gear.html] Trans ratios / FD ratio / tire size; less mechanical leverage = more DT loss [dyno your car in 1st gear vs. 6th gear to see the effect of mech. leverage) Rotating mass; more rotating mass requires more energy = more DT loss [pick up something that weighs 1 lb, then pick up something that weighs 1000 lbs and decide which took more effort] Gear tooth angles, weights, and ratios don't change over the course of any given RPM band (forget shifting gears) so you can consider these "fixed" or "constant" losses. The "variable" side of DT loss changes in relation to power & speed: Friction - input/output shaft bearings, diff bearings, wheel bearings, tire friction - all increase proportionately with speed. Low RPM = lower DT losses / High RPM = higher DT losses You also have friction between the trans gears and FD gears. And it shouldn't be too hard to understand that the friction between two gears in a 200 HP car will be less than the friction between two gears in a 400 HP car. DT loss will be proportionate to the difference in power. Simply put; the gears are transferring more power, more power = more friction = more DT loss RPM/Speed goes hand-in-hand with this. Higher speed = more gear tooth engagements within a given period of time = more DT loss. Again, the loss will be proportionate to speed. There's also centrifugal losses and torque converter losses and one could write a doctorate thesis on the topic as a whole. But I just wanted to give some food for thought because DT loss isn't a fixed value. And you really need some qualifiers before you can say it's just a fixed percentage as well.