drive train loss - The 1947 - Present Chevrolet & GMC Truck Message Board Network

RAB38 · 09-27-2007, 02:54 PM

I am wondering what you guys think drive train loss would be on our trucks my truck has a turbo 305/np205 1 ton running gear and 38" tires. I am thinking the losses would be somewhere near 40%. I know this is not an exact science becasue all vehicles are different. Any one thoughts?

Elwayno · 09-27-2007, 04:31 PM

Well in a car like an old mustang you can expect 15% in an auto like a C4 and 20% in a C6 which is the heavy duty auto trans and one of the biggest torque suckers there is. So take 15% and add in for the Transfer case and bigger axles and you can figure more than 20% but I think 40% may be a little high.

Burt4x4 · 09-27-2007, 04:36 PM

I was told 30% loss when I had my K5 Dynoed, that is from the crank to the tires.
No clue how acurate that is but hey I got 390 Torque & 285 HorsePower at the rear tires so I'm happy..

Any clue on how you take my tire numbers and convert to crank numbers?

Elwayno · 09-27-2007, 04:48 PM

divide the number by the percentage. So 285 / by .7 for 70% gives you 407. 390/.7=557 Remember that the 30% is there estimate though. If it is 20% then the numbers are lower. Different tires can suck up different amounts of power. I know that on a Turbocharged Hayabusa 2 different tires can make a 20Hp difference on a 300Hp machine.

LONGHAIR · 09-30-2007, 05:30 PM

It's called parasitic drag...This is the amout of power required to turn the drivetrain components. Calculating it as a percentage is not exactly fair though. For example: a certain transmission requires a certain amount of power to turn it's internal works, but it is not related to the engine turning it.
So for simple math, if it takes 40 horsepower to turn your transmission, it would be 20% of a 200 HP engine.....but that would only be 10% of a 400 HP engine.
The transmision is part of the parasitic drag, as is the tranfer case and the differential. The tire/wheel combination is a little harder to figure though. The tire width effects the contact area with the ground, which changes it's load/drag. It's total weight has some effect too, but diameter is not a fair comparison either.
A taller tire is actually easier to roll and it turns slower at the same vehicle speed......but it does have an effect on the engine because of gear ratio. To have all things equal, you must change gears to compensate for tire diameter.

All in all it is very hard to calculate, even the available traction of the ground can affect this.

09-27-2007, 02:54 PM	#1
RAB38 Registered User Join Date: Nov 2005 Location: Southern Maryland Posts: 164	drive train loss I am wondering what you guys think drive train loss would be on our trucks my truck has a turbo 305/np205 1 ton running gear and 38" tires. I am thinking the losses would be somewhere near 40%. I know this is not an exact science becasue all vehicles are different. Any one thoughts? __________________ 72 Blazer CST 383 stroker roller, fuel inj, t350,NP205, D60 front, 14b rear, detroit locker, 38 x15.50 mtz's, welds, cross over steering, custom cage,Line X Spray in liner, House of Colors Tangelo Pearl Orange

09-27-2007, 04:31 PM	#2
Elwayno Registered User Join Date: Mar 2007 Location: Livermore, CA Posts: 34	Re: drive train loss Well in a car like an old mustang you can expect 15% in an auto like a C4 and 20% in a C6 which is the heavy duty auto trans and one of the biggest torque suckers there is. So take 15% and add in for the Transfer case and bigger axles and you can figure more than 20% but I think 40% may be a little high.

09-27-2007, 04:36 PM	#3
Burt4x4 Registered User Join Date: Feb 2000 Location: Modesto, CA Posts: 1,842	Re: drive train loss I was told 30% loss when I had my K5 Dynoed, that is from the crank to the tires. No clue how acurate that is but hey I got 390 Torque & 285 HorsePower at the rear tires so I'm happy.. Any clue on how you take my tire numbers and convert to crank numbers? __________________ 1972 K5 MPFI454/Sm465/Np205/D60/14FFd/Re-Centerd H1s w/Swamper Iroks

09-27-2007, 04:48 PM	#4
Elwayno Registered User Join Date: Mar 2007 Location: Livermore, CA Posts: 34	Re: drive train loss divide the number by the percentage. So 285 / by .7 for 70% gives you 407. 390/.7=557 Remember that the 30% is there estimate though. If it is 20% then the numbers are lower. Different tires can suck up different amounts of power. I know that on a Turbocharged Hayabusa 2 different tires can make a 20Hp difference on a 300Hp machine.

09-30-2007, 05:30 PM	#5
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Re: drive train loss It's called parasitic drag...This is the amout of power required to turn the drivetrain components. Calculating it as a percentage is not exactly fair though. For example: a certain transmission requires a certain amount of power to turn it's internal works, but it is not related to the engine turning it. So for simple math, if it takes 40 horsepower to turn your transmission, it would be 20% of a 200 HP engine.....but that would only be 10% of a 400 HP engine. The transmision is part of the parasitic drag, as is the tranfer case and the differential. The tire/wheel combination is a little harder to figure though. The tire width effects the contact area with the ground, which changes it's load/drag. It's total weight has some effect too, but diameter is not a fair comparison either. A taller tire is actually easier to roll and it turns slower at the same vehicle speed......but it does have an effect on the engine because of gear ratio. To have all things equal, you must change gears to compensate for tire diameter. All in all it is very hard to calculate, even the available traction of the ground can affect this.



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