Transmission Losses

[Mad Professor 7]

I run a Rolling Road down here on the good old "Isle Of Wight".

 

Our dyno only reads power @ wheels, but the avg transmission loss we see is norm 15-20% FWD.

We have not yet seen anything FWD with a higher loss then 20%.

[miamistu 1]

I run a Rolling Road down here on the good old "Isle Of Wight".

 

Our dyno only reads power @ wheels, but the avg transmission loss we see is norm 15-20% FWD.

We have not yet seen anything FWD with a higher loss then 20%.

 

How is it worked out?

[Rob_the_Sparky 9]

I've just read an article in PPC magazine about rolling roads written by Dave Walker and he says the exact opposite of the above. The at the wheels power figures can be changed by altering the tyre pressures, different size tyres and running in different gears.

 

Read the article again, it also says coast down losses are also unreliable and that a rolling road is good for setting up and tuning engines. It is not a tool for measureing power output, if you want that then use an engine dyno...

[Faz85 0]

i tought trany losses (friction and inertia i think getting the power from the engine to the wheels) is proportional to the power. if your putting more power in to turn the rollers then equal and opposit andf all that and the there will be more stress on the components, like wheels and gears in 'box.

 

please correct me if i'm wrong but it seemed logical to me.

 

The transmission losses (bearings and fluid drag) are mainly dependant on the engine speed NOT the power or torque. there will be a marginal increase in gear friction at higher power due to sliding friction, but it would be small. Richie is rite in that the inertia wont change, thats dependant on the geometry and mass of the gears, and nothing else.

 

As was mentioned by Normski, the RR figures also depend on the gear your in. its worth pointing out that the 4th gear on the 1.9 is close to 1:1, which would give fewer losses on the RR, and would give a greater power reading.

[Emmy Seize 8]

i tought trany losses (friction and inertia i think getting the power from the engine to the wheels) is proportional to the power. if your putting more power in to turn the rollers then equal and opposit andf all that and the there will be more stress on the components, like wheels and gears in 'box.

 

please correct me if i'm wrong but it seemed logical to me.

 

Think of it this way : Take two people, one rather well trained and strong, the other one an absolute weakling.

 

Let both of them try to lift a crate of ale (or whatever, if you don´t like ale).

 

Then ask yourself the question: Is the crate heavier when lifted by the strong person ?

 

Obviously not !

[david932 0]

i had a chat with LAD recently just to ask a technical question. the guy ignored my question completely and ended up banging on for 15 mins about how i should sell my gti6 engine and give him 4grand to build me a super dooper scooby eating 180bhp 1.9 8v. i did try to explain that i was on a buget but would he listen... no. after potilely listening to his point of veiw, i dived in to outline the fact that the engine i have is over £3500 cheaper and not far off that figure anyway!

 

on the rr point i took my modified clio williams to have it mapped it made 157.3atw which is about what i expected but shockingly 199.8atf(corrected to 192) does this sound right?

 

the second time i went back (same rollers) had changed the centre section from a striaght through to a silenced section and it made 149.7atw and 186.9atf. altho this time though the print out said "rear wheel drive" and not front. surely you would get more loss through rears wheel drive? im not sure why he would try and twig it in this way tho

Edited March 9, 2007 by david932

[Faz85 0]

Did he know you'd changed the centre section? maybe hes trying to make the power loss from a silenced centre section look worse than it actually is. Apparently the coastdown losses are roughly 17% for rear wheel drive and 15% for front wheel drive, so it would make a little bit of difference.

Edited March 9, 2007 by Faz85

[Normski 1]

Just thinking about it, how can the transmission loses (tyre friction included) be related to the engine power? Because the rolling road measures them while the car is in neutral.

[Ahl 4]

Perhaps because it only ever creates an esimate?

I've never really delved deeply into rolling road theory but im pretty sure thats there is no way for one to truely know the transmission loss. So it must be an estimate. Some good esimates, some bad estimates, and some esimates buggered about with by the operator so as to appear as anything they like.