Transmission Loss

[boldy205 74]

Hi, just wondering how much transmition/tyre etc loss people had on a Std. 1.9 box in a 205 GTI when rolling roaded?? So basicaly how much to add to the BHP at the road wheels?

Thanks

Matt.

[Sandy 189]

It depends on the rollers, calibration, strapping, tyres etc, but usually about 15-18% at peak power.

[CaptainK 11]

I only ever use the "At The Wheels" value when comparing Rolling Road figures as thats the "true" reading. The "At The Flywheel" readings are just a calculated guess - or in some cases a big guess. I've seen it before on other forums where a car gets rolling roaded at say 130bhp ATW (guess of 170bhp ATF), but the owner expected 200bhp ATF so the rolling road people "force" a lie and make it say 210bhp ATF to keep the car owner happy. After all, a fake big number is impressive in the pub when boasting with your mates.

 

So make sure the Rolling Road people give you that charts and show you the ATW figures.

 

As for the transmission loses on a 1.9 GTi, I had mine RR'd at 88bhp ATW and the RR person said that would be about 110 - 115bhp ATF.

[Guest eddie 309]

thats a pretty fair amount of transmission loss tbh seen alot worse

had a mk2 golf that mad 80bhp atw and 139 atf but my gearbox turned out to be pooop

[Mikey G 3]

I normally stick to the same rollers at Powerstation and i regularly see cars seeing around 30% losses. The last time i went there a Saxo kitcar turned up with straight cut sequential gearbox and that also lost around 30%, Yet a RWD Mustang lost around 27%.

[Rob Thomson 6]

Powerstation's rollers are notoriously dodgy, though.

 

My good old 309 Mi16 made 172bhp ATF on their rollers. A nice number, perhaps, but only 125bhp ATW gives the real story.

[Mikey G 3]

Powerstation's rollers are notoriously dodgy, though.

 

My good old 309 Mi16 made 172bhp ATF on their rollers. A nice number, perhaps, but only 125bhp ATW gives the real story.

 

There are lots of dodgy rollers about though, some a lot worse than others. My point is though if you stick to the same ones you have a better chance of making comparisons for any alterations you have made.

 

Would prefer an engine dyno in my shed

[Rob Thomson 6]

My point is though if you stick to the same ones you have a better chance of making comparisons for any alterations you have made.

Yep, absolutely.

[boldy205 74]

Intresting stuff! i just got back from the Rolling Road and mine made 136BHP at the road wheels. Its a 1.9MI16 twin 45s and Megajolt mappable ignition. What do people recon to that??!

[Pugnut 9 1 Cars]

Intresting stuff! i just got back from the Rolling Road and mine made 136BHP at the road wheels. Its a 1.9MI16 twin 45s and Megajolt mappable ignition. What do people recon to that??!

 

 

Its Fast............................................

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

on paper

[boldy205 74]

Its fast on paper, just the driver needs to have a rolling road tune up!!!

So any one have any idea what the power at the flywheel might be??

[Jer309GTi 3]

Shouldn't worry bout it mate, as long as you have fun in it!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(And you know my 405 is quicker )

[boldy205 74]

ha!! indeed, i think we sould have them on the weigh bridge soon too! be intresting!!

[taffycrook 2]

rolling road losses are a bit of a mine field.

Most of what you read is just plain wrong, almost all of what your hear is rubbish.

The formula for rolling resistance is one with serveral variables. One of which is mechcanical efficiency.

It is this that is often mistaken for the same thing as rolling road losses.

 

The biggest loss on the rollers is the force required to compress the tyres in two places, the faster you go the more times the force is required.

So the losses on the rollers are tied to speed, diameter of the tyre, the rollers, pressure in the tyre, weight of the vehicle, mechanical efficiency, and the way in which they are calculated.

 

Most modern dyno's measure the losses they don't guess them.

The operator can fudge the figures by doing the test in a way that the final figure may be higher than it is but this has little to do with the losses.

 

But to answer the question a normal 205 on the rollers I use has a loss of around 28-33 bhp at around 120 mph.

A standard 1.9 normally shows around 90 bhp ATW (120-123 fly)

std mi16 135 bhp ATW (163-168 fly)

 

This is a SUN RAM 12, twin roller eddy current dyno.

 

It is just wrong to add a % to a ATW figure, as you can see from the above example the same car with the same gearing similar weights, tyres, but a faster more powerful engine will have very similar losses in the actual figure but as a % may vary as much as 7% As in the above example.

But if it was to reach a higher speed the losses may look similar due to the increased losses brought on by the increased roller speed.

[Sandy 189]

Flywheel figures from rolling roads are always estimated. You can add what you like to a ATW figure, it's only ever an estimate. Experience of similar cars on the same rollers some of which have also been run on a bench dyno, will enable you to make reasonable percentage estimates of the losses. The important element is experience of the set up being considered. Coast down losses don't truly represent the losses under load.

[taffycrook 2]

Flywheel figures from rolling roads are always estimated. You can add what you like to a ATW figure, it's only ever an estimate. Experience of similar cars on the same rollers some of which have also been run on a bench dyno, will enable you to make reasonable percentage estimates of the losses. The important element is experience of the set up being considered. Coast down losses don't truly represent the losses under load.

 

Sandy flywheel figures on modern rolling roads are measured not estimated.

Coastdown losses, are not exactly as under load but nor is the power produced the same as on the road or dyno cell.

It is the tyres and the contact surface that differs so much from normal driving that gives such high losses. The 0.5% difference in mechanical efficiency of the transmission is not important compared to the huge losses in the tyres.

 

If all the rolling road did was estimate the final figure why not just stop at the peak power, why coast down.

It is during this coast down that the rolling losses are measured

Its funny that its ok to measure the torque that way during the run, but it some how guess it on the way back down.

 

I used to sell rolling roads, and the miss information out there is amazing.

It is a tool used correctly will give very repeatable acurate results, however not all are used correctly and not all operators understand how they work. Even fewer customers have any idea, so the bullsh*te factor is high.

[Sandy 189]

I used to sell yacht paint, I knew alot about it, but had very little experience of using it! I appreciate what you are saying, but I disagree with some of it because it doesn't stack up to me or reflect what I have observed.

 

I'm going to sound a bit like DB here, if you are physically measuring the power at the wheels, you can only measure power at the flywheel if you have an exact measurement of what is lost through the transmission and tyres. But since you cannot separate the losses under load, you don't have a precise measure of what the real transmission/tyre losses are. The tyre deflection during coast down, compared to under load alone will indicate to you that it's not the same thing. You can estimate the difference by thumb or by calculation, but that means the losses and hence the flywheel figure are estimated, not measured.

[Ryan 99]

The coastdown "losses" are in fact the energy stored in the rotating components in the form of inertia - they are not real transmission losses, and are only loosely related to them at best. You can measure them as accurately as you like, but you're still measuring the wrong thing.

[taffycrook 2]

Ryan,

 

The energy you refer to has to be created by the engine, some of which is wasted the major factor here is the tyres and mechanical eficiency, both of which can be measured by the dyno. As the same amount of engergy must be used to deform the tyres on coast down as the power run or we are creating energy, the mechanical efficiency is slightly different due to different forces in operation. But it is soo little it is not significant enough to worry about. Plus this factor is constant for that car and the difference from car to car not that much anyhow.

 

 

Sandy,

 

I used to be part of a development team on the design and use of the dynos, mainly on software interfaces but had to understand the operating concepts. I have been using them for almost 10 years and it is this experience I am refering to.

It was in the selling of this product I came across the most product bullsh*te.

 

I have said this before and I am willing to prove it again, but come to the dyno I use.

We will run the same car twice, in 3rd then 4th gear.

The flywheel figure will be within 2% the wheels figure will be different.

 

How can that be?

 

Which is correct?

 

Why are the flywheel wheel figures so similar?

 

Answer the above and it all becomes clear.

[Sandy 189]

The method you use to estimate the flywheel power may appear to be well honed and repeatable, but it is still estimated flywheel power, not measured flywheel power, by definition. The only way you can measure flywheel power is to put the engine on a bench dyno, with the load connected to the flywheel.

 

Get your head around that and it all becomes clear, to use your highly patronising tone!

 

Ryan, the transmission losses are principally by heat generated by gear meshing action and tyre distortion. The gear meshing friction doesn't vary as much as the tyre distortion though, from loaded to unloaded.

[saveloy 8]

Generally speaking, a 205 GTI will lose 21% through its transmission on stanard gearbox oil, and 16% if it is using synthetic oil.

[Dj_mini 7]

Would you have bigger loosses from bigger heaver wheels / tyres over small light wheels / tyres as it would take more energy to turn them?

[Sandy 189]

It depends on the method of measurement essentially. Steady state measurement against a brake won't be affected by inertia, but acceleration against a mass will. The type and size of tyre will vary the losses to some extent, because they will behave differently under load and off load.

[boldy205 74]

Yikes this has all got a bit out of control!! Im happy with saying i love driving the car, the sound of the carbs is just lovley and well, lets say its a good competitior for a scooby around castle combe at the rally day, so im happy!!! Just keeping the engine as is now, im sure theres more grip to be had from it, Thats the next plan of attack!!

Thanks for all the replies!!

[Sandy 189]

Exactly, how it drives it what's really important. One of my TB'd 106 1.6 8v's went to a rolling road day in south wales and made the same power and torque as a 1.6 16v, really nothing in it. The 16v owner went around the block in the TB'd 8v one and was completely astonished by the responsiveness and how much quicker it felt. Later at Llandow, they went out on track at the same time and the TB'd 8v was visibly quicker. Same weight and gearing. The numbers never tell the whole story anyway.