Dyno fail. FAO: Scubascorpion

Well no, because you lot are stating that this figure is altered because it is measured across two rollers per wheel.

If that figure was measured at the wheel, it would be the same as that measured with a single roller setup.

Now the power exerted by the wheel does not change in each instance, however, the power received by the roller may, therefore you are measuring the power at the roller in the case of a dual roller setup.

Unless you know of any roads where your tyre makes contact in two places?
 
The one big wheel part is irrelevant, all that means is the surface is moving instead of the vehicle.

Seriously, its slightly bemusing how many people seem to think they are talking to an idiot, yet come out with such idiotic responses themselves.

Man up, admit you are wrong, and lets get on with our lives.
 
Scuzi said:
Does that mean that my car puts out 170bhp at the wheels? I'm pretty sure it doesn't. I understand that it's a measurement and not the actual power output but why print it if it's wrong?
Click to expand...

its not "wrong"

its the "right" measurement for the power at the wheels when put on a dyno with 2 rollers. This however is different for the power at the wheels when its put on the road.

Would putting "wheel horsepower when on the dyno" make it easier to understand ?

MikeHiow said:
Unless you know of any roads where your tyre makes contact in two places?
Click to expand...


this is where the dyno has lost you. The Dyno was designed from the ground up to give accurate flywheel figures, or at least attempt to gain as accurate as possible. Two contact patches per wheel is a better more accurate way of measuring the drag (so maha say) and thats why they put 2 rollers there.

They arent interested in providing the yanks with accurate RWHP figures, they are interested in flywheel figures, so thats why they put 2 rollers on there, and didnt gave a damn about what ouput the dyno gives for "wheel horsepower"
 
Last edited:
You're suggesting that the power at the wheels changes depending on which type of dyno they are on? How is that possible? The engine outputs the same power regardless.

Like I say, that may be the power at the rollers in the case of the Maha dynos, but it is not the power at the wheels.
 
MikeHiow said:
The one big wheel part is irrelevant, all that means is the surface is moving instead of the vehicle.
Click to expand...

thing is though, unless the roller is the exact same diamater as the tyres, will the contact patch on the roller not be a different shape and size to the contact patch on a flat road ?

mjt said:
How can it be any different on the road?
Click to expand...

because the maha dyno measures it with 2 contact patches per wheel. A road doesnt have these, ergo they are different.

MikeHiow said:
You're suggesting that the power at the wheels changes depending on which type of dyno they are on? How is that possible? The engine outputs the same power regardless.

Like I say, that may be the power at the rollers in the case of the Maha dynos, but it is not the power at the wheels.
Click to expand...

no no no

this is not a power that is "OUTPUT" this is a force that is exerted upon the internals of the dyno. That force is less when it has to turn 2 rollers instead of one.

Thats all dynos measure, the force put on them by the car. They cant actually measure the power at the wheels, merely the forces the wheels put on the dyno.
 
Last edited:
The rolling circumference of the wheel is irrelevant when measuring the power exerted by the wheel.

Yes, the Maha dyno mesaures it with two contact patches, therefore, the power it records is the power at the rollers, not the overall power at the wheel.

Where as, with one contact point, all the power at the wheel is exerted onto the roller minus a tiny loss in heat/noise during the transfer of that power to the single roller. Thus this is a far more accurate representation of the power at the wheels.

Like I say, you can't take a constant, and then take two different variables invariably related to that constant and claim they are both accurate.

Are we getting somewhere now?
 
MrLOL said:
thing is though, unless the roller is the exact same diamater as the tyres, will the contact patch on the roller not be a different shape and size to the contact patch on a flat road ?



because the maha dyno measures it with 2 contact patches per wheel. A road doesnt have these, ergo they are different.



no no no

this is not a power that is "OUTPUT" this is a force that is exerted upon the internals of the dyno. That force is less when it has to turn 2 rollers instead of one.

Thats all dynos measure, the force put on them by the car. They cant actually measure the power at the wheels, merely the forces the wheels put on the dyno.
Click to expand...

Right then, and what is power if it isn't force(well, work, amounts ot the same thing) exerted per unit of time?
 
You can argue about the definition of power all you want.

If it makes everybody happy write off to maha and tell them that the figure they measure isnt the power at the wheels figure and they shouldnt be quoting it since its power at the dyno. Will that make everybody feel happier ? its just semantics
 
MrLOL said:
this is not a power that is "OUTPUT" this is a force that is exerted upon the internals of the dyno. That force is less when it has to turn 2 rollers instead of one.
Click to expand...

No, the Force exerted by the wheel is the same.

Again, Single roller "power at the dyno" will give an accurate representation of the power at the wheels.

Clearly a double rollers "power at the dyno" does not give an accurate representation of the power at the wheels (although with the correct maths/setup, there is no reason why it could not), therefore cannot be considered as such - so the issue with these Dynos is incorrect terminology? Wouldn't you agree?
 
Last edited:
MikeHiow said:
No, the Force exerted by the wheel is the same.
Click to expand...

upon what though ?

we're not measuring the force exerted up on the dyno wheel in contact of the road. We're measuring the force on the generator inside the dyno, which is less as its had to spin 2 wheels instead of one.

Clarkey said:
It isn't 'just semantics', it's basic physics.
Click to expand...

Didnt say that, arguing about what the maha dyno actually measures, is however

MikeHiow said:
so the issue with these Dynos is incorrect terminology? Wouldn't you agree?
Click to expand...

yes, but the maha dyno was never created for people to use WHP figures. It was created for fly figures.

Its just people like you that sieze upon that figure as an excuse its broken. Nobody tried to say the wheel horsepower figures were comparable with other dynos ;)
 
Last edited:
You are essentially now repeating what I said ages ago, you just refuse to admit that what I'm saying is correct.

Yes, you are measuring the force on the dyno, therefore it is not the force exerted by the wheel, as there is clearly force not being measured somewhere (presumably in the second roller).
 
MikeHiow said:
You are essentially now repeating what I said ages ago, you just refuse to admit that what I'm saying is correct.

Yes, you are measuring the force on the dyno, therefore it is not the force exerted by the wheel, as there is clearly force not being measured somewhere (presumably in the second roller).
Click to expand...

*yawn*

ok.
 
PMKeates said:
If we have a competition for "most hilarious Motors argument of 2010", I'm probably going to vote for this.
Click to expand...

I just wanted to know why the Powerstation graphs always had inaccurate data, not knowing what we know now, one could be forgiven for considering accurate ATW figures and overzealous ATF figures, a common trend in so many dynos these days.

I'm happy, I now know why they are wrong, I'm just left mystified as to why its never been flagged/mentioned/fixed.
 
So essentially this has all boiled down to MikeHiow being unhappy they call their measured figure Wheel Power, rather than Roller Power because he is unable to directly compare this figure with a dyno designed to give absolute wheel horsepower outputs?
 
You must log in or register to reply here.
Back
Top Bottom