does bodyweight affect a dyno result?

# Thread: does bodyweight affect a dyno result?

1. ## does bodyweight affect a dyno result?

Hi guys,

I was never the smart guy in physics class, so i'd thought i'd ask...

If I get a dyno test done on my bike by a fat guy, will the result be different than a lighter person?

Also... where can I get a dyno test done in Vancouver, Burnaby or Richmond?

Thanks and ride well
Vince

2.

3. no because the bike is not actually moving, I'm sure someone with a physics background can explain it better than I can... I would like to know why overall gearing( ie chaning sprockets) doesn't affect dyno readings, it was explained to me before but i'm dumb and forgot.....

Check with VPR dyno's or www.vpr-dyno.com....

4. It does effect the ass groove that you worked so hard to perfect on your seat

5. Originally Posted by lowlife
no because the bike is not actually moving, I'm sure someone with a physics background can explain it better than I can... I would like to know why overall gearing( ie chaning sprockets) doesn't affect dyno readings, it was explained to me before but i'm dumb and forgot.....

Check with VPR dyno's or www.vpr-dyno.com....
The dyno that measures power by the wheels is the inertia-type dyno (also called an acceleration or drum dyno). Basically, an inertia-type dyno consists of two great big heavy drums hooked up to a computer. An inertia dyno uses the power of the engine to accelerate the drums to speed. The computer measures the time it takes to get up to speed, and the horsepower is determined from these numbers. Rider weight on a dyno makes no difference because the rear wheel is spinning a roller, instead of being on ground which isnt moving. When a bike is rolling around in the real world it has to rely on the tyres to obtain friction so that the bike can move forward, as the bike moves forward it has to carry its own weight, otherwise it wouldnt be moving at all.

6. Originally Posted by cam
The dyno that measures power by the wheels is the inertia-type dyno (also called an acceleration or drum dyno). Basically, an inertia-type dyno consists of two great big heavy drums hooked up to a computer. An inertia dyno uses the power of the engine to accelerate the drums to speed. The computer measures the time it takes to get up to speed, and the horsepower is determined from these numbers. Rider weight on a dyno makes no difference because the rear wheel is spinning a roller, instead of being on ground which isnt moving. When a bike is rolling around in the real world it has to rely on the tyres to obtain friction so that the bike can move forward, as the bike moves forward it has to carry its own weight, otherwise it wouldnt be moving at all.
But given this explanation, gearing would affect HP reading, because shorter gearing(or doing the run in a lower gear) would accelerate the drum faster. Also, we have seen in Canadian Superbike racing, that a worn rear tire (ie lighter) will give a higher HP reading than a fresh tire. The lighter tire spins up faster. I don't understand either how gearing won't affect the reading on an inertia dyno, but apparently it does not. ???

7. Torque is a function of leverage and is affected by gearing.
HP is a function of work over time and is not affected by gearing per se. There will be an optimal gearing that will permit the motor to accelerate the dyno at the fastest possible rate, but this gearing will correspond to the optimal engine RPM for maximum HP output.

I’m not an expert on these things, and I may have some wires crossed, as have just spent the day in the sun, but that’s how I see it

8. Torque is not affected by gearing. Torque has no time requirement.Yes, Hp is a function of work(torque) over time. But, accelerating the drum faster (time) gives a higher HP reading. A litrebike will accelerate the drum faster than a 600 will, but a 600 with lower gearing, a lighter rear wheel, a light qualifying tire with also accelerate the drum faster. I still have never heard an adequate explanation for this.

9. glad to see that I'm not the only one consufed.....I think we should consult Tee Tee, he knows everything

10. Originally Posted by japhrodisiac
... a lighter rear wheel, a light qualifying tire with also accelerate the drum faster. I still have never heard an adequate explanation for this.
The commonly used dynos estimate power based on the rate at which a wheel of known inertia is accelerated. There are rotating components on the bike which are accelerated as well, such as the crankshaft, transmission, chain, and rear wheel. Dynos have an arbitrary fudge factor built into them to compensate for those extra components. If a particular bike has lighter components, the dyno will overestimate the power produced.

11. Gearing doesn't effect dyno readings. low gearing may accelerate the drum faster but the measured top speed will be lower, accel and speed are used by the software to calculate HP.
Lighter rotational mass (worn tire, 520 chain etc) will show higher HP. Dynojet software use a universal constant for the estimated mass of the rotating driveline(it's considered part of the drum) So if your driveline has less mass than the estimated mass your HP readings will be higher. If your rotating mass is higher your HP will show slightly less. Bad news for Harleys....

12. The gearing won't affect the ammount of power, just how the power is delivered. It would change the acceleration and the torque but not the net power because nothing is changed with the motor.

In theory, a heavier rider will apply more normal force to the rear wheel and there will be less slip, and more of that power can be measured, but bikes are strapped down so it won't matter. A stickier tire will also result in less slip too.

13. Originally Posted by japhrodisiac
Torque is not affected by gearing.
??????????

14. Originally Posted by lowlife
.....I think we should consult Tee Tee, he knows everything
Nope, still wondering why the sky is blue.......

A mass type rear wheel dyno will be affected by the mass of the bike's rear wheel assembly and the weight of the chain drive as well as the weight of the trasmission gears, any engine flywheel in the engine and the weight of the clutch basket and plates. In short anything that revolves and spins to a faster speed during the runup. However the mass of the drum is very high compared to any of that other stuff so it's fairly minor but it is there so you guys that suspect that stuff are right. But it won't matter for comparative testing of setup work on a given bike since the same bike is then accelerating the same parts for each test and thus the results are directly comparable (barring a major air pressure change between tests).

I'm not that up on my dyno stuff but I'm guessing that the overall HP won't change with sprocket changes because the dyno computer sees a higher torque but lower redline speed and thus the math spits out the same HP reading just as it should do.

15. your all fuking wrong its stickers ,paint and chrome that affects HP and tricks the dyno . idiots

16. Originally Posted by TeeTee
I'm not that up on my dyno stuff but I'm guessing that the overall HP won't change with sprocket changes because the dyno computer sees a higher torque but lower redline speed and thus the math spits out the same HP reading just as it should do.
thank you that one makes sense.....

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