• Thought I d share this

    Thought I'd share this

    10 comments
    • Somebody amongst us "must" know what are the indicative torque values at the wheel with all those combos....

      ....There must be someone among us here.... Let's find out who he is

    • Not without a dyno

    • "Indicative" is different from "actual". Indicative values involve computation not as determined by dyno ;)

    • Changing the rotational force, I'm thinking wouldn't really change actual torque value at the wheel. Nothing that notable I wouldn't think. In the end you're either spinning the rear wheel faster or slower. A fly wheel weight slow the rotation of the crank, but has an added torque effect. To me, it's the feel and outcome of the change. The only numbers that matter is my number of stalls, crashes and lap time lol

    • If we compute for the torque at the wheel we have to know all the friction coefficients of all the rubbing parts from the tranny to the rear sprocket, even up to the rubber-type of the tires. We need Yami's sheet on that.... And I don't know where to get them from unless, perhaps, I'm an engineer from the company.... As far the type of ground (soil, rock, mud, ice, sleeth or slouch etc) where the rear wheel will get its traction that can be estimated or reference in the internet.... Else, we do a dyno run with at least 3 different final gear combos and interpolate and extrapolate the values for all of the others.... With a Yamaha's published 31 lb-force ft of torque at the tranny at the standard tranny gear ratios, we can then back-calculate how much really are the total parasitic or friction losses at the wheel per final gear combo

    • To many mitigating factors, as you stated, to ever get a real number.

    • Dang, and i get lazy just by thinking it LOL!

    • I recommend crossing your fingers, not holding your breath haha

    • By MXA dyno data, the standard YZ makes a peak 46.8 hp at 8800 rpm at the wheel. This YZ is at final-gear ratio of 3.57 (50T rear/14T front).

      (46.8 hp x 5252)/8800 = 27.93 lb (force)-ft torque

      27.93 lb(force)-ft multiplied by 3.77 (from 49T rear/13T front) divide by 3.57, must mean, as an example:

      27.93 x (3.77/3.57) = 29.49 lb (force)-ft of derived torque at 8,800 rpm for a 3.77 final gear ratio, assuming no added friction coefficient from the front sprocket and lesser friction from the rear sprocket.

      The estimated peak torque of 31 lb (force)-ft on the standard YZ is located at 7500 rpm. The power at that point is therefore around 44.27 hp.

      But all such deduced values are just trivial since they are "after" a dyno run at the wheel has been performed, hence the values are reduced already or just "translated" or "transferred" values, unless MXA did an engine-mount dyno run to see comparison between the engine-hp and wheel-hp.... We need all those friction coefficients on all the parts from them Yami design engineers just to be able to see what the heck is the plausible engine-hp and engine-torque reckoned after doing a wheel-mount dyno run, and how efficiently power is transferred into the wheel. You think there is about 10-12% parasitic loss from the engine to the wheel? I don't know honestly man

    • Yes!!! so many people forget about gearing they think its all in the pipe