FD failure.......mileage?

The gear it's in will only affect the engine; the torque applied to the FD will remain the same but, a lighter touch on the throttle will reduce the loads all round.

Not really. A gearbox is a torque multiplier so low gears will put more pressure on the final drive than high gears.
 
Not really. A gearbox is a torque multiplier so low gears will put more pressure on the final drive than high gears.


Is it not the case that a certain value of torque is required to be applied to the fd to propel the
bike forward at a certain rate and the torque value will be the same (albeit at a lower/higher rpm)
choose what gear is selected if the speed remains the same.

The gearbox may be a torque multiplier but it is multiplying the engine torque but that does not
alter the torque required at the FD to do a certain amount of work, ie. propel the bike forward
at a given rate. At a constant speed the required work rate remains the same whatever the gear selected.
 
Is it not the case that a certain value of torque is required to be applied to the fd to propel the
bike forward at a certain rate and the torque value will be the same (albeit at a lower/higher rpm)
choose what gear is selected if the speed remains the same.

The gearbox may be a torque multiplier but it is multiplying the engine torque but that does not
alter the torque required at the FD to do a certain amount of work, ie. propel the bike forward
at a given rate. At a constant speed the required work rate remains the same whatever the gear selected.

I agree, gradual acceleration must be easier on the final drive than wheelying it between every gear change.
 
Is it not the case that a certain value of torque is required to be applied to the fd to propel the
bike forward at a certain rate and the torque value will be the same (albeit at a lower/higher rpm)
choose what gear is selected if the speed remains the same.

The gearbox may be a torque multiplier but it is multiplying the engine torque but that does not
alter the torque required at the FD to do a certain amount of work, ie. propel the bike forward
at a given rate. At a constant speed the required work rate remains the same whatever the gear selected.

If you hit the throttle in bottom gear (assuming the bikes doesn’t wheelie) the final drive will see more load on the gears than doing the exactly same in top gear.
In top gear the final drive is turning faster so torque is spread across more turns of the back wheel (less force per foot of road). So load on lower gears is always higher at the final drive in lower gears - same power goes into less road.
Load is the same at the engine end regardless of gear as that’s the bit making the power.
This is proven by anyone with a weak clutch. It won’t slip in bottom gear as the torque goes out to the final drive. It will slip in top gear as the torque has not been multiplied so engine works harder per crank revolution.
Bikes (not BMW boxers) with step down gearing at primary drive need a bigger clutch and gearbox than bikes running the first motion shaft at engine speed. The step down primary ratio has multiplied the torque.

The final drive has to be specced for engine torque x the bottom gear ratio. It also has to consider torque vibration and load reversals that give much higher peak loads.

Slam the throttle open & shut in bottom gear and we can expect the wheel to spin or lock. Do the same in top gear and it’s nothing like as dramatic.
 
I think you are talking different things to my original post. I stand by my position and
cannot explain it any clearer but, i'm going to leave it there as i have neither the time
nor the patience to persue this through post after post as tends to happen with this sort of thing.
 
You can maybe explain why farm tractors have a huge back axle, yet never go above 30mph when HGVs making the same power have smaller back axles?
 
Maybe it's to do with the size of the rear wheels you need a bigger reduction gear due to the circumferance of the rear wheels.
 
You can maybe explain why farm tractors have a huge back axle, yet never go above 30mph when HGVs making the same power have smaller back axles?

Epicyclic reduction hubs to spread the torque and reduction away from the crown wheel so keeping it a manageble size for a truck application. Tractors tend to have more going on inside those casings. I have a tractor and know this. Anyhow, you have drawn me back in, it'll not happen again 😀
 
It’s immaterial how it’s done. And anyway those tractor epicyclics are there to handle the higher torque of low speed power.
Power = force x distance
In rotating machines power = torque x speed (rpm).
Keep power the same but reduce the speed and torque has to increase. Gears, hydraulics, electric drives - makes no difference it’s all basic physics.

Simples.
 


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