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Old 05-01-2018, 07:23 PM   #39 (permalink)
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Originally Posted by ASV View Post
I had read the study a number of years ago

a chain starts off with fantastic numbers at lower speeds and power levels
but the friction builds fast as power goes up

with a conventional motorcycle belt you start with crummy numbers
from the needed high pre tension
but it never really gets much worse even if you pour on the power

yeah that's why I prefer a microv belt, with as little as 10 pounds it becomes self locking
and it still has the self leveling friction curve but has far better power consumption at low power levels
this is what makes it a favorite with car designers
This is not really correct.
A chain starts out with little friction, and does increase in friction the higher your speeds go.
But the same is also true for a CVT belt.
It starts out with higher friction, but then it'll switch to where the belt occupies both the driven and driving pulley on the same diameter.
This is where the belt is performing at it's peak efficiency, because it's bending diameter is the largest on both ends.
When you accelerate further the driving pulley's grip will have a larger radius, and the driven pulley will have a smaller radius, at which most of the heat transfer happens in the driven pulley.
And one of the ways you know a chain is more efficient than a belt, is because a chain will always be cooler than a belt.
A chain also rotates slower than a belt, and is longer, but even if not, it just doesn't have the slippage a belt has. And the higher the speed, the higher the forces, the higher the heat dissipation, and the higher the heat, the more the belt will slip (a quality of rubber, unfortunately).

Anyway, it just comes down to a belt has a lower low speed efficiency than a chain, medium or comparable mid speed efficiency, and a MUCH lower, high speed efficiency than a chain.
And the higher the speed, the more a CVT with rubber belt loses out to a chain.

Modern cvts don't have belts, but also are based on chains, or metal belts that have metal parts as belt (not rubber). They not only are more efficient, but more durable as well.
They're also a lot more costly (about 10-15x more costly).
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