Can a cassette with gears withstand the abuse of a gas engine? Knowing a human can put a lot of pressure on there but shifting with and engine could be problematic I am thinking. What is the best answer from the forum? Sure would be easy to go a little faster etc. gphil
Quality bicycle components seem to be able to withstand the average 2-3hp output of many of the commonly used motors with little issue - but much depends on the exact components in question, their expected application & your experience & maintenance habits... so results vary somewhat depending, there is no "best" answer really, only what you may find best for you.
In my experience I've found while jackshafted cassette & derailleur systems do work - they're not any less prone to all their usual finicky behaviors for being motorized, they'll even pick up a few due to speeds & loads. This doesn't mean they shouldn't be considered, only that like everything there's a trade off. For the relative simplicity & inexpense of just using what your bike came with, it's not a bad first choice at all - but any missed shifts, speedshifting or skipping from maladjustment can fracture teeth from cogs & any excessive chain slack, binding links or excessively thick lubrication can cause the chain to snarl the rear derailleur on the return (slack) side, which usually results in a mangled derailleur.
I prefer aftermarket, new 3sp IGH (internal gear hubs) such as:
http://www.sturmey-archer.com/products/hubs/cid/3.html for their far less temperamental attitude - while you can ofc still destroy components through misuse (missed shifts, speedshifting), generally once set you've no longer any maintenance or adjustment concerns save chain lube, yet even if you manage to throw a chain for whatever reason, the hub itself remains undamaged.
No matter the system there's pretty much the one thing that shouldn't be done - shifting without backing off the throttle (speedshifting), provide ya refrain from that all should be well.
Insofar as the difference between having 3 & 6 or even 7 or more gears, I've found in this application it makes little difference & in fact prefer only the three as the stock cassette's gearing is so close you end up wanting to skip every other, essentially using it as a cumbersome three speed. Yes, this can be modified - but we're back to preference again lol
...& incidentally, shiftkits/jackshafts do not help you "go a little faster" if you mean absolute maximum possible top speed as if anything, the marginal amount of increased drag/friction of the additional bearings, chains & redirects
reduce the possible top speed. Provided the finals (ratio) works out the same, a direct drive will always have a somewhat faster maximum speed. What being able to shift provides is improved acceleration, improved hill climbing/cargo hauling ability & a lower possible cruise RPM for bettered efficiency & rider comfort (noise/vibration reduction).
For that, all of my gas bikes are shifters now & if you've any interest & some basic fabrication experience - ya outa search out some of the DIY jackshaft assemblies here as even if you don't build one it's interesting to see the alternatives & advances, if only for the next build or w/e
