Quote:
Originally Posted by coops
I meant to ask this when you did the Q bike flecc: how difficult is it to bend & reshape the frame i.e. the rear stays for these projects? How much care is needed? I read somewhere that aluminium frames should not be "spaced" i.e. stretched/bent as they are weaker than alloy (flecc-note:think you mean steel here) frames for that: is that not true, or must it be done judiciously and by an experienced metalworker?
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It's not true that alloy frames can't be bent Stuart, but alloy tubing can fail very suddenly, instead of giving way gradually as with steel. It's a matter of "feel" and experience, and I doubt it's possible to teach or learn quickly. Working with various materials over years gradually gives the experience necessary. The best guidance is first to try the expansion by hand and "read" from the feedback feel of the strain on the metal. Here's an example of me demonstrating a tube change method without wheel removal on an alloy frame Twist, the "fightback" of the frame telling me how far I can go:
Quote:
Originally Posted by coops
Also, would it be easier or harder to mount a front hub motor in suspension forks? Can over-wide front suspension forks be had for the purpose? Or better to just rear-mount for comfort, traction etc. and accept some possible gearing compromise (currently I have a 7-speed freehub with 3 front chainwheels...).
Stuart.
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A rear mount motor is easier if you can have one complete with freewheel thread. Although multi sprocket freewheels are undoubtedly weaker than cassettes, too much can be made of this for electric bikes. The fact that the bike is assisted means that the derailleur will be doing much less work than if it was on an unassisted bike, and that's why I'm quite happy to use freeewheels on my two project bikes.
There need be no gearing compromise. Whatever you do don't keep that excessive number of gears on an electric. Yes, you do need a reasonably good gear
range, but an e-bike absolutely does not need a large number of gears due to the gear-gap bridging power of the motor. Some like Powabyke offer 24 speed setups, but that's just to give a good range with a cassette system, that number of gears being quite ridiculous. I view that as poor design.
An illustration is my Torq that was. Even in my very hilly area I only ever used about four of the eight gears, constantly skating backwards and forwards across the intermediate ones, barely pedalling on them. It's a relief to have the 5 + 1 megarange system now on both Q and T bikes. Even in that system only the top three gears are used most of the time, four at most usually. The megarange first gear large sprocket is only a "get home up a hill with flat battery" gear usually, just occasionally used on a really tough hill like a 1 in 5. Likewise the second gear mainly for a difficult hill like 1 in 6 typically. With a motor assisting, the upper three are enough for nearly all our roads.
There isn't a big choice of multi freewheels, and they are only from Shimano. These are the current range:
Cadet: seven speed, 14 to 24 teeth, 179%
Cadet: five speed, 14 to 24 teeth, 179% range
Cadet: six speed, 13 to 34 teeth, 262% Megarange
HG.50: seven speed, 11 to 34 teeth, 309% Megarange
Dismiss the first as you need a bigger range and an e-bike doesn't need such close spaced gears.
The second also has too small a range.
The third is the second one but with it's 14 tooth sprocket changed to a 13 and a large 34 tooth on the back. This is my favourite for e-bikes.
These three are all a budget series as the Cadet name implies. The fourth one uses the sprockets of the third, plus an 11 tooth on the front. Because that's so far out from the inside bearings of the freewheel, it has to have a stronger bearing centre section, so the usual price is £19.99 instead of £9.99 for each of the others. Again I'd question if seven gears are really needed.
The official reason for having many sprocket gears is that the narrower the gap between the number of teeth on adjacent sprockets, the slicker the change, and that's true for Campagnolo and SRAM derailleurs.
But it's not true for Shimano, who use methods that enable smooth wider gap changes. There are three methods.
The first is that Shimano sprockets are shallow, the teeth cut off short so it's much easier for the chain to move off sideways. This also has the disadvantage of higher wear, but Shimano don't mind you having to buy replacements!
The second method is tooth staggering, intermittent teeth bent sideways out of line. This creates more gear noise, but it does give intermittent better chances for the chain to leave or enter as the teeth pass.
The third method is by indenting the sprocket sides with ramp indentations. These engage with the link rivet ends and help carry the chain upwards as the sprocket slips past the chain after it leaves the preceding sprocket, and this in particular is how a chain can change slickly, even direct from a 24 tooth to a 34 tooth sprocket.
The rest of the secret is just keeping it correctly adjusted.
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but this aspect has so far been an obstacle to progress because all good powered hub motors won't fit standard dropout sizes.
also its quite light really...
sorry 'bout that: very good point the advantage of fewer gears, but good range, as you say, with the motor assist - thanks.
if necessary... I'll take full responsibility, don't worry 
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