brake mods to change from 26" to 24" wheel?

Chalo wrote:
bob mcree wrote:

i could increase my battery weight from 30 to 40 pounds to go from
36V to 48V but all that extra battery wouldn't let me go any further,
just faster. if i can't get going 25 mph or so because of hills, the
extra battery would buy me almost nothing.


Speaking of almost nothing: I think that's what you will get for your
trouble if you switch from a 26" wheel to a 24" wheel. You will need a
bigger change in wheel diameter to get a significant improvement in
efficiency and mechanical advantage.

you're right of course. the 26 to 24 switch will only increase RPM by
less than 10%. that might be enough to make a difference but it might be
a lot of work for not much gain. i just didn't imagine putting a smaller
wheel on. a 20" would increase by almost 25% and that would be
significant. it would lower my top speed by 25% too, and that might be a
real problem. that would take me down to 15 mph or so max motor assisted
speed.

I'll look into the forks you mentioned.

Something like this would allow you to use pretty much any wheel size
you chose. Mounting a front brake would be another matter.

well, i need a front brake... using the motor for braking just isn't
good enough.

Chalo Colina

bob mcree wrote:
Chalo wrote:
bob mcree wrote:

i could increase my battery weight from 30 to 40 pounds to go from
36V to 48V but all that extra battery wouldn't let me go any further,
just faster. if i can't get going 25 mph or so because of hills, the
extra battery would buy me almost nothing.


Speaking of almost nothing: I think that's what you will get for your
trouble if you switch from a 26" wheel to a 24" wheel. You will need a
bigger change in wheel diameter to get a significant improvement in
efficiency and mechanical advantage.

you're right of course. the 26 to 24 switch will only increase RPM by
less than 10%. that might be enough to make a difference but it might be
a lot of work for not much gain. i just didn't imagine putting a smaller
wheel on. a 20" would increase by almost 25% and that would be
significant. it would lower my top speed by 25% too, and that might be a
real problem. that would take me down to 15 mph or so max motor assisted
speed.

I'll look into the forks you mentioned.

Something like this would allow you to use pretty much any wheel size
you chose. Mounting a front brake would be another matter.

well, i need a front brake... using the motor for braking just isn't
good enough.

The 20" wheel thing might also work with a new fork with disc tabs
that's either 29'erish, suspension corrected, or a suspension fork.
Then you could run a front disc brake. I haven't thought about it much
but you could probably get the geometry in the right ballpark with the
right 20" size and tire size, as there's a lot of room between 406's
with the smallest tires you can get for them and 451's with the
largest. I'm not sure how the rake and trail on this would work out.
Also don't know what kind of headtube and headset your bike has, but if
it's 1" threaded then this will be a pain.

wrote:

do one metric, one...

so, like, one and change in american?

bob mcree wrote:

i just didn't imagine putting a smaller
wheel on. a 20" would increase by almost 25% and that would be
significant. it would lower my top speed by 25% too, and that might be a
real problem. that would take me down to 15 mph or so max motor assisted
speed.

Remember you'll have more thrust available; that will allow the motor
to spin up to a higher RPM and your top speed may not fall much.

I'll look into the forks you mentioned.

Something like this would allow you to use pretty much any wheel size
you chose. Mounting a front brake would be another matter.

well, i need a front brake... using the motor for braking just isn't
good enough.

If you have an unusually good bike shop in your area, you could have
cantilever studs brazed onto a fork like that. If you are on friendly
terms with a machinist, you could persuade him to make you a clamp-on
fork bridge that you could use to mount a caliper brake, which you
could slide up or down to get a perfect fit with whatever wheel.

Chalo Colina

If you have an unusually good bike shop in your area, you could have
cantilever studs brazed onto a fork like that.

thanks for the advice. a disc brake is impossible because the hub motor
takes up all the space between the forks. i am going to ask my welder
friend about putting on some different mounts...

-bob

bob mcree wrote:
Hi, for reasons of getting higher RPM for better performance of my hub
motor, i'm considering changing the front wheel on my old TREK 950 from
the stock 26" to 24". Can I get center pull brakes that will attach to
the stock braze-ons with longer arms for the smaller wheel? thanks...

Probably not but you can certainly move the brazed on brake
posts to the proper location.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

On Sat, 21 Jan 2006 04:15:19 GMT, bob mcree
wrote:

bob mcree wrote:
there's an interesting phenomenon that has been empirically shown to be
true in general; that increasing the voltage on an ebike will give you a
faster top speed but will not increase your range. this seems
counter-intuitive but it has been demonstrated to be true time after
time. i could increase my battery weight from 30 to 40 pounds to go from
36V to 48V but all that extra battery wouldn't let me go any further,
just faster. if i can't get going 25 mph or so because of hills, the
extra battery would buy me almost nothing. -bob


I could be wrong, but it seems to me that range on an ebike will be
proportional to battery capacity (Amp-hour rating) while top speed
will be proportional to voltage. This is for a similar current draw
at each voltage, of course, which may not be a very good assumption.

Does this fit with your experience?

Dave wrote:
On Sat, 21 Jan 2006 04:15:19 GMT, bob mcree
wrote:


bob mcree wrote:

there's an interesting phenomenon that has been empirically shown to be
true in general; that increasing the voltage on an ebike will give you a
faster top speed but will not increase your range. this seems
counter-intuitive but it has been demonstrated to be true time after
time. i could increase my battery weight from 30 to 40 pounds to go from
36V to 48V but all that extra battery wouldn't let me go any further,
just faster. if i can't get going 25 mph or so because of hills, the
extra battery would buy me almost nothing. -bob



I could be wrong, but it seems to me that range on an ebike will be
proportional to battery capacity (Amp-hour rating) while top speed
will be proportional to voltage. This is for a similar current draw
at each voltage, of course, which may not be a very good assumption.

Does this fit with your experience?


every motor has an RPM at which it runs most efficiently. the motor may
not have enough power to reach that RPM if the gearing is too high.
reducing the wheel diameter would let my motor run at a speed where
it runs more efficiently. yes more voltage gives you more speed but
different motors run most efficiently at different speeds depending
on the gearing/wheel diameter.

-bob