single speed freewheel on long axle

[izeman]

what would be the best way to install a single speed freewheel on a 9c axle? i'd like to use the smallest available.

what freewheels do i need?
do single speed freewheels have different threads? are those BSA (1.37 x 24) as well?
where on the axle (left/right side) would i install it? should i use spacers, or just screw it on till it fits?

 

[izeman]

would this one be ok?
http://www.ebay.de/itm/Shimano-Freewheel-SF-MX30-18T-BMX-Single-Speed-NEW-/120825795491?pt=Cycling_Parts_Accessories&hash=item1c21c753a3#ht_500wt_1287

 

[neptronix]

Smallest one you can find is 16T.

Good for pedaling at 10mph when you add in the fact that you have to use the inner or middle chain ring, lest you have a rediculous chain angle.

So yeah, i hope you aren't looking to pedal any.

 

[izeman]

thanks. i try to see what the biggest front chain ring is that will fit. i don't think about gears. with my 26" mtb with puma/bmc motor i just switch between middle and large chain ring. middle one to launch and big one for cycling. i never thought that low gears could become soooo useless.

 

[neptronix]

I fit a 40T in my middle chain ring on the mid 2000's Treks, and even that had some notable angle, but not too bad. I think the pedal speed was about 12mph.

 

[izeman]

I fit a 40T in my middle chain ring on the mid 2000's Treks, and even that had some notable angle, but not too bad. I think the pedal speed was about 12mph.

i'm not sure i understand what you want to tell me. as i'm planning to install a bmx-like gearing (so only 1 gear) i can shift the rear freewheel to whatever position i like. i'm just not sure if this could be a problem for the long axle (as shown in the picure above. normally you screw a 5/6/7/8 gear pack on the axle. this is one stiff unit. i want to install some washer (or better tube) and position the freewheel where it fits best. will this put some unwanted tress on the axle ?

 

[izeman]

i just try to calculate:

50 teeth front
16 teeth rear
80 rpm at the crank

= 250 rpm at the wheel

1 rotation of a 20" wheel is about 1.5m

= 22.5 km/h or 13.5 mi/h

that's really slow. whereas 50/12 on a 26" gives you 40 km/h or 24 mi/h

 

[Alan B]

There are two sizes of threads for freewheels. The usual inch measurement one, and a smaller metric thread on some BMX hubs for smaller freewheels. Single speed freewheels below 16 teeth are generally using this metric thread and won't fit a hubmotor.

The standard thread single speed freewheels generally don't go below 16 teeth. There are a couple of exceptions that get lower, but they have reliability problems. So 16 is probably the size to use.

Some folks use a two speed crankset to solve this problem. One example is the Schlumpf speed drive crank with 1:1 and 1.6:1 rates. So this helps a lot since it makes the front chainring effectively 60% larger. So you can set it up with two speeds, one for pedaling with no motor, and one for pedalong along with the motor.

Schlumpf has a high speed drive crank that is 1:1 and 2.5:1. This is perhaps the best choice. These units are pricey. There are a couple of other manufacturers of internally geared multispeed cranks. Schlumpf has licensed a lower cost unit from Taiwan as well.

These multispeed cranks generally have a planetary gear and clutch arrangement in the bottom bracket and in the core of the chainring. Some shift by tapping a button on either side in the end of the crank at the bottom bracket, others have some other type of shifting.

 

[izeman]

... This is perhaps the best choice. These units are pricey ...

pricey is least to say schlumpf is swiss, and they adjust their prices to swiss watches *ggg*
no joking - those are wonderful mechanical parts, but out of my price range.

 

[cwah]

I'm interested too on the single speed problem. It's very difficult to find information around that.

 

[Alan B]

The Taiwan version of the Schlumpf was a lot lower in price. It has the 1.6x ratio and takes a standard chainring.

 

[izeman]

The Taiwan version of the Schlumpf was a lot lower in price. It has the 1.6x ratio and takes a standard chainring.

do you maybe got a source for that? i can't find it googling for "taiwan schlumpf" or similar doesn't show any results.
thx

 

[Paul_G]

Smallest one you can find is 16T.

Good for pedaling at 10mph when you add in the fact that you have to use the inner or middle chain ring, lest you have a rediculous chain angle.

So yeah, i hope you aren't looking to pedal any.

I found a 15 tooth freewheel that will fit my Bomber. It’s a 15T AC Racing 888 and uses a shimano bottom bracket tool to remove it that has a hole of 1” so it will fit right over the shaft. AC has found a way to place the pawls outboard, making a 15 tooth viable.

http://www.planetbmx.com/shop/bike-components-parts/freewheels/ac-15-tooth-888-freewheel-fits-all-skyway-wheels-/prod_305.html

Removal tool for the 15T http://www.amazon.com/gp/product/images/B002V16050/ref=dp_otherviews_1_MAIN?ie=UTF8&s=sporting-goods&img=MAIN&color_name=x

Now all I need is a BMX type remover for the 16T that came with the bike and I can see if it fits as advertised.....so its untested as yet

 

[dogman dan]

I understand losing the derailur, but why not just use a regular 7 speed cluster, put it on the 11 tooth gear, chuck the derailur and run it single speed like that. Those unused gears that ugly? This also lines up your chain with a 48t large chainring.

Or is it a fixie frame, where you have a 110 mm dropout? Then you'd be using a 16t screw on freewheel. In that case, you'd need to cut the axle shoulder deeper, since the 9c motor has it's axle shoulder at 135 mm. then you'd need a honking stack of washers on the outside of the dropout , unless you got it threaded deeper. Or build a pinch dropout for that side.

 

[Brentis]

I understand losing the derailur, but why not just use a regualr 7 speed cluster, put it on the 11 tooth gear, chuck the derailur and run it single speed like that. Those unused gears that ugly?
...

+1

This is exactly what I did on my "Ghetto" build.(see sig.)
I mostly pedal when the motor slows more than 10% (up steep hills/trails).
Running a 3 ring front & a 7 spd 32-11 tooth freewheel, I removed front & rear derailleurs,
effectively making my bike a Single speed. 48t-11t.
The 7 spd freewheel kept chain line nice a straight on the largest ring.
It still had OK alignment on the second ring, so keeping it a 2 spd is possible.
I tried single speed freewheel but the spacing issue/chain alignment
as well as the metric threading prevented it.

Good luck

 

[izeman]

Or is it a fixie frame, where you have a 110 mm dropout? Then you'd be using a 16t screw on freewheel. In that case, you'd need to cut the axle shoulder deeper, since the 9c motor has it's axle shoulder at 135 mm. then you'd need a honking stack of washers on the outside of the dropout , unless you got it threaded deeper. Or build a pinch dropout for that side.

i wanted to make a notice on my "to think about list" while "engineering" that bike and putting parts together.
i want to install the 9c in a felt sector pro

as i have no experience with bmx bkes (and haven't bought the bike yet) i didn't think about bmx's shorter axles. those are NOT 135mm, are they?
so i may have to put the axle in the lathe and cut some cm/mm off? but then it will be out of center.

any ideas?

 

[dogman dan]

Since you are using a rim brake, you may be able to cut some meat off each side and keep the wheel centered. Dishing it much is not the way to go.

And yep, you are stuck with 16 teeth. Not a 135 because it was never designed for a big cluster of gears. On the other hand, put much volts in there, and Ypedal? My dirt bike for example, on a typical ride, I never try to pedal till I'm going less than 5 mph up some wall. So it stays more or less permanently in the lowest gears.

 

[izeman]

... Or build a pinch dropout for that side.

what do you mean by that? i'm no native english speaker and don't know that term? any pictures?

 

[izeman]

Since you are using a rim brake, you may be able to cut some meat off each side and keep the wheel centered. Dishing it much is not the way to go

this shall be DISC modded. with a suspension fork and maybe magura gustav m brakes which are said to fit a 9c.
i will have to weld/solder brake mounts to the frame. no problem tough.
btw: dishing with a radial spokes setup is not that easy anyway when spokes are only 60mm long

 

[izeman]

... On the other hand, put much volts in there, and Ypedal? My dirt bike for example, on a typical ride, I never try to pedal till I'm going less than 5 mph up some wall. So it stays more or less permanently in the lowest gears.

you are right. i calculated possible speed with pedalling in another thread. 50/16 teeth and 80rpm give 13mi/h or 22km/h.
i'm planning a 18s or 24s setup with a 9s 2805. so i MAY not be able to pedal along *ggg* but riding a bike w/o pedalling feels unnatural to me, so i might just pretend to pedal

 

[Alan B]

The singlespeed freewheels below 16 teeth either have poor reputations or are the wrong thread.

Hope yours works out.

 

[izeman]

The singlespeed freewheels below 16 teeth either have poor reputations or are the wrong thread.

i'll stick with 16t anyway. doesn't make that much of a difference if a maybe take a 15t. and afaik there is nothing like a 11t (which would give me 32km/h pedalling) with right thread anyway.

 

[dogman dan]

Sorry, a pinch dropout grabs the axle by the flats so no nut is needed.

Other examples in dropout threads and torque arm threads. Here is my version. The purpose in this case is to controll torque better than an oval hole, by tightly pinching the axle flats so they can't rotate. With enough power, you can still twist an axle though.

Thinking about it, you'd still need to cut the axles flat part further in anyway, if you are moving the axle over that far.

It's not going to be real easy to do if your dropouts are that close together. You might be able to bend an aluminum frame wider some, but the best thing might be to start looking at steel frames you can fool around with eaiser. Bend em, weld em, all much easier with steel. Then you can go to the 7 speed gear, 11 tooth, and use a larger front chainring with the smaller cogs taken off.

 

[izeman]

thanks for explanation!

i'd like to go with a steel frame, but those are hard to find. and if you find one, all parts else are crap, and exchanging them for good ones will cost more than a new alu bike.

if i add rims, hubs, brakes, saddle, handle bar, etc ... it's 400.- easily.

 

[izeman]

i just checked one of justin's pic of the rear 9c motor and did some photoshop work (as i don't have the original motor to do some measuring)
if i want to use it in a bmx frame w/o bending the frame the axle has to be shortened to 110mm. but only on one side, because otherwise the disc brake will not fit - it maybe possible to move the hole brake a bit to the left as i will have to weld brake mounts to the frame by myself.

so here comes the question: i tried to figure out where the rim has to be to be in line with the middle of the axle - yellow line-dotted line. is it possible to install the rim that way? or will it fail at the rim is too far one the left side?