Converting from 9-Speed Cassette to 7-Speed Freewheel

[joshseitz]

First-off, I'd like to confirm that it's NOT possible to run a 9-speed freewheel with a MAC geared motor in aluminum 135mm dropouts. If this IS possible, please explain.

Assuming it's not possible and would have to go to 7-speed, do I simply need to change the shifter to 7-speed, and adjust the upper and lower limits on the existing 9-speed derailleur, or do I need a 7-speed specific derailleur as well?

Additionally, can anyone recommend a quality 7-speed shifter (and derailleur, if required)? I generally prefer twist shifters as they can be moved over to the left side easily so as to dedicate my right hand to throttle duties.

 

[biohazardman]

There is a good chance than you can do the change over as you have outlined without the derailleur change. Shimano stuff will probly index correctly. Sram is another matter they have some Shimano compatible derailleurs and some that are Sram compatible only. I'm not sure about moving the seven speed shifter to the left side though possible it will need to be upside down and werq backwards if I am thinking correctly at the moment.
Since you live in Portland you might want to think about enclosing your throttle to get it out of the rain. You can install a throttle under the seat or in a rear bag and use a cable to actuate it. Remove your front derailleur shifter spring and use the twist shifter or a trigger shifter assembly as is, I have used both, for your throttle. Wet throttles have been linked to an involuntary full throttle situation on numerous occasion here on the forum. There are many ways of doing things so don't get stuck thinking it has to be one way or the other.

Used the twist shifter with spring removed on my first build for the throttle.
http://goldenmotor.com/SMF/index.php?PHPSESSID=bb306a693b5a231beb0c5633743b0d1d&topic=279.msg3408#msg3408

Used the trigger shifter stock on the second.
http://endless-sphere.com/forums/viewtopic.php?f=5&t=33122#p481301

I have used the cheap Shimano and Sram twist shifters both werq fine.

 

[joshseitz]

Thanks Biohazardman. I've seen your remote throttle before and considered as a possible solution. I also like the idea of using a shifter (or perhaps an ATV throttle) to drive the pot.

I'm also considering a more substantial throttle like the Magura or AWI: http://www.electricscooterparts.com/throttles5kohm.html
I haven't yet wrapped my head around using a 5K ohm throttle with a standard controller. That will be another post entirely.

And I have reversed (inverted) twist shifters to use them on the left side, and I was accustomed to it in no time.

To be sure, there is no chance of retaining a 9-speed cluster (obviously I'd have to use a freewheel instead of the original cassette) in a standard 135mm dropout, right?

 

[d8veh]

Te worst thing about going from a cassette to a free-wheel gear-set is the change from 11T to 14T top gear, which makes it difficult to pedal comfortably past 15mph. DNP do a free-wheel with 11T top gear, which you can get from Ebikes.ca. I've squeezed in an 8 speed before with a short spacer on the axle.

I've done what you want about five or six times, and never had to change the derailleur or changers. Normally, it's just a case of re-setting the end-stops on the derailleur. You have to bear in mind that you'll be in top gear most of the time, and you'll hardly ever have to go down to the lower gears, so if the indexing isn't exactly right, it's not much of a problem as long as the top three are good.

 

[dogman dan]

Once you have a 7 speed freewheel on the rear motor, you will very likely have to replace the shifters. They won't index right on the wider spaced gears of the 7 speed freewheel. But like said above, if you don't shift, no big deal. On a street ride, top gear may be all you ever need.

It's possible you might be able to use the same chain, If so, you won't run into wider chain being tight going through the derailleurs. Maybe the chain wears a bit faster if it's narrow for the freewheel, but no big deal really as long as it will sit all the way onto the gear.

The derailleurs will need the stops adjusted, but should work fine.

I have found converting 8 speed to 7 can work ok. But it still indexes well on only about 5 of the gears. Generally you pick your high gears, and let it clack if you put it on the big rear gear. If you need that gear, a quick twist on the shifter can get it lined up.

The quick fix is to just get a non indexing, old school lever shifter. I did that on my cargo bike, which seldom shifts. Easy to index that to top gear, and then it's just fine tune it for other gears. I grew up with that kind of shifter, so I do it with no thought at all.

But on the dirt bike, I do shift a lot, and do like a trigger shifter that indexes good.

 

[joshseitz]

So to be sure, 8-speed and 9-speed freewheel clusters (or cassettes for that matter) are the same overall width, though the 9-speed is more closely spaced together and uses a narrower chain, right?

So if I can squeeze an 8-speed onto a MAC on a 135mm dropout (by addubg spacers on the axle), I could just as easily swap to a 9-speed freewheel (like the 11T DNP from CellMan) and continue with 9-speed shifters and derailleurs correct?

Where do the spacers go on the axle, and are they effectively used to widen a 135mm dropout. If so, I wouldn't think that aluminum full-suspension chainstays would permit much flex?

Any simple diagrams to illustrate spacer/washer sequence?

thanks!

 

[vptech]

I just installed the 11T DNP from CellMan on my aluminum with 135 drop outs. Works perfect with a washer on inside and then the usual outside of the drop outs. Only needed the slightest adjustment on the derailer. It is a tight fit but not a stretch. The new E-brake lever didn't work with my shifter but I just flipped the shifter upside down and all is perfect.

 

[d8veh]

The spacer or washer needs to be 12mm inside diameter and 20mm outside diameter. You can sometimes find them like that otherwise you have to file out a standard 10mm washer or file down a 12mm one. All this assumes that your motor has a 12mm axle.

Did you coonsider getting a cassette motor that would save all this hassle? Which motor do you want to fit?

 

[joshseitz]

Did you coonsider getting a cassette motor that would save all this hassle? Which motor do you want to fit?

I do think a cassette motor would be ideal, but it seems that most are of the lighter-duty variety. I'm of robust build and plan on supplying a delivering a fair amount of power (60V 20-25A), so I figured a 10T MAC would work well for me since they're pretty heavy-duty for a gear motor, right?

Are there any comparable gear motors to the MAC/BMC that accept cassettes? Thanks.

 

[docnjoj]

I'm also considering a more substantial throttle like the Magura or AWI: http://www.electricscooterparts.com/throttles5kohm.html
I haven't yet wrapped my head around using a 5K ohm throttle with a standard controller. That will be another post entirely.

How do you ground one of these throttles?
otherDoc