Higher Gear Sprocket??

[Green Machine]

I have just finished building my dream electric bike with much help from Illiad, Nick (Mr electric).

It has the bmc 1000 on a very high end downhill mountain bike set up with 6 inch of travel.

One small problem i am having is my highest gears are not high enough.

I have a shimano deore xt crankset and its highest geared ring is 44 teeth...which looks like a standard for mountain bikes.

Does anyone know how i can move up to a bigger ring on that crank and where i could find such a ring?

Or do i need to replace the crankset...and if i replace the crankset would a shimano roadbike crank work in its place (are shimano mountain bike cranks interchangeable with roadbike cranks)

Thanks for any advice anyone could offer.

 

[recumbent]

I had the same issue and the answer is easier than you might think. Simply go on line at http://www.hostelshoppe.com , they have front gear rings made by"Vuelta" USA which bolt to your exsisting crank, 10 minutes easy work.

I changed to internal gears ( Sram i-9) and my final drive choice in front was 48T sprocket, i threw the smaller front chainrings away because you actually don't need them anymore, and get extra valuable space on your handlebars for your throttle instead of the front derailer shifter. The chain rings cost about $26, all sizes available.
Remember that only a few teeth make huge difference. Good luck with youir build.

 

[dogman dan]

Most long travel FS mountianbikes don't have the clearance at the rear swingarm for much bigger than 48 teeth. I got lucky with my cheap wallmart bike and was able to use a MTB crank with a 56 tooth big ring bolted on. But on my current commuter, A giant with 6" rear suspension, I'm limited to 46 tooth that I have on it now. On that bike I have an 11 tooth rear sprocket that makes 30 mph pedaling comfy. So start by getting a smaller gear on the rear cluster, and then see how big a chainring you can fit on your bike before buying a 50 tooth or larger. In most cases a roadbike crank will not fit, since the whole frame is designed slimmer. The pedal itself may hit the swingarm if you try to use a road crank. But for sure you can buy a bigger ring, just make sure it won't rub, and that the front derailur can be move up enough to fit the new ring. 48 is likely to be the biggest you can go.

 

[Drunkskunk]

I got past the swing arm issue on my DH by running a wider crank spindle. I think it was a 129mm. That let me fit a 52 tooth with ease, although the derailer won't extend far enough to function like this.

 

[dogman dan]

I was going to do that, to run a road bike 52 tooth crank. Then I found the cheap wallbike allready had the biggest spindle I could find. However, how the crank sits on the spindle can vary from crank to crank. The one I put the 56 tooth sprocket onto happend to also be one that mounts so the big gear sticks out farther than the road bike crank. So bottom line, you have to just try stuff and see what works. With 11 tooth rear cogs, 48 tooth front gets you enough gears for 30 mph for sure.

 

[Green Machine]

Thanks for all the advice guys....

I found a 48 tooth ring that bolts on to my particular sprocket by talking to a mountain bike specialist and gears and sprockets an online mountain bike store.

He was able to look up my particular crank set and order just the right ring. He said 48 tooth was the maximum.

I would just love to install a time trial crank set (super high tooth range) on my bike but there is a big question whether it will work at all, and even if it did work it would involve changing lots of components on my bike, and i am not sure i need it.

48 tooth might work fine....i will report after i get it if it is enough.

Basically i want to just be able to pedal assist at 35 mph without loosing my shoes.

 

[deardancer3]

Dont forget the mention of getting an 11 tooth rear cluster.
With a 48 front that will take you to 30mph for 90 rpm at the crank.

http://www.sheldonbrown.com/gears/

 

[Drunkskunk]

Dont forget the mention of getting an 11 tooth rear cluster.
With a 48 front that will take you to 30mph for 90 rpm at the crank.

http://www.sheldonbrown.com/gears/

I dream of finding a 11-34 7sp Shimano Megarange freewheel cluster. Wish they still made them.

 

[Mark_A_W]

I used to run a 48t front ring. With an 11t rear it is fine until about 60kmh.

Now I have an adapter made by TPA here, and it allows me to fit a 5 bolt 56t to my 4 bolt mountain bike cranks.

I've never used the 11t gear with this setup, the 13t is good to well over 65kmh. I actually want a 34-13t seven speed freewheel.

 

[urace4me2]

Don't know the clearance issues with full suspension MTB but my hardtail Sedonna I swapped to a road crank and so I have a 53 ring on it. I have a 55 and 56 ring not being used right now. As long as I can slide the front deraileur up higher it will work, .... and lengthen the chain. The 53 - 12 is really enought though. If your running 48 volts I guess helping it along at 29 mph would be sweet with a 56. On 36 volt, (scared to fry my SLAs), above about 23 It's all me pedalling. Not good on a brushless direct drive. Too much drag.

 

[Green Machine]

Ok so i recieved the 48 tooth and bolted on today, and spent the evening blasting through golden gate park at around 35mph at 40 amps. My small gear is 13 freewheel, and i heard that is small as i can go with the hubmotor i have.

Although it is considerably better with the higher gear, it could be a lot higher for these speed to really give sum Umph in that pedal assist.

I have PMed TPA and he is sending me the adapter so that i can try a 56 tooth sprocket...

I will have to sacrifice the middle and lower ring of the front crankset but to me its worth it. The great thing is not only will i have a nice high gear, but also i can get rid of the front derailer, cable and shifter..so less clutter on the bike. The only big negative i see is that whenever i have a battery die or motor/controller failure...pedaling home will be much harder without the 27 speeds.

 

[dogman dan]

Sure you can't find an 11 tooth screw on 5 speed freewheel? Not even at Ebikes-ca?

 

[Green Machine]

Sure you can't find an 11 tooth screw on 5 speed freewheel? Not even at Ebikes-ca?

Your right...went to that site and couldnt find anything at first (navigation is a little confusing over there) but then did a search for freewheel andl like magic...they have a 7 speed freewheel and a 8 speed freewheel AND a 9 speed feewheel with 11 teeth. THanks for that piece of wisdom...I would have never found that on my own.

I want to try the 9 speed freewheel since i have a 9 speed shifter...i hope it fits and works with my oversized front sprocket...the range might be too wide (between my lowest gear and highest gear)...

Has anyone tried a 11 tooth gear with a bmc motor?

 

[dbackmtb]

Extreme
I also have the shimano deore xt crankset which is 22/32/44 teeth. You say you replaced the 44 with a 48t and it worked. Would it be possible to setup your crankset with the existing rings to 32/44/48 ?

 

[Mark_A_W]

Extreme
I also have the shimano deore xt crankset which is 22/32/44 teeth. You say you replaced the 44 with a 48t and it worked. Would it be possible to setup your crankset with the existing rings to 32/44/48 ?

22/44/48 would be possible.

The 22 uses a different BCD.

 

[Green Machine]

Extreme
I also have the shimano deore xt crankset which is 22/32/44 teeth. You say you replaced the 44 with a 48t and it worked. Would it be possible to setup your crankset with the existing rings to 32/44/48 ?

That is a very interesting idea..Mark said the 22 uses a different bcd..what is a bcd?

I would be interested in doing this if i could simply because the range of gears seems to be too great at 22/32/48...some gears are jankey.

 

[Mark_A_W]

Bolt Circle Diameter.


The granny gear bolts on the back of the crank - uses different holes.


You probably wouldn't be able to change from 22 to 44 smoothly anyway....that's a big jump.

 

[Green Machine]

Well i guess its ok anyway since i ride almost always in highest gear.

The only time i use anything lower than the highest gear is when the battery or motor has died....then i am pedaling home...and here in SF and not yet in great bike shape...those lower gears are a must

 

[Green Machine]

so got the 11 tooth freewheel from ebikes-ca

However when i hooked it up to the hub motor it didnt work..the chain doesnt seem to be the right thickness and so the chain gets caught in between the gears of the freewheel.

I just replaced my chain recently and it was like 40 bucks...darn.

I am going to take the freewheel to a bike shop tomorrow and see if i can get a chain that is compatible both with the new freewheel and the front sprocket.

I am afraid this rear freewheel was made for roadbikes or something.

 

[Mark_A_W]

What speed did you have before, and what do you have now?

7 and 8 speed chains are a different width to 9 speed chains. You'll also need to match the shifters to the freewheel.

 

[dogman dan]

If you have 8 or 9 speeds, the chain is really skinny, to pack in more gears into the same space. Usually the last two cogs on a casette are seperate. But screw ons are pretty much set as is. To run fat chain, your derailurs may be too narrow, argggh!

You are getting into some of the stuff that kept me riding that cheap mongoose another year. Once I had a bike that fit that 56 tooth sprocket, I was not wanting to lose that much.

 

[Green Machine]

I do have the converter from TPA to run a 56 tooth sprocket up front...i am not sure which 56 gear sprocket to run.

I probably have to take this stuff into a bike shop and have them help me figure it out.

It is getting complicated

 

[dbackmtb]

Which 11T did you get. Justin sells 3 models. I will be ordering his 9 spd 11t (40mm) to replace my existing 9 spd cassette and chain in case my 7spd 11-34 megarange doesn't work, though I believe either one will work.

 

[ErbiumYAG]

I just changed out the 44T chainring on mine. I had one hell of a time finding something larger than 48T with a 104 BCD bolt pattern; but by luck I finally came across this 52T in my bolt pattern. https://www.jrbicycles.com/storefront/index.php?act=viewProd&productId=2127 It matches up well with my 9C 2807. In the highest gear I can now add an additional 3 mph. With the 44T, I'd have to pedal like mad just to get an extra 1 mph.

 

[Mark_A_W]

I do have the converter from TPA to run a 56 tooth sprocket up front...i am not sure which 56 gear sprocket to run.

I probably have to take this stuff into a bike shop and have them help me figure it out.

It is getting complicated

Any 56t will work.

I thought your issue was at the other end?


You still didn't tell us how many speeds you are running at the rear, and what size chain you have.

If you went to 7 speeds at the rear, with a 9 speed chain, it probably would fall in between. You'd also need new shifters.