Drivetrain dilemma

Jun 5, 2017
42
2
40
Caerleon, S.Wales
#1
I've just finished re-building the e-bike ready for summer commuting. Part of the rebuild was an all new handlebar setup because I wanted stripped back, no clutter bars due to my old setup being very "busy". To achieve this I fitted new, wider bars with new grips and I removed the throttle, ignition key barrel and regen/kill switch. This enabled me to fit a trigger shifter under the bars in place of the old over bar SIS shifter along with the new SRAM Guide RE brakes, which are awesome by the way!

Anyway the point is that without a throttle, I now rely on PAS for power but I'm spinning out at 16-18mph due to the available gear ratios with the 1x7 setup. I'm stuck with the 7spd freewheel (Shimano MF-TZ21) threaded on to the hub motor so I have to address the chainring. I currently have a 38T raceface narrow wide ring fitted on the inside of the crank spider that originally held a 3x setup. This gives a perfect chainline and I have no chain retention issues.

Yesterday I ordered a blackspire 46T chainring and a new chain before realising a problem - the larger chainring will interfere with the chainstay if fitted on the inside of the crank spider so it will have to go on the outside which is going to push the chainline out by about 10mm (guess). This means quite a crossed up chain in the lower gears. Also, the new chainring is not narrow wide so I wonder if it will try to derail - at least it is not a ramped chainring, it's a 1x specific DH type. I'm using a 9spd chain and don't think I can go to a more flexible 10/11spd as they may be too thin for the old-school 7spd freewheel.

I "think" with the chainring fitted to the outside of the crank spider it will be positioned roughly between the original middle and big ring. I suspect I will spend most of my time on the bottom half of the freewheel which is OK, but there are some steep uphill standing starts on my commute due to cycle gates which are a pain and will require 1st gear and a high PAS level.

So I guess the question is, do we think a 9spd chain will drop off the chainring when on the larger rear gears, with a chainline 10mm out from perfect?
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
862
362
Basildon
#2
The problem with increasing the chainring size is that you raise the gearing in bottom gear too. Instead, you should fit a DNP freewheel with 11T top gear. It will inrease your spin out speed by around 30%, which you'll find much more realistic. It won't change your bottom gear.
https://www.ebay.co.uk/itm/DNP-Epoc...2f2eeb6f5d:g:1acAAOSwBCdcrgHO&redirect=mobile

Make sure you click the 7 speed version of this one.
https://www.aliexpress.com/item/Ori...e7-4296-8f7d-404af70104b7&transAbTest=ae803_3
 
Jun 5, 2017
42
2
40
Caerleon, S.Wales
#3
Well blow me, for all the searching for an 11T freewheel I did and gave up through not finding one! :) Thanks
 
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vfr400

Esteemed Pedelecer
Jun 12, 2011
862
362
Basildon
#4
The question of where to get 11T freewheels has been running ever since we had electric bikes. It's very rare that we ever lose sight of them.
 
Jun 5, 2017
42
2
40
Caerleon, S.Wales
#5
The question of where to get 11T freewheels has been running ever since we had electric bikes. It's very rare that we ever lose sight of them.
Understandable given the extra top speed that electric bikes afford us. Iv'e ordered a freewheel and arranged to return the new, yet to be delivered chainring and chain!
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
862
362
Basildon
#6
Last edited:
Jun 5, 2017
42
2
40
Caerleon, S.Wales
#7
Don't forget you need the tool to get the old one off. The tool needs to have a hole large enough to clear the axle. DNP tools work and are cheap, but last time I looked there weren't any on EBay. Try Aliexpress.
I see what you mean, I've had a look and there a few listed as being 14mm axle compatible, though none in the UK. I think I have a cassette tool at home, I'll check. If it just needs drilling out to clear the axle then I can do that at work.
 
Jun 5, 2017
42
2
40
Caerleon, S.Wales
#8
It looks like cassette and freewheel removal tools are two different things, is that right? I assume different spline configuration?

Either way they're cheap enough to pick up locally and run a 15mm bit through on the pillar drill.
 
Jun 5, 2017
42
2
40
Caerleon, S.Wales
#12
They're often hardened, so not easy to drill.
That's fine, I work in manufacturing and have a full workshop at my disposal with cobalt drill bits and a pillar drill, I'll find a way! If it can't be drilled I'll have my machinist make a new one from scratch :)
 

Woosh

Trade Member
May 19, 2012
10,067
2,337
Southend on Sea
wooshbikes.co.uk
#13
That's fine, I work in manufacturing and have a full workshop at my disposal with cobalt drill bits and a pillar drill, I'll find a way! If it can't be drilled I'll have my machinist make a new one from scratch :)
The DNP freewheel tool has thinner wall compared to a normal Shimano freewheel tool.
you don't need the DNP freewheel tool right away, only when you have to remove the DNP freewheel.
 
Jun 5, 2017
42
2
40
Caerleon, S.Wales
#14
The DNP freewheel tool has thinner wall compared to a normal Shimano freewheel tool.
you don't need the DNP freewheel tool right away, only when you have to remove the DNP freewheel.
So does that mean the DNP freewheel has a different ID or spline pattern to the Shimano?

I.e. If the shimano tool (drilled out) goes over the 14mm axle, why does the DNP version have a thinner wall?

EDIT: Think I answered my own question. Apparently the only thing different about the DNP tool is the larger centre bore allowing it to fit over hub motor axles. However, it looks like the park tools freewheel remover will fit too, based on this picture I found and is advertised as fitting DNP AND shimano freewheels.

Therefore a shimano tool drilled out (if required) should fit. The thing is, the website picture of the locally available tool doesn't show the centre bore, so it may well be large enough to start with.
 

Attachments

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RossG

Pedelecer
Feb 12, 2019
98
39
#15
Coincidently I've just replaced my freewheel with a DNP 11t. If you want to guarantee getting one you can go here...

https://www.ebay.co.uk/itm/153425869545?ViewItem=&item=153425869545

I did find I had to jiggle the derailleur slightly, although the gear block was the same width as the old one the whole set of cogs were positioned about 2mm further out towards the wheel bolts. In other words the block was 2mm further away from the motor when fitted in position. Not huge problem as the cog spacing is the same anyway.
 
Jun 5, 2017
42
2
40
Caerleon, S.Wales
#16
Coincidently I've just replaced my freewheel with a DNP 11t. If you want to guarantee getting one you can go here...

https://www.ebay.co.uk/itm/153425869545?ViewItem=&item=153425869545

I did find I had to jiggle the derailleur slightly, although the gear block was the same width as the old one the whole set of cogs were positioned about 2mm further out towards the wheel bolts. In other words the block was 2mm further away from the motor when fitted in position. Not huge problem as the cog spacing is the same anyway.
Cheers Ross, I already ordered one on a "buy it now" which has been dispatched already.

Interesting that the cogs sit further out as currently I have to REALLY fine tune the derailleur to prevent it rubbing on the hub motor in 1st gear, so this will help.
 
Jun 5, 2017
42
2
40
Caerleon, S.Wales
#20
I think a little confusion came from DNP selling an apparently specific one for their freewheel. Hopefully sorted now though, just have to wait for the 11T freewheel to arrive.
 

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