Just looking for some advice please.

[mmcc81]

Hi all,

Firstly thanks in advance for any responses to this post, I really do appreciate all replies.

I'm hoping to get some advice one wether it's possible to fit a rear hub motor to a bike the has a 12 gear cassette.

I really want to fit a 750w or 1000w rear hub to my cube acid 2022 XXL but I'm not sure if have enough space to fit either with a 12 speed cassette.

If anyone has any advice or experience fitting either of the hub sizes to a bike the the 12 gear I'd love to hear back from you.

Many thanks in advance.

M

 

[saneagle]

Everything good on your bike will be wasted when you fit such a motor, especially the gears. 12 speed gears would just be a liability when you'll keep needing to shift three at a time. If you need that sort of power and weight, you'd be much better off getting a steel framed 7-speed £60 catalogue bike off Facebook ads to convert and keeping your Cube as it is, or sell it. Apart from the steel frame, the only other important thing is disc brakes, which you must convert to hydraulic.

Other considerations are the very small chainwheel means that you won't be able to pedal fast enough, and there's probably not enough clearance to increase it by much, and you'd have to use some creativity to find a way to fit a pedal sensor.

An experienced converter could probably do something with it, but it's a long way from ideal for a first attempt. Forget about one of those big heavy 1000w direct drive motors. I can guarantee that you won't like the results.

Why do you want to do this conversion and what are you expecting to do with the bike afterwards?

 

[Peter.Bridge]

I was thinking of a donor bike for my next rear hub conversion

Does this seem a reasonable list for minimum faff ?

1) 6-8 cassette / freewheel gears
2) hydraulic disc brakes
3) Square taper bottom bracket with 5mm gap for left hand side PAS sensor
4) Space to fit downtube battery on frame

 

[Woosh]

... and LCD only, no throttle! Keep the wiring neat and tidy.

 

[Bikes4two]

..... and unless you particularly want it, don't bother with front suspension - the bike will be heavy enough with the motor and battery, let alone the weight of some cheepo suspension that probably achieves less than wide tyres run at a lowish pressure.

So that means a frame that can accept wide tyres if you need them that is.

 

[Cadence]

I was thinking of a donor bike for my next rear hub conversion

Does this seem a reasonable list for minimum faff ?

1) 6-8 cassette / freewheel gears
2) hydraulic disc brakes
3) Square taper bottom bracket with 5mm gap for left hand side PAS sensor
4) Space to fit downtube battery on frame

I wouldn't necessarily rule out V-brakes. My 1992 Giant steel framed MTB (no suspension and nice curved steel forks) cost me the princely sum of £35.00 on ebay. Yes, I've spent a bit on it (chain, bottom bracket and freewheel), but after swapping the cantilever brakes for some good second hand Tektro V-brakes with new BBB Tristop pads it manages to stop quickly enough at 20mph with my 350w. rear hub kit fitted.
The gears are 3 x 7 with 48-38-28t chainset and 14-28t freewheel. With road-orientated tyres, mudguards, rear rack and a decent rear propstand it is more of a touring bike and no lightweight, but still quite agile on 26" wheels. If I wanted to reduce the weight at all, I'd probably ditch the triple chainset as I'm mostly only using the big ring, but it is my "insurance policy" to get me home if the lecky bits fail - something I hope will never happen!

 

[Woosh]

Additional problem with v brakes is rapid wear of the braking surface on the rim. This is made worse if you have a rear hub, the increased inertia eats the rim in about 2,000 miles.

 

[Cadence]

Additional problem with v brakes is rapid wear of the braking surface on the rim. This is made worse if you have a rear hub, the increased inertia eats the rim in about 2,000 miles.

I'm sure you are right, but I suppose it really depends on what you use your bike for and how much heavy braking you do. Following the advice of the late, great Sheldon Brown I do most of my braking with the front brake.
Braking and Turning Your Bicycle (sheldonbrown.com)
I grew up with caliper brakes, short rubber pads (or "blocks" as they were called then) and chromed-steel rims. Emergency stops in the wet were definately "character forming"!

 

[Bikes4two]

Additional problem with v brakes is rapid wear of the braking surface on the rim. This is made worse if you have a rear hub, the increased inertia eats the rim in about 2,000 miles.

That's an interesting comment about rim wear and I'm suprised that this is the case (but I'm certainly not doubting what you say given your day job ).

When you say 'increased inertia' is this something above and beyond just the weight/mass of a hub motor?

I've done many thousands of miles on fully loaded tourers using rim brakes (including Maguras on our tandem) and rim wear has never been an issue - have I been lucky with my choice of rims our is there some other physical phenominom with hub motors here?

Oh yes, and I am very confident with my Deore V-brakes on my 20Kg mid motor conversion (plus my 90Kg fat ass of course!).

There's no doubt though that nicely modulated hydraulic brakes are very nice if the donor frame has the fixing points and the wallet is suitably equiped.

Personally I'd put the ideal frame with v-brakes ahead of a less than ideal frame with hydraulic brakes - choices choices!

 

[saneagle]

I was thinking of a donor bike for my next rear hub conversion

Does this seem a reasonable list for minimum faff ?

1) 6-8 cassette / freewheel gears
2) hydraulic disc brakes
3) Square taper bottom bracket with 5mm gap for left hand side PAS sensor
4) Space to fit downtube battery on frame

You don't need hydraulic disc brakes on the donor bike. Cable ones are OK, but as part of the conversion, you should change them to Hydraulics, which is a 10 minute job and costs about £40 if you get used ones. Bikes already fitted withhydraulic brakes will be a lot more expensive and tend to have other expensive and inconvenient parts, but something like a 2010 Carrera Kracken has them, like this build. There were no downtube batteries in those days:

New build Carrera Kracken conversion.

Here are a couple of photo's of my new build which I have had a lot of help from D8veh. I am waiting for some parts, but as you can see it is starting to take shape. This is going to be a really good hill climber, and extremely stealthy. The rack was made using some round aluminium rod which...

www.pedelecs.co.uk

 

[Woosh]

When you say 'increased inertia' is this something above and beyond just the weight/mass of a hub motor?

I have seen a few damaged rims where both front and rear brakes are V-brakes.
This does not happen when the front is disc and rear is V-brakes or when the motor is a crank drive.

 

[saneagle]

That's an interesting comment about rim wear and I'm suprised that this is the case (but I'm certainly not doubting what you say given your day job ).

When you say 'increased inertia' is this something above and beyond just the weight/mass of a hub motor?

I've done many thousands of miles on fully loaded tourers using rim brakes (including Maguras on our tandem) and rim wear has never been an issue - have I been lucky with my choice of rims our is there some other physical phenominom with hub motors here?

Oh yes, and I am very confident with my Deore V-brakes on my 20Kg mid motor conversion (plus my 90Kg fat ass of course!).

There's no doubt though that nicely modulated hydraulic brakes are very nice if the donor frame has the fixing points and the wallet is suitably equiped.

Personally I'd put the ideal frame with v-brakes ahead of a less than ideal frame with hydraulic brakes - choices choices!

When moving on a bike, your energy is proportional to the square of your speed, so if you go twice as fast, you have four times the energy that needs to be disipated to stop. The average speed of an unassisted bike is about 10 mph for which rim brakes might be fine, but if you were to fit a motor and travel at 20 mph, you'd need 4 sets of rim brakes on each wheel to stop equally as quickly.

Your mass would increase by about 10% when fitting a kit, but energy is directly proportional to mass, so the additional energy you need to disipate when braking is only 10% to counter the additional mass.

It's the higher speed that's the issue. If you only increased your speed from 10 mph to 14 mph, you need double the braking.

Depending on your own mass, some people would be OK with rim brakes on a 15 mph electric bike, but if you're say 85kg +, they're not going to be enough.

Rim wear will also double if you increase your average speed from 10 mph to 14 mph, and quadruple if you go to 20 mph, and, if you made a 30 mph bike, it would wear at ten times the rate when you include the 10% for the extra mass.

It's all simple physics - the rules that none of us can bend or avoid.

 

[Peter.Bridge]

Thinking of this one

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24 peed with Shimano Alivio quick shift gears&hydraulic disc Brakes

Anything I should check if I go and have a look?

(Thinking rear hub conversion, might try and get one where I can dual use the 48v 20ah battery that I have on my BBS02B conversion)

 

[AndyBike]

I grew up with caliper brakes, short rubber pads (or "blocks" as they were called then) and chromed-steel rims. Emergency stops in the wet were definately "character forming"!

The bitd xc racing was the thing for that(even in the dry) if there was a turning coming up you really needed to apply the brakes a good way back to hopefully scrub off enough speed to be able to make the turn and not go crashing into the bushes instead.
When it was wet pretty much everyone went soaring past the turn and lost it in the rough so to speak.
V's made a big improvement, but only really in the dry, I did slightly better because I was using Shimano XTR's on ceramic rims.

Hydraulic discs changed everything.


As to fitting 12 speed on a rear motor- as above kind of lost in translation a bit. I've 12 speed, but thats on a mid drive, and even then I dont think I've ever needed to use any more than about 5 of the 12.

 

[Bikes4two]

Thinking of this one

Anything I should check if I go and have a look?

On the face of it I reckon that's a great bike for a conversion. Obviously you need to check it out as you would any bike in terms of whether it's mechanically sound, the frame is the right size for you and you are comfortable riding it.

A good price too.

 

[scbk]

My older electric conversion (rear hub motor) is on V brakes, I think I did about 3,800 miles then the rear rim needed replaced.

When I was buying a new bike to convert I went for hydraulic discs, which are much more suited to my use (hills, heavy loads, higher speeds)


Personally I would be wary of buying a second hand bike unless I knew the seller, I don't want to be funding bike thefts.

 

[AndyBike]

When I was buying a new bike to convert I went for hydraulic discs, which are much more suited to my use (hills, heavy loads, higher speeds)

Thats where they excel. Can you imagine though trying to use simple calipers or even V's on a heavy bike in the wet*. Scary

* Before the usual dissenting voices. Tandems sometimes carried TWO caliper brakes on the front and had a drag brake set up on the rear, as well as a stopping brake. So even back then the failures of caliper brakes were evident. Since they moved over to hydraulics, none of these extras were needed.

 

[Peter.Bridge]

..Personally I would be wary of buying a second hand bike unless I knew the seller, I don't want to be funding bike thefts.

Yes, agreed, will definitely check out the seller and the bikes "history" and If they have any documentation/ service history

The seller says
"Bike is 6 or 7 years old it has had routine maintenance, there are no issues it’s not used regularly"

 

[esuark]

My older electric conversion (rear hub motor) is on V brakes, I think I did about 3,800 miles then the rear rim needed replaced.

When I was buying a new bike to convert I went for hydraulic discs, which are much more suited to my use

Agreed: I did just over 6000 leisure miles summer and winter with v brakes and noticed the rear rim was getting worn. I figured it would easier and cheaper to replace the complete bike with one that had discs than rebuild the wheel, which is what I did. Swapping my preferred components over.

 

[Bikes4two]

Tandem Braking - I've no doubt they existing but I've never seen a tandem with two caliper brakes on the front and I've been riding tandem with other for 15+ years.

On our tandem we have caliper brakes front and rear and they are excellent but that's no doubt down to them being Magura HS33 hydraulic brakes. We do have a 3rd brake on the rear wheel - a cable operated disc but we rarely use it and believe me, we've been down some steep hills fully touring loaded too.

One of the considerations in the heavy big/heavy load scenario, is heat dissipation of the braking system. I have heard of inner tubes giving out under heavy rim brake braking, but not experienced that myself and certainly in the rare ocassion I've worried about the tendem rims geting hot, I have used the rear disc brake to take some of the load.

I've had bikes with hydraulic discs too and they are great, no doubt, and if I had the choice between two equal bikes, one with calipers and one with disc brakes, I'd probably opt for discs.

It so happens though that on my two current ebike conversions, one bike came with V-brakes and the other with dual pivot calipers (and I've fitted V-brake levers for them) and firstly they can't take disc systems but more significantly, I've not had any problems stopping with what I've got.

The effectiveness of caliper systems varies enormously depending on the components used e.g. brand of caliper and lever, brake block material and rim material. On my Trek carbon bike (now languishing in the bike shed somewhat having discovered e-biking!) the Campagnolo dual pivot brakes on Campag rims are simply excellent wheras I've had cheaper systems from Shimano that are crap!

Bottom line is, don't dismiss an otherwise excellent bike just because it hasn't got disc brakes.

PS - a tip for those using rim brakes - inspect the brake blocks regularly to spot and remove any embedded grit or other detrius, especially so if your brakes sound a bit gritty when applied. If you don't do this then the rims will wear more quickly.

Rim thickness can be measured with an iWanson guage - cheap to buy - as a guide I consider the rim for replacement when thickness is down to 1mm.