Broken spokes on Urban Mover rear wheel.

[dickbris]

Has anyone had problems with broken spokes on an Urban Mover; specifically back wheel on an UM44. I had two go in July'07 and complained to UM (who take a lot of complaining before they agree to do anything). Eventually they replaced the complete back wheel with a new one (at least that is what I was told). Within 6 weeks spokes started going again. Apparently I am the only person in the world this has happened to and it defies the laws of physics.

Now I have taken the bike to a local bike shop in Bristol to get it re-spoked (paid for by UM) and they have stopped selling UM because of the service support provided (not). According to the man in the shop, who seems to know what he is talking about, the hub on the UM44 (well anyway on mine) has a rim where the holes for the spokes are that is too thick. As a result the spokes move and where against rim, one goes and then it is curtains for several more. This does make sense as it is always the hub end of the spokes where then go, and right where they go through the hub rim. I understand that if spokes go due to misuses (eg. curb jumping) they tend to go at the rim end.

In any event the shop has remade the wheel with a stronger pattern and have put washers where the spokes go through the hub holes to stop the rubbing. To me this all sounds like a design fault and/or poor design margins, and it is difficult to believe this has not happened before (a) with other users with a design that is now basically several years old (b) manufacturers design testing.

Any similar experiences from other users?

 

[flecc]

In fact nearly all spoke failures are at the hub end, regardless of cause, in part due to the way spokes are manufactured.

Alloy hub shells are rather thick at the spoke rim point and wear can occur when the spokes flex, and this is worse when it's a motor hub due to the torsional twist of the motor drive. There have been similar experiences with other motor hubs, a tiny minority of Torq owners getting the same.

In my experience these Chinese motor wheels often have inadequately tensioned spokes, and that makes the flexing worse. Just rebuilding the wheels with higher spoke tensions can be enough, and I have no problems on my two bikes, both using the Torq/Quando motor, after rebuilding the wheels.
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[dickbris]

Thanks for the very quick response. This is encouraging and hopefully after this re-build I'll have a long period of trouble-free cycling....it would be nice.

 

[flecc]

I hope so for you too, I've heard a number of times how UM can be less than helpful when problems occur. Thank goodness the dealers can make up for it sometimes.
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[barnabear]

Broken spokes on UM 24

I've had a UM24 since mid September 2007, and have been plagued by broken spokes on the rear wheel.

I took the bike back after about 150 miles with an electrical problem, and 3 spokes were found to have failed on the rear wheel.

After about the same distance, another spoke failed after an emergency stop.
I checked the spoke tensions and found that the tensions were generally very high and that the spoke tensions on the sprocket side were all higher than those on the other side - thus the wheel was dished.

It seemed to me that there was very little room to accomodate the rim were the spoke tensions to be evened out - it seemed that the wheel would have to be dished to fit within the frame, brake furniture and mudguard.

I returned the bike to the shop and pointed out the problems. The shop agreed to replace the spoke and retension the wheel.

The shop replaced the broken spoke and another which "looked wrong". They reduced the tensions "within specification", but said that they had not been able to even out the tensions between the two sides.

One of the spokes feels loose, and the wheel rattles when I brake.

Even so, I have now travelled another 300 miles but have just had a further spoke break, so I have returned the bike again for repair. They are awaiting spokes to come in, hopefully today.

All of the spoke failures have been on the sprocket side.

The shop seemed to imply that they are seeing spoke failures on at least one other UM24 - they have used up at least one pack of 10 spokes (I account for only 5 of that number).

The shop also pointed out that the spokes are very stiff - there is very little give, so they may be brittle. Presumably this is due to their material - stainless steel.

I have put these problems to Keith Chamberlain of Urban Mover. He strenuously denies any possibility that the geometry of the frame/brake furniture/mudguard requires the wheel to be dished. However he has invited me to return the bike to him for inspection (at my own cost). Since I live about 120 miles away from Cheltenham, this would be very expensive for me, I would have to take a day off and this is hardly achieving the emissions savings that I was aiming at.

Furthermore I have been repeatedly blamed for the failures - I must be abusing the bike. However I have just been using the bike for commuting to and from work, or shorter trips into the city centre. I have no motivation for abusing the bike.

I have to say that although Keith comes across as a really nice guy, I am thoroughly fed up with the ownership issues with the UM24 so far.

When it works it's great, but these repeated spoke failures combined with Urban Mover's head in the sand approach to customer support means that I cannot recommend them. Plus, the resale value of the UM24 will be very low due to this fault. Probably even lower when people Google this append.

I may well have to invoke the Sale of Goods Act, but I'd really much prefer a technical solution to the problem.

 

[john]

It seemed to me that there was very little room to accomodate the rim were the spoke tensions to be evened out - it seemed that the wheel would have to be dished to fit within the frame, brake furniture and mudguard.

As far as I know, back wheels are always dished and the tension is different on each side, although all spokes on one side should have about the same tension if the rim is not buckled.

When people have had broken spokes, the advice seems to be to rebuild the wheel with new good quality spokes and no further problems occur. This was certainly the case for me.

 

[Wizard9956]

Hi Dickbris , which shop in Bristol are you using for your wheel repair ?

atb
Wizard

 

[barnabear]

No, I don't think that back wheels should be dished - that would always make the wheel weaker than necessary.

According to Keith Chamberlain of Urban Mover ....

"It should be possible to ensure true the wheel normally by any experienced cycle technician who has qualified in the art of wheel truing. Therefore the wheel would be symmetrical and not dished."

Why do you think that back wheels are always dished?

 

[john]

This is what Wikipedia has to say on the subject:

"Dish

Due to the need to mount multiple drive-train sprockets and disk brake rotors usually to only one side of a hub, and the need to have the rim be centered with respect to the frame or fork, spokes may be asymmetrical, with shorter and usually higher-tension spokes on the side with the additional components. This is referred to as dish. There are special tools, called dishing gauges, which indicate whether or not a rim is centrally positioned with the correct amount of dish.

Several different techniques have been tried to minimize dish. These include moving both hub flanges inboard the same amount, and placing spokes holes asymmetrically in the rim."

 

[flecc]

A high proportion of today's bikes use derailleur gears, and dished wheels are the norm, not the exception.

It's not true that a dished wheel is necessarily weaker, if the spoke threading pattern is correct, the hub flange design suitable and the build of good quality, the strength is effectively little different.

Even the most extreme dishing can perform perfectly under the toughest conditions. Here's an extreme example I built for my Q bike which is run with fairly hard tyres and very large loads, plus trailer towing:

Wheel build

As shopping bike

Towing

None of it causing any spoke or build trouble over 4600 miles on roads like this
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[fcurran]

Hi Dickbris , which shop in Bristol are you using for your wheel repair ?

atb
Wizard

Powabyke have a very good dealer in Fishponds called Fred Baker Cycles 0117 965 5510. He can rebuild wheels and service most electric bikes.

Regards

Frank

 

[barnabear]

Interesting, but I think that on the UM24 the frame is designed to accommodate the asymmetry due to the block etc.

Keith Chamberlain, who after all designed the bike, seems to think so.

Whether any weakening is acceptable will depend on the loading that the wheel experiences.

Talking with some of my colleagues, they feel that stainless steel is not an ideal material for spokes. They feel that it is too brittle.

Yes I'd like to get the wheel rebuild with higher quality spokes, so my next question is where could I get replacement spokes for the UM24 back wheel made of a stronger/less brittle material?

According to my local bike shop, the existing spokes are already the thickest gauge that he has even seen.

Thanks in advance ...

 

[flecc]

Interesting, but I think that on the UM24 the frame is designed to accommodate the asymmetry due to the block etc.

It's certainly true that some frames are designed asymmetrical to accomodate the cassette, it's mainly lightweight sports bikes that avoid that and use dishing to attain the lightest possible weight commensurate with the required strength.

Yes I'd like to get the wheel rebuild with higher quality spokes, so my next question is where could I get replacement spokes for the UM24 back wheel made of a stronger/less brittle material?

According to my local bike shop, the existing spokes are already the thickest gauge that he has even seen.

Thanks in advance ...

There's general agreement in the industry that thickness alone doesn't necessarily mean strength, and some of the strongest spokes are the waisted kind, only thick at the ends. The build quality overrides any strength of spoke issue, poor builds alway result in failures.

I've rebuilt motor wheels with no subsequent trouble experienced using perfectly standard British made 14 gauge stainless steel spokes listed on this page at SJS, and this sort of spoke are in both my current bikes wheels, both rear motor like yours, one a 20", one a 700c.

That said, taking Frank's advice and using that experienced Powabyke dealer would be a safe bet.
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[barnabear]

Thanks for that, but I'm in Southampton so Bristol is a bit far away - I'm trying to keep my carbon footprint down (and save diesel now).

Any other suggestions a bit nearer Southampton please?

Thanks in advance ...

 

[flecc]

Yes, your Powabyke dealer is here, and as you see, they are an approved service centre so should be able to handle a motor wheel build/repair:

Portswood Cycles Approved Service Centre

3 St Deny's Road
Portswood
Southampton
Hampshire
SO17 2GN

Tel : 02380 556470
Fax : 02380 556470
Email : sales@portswoodcycles.co.uk
Web : www.portswood cycles.co.uk
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[barnabear]

Portswood Cycles is my local bike shop, the one that I have bought from and been using to date. They are struggling with the issue.

Any other suggestions please?

 

[fcurran]

Portswood Cycles is my local bike shop, the one that I have bought from and been using to date. They are struggling with the issue.

Any other suggestions please?

?!?! Portswood Cycles are usually very good so Im suprised to hear this! What part are they struggling on?

 

[flecc]

Giant's electric bikes have been hub motored for some while now, and they have "electric" dealers. Their Southampton one is:

Peter Hansford Ltd
Bridge road, Park Gate
SO31 6BX Southampton

phone: 01489 573249 | fax: 01489 573249
parkgate@peterhansford.co.uk
www.peterhansford.co.uk

There's also Powabyke dealers at nearby locations like New Milton and Portswood etc, including some who are approved service centres. Here's the link to find Powabyke dealers in both Hampshire and Dorset:

Powerbike Dealer Directory

And here's the Giant one to do the same. With this one, enter a location or county, then check the "Electric" check box below and then click the Search button:

Giant Dealer Directory
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[barnabear]

They are struggling to find a suitable technical fix to the issues of the spokes breaking. The spokes are the thickest gauge that they have come across, and they don't have a proposal for a stronger engineering solution.

The wheel builder there has commented that he feels there is little flex in the spokes so he feels that they are probably brittle. The spokes are stainless steel.

So it's a struggle to find a stronger spoke, but I guess the good news is that the hubs and rims will take a thick spoke.

What material would be better than stainless steel, and where could I source such a replacement spoke?

Thanks in advance ...

 

[flecc]

Yes, I saw that from your earlier post, but it's not something I agree with. I've never had any trouble with stainless steel spokes and neither have any of my friends in the trade to my knowledge.

You saw my earlier illustrations of an extremely dished wheel and my use of stainless spokes, and the extreme applications they are subjected to, far tougher than anything you are doing with the UM. In the 700c wheel bike the motor wheel has a narrow tyre run at 80 lbs pressure, so again a high stress situation. That was a Torq wheel, and they gave spoke breakage troubles for some users, but the good rebuild solved that as it usually has when 50cycles rebuilt those wheels for their customers.

Frank may have an alternative suggestion, but I can't suggest anything better.
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