Building new wheel for the Torq

[JamesC]

I would welcome advice for selecting the best rim and spokes to build a new front wheel for my Torq 1.

The Torq has a powerful hub motor and rim brakes (Magura HS11) in a 700C sized wheel, and seems prone to broken spokes just above the knuckle at the hub. I suspect that this is a brittle point on the spoke, close to the bend, and that metal fatigue is the cause of the breakage.

Details on the original rim are:
Weinmann XTB-24
700C x 28C / 38C
ETRTO 622 x 20
36 spoke (determined by the hub motor)
Double Wall, Al alloy 6061-T6
Schrader valve

I have been looking at Mavic and DT Swiss rims to use in a new wheel, and wondering what are the main features to think of when building for a hub motor.

The standard wheel is "2 cross" lacing which seems unusual in a normal 700C wheel. I guess that the large diameter (approx 140 PCD) of the hub motor must be the reason not to use a "3 cross" pattern, yet I wonder whether a flatter angle would transmit the motor forces better.

I have also read that "double butted" spokes, which have a thinner diameter between the two ends, might be a little more "stretchy". Could this help to reduce the fatigue at the knuckle ?


I am sure that the build quality will be all important, but I would welcome ideas on the best components before I get started.

Thanks
James

 

[HarryB]

It would certainly be good to get to the bottom of why some Torq wheels keeps breaking their spokes. I haven't had a single spoke go and I go over the worst of roads. Plenty of others have had problems though.

I think you just need to do a full rebuild with new spokes from say SJS cycles - are you interested in doing it yourself? Shops will charge about £25 for the work. As for 3 cross or 2 cross I would stick with the standard 2 cross with your original rim unless you have lots of wear. I had a wheel rebuilt with a Tongxin motor and the shop said 2 cross was fine with the larger hub and the Torq is larger than the Tongxin.

Mavic rims are pretty good value, double walled so strong and with a wear indicator so recommended if you want to replace the rim.

 

[flecc]

If the build is satisfactory, the original components all perform ok for most owners. Rebuilds have also been ok with lighter 14 gauge spokes and I don't think any special components will necessarily produce any improvement.

I agree that a 36 spoke build might be better for the motor drive, but the spoke nipple angle in the rim with the large hub might be such that the nipple head doesn't seat properly.

I've found the standard ex works build is generally too slack, allowing the spokes to flex about too much, and I think that's the source of most problems.
.

 

[JamesC]

Thanks HarryB and Flecc.

Two things have been noticeable on the original wheel:
a) It does feel as though the spoke tension could be increased, but in most instances the adjustment has used up pretty much all of the thread. So I wonder whether the Weinmann rim could benefit from a spoke of 251 or 252 mm rather than the quoted 253 mm.

b) I have no experience of wheel building, but I am surprised at the amount of curve in the spokes that is caused by the second crossover. An inner spoke crosses on the outside of an outer spoke, which seems to put it a long way off a direct line from hub to rim.
If the inner spoke remained on the inside, then the path from hub to rim would be straight.
Is it normal for a spoke to be bowed due to the crossover, or is that a feature of the unusual dimensions of a motorised hub ?

HarryB - the Mavic rims all seem to be drilled for the smaller Presta valve. Do you know if they can stand being opened out for Schrader, as I prefer this more universal setup (Schwalbe tubes and Marathon+) ?

James

 

[flecc]

The bowing is marked, and it is a function of the shorter spoke length due to the larger hub. The same marked bowing in the same position is evident on the three cross build on a smaller 20" wheel for example.

I always use Schraeder valves and have drilled out Mavic rims without any problem.
.

 

[HarryB]

Certainly they come with an opening for Schrader as that is what I have - the Mavic A319.

ps I think they are drilled for the larger size but then have an adaptor for the presta valve.

 

[JamesC]

Certainly they come with an opening for Schrader as that is what I have - the Mavic A319.

ps I think they are drilled for the larger size but then have an adaptor for the presta valve.

Thanks - it is the Mavic A319 that I have been looking at, but I must have misread the valve hole size.

I have just noticed something on my Torq that would not have been my natural choice if I was lacing the wheel from scratch - the choice of inside or outside pulling spoke.

I believe the rim is central on the hub motor without any dishing, and the braking is central, being on the rim. However, the pulling spoke on one side is an outer spoke and on the other is an inner spoke.

So far, a total of 6 of the 36 spokes have broken of which 4 are from the 9inner spokes on the side where inners are NOT pulling.

I suspect fatigue as none broke in the first 1200 miles and having now reached 1700 miles, they are going more frequently.


Given the symmetry of the front wheel, and having less broken spokes to date on the side where the inners are the pulling spokes, I favour lacing the new wheel with inner spokes being the pullers on both sides.

Does this logic sound reasonable ?

James

 

[flecc]

I'm not too confident about that James, you could suffer spoke head breakages instead. I'm more inclined to believe that you've suffered from a batch of some faulty spokes, given that the breaks are unusually at the thread end. Most of the cases of spoke breakage on Torqs seem to have been at the hub end.

In your position I'd stick to the standard build using all new spokes.
.

 

[JamesC]

I'm not too confident about that James, you could suffer spoke head breakages instead. I'm more inclined to believe that you've suffered from a batch of some faulty spokes, given that the breaks are unusually at the thread end. Most of the cases of spoke breakage on Torqs seem to have been at the hub end.

In your position I'd stick to the standard build using all new spokes.
.

Sorry Flecc - bad description on my part - all breakages are at exactly the same point at the HUB end, breaking off the complete right angle bend.

Also worth asking other Torq owners whether their wheels are also laced with inner spokes pulling one side of the hub and outer spokes pulling on the other side of the hub.

I was wondering whether any difference in wheel build could explain the difference in spoke breakage.

James

 

[flecc]

Understood James, yes, that's the norm for the minority who have suffered this.

Rebuilds do seem to have cured the problem, though I know of one user who still suffered breakages afterwards. Of course I've no way of knowing the quality of the rebuilds.

Hopefully some other Torq 1 owners can feed back the information you asked for on the spoke direction.
.

 

[Ian]

There's lots of good advice here. Note the advice on stress relief, I'm wondering if this was not done properly on those Torqs that are prone to breaking spokes. It is an automatic part of the process on machine built wheels with two arms forcing opposite spoke pairs together, but there must be adjustments on the machine.. with the potential for error.

 

[JamesC]

Thanks for all the leads - the bike is goes so well in all other respects. A good rebuild with a full set of spokes will likely do the trick.

James