Wheel building machines

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Brucey
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Re: Wheel building machines

Postby Brucey » 9 Jun 2020, 4:25pm

I agree with CJ that dished wheels are a terrible idea and that there are various ways of addressing this problem.

However I also note that the factors that influence spoke breakage are a bit more subtle than 'high tension = always bad'. IIRC some FEA analysis that was carried out (which simulated out of the saddle climbing on a typical dished rear wheel) indicated that the largest cyclic stresses (worst fatigue loading) would be seen on the NDS 'leading' spokes, not the more highly loaded DS spokes. Indeed I have encountered some wheels where the NDS spokes break and the DS ones don't, even though the mean stresses in the former are far lower than the latter.

I guess one way of looking at it is that, in practice, good spoke fit and/or stress-relief (or lack thereof) can trump everything else. In an ideal world you would have good spoke fit, good stress relief, and an inherently better wheel design. In this make-do-and-mend World we live in, two out of three ain't bad, and in the absence of commonly available parts for 'better wheels' is a more realistic objective.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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CJ
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Re: Wheel building machines

Postby CJ » 9 Jun 2020, 6:30pm

Brucey wrote:I agree with CJ that dished wheels are a terrible idea and that there are various ways of addressing this problem. However I also note that the factors that influence spoke breakage are a bit more subtle than 'high tension = always bad'. IIRC some FEA analysis that was carried out (which simulated out of the saddle climbing on a typical dished rear wheel) indicated that the largest cyclic stresses (worst fatigue loading) would be seen on the NDS 'leading' spokes, not the more highly loaded DS spokes. Indeed I have encountered some wheels where the NDS spokes break and the DS ones don't, even though the mean stresses in the former are far lower than the latter.

I agree, and didn't say high tension is always bad. Too slack is just as bad and I have also received plenty of reports where the left-side spokes failed instead. The reason for that seems to be their tendency to loose all tension momentarily when the bit of rim they're attached to is pushed up by the road. A spoke goes slack, the bent end shifts in it's hub-flange hole and then snaps back into place - perhaps a bit out of place now. And that ain't good for it: tends to nod its little head off. So yer back wheel is a balancing act between too slack on the left and too tight on the right, either of which can lead to no end of trouble on tour, or the journey to work. And odd things happen to the structural stability of a wheel when one or two spokes go completely slack under load. The tension changes experienced by other nearby spokes ramp up, those nearest losing tension even faster, whilst distortion of the rim can cause some spokes out to the sides to become even tighter than those at the top of the wheel holding up the hub! So any spoke going completely slack at any time is something you really want to avoid.

I didn't mention another key benefit of equalising the stresses left and right. Equal stress means equal elongation, it means the slender spokes on the left extend the same amount under their lower tension as the tighter, stouter spokes on the right. So when that section of rim is pushed up by the road, left and right spokes relax by equal amounts. Neither goes completely slack before the other and the rim is not pulled to one side as it is pushed toward the hub, as happens in a typical back wheel - never mind how nicely you fit and stress-relieve those same-both-sides spokes. This makes our well-designed wheel less prone to buckle when run over a pothole etc.

I guess one way of looking at it is that, in practice, good spoke fit and/or stress-relief (or lack thereof) can trump everything else. In an ideal world you would have good spoke fit, good stress relief, and an inherently better wheel design. In this make-do-and-mend World we live in, two out of three ain't bad, and in the absence of commonly available parts for 'better wheels' is a more realistic objective.

No. Design trumps everything else. Front wheel spokes don't fatigue even when the wheel is mass-produced with poor spoke fit and no stress relief, because at least it's designed right. Get that ONE thing right and the other two can be merely so-so. THAT is the best way to cope with the imperfections of this world, where single-butted spokes are nevertheless quite available enough.

Paying for a craftsman wheelbuilder to optimise the tensions, finesse the spoke fit and stress-relieve a back wheel with the same spokes both sides is like gold-plating a toffee teapot. It'll look lovely and the metal will probably keep it standing up, but inside you'll always know it's made of toffee!
Chris Juden
One lady owner, never raced or jumped.

markjohnobrien
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Joined: 4 Oct 2007, 8:15pm

Re: Wheel building machines

Postby markjohnobrien » 9 Jun 2020, 7:21pm

That last paragraph is lovely description - “toffee teapot” - made me laugh.

Brucey
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Re: Wheel building machines

Postby Brucey » 9 Jun 2020, 7:31pm

I think we are going to have to agree to disagree to some extent here, in that badly built front wheels break spokes too, just not as quickly as badly built rear wheels.

I agree that spokes going fully slack on the NDS is pretty deadly; if the nipple doesn't slide in the rim then the slack spoke suffers Euler type buckling and this can result in high local bending stresses at both ends of the spoke. DB spokes help here twice over; first by allowing more stretch and second by allowing the spoke to flex more easily in the mid-section (thus sparing the ends from high bending stresses) should the spoke go full slack.

I kind of live in hope that wheelbuilding machines will eventually build good wheels consistently, but AFAICT it ain't happened yet and as you say building a flawed design is always going to be an uphill struggle.

If components were more readily available for building better wheels (eg implementing 2:1 spoking in a 36h wheel) then I'd do that like a shot. As it is one can only dream of such things and in the meantime be content with building wheels (using conventional parts) as well as is possible. I honestly can't remember when I last broke a spoke in wheels that I have built; I must have done between 100 and 200K miles without this happening; some teapot.

cheers
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CJ
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Re: Wheel building machines

Postby CJ » 10 Jun 2020, 12:21pm

Brucey wrote:I think we are going to have to agree to disagree to some extent here, in that badly built front wheels break spokes too, just not as quickly as badly built rear wheels.

Okay, it is possible. I even had a spoke break once in my front wheel. It was an early stainless-steel spoke, Saba brand. They were notoriously weak and soon disappeared from the market. I bent one around the column of my workstand, it sprang back a little bit, then a 'rustless' (galvanised high-tensile steel spring wire) spoke of identical gauge, which recovered to more than double the diameter of the Saba stainless. Eventually stainless became just as good as rustless, maybe even better now, and the Saba brand was history. But I'm guessing Brucey is old enough to remember it.

Whatever: in 31 years answering CTC members' problems I never had anyone complain about breaking front wheel spokes, only rear and lots of them! This problem regularly turned someone's annual holiday, planned, saved up for and anticipated all year, into a miserable hunt for bike repairers with the correct block-remover and skills, to repair the rear spokes that broke one-by-one throughout the fortnight.
Chris Juden
One lady owner, never raced or jumped.

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CJ
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Re: Wheel building machines

Postby CJ » 10 Jun 2020, 12:38pm

Brucey wrote:If components were more readily available for building better wheels (eg implementing 2:1 spoking in a 36h wheel) then I'd do that like a shot. As it is one can only dream of such things and in the meantime be content with building wheels (using conventional parts) as well as is possible.

In that case I trust that you do indeed use thicker spokes on the right and thinner on the left of rear derailleur wheels, for I can tell that you have the intelligence to see that is the next best thing, using conventional parts.

Please join me in urging those who may not have access to a wheelbuilder with your skills, to insist on this prescription of differential spoking. We both know that it could make the difference between a happy touring holiday and a spoiled one.
Chris Juden
One lady owner, never raced or jumped.

Brucey
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Re: Wheel building machines

Postby Brucey » 10 Jun 2020, 1:24pm

in fairness I have arguably 'cheated' in that I long ago realised that 'standard' wheel dishing caused so many problems (in my use) that I have largely avoided it. So the tension balance in most of the derailleur wheels I have built and used myself has been less bad than you might otherwise obtain.

I've experimented with wheel builds where I've deliberately used a really good lubricant on the NDS spokes and nipples; the rim stiffness and service conditions also affect how slack the spokes might get in service. If the spokes are going slack in service, the NDS nipples will start to back out. If it happens very quickly then you know you have overdone it and the wheel is probably an unworkable combination and needs a stiffer rim, less dish etc. If it happens but not as quickly then it is probably workable provided threadlock is used on the NDS nipples; I'd sooner not use any at all of course but it seems to work this way.

I've favoured DT spokes for as long as I've been able to buy them (which is nearly forty years now). I don't necessarily think they are better than other brands can be, but (by accident or otherwise) I have yet to find a duff batch of DT spokes whereas I have found duff batches from pretty much every other major spoke manufacturer. I don't think any manufacturer has processes that are 100% immune to faults, but their QA/inspection systems may be good enough to prevent any duffers from ever leaving the factory. In recent years DT has set up manufacturing plants all over the world and I do worry that they perhaps won't be able to implement the same QA standards in every single one. In my mind the main reason for not using DT spokes would be their horrendous cost in the UK. So I am daft enough to think that I will spot some manufacturing faults in other (cheaper) brands and I will use those these days. Until the next time I don't, probably.

I confess I do vaguely remember Saba as a brand but I don't remember using Saba spokes. I am of an age where I'm starting to be worried about forgetting all kinds of other things.... :wink: :roll:

I do agree with the use of different spokes each side of a derailleur rear wheel; however if the dish is made low enough this becomes less significant. I note that in the MTBs offset back ends are quite common now; I wonder if they will reappear in the touring world?

cheers
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Pebble
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Re: Wheel building machines

Postby Pebble » 10 Jun 2020, 3:08pm

Brucey wrote:I think we are going to have to agree to disagree to some extent here, in that badly built front wheels break spokes too, just not as quickly as badly built rear wheels.

I agree that spokes going fully slack on the NDS is pretty deadly; if the nipple doesn't slide in the rim then the slack spoke suffers Euler type buckling and this can result in high local bending stresses at both ends of the spoke. DB spokes help here twice over; first by allowing more stretch and second by allowing the spoke to flex more easily in the mid-section (thus sparing the ends from high bending stresses) should the spoke go full slack.

cheers


When you say "Deadly" are you referring to the wheel or rider?

As you know I have just built my first wheel and i'm pretty nervous about the dam thing.

How often should I check for loosening spokes, could I rely on one of these spoke tensioning gauges to determine loosening? (they were all about 27 on the NDS (non drive side?))

Brucey
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Re: Wheel building machines

Postby Brucey » 10 Jun 2020, 3:22pm

deadly for the wheel, not (immediately) so much the rider. Unless you are tone deaf then simply plucking the spokes and monitoring the wheel for truth will tell you most of what you need to know.

BTW '27' means nothing unless you specify the tension meter type and the exact spokes used. Even then you need a calibration chart. Spoke tensions are usually expressed in kgf.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Pebble
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Re: Wheel building machines

Postby Pebble » 10 Jun 2020, 4:13pm

Brucey wrote:deadly for the wheel, not (immediately) so much the rider. Unless you are tone deaf then simply plucking the spokes and monitoring the wheel for truth will tell you most of what you need to know.

BTW '27' means nothing unless you specify the tension meter type and the exact spokes used. Even then you need a calibration chart. Spoke tensions are usually expressed in kgf.

cheers

The 27 to me is no more than a number, with the idea of using the same gauge on the same spokes at a later date to see if they had altered. As spokes did vary in tension I noted each one in turn so as I can monitor changes, on the NDS they varied from 26.5 to 29 with an average of 27.6. (is that good or bad?) in an ideal world should they not all be the same. I aimed for that number to match the wheel on the bike! I really do not know what I am doing :D

One unexpected event I noted that surprised me, when I fitted the tyre and inflated it, the centre of the wheel moved 0.8mm to the drive side ?

The meter I bought was
https://www.ebay.co.uk/itm/Road-Bicycle ... 592e65a399
and spoke length 293.5 & 291
no idea what type of spoke other than stainless with brass nipples, they were off the last wheel

used grease as a lube

JakobW
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Location: The glorious West Midlands

Re: Wheel building machines

Postby JakobW » 10 Jun 2020, 7:45pm

Pebble wrote:One unexpected event I noted that surprised me, when I fitted the tyre and inflated it, the centre of the wheel moved 0.8mm to the drive side ?


Inflating a tyre on a rim causes spoke tensions to drop; because of the differential tensions on the DS and NDS the rim will tend to pull over to the DS.

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CJ
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Re: Wheel building machines

Postby CJ » 10 Jun 2020, 11:23pm

JakobW wrote:Inflating a tyre on a rim causes spoke tensions to drop; because of the differential tensions on the DS and NDS the rim will tend to pull over to the DS.

Another advantage of differential spoking to balance the dish (thicker on the right, thinner on the left, so that stresses and elongations are equal in spite of the necessarily different tensions) is that does not happen - or not anything like as much. As the rim shrinks under the inner-tube's inward pressure, spokes from both sides of the wheel relax equally and the rim remains very close to central.
Chris Juden
One lady owner, never raced or jumped.

NickJP
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Re: Wheel building machines

Postby NickJP » 11 Jun 2020, 12:14pm

Brucey wrote:I do agree with the use of different spokes each side of a derailleur rear wheel; however if the dish is made low enough this becomes less significant. I note that in the MTBs offset back ends are quite common now; I wonder if they will reappear in the touring world?

Maybe more touring frames should be constructed with tandem rear spacing, so that the rear wheels can be completely dishless. In almost 40 years of touring on tandems, we have yet to suffer a broken spoke, and the all-up weight of my wife and myself plus full touring load and tandem is slightly over 400 lbs. And we don't use 48-spoke wheels, either. Since 1987, all our touring has been on 36-spoke wheels with 26" rims.

PhilD28
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Re: Wheel building machines

Postby PhilD28 » 11 Jun 2020, 12:26pm

NickJP wrote:
Brucey wrote:I do agree with the use of different spokes each side of a derailleur rear wheel; however if the dish is made low enough this becomes less significant. I note that in the MTBs offset back ends are quite common now; I wonder if they will reappear in the touring world?

Maybe more touring frames should be constructed with tandem rear spacing, so that the rear wheels can be completely dishless. In almost 40 years of touring on tandems, we have yet to suffer a broken spoke, and the all-up weight of my wife and myself plus full touring load and tandem is slightly over 400 lbs. And we don't use 48-spoke wheels, either. Since 1987, all our touring has been on 36-spoke wheels with 26" rims.


Wider rear spacing can sometimes lead to issues with wider pedal stance and an increase in Q factor which may or may not be acceptable, it wouldn't be acceptable to me, the lower the Q factor the better.
I build many expedition wheels, always using different gauge L & R spoking, and with the right choice of rims/hubs and spokes, wheels, particularly 26" wheels, can be build strongly enough for almost any expedition bike. I've yet to hear of one of the wheels I've built using 36 spokes on 135mm hubs ever break or have a spoke fail, so I respectfully suggest that 135mm spacing is all that's required in practice. Of course anything you can do to even the amount of strain in either side spokes by reducing the dish or varying spoke gauge is always welcome.

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fausto99
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Re: Wheel building machines

Postby fausto99 » 11 Jun 2020, 12:56pm

CJ wrote:
JakobW wrote:Inflating a tyre on a rim causes spoke tensions to drop; because of the differential tensions on the DS and NDS the rim will tend to pull over to the DS.

Another advantage of differential spoking to balance the dish (thicker on the right, thinner on the left, so that stresses and elongations are equal in spite of the necessarily different tensions) is that does not happen - or not anything like as much. As the rim shrinks under the inner-tube's inward pressure, spokes from both sides of the wheel relax equally and the rim remains very close to central.

Well! I never knew that. The things you learn! Every day's a school day.