Author Topic: Wheel building for dummies (Read 8235 times)

ElyDave · « **Reply #25 on:** 28 November, 2017, 08:31:21 am »

Thanks Brucey, great help for a novice, as always. I really appreciate guys like you helping open up these dark arts.

Roger Musson also goes through the formula in one of the appendices to his book, based on the cosine rule, so I'm surprised that he ends up with different lengths, must be an assumption in the calculator somewhere. If I get time, perhaps over Christmas I might get round to constructing myself a spreadsheet calculator, just to get to grips with it in my own mind.

Seems like tonight's job is to strip down those two wheels and get measuring ERDs.

Samuel D · « **Reply #26 on:** 28 November, 2017, 09:40:54 am »

Quote from: ElyDave on 28 November, 2017, 08:31:21 am

Seems like tonight's job is to strip down those two wheels and get measuring ERDs.

An easy way to measure the ERD is to measure the outer rim diameter (with a yardstick or equivalent) and then drop a nipple into a spoke hole and measure how far below the rim edge lies the top of the nipple. This can be done by bridging the rim flanges with a ruler and holding a matchstick between the ruler and the top of the nipple; pinch the matchstick with your thumbnail to mark the distance between top of nipple and top of ruler, and then measure that distance and subtract the thickness of the ruler (e.g. 1 mm). Subtract twice the result from the rim diameter to get ERD.

If you have a vernier calliper, you can replace the matchstick with the calliper’s depth probe.

Somnolent · « **Reply #27 on:** 28 November, 2017, 08:59:50 pm »

Quote from: ElyDave on 28 November, 2017, 08:31:21 am

Roger Musson also goes through the formula in one of the appendices to his book, based on the cosine rule, so I'm surprised that he ends up with different lengths, must be an assumption in the calculator somewhere.

AIUI in his latest version he now allows for the elasticity of the spokes, and to keep things simple for us numpties he now gives a "minimum" length (from which you never round, and it is perfectly acceptable to round up by 2 mm) rather than the theoretical 'perfect' length from which you may round down by only a little ** and round up by a little bit more⁺⁺.

** rounding down by less than 1mm is usually OK, any more than that and lacing might get tricky
⁺⁺ rounding up by more than 2mm from the 'perfect' length and you run the risk of bottoming out the thread.

ElyDave · « **Reply #28 on:** 28 November, 2017, 11:32:00 pm »

Seems not in his theoretical calcs, but I wonder whether he has a factor in the online version?

Anyway, tonight's dismantling started well, but became problematic when one of the disc screw heads rounded off and needed to be drilled out - seems a gorilla with a spanner had mounted them originally. So I never got as far as measuring the rim, but I do know that the L&R spokes were the same length.

ElyDave · « **Reply #29 on:** 30 November, 2017, 09:39:26 pm »

So dismantled both wheels, and measured ERD. Used the method of two spokes in opposing holes, screwed into nipples so the spoke was flush with the top of the slot.

ERD = distance between bottom of nipples plus 24mm. Measured each one at three different positions.

Gave me
604mm for the Exal LX17 vs the 601mm on the web
539 for the Mavic XM719 vs 543 on the web

Plugged those into my spreadsheet and online calcs and got spoke lengths within 1-2mm of the ones I removed from the wheels.

Here's the thing I'm slightly confused at. Two different front hubs

Deore XT XM 756, 20mm centre to left flange, 35mm centre to right, 61mm PCD
DH-T8000, 19mm centre to left, 30mm centre to right, 70mm pcd

My plan is swapping hubs. So plug the new hub/rim diameters into the calcs, and it gives only 1mm difference between spoke lengths. Does that seem right?

If so can I use 290mm spokes for 289.9/290.8, and 258mm for 258.9/260.5. From comments the latter seems no (longer better than shorter)

grams · « **Reply #30 on:** 01 December, 2017, 11:17:45 am »

Quote from: ElyDave on 30 November, 2017, 09:39:26 pm

My plan is swapping hubs. So plug the new hub/rim diameters into the calcs, and it gives only 1mm difference between spoke lengths. Does that seem right?

The width of the hub makes very little difference to the required spoke length due to being almost perpendicular to the spoke's length. And if you're using a lacing pattern where the spokes attach to the hub at a sharp tangent, the diameter also makes only a small difference.

Quote

If so can I use 290mm spokes for 289.9/290.8, and 258mm for 258.9/260.5. From comments the latter seems no (longer better than shorter)

The first three are probably ok but you might be pushing your luck with that last one. If you have the time try building it up and see where the spokes end up relative to the nipples - your main concern is getting enough turns on the thread that they can't pull out (or can be threaded on in the first place!).

Brucey · « **Reply #31 on:** 01 December, 2017, 12:15:36 pm »

601mm is probably an NSD value masquerading as an ERD value, hence 604mm ERD for LX17.

539mm is pretty close to the usual ERD value for XM719 rims in 559 size. Dunno where you got 543mm from...?

Because with x3 spoking the spokes are close to tangent the hub diameter only weakly affects the spoke length.

From you lengths I assume that you are building 32x3 with the LX17 on the DH-T8000, and the XM719 onto the HB-M756?

If so the 290mm spokes will probably be OK for the former but 260 or 261mm would be best for the latter build.

cheers

ElyDave · « **Reply #32 on:** 01 December, 2017, 03:09:23 pm »

Thanks guys

can't remember where the 543 came from, may even have been Mavic's site itself.

I'm going to get started on the DH-T800/Exal LX17 this evening if I can, get the lacing done and then give myself plenty of time to get the truing sorted before Christmas.

ElyDave · « **Reply #33 on:** 01 December, 2017, 10:38:12 pm »

I quite enjoyed that, even though it was a first and required a decent level of focus, and reference to the book, I liked the nice calm, methodical sequence. I stopped at the point of primary tensioning, rather than starting truing when I know I didn't really have time to focus on it

Home made nipple driver worked a treat.

ElyDave · « **Reply #34 on:** 10 December, 2017, 10:24:28 am »

Decided to start the second wheel as well. Seems to be going much better than the first.

I'm struggling with radial trueness on the first one. I think I paid more attention to the initial tensioning second time around. Will have perhaps one more go at the first one, and may even think about dismantling and restarting that one.

Brucey · « **Reply #35 on:** 10 December, 2017, 03:18:27 pm »

re the radial truing; if the wheel has a bit of a 'hop' in it or a dip this could be a feature of the rim (esp near the joint) or it could just be the nipples wound on uneven amounts. Used rims are rarely perfect, BTW.

IME it is a very good idea to get the wheel largely round (radially true) and so forth before you get anywhere near full tension. The reason for this is that to (say) correct a 1mm hop, you will probably need to wind some nipples two full turns, which knocks hell out of them if said spokes are at full tension already. Anyway the amounts of movement that are required for radial truing are considerably larger than are normally needed for lateral truing.

If the overall tension isn't enough in the wheel you can always go round and add 1/4 turn to every spoke later on. If the tension is already high in your problem wheel I'd suggest backing every nipple off 1/2 turn, radially truing it, and then wind the tension back into it if necessary.

Regarding Roger Musson's spoke calculator; his calculator allows for spoke stretch (he tells me) assuming that you wind the spokes up to 120kg where possible. The spoke gauge is allowed for. This could/should make the spoke calculations more accurate, but in many cases this (combined with a slightly different ERD measuring and rounding regime from most others) just confuses people because they get different answers from when they use other spoke calculators. The corrections for spoke stretch are smallish, being typically about 0.5mm.

In addition this may not always be the major source of error in spoke length calculations anyway; spokes and hubs vary in how they fit together, and different methods of stress relief cause different amounts of settling in the spoke itself and a typical aluminium hub, too. I recently did some tests in which the apparent length of spokes (the same spokes, in the same hub even without the effects of settling in the hub) varied by about 2mm. The differences arose because of the use of spoke washers and the method of stress-relief, within realistic bounds.

hth

cheers

ElyDave · « **Reply #36 on:** 10 December, 2017, 03:26:22 pm »

Cheers Brucey,

the Mavic has a definite dip at the join, quite obvious and I've not tried to correct it.

I might just do that backing off and have another go with the Exal rim.

ElyDave · « **Reply #37 on:** 15 December, 2017, 07:51:17 pm »

Right, first cock-up. Armed wth newly built dishing tool, a variant on Roger Musson's (mark 2 design, cheaper simpler, is already in my BRANE).

Checked dishing, needs adjusting.
Tighten spokes on RHS, gap is bigger that side.
Hmm, no better, actually worse. Must be doing it right surely.

Go back and read the boook again - DOH

remember : Read twice, adjust once

ElyDave · « **Reply #38 on:** 17 December, 2017, 04:18:28 pm »

decided to start again with the Exal rim, I think I'd got far too much tension in the wheel to be able to sort the dishing, adn was just making it worse. Some of the spokes were near the bottom of the threads and I'd managed to round a nipple off. Backed them all right off to the spokes at the top of the nipples and will start again.

Going better with the Mavic as I'm trying to correct the dish much earlier in the process and I think I'm taking it a lot steadier

grams · « **Reply #39 on:** 18 December, 2017, 09:41:07 am »

Heavily dished rear wheels are the worst. You end up with very tight, almost vertical drive side spokes that do almost all of the work of holding the rim where it should be, and non drive side spokes that have to be kept loose to stop them pulling the rim across, which means they're doing very little.

It's a battle to not overtighten the drive side, get at least some tension in the NDS and still have the dishing and truing correct. Good luck.

ElyDave · « **Reply #40 on:** 20 December, 2017, 08:40:47 pm »

I think I have one finished.

Dishing is within one mm and lateral trueness is good enough for me. I plan on getting a tyre on it tomorrow and giving it a test. What could possibly go wrong?

Brucey · « **Reply #41 on:** 20 December, 2017, 09:30:48 pm »

Quote from: ElyDave on 20 December, 2017, 08:40:47 pm

.... I plan on getting a tyre on it tomorrow and giving it a test. What could possibly go wrong?

well.... you could lose tension once the tyre is inflated, enough to cause worries about there being enough tension on the slack side of a dished wheel. It is also possible for a straight wheel to go slightly out of true once the tyre is inflated.

Some rims are worse for both things than others. It isn't a bad idea to use threadlock on the slack side spokes of dished wheels, since this helps to prevent the nipples from backing out, whilst usually not causing the nipples to be impossible to adjust later on.

If the wheel is to see winter conditions, it also isn't a bad idea to treat both the hub and rim anchorages with some kind of corrosion protection. I use waxoyl, run in with a hairdryer. You can wipe away any excess quite easily. This lurks in any crevices that might otherwise fill with nasty salty water, and helps to prevent corrosion, and related things like rim/hub flange cracking .

cheers

ElyDave · « **Reply #42 on:** 21 December, 2017, 01:46:16 pm »

well,

a very slight re-truing needed after mounting the tyre.

Half a dozen pinging spokes when I set off. Checked as still true when I stopped halfway round the ride, vs a brake block.

first 50km on my own wheel, and I'm perfectly happy to use it as intended for the next ACME Anvil Audax.

When washing the bike I noticed a rather nasty grinding coming from the rear hub (Shimano WH-500) that I've rebuilt once already, and is showing some signs of corrosion on the lock nuts. Perhaps it was all leading to this point to utilise these newly learned skills.

Brucey · « **Reply #43 on:** 21 December, 2017, 05:08:35 pm »

it isn't at all unusual for small amounts of dirt to get in the gap between the hubshell and the freehub body, and for this to make a dreadful racket for a while, until it works its way out again.

cheers

ElyDave · « **Reply #44 on:** 21 December, 2017, 05:22:06 pm »

This is non-drive side. I rebuilt drive side a couple of years ago after the freehub bearing face disintegrated.

I might wait and see as you suggest as the hub is now obsolete, 24h and no obvious replacement, which might necessitate new hub, rim and spokes rather than hub replacement.

Brucey · « **Reply #45 on:** 22 December, 2017, 02:44:37 pm »

if you really want to the bearing insert can be replaced. It is a lot of work though.

If these bearings are failing inside two years then this strongly indicates that you could do better in the way of lubrication and adjustment.

Possibly you did as well as shimano did when they built the hubs, which isn't really good enough either...

cheers

ElyDave · « **Reply #46 on:** 22 December, 2017, 03:05:11 pm »

The wheel is approx. 10 years old, two years ago I replaced balls and freehub on the drive side and IIRC, replaced the balls on non-drive at the same time. Adjustment was tricky to get the right degree of freedom without either binding or sloppiness, half a knats fart of turn on the spanners.

From what I've read on the web, I'm lucky to have got ten years out of them

Brucey · « **Reply #47 on:** 22 December, 2017, 04:29:59 pm »

Quote from: ElyDave on 22 December, 2017, 03:05:11 pm

Adjustment was tricky to get the right degree of freedom without either binding or sloppiness, half a knats fart of turn on the spanners.

cartridge bearings are manufactured to tolerances of a few microns, but with a little care you can do better than that with a set of cup and cone hubs. One degree of cone adjustment is about 2.8microns. You should be shooting for about three degrees movement being the difference between adjustments that you make.

However most folk go wrong not just because they don't understand this, but they also don't understand that the axle is compressed by the action of the QR. This compression is typically in the range of 50-80 microns. You can demonstrate that this is happening by putting some washers where the dropouts would go on a loose wheel and tightening the QR down.

Basically you will soon find if you adjust the hub to give no play with the QR slack, the hub bearings will be busy grinding themselves to atoms when the wheelset is in use, i.e. the preload on the bearings is vastly in excess of the service load. The correct adjustment is to have a little free play in the bearings that just disappears as the QR is tightened. This adjustment is easily achieved if a hub vice is used.

The difference between expensive hubs and cheaper hubs is that you don't feel so easily when the adjustment is too tight with expensive hubs. The bearings will still be suffering just the same if the adjustment is wrong, hence you should feel the free play just disappearing as the QR is tightened as a guide to continued good adjustment.

[BTW with rim brakes and vertical dropouts, QR pressure is not critical within a fairly wide range, so can be used to make fractional adjustments to axle compression and therefore bearing clearance.]

You would be amazed at how many allegedly 'professional bike mechanics' don't know how to adjust QR hubs properly....

Quote

... From what I've read on the web, I'm lucky to have got ten years out of them....

with all due respect, most of what you have read will have been written by people that basically don't know what they are talking about, and have carried out poor or non-existent maintenance. If correctly adjusted and lubricated, the bearings in even relatively cheap shimano hubs will last many tens of thousands of miles.

In shimano pre-built wheelsets, it is perhaps not worth being as careful as you might be otherwise; unless you intend to rebuild the wheels on different rims when they wear out or get broken, all the hubs have to do is to out-last the wheel rims. They should breeze through that with only one or two services, if the right lubricant and adjustment technique is used.

cheers

ElyDave · « **Reply #48 on:** 22 December, 2017, 06:39:05 pm »

Thanks, as usual, Brucey.

From your description, if anything I may have been a little slack, wanting to avoid excessive pre-load. I was thinking back to replacement car wheel bearing where you loaded the castellated nut to just past the split pin hole and then slackened off again to allow for expansion with heat. I realise this is not so much of a problem with a bike.

Anyway, first step is of course to dismantle it and inspect

Little Jim · « **Reply #49 on:** 05 January, 2018, 10:33:19 am »

Firstly apologies if this is a thread hijack, but it did look like an appropriate place.

A spoke lacing question: Roger Musson describes "inside", "outside", "pushing" and "pulling" spokes to describe the four different ways that a spoke can be placed in the wheel (assuming that you are not using radial spoking). So far so good. He then goes on to say that in his opinion it makes no difference to the wheel if the pulling spokes are on the inside or outside (and the same for the pushing spokes) which makes sense to me. Someone I know has done the Cytech level three course which includes wheel building and they (Cytech) are most insistent that a disc braked wheel should be built in one particular way (but I can't remember which!) and the course book that he showed me confirmed this. I can't see that the distribution of forces (or the loading) is going to be any different depending on whether the pushing and pulling spokes are on the inside or the outside but then I'm a Civil Engineer and not a Mechanical Engineer. Anyone care to enlighten me please?

Author Topic: Wheel building for dummies (Read 8235 times)

Samuel D