Author Topic: One for the wheelbuilders  (Read 832 times)

One for the wheelbuilders
« on: July 29, 2020, 08:16:58 pm »
Anyone with arcane databases of these things know the ERD of Bianchi 700c NTH 520 rims?
And what might be a good contemporary replacement if I wanted to swap a new rim onto existing hub and spokes?
It's an old (90's) Campag 9 speed set up serving on the, ahem, turbo trainer and today I leapt from the bike startled by gunshots to find big bulgey deformities in the rim. Don't want to upgrade the whole drivetrain. I'm guessing old campag 9speed hubs hard to come by these days so thought I'd try replacing the rim.
So, if you know please share what rim would serve?
I don't see any Bianchi rims on spocalc. The web tells me the Bianchi NTH 520's were manufactured by FIR. Might they be re-badged FIR SRG30's?

Re: One for the wheelbuilders
« Reply #1 on: July 29, 2020, 08:58:53 pm »
Just take out two opposite spokes and measure it.  If you don't know how, post back and I'll explain.  It has to be accurately done.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: One for the wheelbuilders
« Reply #2 on: July 29, 2020, 09:15:39 pm »
Well I've got one of those steel rulers with measuring apertures for bearings, spokes and nipples, so I think I dangle my spoke from its 'elbow' and measure to the end, no?
Intriguing.. to proceed thusly would I not also need a host of hub flange and OLN measurements?

LittleWheelsandBig

  • Whimsy Rider
Re: One for the wheelbuilders
« Reply #3 on: July 29, 2020, 09:44:52 pm »
Rog is not talking about measuring spoke length but using a pair of spokes (and nipples to measure the ERD.
Wheel meet again, don't know where, don't know when...

Re: One for the wheelbuilders
« Reply #4 on: July 29, 2020, 10:09:36 pm »
Put two nipples in opposite holes.  Check they really are opposite!  Measure between the ends of the nipples.  Now add twice the length of one nipple, usually 2 x 12mm but do check.  Nipple length does not include the flange that stops it going all the way through the rim hole.

It helps to have someone hold your nipples while you measure  ;)

Remember, you must be accurate.  ERD is the most critical dimension in calculating spoke length.

The FIR SC200 rims I built up the other week had an ERD of 600mm, but there is rarely standardisation across the range.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: One for the wheelbuilders
« Reply #5 on: July 29, 2020, 10:18:30 pm »
I put spokes in my nipples and measure the gap between the the two ends. (You can pull them tight)  Add on 2x spoke length = ERD. Simples.

Re: One for the wheelbuilders
« Reply #6 on: July 29, 2020, 10:29:33 pm »
the only reason you want to know the ERD of the rim is because you want to rebuild the wheel with the old spokes if possible, right?


Well if that is the case you are 100% wasting your time trying to measure the rim.

  It won't tell you anything definitive (*) and it may not work at all; if the wheel is out of shape you can't take a good ERD measurement off it anyway.

(*) It is hardly ever the case that the spokes were the perfect length for the wheel anyway. You need to know exactly what length the spokes are if you are presented with a choice of rims slightly smaller or larger ERD than the original; one way will work (and may give you a better wheel than the one you started with) and the other way will be hopeless.

So I would recommend that you remove a few spokes and measure those, along with the hub, and work out what ERD will build into good wheels using those parts, instead of messing about trying to measure scrap rims.

cheers

Re: One for the wheelbuilders
« Reply #7 on: July 30, 2020, 07:44:10 am »
It’s not unlikely of course, that drive and non-drive spokes will differ in length.

To keep you going, I think that any 9,10,11 speed Campag is likely to take your cassette.

Re: One for the wheelbuilders
« Reply #8 on: July 30, 2020, 08:18:16 am »
Didn't 'old' campag 9 differ from the later campag 9 in their rear hubs' capability to take the 10 and 11 cassettes?
Anyway, thanks for all the input but that's proliferating some. Unlacing to take those measurements is effectively a wheel un-build followed by a wheel build, no?  :facepalm:

Was thinking to source a near enough equivalent ERD rim, tape it to the current wheel and swap the spokes over one by one to keep me right, leaving me with a bit of tensioning, truing and dishing tops.. 

Think I'll just buy a new bike.

Re: One for the wheelbuilders
« Reply #9 on: July 30, 2020, 08:36:59 am »
taking a few spokes out and measuring them is not the same thing as unlacing the wheel.

The issue is 'near enough equivalent ERD'. 

By the time you have measured a bent rim (badly), assumed it is a particular model that you can't get any more, and assumed that the quoted ERDs for two rims compare with one another accurately, etc there is plenty of scope for going wrong.

You asked for advice from wheelbuilders; moaning about the extra two minutes taking a few spokes out and putting them back in again, when this could spare you hours of frustration, seems somewhat churlish.


Re: One for the wheelbuilders
« Reply #10 on: July 30, 2020, 08:40:45 am »
If it is just for turbo duty surely the quickest, easiest and probably cheapest is to buy someone else's worn but serviceable wheel.

citoyen

  • Occasionally rides a bike
Re: One for the wheelbuilders
« Reply #11 on: July 30, 2020, 09:03:08 am »
Think I'll just buy a new bike.

Always the best policy.

But I would take Brucey's advice - buy a new rim, measure it, then buy the correct length spokes.

Lacing a new wheel from scratch is not the hardest part of the job in my experience.
"The future's all yours, you lousy bicycles."

Re: One for the wheelbuilders
« Reply #12 on: July 30, 2020, 09:13:18 am »


But I would take Brucey's advice - buy a new rim, measure it, then buy the correct length spokes.


that is not quite what I was saying.  Re-rimming the wheel is quicker and easier, but the best way of knowing that your rim is going to fit is to know what length spokes you have, not to try measuring a knackered rim.

Assuming the wheel was straight, seeing how consistently the spoke ends finish in the nipples will give you some assurance that the spokes in the wheel are all uniform in length. So will the markings on the spoke heads; if a wheel is repaired then the new spokes rarely match the original ones in make or exact length.  If that is a 'pass' on both points then you only need remove and measure  one or two spokes from each side of the wheel in order to be absolutely confident about the spoke lengths you have.

cheers

citoyen

  • Occasionally rides a bike
Re: One for the wheelbuilders
« Reply #13 on: July 30, 2020, 09:24:44 am »
the best way of knowing that your rim is going to fit is to know what length spokes you have, not to try measuring a knackered rim.

Ah! Yes, I see what you mean now.
"The future's all yours, you lousy bicycles."

Re: One for the wheelbuilders
« Reply #14 on: July 30, 2020, 04:32:29 pm »
taking a few spokes out and measuring them is not the same thing as unlacing the wheel.
The issue is 'near enough equivalent ERD'. 
By the time you have measured a bent rim (badly), assumed it is a particular model that you can't get any more, and assumed that the quoted ERDs for two rims compare with one another accurately, etc there is plenty of scope for going wrong.
You asked for advice from wheelbuilders; moaning about the extra two minutes taking a few spokes out and putting them back in again, when this could spare you hours of frustration, seems somewhat churlish.

Steady on, Brucey old boy. Putting nipples or nipples and spokes in opposite holes on the rim to measure v carefully the distance between them pre-supposes you've moved the rather lumpy hub out of the way first, does it not?
And if you think this is moaning or churlish you should see some of my earlier work. I appreciate everyone's input, am deeply respectful of - if not reverential to - the Master Guild of Wheelbuilders, and am not really going to buy a new bike.
Perhaps ease off the emotional tension 1/16th of a turn? :)

Re: One for the wheelbuilders
« Reply #15 on: July 30, 2020, 06:39:13 pm »
Just buy a new bike!

Re: One for the wheelbuilders
« Reply #16 on: July 30, 2020, 08:13:58 pm »
Don't be a churl. ;D

Re: One for the wheelbuilders
« Reply #17 on: July 30, 2020, 09:30:19 pm »
taking a few spokes out and measuring them is not the same thing as unlacing the wheel.
The issue is 'near enough equivalent ERD'. 
By the time you have measured a bent rim (badly), assumed it is a particular model that you can't get any more, and assumed that the quoted ERDs for two rims compare with one another accurately, etc there is plenty of scope for going wrong.
You asked for advice from wheelbuilders; moaning about the extra two minutes taking a few spokes out and putting them back in again, when this could spare you hours of frustration, seems somewhat churlish.

Steady on, Brucey old boy. Putting nipples or nipples and spokes in opposite holes on the rim to measure v carefully the distance between them pre-supposes you've moved the rather lumpy hub out of the way first, does it not?.....

well maybe, but if you read what I wrote you will see that I was advocating no such thing; the idea of removing a few spokes is so that you can measure the spokes since they determine what rim might be suitable for a re-rim.

My whole point is (I'll say it again....) that trying to measure a knackered rim is very  likely to be a waste of time.

So my suggestion is....

a) check how the spoke sit in the nipples; mainly to see that they are uniform on each side (meaning all the spokes are the same length each side)
b) check the spoke heads to be sure that you have a matched set of spokes
c) remove one or two spokes from each side of the wheel (easiest if they are outbound BTW), measure them, and put them back
d) use a spoke length calculator to reverse-calculate the correct rim ERD for the parts you have
e) get a new rim of that ERD and re-rim the wheel in the usual way.

For example if the wheel is 32x3 built onto a small flange rear hub with 292mm DS/294mm NDS spokes  then you know that you should be looking for a rim that is 601-602mm ERD ideally. 600mm ERD and the spokes will be out of the top of the nipples slightly and larger than 603mm ERD will leave the DS nipples increasingly susceptible to (sweat-induced on a home trainer) stress corrosion cracking.

Quite possibly sweat was responsible for the rim failure you have just had, but it might be a legacy from an earlier bout of winter road use.

cheers

Re: One for the wheelbuilders
« Reply #18 on: July 31, 2020, 12:48:18 am »
the only reason you want to know the ERD of the rim is because you want to rebuild the wheel with the old spokes if possible, right?


Well if that is the case you are 100% wasting your time trying to measure the rim.

  It won't tell you anything definitive (*) and it may not work at all; if the wheel is out of shape you can't take a good ERD measurement off it anyway.

(*) It is hardly ever the case that the spokes were the perfect length for the wheel anyway. You need to know exactly what length the spokes are if you are presented with a choice of rims slightly smaller or larger ERD than the original; one way will work (and may give you a better wheel than the one you started with) and the other way will be hopeless.

So I would recommend that you remove a few spokes and measure those, along with the hub, and work out what ERD will build into good wheels using those parts, instead of messing about trying to measure scrap rims.

cheers

^^^^ This but you shouldn't even need to measure the hub, the details should be available in wheelbuilding databases already. Reliably measuring hub widths is not particularly easy in a built-up wheel but the flange diameters are easy and are the more critical dimension if you need to check the published figures. Given your spoke length and your hub dimensions any number of spoke length calculators, on- or off-line, can be used to reverse calculate the ERD. The hardest bit will be looking for a rim with the same ERD. If it's a couple of mms either way that isn't going to effect your chosen procedure of  taping the rims together and swapping the spokes (which is not how I would have done it but WTH we live in a free world!)

re the original failure. You haven't had the roller pressure on the turbo adjusted too tight, have you?

Re: One for the wheelbuilders
« Reply #19 on: July 31, 2020, 07:15:29 am »
Beware of wheelbuilding databases.  The data is often crowdsourced and can be wrong.  I was caught out because the measurements for a Campag track hub were off by enough to make the spokes more than 2mm too short.  Always best to measure.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: One for the wheelbuilders
« Reply #20 on: July 31, 2020, 08:44:50 am »
all databases and manufacturer's figures for ERDs etc are potentially misleading. However not all measurements are equally important, depending on the wheel build.

 For example rim ERD is always important and hub diameter is equally important in radial builds. But when the wheel is built full tangent or near tangent, the exact hub flange diameter becomes far less important; a little analysis of a near tangent build may tell you that in some cases the hub flange diameter needs to be ~10mm 'wrong' (or different) in the calculations in order to make a ~1mm difference in the spoke length.

cheers


Re: One for the wheelbuilders
« Reply #21 on: July 31, 2020, 10:46:39 am »
Edd (which I think uses the Spocalc database) still has the wrong data for Campag Record Pista, which is quite strongly asymmetrical in reality.  Or they're not distinguishing between original and "sheriff star" hubs.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: One for the wheelbuilders
« Reply #22 on: July 31, 2020, 10:58:55 am »
What annoys me is when you find a manufacturer quoted ERD and then other websites (SJS Cycles springs to mind ... ) quote a completely different figure. 

This just isn't helpful.

Re: One for the wheelbuilders
« Reply #23 on: July 31, 2020, 01:16:08 pm »
Edd (which I think uses the Spocalc database) still has the wrong data for Campag Record Pista, which is quite strongly asymmetrical in reality.  Or they're not distinguishing between original and "sheriff star" hubs.

'they' are not distinguishing much; the entries are user-generated and I'm not sure how 'garbage entries' (of which there are plenty) are removed. I have suggested that entries which are 'proven good' or are 'favourites' can be marked as such in a dialog for each user, or voted for, but probably it is more complicated than I would think, or might detract from the ease of use for everyone else.

FWIW I just checked the EDD database and there are entries for CR and NR 'pista' which appear to be garbage, and entries for CR and NR 'track' which appear to be more reasonable.

If you understand when errors in measurements make a real difference you are much less likely to come unstuck.

cheers

Re: One for the wheelbuilders
« Reply #24 on: July 31, 2020, 03:56:56 pm »
Well  done everyone for not using this as opportunity for mild double entendre....

Hold my nipples....