Rigida Chrina ERD - which database is right (if any)

[CJ]

I could have started a new thread, but having fallen on this one during my investigations, I decided to bring it back from the dead!

I'm buying a rim, and finding this "ERD" dimension in the catalogue I thought I might use that to calculate the spoke length, rather than my trusty Spoke Length Chart, that takes a more approximate approach but has never let me down all the same. Even better, thought I, would be to add "ERD" dimensions to the chart. Then people could compare the ERD of their chosen rim, halve the difference and add or more likely subtract that from the given spoke length. So I tried to work out how my chart matched up with ERDs of a few rims for which I had the other key dimensions. No clear pattern was emerging that made any sense to me, so I turned to Wikipedia where I found this discussion.

Apparently: there is no agreement upon where exactly ERD should be measured! Some (e.g. Mavic so it seems) measure to the nipple seat, whilst others (e.g. Damon Rinard with his adopted-by-Sheldon-Brown Spocalc) measure to the end of the spoke. According to DT that makes about 4 or 5mm difference, but DT's help pagelet causes even more confusion by first claiming that their ERD is measured at the nipple seat and then explains a method of finding the ERD of a rim that apparently yields the spoke end diameter, confirmed by their statement that so many mm needs to be added to Mavic's ERD figures in order to use DT's tables and Spokes Calculator!!!

So the confusion is complete, with even the mightly DT apparently not knowing (to coin a polite and aposite phrase) its thread from its elbow!

I think we all now know why there are two conficting numbers for the ERD of a Rigida Chrina rim (two clusters of four numbers actually) one 5mm bigger (or thereabouts) than the other.

I think we should abandon the term "ERD", about which there is apparently no agreement as to what exactly it means (some even confusing it with tyre size), and invent two new terms: "NSD" for nipple seat diameter and "SED" for spoke end diameter. But cycling has always loved confusion better than logic, so I'll not hold my breath.

[fatboy]

I'm buying a rim, and finding this "ERD" dimension in the catalogue I thought I might use that to calculate the spoke length, rather than my trusty Spoke Length Chart, that takes a more approximate approach but has never let me down all the same.

I have been looking into this when trying to re-rim a wheel without needing to replace the spokes (it's a hack bike!) and it is incredibly confusing. I like your chart method but how should I account for wheel dish for a rear wheel?

[CJ]

I like your chart method but how should I account for wheel dish for a rear wheel?

Don't bother! I never have!

The theoretical difference in spoke length is seldom as much as 1mm and you have something like plus or minus 1.5mm tolerance to play with. And spokes only come in 2mm increments anyway, so just pick the nearest size.

Err on the short side if you're worried about running out of thread or the spokes sticking out the tops of the nipples (which doesn't matter now that nipples live down rabbit-holes where the inner tube can't get at them!) and err on the long side if you worry instead about the heads of the nipples snapping off cos the spoke doesn't reach the top of the neck.

You've guessed it: I tend to round up rather than rounding down. Plus you can always cut a bit off a spoke - even roll a bit more thread - but never stick any extra on! Not that I've ever had to do that mind, merely on account of dish.

Another thing: if you build dished wheels the way I recommend, with heavier, hence stiffer spokes on the right and lighter, stretchier ones on the left, the extra extension of those left spokes will offset part of the theoretical length difference.

[deliquium]

Just yesterday I built a pair of wheels using Rigida Chrina rims and Shimano 6600 Ultegra Hubs. I agree with CJ - ERD = confusion (one man's/company's EFFECTIVE RIM DIAMETER etc) - Rigida say 608mm on their website, Spa Cycles quote 603mm on their website.

So I thought it best to make my own mind up. I used Wheelpro measurement technique - two lenghts of old spokes cut to 200mm long from the threaded end - screw on a nipple until the end of the spoke thread is level with the bottom of the slot on the nipple (not the end of the nipple) - put both through opposite holes on the rim and measure the gap between the chopped off spokes - then add 2 X 200mm (400mm).

I came up with 607 for the Chrina - I used spokes accordingly and all was hunky dory.

When I laced up the wheels, I discovered that Rigida now engrave these rims with 14 622 607 36 10 G.

14 presumably refers the internal width of the rim which actually measures 13.5mm!

622 we all know about = 700c

607 presumably is some stab at an ERD?

36 is the hole count

NO idea what 10 or G refer to.

But given that most spokes only come in 2mm incrementals - it's hardly a fine art

And we'd have less to moan about on our beloved forum

[Mick F]

Just yesterday I built a pair of wheels using Rigida Chrina rims and Shimano 6600 Ultegra Hubs. I agree with CJ - ERD = confusion (one man's/company's EFFECTIVE RIM DIAMETER etc) - Rigida say 608mm on their website, Spa Cycles quote 603mm on their website.

So I thought it best to make my own mind up. I used Wheelpro measurement technique - two lenghts of old spokes cut to 200mm long from the threaded end - screw on a nipple until the end of the spoke thread is level with the bottom of the slot on the nipple (not the end of the nipple) - put both through opposite holes on the rim and measure the gap between the chopped off spokes - then add 2 X 200mm (400mm).

I came up with 607 for the Chrina - I used spokes accordingly and all was hunky dory.

I can tell you what I measured.
I've made two sets of Chrina wheels.
603.5mm

Same method as you.
Why the difference?

[531colin]

................... you have something like plus or minus 1.5mm tolerance to play with.................. .

I just measured a Sapim double butted spoke and 12mm nipple. There is exactly 2 mm. between the nipple just covering the last thread and the spoke level with the top of the nipple.
To listen to some of our customers you would think it was the end of the world if, on a pair of wheels, there was a single thread showing, or a single spoke end visible above the nipple.

[deliquium]

Same method as you.
Why the difference?

It doesn't matter Mick F - your wheels are ok?

Mine are.

Maybe the rims have changed?

[deliquium]

To listen to some of our customers you would think it was the end of the world if, on a pair of wheels, there was a single thread showing, or a single spoke end visible above the nipple.

Colin, don't you apply rim tape before letting the "customers" in question receive their wheels?

[Mick F]

It doesn't matter Mick F - your wheels are ok?
Mine are.

Mine are marvellous, not just ok!

[531colin]

To listen to some of our customers you would think it was the end of the world if, on a pair of wheels, there was a single thread showing, or a single spoke end visible above the nipple.

Colin, don't you apply rim tape before letting the "customers" in question receive their wheels?

"Don't tell them, Pike!"

[fivebikes]

There's nothing more annoying to me to see threads showing! As much thread as possible should be in the nipple.

I have a Chrina/Sora wheelset bought on Ebay for about £40.00 18 months ago. On both wheels a turn or two of thread shows on quite a few spokes.I did worry at the time but trouble free use and a bit of road grime has stopped me worrying. Aside from cosmetics, is there any greater risk of spoke breakage than with a generally more accurately built wheelset?
BTW my Spa wheels are perfect!!

Jeremy

[gbnz]

Same method as you.
Why the difference?

It doesn't matter Mick F - your wheels are ok?

Mine are.

Maybe the rims have changed?

I've four Rigida Chrina rims, three of which are identical and one of which seems to be oversized. It's been impossible to fit a standard 700cc tyre to the oversized rim(Vittoria, Continental, Scwalbe) - I've spent 2-3 hours attempting to, breaking two tyre levers in the process, the LBS with years of experience was also defeated. Said tyres slip onto the other Chrina rims without an issue.

They were all bought from Spa, two in 2008, two in 2010 (At different periods).

I've had to resort to using a cheapo Michelin Dynamo tyre, as it's the only tyre I've been able to put on

[531colin]

I've four Rigida Chrina rims, three of which are identical and one of which seems to be oversized. It's been impossible to fit a standard 700cc tyre to the oversized rim(Vittoria, Continental, Scwalbe) - I've spent 2-3 hours attempting to, breaking two tyre levers in the process, the LBS with years of experience was also defeated. Said tyres slip onto the other Chrina rims without an issue.

They were all bought from Spa, two in 2008, two in 2010 (At different periods).

I've had to resort to using a cheapo Michelin Dynamo tyre, as it's the only tyre I've been able to put on

And, of course, you won't know this until you have built it into a wheel, at which point you won't want to send it back!
There is bound to be variation in anything manufactured, I wonder what the tolerances are, or if there is any generally-accepted figure for tolerance.
One wheelchair I regularly work on has one wheel the tyre goes on easily, the other wheel is always a challenge.

[531colin]

........... On both wheels a turn or two of thread shows on quite a few spokes................... is there any greater risk of spoke breakage than with a generally more accurately built wheelset?

I have never seen any failures which I attributed to the threads not being completely covered by the nipple, I think its just one more thing for the wheelbuilder to obsess over.
We don't have enough to think about, getting the rim label to read from the right side of the bike, the hub label to line up with the valve hole and be readable while sat on the bike, pulling spokes on the outside of the flange on both sides of a flip-flop or disc hub.........You've no idea........

[gbnz]

And, of course, you won't know this until you have built it into a wheel, at which point you won't want to send it back!
.

It took me about four months to finally recognise the problem, having never experienced it previously I'd originally blamed it on a specific tyre (Which I and other's had an issue with).