Can anyone explain what the ERD figure is and how it works for spoke length calculation.

I’m curious as I have Straight Pull Hope III Hubs with 4.2d DT Rims which I wouldn’t mind swapping over to ZTR Flow… but, I’ve been told spoke length is different and Straight Pull Spokes aren’t easy to get hold of at all. Is this rubbish? Anyone know?

It would be nice to know the principal anyway behing ERD or be pointed at some good explanation online somewhere?

I’ve done Pro III with mavic 819s using 256mm straight pulls, IIRC. Flow are 2mm less ERD than Mavic, so allowing for the special 16mm spoke nipple that you need with the 819s, the Flows will build up nicely with 257/258 and standard length 12mm nipples (and that is correct that there is only 2mm allowed for a 4mm difference in nipple dimensions). Allegedly. I’d need to find the spoke box to confirm the size I used.

I did all the calculations from first principles at the time. ERD is the diameter of the rim from the seat where the spoke nipple rests on one side to the opposite spoke hole seat.

[double post]

the principle behind ERD is covered well by Sheldon as ever (RIP)

Thanks peaslaker… I literally have no idea myself about this topic but if I know I’m buying the right spokes then I’ll just get them cos I’ve got someone who’ll build them up for me if I give me the stuff thats needed. If you can confirm your thinking that’d be great.

Don’t suppose you can point me to where I can get the right length online? …and whether there’s any choices of butted, double or triple butted, silver, black ??

Thanks for help so far, I’ve been wanting to change the rims for ages now.

Any luck confirming the spoke length you had. Based on your logic I looked for both 257mm and 258mm straight pull spokes so I can get them if you reckon thats definitely correct but I’ve had no luck.

surely its worth giving Hope a call/email as they are now building these rims onto Pro3’s so will be able to tell you all this information as they are building them inhouse.

Sweep, go to the sheldon brown site as suggested and learn about wheelbuilding and the factors involved. without wishing to get into a bun-fight about it you will learn nothing from

Flow are 2mm less ERD than Mavic

, even if that is accurate.
you will also find out all about spokes, butted, double, triple or plain-gauge as well.
it’s all well written stuff that’s pretty easy to understand. you may even find yourself inspired to build the wheel yourself.
as an example a friend of mine was convinced i’d bought the wrong spoke length for a wheel build i did recently, despite the fact that we were using different ( mavic ) rims, and was surprised when the build came out ok.

Well, I’ve spoken to hope and to someone who’s taken their ‘Pro3 with 4.2d’ wheelsets apart.

Firsty, hope confirmed that they are making them with the ZTR Flow Rims, so I asked them about supplying the spokes and surprisingly they told me they’re using the exact same spokes for the ZTR Flow and the DT4.2d rims. I double checked as much as I could with them and they were positive about it. So no shelling out for spokes.

I spoke to a friendly chap at JustRidingAlong where I plan to buy the Flow rims and he said at first that they’d ‘have to be different’. He went on to say that there was 8mm less ERD on the Flow so in theory the spokes needed will have to be 4mm shorter than what I have.

He also told me that ‘having had the ones I have apart before’ that he recollected that the spokes seemed a bit short really, to the tune of 2mm so I MIGHT get away with it and Hope might well be doing that. If they were still too long then they could be ‘cut a little’ but there’s a chance some more thread would also have to be made.

The simpler option would probably be even to sell my wheels ‘as is’ and buy these new ones on the ZTR Flow rims from Hope when they come out. I completely forgot to ask when they are going to be available or how much they might cost.

So… there you go… for the potential pitfalls of changing them I’m probably much better off selling the ones I have and buying the new set instead with a top up of money. If I relace on new rims the rims will cost over £130 by the time I get them to the door and I’ll have to flash a few quid to get them laced up.

So, might have a great condition Hope Pro 3 on DT 4.2d wheelset to sell any minute, we’ll see. Better make another call to Hope to see when the new ones will be out and how much they’ll be.