Spoke calculator advice

[zmudshark]

I'm building up a set of Mavic OP's to Campagnolo Daytona hubs.

I get lengths about 1.5 - 2mm longer using Edd, as opposed to Pro Wheel Builder. I'll be using DT spokes/nipples.

What would the hive do?

TIA.

[DRZRM]

Not sure what Edd is, but PWB has been spot on for my last 5 or 6 builds. I trust that website.

[classtimesailer]

Something is wrong. 1.5 to 2mm difference is more than I ever got unless I did something wrong--like using the wrong number of crosses or the wrong hub/rim.
Best for me is measuring myself and using Roger Musson's.
http://www.wheelpro.co.uk/spokecalc/

[Mark McM]

It looks like the Edd calculator is using the ERD (Effective Rim Diameter) of the Mavic Open Pro, the ProWheelBuilder calculator is using the Spoke Seat Diameter supplied by Mavic.

Spoke Seat Diameter is the diameter to the surface where the spoke sit - in other words, it is the directly measured diameter to the spoke seat.

However, when sized correctly, the spokes shouldn't stop exactly at the diameter of the inside rim surface - they should continue into the head of the nipple, which is about another 1.5 mm.

Effective Rim Diameter is equal to the Spoke Seat Diameter plus an additional 3mm (1.5 mm per side) to account for the extra spoke length needed to reach into the nipple head.

Most rim manufacturers specify their rim dimensions in ERD, which can be inserted directly into standard spoke length calculators. But Mavic specifies Spoke Seat Diameter instead, which means you have to manually add the extra 3mm when inserting the data into a spoke length calculator*. It appears that the Edd calculator has done this for you. But the ProWheelBuilder calculator uses Mavic's Spoke Seat Diameter, so you have to add the compensating factor your self.

*In reality, you can perform the manual compensation either before or after the spoke calculation formula. For pre-calculation compensation, increase the rim's Spoke Seat Diameter by 3mm. For post-calculation compensation, add 1.5 mm to the spoke length.

[zmudshark]

Originally Posted by DRZRM

Not sure what Edd is, but PWB has been spot on for my last 5 or 6 builds. I trust that website.

https://leonard.io/edd/

[zmudshark]

Originally Posted by Mark McM

It looks like the Edd calculator is using the ERD (Effective Rim Diameter) of the Mavic Open Pro, the ProWheelBuilder calculator is using the Spoke Seat Diameter supplied by Mavic.

Spoke Seat Diameter is the diameter to the surface where the spoke sit - in other words, it is the directly measured diameter to the spoke seat.

However, when sized correctly, the spokes shouldn't stop exactly at the diameter of the inside rim surface - they should continue into the head of the nipple, which is about another 1.5 mm.

Effective Rim Diameter is equal to the Spoke Seat Diameter plus an additional 3mm (1.5 mm per side) to account for the extra spoke length needed to reach into the nipple head.

Most rim manufacturers specify their rim dimensions in ERD, which can be inserted directly into standard spoke length calculators. But Mavic specifies Spoke Seat Diameter instead, which means you have to manually add the extra 3mm when inserting the data into a spoke length calculator*. It appears that the Edd calculator has done this for you. But the ProWheelBuilder calculator uses Mavic's Spoke Seat Diameter, so you have to add the compensating factor your self.

*In reality, you can perform the manual compensation either before or after the spoke calculation formula. For pre-calculation compensation, increase the rim's Spoke Seat Diameter by 3mm. For post-calculation compensation, add 1.5 mm to the spoke length.

I was wondering the same thing, but couldn't express it as clearly. It's a Mavic thing?

If I'm not totally confused, the Edd numbers are what I want, correct?

Edit: If I need 296.5 F and 295.9 LR, I should be okay using 296 for both, yes?

[Tony T]

Are you searching the edd database?
If so, don't — input your own measurements into the edd calculator.

[zmudshark]

Originally Posted by Tony T

Are you searching the edd database?
If so, don't — input your own measurements into the edd calculator.

It would seem that @Mark McM nailed it, just want to confirm.

[Tony T]

I've found the Edd database to give incorrect results for set of H Pius Son wheels I built, however, when I input my own measurements, the results were the same as the DT Swiss Calculator and Spokcalc.

Note, In response to a question regarding a measurement in the database:

Leonard Ehrenfried Mod Stefan Vapaa • 2 years ago
I don't really have a way to verify the measurements that people send me.
I usually do a quick sanity check and then just approve the measurements.

Just saying that the edd calculator is correct but the database is not always correct, so better to do your own measurements,
including ERD (if you haven't done so already)

[Mark McM]

Originally Posted by zmudshark

I was wondering the same thing, but couldn't express it as clearly. It's a Mavic thing?

If I'm not totally confused, the Edd numbers are what I want, correct?

Edit: If I need 296.5 F and 295.9 LR, I should be okay using 296 for both, yes?

Originally Posted by zmudshark

I was wondering the same thing, but couldn't express it as clearly. It's a Mavic thing?

If I'm not totally confused, the Edd numbers are what I want, correct?

First, a quick correction on the nomenclature in my previous post: When I wrote "Spoke Seat Diameter", I really meant "Nipple Seat Diameter".

Mavic is the only rim manufacturer that specifies Nipple Seat Diameter - just about everyone else specifies ERD instead.

If you take a look at the Edd calculator, you'll see that for the Open Pro it says "ERD is Mavic's Nipple Seat Dia + 3mm for nipples" and the numeric value used is 605mm ( = 602mm + 3mm). When you select the Open Pro with the ProWheelbuilder calculator, it uses a value of 602mm for the rim, which is the number supplied by Mavic, and which apparently has not been compensated for the nipples. So, the Edd calculator should give a more correct spoke length in this case.

Just for giggles and yucks, I tried both spoke length calculators but substituting the Velocity A23 rim. Both calculators used 601mm for the rim diameter, and gave spoke lengths within 1/2 millimeter from each other.

Like Tony T says, for any formula, the output is only as good as the input. If the input values are off, the output value will also be off. And even if the stated dimensions are accurate, they may be using a different measurement method (e.g. ERD vs. Nipple Seat Diameter, center of flange vs. outside of flange, etc.). That's why, whenever possible, I measure component dimensions directly.

[bikingshearer]

I've built a wheel or two with Mavic Open Pros and Campy hubs using Edd (both the calculator and the database). Spoke lengths came out fine.

[zmudshark]

The rims will be here tomorrow, thanks to @thwart.

I have the Wheelsmith kit, so I'll double check everything.

I guess the lazy way out is lazy.

Thanks for the great advice, as always.


Edit: Do we have a spoke exchange here for unused new spokes?

[staggerwing]

It is not that hard to check directly to confirm:

http://www.parktool.com/blog/calvins...e-rim-diameter

[zmudshark]

Originally Posted by staggerwing

It is not that hard to check directly to confirm:

http://www.parktool.com/blog/calvins...e-rim-diameter

As I said, I have the Wheelsmith kit, with the rods. Just looking for a shortcut to get spokes ordered before rims arrive.

[ColonelJLloyd]

Originally Posted by zmudshark

Edit: Do we have a spoke exchange here for unused new spokes?

I thought there was an old thread, but a quick search didn't turn it up.

What lengths and counts? Happy to help if I have them stashed. If I do, they would be Sapim Race.