Buying rims by ERD

Veggie said:

I'm gathering parts to build a 26" rear wheel. Why do many (all?) of
the catalogs and website list rims by ERD, and not simply the total
wheel size?

I've seen ERDs of 540mm, 543mm, 546mm. From what I could tell from
various FAQs, the ERD is the inside diameter of the rim. So 540mm is
about 21.5", add 2" for the rim itself, and another 2" for the tire, and
I get around 26".

So is a rim with ERD 540mm the right one for a 26" wheel?

These are all 26" rims. ERD is necessary so you know what sized spokes
to build it with.

Veggie said:

I'm gathering parts to build a 26" rear wheel. Why do many (all?) of the
catalogs and website list rims by ERD, and not simply the total wheel
size?

I've seen ERDs of 540mm, 543mm, 546mm. From what I could tell from
various FAQs, the ERD is the inside diameter of the rim. So 540mm is
about 21.5", add 2" for the rim itself, and another 2" for the tire, and I
get around 26".

ERD is only of interest if you're building your own wheels. You need to know
ERD to calculate the required spoke lengths.

The nominal size of a 26" MTB rim is 559mm bead seat diameter.

http://sheldonbrown.com/harris/rims/559.html

Art Harris

In article <[email hidden]>, Veggie

Quoted message said:

I'm gathering parts to build a 26" rear wheel. Why do many (all?) of
the catalogs and website list rims by ERD, and not simply the total
wheel size?

I've seen ERDs of 540mm, 543mm, 546mm. From what I could tell from
various FAQs, the ERD is the inside diameter of the rim. So 540mm is
about 21.5", add 2" for the rim itself, and another 2" for the tire, and
I get around 26".

So is a rim with ERD 540mm the right one for a 26" wheel?

Yes. ERDs vary with different MTB rims - V, double and single wall,
it's the bead diameter of the rim (at 559 mm) that is the defining
constant of a MTB rim's specs.

The ERD is a requirement of calculating the spoke length for lacing up
the rim. This is convenient to know if a rim on an otherwise
serviceable wheel has given up the ghost: if the replacement rim has an
equal ERD it can simplify - and discount the cost - of resurrecting the
wheel. For instance, the rim on my rear Mavic Helium wheel needs
replacement; replacing it with a Mavic Open Pro - a rim with an equal
ERD - will not require new spokes.

Luke

Veggie said:

I'm gathering parts to build a 26" rear wheel. Why do many (all?) of
the catalogs and website list rims by ERD, and not simply the total
wheel size?

I've seen ERDs of 540mm, 543mm, 546mm. From what I could tell from
various FAQs, the ERD is the inside diameter of the rim. So 540mm is
about 21.5", add 2" for the rim itself, and another 2" for the tire, and
I get around 26".

So is a rim with ERD 540mm the right one for a 26" wheel?

ERD is the effective rim diameter, measurement for spoke length
calculation. ALL are 26 inch rims, in that they can use 26inch tires
and can be used on a bicycle for 26 inch wheels.