Some Rim ERD Questions

[BCDrums]

I'd like to replace a rim with a flat spot without replacing the wheel's
spokes- it's on a bike I rarely ride, so I'm looking for the least
expensive fix The current rim is a Mavic MA40. My copy of Spocalc says
this rim has an ERD of 613. But here's what it says in Spocalc:

"Mavic MA40 (ERD is Mavic's spoke support dia + 3mm for nipples)"

I'm not sure what that means for the ERD of a new rim. Should I be
looking for a rim with an ERD of 613, or 613-3 (610)?

Also, is there any leeway on the ERD for a new rim? Can I get away with
613 or 611?

Would anyone care to suggest a favorite (inexpensive) rim with the right
ERD? The bike is an old tourer (a Tanguy) on which I once rode
cross-country.

Thanks!
BC

 

[Art Harris]

BCDrums wrote:
> "Mavic MA40 (ERD is Mavic's spoke support dia + 3mm for nipples)"
>

My version of Spocalc just lists the MA-40 as 613 mm with no note.

I think they're saying that the nipple head has some thicknes, so the
top of the nipple is about 1.5 mm above where the nipple rests on the
rim.

Also, some folks like to have the spokes flush with the top of the
nipple, others like then to come to the botton of the slot in the
nipple.

If the spokes are too long, the nipple can bottom out and yoy won't be
able to get enough tension. If they're too short you might not have
enough thread engagement.

I usually calculate the spoke length using the given ERD, and then
subtract 1 mm from the resulting spoke length when ordering.

> I'm not sure what that means for the ERD of a new rim. Should I be
> looking for a rim with an ERD of 613, or 613-3 (610)?
>

First, see where the spokes end in the nipples of your current wheel.
If they're just right, I would get another 613 mm ERD rim. If they're
a little short, you could go with a slightly smaller ERD rim.

You don't have to be dead on, but it's better for the spokes to be 1
or 2 mm shorter than ideal rather than 1 or 2 mm longer.

Art Harris

 

[landotter]

On May 10, 7:05 am, BCDrums <[email protected]> wrote:
> I'd like to replace a rim with a flat spot without replacing the wheel's
> spokes- it's on a bike I rarely ride, so I'm looking for the least
> expensive fix The current rim is a Mavic MA40. My copy of Spocalc says
> this rim has an ERD of 613. But here's what it says in Spocalc:
>
> "Mavic MA40 (ERD is Mavic's spoke support dia + 3mm for nipples)"
>
> I'm not sure what that means for the ERD of a new rim. Should I be
> looking for a rim with an ERD of 613, or 613-3 (610)?

If the spoke is still recessed a couple mms into the backside of the
nip, you should be able to get away with a Sun CR18 with an ERD of
611. Wrong color, of course...