I was thinking of converting my current SRAM 3x7 hub to a SRAM Dual Drive 3x9. The local bike shops don't think this is possible as it requires spreading the rear stays out by as much as 2.54 cm to fit it in. Is there any one on the forum that currently has a SRAM Dual Drive on their bike? I would appreciate some tech info and SRAM won't reply to my e-mail either from USA or Europe.

I've never attempted it on an aluminum frame. The general consensus is that the stays on aluminum frames can't be spread.

I've spread the stays on several steel frames with satisfactory results. You generally don't have the mallability and heat treating issues with steel frames, but many shops still won't do it because it will void your frame warranty.

2.54mm is not a lot of difference for a steel frane. You could let a spacer keep it spread without a cold set.

I have a lot of clearand on my 3X7 dual drive between dropouts, especially the left.
If you have Al, maybe you could measure to seel if you have the 2.54mm clearance-just dont try and spread, keep the same spacers. You might slide the wider carrier/new hub in there without needing to spread. Remember, you can shift the hub left, so you don't need all that clearance on the sprocket side.

What bike is this on?

he said CM, meb. thats about an inch. and thats a fair amount. I wouldn't do it, steel or aluminum.

I didn't notice the cm-since the cassette is about 4 mm wider I expected the spread would be proximate.

Anyone know why the LBS needs to spread it so wide?

You might be able to go to 3x8 by replacing your spacers with a set designed for a 9-speed hub.