Rear der hanger extension
 

so i just came across this concept and order one after checking to see if i could go up a few teeth on rear cassete.
small road der. old 9 speed was limited.
do theses things work

There have been many threads on this subject. I would only consider one of those things if there were no derailleur that would work with the cassette you want to use. For 9 speed Shimano road, any 9 speed Shimano MTB rear derailleur will work and most will go up to a 34t or 36t cassette. I have this one on my 9 speed gravel bike with an 11/34 cassette. https://www.amazon.com/SHIMANO-Deore.../dp/B00WJGWJUC

i did consider but i have dura ace and love it. for $20. i hope it works. need new larger cassette so time will tell.

Yes, works. I got a long cage (Force) RD, as per dsaul's opinion above,

but the roadlink/ Red combo was lighter so kept that to run 11/34.

The chain is just slack in small/small but I never use that anyway.

I have one and use it with success, but only a week at a time, when I take a week to go riding in the mountains of CO.
SRAM Red 10 sp w/34t cassette.

Agree but will add that Shimano 8 speed MTB rear will also work with 9 speed cassettes.

I've done several of this sort of thing on road and gravel bikes. The only gotcha I've run into is that some RDs won't easily accommodate a 34t or 36t cassette. Can't tell you which model numbers but some can easily go a few teeth above spec some can't. Sometimes reversing the B screw or using a longer one works.

But just try it. Used MTB RDs can be found inexpensive on eBay.

I assume it's the a aesthetics of the DA you want to keep. I totally get that. But the the XTR is the equivalent and looks nice. I use anything I can find, but usually shoot for XT or XTR for the higher end bikes. But Deore and SLX work fine.
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Yes, they work!

Yes, they work. I put a 36 tooth low on my touring bike with one.

https://live.staticflickr.com/65535/...cf820562_o.jpg_IMG4968 by Stuart Black, on Flickr
https://live.staticflickr.com/65535/...183a26b7_o.jpg_IMG4968 by Stuart Black, on Flickr

The 9 speed XTR derailer would quite work well with a 36 but the Wolftooth RoadLink made the complaining a lot less.

One caveat: The RoadLink is delicate so be careful putting any leverage on it. I also had to modify my derailer hanger to make it work with the Cannondale. It just took a bit of filing to make it fit. I wouldn't suggest doing it on anything other than a replaceable hanger, however.

A hanger extension will allow your derailleur to clear larger cassette sprockets, but it will not increase the wrap capacity of your derailleur. E.g. a short-cage derailleur would be unlikely to wrap enough to handle an 11-40 cassette even with a hanger extension.