I think the reasoning is that short-cage RDs are often also designed for smaller cassette cogs, so you would get a smaller chain gap with a given cassette than a "mountain" RD that is rated for larger cogs. That should shift a little better, but you can do a lot with the B-screw adjustment on the longer-cage model. And since you're considering a 26-30T big cog anyway, I don't think a long-cage RD would be so bad at shifting. (If you wanted to do a triple plus a corncob, then I'd probably try to make a "road" RD work.) :thumb:

Funny you should say that because I've considered it many times with the desire to simplify a drivetrain and close the gaps (gear ratios). Not like any of this is terribly important, but I obssess about bikes and mechanical stuff in general. IOW's, I do like tinkering for fun. A 2x8 or 9 is about ideal for me as long as I can get low enough and high enough gears. Hard to do a corncob on an 8 or 9spd drivetrain and still do it to it in the hills. For me, anyway. I prefer a nice balance between spin and mashing...haha

Oh...
Then why make short cage mtb derailleurs? Deore, XT, XTR, etc
Also, how do you mean about the B screw adjustment?

Good question! I suppose at the highest levels of MTB competition, maybe people were using tighter cassettes and going faster, and having parts that were a little more "road" helped.

Sheldon Brown's page has some good stuff about the B-tension screw here: https://www.sheldonbrown.com/deraile....html#btension Usually, he discussed it in the context of wanting to put on a cassette with bigger cogs for lower gearing, so needing to turn the screw in to clear the cogs. I'm generally thinking about it from the opposite direction, and quite often remove the B-screw entirely. ;)

Okay. I thought that might be where you were going with it. Honestly, I'd never made a correlation before with shifting quality and the B screw. Thanks!

I remember my race bike (A PAramount PDG ) had a 12-24 rear , 105 short cage derailleuer , and indexed fine with Gripshift. None of the climbs were big enough to justify a bigger cassette in my area - especially when you had a triple up front --- but 90% of the time, the granny was removed and i rode it as a double --- wish i had a pic of that setup for this thread .

Ahhhhh , to be 23 and in shape again

I think it was about more chain wrap and ground clearance.

FWIW i have two vintage mtb's, one with a long cage M735 XT rear derailleur, the other with short. The short cage has noticeably less chain slap. Of course, all factors are not equal (spring may be more worn/weaker on the long cage, etc)