Originally Posted by
Mikebike12
Ok, here's a dumb question based on your suggestion. Is there an actual difference between a road derailleur and a MTB derailleur? I see that the one you recommended has a longer cage so it would definitely do the job but I get the feeling that it is just the name tag on it. Is that right?
Not really. There are some MTB derailleurs that only work with MTB shifters, but the general function and mounting of them is the same as road. The real difference came about the time 9 speed came out for road and MTB. Until then 28t low cogs were the max for both, but with 9 speed Shimano MTB the derailleurs could start handling much larger cogs. And then the next change was the MTB derailleur shift ratio stopped being compatible with road. That's why Shimano 9 speed keeps coming up - they work with (nearly) everything 6-10 speed road.
Today, road derailleurs can even have super wide capacity, but your older system isn't compatible with the newest stuff. So we are fortunate that Shimano keeps making 9 speed Deore.