Ask Levi: Should I Upgrade my Rear Derailleur?

Today let’s look at possible upgrades for a new road bike…

hi there! i’m just new in road biking and my bike has shimano 105 components. can i replace the 105 derailleur with a shimano rd-7900 dura ace? im not satisfied with the 105 rear derailleur. is it compatible or do i need to replace all the components with dura ace? thanks!

-Derailled Dan

Hi Dan,

If you have a newer bike with 10 speed components (i.e. 10 cogs on the rear wheel,) then you can mix-and-match most of the components like you want. The general rule is, “as long as everything is Shimano, you’re fine.” (Don’t mix Campagnolo in there.)

However, there was a slight change the the cable pull ratio on the newest 7900 shifters and derailleurs. That means if you put a 7900 rear derailleur on there, you would also need the matching 7900 shifter. The other parts should be compatible. (Always look at Shimano TechDocs to be 100% sure.)

But just because you can, doesn’t mean you should. In my opinion, going from a Shimano 105 to Dura Ace rear derailleur is a waste of money. The Dura Ace will be lighter, but there will be very little performance difference overall (especially if the rest of the bike is 105.)

When setup properly, the 105 rear derailleur should shift flawlessly. These days, Shimano 105 works very well. You may see a very slight improvement in performance with Ultegra, Ultegra SL, or Dura-Ace, but what you’re paying for is the weight savings. You could actually see a decrease in durability with certain upgrades (since they sacrifice strength and durability for weight savings.)

And if you were going solely for weight savings, I’d switch the entire bike from Shimano 105 to SRAM Rival, which is cheaper and lighter than Shimano Ultegra!

So here’s what I would do:

If I were you, I would buy top-of-the-line wheels and tires, and I’d also replace the shifters before replacing the rear derailleur.

And since the shifters are 105, they should be fine. I’d only replace them if you actually had shifting problems once the drivetrain was set up properly. (That’s the key here – even some mechanics don’t get the drivetrain set up properly when you’re paying them to do so.)

Put things in perspective – $300 for a rear derailleur is a lot of money. I can’t see putting a $300 derailleur on a bike unless the bike is $3000 or more, and I don’t know of any bikes spec’d with a 105 group that fall into that category.

So if you want to spend money, spend it on wheels and tires first. Perhaps some Williams System30 wheels and Michelin Pro3 Race tires.

But other than that, I’d just save the money so that you can afford to replace the chain, cassette, and chainrings as they wear out from normal use.

Not that upgrading drivetrain components is a bad thing, but being new to road biking, you might not appreciate the fine details of the high-end components (as I mentioned already, there’s not much difference,) and you wouldn’t get the true feel of Dura Ace when you just mix one DA part into a 105 drivetrain.