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I currently have a 9 speed 11-25T cassette on my road bike. I'm thinking about switching to a different cassette with more teeth on the climbing gear. The cassette I'm currently look at is a Shimano CS-5700 10 Speed Cassette.

Can I swap my cassette from 9 speed to 10 speed without swapping my rear derailleur?

Is a 10 speed cassette wider than a 9 speed cassette or is the spacing between the gears wider?

Do I just need to adjust the wire tension in order to alter how much the derailleur moves when shifting in order to accommodate for the difference in spacing?

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4 Answers 4

up vote 9 down vote accepted

The spacing between 9 speed and 10 speed is controlled at the shift lever.

A 10 speed rear dérailleur will work with a 9 or 10 speed cassette and shifter. A 9 speed rear dérailleur is not compatible with 10 speed.

The width of the chain and the cogs is the biggest issue. The pulleys on a 10 speed dérailleur are narrower, and a 10 speed chain will not rest correctly on the jockey pulleys of a 9 speed dérailleur.

That does not mean it will not physically work, only that the shifting performance will be slow, you may drop gears unexpectedly, or have the chain skip unexpectedly.

Long story short, 10 speed should be 10 speed all the way throughout your bike for it to work consistently and properly.

Cable tension has nothing to do with cog spacing. That is designed into the shift lever. It is not adjustable, except by replacing the shifter. I hope that helps.

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So it looks like I have a black Shimano 105 RD-5500, which Shimano lists as a 10 speed derailleur. So does this mean I can safely go from my 9 speed cassette to a 10 speed cassette? –  Jakobud Apr 26 '12 at 19:40
    
If you have 10 speed shifters, yes. –  zenbike Apr 26 '12 at 21:07

As far as my knowledge stretches, the shifters control how far the derailleur moves with each shift so as long as the number of speeds on the cassette = the number of speeds on your shifters you will be fine. But be careful when selecting cassettes as you need a 10 speed wheel to run a ten speed cassette.

SO BASICALLY THAT IS A YES BUT YOU MAY NEED A NEW WHEEL OR HUB!

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Not entirely true. It's more important that the pitch of the shifter be the same. There have been 7/8 speed clusters with several different pitches over the years. –  Daniel R Hicks Jul 16 '12 at 11:42

After a decade of riding, I rebuilt my bike, which came with Ultegra 9-speed shifters and derailleurs.

I replaced some parts, including the shifters. No new 9-speed shifters were available, so put on 10-speed Ultegras.

I kept the 9-speed rear derailleur in place. I took off the 9-speed cassette, put on a 10-speed cassette, and started riding.

Worked fine — no adjustment needed! Go figure.

I've not had any problems in several years and many miles on this hybrid arrangement.

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The derailleur itself does not have any say on how many sprockets you can use or the distance between them, it is only limited by how close or how far away from the dropout it can get. For the most part you could probably use the same derailleur, but you might need to adjust the high and low limiting screws.

The real problem is with the shifter. Back in the old days, they only had friction shifters where you, the rider, had to fine tune the location of the derailleur by yourself. If you have that kind of shifter there is no problem. If you have a modern indexing style shifter where you just click a button and it jumps to the location for you then you might have to do a bit of tweaking or totally replace the shifter. Adjusting the cable only fine tunes the alignment of the derailleur to the sprocket and has almost nothing to do with the number of sprockets you can use.

But, before you do anything, check to see if your rear forks are wide enough to take an extra sprocket. You might even need to change the rear wheel altogether. I would take it into a bike shop and let them take a look at it. If they are worth buying from, they will give you some straight advice.

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