I have a bike front derailleur and rear derailleur are Shimano Sora, I don’t know if it can be replaced with Shimano DURA-ACE
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2 Answers
Shimano Sora is a rather low-end Shimano road bike groupset. (Only lower spec being Claris). Currently it is at R3000, a 9-speed generation. Thus it uses the standard "road" 6-10 speed (exceptions: Tiagra 10-speed, GRX 10-speed) / "MTB" 6-9 speed cable pull ratio in the rear derailleur.
Shimano Dura-Ace is the top-end Shimano road bike groupset. It is today a 11-speed groupset, and thus using the 11-speed "road" cable pull ratio.
Neither of these groupsets is a "MTB" groupset, although the Sora rear derailleur actually matches the "MTB" 6-9 speed cable pull ratio. So I presume if you don't need bigger cogs than what the Sora rear derailleur supports and if you don't need more capacity than what the Sora rear derailleur supports, you could use a Sora rear derailleur with "MTB" shift levers.
The current Dura-Ace is not compatible with any "MTB" cable pull ratio. Presumably if you are able to find a 10-speed Dura-Ace rear derailleur, it could be compatible, but then you have to check if it has enough capacity and if it supports big enough cogs. Being intended for road racing, it probably only supports tightly spaced cassettes with big sprocket not being that big, and may not have enough capacity for a triple "MTB" crankset.
I'd say using Sora rear derailleur on a mountain bike is rather odd, but might work if it doesn't have a 10-12 speed system. Replacing it with Dura-Ace would be even more odd and a waste of money, plus probably wouldn't even work.
Cost
Dura Ace is the top-end of the shimano groupset range. Sora is not-quite bottom, with Claris being the road groupset below. There are non-road-specific groupsets of "Tourney" and no-name further below that.
Between them are tiagra, 105, Ultegra, then Dura Ace.
As you climb the ladder of groupsets, the cost goes up and the weight goes down. This can also result in a shorter lifespan for the high-end components.
Example - a quick look across https://www.wiggle.com/cassettes shows
- Dura Ace R9100 cassette €212.21 - €246.41
- Ultegra R8000 cassette €87.23 - €103.03
- 105 5700 cassette €55.99
- Tiagra HG500 cassette €38.07
- Sora HG50 cassette €9.54 - €36.95
So a DA cassette is ~double the cost of the next one down. If you're racing professionally, where grams count and sponsorship pays for your parts, then DA makes sense. For us mere mortals, that's just too much money.
Also note that lower groupsets have different numbers of gears, so replacing one part will probably have a knock-on effect, where you need a new shifter, then a new chain, and so on.
Given your bike has Sora now, the rest of the bike will be of similar construction. Massively upgrading the drive train will not make a low-end bike into a high end bike.
Advice: If you want a bike equipped with Dura Ace, buy one that is so-equipped already. Do not sink money into the bottomless pit of upgrades.
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1As noted several times, the rest of the bike does not have to be bad just because it has Sora or Claris. My Claris bike was also sold with 105 (which was not available, else I would have bought it), the only difference was the groupset. Otherwise the same frame, same wheels, hubs,... Now they also have a one level higher one with Apex 1x11, but still a lot is in common, including the frame (except for the paint) and the wheels (althou with better tyres). Of course, DA is completely somewhere else and will be sen on top full-carbon-fiber models. Jul 28, 2021 at 20:29
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1The top 5 cogs on Dura Ace are titanium. Ti is softer than steel, and those cogs wear very fast. I think that many DA parts are at least as durable as 105 or Ultegra, but the cassette is absolutely not one of those. Jul 28, 2021 at 21:22
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1Even many pro teams use Ultegra cassettes rather than Dura Ace, its a large cost saving for the team over the a season and in many cases is a good alternative to adding weights to the bike to hit the weight limit.– Andy PAug 2, 2021 at 8:25