CaptCarrot

As above, I am upgrading a 24 speed to a 27.

The front tripple is 24, 34, 42 and the rear cassete is currently 11-32. If I have done my math correctly, this gives me a max xhain wrap of 39.

Now I know that I will have to match a 9 speed chain and cassette (looking at 11-34), that is no problem. Also I will have to upgrade the rear shifter.

But will I have to upgrade the rear mech?

I don't have a huge budget, and I happen to be quite partial to my cheap and cheerful Shimano Acer RD-M340.

It fits all of my requirements...

• Max. Sprocket: 34T
• Min. Sprocket: 11T
• Max. Front Diff: 20T
• Total Capacity: 43T

Apart from the fact it is only "rated" for 7/8 speed use.

As it has a capacity of 43T and the max chainwrap from a 24-34-42 x 11-34 would be 41, in theory there should be no problem.

Should I risk it, or should I get a 9 speed rated rear mech?

kenhill3

No problem that I can see. Rear mech doesn't care how many cogs ya got.

maddmaxx 

As long as the teeth on the derailleur pulley's aren't too "fat" for the slightly narrower links of the 9sp chain then it won't care. Most 8 speed derailleurs I've seen work just fine for 9. You can wait and replace this later as necessary.

You will find that if you step up someday to even a relatively inexpensive Deore rear derailleur, that the shifts may (just may) be a little crisper. You might also not notice the difference.

Steev

9 speed chains are narrower on the outside. The inside dimension is still 3/32", just like 7, 8, 9 and 10 speed.
I don't see much point in the OP doing this, what are you hoping to gain here?

CaptCarrot

The front crankset and rear mech were replaced a little while ago, but funds did not allow to replace cassette and chain. These are now worn, and my shifters are not catching properly (the ratchet mech is worn). There is no great diff in price to u/g from 24 to 27 so I thought I might look into it, but I didn't want to splash out on a new rear mech.

Sixty Fiver

A 9 speed cassette with a 34 low is going to be an xt level part (if you use Shimano) and a 9 speed shifter will also be needed... I would presume this is a mountain bike by the 24/34/42 front chain rings.

The Acera is an okay rear mech but a Deore would be better and an XT better still... they really don't care how many cogs are back there.

If you have to replace the rear shifter anyways then upgrading to a 9 speed makes good sense.

bikinfool

Are you sure the shifters are worn or is possible the old grease is just getting gunked up? You might try flushing the shifters with liberal amounts of WD40 or similar while working the shifters. If that frees them up just be sure to spray in some lube...cheaper than upgrading (if you could say it's an upgrade to 9 from 8).

CaptCarrot

Well I'll give that a go, but they are missing the biting point and the lever just swings all the way with no resistance.

Steev

With that symptom, you'll likely see sucess

CaptCarrot

Thanks.

On a side note, I just popped into Halfords (I'm in the UK) and picked up a set of 27speed Mega9 compatible Deore Rapid Fire SL (SL-M511) for £10 (out of the bargin bin).

I am contemplating keeping or ebaying. My only dislike is the displays are not numbered, but for a tenner I ain't arguing.

And to put that into perspective for you foreigners

£10 UK = $14.25 US = €11.17 EU at current rates (YMMV)

Anyway, the reason for telling you this is because the guy in the shop said that really, yiou need a deore mech to go with the shifters, otherwise it may not track properly.

Is he telling the truth, or will my Acera mech be fine?

tommyd49

If you put any thing other than a Deore rear mech on, your bike will burst in to flames.

CaptCarrot

I'll read that as my Acera will be fine then?

I think he was just trying to get me to drop some more cash.

tommyd49

Yep, that's Halfords for ya! Still, good deal on the shifters.

CaptCarrot

tis what I thought. So far my best deal on cassette and chain (8 or 9 speed) is £25-30. This is for Shimano HG50/53.

I have had poor result mixing shim and non shim in the past, so I am trying to keep it as close together as possible.

You never know... I may drop the extra and get the deore rd, but if the acera is going to work fine I don't really see the need, apart from psychological.

CaptCarrot

BUGGER

Oh well, looks like my acera is out the window... just took another look at my front cranks (cheap an cheerful) SR Suntour Duro

I got my numbers the wrong way round. It's not 24/34/42, it's 22/32/44. Meaning my front difference is 22 (2 more than the Acera allows) and my chainwrap therefore would be 45 (again, 2 more than allowed)

Bill Kapaun

You're probably still good if you size the chain properly. ans stay off the smallest cog with the smallest ring.

CaptCarrot

Cheers - There is no way I ever shift into BB or SS anyway. I tend to use a range of 3 gears for each of B and S, and a range of 4 for M when shifting. So that won't be a problem.

Cheers for that.



On another note, I did stumble across this...

Wondered what anybodys opinion on this would be as it is sheap, but I am not going to be riding thousands of miles so it may be adequate.