Rear Mech upgrade

samg123

Currently have a Tiagra 9 speed rear mech on an 8 speed cassette. The mech is getting a bit rusty and generally knackered (was very poorly looked after by previous owner) so I'm looking to upgrade.
My question is what compatibility issues do I need to look out for? I know I only need a short cage, apart from that is there anything I should look out for?

ugo.santalucia

Waste of money... give it a good clean with WD40 and a brush, oil the spring and if needed wipe the rust away from the nuts with some fine abrasive paper (polishing grade).

Rear mechs are all the same in therms of quality and performance. You can buy a Dura Ace and you will notice no benefit

Pseudonym

ugo.santalucia wrote:

Rear mechs are all the same in therms of quality and performance.

not exactly.....rear mechs may all be the same in terms of functionality, but claiming they are all the same in terms of 'quality' is nonsense, because they obviously aren't. Higher quality usually equates to a slicker shift, so you can't really claim they are the same in terms of 'performance' either...

StorckSpeed

Try giving it a good clean and lube first.
If you need to get a replacement then stay away from any Campag compatable rear mech's. Stick to either Shimano, SRAM or MicroSHIFT. Most rear mechs available now are labelled as 10 speed but if you get one and fit it to your bike it will happily work with 8 speed, (I have an old hybrid I've doen this with). The gear spacing seems to be dictated by the shifters and the amount of cable released with every click and not the rear mech itself.

Yossie

Just go for anything Shimano in your price budget - 8, 9, 10 speed will work with your 8 speed cassette. Anything will work (as far as I know). If you have a short cage on at the mo' and don't intend to massively change the ratios of your cassette (ie chuck a mahooosif 38 tooth on there) then go short cage again.

If you go 10 speed it also means that if you want to upgarde the shifters/cassette at anytime you will have the option to.

Whack some new cables on at the same time.

All rear mechs aren't the same - as you go up the range they get better - shifting action, weight, etc. What they do - ie move a chain up a cassette - is the same, but how they feel, how they perform and the functionality is different.

If your mech is buggered and shot then it'll feel cack everytime you shift gear - take it off, chuck it in next door's garden.

You'll feel the most benefit when you team an upgraded mech with upgraded shifters. As Ugo has kindly mentioned D/A - the feel of new D/A with perfectly set up cables on a warm summer's day riding behind Mrs Yossie - oooh, you can't beat it.

HTH

Y

ugo.santalucia

Pseudonym wrote:

ugo.santalucia wrote:

Rear mechs are all the same in therms of quality and performance.

not exactly.....rear mechs may all be the same in terms of functionality, but claiming they are all the same in terms of 'quality' is nonsense, because they obviously aren't. Higher quality usually equates to a slicker shift, so you can't really claim they are the same in terms of 'performance' either...

You press the button, it shifts the gear.... if it does that quick, and Sora does it as quick as DA, then all is good and well, the alleged quality "feel" is all in your head. Is it not that your Sora is on a winter bike, full of crap and salt, while the DA sits nice and clean on your best bike? Swap them and try the "feel" game a few months later

Difference in weight between the bottom of the range and top is around 50 grams, give or take it's the weight of a loud fart

styxd

Yes, all rear mechs are near enough the same. All they are is an arm with a few pivots and a spring.

The shifters & cables determine how well your mech shifts.

Pseudonym

ugo.santalucia wrote:

You press the button, it shifts the gear.... if it does that quick, and Sora does it as quick as DA, then all is good and well, the alleged quality "feel" is all in your head. Is it not that your Sora is on a winter bike, full of crap and salt, while the DA sits nice and clean on your best bike? Swap them and try the "feel" game a few months later

Difference in weight between the bottom of the range and top is around 50 grams, give or take it's the weight of a loud fart

it's just that you said they were all the same in terms of quality - 'high-end' carbon, titanium and sealed bearings v 'low-end' die cast aluminium, steel and plastic bushes suggests there is a clear difference quality. Perhaps you chose your words poorly, I dunno...

ugo.santalucia

Pseudonym wrote:

ugo.santalucia wrote:

You press the button, it shifts the gear.... if it does that quick, and Sora does it as quick as DA, then all is good and well, the alleged quality "feel" is all in your head. Is it not that your Sora is on a winter bike, full of crap and salt, while the DA sits nice and clean on your best bike? Swap them and try the "feel" game a few months later

Difference in weight between the bottom of the range and top is around 50 grams, give or take it's the weight of a loud fart

it's just that you said they were all the same in terms of quality - 'high-end' carbon, titanium and sealed bearings v 'low-end' die cast aluminium, steel and plastic bushes suggests there is a clear difference quality. Perhaps you chose your words poorly, I dunno...

I give you that... you are right about bearings vs bushings... haven't thought of that... that said, they are in such a place that it's difficult to keep them clean and greased, the benefits are therefore often irrelevant.
Carbon, titanium, alloy, no difference whatsoever on a derailleur: mechanically it's under very low load, therefore any material will last forever and perform well... thanks to the original Campagnolo design of the parallelogram (look at Gran Sport 1950), the device itself is by nature overengineered and even wacky attempts to make them ultra light have been succesful... Simplex used to make a derailleur out of plastic and it was fine... I recall another plastic model from Ofmega, which was fine too