replace cassette for lower gearing

[afl2]

I have shimano tiagra HG50 9 speed 12-25t cassette and would like more lower end gears to get me up some hills.
I have seen some HG50 on the web with 34t but am not sure if compatable for a road bike.
Would i also have to change anything else on the drive train system to compensate for lower gearing? Is there a limit to what i can do??

 

[HLaB]

Get a expert opinion but without changes the usual maximum a a short road derailleur can handle is 27 or 28. So I suspect you'd need a longer cage to handle the 34t. The other thing you'd need is a new longer chain.

 

[TheDoctor]

The cassette will go straight on - that's the good news.
The bad news is that a road mech won't cope with a rear sprocket much bigger than 28T. For a 34T you'd need an MTB rear mech, and probably a new chain, as your current one won't be long enough.
That makes your shopping list :-
Rear cassette £18, Shimano MTB rear mech £30, and a new chain £10 or so.
Possibly an obvious question, but you do have a compact chainset, don't you? That's a cheap and easy way of lowering your gears if not.

 

[TheDoctor]

Double posted...

 

[Gary E]

I put a mega-range (14-34T) on my mountain bike. If you Google the model of your deraileur you'll be able to find the maximum amount of teeth it can handle (mine couldn't so needed replacing). I also had to lengthen the chain by a few links.

 

[slowmotion]

I hope this isn't too scary, but it really is worth a read as an introduction to gear stuff. Good luck.

http://www.stanford.edu/~dru/triplecheat.html

 

[2Loose]

They do a 27T Tiagra 9spd cassette nowadays, which will defo fit and give you a quite substantial drop in gearing without changing anything else on the bike.

 

[the_mikey]

I've done exactly this on my road bike: 11-32 9 speed cassette (SRAM PG950) , a MTB derailleur (Shimano XT) , and a new chain on my tiagra equipped bike.

 

[rockyraccoon]

As above. Check shimano tech docs (google it) for rear mech capacity. You will also need a few specific tools to do the job.

 

[Flattrackhero]

I swap between a campag veloce 11-25 and 12 - 29 depending on terrain on my summer bike with no adjustments required


---
I am here: http://tapatalk.com/map.php?ehw2on

 

[youngoldbloke]

Quote from an earlier posting Put a new 12-32 cassette (7 speed) on my Peugeot 525 - now winter bike - it shouldn't work with the Shimano short cage mech, but popped the wheel back in and turned the cranks, moved through the gears. Smooth as silk. No adjustments required, didn't have to increase chain length either. Moral seems to be - try it and see!
I had previously fitted a 12-28 with 48/38 chainrings, replacing the original 13-26 (with 52/42). I think at that point I increased the original chain length by 1 link. The rear changer - now almost 20 years old - is an Exage 500.

 

[PpPete]

There are all sorts of things that might or might not work. Take a close look at your rear derailleur. There will be a part number on it somewhere. If that's Tiagra it will be something like RD-4xxx-YY (xxx being 3 more digits and YY being two letters, either GS or SS)
Then you can head on over to Shimano's technical docs and find out what the "offical" capacity is. You can usually get away with a small number of teeth more than they say.

 

[afl2]

Clearly a lot to consider.I do have a compact 50/34t front.
Will do some more home work and get back to you all.Thanks for the advice.

 

[lejogger]

Check out the SRAM Rival gruppo for ideas. That's what I've got on my commuter/tourer/winter job. It combines a 50/34 Chainset with a 11-32 cassette. The rear mech is a mid-long cage... it may be that you only need to swap the cassette and the mech. I use a standard length KMC chain.

Gets me up anything even when fully laden with touring gear.

Edit: Shimano and SRAM are usually compatble with each other

 

[Tomba]

I recently done the same. Went from Tiagra rear mech and a 12-26 cassette to a Sram PG950 11-32 cassette. I had to change the rear mech to a MTB one (Shimano SLX) and also had to change the chain.
I got all my bits from Merlin Cycles as they were doing a sale. No idea if its still running though.

The only problem I ran in to was the outer gear cable from the chain stay to the mech. The one I had on was slightly too long because of the angle the cable goes in to the SLX mech, so I shortened it after a bit of trial and error and it works now.

Sounds like a major job but if I can do it anyone can. I also got help from a very knowledgeable person on the forum