Converting 53/42 to a compact

spezial

My winter bike has big old 53/42 gears on the front, which is a bit tough on the legs going up really steep ones, so just wandered what the cheapest option is to change it over to a 50/34 or such like?


I'm hoping it's a nice cheap job, rather than needing to buy a new crankset, but I don't know how much of a process getting the chainrings off a crankset is, and whether this might have an affect on the rear part of the gearing too.

Any experiences/advice would be great.

softlad

assuming you have a standard double chainset, then your only option is to buy a complete new chainset - you will not be able to fit compact rings on your existing crank arms...

spezial

It is a standard set, so look like I'm doomed to buy a new chain/crankset.

Is that all I'll need, no new mechs or such like?

Stellite

You might need a new chain

tenor

If you are running Campag just fit a 39 inner and a 13-29 cassette - same range as a 50/34 with 12-25.

GavH

I did pretty much the same thing a couple of years ago. Total work involved:

1 - Removing old Square-taper BB and chainset.
2 - Fitting new HTII BB (@£15) and Tiagra compact chainset (@£45) (I didn't get any work done to the BB shell as it did not appear to need it)
3 - Lowering the front mech slightly to accomodate the newer, smaller outer chainring
4 - Tweaking the rear mech to ensure it indexed properly.

As I said, the cost was not huge and the overall time, despite my then relative inexperience was maybe 60-90 mins. I reckon someone who knows what they are doing would take a fraction of that.

synchronicity

I think you might only need shorten the chain by a few links if it's not too old.

richiebones

you can...with shimano (dont know about the rest) but you need to find a 50 toothed chainring with a 130 BCD and make sure the smaller ring is no more that 16 tooth difference from the larger.

http://www.dotbike.com/ProductsP5086.as ... aign%3dDDI

Pokerface

If your problem is just going up hills - why not simply replace the inner chainring with a standard 39 instead of the 42?

Pretty simple fix.

satanas

^ <sigh> Maybe he'd like a gear enough lower to be comfortable? :roll:

It's not clear from what's been said above, but the smallest rings that will fit various cranks are:
144 BCD (old Campag Nuovo Record, etc) 41T; 42T is much easier to find
135 BCD (newer non-compact Campag) 39T
130 BCD (Shimano and copies) 38T; 39T is the smallest size from Shimano
110BCD (most compact cranks) 33T; 34T is much easier to find

TA offers rings in the smaller sizes above (41, 38, 33T).

Smaller BCD's than this are generally MTB territory, and anything else is relatively non-standard and/or obscure, so maybe not cost-effective.

Pokerface

^--- NO need for a :roll:



As mentioned by another poster - a 39T and a 29 on the back will offer the same range as a 34T with a 12-15 on the front.

Much cheaper than a whole new chainset. And a whole lot easier to climb than with a 42T on the front (which is what I have on my winter bike. It's not easy at all!)

spezial

Thanks for all the advice everyone!

Thought this thread had died, as the Forum didn't notify me via e-mail that there had been any responses, but there have been loads!

GavH wrote:

I did pretty much the same thing a couple of years ago. Total work involved:

1 - Removing old Square-taper BB and chainset.
2 - Fitting new HTII BB (@£15) and Tiagra compact chainset (@£45) (I didn't get any work done to the BB shell as it did not appear to need it)

The current chainset is a Bontrager one on a Trek 1.2 from a few tears ago, would I need to replace the BB on it if I added a new Shimano compact set?

Also, where did you pick up a Tiagra chainset for £45!? That's well cheap!

spezial

Pokerface wrote:

If your problem is just going up hills - why not simply replace the inner chainring with a standard 39 instead of the 42?

Pretty simple fix.

This sounds great, as I mentioned in the post above, it's a Bontrager chainset, but I would assume replacing chainrings is possible on any chainset?

Also, does the gearing work reliably with such a disparity between the big & small ring?

spezial

Pokerface wrote:

^--- NO need for a :roll:



As mentioned by another poster - a 39T and a 29 on the back will offer the same range as a 34T with a 12-15 on the front.

Much cheaper than a whole new chainset. And a whole lot easier to climb than with a 42T on the front (which is what I have on my winter bike. It's not easy at all!)

It is a climbing related thing, yes! My summer bike has a 50/34 on it, with 12-25 on the back, which has got me up everything I've tried to climb this year, so just wanted to replicate this on the winter bike.

Pokerface

Spezial wrote:

Pokerface wrote:

If your problem is just going up hills - why not simply replace the inner chainring with a standard 39 instead of the 42?

Pretty simple fix.

This sounds great, as I mentioned in the post above, it's a Bontrager chainset, but I would assume replacing chainrings is possible on any chainset?

Also, does the gearing work reliably with such a disparity between the big & small ring?

If you replace the entire chainset with a Shimano one, you will also need a new BB as Bontrager uses a GXP one (different than Shimano).

Replacing the inner chainring is just a matter of undoing the little bolts on the chainrings and putting on a smaller inner ring. A 39 to 53 shift is the standard shift for that chainset and will not give you any shifting problems at all.

You can buy pretty much ANY 39T inner chainring with a BCD of 130 and that is Shimano-compatible. Truvativ and Stronglight sell many of them and they are dirt cheap.


Or you can buy a compact (50-34) and use the same wheels as your other bike to replicate the climbing ability of your other bike. You can buy a cheap compact chainset if you look around. Any Sram one will work with your existing BB or you can buy a new Shimano BB (under £20) if you get a Shimano compact.

Pokerface

Are you talking about putting a new chainset on (50-34) - or just replacing the 42T with a 34T? You won't be able to replace the 42T with a 34T - you can only replace it with a 39T.

If you replace the whole thing with a new 50-34 chainset, shifting won't be a problem at all.

spezial

Pokerface wrote:

Or you can buy a compact (50-34) and use the same wheels as your other bike to replicate the climbing ability of your other bike. You can buy a cheap compact chainset if you look around. Any Sram one will work with your existing BB or you can buy a new Shimano BB (under £20) if you get a Shimano compact.

Think I'm gonna have to go with this option, as I don't think a 39T will be enough of a jump gearing wise, and by the time I've bought a new cassette with a 29 on it it'll probably work out the same price as a new/2nd hand chainset.

Also, can't be riding round with a 29 cog on the back!

rake

:roll:

spezial

Spezial wrote:

Also, can't be riding round with a 29 cog on the back!

A joke, of course. I would be first in the queue for the MTB ratio triple if I was going up anything serious.!

One final question then I'll get out of everyone's hair - some chainsets are listed as being "9-speed" or "10-speed", surely this doesn't make a difference if it's just the front ring I'm changing?

Garry H

10 spd chains are slightly narrower. In reality though it will probably work. I run 9 spd on "10 spd" chainrings and it works fine.