Lowering the gearing

[steveindenmark]

Please excuse my inability to express this in technical jargon. I can ride up any mountain but my mechanically knowledge is sadle lacking.

I recently bought a Koga Roadchamp to set up for light touring. At the moment it has a Tiagra 10 speed gear shifter, the crankset is 50 x 39 x 30. The deurailler is Shimano 105.

I recently took it to Cornwall and found that when it is on the large crank ring I only use 5 or 6 gears, even on the flat. I also find that I need more gears in the lower range.

My idea is to change the gearing to something like the Dawes Galaxy whose crankset is 48 x36 x26. But I am not sure how to do this. I would like to do it with as little disruption to the bike as possible.

Do I just need to order the correct crankset and change it over with the crankset that is on now? The bike has only been ridden about 50 miles, would it need a new chain?

I am hoping to have this sorted for Mallorca in September and so any help would be appreciated.


Steve

 

[Cubist]

It may be cheaper and simpler to put a bigger cassette on. What cassette is on it at the moment? My compact 105 is 50-34 front and 11-32 cassette, but I also had a triple with a 30 front and 27 or 28 rear for much the same gearing. . Depending on your rear mech cage length, you may be able to go up to a 30T cassette. A medium cage 105 will work with up to 32 teeth on a cassette.

 

[ColinJ]

If you go for a new chainset, take a look at the lovely Stronglight Impact triples at Spa Cycles. I just bought one for my Cannondale. I chose 48/38/28 but they also go lower, e.g. 46/36/26, or even 46/34/24. It needs an old-style square taper BB such as the Shimano UN55 which you can pick up really cheap at Chain Reaction Cycles if your current BB is not that type.

You should be able to use your current chain, but might have to shorten it slightly.

 

[Nigelnaturist]

The FD will be fine down to 28/26 I did it using Sora kit when I started using the similar to what @ColinJ suggested but a cheaper version SPA CYCLES XD-2 Touring Triple Chainset
@Cubist range is always the answer. the 105 GS is designed to work with 32th on the rear only on a double not a triple, though my 5701 did but I only had set up like that for one day the day my right shifter broke (not sure if thats what broke it)
@ColinJ are those rings just straight ones (i.e. no ramps) on a shimano triple, I have been trying to get an answer to a question I have in my head, can you go from 38th middle to 52th I know 50th should be fine, what I keep reading though is that the shimano triple shifters need ramps on the chainrings, however I have had straight rings and whilst on the sora the shift from 30 to 40 needed an extra little pull, the 38-48 I had set up two years ago seemed fine (but it is a long time ago) If I cant do 38-52 it will have to be 38-50 i find the jump from 17 to 19 a little big ect ect... and just lose 4" from the top end.
http://www.spacycles.co.uk/products.php?plid=m2b0s109p2000

 

[ColinJ]

@ColinJ are those rings just straight ones (i.e. no ramps) on a shimano triple, I have been trying to get an answer to a question I have in my head, can you go from 38th middle to 52th I know 50th should be fine, what I keep reading though is that the shimano triple shifters need ramps on the chainrings, however I have had straight rings and whilst on the sora the shift from 30 to 40 needed an extra little pull, the 38-48 I had set up two years ago seemed fine (but it is a long time ago) If I cant do 38-52 it will have to be 38-50 i find the jump from 17 to 19 a little big ect ect... and just lose 4" from the top end.

I haven't actually finished rebuilding the bike yet so I can't tell you how good the front shifting is!

The rings do not have ramps or shortened teeth, but they do have pins to help up-shifts.

In the past, I have filed down a couple of teeth on unramped middle rings to assist shifting - making it easier to get the chain on and off. I just took the first 3 or 4 mm off the top of the teeth and it definitely helped. Only do it if you have to, and start off with a couple of mm. You can always file a bit more off later, but you can't put the filings back on!

I bought an Ultegra 6703 triple front mech for the system. According to Shimano, the minimum difference between middle and big rings for that mech should be 13 teeth. That would be a 51 tooth big ring for me. I'll see if I can get it to work acceptably with the 48 tooth big ring. If I can't, I'll have to buy a 51 or 52 (or reduce the middle ring to a 35, but I think that might be too small).

 

[Nigelnaturist]

I haven't actually finished rebuilding the bike yet so I can't tell you how good the front shifting is!

The rings do not have ramps or shortened teeth, but they do have pins to help up-shifts.

In the past, I have filed down a couple of teeth on unramped middle rings to assist shifting - making it easier to get the chain on and off. I just took the first 3 or 4 mm off the top of the teeth and it definitely helped. Only do it if you have to, and start off with a couple of mm. You can always file a bit more off later, but you can't put the filings back on!

I bought an Ultegra 6703 triple front mech for the system. According to Shimano, the minimum difference between middle and big rings for that mech should be 13 teeth. That would be a 51 tooth big ring for me. I'll see if I can get it to work acceptably with the 48 tooth big ring. If I can't, I'll have to buy a 51 or 52 (or reduce the middle ring to a 35, but I think that might be too small).

What I read was that shimano triples tend to be short in the travel and rely on the the ramps and pins to make the transition smooth and quite, in other words a bad shift, but in may experience this isn't quite right (not that two years is much), my avg gear is about 61" 40x17 but as i said the jump from 17-19 I find to big sometimes (end up spinning to fast) and would love a 40x18 but its not an easy combo to get drop the 12th in favour of starting at 13th again a little difficult though I think I could get away with an Ultegra 13th starting point, so the only other option is a 38th dropping the gearing on the back by a gear still have the 17-19 jump but as at this range I would be climbing the two teeth become less noticeable.

@steveindenmark sorry to pinch the thread a little, but its a query I have been trying to sort out for a while.

 

[boydj]

An alternative to the bigger cassette, would be to buy some slightly smaller chainrings to swap in - possibly in combination with a new cassette.

On my triple, I use the middle ring most of the time. the big ring comes in on the flat with a tailwind or downhill. If I were in your position, I'd get a bigger cassette and a 28-tooth granny ring to help with the hills.

 

[steveindenmark]

I have the problem at both ends Boyd. I am never going to use all the top end gears so I need to change that ring from a 50 to a 48 or 46. I also need more gears at the bottom end so I need to change that from a 30 to a 26 or 24. I am sure I will sort out now I have help.

Steve