wife's triple...difference in mid chain ring distance....

[matata]

Hi guys, the wife wore out her triple chainset on her hybrid (cheapish Cannonade). I replaced the set with a spa triple set with the view to easier gearing as well. Spa recommended 47 mm from the centre of the down tube to the centre of the mid chain ring with a 113 bb. When I took the original chain set off I noticed the original mid chain ring was 50/51mm out. It was all original and worked perfectly. When I put the Spa triple on the middle chain ring was now 47 (as recommended by spa) and other than reindexing it works fine... I thought the industry standard was 47mm or do manufactures put on what they can get away with? To bring it out to the same as the original I would need a longer BB but I don't feel its necessary unless someone tells me otherwise. Ta Nik

[reohn2]

If it's working well you don't need to worry,though you may need to adjust the limit screws accordingly on the front mech .
47mm chainline is road standard,50mm is MTB but there's plenty of leeway

[alexnharvey]

Ideally, the middle ring and middle of the cassette align, maybe not too much difference in practice if nothing fouls.

[Tompsk]

Ideally, the middle ring and middle of the cassette align, maybe not too much difference in practice if nothing fouls.

I did this with my Spa triple with a 9 speed cassette. I had to get a shorter bottom bracket than recommended and even had to remove a tiny bit of the centre of the driveside chainset arm aluminium to clear the spline on the bottom bracket. All seems to line up ok but with more trimming needed when riding on the front changer than desired, perhaps due to 9 speed chain with a Tiagra 10 speed front changer?

[matata]

Mmmmm...that 50mm cm chain line would make sense after looking at my wifes original set up...Why would they do that compared to a road bike 47mm?
IN THEORY i'm I not best then keeping the original 50mm? Nik

[Tigerbiten]

Which are your wifes most commonly used gears and would moving the chainrings inwards improve their chainline ??
Thats working on the theory that a straighter chain wears less.
Also in theory moving the chainring inwards means that you'll need less force to move the derailleur outwards to the large ring.
But you also need to check that when moving the derailleur more inwards that it doesn't interfere with anything.
So it's really a 50-50 call.

Luck .........

[reohn2]

Mmmmm...that 50mm cm chain line would make sense after looking at my wifes original set up...Why would they do that compared to a road bike 47mm?
IN THEORY i'm I not best then keeping the original 50mm? Nik

It's working well,the chainline is now 47mm with the new Spa c/set AIUI.The difference is 3mm in favour of approx one lower gear ,so unless she rides predominently a big gear all the time your wife is in fact better off

[Brucey]

the 50mm chainline standard comes from mountain bikes, and is (allegedly) 'necessary' to get the chainrings to clear the stays and/or the chain to clear the tyre in bottom gear otherwise. If you do your sums you will find that even with a 135mm back end a 50mm chainline is not centred over the sprocket cluster (for 8,9,10s etc).

I won't use stuff that gives me a 50mm chainline unless it is absolutely unavoidable (which it is on some of my MTBs). I will otherwise go to some lengths to reduce the chainline to a minimum, because this gives me a better chainline in the gears where it matters and it also reduces Q values. I basically don't like riding large Q values; I believe it isn't terribly efficient either, but I have not proved that other than anecdotally.

cheers