triple chain line question

Reid Priedhorsky said:

Hi folks,

Is it possible to rig a triple crankset such that the large ring has okay
chainline to all the cogs and only the middle and lower are restricted?

If so, how many cogs could I expect to lose due to chainline issues on the
middle and lower rings?

I measured my current triple, and while the derailer cage itself has 7-8mm
to go before it bumps the seat tube, there is a roller with only 1-2mm
left.

You'll need to move the crankset inwards by using a BB with a shorter
spindle. I think you'll find the biggest problem in doing this isn't
the deraileurs, but the inner chainring rubbing the right chainstay.

Cheers

Joel

--
Human Powered Cycles | High quality servicing
[email hidden] | Low cost 2nd hand bikes
www.humanpowered.com.au | Bicycle re-use centre

Joel Mayes said:

Reid Priedhorsky said:

Hi folks,

Is it possible to rig a triple crankset such that the large ring has okay
chainline to all the cogs and only the middle and lower are restricted?

If so, how many cogs could I expect to lose due to chainline issues on the
middle and lower rings?

I measured my current triple, and while the derailer cage itself has 7-8mm
to go before it bumps the seat tube, there is a roller with only 1-2mm
left.

You'll need to move the crankset inwards by using a BB with a shorter
spindle. I think you'll find the biggest problem in doing this isn't
the deraileurs, but the inner chainring rubbing the right chainstay.

Cheers

Joel

I think this setup would want a longer range mountain bike dérailleur in
the rear to cover the extra range. I tried a 22-36-58 front with a 14-39
rear (Antique Sun Tour Alpine gear) and found that at the limits the
chain was either way loose (22/14) or bound up (58/39), even though
those gears don't make much sense. It was Ebay's fault for putting such
tempting bike stuff up there.
Off set is a real problem since I have found at least 3 different
offsets on square mount crank sets. I have one that is a real odd duck
that has the square hole turned 45 degrees from the normal.
If you want to experiment, spend a little on some stuff from Ebay, but
be careful to ask if the individual chain rings are changeable and not
just a Chinese tack weld.
Ride, mechanic, ride some more, repeat.
Bill Baka

Bill said:

Joel Mayes said:

Reid Priedhorsky said:

Hi folks,

Is it possible to rig a triple crankset such that the large ring has okay
chainline to all the cogs and only the middle and lower are restricted?

If so, how many cogs could I expect to lose due to chainline issues on the
middle and lower rings?

I measured my current triple, and while the derailer cage itself has 7-8mm
to go before it bumps the seat tube, there is a roller with only 1-2mm
left.

You'll need to move the crankset inwards by using a BB with a shorter
spindle. I think you'll find the biggest problem in doing this isn't
the deraileurs, but the inner chainring rubbing the right chainstay.

Cheers

Joel

I think this setup would want a longer range mountain bike dérailleur in
the rear to cover the extra range. I tried a 22-36-58 front with a 14-39
rear (Antique Sun Tour Alpine gear) and found that at the limits the
chain was either way loose (22/14) or bound up (58/39), even though
those gears don't make much sense. It was Ebay's fault for putting such
tempting bike stuff up there.

I think the OP wanted to be able to use all the rear cogs with the outside
chainring while maintaining a reasonable chainline. Nothing was said about
the size of the rings being used (could be running 36,37,38 chainrings for
all we know).

Cheers

Joel

--
Human Powered Cycles | High quality servicing
[email hidden] | Low cost 2nd hand bikes
www.humanpowered.com.au | Bicycle re-use centre

Joel Mayes said:

I think the OP wanted to be able to use all the rear cogs with the outside
chainring while maintaining a reasonable chainline. Nothing was said about
the size of the rings being used (could be running 36,37,38 chainrings for
all we know).

Yes, something like 46-36-24 with a 12-34 or somesuch in the back. Right
now I have 52-42-30, and with an 11-32 in the back I don't have too much
use for the 52-tooth chainring, but a lower granny would be great.

I guess the main question is, how can I know how short a BB I can get away
with before buying one and trying it out?

Thanks and take care,

Reid

Reid Priedhorsky said:

Joel Mayes said:

I think the OP wanted to be able to use all the rear cogs with the outside
chainring while maintaining a reasonable chainline. Nothing was said about
the size of the rings being used (could be running 36,37,38 chainrings for
all we know).

Yes, something like 46-36-24 with a 12-34 or somesuch in the back. Right
now I have 52-42-30, and with an 11-32 in the back I don't have too much
use for the 52-tooth chainring, but a lower granny would be great.

I guess the main question is, how can I know how short a BB I can get away
with before buying one and trying it out?

Thanks and take care,

Reid

Measure the current clearnance + current BB length and do some math :-)
There are two many variables to get an answer here

You do need to think about why you want to do this though, I can't see
any advantage in using the outer chainring of a triple predominately.

Cheers

Joel
--
Human Powered Cycles | High quality servicing
[email hidden] | Low cost 2nd hand bikes
www.humanpowered.com.au | Bicycle re-use centre

Joel Mayes said:

Reid Priedhorsky said:

Joel Mayes said:

I think the OP wanted to be able to use all the rear cogs with the outside
chainring while maintaining a reasonable chainline. Nothing was said about
the size of the rings being used (could be running 36,37,38 chainrings for
all we know).

Yes, something like 46-36-24 with a 12-34 or somesuch in the back. Right
now I have 52-42-30, and with an 11-32 in the back I don't have too much
use for the 52-tooth chainring, but a lower granny would be great.

I guess the main question is, how can I know how short a BB I can get away
with before buying one and trying it out?

Thanks and take care,

Reid

Measure the current clearnance + current BB length and do some math :-)
There are two many variables to get an answer here

You do need to think about why you want to do this though, I can't see
any advantage in using the outer chainring of a triple predominately.

Cheers

Joel

I have to side with the math solution since I have seen too many
variables on BB length and cranks.
A 52/11 is only good at my strength level for extra speed on downhills
and even that is questionable. On the flat roads it is good for maybe a
really lazy 10 MPH while still building up some strength in the legs.
A cadence of only 25-30 is a bit low, but good for those lazy days.
Bill Baka