Chainline - 8sp triple

General Help
1

Gudday

My friend brought her bike over, saying that the chain was slipping in all gears. Not surprising; it was absolutely knackered, every cog and chainring. I’ve replaced the cassette and I have a Deore M590 crankset to fit, but I’m having chainline issues.

I measure the chainline of the cassette at 38mm, which is a bit weird. There are no spacers on the RHD to swap to the left to redish, so that’s out. The Deore M590 has a chainline of 47.5mm if centred. I can put two spacers on the LHS and get a 45mm chainline, but the left pedal ends up being 5-8mm further out than the right pedal. She wants the same gearing that she had, which was 28/38/48. I didn’t measure the original chainline, but maybe I should have. I imagine it must’ve been 45mm though, which might account for it being so warn out.

Anyway:

  1. In your opinion, how big of a deal is not having the crank centred, as in, having the left pedal further out than the right, using platform pedals?

  2. How big of a deal is running a 45mm crankset chainline with a 38mm rear? I imagine it’s less than ideal. Worse if I centre the crankset with a 47.5mm chainline.

My options are:

  1. Trying it out with what I’ve got

  2. Getting something like a Tiagra triple, but it’s 30/40/50, 10sp, and still a 45mm chainline, or 42.5mm if I space it out to the left

  3. Sourcing a square taper triple and getting it as far in as possible according to the BB axle length. This would probably require me changing the chainrings, adding to the cost.

  4. Convincing her to go compact double, but she’d like a low gear for touring.

The FD is not an issue. It has plenty of room to move in and out.

2

what’s the bike? rear spacing? the deore M590 is a mtb crankset, designed to work with 135mm rear spacing

if she’s running flat pedals i wouldn’t worry about it, her feet will naturally compensate for the slightly off centred pedal.

3

Yeah, it’s 130mm rear spacing. I was looking at using the M590 cos I have one here and I thought with a 42.5mm rear chainline, it might be OK. 38mm is a bit much though eh. I’m looking at square taper cranksets now. Sugino XD600s look the go, but she’s going to be a bit surprised by the price I reckon.

4

7mm off chainline is only about two cogs at the back yeah?

kinda depends a lot on what gears she pedals in most I reckon i.e what the cruising gear is, and not such a big deal with a triple but it would mean you;d have to be more vigilant changing the front rings to adjust for chainline.

TBH honest I don’t find chainline is that a big a deal as long as its pretty good, more important on a 1x and 2x setups.

Also, just msged you about some square taper triple/double I have.

Also I run my hollowtech cranks with all the spacers on the NSD (or maybe two) to get a better low gear chainline for my 1x10 MTB, don’t notice the offset.

5

Responded. Ta! (Have dug up an old Exage LX biopace triple to try out)

Cool, that’s the kinda thing I wanted to know. Is that on platforms or clipped in?

6

Clipped in, well I notice the wider Q than my CX/SS/rawland but not the offset.

but then I very rarely ride my MTB for more than 3hrs at a time too.