Chainline again sorry

[webber]

Im still looking at a lower gear setup for my condor tempo 120mm spacing using a white industries dos sprocket https://www.hubjub.co.uk/white-industri ... -255-p.asp and a double chainset which will be a spa one https://spacycles.co.uk/m2b0s109p2016/S ... chainrings so i can get the chainring size i want but dont know what length bottom bracket to get ?? Any help would be excellent

[Brucey]

with a single freewheel on a typical 120mm flip-flop hub the chainline is about 45mm. With a 'road double' the middle chainline is about 45mm too, meaning that the inside ring is about 41mm and the outside ring is about 49mm.

I'd imagine that with the twin sprocket freewheel you will get chainlines of ~45 and ~51-53mm but since hubs vary and the exact dimensions of the freewheel are not listed it is impossible to say.

Similarly if the chainline is +/- 1mm on a derailleur gear setup this is usually non-critical. But with your setup it might be. Specifically

a) the chainline won't be exact anyway ( a variation of 0.1mm on the taper fit makes a significant difference to the chainline) and
b) if the chainline you need is tighter than normal and the chainring is larger than normal, there is no guarantee that the inside chainring will clear the RH chainstay.

To get the chainline 'perfect' I'd suggest that you measure up the freewheel, do a trial chainset fit (with a BB spindle that is slightly too long, and of the same make as you intend to use) and then buy a BB that is going to give the correct chainline, to suit your frame and/or the way your freewheel sits on your hub. You can fine tune everything by slightly respacing the hub and/or respacing the BB slightly eg by using a spacer behind the RH cup. it is also possible to respace the chainrings by using spacers on those too.

cheers

[fausto99]

Difficult to say from a distance. Could you try to get some guidance from Condor?
Can you not extrapolate from your existing setup? Try it with your existing BB. It may be close enough. If not, go incrementally from there with a longer or shorter Shimano sealed unit. They are available in a fair range of different lengths.

[fastpedaller]

If they are the same as my xd2 chainsets, then the double is the triple anyway! By way of explanation, the casting/forging is the same for the double and triple crank - the drilling and tapping of holes in the inside of the part provides the fixing for the inner ring (IIRC at 74mm pcd). So if you want to go a bit lighter (or 'future proof' in case you ever want the triple facility) you can buy the triple cranks. Are you using a double ring or single? If using single it may be better economically to buy cranks and one ring (I just followed the link OP provided). Using the same cranks with a 110 bb gave me a chainline of 47mm on the inner ring. As others have said it's best to check with the actual bb and cranks, as it can vary. As it looks like the op is using a 'double freewheel' (other link in op) then there will be some variation in chainline anyway.

[webber]

The idea is to use a double with 2 teeth apart 48/46 with a 17/19 on the back so ive got 48-17 and 46-19 for hilly areas but the same wheel placement so wont have to worry about chain mudguards etc

[Brucey]

46T is quite a big ring to install on a tight chainline; not every frame will take it without some manipulation of the chainstay.

cheers

[webber]

Im getting new wheels as well so if i use one of these hubs https://www.sjscycles.co.uk/hubs-other/ ... track-hub/ i can run smaller sprockets at the bach and smaller chainrings would this help

[Brucey]

I would suggest that you try the chainset you want rather than buy different sprockets etc. In general terms larger chainrings and sprockets are more efficient, run smoother and last longer, so are a better idea.

cheers