Mix road and mtb gears, advice to get thru chain line alignment

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Good evening,
Please apologize the long post.
I am willing to add a custom Thorn Audax to my bicycle family and I need advice in putting together the specifications. To be said that I am a DIY guy and I wish to put the bicycle together by myself also sourcing several places / re-using parts.
The bicycle will have bar end shifters and 27 speeds (if 30 would be possible even better) and would be used to train and cycle with friends and take part to audax (mainly 200-300 km) events. I would possibly try to take part to longer audax events up to Paris - Brest - Paris or Mille Miglia.

Front:
I wish to install a Stronglight impact triple chainset, it has a 45 mm chainline, the manufacturer advice using a 115 mm JIS bottom bracket. To me this chainset make sense for the combination quality, price, weight, availability in several chain rings sizes.
I am not such a pro to appreciate external bearing / plenty old square taper bb stiffness difference but have to admit I didn't have make huge use of external bearing cranksets to appreciate the difference, advice is welcomed.

Rear:
I wish to use an MTB rear derailleur to have the possibility of using MTB cassettes. I was thinking in a Shimano LX or XT to be used with Shimano bar end shifters (cheaper than SRAM and proven excellent quality)
Shimano MTB rear derailleurs have 50 mm chainline.

Wheels:
I would use both my current road mavic aksium wheels, both custom MTB hub / dynohub equipped wheels. The latter not yet put together so I could change opinion and use road hub if it make sense. Advice welcomed.

Issue:

Chainline:
does it make sense put a 10 mm wider spindle to match front and rear chainline? UN54 Shimano BB is not available in 125 (115 mm spindle BB would give me 45mm chianline according to manufacturer spec): better a 122 or 127 mm spindle BB?

Front derailleur:
What derailleur to use? MTB one? I see that thorn sjs use tiagra front derailleur, why?

Rear derailler: are you aware of any 9 or 10 speed road (or otherwise 45 mm chianline) long cage rear derailleur that could be used in combination with 11-32(4) cassettes and would save me chain line issues?

Wheels:
would mixing road and mtb hub wheels create chainline issues or is fine?

Thank you very much!
 

frank9755

Cyclist
Location
West London
What you are advocating is very much a standard modern touring bike setup. For example, my Super Galaxy has a Stronglight Impact chainset, Tiagra STIs and front mech, LX rear mech and an 11-34 cassette, and it all works well.

The Impact is lighter than most external bearing chainsets, longer lasting, and, as you are not racing, stiffness is not an issue.

Your chainline should be fine with the recommended BB. NB I've just checked Spa's site and they say JP400 110mm (which I think is what I have on mine). This is something where working it out doesn't necessarily get the right answer, but if you do searches on, in particular, the CTC forum and talk to people like Spa who build these bikes, then 110mm with 135mm LX hubs is what people tend to use.

Is your front bar-end shifter indexed? Assuming it is then you would need to have a 'road' front mech such as the Tiagra for it to work properly. Mountain bike ones require more cable pull.

For your rear mech an LX would be the obvious thing to use, but any other long cage Shimano mountain mech would do. Some people like the Acera one with its big jockey wheels.

Also I don't understand what you mean by mixing wheels. We are talking about the rear and you either have one or the other - 130 or 135mm OLN. What am I missing?

Good luck with the build!

Edit - just seen you are outside the UK, so here are some links (but do come back here if you want to discuss further):
Spa Cycles - a leading UK touring bike shop
CTC forum - where there is most expertise on this sort of thing
 

RecordAceFromNew

Swinging Member
Location
West London
Just to add to Frank's response:
1) mtb rear chainline is never 50mm, it is in fact never more than 46mm even for 135mm hubs. 50mm is however the typical mtb front triple chainline.
2) surprised that you are planning on using both road and mtb rear hub wheels regularly since they have different over-locknut distance, even if the frame is steel/flexible.
3) choice of rear mech has no effect on chainline, imho you should get a long cage (SGS) mtb rear mech to avoid chain wrap capacity challenges.
4) a road front mech will allow front indexing with shimano bar-end shifters, and would not suffer reach issue with road chainset.
 
OP
OP
V

Vinalopo

New Member
Hi, first of all thank you for your help and clarification, it means a lot getting this knowledge.

I still haven't sources parts, I was convinced shimano 9 speed bar end were indexed for both mechs but I am not sure and manufacturer tech doc does not help.
I didn't knew Road and MTB had a front derailleur cable pull, as far as you say there is no chainline issues I will definitely go for a road front mech such a 105 or Ultegra.

I would probably go for a LX rear mech, I have used several thousands km one of them -also on fully loaded tours- without special issues and treating it with special care so I am quite confident on its reliability; not sure the aprox € 20 difference justify choosing an XT top normal but I could be proven wrong.

Wheels, I have those Mavic and have no issues since I use them, Aksium are low range wheels but to train they are not bad. I wouldn't trust them for long audax or non good pavements. I believe MTB hubs use to be more reliable and I could benefit of more reduced wheel dish but I pick your advice and will go for road rear hub, probably 36 holes, I will seek advice for a not too expensive but reliable hub from the LBS I will ask to build them. If you can give me some advice please shoot, I would really appreciate them.

Thank you again
 

RecordAceFromNew

Swinging Member
Location
West London

Wheels, I have those Mavic and have no issues since I use them, Aksium are low range wheels but to train they are not bad. I wouldn't trust them for long audax or non good pavements. I believe MTB hubs use to be more reliable and I could benefit of more reduced wheel dish but I pick your advice and will go for road rear hub, probably 36 holes, I will seek advice for a not too expensive but reliable hub from the LBS I will ask to build them. If you can give me some advice please shoot, I would really appreciate them.

In terms of wheels I agree 135mm mtb hub wheels have advantage in having less dish and should be more reliable. I believe Thorn sells some frames set at 133mm to allow use of 130mm and 135mm hubs, but if I had a Thorn 853 I would definitely not try to force fit a hub into the frame.


Whichever hubs you end up picking, I would suggest including Mavic Open Pro in your choice of rims.
 

Zoiders

New Member
Most non-disc/older pattern MTB wheels don't in fact have less dish, they tend just to have a longer axle and the same width hub shell and flanges, some cross country race teams have been known to rebuild road hub shells on MTB axles as a weight saving measure.
 
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