Alpine double

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Brucey
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Re: Alpine double

Postby Brucey » 29 Oct 2018, 8:59am

ANTONISH wrote:I've also had the odd problem with chain suck (not this bike) and I wonder if it's worse with a short wheelbase.


It is worse with small chainrings; the reason is twofold, I think;

1) the chain tension is higher for any given pedal pressure (causing more rapid hooking wear) and

2) the chain wrap on the chainring is shorter.

On the latter point with a 26T chainring there are only ~13 links in mesh with the chain (less than that with a long arm mech) and the chances of a slightly hooked chainring 'hanging on' to the chain are substantially increased. By contrast I have never heard of chainsuck being caused by a hooked chainring of reasonably large size.

cheers
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squeaker
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Re: Alpine double

Postby squeaker » 29 Oct 2018, 9:43am

RickH wrote:
Valbrona wrote:I just can't quite believe that a bike company is supplying touch-up paint. And with a brush!

My Kona Sutra came with a little pot of touch up paint, with a brush inside the cap, in the box of bits that came with it. :D

Likewise, my gloss black Cotic RoadRat came with touch up paint with internal brush (mind you, it was called 'anti-Raven black' IIRC :roll: )
"42"

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hondated
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Re: Alpine double

Postby hondated » 29 Oct 2018, 10:10am

Valbrona wrote:I just can't quite believe that a bike company is supplying touch-up paint. And with a brush!

You know it is not until you give a chainset a good test you find the faults/shortcomings, no matter how much testing you might do with it in a workstand.

I could see myself on an Alpine double if triples ever get phased out entirely.

Might be wrong but I think the Campag triple on my Bianchi already has been.

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Chris Jeggo
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Re: Alpine double

Postby Chris Jeggo » 29 Oct 2018, 10:20am

Brucey wrote:It is worse with small chainrings; the reason is twofold, I think;

1) the chain tension is higher for any given pedal pressure (causing more rapid hooking wear) and

2) the chain wrap on the chainring is shorter.

On the latter point with a 26T chainring there are only ~13 links in mesh with the chain (less than that with a long arm mech) and the chances of a slightly hooked chainring 'hanging on' to the chain are substantially increased. By contrast I have never heard of chainsuck being caused by a hooked chainring of reasonably large size.

cheers

I had this problem with a 40/24 set-up. It wasn't just hooking. The 24t sprocket (steel) deformed, raising burrs and thus thickening the sprocket. Filing off the burrs solved the chain suck problem. It didn't recur, IIRC, or maybe just once more but less seriously, because the deformation had made the tooth profile better match the roller.

reohn2
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Re: Alpine double

Postby reohn2 » 29 Oct 2018, 10:33am

Chris Jeggo wrote:
Brucey wrote:It is worse with small chainrings; the reason is twofold, I think;

1) the chain tension is higher for any given pedal pressure (causing more rapid hooking wear) and

2) the chain wrap on the chainring is shorter.

On the latter point with a 26T chainring there are only ~13 links in mesh with the chain (less than that with a long arm mech) and the chances of a slightly hooked chainring 'hanging on' to the chain are substantially increased. By contrast I have never heard of chainsuck being caused by a hooked chainring of reasonably large size.

cheers

I had this problem with a 40/24 set-up. It wasn't just hooking. The 24t sprocket (steel) deformed, raising burrs and thus thickening the sprocket. Filing off the burrs solved the chain suck problem. It didn't recur, IIRC, or maybe just once more but less seriously, because the deformation had made the tooth profile better match the roller.

I've also had this problem with steel 24t inners on tandems,initially the drivetrain would emit a ticking clock like sound,more noticeable when climbing,as you say filing the burrs off eliminated the problem.
I initially thought that could the problem mentioned in my OP,until I checked it with the bike hung up in the workshop and found what was happening was the protruding chainring bolts were occasionally trapping the chain between them and the teeth of the inner.
Whereas recessed bolts(it's the slotted nuts really)should be flush with the middle ring inner face(outer on an Alpine double) to provide a clean face for the chain to shear off onto the inner ring.
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jerg
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Re: Alpine double

Postby jerg » 1 Nov 2018, 11:58am

I've occasionally thought about going to an alpine double (more out of curiosity than anything) for touring.

I'm currently running a modified 105 triple (50/39/26) on my Vaya with an 11-34 on the back and 105 STI shifters. I hardly ever use the big ring (going downhill is for resting !). I'd thought of maybe swopping the 26T for a 24T and replacing the big ring with a chainguard, so having a 24/39 or maybe 24/42 (ish). At what point would the jump from the little to middle ring be too much for a triple mech? Would I have to swop to a double and would this also mean a change to a double STI lever (or use a bar end lever). As I said, mainly idle speculation on my part and am I foreseeing problems that don't exist?

Alternatively - what about a 24/39/46 triple? I might at least use the big ring a bit more :)

pwa
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Re: Alpine double

Postby pwa » 1 Nov 2018, 12:13pm

Assuming the frame allows the front mech to be slid down a bit, the question becomes becomes how to reduce ring sizes in such a way that the angle of descent from largest, through middle and down to smallest replicates the angle on the rings the mech was designed for. So, for example, if you reduce the size of an outer ring (on a triple) you need to reduce the middle and smallest similarly. But if you reduce too far your mech cage shape will be in danger of being too much of a mismatch for the smaller rings.

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meic
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Re: Alpine double

Postby meic » 1 Nov 2018, 12:24pm

I am not sure how a 24/39/46 would fit into the scheme of things but when the middle and outer rings are fairly close in size you can just revert to a double's derailleur instead of a triple's.
Yma o Hyd

reohn2
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Re: Alpine double

Postby reohn2 » 1 Nov 2018, 1:00pm

jerg wrote:I've occasionally thought about going to an alpine double (more out of curiosity than anything) for touring.

I'm currently running a modified 105 triple (50/39/26) on my Vaya with an 11-34 on the back and 105 STI shifters. I hardly ever use the big ring (going downhill is for resting !). I'd thought of maybe swopping the 26T for a 24T and replacing the big ring with a chainguard, so having a 24/39 or maybe 24/42 (ish). At what point would the jump from the little to middle ring be too much for a triple mech? Would I have to swop to a double and would this also mean a change to a double STI lever (or use a bar end lever). As I said, mainly idle speculation on my part and am I foreseeing problems that don't exist?

Alternatively - what about a 24/39/46 triple? I might at least use the big ring a bit more :)


I think you'd be pushing he envelope with 24/42t perhaps 24/40 may work much better and if You're not using the big ring presently it's sort of indicating a 39 or 40t wold be big enough.
On my Vagabond I've left the triple front mech* in the same position as it would be if using the 39t as a middle ring which is the optimum position for the mech/39t ring.

*I built up the Vagabond with a low clamp RSX 7sp triple mech but because the pivots and cable clamp were behind the seatube and were collecting all the muck without a mudguard fitted,so I changed it for a triple 10sp Ultegra road mech which positions the pivots and cable clamp over the top of the chainset, giving more room behind the seatube and moving the pivots out of the muck stream.It's also helped with mudguard clearance that I fitted yesterday :)
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andrew_s
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Re: Alpine double

Postby andrew_s » 1 Nov 2018, 2:33pm

jerg wrote:Alternatively - what about a 24/39/46 triple? I might at least use the big ring a bit more :)

The trouble with that is that the inner cage plate on the mech will hit the side of the middle chainring teeth, either preventing the shift entirely, or leaving the chain scraping against the mech when using the smaller sprockets.
Most triple mechs require at least a 10T difference between middle and outer, and some need 12T.

You could try just moving the mech up the seat tube (3 extra teeth on the middle equates to having to raise the mech 6 mm), but you could be left trying out assorted double and old (vintage) triple front mechs to try and find something that works adequately.

jerg
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Re: Alpine double

Postby jerg » 1 Nov 2018, 3:54pm

[quote][I think you'd be pushing he envelope with 24/42t perhaps 24/40 may work much better and if You're not using the big ring presently it's sort of indicating a 39 or 40t wold be big enough.
On my Vagabond I've left the triple front mech* in the same position as it would be if using the 39t as a middle ring which is the optimum position for the mech/39t ring./quote]

Thanks for that. As I said, idle speculation at the moment, but if I do fiddly with the existing set up I might just replace the outer ring with a chainguard - or do the job properly and replace everything with a spa triple with better spaced gears.

Are you using bar end shifters on the Vagabond?

I've currently got two of the same bikes as yourself (Vaya and Longitude) and am wondering where the Vagabond fits in. It's also on my possible lift of bikes to build up but that would look like I'm stalking you :)

reohn2
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Re: Alpine double

Postby reohn2 » 1 Nov 2018, 7:42pm

jerg wrote:
[I think you'd be pushing he envelope with 24/42t perhaps 24/40 may work much better and if You're not using the big ring presently it's sort of indicating a 39 or 40t wold be big enough.
On my Vagabond I've left the triple front mech* in the same position as it would be if using the 39t as a middle ring which is the optimum position for the mech/39t ring.


Thanks for that. As I said, idle speculation at the moment, but if I do fiddly with the existing set up I might just replace the outer ring with a chainguard - or do the job properly and replace everything with a spa triple with better spaced gears.

Are you using bar end shifters on the Vagabond?

I've currently got two of the same bikes as yourself (Vaya and Longitude) and am wondering where the Vagabond fits in. It's also on my possible lift of bikes to build up but that would look like I'm stalking you :)

The Vagabond is a bit of an indulgence,TBH I rather fancied a drop barred go anywhere bike that could take a fair sized knobblie and yet wasn't a slug on tarmac,I've built it up with 700 x 50 Marathon Supremes which are great most of the time but I plan on fitting a pair of 700 x 2.1 WTB Nanos for the mucky stuff,whether the rear will fit under the mudguard remains to be seen,if only Mr Genesis had made the chainstays 15mm longer it defintitely would and I'd be touting this bike as a Surly Disc Trucker killer.

I have Kelly Take Offs on both Vaya and Vagabond.The Vaya has Dura Ace 9sp D/Tube levers fitted and the Vagabond has 9sp bar end levers fitted in the Kelly's,though I prefer the D/Tube levers.
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peterh11
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Re: Alpine double

Postby peterh11 » 3 Nov 2018, 7:55am

Interesting. What have you all done about the bottom bracket length? Have you simply kept the one which was recommended for the triple, or swapped in a longer one?

I am wondering about using the Spa solution of the triple with a chain guard instead of the outer, and NOT using a longer BB axle but instead aiming to set the chainline so that the outer is lined up with the centre of the cassette, so that I can use all the cogs on the cassette with the outer, say a setup of 26x42 front and 11-32 (10 or 11 speed) at the back.

I think this would allow me to treat the bike almost like the currently fashionable 1x setups but with a handful of low gears for steep hills. The larger cogs on the cassette would more or less replicate an existing setup with 26/36/46 chainrings. And if I am using STI (say 105) then shifting on the left is simpler than with a triple.

Have others set it up this way, and does it work well for you? Or have you found some serious downsides?

Peter H

tatanab
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Re: Alpine double

Postby tatanab » 3 Nov 2018, 8:15am

peterh11 wrote:I am wondering about using the Spa solution of the triple with a chain guard instead of the outer, and NOT using a longer BB axle but instead aiming to set the chainline so that the outer is lined up with the centre of the cassette, so that I can use all the cogs on the cassette with the outer, say a setup of 26x42 front and 11-32 (10 or 11 speed) at the back.

That is what I have done in this photograph. Campag Record triple crank on triple bottom bracket, 40/24 with a cyclocross bashguard in the outer position. 40T ring lines up with middle of the cassette. All 10 rear gears run sweetly on the 40 ring and the chainline on the little ring is therefore very good for when the small ring and big sprockets are used. This has been my touring set up for 7 years now.

0000982.jpg

Bonefishblues
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Re: Alpine double

Postby Bonefishblues » 3 Nov 2018, 8:20am

What ratios do you run at the rear, out of interest?