Alpine double

[tatanab]

12/28 on the rear. This gives me gears of 90" to 40" on the big ring which used to be my entire touring range up until 25 years ago along with overlaps. Now I have that range in sequential gears.

[pq]

I'm nearly finished rebuilding my fast tourer with a Record triple like that. I'd intended running it as a double because the 53 big ring the chainset came with is insane on a tourer, but when it came to actually build it up, the front mech I have is designed to work with the original 3 chainrings and if I'm going to fit a bash guard, it might as well have teeth on it and be a chainring.

What I did do to make the gears more sensible, is build a (10 speed) cassette from an old Mavic M10 I had lying around and a few individual Marchisio sprockets I bought for the purpose - it's 15 - 28. That gives me a top gear of around 94" which is still too high, but not crazy, and very closely spaced gears. Given a free choice I'd have used a bigger big sprocket, but I couldn't find one to suit (complications with using a Shimano pattern hub on an otherwise Campag drive train)

So why are people using bash guards with these set-ups? I've never felt the need for one on a road bike, and if you do want to fit one, why not make it work as a chainring?

[meic]

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 would leave it as was as I do my hardest work in the lowest gears and always find chainlines to be too wide to begin with. Admittedly losing the outer ring will make the wide chainline more agreeable as using 40-11 will be taking the place of 50-14, 12 & 11.

[tatanab]

IGiven a free choice I'd have used a bigger big sprocket, but I couldn't find one to suit (complications with using a Shimano pattern hub on an otherwise Campag drive train)

Same for me, Campag spacing on Shimano splines. I too use Marchisio.

So why are people using bash guards with these set-ups? I've never felt the need for one on a road bike, and if you do want to fit one, why not make it work as a chainring?

Because I did not want a third chainring. Previously my set up was 50/40/24 triple with 15/28 (like you) 8 speed. When I went to 10 I thought I would try something different so went to the Alpine double. To try it out I used parts I had rather than buy another chainset, and I have stuck with it because I like it. The bash guard looks fairly neat I think, but finding a 135PCD one was not easy and I bought that one from the USA. Not expensive, indeed cheaper than a third ring.

[pq]

But why not use shorter chainring bolts and no bash guard?

[Brucey]

I guess if you use a third ring position to hold a chainguard, you can make it so that the FD sits snug over the larger chainring and you will get really good shifts; better than the middle-inner shifts of a triple. A double at the front also allows you a wider choice of shifters. And a chainguard keeps your trousers cleaner.

But overall I agree that these are (or should be) fairly peripheral concerns and all things being equal, it would make more sense to use a third ring if you are carrying it around anyway and/or putting up with the increased Q of a triple. With a shimano-based system, you can more easily get really low gears this way, and with a custom cassette you can have sensible high gears too.

cheers

[tatanab]

But why not use shorter chainring bolts and no bash guard?

Because for my taste it looks scruffy.

[pwa]

The reason I made up (Spa) Alpine doubles on cranks designed for three rings was simply to give lower gears on two bikes that had STI levers for double, not triple, and the levers are costly to replace.

[reohn2]

But why not use shorter chainring bolts and no bash guard?

Because for my taste it looks scruffy.

Ditto.

[reohn2]

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 would've left it at triple length (115mm) on the Vagabond but due to the chainstays being a lot wider near the BB to accomodate a 2.1inch knobblie I had to go with a 121.5mm one so the 39t ring clears it.
On my Salsa Vaya that isn't a problem and so the 115mm BB was left in place.
The chainline for both bikes is near straight in the cruising gears.

[reohn2]

I guess if you use a third ring position to hold a chainguard, you can make it so that the FD sits snug over the larger chainring and you will get really good shifts; better than the middle-inner shifts of a triple.

I'm using a road triple front mech on both bikes which is set as if for a triple and gives seem less shifts both up and down

A double at the front also allows you a wider choice of shifters.

That's a plus for STI users

And a chainguard keeps your trousers cleaner

.
Yep

The great thing about the Alpine double I'm finding,is that I can slam the front friction lever from stop to stop without any potential over shifts which can occasionally happen with a triple and friction lever

[peterh11]

I guess if you use a third ring position to hold a chainguard, you can make it so that the FD sits snug over the larger chainring and you will get really good shifts; better than the middle-inner shifts of a triple.

I'm using a road triple front mech on both bikes which is set as if for a triple and gives seem less shifts both up and down

A double at the front also allows you a wider choice of shifters.

That's a plus for STI users

And a chainguard keeps your trousers cleaner

.
Yep

The great thing about the Alpine double I'm finding,is that I can slam the front friction lever from stop to stop without any potential over shifts which can occasionally happen with a triple and friction lever

Similar to my thinking:

I did have a TA Cyclotourist double chainset with small rings on it, and I liked the very simple front shifts between chainrings. The “alpine double” would give me plenty of gears and range, let me have a wider choice of derailleur and (especially STI) gear levers, and overall make a simpler setup with a standard cassette (have been using custom Marchisio-based cassettes for a while, but I believe the cogs are no longer being made).

Still thinking about it though. To be fair, after a few years riding with a Spa XD-2 triple on another bike with friction shift lever on the LH Kelly Take Off, I very rarely miss a shift.

As regards Q-factor, actually I find the Spa triple very comfortable in that regard. The TA was really too narrow for me. So keeping the slightly wider spacing would be just fine.

Thanks all
Peter H

[BigG]

Despite reohn2's comments near the top of this thread, his preferred 9-speed cassette actually has its biggest gap at the top end from 11T to 13T, a gap of 18%. The biggest gap at the bottom end is from 26T to 30T, a gap of 16%. Keeping a reasonably constant percentage gap as he does gives the most subjectively even spread of gears. I would however go further and suggest that bigger percentage gaps are acceptable, even desirable, at the lower end. This results from the difference in the retarding forces that we face. In low gears the major retarding force is likely to be gravity which for a given slope is linear with speed. In high gears wind resistance is the main opposition and this increases much more quickly than speed making smaller gear gaps seem more appropriate. Shimano went a bit too far with their Megarange cassettes, but a more modest version of this works well. For myself, I stick to a half-step and granny in which the drop onto the small ring automatically doubles the gear gap. No to everyone's taste but it suits me.

[meic]

To make a 14,15,17,19,21,23,26,30,34 this gives me a close enough progression

No 11-13 gap there.

[reohn2]

To make a 14,15,17,19,21,23,26,30,34 this gives me a close enough progression

No 11-13 gap there.

Beaten to it

Personally I find the standard 11-34t 9sp cassette has too wide a progression in the midddle most used gears and the 11,13t sprockets useless to me.
On a recent ride I spun out top 39×14 at 24mph(tailwind,slightly down hill ).where I a stronger rider than presently,I'd revert back to a triple 24/34/46t which would provide a big enough top for most riders and those it doesn't there's the option of 48t 50t or 52t rings to compensate.
How any but the strongest of riders turn over 52 x11/13/14t top gears with a comfortable cadence is beyond me