Gearing down...

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Bonefishblues
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Gearing down...

Post by Bonefishblues »

I'd appreciate some advice please.

I recently bought one of these from a Forum member: http://www.bikepedia.com/quickbike/Bike ... odel=Sutra

A really nice bike, and in lovely condition, and just about original spec. Before I bought it I had the notion that the gearing would be slightly too high for me, and so it's proving.

It has a 14-25 rear cassette fitted, and I know the obvious thing to do is to change this for something like a 14-34 but the problem's not really at the rear, it's the road triple chainset up front.

With that in mind, could I get away with replacing the current chainset with something like a 48-36-26 Deore chainset which would give me a very useable set of ratios and retain the rather nice close ratio gearing at the back?
markfh
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Re: Gearing down...

Post by markfh »

The smallest inner chainring available on "road" chainsets appears to be 30 teeth so you might have to look at other options. One problem you might encounter is the difference between road and mtb chainlines. The reason for mentioning this is that the spec list you link to says that the front derailleur is a 105, which is a road mechanism and hence designed for a narrower chainline than something like a deore (MTB) chainset. It would be worth checking what the chainline is currently and also the range of adjustment available on your current front derailleur as this will help identify what options are available to you. Unfortunately the Shimano road and mtb front derailleurs use a different cable pull and so it is not as simple as just changing the front derailleur to a mtb one if the current front derailleur cannot be adjusted far enough to be used with a mtb chainset.

If you don't mind changing to a square taper bottom bracket then there are quite a few options available to you as by selecting a suitable length for the bottom bracket (axle) it is possible to set the actual chainline.

If you need to find out how to measure the chainline and also the range of chainlines used see http://www.sheldonbrown.com/chainline.html.
fatboy
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Re: Gearing down...

Post by fatboy »

If you don't mind a big jump between middle and granny you could just change the inner ring. I don't know the BCD of the chain set but the equivalent Shimano one can take a 24 tooth inner.

If you want to change the chain set contact Spa who sell good square taper chain sets whose chain line can be set by bottom bracket length.
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Erudin
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Re: Gearing down...

Post by Erudin »

What crankset/shifters have you got? I swapped the inner ring on my Tiagra 4503 9 Speed Road Chainset from 30 to 26 (Stronglight 5 Arm 74mm P.C.D Chainring) to get lower gearing. The advantage of this approach is you don't need to alter the front mech/shifters and it's cheap to do.

You can fit a mtb chainset like the deore if your shifter is compatible (eg bar end/downtube) but you will to fit need a compatible front mech as well.
Last edited by Erudin on 31 Aug 2014, 8:46am, edited 2 times in total.
RonK
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Re: Gearing down...

Post by RonK »

I have exactly this setup on my touring bike. Chain line and derailleur travel won't be a problem. What may be a problem is the derailleur cage not having enough curve around the smaller rings for smooth shifting, the other is that the derailleur cage may foul the chainstay when lowered to the correct height.

Intitially I had to bend the cage to get enough clearance, but the ultimate solution is to use an IRD Alpina-D derailleur, which is optimised for smaller chainrings.
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Bonefishblues
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Re: Gearing down...

Post by Bonefishblues »

Thanks gents - the bike is as the spec posted so STi dual levers at the front. I do want to go a little smaller than a 30 ring at the front, say 26 or so, which is near as makes no difference 1:1 which will be fine, I think (no loads being carried except me) so simply changing chainrings on the existing FSA Chainset's a dead end I think (perhaps somebody could absolutely confirm?), hence looking at alternatives.

It does seem to be the front mech that's likely to be the limiting factor, and nobody will really commit as to whether the 105 will handle smaller diameter rings, albeit with much the same range as previously (so the rear shouldn't foul, I guess?). It's useful to have that linky to the IRD unit, which I assume would work with my shifters (could you confirm)? Hopefully all would be well and it would work with another chainset, but good to know there's a fallback if required.

I have had a conversation with Spa, but was being "strongly advised" by an individual whose name has come up in dispatches on the Forum from time to time that I was going the wrong way about it. Maybe I am, but hey ho :wink: .

I'm agnostic about the chainset I fit. I'm not wedded to an external BB so the Deore's not a given. What would others recommend from the Spa range? I think, from playing around with Sheldon's gear modeller, I'd be going with a 48-36-26 or perhaps 46-36-26 (which has a nice symmetry given that's what I used to tour on in the 1980s :) )
fatboy
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Re: Gearing down...

Post by fatboy »

I know that sora front mechs work with lower gears. You could always downgrade the front mech but chances are what you've got will work with a bit of messing about. Us the mech braze or band on. If braze on you may be more limited
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Bonefishblues
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Re: Gearing down...

Post by Bonefishblues »

It's a braze on, but is right at the top of its adjustment, with c1cm of downwards adjustment possible. Any idea what the effective diameter of a 52 tooth vs a 46/48 tooth is?
Edwards
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Re: Gearing down...

Post by Edwards »

CJ has put something on here that I think was put the front on the small ring. Then to engage the highest gear at the rear that you will use in the small front ring.
You then measure the distance from the bottom of the front mech gap to the chain. For every 2mm gap you can change the front ring by one tooth smaller.

I have no idea where to find the article but it may be in the Technical To Good To Loose.
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RonK
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Re: Gearing down...

Post by RonK »

Bonefishblues wrote:It's useful to have that linky to the IRD unit, which I assume would work with my shifters (could you confirm)? Hopefully all would be well and it would work with another chainset, but good to know there's a fallback if required.

I'm agnostic about the chainset I fit. I'm not wedded to an external BB so the Deore's not a given. What would others recommend from the Spa range? I think, from playing around with Sheldon's gear modeller, I'd be going with a 48-36-26 or perhaps 46-36-26 (which has a nice symmetry given that's what I used to tour on in the 1980s :) )

I'm using Ultegra 6510 9 Sp levers. Your 105 levers will be fine.

I've seen a few complaints about premature bearing wear, but the Hollowtech bb is very easy to work with and I'm happy with mine. Plenty of aftermarket bearing upgrades available too, even Phil Wood does 'em.
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Erudin
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Re: Gearing down...

Post by Erudin »

According to what I found on Google the TruVativ Rouleur GXP, 30/42/52 crankset accepts 130mm bcd chainrings and a 74mm bcd small ring.
NetworkMan
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Re: Gearing down...

Post by NetworkMan »

My Dawes Audax has a 52-42-30 chainset and has been modified with a mountain bike rear mech and an 11-32 cassette. This gives me a gear range of 25 to an absurd-for-me 125 inches. The Shimano road chainset takes has a BCD of 130 mm for the larger two rings and 74 mm for the small ring. A traditional touring chainset has a large ring BCD of 110 mm but the BCD for the small ring is the same. I expect your chainset is like mine.

Why not fit an 11-32 cassette and mountain bike mech and see if 25 inches is low enough?

If not then you can consider changing to a smaller inner ring.

By the way I find the 42 T middle ring and 11-32 cassette near ideal since the central 7 sprockets cover 40-93 inches and I rarely need to use the front changer - mostly just to improve chainline or get gears lower than 35 inches (the minimum on the middle ring). Down here in in South Devon changes of gradient are very rapid and a close ratio cassette would be a real nuisance. YMMV.

If you have road STI then a move away from the 52-42 T combination to anything smaller increases the risk of trouble changing and it gets hard to predict just what will work and what won't. That is why I have stayed with the 52-42 T though I may go one gear lower by fitting a 26 T inner ring at some stage. That will be exceed the 43 T capacity of the mountain mech at the back but I don't care since I wont be using the small cogs with the small ring. Remember too that 52:48 is only 1.08 - or one close raio gear at best.

I also recall CJ's article about reducing inner ring size and agree it's 2 mm per tooth.

Another thought. If the 11-32 casstte is not close enough ratio then you can build one by splitting two others and combining them. Much about this on teh Web I'm sure. You could certainly build a 13-32 like this. I wondered about it myself and then decided I didn't need the closer ratios. Again YMMV.
Valbrona
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Re: Gearing down...

Post by Valbrona »

Bonefishblues wrote:With that in mind, could I get away with replacing the current chainset with something like a 48-36-26 Deore chainset which would give me a very useable set of ratios and retain the rather nice close ratio gearing at the back?


You have a road-specific FD and a road-specific crankset.

If you buy an MTB crankset with the desired chainrings it may not work with your FD because the chainline may not match the FD. You cannot fit an MTB-specific FD because these don't work with drop bar STI levers.

Your easiest ssolution is to buy a road-specific crankset with smaller chainrings, and something like the Stronglight Impact/Sugino XD2 (both available from Spa) springs to mind. You can get these with 48-36-26, but don't go too small on the outside becasue you may not be able to get your FD low enough down the seat tube.
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NetworkMan
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Re: Gearing down...

Post by NetworkMan »

Your easiest ssolution is to buy a road-specific crankset with smaller chainrings, and something like the Stronglight Impact/Sugino XD2 (both available from Spa) springs to mind.


Maybe. It depends how low you want to go. If you buy a new chainset with a 26T inner ring and do nothing else you'll gain a ratio 15% lower. I call that one gear. You could likely fit a 26T inner ring to your existing chainset anyway and the smallest available inner ring with either chainset is 24T or 25% lower. Would that combination work with your existing FD? If you fit a cassette with a 32 T cog and a mountain bike mech you gain a ratio 28% or two gears lower.
Brucey
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Re: Gearing down...

Post by Brucey »

yeah but you can buy a 24T ring in 74mm BCD for about seven quid.

cheers
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