Lowering the gears on a Shimano 2x9 transmission

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pq
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Lowering the gears on a Shimano 2x9 transmission

Post by pq »

I've been asked by a friend to sort her bike out. It needs a new front mech becasue the existing one has seized, but she also wants the gears lowered.

The bike started out as a road bike with a 50/34 chainset and a 12/27 cassette, 9 speed, Tiagra short cage rear mech and Tiagara front mech. At some point it had a flat bar conversion, so it now has trigger shifters which work fine. Not going to fit a triple, so a bigger cassette and mechs to match is what I'll be doing.

I'm a decent mechanic so swapping the necessary bits is no problem, but I'm not well up on Shimano compatibility issues, so I'd like to check what I'm planning to do will work, and whether anyone has any better ideas. I'm in France so UK suppliers aren't a great idea.

So this rear mech: https://www.bike-discount.de/en/shimano ... -m2000-sgs
This cassette in 11 - 36 flavour: https://www.bike-discount.de/en/shimano ... d-cassette
This front derailleur: https://www.bike-discount.de/en/shimano ... amp-34.9mm
+ a new chain of course.

So will this work? By my reckoning it will.
Can I get a lower bottom gear? I notice there are bigger cassettes but I can't see a rear mech which will cope with them.

Thanks!
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531colin
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by 531colin »

Using the inner and middle rings of a triple chainset as a double (eg 24/40T) will get much lower gears without the big jumps of a wide range cassette, and without a new R. mech.
Jamesh
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by Jamesh »

Yeap that should do I.

Why do you need to change the FD?

Also many of us rate the 9-10spd deore xt Rd, more than newer ones.
slowster
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by slowster »

I think the components will work, but I would first want to clarify exactly what she wants/needs/prefers.

- How low a bottom gear would she prefer/need?

- Does she make much use of her current top gear(s)?

- How does she find the one tooth gaps of the top half of her current cassette? For touring and general riding, many would find that they needed to shift two sprockets at a time because those gaps were too small.

The link below provides a visual representation of her current gears and the proposed new cassette.

http://www.ritzelrechner.de/?GR=DERS&KB ... 7&UF2=2150
pq
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by pq »

Well, I haven't actually explained everything I'm going to do. 50/11 is an absurd top gear - she never uses the 12 she has and would be quite happy losing a few more. Low gears are the priority, although she can't say how low. So if I use this cassette, I'll rummage around in my big box of odd sprockets and turn it into something a bit different, probably a 13/36. Actually she got the idea from another friend's bike I've tinkered with - that now has an oddball Miche cassette but on an 11 speed system which doesn't seem to exist for 9 speed - and didn't require changing the rear mech either.

A more obvious solution to this would of course be to change the chainset for a double with whatever chainrings would give the desired ratios with the existing cassette. But there don't seem to be any good options for this. I could do what Spa do and bodge a triple into a double but then I'm into unknown territory trying to get the front mech to work on chainrings which will no doubt be in a different position to the originals (or tinker with the bb so they stay in the same position), which is a can of worms I'd sooner not open. There are 46/30 chainsets around, but they're rather pricey and won't give gears low enough without swapping the cassette.

I'm changing the front derailleur becasue it doesn't work. The pivots are very stiff, so it will barely downshift in my workstand - no chance on the road, and it's entirely lost the last bit of travel so the chain scrapes in the lower gears.
One link to your website is enough. G
mattsccm
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by mattsccm »

Bung a MTB double on. 28/42 chainrings. Most road mech will cope. Mine do anyway.I use mine with a 32 t rear to climb 30% stuff as a fat unfit old man. Bear in mind that modern small ring doubles are nowt much more than a triple with the missing outer and the ledges for that smoothed off. Nearly as ugly as a triple with out its outer.
Get on Sheldon Browns site and use the gear calculator. Put your current ratios in and play with options until you find something that gives you what you need.
slowster
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by slowster »

pq wrote: 23 May 2022, 8:55pm I could do what Spa do and bodge a triple into a double but then I'm into unknown territory trying to get the front mech to work on chainrings which will no doubt be in a different position to the originals (or tinker with the bb so they stay in the same position), which is a can of worms I'd sooner not open.
From what you write, a super compact double based on a converted road triple is the solution which is most likely to give her the gears she wants. GRX double chainsets and the like typically only offer/allow 46/30, whereas the converted triple gives options from 46/30 down to 40/24. As you note, GRX chainsets are expensive, and moreover use a 2.5mm wider chainline than road standard, and so have their own front derailleur.

Assuming you use a square taper chainset, like the Spa Super Compact (which I understand is the Sugino TD-2, and which might be available in the EU under the Sugino brand or the Stronglight brand), selecting a suitable bottom bracket should not be too difficult. Brucey published the stickout measurements for Shimano bottom brackets here - viewtopic.php?t=105385, which make it easy to calculate the impact of different BBs on chainline.

As for getting the front mech to work, Shimano specify a minimum chainring size of 46t for your proposed front derailleur. However, Shimano is usually conservative with its specifications, and I suspect you could get away with less, possibly even 40t. The other potential difficulty is the tail of the cage fouling on the chainstay in the small ring. That will be dependent upon the particular mech and the chainstay shape/angle. It might be possible to overcome that by raising the derailleur more than the recommended 2mm above the big ring, or by choosing a different mech. For example, I have a Spa 40/24 Super Compact, and I replaced my front derailleur because it was a Microshift model with a longer cage than a Shimano mech, and consequently did foul on the chainstay.
cycle tramp
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by cycle tramp »

pq wrote: 23 May 2022, 1:31pm I've been asked by a friend to sort her bike out. It needs a new front mech becasue the existing one has seized, but she also wants the gears lowered.
In my experience the reason why the front mech seizes is due to lack of use... the rider just doesn't change gear at the front, so it gets covered in road dirt and mud, which then stays and builds up because there's no movement of the mech to move the road dirt. Then it rains and the rider splashes through some puddles which makes the road dirt on the mech moist and then the steel parts rust together.....

Personally I'd speak with the customer and ask them how many times they used the front mech - if they didn't because don't like using it then I'd consider a single ring on the front...

..if the mech was frozen over the big ring, and couldn't move or the rider didn't want to move it, then I'd consider something like a 42 or 38 tooth ring.. and it may explain why the rider has requested lower gears...

..However if the rear mech was seized over the small chain ring and the rider wants lower gearing, then I'm wondering if there's an issue with crank size or bike fit for the customer.
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pq
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by pq »

Yes, it will be lack of use. My friend is often not around, so the bike just sits there when she's away, and she won't ride in the cold either. When she is around, it gets ridden regularly.

It's hilly around here, so I don't think 1x is the way to go. It's an old bike and if all it needs after all this time is a cheap front mech, I think that's fine. Maybe in another 20 years it'll need changing again, which is also fine.
One link to your website is enough. G
djnotts
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by djnotts »

Rear mech dropper/extender (Sunrace c. 15 quid is fine) and a 11-40/42 cassette easiest, cheapest and indeed best solution.
peetee
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by peetee »

EDFA0CFB-ABBA-4934-A113-2D92C0C07AEA.jpeg
My partner has a gravel bike which I built for her. She has limited power and is very much a leisure rider. Her bike has a 36/22 crankset and a 11-32 cassette with Shimano 8 speed drop-bar shifters and Campagnolo 9 speed triple front mech. Gear change is faultless with no compatibility issues. The cranks are Thorn triple with individually selected rings mounted on the inner and middle positions. The bottom bracket is square taper and the length was selected so that chain line was optimised.
She had no trouble climbing 30% hills on a recent holiday.
I see no reason why this crank set-up could not be combined with a 9 speed rear system.
The older I get the more I’m inclined to act my shoe size, not my age.
pq
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by pq »

Thanks everyobe for your advice. In the end I plumped for my original solution. I don't want the uncertainty and tinkering of the smaller chainring option - this needs to just work and I don't have massive amounts of time to spend on it. I also don't like hanger extenders - I'm using a couple on my bikes and they mess up the shifting for reasons which are obvious when you see the huge gap they create between the upper jockey wheel and the sprocket.

However I'm now regretting this. Fitting all the parts was of course quick and easy, but getting the front derailleur to stop scraping on the big chainring I'm starting to think is impossible. The cage it seems is too narrow - no amount of fiddling with the height, the angle or the cable routing allows more than 5 sprockets to be useable without the chain scraping on the front mech on one side, the other side, or usually both. It's like it's designed to work on a narrower chain, but the link in my original post says it's for a 2x9 system.

I'm familiar with finiky front mech set ups but I've never had one so comprehensively defeat me as this one has done. So have I bought the wrong front mech? Have I missed something obvious? I must admit I rarely use Shimano stuff myself, so maybe that's it...
One link to your website is enough. G
ElCani
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by ElCani »

You don’t say exactly what shifters you’re using, which could be key. If they’re going to work with the front mech you linked in the OP, then they need to be 9 speed flat bar road shifters. An MTB flat bar shifter (of any speed) won’t play nicely with a road front mech.

If you do have a 9 speed double flat bar road shifter (which is perfectly possible if the earlier flat bar conversion was done properly) then it should have two positions for each chainring, an inner and an outer. This feature is known as ‘trim’ and allows you to adjust the mech to prevent rubbing in extreme chainlines. MTB front mech do not have this. If the front mech cable is over tightened these extra positions can ‘disappear’ which could be your problem. But I also notice you don’t mention adjusting the limit screws on the front mech, which is obviously a key step in setting one up.

Good luck!
slowster
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by slowster »

That front derailleur has two settings depending upon the angle of the cable from the bottom bracket. See page 13 of the following manual. Assuming you do not have the measuring tool to determine the correct setting, have you tried both settings?

https://si.shimano.com/pdfs/dm/DM-RBFD001-01-ENG.pdf

As per ElCani's comments, according to the manual the matching STI shifter has a trimming function - see page 19 and onwards. What are the shifters fitted to the bike?
pq
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Re: Lowering the gears on a Shimano 2x9 transmission

Post by pq »

Ah, I think you've hit the nail on the head, the shifters have no trim - I need to set it up so there's no rub on any (or at least most) of the sprockets which seems to be impossible. I know nothing about the flat bar conversion, I didn't do it.

I don't know what the shifters are - I can't read the model number. But they are flat bar shifters with no trim. I've tried both possible cable routings and it makes no difference - which given the problem I have isn't surprising.
One link to your website is enough. G
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