Lowering gearing

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tyreon
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Lowering gearing

Post by tyreon »

Advice please: I have an elderly looped frame bicycle with metal chaincase and which I use for shopping/commuting. SA hub. I lowered the gearing a tad by replacing the rear sprocket with something large some years backr. Now I want to go lower still,but cannot increase the sprocket on the rear hub because it would interfere with the chaincase(the chaincase would not fit over the wanted rear sprocket). I have 44 tooth chainwheel on the front. Can I go down to 42 or 40!,and would 42 be a significant difference? I just want that little bit lower gearing for going-up-with-ease a hill I cycle into town. I can get up the hill with present gearing,but my knees don't like it and I don't want to shop in lycra.
I really don't want to get rid of my bike,but don't want to lay out x2many pounds for a complete bike overhaul. Resolvable,or one o these 'complex jobs' wherein first this,then that, is changed and my wallet begins to hurt?
tyred
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Re: Lowering gearing

Post by tyred »

Perfectly possible but the challenge will be finding a cottered chainset in the size you want. Ebay is your friend.

You could also look to finding a cottered double chainset with removable rings and take off the big ring although I'm not too sure how this would work with a chaincase and unfortunately most cottered double chainsets don't have removable rings and you will probably need a different bottom bracket axle.

If it's not a Raleigh and has standard BSA threading, you could convert to cotterless and have endless choice of chainwheels.

What size is your current rear sprocket. I was able to fit a 23t sprocket inside my steel chaincase (it's actually a Shimano sprocket but fits the SA hub just fine).

A 2 tooth difference on the front won't make a huge difference to overall gearing.

Perhaps you could look for a 4 or 5 speed sturmey hub which will offer a lower bottom gear.
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cycleruk
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Re: Lowering gearing

Post by cycleruk »

44 down to 40 will make a 9% difference.
No reason that I know of why you can't except for the practicalities of changing the rings.
As Tyred suggests may be more practical to get a complete replacement chainset and bottom bracket.
You'll never know if you don't try it.
tyreon
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Re: Lowering gearing

Post by tyreon »

Thanks both for reply: ta. So...40 tooth chainwheel easy to source with bottom bracket? Shorten chain length? Gotta go out and check rear sprocket teeth number. From memory I was lucky chaincase cleared my increased sprocket: 2 more and the sprocket wouldn't have had clearance to turn.
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Mick F
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Re: Lowering gearing

Post by Mick F »

If it is a Raleigh, you can do as I had done to my Raleigh Chopper.

The Raleigh BB shell is too wide for square taper bottom brackets, but by buying a new ST spindle you can cut it in half, and "telescope" a sleeve mid-way. Tack weld it and offer it up. If you need an adjustment to the length between the bearings, you can adjust it.

When happy, weld it up solid. By using a V block, you can get it true, and you can then use a ST chainset and the world's your oyster from then on.

The main problem you will have, is finding a friend with a lathe and the equipment plus the correct skills. :wink:
Mick F. Cornwall
tyreon
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Re: Lowering gearing

Post by tyreon »

With my dicky back and your tech knowledge,Mick...I have started up the car and am heading down to Cornwall(?) No,no lathe,and your tech speak I no-comprendo. I just sorta wanted to know how complex/£-taking this job would be. Now I know it can sorta-be done,I will phone my lbs to sort out further details.What I didn't want is a job where its rebuilding a rear wheel with a new hub or wot-not. Any major work and I'd continue to walk up the hill...or look to getting a new step thru machine...7 speed derallieur would almost be overkill
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Mick F
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Re: Lowering gearing

Post by Mick F »

Sorry for blinding you with science. :oops:

First question, do you have cotter pins holding your cranks onto the bottom bracket spindle?
Second question, is your bike an elderly Raleigh?
Mick F. Cornwall
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531colin
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Re: Lowering gearing

Post by 531colin »

http://www.ebay.co.uk/itm/414-Industries-BMX-Alloy-Chainwheel-/110881098227?pt=UK_sportsleisure_cycling_bikeparts_SR&var=&hash=item19d10749f3
£6 for a 39T chainwheel from E bay.....cut down your existing chainwheel, bolt this one to it.....chainline will be a few mm. out, does it matter?
....there will be others....

Edit....will be easier to bolt the BMX chainwheel to the back of the existing chainwheel.....then you can space out the BB cup to get the chainline right?
tyreon
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Re: Lowering gearing

Post by tyreon »

Ah! I see I have two of this forums techies on board. Respect!

No,I don't have a Raleigh,I've got a Kynast,a German job. It doesn't have cotter pins. I picked it up s/h then had to have a bottom bracket specially put in to go with the new chainset. The original b/bracket/chainset went awry. Think the lbs had to 'cement' the bottom bracket in as the threads were stripped. Anyways,its all worked well with the machine up until the present when (my)age and my knees aren't what they were.

It wont be a job I will undertake,but sometimes (some)bikeshops can't/wont source products because they're obsolete or difficult to source. Coming on here,reading some stuff sometimes helps out in repairing jobs myself,or helping (some)bikeshop employees execute a 'difficult job'. Also,I can go to the shop and sound like I know what I'm talking about!!
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Mick F
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Re: Lowering gearing

Post by Mick F »

tyreon wrote:Ah! I see I have two of this forums techies on board. Respect!
That's fine!
Some of us are on here a lot. :D

tyreon wrote:No,I don't have a Raleigh,I've got a Kynast,a German job. It doesn't have cotter pins.
That's good.
The world is your oyster. You should be able to get a chainset with a smaller chainring easily enough. Your local bike shop should be able to sort you out or advise specifically.
Mick F. Cornwall
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mjr
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Re: Lowering gearing

Post by mjr »

If it's a 3-speed SA hub (like my 1990s AW) then I've read that you shouldn't have a sprocket more than half the size of the chainring... but I've also read that that's conservative.

If it's currently on 26x1⅜ (Roadster/Hollandrad), then I think 44/20 (I'm guessing 20t because you write that it can't go bigger, so I guess there's at least a few larger sizes) will be giving about 43" bottom gear, while 39/20 would drop that to 38".

For comparison, I think my 3 has about 45" bottom gear (46/20) but the toughest slope I do often on it is only a 20m 10% bridge ramp; and my hybrid has about a 32" bottom gear which does 10% pretty easily, but I never could sustain more than 150m of 25% climb on it. I'm OK with dismounting from the 3 for the steepest hills - I did on the hybrid too :lol: So... how bad are your hills?

Also, could the chaincase be replaced or would that be sacrilege?
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
All the above is CC-By-SA and no other implied copyright license to Cycle magazine.
tyreon
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Re: Lowering gearing

Post by tyreon »

mjr: I'm going to my garage,my least favourite place at this time of year. My chaincase is all but sacrosanct: postmans red. I'm gonna count my rear cog no. 'Phoned bike shop yesterday: "Will get back to you". Oftentimes they don't! Am I now to think getting that 40tooth chainwheels difficult? So...how's about a new rear sprocket...if it will fit into the chaincase!If it will not break a 'Sheldon Rule'!If it will be easy(all things considered). See? The stress is building up! The 2 minute job is now working up to phone lbs x4 times,they 'will get back'(sure!!),I'll do the job(hold on,I gotta take account of this,now that,now this again...) What over-the-counter medication works for patience and persistence!
Bikefayre
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Re: Lowering gearing

Post by Bikefayre »

The one thing I'd personally recommend is modern tyres with a special low rolling resistance compound, that not only makes the bike faster but will also make it climb quicker. For my own bikes use Oregon chainsaw 2-stroke oil as it dramatically reduces the drag. For example instead of the standard horrible 590 tyres have replaced one with the Schwalbe Marathon Plus Evo wheelchair tyre which has worked a treat for over three years. Older bikes suffer from steel components, so over time replace with alloy and you could fit plastic mudguards as this too will reduce weight. sjscycles.co.uk are a good place to go and get help with the older bikes. One simple solution is to fit a smaller rim on the rear, on mine have reduced it from 622 to a 590 which for a single speed makes a big difference. Also a square taper axle will fit a cotter pin bike as have done this and fitted a modern vintage style second hand chainset which not only kept the look of the old road bike, late 'seventies, but also dramatically reduced the gearing. We need more details and if you are stuck e-mail me at womblebikesscotland@outlook.com as have bikes that over 25 years old so can easily help you.
tyreon
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Re: Lowering gearing

Post by tyreon »

Stay with me,I'm nearly there.

Rear sprocket teeth number on S/A: 20. I could go to 22 but that might start to interfere with the top of my chaincase. But what gearing would that give me?

LBS now informs me that they can supply 40 or 38 tooth chainwheel. This with 20 tooth rear sprocket would give me what? in gear inches.

Present set up 44 tooth chainwheel and 20tooth rear sprocket.

Two hills,two crook knees and 5-10kgs o shopping and wanting to remain in mufti(not lycra)restrict higher speeding
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mjr
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Re: Lowering gearing

Post by mjr »

As far as I can recall, it's ( Wheel size * front teeth / back teeth ) * 0.75 (for SA3 bottom gear), so present is 0.75 * 26" * 44t / 20t = 42.9"; a 22t on the back would give 39"; a 38t on the front with 20t on the back would give 37.05"
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
All the above is CC-By-SA and no other implied copyright license to Cycle magazine.
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