How low can you go?

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BambooKiro
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How low can you go?

Postby BambooKiro » 23 Jun 2020, 2:39pm

If the gearing on a Genesis Tour de Fer 10 needs lowering, what is the best way to go about it? Smaller chainring or larger cassette?

The specs at the moment are:
Chaniset: Shimano Claris FC-R453, 50/39/30T
Rear derailleur: Shimano Sora RD-R3000 cage length GS
Cassette: Shimano Acera CS-HG300-9 11-32T

Fitting a larger cassette seems like the best option, but how big of a cassette can be fitted before the derailleur wont clear it on the largest sprocket?

Thanks

rotavator
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Re: How low can you go?

Postby rotavator » 23 Jun 2020, 2:50pm

Shimano's spec sheet indicates the max spocket for that RD is 34T and total capacity is 43T:
[url]
https://bike.shimano.com/en-EU/product/ ... 00-GS.html[/url]
Last edited by rotavator on 23 Jun 2020, 2:51pm, edited 1 time in total.

whoof
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Re: How low can you go?

Postby whoof » 23 Jun 2020, 2:51pm

The inner chain ring is 74 mm BCD so will take a 24 tooth ring.

Marcus Aurelius
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Re: How low can you go?

Postby Marcus Aurelius » 23 Jun 2020, 2:52pm

rotavator wrote:Shimano's spec sheet indicates the max spocket for that RD is 34T:
[url]
https://bike.shimano.com/en-EU/product/ ... 00-GS.html[/url]

That depends on the chainset as well. With a compact chainset you may get away with 34 teeth, with a semi or standard, it would be very close to being a chain jammer in certain ratios.

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The utility cyclist
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Re: How low can you go?

Postby The utility cyclist » 23 Jun 2020, 7:17pm

A 24T is by far the best option, it's quick, the least expensive and requires no change in the chain in my personal experience and won't need a change in derailleur either.
A 30T to a 24T is approximately a 20% reduction in gear ratio.
I've done this on several bikes, it's been absolutely essential for me for some rides/slopes.

You can get a 23t for an even lower gear but they aren't common and they aren't cheap, lower count than that and you need a different chainset (MTB) which generally presents its own set of issues.

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BambooKiro
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Re: How low can you go?

Postby BambooKiro » 24 Jun 2020, 4:17pm

whoof wrote:The inner chain ring is 74 mm BCD so will take a 24 tooth ring.


Shimano won't sell a 24T inner chairing for the Sora crankset.

Does anyone else do it? It's the 4 bolt type, with the non-symmetrical bolts.

Image

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The utility cyclist
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Re: How low can you go?

Postby The utility cyclist » 24 Jun 2020, 4:53pm

Ah, the modern Shimano bag of poop triple chainset, even worse than the 4 bolt double and pushes their even worse wide spaced expensive cassettes that nee yet another rear derailleur derivation that get uglier each time!

I'd pull the modern SORA and get an older/better triple chainset, Shimano and their narrow sighted tail wagging are progressively/year on year piddling me off with their ignorance of what most people want gearing wise, that's before you even get to the fact they are binning off triple shifters in all but the lowest road groups and even then in limited numbers such that SORA triple STIs are in places 75% the cost of what I paid for my Dura Ace 9001 STIs!

slowster
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Re: How low can you go?

Postby slowster » 24 Jun 2020, 5:25pm

It's probably worth while taking a step back at this point and asking yourself if the only shortcoming of your current gearing is that you need lower bottom gear(s). For example,

- how often do you use the top gears? 50 x 11 and 50 x 12 give gears of 124 and 114 inches respectively, which are far too high to be useful on a touring bike.

- what chainring and sprockets do you normally find yourself using when riding on the flat in the middle of a ride? Ideally you want to use the middle sprockets most of the time, e.g. if most of the time you find yourself using the 39 tooth chainring with the larger sprockets you would probably do better to have a smaller middle ring.

It may be therefore that the best solution would be to replace the chainset. Something like 46/36/24 would probably give you a much better range of gears, including the lower bottom gear you seek. This is a visual representation of the two gear ranges. The outer/inner tooth difference slightly exceeds the 20 tooth maximum Shimano typically specify for their front derailleurs, but I expect it would be OK (whereas 50-24 is potentially more likely to be problematic). Changing the chainset would also enable you to switch to one that used the standard 5 arm BCD, chainrings for which are much more widely available and in a wider range of tooth sizes. Unfortunately Shimano road triple chainsets are only available with 50/39/30 chainrings, so you would need to buy another brand chainset.

The front derailleur would need to be lowered (around 2mm per tooth, so ~8m if switching from 50t to 46t), and you may need to check that the tail of the front derailleur would not foul on the chainstay.

whoof
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Re: How low can you go?

Postby whoof » 24 Jun 2020, 6:19pm

BambooKiro wrote:
whoof wrote:The inner chain ring is 74 mm BCD so will take a 24 tooth ring.


Shimano won't sell a 24T inner chairing for the Sora crankset.

Does anyone else do it? It's the 4 bolt type, with the non-symmetrical bolts.

Image

I got the info about it being 74 mm 5 arm from here


https://www.sjscycles.co.uk/chainrings/ ... black-30t/

If it's four arm then 30 T is your limit.

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BambooKiro
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Re: How low can you go?

Postby BambooKiro » 25 Jun 2020, 10:54am

slowster wrote:The front derailleur would need to be lowered (around 2mm per tooth, so ~8m if switching from 50t to 46t), and you may need to check that the tail of the front derailleur would not foul on the chainstay.


Will the existing shifter and derailleur combination work with a MTB chainset FC-T4060 Alivio 48 / 36 / 26 teeth?

Image

slowster
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Re: How low can you go?

Postby slowster » 25 Jun 2020, 4:35pm

BambooKiro wrote:Will the existing shifter and derailleur combination work with a MTB chainset FC-T4060 Alivio 48 / 36 / 26 teeth?

Shimano road and MTB triple chainsets have different chainlines, and I would not expect a road front derailleur to work - certainly not work well - with an MTB triple.

In your shoes I would replace the chainset and bottom bracket with a Spa chainset and a suitable square taper bottom bracket, e.g. Shimano UN55.

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Mick F
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Re: How low can you go?

Postby Mick F » 25 Jun 2020, 4:58pm

How low can you go?

The world is you oyster (or lobster?) by fitting a 3sp hub into the wheel.
I see you have a disc brake, so fit a CS-RK3 that'll take a 10sp cassette.

https://www.sjscycles.co.uk/hubs-intern ... sette-hub/
Mick F. Cornwall

rmurphy195
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Re: How low can you go?

Postby rmurphy195 » 25 Jun 2020, 9:25pm

Either a smaller chainring or a larger cassete, or both.

Fitting smaller chainrings - be aware of the capacity of your front mech if only changing theb smallest ring. If changing the biggest, you may need to move the front mech down the seat tube a bit, which may result in the tail of the mech fouling the chainstay.

Fitting bigger sprockets - again, check the capacity of the rear mech, and of the setup overall. Check also the gaps between sprocket sizes, you may end up with a big jump somewhere that gets on your nerves!
Brompton, Condor Heritage, creaky joints and thinning white (formerly grey) hair
""You know you're getting old when it's easier to ride a bike than to get on and off it" - quote from observant jogger !

djnotts
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Re: How low can you go?

Postby djnotts » 27 Jun 2020, 4:56pm

The utility cyclist wrote:Ah, the modern Shimano bag of poop triple chainset, even worse than the 4 bolt double and pushes their even worse wide spaced expensive cassettes that nee yet another rear derailleur derivation that get uglier each time!

I'd pull the modern SORA and get an older/better triple chainset, Shimano and their narrow sighted tail wagging are progressively/year on year piddling me off with their ignorance of what most people want gearing wise, that's before you even get to the fact they are binning off triple shifters in all but the lowest road groups and even then in limited numbers such that SORA triple STIs are in places 75% the cost of what I paid for my Dura Ace 9001 STIs!


Just so. Removed new Tiagra triple from my carbon road bike, bought barely used 105, changed 30 to 26, sold the Tiagra. Net cost very low - and as a bonus now 105 throughout.

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The utility cyclist
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Re: How low can you go?

Postby The utility cyclist » 27 Jun 2020, 7:37pm

djnotts wrote:
The utility cyclist wrote:Ah, the modern Shimano bag of poop triple chainset, even worse than the 4 bolt double and pushes their even worse wide spaced expensive cassettes that nee yet another rear derailleur derivation that get uglier each time!

I'd pull the modern SORA and get an older/better triple chainset, Shimano and their narrow sighted tail wagging are progressively/year on year piddling me off with their ignorance of what most people want gearing wise, that's before you even get to the fact they are binning off triple shifters in all but the lowest road groups and even then in limited numbers such that SORA triple STIs are in places 75% the cost of what I paid for my Dura Ace 9001 STIs!


Just so. Removed new Tiagra triple from my carbon road bike, bought barely used 105, changed 30 to 26, sold the Tiagra. Net cost very low - and as a bonus now 105 throughout.

Tiagra 4700 left triple and 105 11 speed is on my ti tourer, from my initial use the Tiagra 4700 is better than the 6700 triple on my other bike, the 6700 STIs are going for a song on ebay at the moment due to the shortages/ceasing production in the higher spec stuff.