chainset width / stance width

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ChrisF
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Joined: 22 Mar 2014, 7:34pm

chainset width / stance width

Post by ChrisF »

I'd like to reduce the stance width (width between pedals) on my Galaxy tourer. I'll sort out the minimum BB length, but I'm puzzled by the chainset. I currently have a Stronglight 26/36/46 which appears to be very 'wide': there's a big gap (about 12mm) between the crank arm and the front changer, and it's 30mm from the outside of the large ring to the outside of the crank arm - anyone know why this is?
20210726_135312.jpg
Would another chainset (e.g. this one https://www.sjscycles.co.uk/chainsets/t ... 26t-175mm/) be any different? (I need a new chainset for another reason anyway).
Thanks
Chris F, Cornwall
freeflow
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Re: chainset width / stance width

Post by freeflow »

Why. Most people would benefit from a wider stance rather than narrower. Let's not follow this up with references to Q factor because, as we know, this measure has no scientific basis.
slowster
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Re: chainset width / stance width

Post by slowster »

You need to know the Q factor (aka tread) of potential replacement chainsets, and compare them with whatever the measurement is for your current chainset (remove the left hand crank, rotate 180 degrees and re-attach and tighten, then measure distance between the cranks outside to outside).

SJS have not specified the Q factor for the Thorn chainset, but Spa for example do specify it for their TD2 and RD2 chainsets, e.g.:

https://www.spacycles.co.uk/m8b0s109p30 ... cral-Rings
ChrisF
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Re: chainset width / stance width

Post by ChrisF »

freeflow wrote: 26 Jul 2021, 2:26pm Why. Most people would benefit from a wider stance rather than narrower. Let's not follow this up with references to Q factor because, as we know, this measure has no scientific basis.
Why? I have 4 bikes; measuring pedal-centre to pedal-centre , three of them are 260mm and the Galaxy is 295mm.
I've recently relaised that I'm getting a painful knee after riding the Galaxy but not the others. Same distance saddle-to-pedal, same pedal type on each, same shoes and cleats. Maybe coincidence, but I want to test it out. I guess my stance width is narrower than average.
Last edited by ChrisF on 26 Jul 2021, 3:30pm, edited 1 time in total.
Chris F, Cornwall
ChrisF
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Re: chainset width / stance width

Post by ChrisF »

slowster wrote: 26 Jul 2021, 2:33pm You need to know the Q factor (aka tread) of potential replacement chainsets, and compare them with whatever the measurement is for your current chainset (remove the left hand crank, rotate 180 degrees and re-attach and tighten, then measure distance between the cranks outside to outside).

SJS have not specified the Q factor for the Thorn chainset, but Spa for example do specify it for their TD2 and RD2 chainsets, e.g.:

https://www.spacycles.co.uk/m8b0s109p30 ... cral-Rings
Thanks. I assume the Q-factor specified is with the recommended BB. 159mm is quite a bit less than my current setup.
According to SJS, the Q factor for my Stronglight is 165mm, but I don't see how it can be quoted in the absence of a BB size.

BTW , rather than removing the left crank, I measured it from downtube to crank on each side, added them together then added the downtube diameter. I don't need to be accurate to <1mm. I hope that's OK!
Chris F, Cornwall
freeflow
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Re: chainset width / stance width

Post by freeflow »

Why? I have 4 bikes; measuring pedal-centre to pedal-centre , three of them are 260mm and the Galaxy is 295mm.
I've recently relaised that I'm getting a painful knee after riding the Galaxy but not the others. Maybe coincidence, but I want to test it out. I guess my stance width is narrower than average.
That's an excellent reason, and a fact that might have helped moderate the responses you got to your query. For myself I went the other way. Adding 20mm pedal spacers eliminated my knee pain (changed effective spacing crank to crank from 174mm to 214mm)
Valbrona
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Re: chainset width / stance width

Post by Valbrona »

Are all of your bikes triples? You get higher stance width with triple as opposed to double chainset, obviously.

(Just got over two months of terrible knee tendonitis after a couple of test rides in new shoes that placed my feet too wide apart).
I should coco.
ChrisF
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Re: chainset width / stance width

Post by ChrisF »

Valbrona wrote: 26 Jul 2021, 8:32pm Are all of your bikes triples? You get higher stance width with triple as opposed to double chainset, obviously.
No, two others are doubles and one is a 1x; I can see that triples need to be wider. But why so much wider? That's what my original question was about - why that wasted 10-12mm outside the derailleur hanger? If that fits an average rider's stance width, then all 1x or 2x road bikes are too narrow.
(Just got over two months of terrible knee tendonitis after a couple of test rides in new shoes that placed my feet too wide apart).
Ah! sorry to hear that, but glad to have found someone with the same problem!
Chris F, Cornwall
Valbrona
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Re: chainset width / stance width

Post by Valbrona »

ChrisF wrote: 26 Jul 2021, 10:05pm
Valbrona wrote: 26 Jul 2021, 8:32pm Are all of your bikes triples? You get higher stance width with triple as opposed to double chainset, obviously.
No, two others are doubles and one is a 1x; I can see that triples need to be wider. But why so much wider? That's what my original question was about - why that wasted 10-12mm outside the derailleur hanger? If that fits an average rider's stance width, then all 1x or 2x road bikes are too narrow.
I guess the chainset you have is just old design, triples having been neglected in preference for doubles. And if you are on 110/74 triple like you are the choice is pretty limited as most triples, eg. Shimano, use 130 outer.

Miche do a modern integrated axle triple 110 BCD crankset, but an IRD tripleizer middle ring is needed to run it with a 74 BCD inner ring.

Incidentally, I run a SRAM Wide-Axle double crankset as a triple 110/74 using aforesaid IRD tripleizer middle chainring.

Or you could forgo existing chainrings and 'upsize' to like a modern Shimano road triple crankset.
I should coco.
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531colin
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Re: chainset width / stance width

Post by 531colin »

freeflow wrote: 26 Jul 2021, 2:26pm........... Most people would benefit from a wider stance rather than narrower. ...........
Got a reference for that?
freeflow
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Joined: 29 Aug 2011, 1:54pm

Re: chainset width / stance width

Post by freeflow »

Google for stance width. Here's a starter for 10

https://blog.bikefit.com/bicycle-stance-width/

and (Foot separation distance)

https://www.stevehoggbikefitting.com/bi ... knee-pain/
TheBomber
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Re: chainset width / stance width

Post by TheBomber »

531colin wrote: 28 Jul 2021, 3:06pm
freeflow wrote: 26 Jul 2021, 2:26pm........... Most people would benefit from a wider stance rather than narrower. ...........
Got a reference for that?
I was surprised by that too. Interesting links, but while they explain how some people would benefit from a wider stance I didn't come across anything to substantiate the 'most' term. Given that increasing the q factor would allow bike manufacturers to make stronger wheels, fit wider cassettes or allow for wider tyres, it seems to me that they are going to great lengths to limit the q factor - presumably because 'most' people don't want to increase their stance? Me being one of them.
Valbrona
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Re: chainset width / stance width

Post by Valbrona »

Most people aren't concerned about stance width as the 'comfortable range' is quite a wide one. It is not until someone finds themselves on some type of pedal/shoe/crank arrangement that places them outside of the 'comfortable range' that stance width becomes an issue.

For performance riders, like pros and serious amateurs, it is different. A Retul fit will give indication of optimal stance width, ie. the width at which power output is greatest for the same/similar effort.
I should coco.
cycle tramp
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Re: chainset width / stance width

Post by cycle tramp »

ChrisF wrote: 26 Jul 2021, 2:12pm I'd like to reduce the stance width (width between pedals) on my Galaxy tourer. I'll sort out the minimum BB length, but I'm puzzled by the chainset. I currently have a Stronglight 26/36/46 which appears to be very 'wide': there's a big gap (about 12mm) between the crank arm and the front changer, and it's 30mm from the outside of the large ring to the outside of the crank arm - anyone know why this is?
20210726_135312.jpg
Would another chainset (e.g. this one https://www.sjscycles.co.uk/chainsets/t ... 26t-175mm/) be any different? (I need a new chainset for another reason anyway).
Thanks
I suspect that the wide gap allows for the crank to pass on the off side of the front mech and the chainring to continue turning on the inside of the front mech, with a large degree of safety allowance.
If this gap was too narrow and the front mech was allowed to swing out too far, due to poor gear settings, then I suspect that the crank arm would collide with the cage of the front mech, possibly causing the rider to crash.
If you were a bike manufacturer you wouldn't want this to happen and taking steps to avoid it might have resulted in generous clearances.
It's time to go :-)
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Mick F
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Re: chainset width / stance width

Post by Mick F »

Valbrona wrote: 26 Jul 2021, 8:32pm Are all of your bikes triples? You get higher stance width with triple as opposed to double chainset, obviously.
Not necessarily.

I have a Stronglight 99 double, but it's also a triple if you change the chainring bolts so you can fit an inner. Very narrow Q and straight cranks.

str99.jpg
str99.jpg (84.39 KiB) Viewed 229 times
Mick F. Cornwall
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