Chainset question

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Hackfall
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Chainset question

Post by Hackfall »

Looking at options around a new chainset and not so keen on the idea of hollowtech after reading up on it. I like my bottom bracket, a square taper titanium. The chainset could lose a little weight, it is an old Rx100 which was once 52/42 but is now 52/39. Looking at this stronglight one below, what I am not sure about is the 107mm, how I can tell if this is suitable for my bottom bracket without having to take my BB apart. is there a way to find out what the old Rx100 was and therefore what my current bb will be. the chainet i am looking at is this:

http://www.ribblecycles.co.uk/sp/road-t ... trochar560
Brucey
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Re: Chainset question

Post by Brucey »

discussed here;

http://forum.ctc.org.uk/viewtopic.php?f=5&t=70959

so if your chainline is correct then you can hazard a reasonable guess at the present spindle length.

You can of course just measure it; the total width across the dustcaps, less the depth each side (with the bolts out).

Most doubles measure less than 150mm total, so you can use ordinary 150mm vernier calipers to take the measurements.

cheers
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cycleruk
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Re: Chainset question

Post by cycleruk »

107mm refers to the overall width of the axle. So you should be able to measure it with the cranks off.
From the reference Brucy posted it gives the impression that the RX100 BB is 113 or 115mm
You'll never know if you don't try it.
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Hackfall
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Re: Chainset question

Post by Hackfall »

just dug a bit more and had a look at the code underside of the crank arm. turns out the existing cranks are earlier again, exage code FC-A400, which according to sheldon brown is 113mm. so that would then indicate my bb is also 113mm i guess? so the stronglight i mentioned being 107mm would not be compatible?? Not sure if there are "bands" of widths you can get away with?
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Hackfall
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Re: Chainset question

Post by Hackfall »

also seen this the same I guess but 113mm this time, spa don't publish weights but i guess i can call and ask:

http://www.spacycles.co.uk/products.php ... 0s109p2799
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CREPELLO
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Re: Chainset question

Post by CREPELLO »

I would measure the existing BB and wouldn't assume that the previous owner fitted the 'correct' length BB. I will fit whatever BB looks appropriate for the bike's set up and not just what the manufacturer says. You might also consider what the ideal chainline is for your bike and it's purpose. Or, with the BB length known, identify a chainset that will fit it.

The Impact chainset is actually made by Sugino... http://www.suginoltd.co.jp/products/touring/xd.html ....who list the intended BB as 110mm. Now, there should only be 1.5mm difference between a 110 and 113 mm BB. So not a lot in it, if your BB is 113.
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Hackfall
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Re: Chainset question

Post by Hackfall »

thanks for that. my current BB is one I fitted myself many years ago and its never wavered, its a titanium, and I have no idea who makes it, and I think I will have fitted one the same width as the original BB with the Exage chainset.

Only way to know I guess is to take everything apart to be absolutely certain.

fortunately the seller of the last link i posted Spa cycles are only 13 miles from me so maybe will visit them also to take a look at it.
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recordacefromnew
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Re: Chainset question

Post by recordacefromnew »

According to Shimano's old crankset and bb combination chart, the FC-A400 has you a 50mm chainline with a 113mm Shimano bb. So if I were you I would measure the chainline - and see if it is c50mm.

Secondly given Ribble is nearly 100% road orientated, the 107mm bb referred to in their Stronglight Ad is for a 43.5mm chainline, as confirmed by http://www.stronglight.com/stronglight/ ... urQ.an.pdf

In relation to a 107mm, a 113mm Shimano UN bb will get your cranks 3mm further out on both* sides - assuming your Ti bb is exactly the same as a Shimano JIS and assuming the current chainline is 50mm, the Stronglight will end up 3.5mm further inboard, which might have implication on the performance of the existing front mech if you are unlucky, but you can certainly check before buying by looking for for clash clearance (with the seat tube) and playing with the limit screws.

Of course square tapered being what it is, even when everything are supposed to be JIS, the above figures can't be expected to be 100% accurate.

* incidentally it is not true, as the other ctc page linked above says, that all Shimano bb spindles are symmetric. For example, compared to the 113mm the 115mm is 2mm longer on the non-drive side - this can be established by standing them on their drive side axles side by side, the fixed cup flanges will be at the same height. It is therefore also not usually that straightforward to id the best UN replacement for a traditional cup and cone.
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CREPELLO
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Re: Chainset question

Post by CREPELLO »

recordacefromnew wrote:* incidentally it is not true, as the other ctc page linked above says, that all Shimano bb spindles are symmetric. For example, compared to the 113mm the 115mm is 2mm longer on the non-drive side - this can be established by standing them on their drive side axles side by side, the fixed cup flanges will be at the same height. It is therefore also not usually that straightforward to id the best UN replacement for a traditional cup and cone.
This baffles me :? . So much so that I started a thread on the subject, which didn't get very far: viewtopic.php?f=5&t=78892&hilit
Where is the logic in adding the extra axle length on the non drive side? :? :? :?

Feel free to contribute to that topic RAFN, and welcome to the forum :)
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recordacefromnew
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Re: Chainset question

Post by recordacefromnew »

CREPELLO wrote:This baffles me :? . So much so that I started a thread on the subject, which didn't get very far: viewtopic.php?f=5&t=78892&hilit
Where is the logic in adding the extra axle length on the non drive side? :? :? :?

Feel free to contribute to that topic RAFN, and welcome to the forum :)


Thanks Crepello. From what I can gather, the "logic" is that such options are essential for fine tuning chainline by spacers (using a limited range of spindle lengths) while not overly messing up the non-drive side crank arm - chainstay clearance or q factor symmetry.
Brucey
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Re: Chainset question

Post by Brucey »

I hypothesised that it might be because the 115mm guts are originally intended to go on a 68mm shell with a chaincase bracket, or just a 70mm shell. Making just one axle/bearing assy in each length has a certain attraction.

cheers
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CJ
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Re: Chainset question

Post by CJ »

And the 115mm isn't the only longer-on-the-left Shimano unit. The 110 gives just the same chainline as the 107, but sticks out 3mm extra on the left.

The logic may be that one can add spacers on the right to fine-tune chainline without mashing a MTB's obese chainstays with the left crank, except that the UN55 110mm unit I recently bought has a shoulder on it's left-side threaded cyclindrical wotsit, so it cannot go any further into the shell. So if I add a 1.5mm spacer on the right, it'll not be secure on the left. Actually to do that requires the borrowing of an un-shouldered wotsit from an old UN73 bottom-bracket unit, which I have spare, but rather than mess around like that I simply put the Stronglight 110mm unit back in, which feels like it's wearing out, but IS symmetrical and might as well have the last few hundred miles wrung out of it!

My bike is NOT a mountain-bike. The tyre is comfortable, not fat, and embraced by perfectly formed titanium tubes, not aluminium 'bingo wings'. I do not need and neither do I want my left crank even further from the frame than the right one needs to be in order to clear the front mech. I remember when most bottom-bracket axles were longer on the right, I still even have some like that in regular use - thank's to Stein's grease injection and sealing kits. There's a good reason for longer on the right: to make room for extra chainrings. I can tolerate the dumbing down to symmetry, but longer on the left does seem a bit daft. Even on a mountain-bike, chainstay clearance is not usually so lacking that one or two mm offset of a symmetrical bottom-bracket would cause a problem. But that's how Shimano make them and it can't be helped.

Back to the OP. If his chainline is genuinely 50mm at present, that's wide for a double on a road bike, for which the standard is 43.5mm. Even MTB doubles are often 47mm. I guess this bike is a road or touring bike. And my advice is keep the chainline as narrow as you can. It makes for smoother running in big and big, which tends to be a useful combination. Unfortunately it looks more likely that Sugino XD cranks will give you an even wider chainline and pedal spread than your Shimano cranks, on the same axle.
Chris Juden
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recordacefromnew
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Re: Chainset question

Post by recordacefromnew »

CJ wrote:And the 115mm isn't the only longer-on-the-left Shimano unit. The 110 gives just the same chainline as the 107, but sticks out 3mm extra on the left.

The logic may be that one can add spacers on the right to fine-tune chainline without mashing a MTB's obese chainstays with the left crank, except that the UN55 110mm unit I recently bought has a shoulder on it's left-side threaded cyclindrical wotsit, so it cannot go any further into the shell. So if I add a 1.5mm spacer on the right, it'll not be secure on the left. Actually to do that requires the borrowing of an un-shouldered wotsit from an old UN73 bottom-bracket unit, which I have spare, but rather than mess around like that I simply put the Stronglight 110mm unit back in, which feels like it's wearing out, but IS symmetrical and might as well have the last few hundred miles wrung out of it!

My bike is NOT a mountain-bike. The tyre is comfortable, not fat, and embraced by perfectly formed titanium tubes, not aluminium 'bingo wings'. I do not need and neither do I want my left crank even further from the frame than the right one needs to be in order to clear the front mech. I remember when most bottom-bracket axles were longer on the right, I still even have some like that in regular use - thank's to Stein's grease injection and sealing kits. There's a good reason for longer on the right: to make room for extra chainrings. I can tolerate the dumbing down to symmetry, but longer on the left does seem a bit daft. Even on a mountain-bike, chainstay clearance is not usually so lacking that one or two mm offset of a symmetrical bottom-bracket would cause a problem. But that's how Shimano make them and it can't be helped.

Back to the OP. If his chainline is genuinely 50mm at present, that's wide for a double on a road bike, for which the standard is 43.5mm. Even MTB doubles are often 47mm. I guess this bike is a road or touring bike. And my advice is keep the chainline as narrow as you can. It makes for smoother running in big and big, which tends to be a useful combination. Unfortunately it looks more likely that Sugino XD cranks will give you an even wider chainline and pedal spread than your Shimano cranks, on the same axle.


I have always wondered if the cylindrical wotsits actually achieve anything from a structural standpoint, given many of them are made of plastic, and whether its secure fit really makes a difference...

You might be pleased to know that in actual fact no conventional Shimano UN bb is longer on the non-drive side, with the 110mm being the sole exception.

I think if the OP gets the Sugino XD compact in the link above his chainline will be c48mm (officially 45mm with 110mm bb, and the 113mm is 3mm longer on the drive side) so narrower than the existing Shimano. I do however agree with you that subject to adequate chainstay clearance and front mech reach range a narrowish chainline makes sense, given the rear chainline is always between 40mm and 45mm irrespective of #speed and rear dropout distance.
Last edited by recordacefromnew on 8 Apr 2014, 11:11am, edited 2 times in total.
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CREPELLO
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Re: Chainset question

Post by CREPELLO »

CJ wrote:The logic may be that one can add spacers on the right to fine-tune chainline without mashing a MTB's obese chainstays with the left crank, except that the UN55 110mm unit I recently bought has a shoulder on it's left-side threaded cyclindrical wotsit, so it cannot go any further into the shell. So if I add a 1.5mm spacer on the right, it'll not be secure on the left. Actually to do that requires the borrowing of an un-shouldered wotsit from an old UN73 bottom-bracket unit, which I have spare, but rather than mess around like that I simply put the Stronglight 110mm unit back in, which feels like it's wearing out, but IS symmetrical and might as well have the last few hundred miles wrung out of it!
Just wanted to point out that Shimano have redone the tooling for the latest UN55. I tried to do this, using a UN?? steel LH cup. It seems that a UN55 has a slightly larger dia body, so probably won't fit a UN73, or any other UN** LH 'cup' (unless UN73 used the same body as the UN55).

In addition, when I tried fitting the UN55 (110mm), the LH cup would bottom out on the cartridge before the shoulder met the BB shell :? . I've measured the shell at 68mm. I used a 1.5mm spacer to allow the LH cup to go all the way. I wonder whether that is a clue to Shimano's thinking on this odd LH axle length stuff we're talking about :?:

I've measured the difference between the chainstays and the rear of the cranks at pedals. The LH is 19mm and the RH is 16mm. My chainline is 43.5mm (130mm OLN). I guess I could a fit a 3mm spacer drive side to balance up left and right and still have a CL of 45mm. My RH heel points inwards a bit so heal clearance is an issue with me, although not on this Dalesman.
Brucey
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Re: Chainset question

Post by Brucey »

remember that those UNxx BB units with plastic LH cups very often have the cup bottom out on the body (and in fact there isn't even a full diameter flange on the cup).

Note also that the two-cup UNxx BB units (eg. UN71/72 IIRC) are also designed to work like that. If not, the centre part would come free.

UNxx units that have an integrated RH cup should only impose radial loads onto the LH cup if the cup bottoms on the frame. However I have often felt that the installation is more secure if the cup bottoms on the centre body not the frame.

I note that in those units where the cup bottoms on the centre body, very tight cups will apply a considerable preload to the bearings. As I have recently noted in another thread, play in a worn unit can mysteriously 'disappear' once the unit is installed, even with a plastic LH cup. Metal cups allow more torque so presumably the effect can be even greater.

With a new unit I think that overtightening the cups could lead to premature bearing failure.

cheers
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