Compact double chainset with square taper and 46T chainring?

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recordacefromnew
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Re: Compact double chainset with square taper and 46T chainr

Postby recordacefromnew » 16 Jul 2014, 3:13pm

Brucey wrote:I estimate that you are out by a factor of two.


Care to show me?

Brucey
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Re: Compact double chainset with square taper and 46T chainr

Postby Brucey » 16 Jul 2014, 3:21pm

in degrees;

1/(2 x tan(1)) = 28.6mm/mm rather than 14.3mm/mm

or have I missed something?

cheers
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recordacefromnew
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Re: Compact double chainset with square taper and 46T chainr

Postby recordacefromnew » 16 Jul 2014, 3:27pm

Brucey wrote:in degrees;

1/(2 x tan(1)) = 28.6mm/mm rather than 14.3mm/mm

or have I missed something?

cheers


Flat is 2 degrees, not "1".

Brucey
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Re: Compact double chainset with square taper and 46T chainr

Postby Brucey » 16 Jul 2014, 3:51pm

I see, so you are saying that the full included angle is four degrees not two degrees. If so (and you are probably right, it is along time since I measured any) I agree.

cheers
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student
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Re: Compact double chainset with square taper and 46T chainr

Postby student » 16 Jul 2014, 8:00pm

:D actually Shimano did these.. RSX, aka "3200 Sora" (so, the predecessor of sora)

http://apro.bikemag.hu/browse/orszaguti ... 41376.html

46-36t, 110 bcd, 5arm spider.. niice. bit pricey though (6000HUF for a square tapered chainset without BB is imho not reasonable.. 15.30 bucks, for a little more, sometimes one can find hollowtech2 cranks second hand)
I'm located outside the UK. Never been there, not even considering getting a work there once I have my degree. :)

OnYourRight
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Re: Compact double chainset with square taper and 46T chainr

Postby OnYourRight » 16 Jul 2014, 10:22pm

Recordacefromnew: thanks for your detailed post. Much of that is new to me.

Just now I measured the taper width of the 110 mm Shimano and the 107 mm Stronglight with a vernier calliper accurate to ± 0.05 mm. They are both 12.75 mm at 1.5 mm from the end. According to your figures this means they are both JIS, which matches my suspicions anyway.

As Brucey says, there may be no significant difference in chainline between the Shimano 110 mm and Stronglight 107 mm. It’s just that the Stronglight collides with the chainset before the bolt (or screw to be more accurate) reaches the required torque.

Although the lip on the Stronglight drive-side cup is a little fatter than the Shimano’s, the surfaces that foul first are the following (using earlier photos and showing the wrong side of the bottom bracket):

Image


Image

There isn’t much in it – it only happens as the bolt is tightened – but it’s enough to ruin the day.

By the way, the bearings in the Stronglight are the smoothest of the four bottom brackets and it's about 60 g lighter than the others. But the surface that fouls is not exactly parallel to the fouling surface of the chainset and consequently touches only across a range of angles coinciding with about five hours on a clock face (can you tell I’ve reached the limits of my technical jargon?). Additionally, the holes for the bolts are not concentric (you can just about discern this in the second photo in this post). So I suppose it’s conceivable I have a bad unit. But the clearances on both sides would be too low for comfort even without these problems.

The 110 mm Shimano works fine, but I need another one because I can’t get the broken bolt out. So I haven’t actually ridden the bike with the 110 mm bottom bracket yet.

Does anyone know which Japanese chainset (a Sugino maybe?) the new-style Stronglight Impact is based on so I might look up its recommended bottom bracket length?

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recordacefromnew
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Re: Compact double chainset with square taper and 46T chainr

Postby recordacefromnew » 17 Jul 2014, 1:05am

OnYourRight wrote:
As Brucey says, there may be no significant difference in chainline between the Shimano 110 mm and Stronglight 107 mm. It’s just that the Stronglight collides with the chainset before the bolt (or screw to be more accurate) reaches the required torque.
.....

Does anyone know which Japanese chainset (a Sugino maybe?) the new-style Stronglight Impact is based on so I might look up its recommended bottom bracket length?


Please correct me if I am wrong. It seems you are finding/saying: i) the 107mm Stronglight clashes on the drive side, ii) the chainline from a 113mm is too great at 46.5mm, while iii) the 110mm Shimano bb delivers the same chainline as the 107mm (which I fully expect) although it doesn't clash because the Shimano cup geometry is different?

If so the fundamental problem, is there isn't any other typical JIS size between the dimensions of these lot I am aware of. Furthermore, if a 113mm JIS delivers 46.5mm, a 107mm or 110mm should deliver the c43.5mm chainline you want, so perhaps what Japanese chainset it derives from is moot anyway for bb selection purpose.

Doesn't it therefore follow that:
1) this chainset/JP400 model (am pretty sure there are more than one) was designed/specified/commissioned by someone in Stronglight who didn't ensure it to be clash free with their own bb/chainset, or
2) the chainset is supposed to go with some other ISO spindle, or
3) you are Superman and torqued the crank bolt a teeny wee bit too much :) , or
4) some other unholy scenario I haven't thought of...

It is probably worth mentioning again that as you said up thread your chainset is not the same as the one in the pic of the Stronglight Impact double at Spa, the 5 arms are orientated differently.

In terms of what to suggest, you found the UN26s don't spin smoothly even when new - this is consistent with my experience so no surprise there. The UN5x are better for not much more £. If I were you I would either: a) get a Shimano UN5x 110mm, or b) wrap one single layer of kitchen tin foil over all 4 taper faces evenly on the drive side of the JP400 before installation. I am suggesting this bodge because it looks like you haven't got the luxury of taking the conventional route of introducing a spacer between the drive side cup and bb shell, due to insufficient clearance on the non-drive side, which e.g. a 110mm could have offered.

Indeed if the clearance on the drive sides is too close for comfort a 1mm or 1.5mm spacer is probably what you could/should introduce with a new 110mm UN5x anyway.

Blimey, I hope not everybody who bought or is buying one of these Stronglight chainset/bb combo has to go through your experience...

Brucey
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Re: Compact double chainset with square taper and 46T chainr

Postby Brucey » 17 Jul 2014, 8:03am

I think the machining on the crank is a bit weird; I wonder if they started making a triple and just forgot to machine the bolts for the inner ring and then called it a double instead. In general terms it is a bit odd for much of the crank boss on a double to protrude inwards past the inner surface of the inner chainring.

Putting some numbers to it (distance from centreline) ;

the RH end of the BB unit will sit at ~37mm (on a 68mm shell with a 3mm lip).

With a 43.5mm chainline the inner surface of a chainring 3mm thickness will lie at approximately 38mm ( 43.5mm less half of the ~8mm chainring spacing and half the chainring thickness).

So if you sight across the inner face of the inner chainring, pretty much anything that sticks out inwards is either going to clash with the BB or is meant to nestle inside the end of it.

In the normal run of things, faced with a clash like yours, I'd probably modify one or other of the parts so that it fitted properly. I'd be somewhat disappointed (but not entirely surprised) if both parts came from the same manufacturer and were meant to fit one another.

I've not tried this with a JP400 but often the bearing unit is simply a push-fit into the RH cup or is held in with a little loctite. If it comes out OK you can modify the cup, then reassemble. If the location diameter and shoulder dimension are as per other BB units, you might be able to use a thinner walled (e.g. steel) RH cup from another unit. I keep a stash of random old BB cups so that I have things that might get me out of a jam like this.

Re removing the broken bolt; try tapping it round with a centre punch first, but this might be a job for the LH drill bit. If the axle is hollow all the way through, you can use a long series RH drill from the other side and that might shift it. If the bolt protrudes at all, you might be able to weld onto it.

BTW what torque setting are you using on the crank bolts? If the bolt hole in the BB spindle is skewed, (or the crank doesn't sit square because of a clash) tightening the bolt normally will cause it to see low-cycle fatigue in bending as the bolt is wound in. Barring excess torque, this is quite likely what caused the bolt to break.

cheers
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recordacefromnew
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Re: Compact double chainset with square taper and 46T chainr

Postby recordacefromnew » 17 Jul 2014, 9:14am

Brucey wrote:I think the machining on the crank is a bit weird; I wonder if they started making a triple and just forgot to machine the bolts for the inner ring and then called it a double instead. In general terms it is a bit odd for much of the crank boss on a double to protrude inwards past the inner surface of the inner chainring.

Putting some numbers to it (distance from centreline) ;

the RH end of the BB unit will sit at ~37mm (on a 68mm shell with a 3mm lip).

With a 43.5mm chainline the inner surface of a chainring 3mm thickness will lie at approximately 38mm ( 43.5mm less half of the ~8mm chainring spacing and half the chainring thickness).

So if you sight across the inner face of the inner chainring, pretty much anything that sticks out inwards is either going to clash with the BB or is meant to nestle inside the end of it.


Good point Brucey regarding the clash calc. You are probably also right regarding the triple origin, it seems from the OP's pic below it is ready for drilling for the 74mm bcd receptacles. You are wasted not working for the Scotland Yard... :wink:

Image

OnYourRight
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Re: Compact double chainset with square taper and 46T chainr

Postby OnYourRight » 17 Jul 2014, 11:28am

recordacefromnew wrote:Please correct me if I am wrong. It seems you are finding/saying: i) the 107mm Stronglight clashes on the drive side, ii) the chainline from a 113mm is too great at 46.5mm, while iii) the 110mm Shimano bb delivers the same chainline as the 107mm (which I fully expect) although it doesn't clash because the Shimano cup geometry is different?

Exactly, with the proviso that I didn’t measure the chainline with the Stronglight 107 mm. While the 107 mm Stronglight clashes on the drive side, it is also perilously close on the non-drive side. In fact, I can’t see a gap at all on that side, though it still turns freely so there must be a small fraction of a millimetre of clearance.

recordacefromnew wrote:If I were you I would either: a) get a Shimano UN5x 110mm, or b) wrap one single layer of kitchen tin foil over all 4 taper faces evenly on the drive side of the JP400 before installation.

A 110 mm Shimano BB-UN55 sounds like a good idea, all things considered. I’m just slightly worried it has some new gotcha when I now know the 110 mm BB-UN26 works!

recordacefromnew wrote:Blimey, I hope not everybody who bought or is buying one of these Stronglight chainset/bb combo has to go through your experience...

I suppose some just ride around happily with the 113 mm bottom bracket recommended by most online shops. However, even the standard chainline of 43.5 mm is a little farther out than I would like (I like using the big-big combo to get over the crest of short hills of that difficulty without dropping to the small chainring for ten seconds), so having the chainline even farther out is something I strongly want to avoid.

Brucey wrote:I think the machining on the crank is a bit weird; I wonder if they started making a triple and just forgot to machine the bolts for the inner ring and then called it a double instead. In general terms it is a bit odd for much of the crank boss on a double to protrude inwards past the inner surface of the inner chainring.

Now that you mention it, it is weird. And I notice the old-style Impact Double was different in this regard, having one fewer step on that central protrusion (though still looking like a triple missing the extra bolt holes).

Brucey wrote:In the normal run of things, faced with a clash like yours, I'd probably modify one or other of the parts so that it fitted properly. I'd be somewhat disappointed (but not entirely surprised) if both parts came from the same manufacturer and were meant to fit one another.

I doubt Stronglight’s capacity to manufacture very much these days – they probably buy most things from a catalogue – and I’m starting to wonder if in this case they noticed the new Impact Double clashed with their JP400 bottom bracket and they resolved the problem by the kludge of a longer JP400. That said, I can’t find any reliable info on this. Here they’re still recommending 107 mm, which is probably wrong info carried over from the old-style Impact.

If I had a workshop I might attempt some kind of modification to avoid the clash. As is, I’ll have to go with a Shimano 110 mm.

Brucey wrote:Re removing the broken bolt; try tapping it round with a centre punch first, but this might be a job for the LH drill bit. If the axle is hollow all the way through, you can use a long series RH drill from the other side and that might shift it. If the bolt protrudes at all, you might be able to weld onto it.

BTW what torque setting are you using on the crank bolts? If the bolt hole in the BB spindle is skewed, (or the crank doesn't sit square because of a clash) tightening the bolt normally will cause it to see low-cycle fatigue in bending as the bolt is wound in. Barring excess torque, this is quite likely what caused the bolt to break.

Understood. The bolt broke off inside the spindle so that nothing protrudes. I can’t get it to budge and have very limited tools to try.

I don’t have a torque wrench so I have no accurate idea of how tight I was going. The bolt broke on the Shimano, not the Stronglight; the former has a concentric bolt hole. I think it was probably just excess torque, and I’ll tell you why. As I was tightening the bolt a wobble in the chainring got progressively smaller. Reasoning that it would continue doing so, and using a good Wera “Hex-Plus” L-key that allows very high torque before rounding the bolt, I tightened it up a bit beyond my comfort zone to try to get rid of a tiny wobble that was probably inherent in the system. Soon enough I felt the tell-tale plastic deformation of the bolt.

Another reason I tightened the bolt so much was that the bolts on the previous bottom bracket came off surprisingly easily, even though I remember tightening them up pretty well too. Perhaps the ‘elbowing’ action of the new light-alloy crank on the taper made itself some room.

I’ll know better next time.

Thanks for your input, all. It is both useful and interesting. At this point I know what to do, though there are still a few unsolved mysteries.

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CREPELLO
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Re: Compact double chainset with square taper and 46T chainr

Postby CREPELLO » 17 Jul 2014, 4:15pm

The cranks look similar to these http://www.suginoltd.co.jp/us/products/touring/xcd.html
http://www.suginoltd.co.jp/us/products/ ... ighty.html
Sugino don't seem to offer a double option for the XCD cranks, so a direct comparison isn't possible. Another name for these cranks is Sugino Alpina.

Looking at the photo of the rear of the spider, the extra metal that extends beyond the taper mount seems unnecessary (apart from in a well engineered set up, it might add some marginal protection from water ingress).

I think that a well worded letter to Stronglight highlighting their shortcomings might be useful to them as well as yourself and others. You might be able to get the cost of a BB out of them if nothing else.

OnYourRight
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Re: Compact double chainset with square taper and 46T chainr

Postby OnYourRight » 17 Jul 2014, 6:44pm

CREPELLO wrote:Looking at the photo of the rear of the spider, the extra metal that extends beyond the taper mount seems unnecessary (apart from in a well engineered set up, it might add some marginal protection from water ingress).

That protruding ring also adds strength, resisting the tendancy of the square taper to split open the crank. With my moderate pedalling power that might not be needed, but I’d rather be safe than sorry with this kind of thing.

CREPELLO wrote:I think that a well worded letter to Stronglight highlighting their shortcomings might be useful to them as well as yourself and others. You might be able to get the cost of a BB out of them if nothing else.

I may yet do that, but the last time I asked for information I got no reply at all.

mschole
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Re: Compact double chainset with square taper and 46T chainr

Postby mschole » 8 Oct 2015, 11:37am

Sorry to revive a dead thread but just wondered if you got your BB and crankset to work after all?

I'm experimenting with shorter cranks over the winter on my TT bike which normally uses a Hollowtech BB and chainset, but finding short cranks for any of the newer BB systems is very ££££. So I'm going with the Stronglight Impact Kid model mostly because the SJS version doesn't come with its own crank fixing bolts. I had already purchased a Shimano UN55 BB though in 110mm width based on SJS's suggestion.

Now it seems that I may need a 107mm BB to fit the Stronglight cranks but from this thread it would seem not? As both Spa Cycles and XXCycle is going to cost me a bit in shipping, I'd rather order once and be done with it. So if I can get the cranks to work with the Shimano 110mm BB that would be ideal of course.

Thoughts?

pickerd1
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Re: Compact double chainset with square taper and 46T chainr

Postby pickerd1 » 8 Oct 2015, 12:40pm

andrew_s wrote:
niggle wrote:What causes problems is when you use inner and middle shifter positions for your 2 chainrings.
If using a triple shifter on a double chainset, you should use outermost clicks with the lower limit screw blocking off what would be the granny position.


I'm interested to know what the problem is?
I like the solution though!

Samuel D
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Re: Compact double chainset with square taper and 46T chainr

Postby Samuel D » 8 Oct 2015, 12:42pm

OnYourRight was me before I started posting under my real name (this account – I no longer use that one). Sorry for the confusion.

Sadly I never did resolve this to my satisfaction. It was rideable but not perfect.

Ultimately I bought some SunXCD cranks and transferred the 46T and 34T chainrings from the Stronglight chainset in this thread to those new cranks. My adventure continued here.

Initially I ran these with a 107 mm Stronglight bottom bracket for a very narrow chainline and Q-factor. Since then I have moved to a 110 mm Shimano bottom bracket and a 1.5 mm spacer on the drive-side. This results in a chainline closer to Shimano’s design intention, a still-narrow Q-factor, and essentially perfect symmetry of tread.

My best guess for the reason for my troubles is that the Stronglight chainset in this thread was in some way non-standard.

Good luck!