Compact double chainset with square taper and 46T chainring?

[OnYourRight]

Well, I eventually got my new chainset.

In case anyone else stumbles on this thread in the future with similar questions to my own, here’s some more info about the Stronglight Impact compact double chainset and its matching JP400 bottom bracket (aluminium-cup model).

Bottom bracket, labelled JP400-107.5 / BSC 1.37" x 24T / 68 x 107.5. Box says “Made in France”:




Chainset packaging, no “Made in France” slogan here! In fact, no country of origin labels at all:




The photo on the retailer’s website suggested I would get a 4-visible bolt model, but in fact I received the newer 5-bolt pattern model. I don’t know if that’s good or bad:




Continuing the confusion, although Stronglight’s website says both the old and new models are hot-forged, the one I got is actually marked cold-forged:




The cranks are labelled 1105 (model number?) and 172.5 (crank length; on a whim I opted for 172.5 mm instead of 170 mm):




Reverse side:




46T and 34T chainrings, as ordered. The rings are finished to a notably higher standard than the cranks, not that I can afford to be fussy at this price:



Since I have a calibrated digital balance for other purposes, here are some precise weights:

Bottom bracket: 255.0 g – lighter than I expected
Left crank (172.5 mm): 212.2 g
Right crank (172.5 mm) with 46T and 34T chainrings: 421.4 g
Bolts: 27.2 g

Stronglight claims 665 g for the chainset, while mine weighs 633.6 g without bolts or 660.8 g with bolts.

Now to install it!

[531colin]

I think they have sent you the BB for the old pattern Impact, and this new pattern Impact double wants 113mm.

[OnYourRight]

I think they have sent you the BB for the old pattern Impact, and this new pattern Impact double wants 113mm.

That would not surprise me, though I did my research as best as I could and came to the conclusion that even the 5-bolt pattern model took a 107 mm spindle.

Then again, my chainset is cold-forged, while everything I’ve read online says the Stronglight Impact, old or new, is hot-forged.

Ordering online is a lottery.

[OnYourRight]

I think they have sent you the BB for the old pattern Impact, and this new pattern Impact double wants 113mm.

You’re right, 531colin; or at least the 107 mm bottom bracket is too short. In fact it’s so short that the right crank actually made contact with the bottom bracket cup when I tightened up the crank bolt.

I wish Stronglight, ProBikeShop (where I ordered the chainset, though their photo shows the old model which would have worked fine – but that’s not what I got!), and the dozens of other websites with incorrect specifications would get basics like this right. Even Spa Cycles were saying 107 mm when I made the order, though they’ve since fixed that.

I installed the chainset anyway using my old bottom bracket, which was about 116 mm (didn’t measure accurately). My new Shimano FD-2400 front derailleur and ST-2300 double shifter (found a new left shifter for £15) actually manage to work despite the ~116 mm spindle, but badly. To get the chain to shift onto the big ring I have to tighten the cable so much that cable tension rather than the limit screw sets the derailleur position for the small chainring. It’s a bodge.

I’ll have to buy another bottom bracket, since I took a three-week holiday in the middle of this and now I’m outside the returns window. Before I do so, may I ask how you know the required spindle length is 113 mm? It sounds plausible given the derailleur behaviour with a ~116 mm spindle, but I wouldn’t mind being sure!

This double conversion has turned into a bit of a fiasco. I bit off more than I could chew. But I have no choice but to keep chewing now.

On a positive note, the new Stronglight chainrings are far quieter than the FSA Tempo ones. The bike is now eerily silent. And the 46T outer chainring is just right for me, as I had hoped.

[geomannie]

Why go through all the hassle to convert to a double, could you not just fit a smaller touring triple?
http://www.spacycles.co.uk/products.php ... 0s109p2000

+1 They may be cheap but I have been running one of these on my tourer for the last 3 years and it absolutely fine.

[willcee]

Reading this , i have a chum who bought the same compact c'set as he has another machine so equipped and is chuffed with the set up.. no issues at all , so he orders what stronglight say fits bracket wise.. ISO or old campag taper.... not JIS or jap [shimano ] std... 2 + weeks later he's still waiting on the harrogate shop to fill his order..
if it was me and you're certain the bracket and chainset are taper compatible i would stick a block spacer of 2 mm under the BB driveside cup and tighten it and see how that works, from the fact that its rubbing on the cup , i think you have jis and iso incompatabilty.. interested to know how you get on.. will

[OnYourRight]

I hope no-one minds if I bump this thread in the hope of yet more help. Sorry!

After the above chainset didn’t work with the Stronglight 107 mm bottom bracket I was sold (right crank contacted bottom-bracket cup when crank bolt was tightened) I bought a very cheap Shimano BB-UN26 bottom bracket with a 113 mm spindle.

Unfortunately it seems to be too long, at least on the right-hand side. I’ve taken photos from all angles to show the problem.



















Measuring very roughly, the distances from bike centreline to inner and outer rings are 44 mm and 51 mm. Too far.

I’ve been riding it like this for months now (shifting actually works pretty well, though the limit screws are at their extremes). But I’m now ready to tackle this problem again, even though I can’t tell you how sick I am of Stronglight’s lack of proper documentation.

It looks like the right crank could come closer to the frame, perhaps actually slotting into the bottom bracket cup (judging from its shape). Is that the way Stronglight Impact chainsets normally sit?

But it doesn’t look like the left crank can go much closer without hitting something (compare to rule in first photo). It doesn’t seem designed to slot into the cup.

So it almost seems like I need a bottom bracket spindle that’s shorter on the right but not the left!

Therefore: HAAALP!

[OnYourRight]

I measured more accurately the chainring distances from the bike’s centreline: they’re 43 mm and 49.5 mm to the nearest half millimetre. That puts the chainline about 2.75 mm outside the nominal road double chainline (43.5 mm).

These threads have some useful information on bottom-bracket weirdness that may apply in my case:

viewtopic.php?f=5&t=78892
viewtopic.php?f=5&t=79452
viewtopic.php?f=5&t=85190

Notably, they suggest some cartridge-style bottom brackets are indeed asymmetric.

Since I’ve tried 107 mm (right crank hits bottom bracket cup/adaptor) and 113 mm (right crank too far out but left roughly correct), I think it’s possible the new-style Stronglight Impact Compact demands a 110 mm bottom bracket, and furthermore that a 110 mm bottom bracket is not much shorter on the left but notably shorter on the right than a 113 mm bottom bracket.

It’s odd that all the online shops seem to recommend 107 mm bottom brackets (likely out-of-date information for the old-style Impact) or 113 mm (including the normally reliable Spa Cycles) for the Stronglight Impact Compact. Unless I’m doing something terribly wrong (very possible!) I can only assume they’re all recommending the wrong bottom bracket.

In the absence of any reliable information whatsoever, I think there’s nothing for me to do now but to buy a 110 mm bottom bracket and try it.

[OnYourRight]

For the sake of completeness …

I did buy a 110 mm bottom bracket (another Shimano BB-UN26). When tightening up the cranks without a torque wrench I sheared a bolt rendering the new bottom bracket useless, but that’s another story and one you probably don’t want to hear.

The good news is that the 110 mm spindle is the correct length! And compared to the 113 bottom bracket, the difference is almost entirely on the drive side.

I amassed a collection of bottom brackets, so below are some photos and info for other poor souls trapped in the Stronglight square-taper mire. (I wish I’d come across something like this while trawling Google.)

Drive side up:

(Huge version.)



Drive side down:

(Huge version.)

From left to right, these are:

• Stronglight JP400 (aluminium-cup model), sold as 107 mm and labelled 107.5
• Shimano BB-UN26 110 mm
• Shimano BB-UN26 113 mm
• RPM something-or-other (original Dawes Clubman unit) 116 mm

Measured spindle lengths to nearest 0.05 mm:

• Stronglight 107 mm: 107.35 mm
• Shimano 110 mm: 111.60 mm
• Shimano 113 mm: 114.20 mm
• RPM 116 mm: 116.15 mm

The photos tell the tale regarding which side the length differences lie, either drive side or non-drive side (note the cups/adaptors are jammed on as far as they go in these photos). And I thought these things were symmetrical!

To sum up: the new-style Stronglight Impact Compact Double with five visible bolts takes a 110 mm bottom bracket, not that you’d ever guess that from the Stronglight website, online bike shops, or even web forums. Apparently everyone is running these with the wrong bottom bracket or sworn to secrecy.

[Brucey]

it seems a bit odd that the crank fouls the RH cup on the 107; the RH axle protrusion looks similar to the 110 and the cup is only a little thicker looking. Is the taper the same do you think?

cheers

[willcee]

YES I agree, Brucey, see my earlier post of last year.. i seem to remember having read something about a changeover to jis taper from the iso.. will

[OnYourRight]

it seems a bit odd that the crank fouls the RH cup on the 107; the RH axle protrusion looks similar to the 110 and the cup is only a little thicker looking. Is the taper the same do you think?

It does seem odd, but foul it definitely does with the Stronglight 107 mm. I can’t really see much difference in the tapers with my eye.

Given your observation, I suppose it’s possible the Stronglight 113 mm recommended by Spa Cycles and other shops is significantly different in length, symmetry, or taper to the Shimano 113 mm – and does actually fit the Stronglight Impact Compact Double. Someone else will have to test that.

By the way, a few months ago I talked to a local bike shop about these issues. The mechanic there seemed to think it was almost pointless going by the numbers with square-taper bottom brackets. His technique was to have a variety of spindle lengths on hand and just trial-and-error his way to a good fit. I suppose this is feasible for a bike shop, but it gets expensive for individuals ordering online.

YES I agree, Brucey, see my earlier post of last year.. i seem to remember having read something about a changeover to jis taper from the iso..

Surely the Stronglight and the Shimano and any other modern bottom bracket would be JIS taper? My understanding is that the Stronglight Impact is a rebranded Japanese chainset, which would make JIS even more likely.

[Brucey]

well as long as there have been ST BBs they have varied somewhat; they have always varied between manufacturers (slightly) and sometimes even different models from the same manufacturer have varied a little.

The tolerances are pretty tight; in round numbers 0.001" variation in taper width at one end will alter the effective length by about 1mm.

Just taking the cranks on and off different spindles a few times can cause the chainline to vary by half a mm IME.

cheers

[recordacefromnew]

It is possible to determine whether a bb is ISO or JIS with a good vernier caliper accurate to within 0.1mm, assuming the manufacturing tolerance is good.

Since both Standards specify 2 degree tapers, the obvious way is to measure the end flats. JIS specifies a dimension of 12.65mm at the end flat, while ISO specifies 12.6mm at 1.5mm from the end.

Since both have 2 degree tapers, a little trigonometry shows that for every 1mm difference in end flat dimension the insertion depth would change by 14.3mm.

Consequently comparing like with like an ISO taper should have an end flat dimension of 12.6 - 1.5/14.3 or 12.5mm. Similarly a JIS should be 12.75mm at 1.5mm from the end.

Various figures have been floating around on the internet regarding the difference for insertion when using the "wrong" taper, but I have never seen a derivation based on Standard specs. From the figures above, assuming components have been made precisely and to spec, the difference is (12.65mm - 12.5mm) * 14.3, i.e. 2.2mm, which means e.g. Sheldon's figure of 4.5mm is far too much.

For those interested, the current ISO spec dated from 1991 (in a 2013 proposal to move towards JIS... ) and many actual JIS measurements (at 1.5mm from the end flat) can be found at http://www.thun.de/fileadmin/user_upload/documents/Glossar/Handout_DIN2.pdf

Back to the OP. That 107mm can't be JIS, or else it would have delivered the same chainline as the 110mm UN26.

[Brucey]

well the chainine might have been right with the 107mm BB but if there was a
clash with the thicker RH cup....?

Incidentally are you sure you have done your sums right? I estimate that you are out by a factor of two.

cheers