spleck

I've ordered an Access XCL frame from Supergo so I can put together a bike for my wife from spare parts. I need a bottom bracket though, and I'm not sure what size to go with. The crank is a Shimano M440 22-32-42 with Octalink. They specify 113 mm or 118 mm. The seat tube is 1.25 in (31.8 mm) and if it matters, the wheels are from a hard rock (joy tech hubs with a SRAM 8-speed cassette).

I was inclined to think 113 mm, but then I saw it mentioned that a 1.25 in seat tube may require me to push the chainline further out. What should I go with?

Thanks...

biker7

Generally two spindle lengths are offered sometimes more. With Campy for example it is 102, 111, 115....102 being for Record. Generally the smaller spindle corresponds to a std size seat tube a longer spindle is for the larger tube to maintain chain line as you correctly mentioned. Since you are running a big tube, I am quite sure it is a 118mm spindle you want. Let others like Sydney confirm this before making your order.
HTH,
George

Retro Grouch 

I've been told, and it makes sense to me, that the differing bottom bracket lengths are to adjust the chainline for 130mm vs 135mm rear dropouts.

sydney

Seattube diameter also matters. Generally the longer one with 11/4" diameter or larger.

Retro Grouch 

Yup, that has a logical ring to it too. 1/8" = about 3mm so a 5mm longer spindle would just cover the difference between a 1 1/8" and 1 1/4" seat tube.

I think it might be interesting if Sheldon were to weigh in on this topic.

sydney

Sheldon mentions that the shorter lenth may give the preferred chainline,but the longer one may be necessary with oversize seattubes.Sometimes you have to live with less then perfect chainline.

spleck

Well, on the chance that I have to live with a less than perfect chainline, I'm going to err on the long side. My wife will probably stay on the two smaller chainrings, so its probably a better choice.

Thanks again.

spleck

Well, I went with the 118mm spindle and I think it was a mistake. The chainline is off by about 3 mm. I wouldn't have thought that would be a problem, but I can't shift to the middle chainring while on the inner most cog. The chainline pulls the chain off the chainring. If I adjust the front derailleur to keep it on the chainring, it rubs on the derailleur. I'm using a SRAM PC-69 chain with an 8-speed SRAM cassette and a Shimano M440 crankset. That should be causing issues right? Would the wider 8-speed chain help?

One note: The front derailleur comes with spacers for different seat tube sizes, for 1 1/4 in, the spacer puts more space on the non-drivetrain side. This seems to keep the derailleur closer to the tube so that you don't need a longer spindle...

I'm guessing my best bet at this point is to get a 113 mm spindle.

sydney

Why would you wat to do that anyway. To me it's just bad shifting technique and wrong thinking.Easier to just not do it.

spleck

Because that's how Park Tool says to adjust the derailleur. Shift to middle chainring and inner cog, then adjust indexing until the derailleur doesn't rub.

Not to mention this works just fine on my 3 other bikes. I would think that from the middle chainring, you should be able to safely shift into any of the rear cogs.

I understand the shifting philosophy, but this is just the main 'tell' that something is amiss.

sydney

Read the highlited part. It didn't print the first time...Also,the derailer adjustment drill starts with the chain on the big cog and small ring.There is no 'adjusting' in the middle ring.

spleck

My Park Tool book says low limit (small ring, big cog), high limit (big ring, small cog), then indexing (middle ring, big cog). But regardless of technique, I don't believe being on the largest cog should force the chain to shift to the smallest chainring.

bellweatherman

Let's assume that the guy has perfect chainline using a 113mm spindle bottom bracket, but less than perfect shifting because of his fat seat tube (1 1/4" = 31.8 mm) pushing the front derailleur too far outwards...

Can he keep his 113mm spindle bottom bracket (better chainline) and address his front derailleur shifting issues by buying a new front derailleur better suited to handle his fat seat tube??? Isn't this a better way to address this problem?

Man, smooth friction front derailleur shifting of the past was a great thing, wasn't it?! Admit it. You know the indexed shifting on the front royally sucks because of compatibility issues such as the one this poor chap is experiencing!

sydney

Why don't you tell us which one that might be??? Both the QBP and Sheldon Brown say go with the longer spindle length with seattubes of 1.25" and greater.I've found no reson to argue the point.

bellweatherman

Absolutely. Don't get me wrong. I see what you are saying and logically using the longer spindle in this circumstance provides the best shifting possible even if his chainline is less than perfect. My only point is to contend is that perhaps there is a way to achieve both. 1) Perfect chainline and 2) Perfect shifting.

Perhaps an ardent product designer might make a widget for this (see #2 below)...
1) Perfect Chainline - Just get the bottom bracket with the spindle that will put the chainwheels in the ideal chainline for the rear cogset
2) A widget designer/manufacturer should've already marketed this idea already... Make a little shim or tab thingy that allows a braze-on front derailleur to be pushed out a few millimeters (0-5mm) out from the seat tube, thus enabling far far greater adjustability than a front derailleur itself can provide. Solves the problem of the fat seat tube effect on front derailleurs!

AHA! What do you think of that idea?! You heard it hear first! Next thing you know someone out there is going to read this thread, make this widget I'm talking about, and get rich off of my idea!
$$ $$

Sheldon Brown

Nope, you've got it backwards. The problem is that the fat seat tube already pushes the front derailer too far _out_ to the right.

The limitation is the fact that the parallelogram mechanism bumps into the seat tube.

When discussing bikes with front and rear derailers, there's no such thing as "perfect" chainline. Optimal chainline will depend on the rider's shifting preferences:

Generally, road bike riders like the front chain line closer inboard, because this allows the big ring to be used with more of the rear sprockets.

Mountain bike riders tend to use the inner chainring much more than road riders do, and with more of the rear sprockets, so they are often better off with a farther out front derailer.

Another example is my Hetchins, which has a 50-28 double, with a 12-28 9-speed cassette. I've got it set so that the 50 tooth chainring lines up with the middle of the cassette, and I can use all 9 gears with the 50.

The 28 only works with the biggest 3 or 4 sprockets, but that's OK with me. I keep it on the 50 tooth almost all of the time, and only use the 28 for the toughest hills, or for when I'm all tuckered out. When I need it, I don't mind that the 28 doesn't give me a lot of different ratios to choose from.

See also my article on chainline: https://sheldonbrown.com/chainline

Sheldon "Chainline" Brown

chinitonorte

This bit of philosophy applies to many facets of life in general.

cuda2k

-- what sheldon said.

I had issues with putting a new (8sp) double 105 crank on my vintage schwinn because the spindle on the old BB was too long. I could have adjusted the front derailleur till I was blue in the face (and nearly did) but I wouldn't have gotten it into the 52 ring of the new crank. It was about then that I learned once again I was still a noob at upgrading and working on bicycles.

Al1943

There is also a way to go in between. You could try the shorter spindle and use a BB spacer to move it out. This type of spacer is available in 1, 1.5, and 2mm. You could effectively make the 113 a 115.

Al