Can't wrap my head around BB spindle lengths. And should I even care?
 

I've been trying to understand the issue with spindle lengths and each and every website that I read leaves me more and more perplexed. I know that is not the case but it feels as if there was some jiggery pockery behind all this. Mind if I ask few questions?

1. Why do I even care about spindle lengths? While I understand that the chain should be parallel to the plane projected by the wheels but given that one would shift the gears and the chain therefore would alter its position, why do I even care about it?
2. When calculating the optimal spindle length, what is the assumed chain position on the rear cogs? Should it be positioned in the middle gear? Or on the one that one uses the most?
3. Manufacturers would provide the spindle length for the crankset. BUT the position of the casette -- and therefore of the chain itself -- also depends on the width of the rear dropouts. On the same bike, with the same crankset, the chain position should be altered depending on whether the rear hub is 130 or 135 mm wide. Why this factor is not taken into account in the manufacturers' specification?
4. Would all spindle lengths fit all the bikes? In my frame, the spindle had 122 mm. The BB is broken now so it needs to be replaced. The crankset is Suntour Radius and I can't find any reliable information regarding the spindle length. Some sources suggest to use a 109mm. With such a short spindle, wouldn't my crankset hit the frame?
5. How do I even calculate the spindle length? What do I need to take into account?

Apologies for posting so many questions but that is like a completely new territory, a terra incognita I've never yet visited.

1- Care because the overall system performance is becoming more and more dependent on best chain lines. If you're running older systems that have no lift pins, have a wide ring to ring center dimension, have long chain stays than the chainline is of less importance but still will come into if you push the limits.

2-Chain line amount (optimal spindle length) isn't measured with the chain anywhere. Chain line is a chainring and a cog set center to frame center dimension. Now one can do a visual check that tells a lot by placing the chain on the most centeral cog and ring and eyeball how the chain runs between the ft and rr.

3- Because since the advent of the MtB there has been a difference between road and MtB intended specs/hub widths. Also some cranksets have a spindle length best for traditional seat tube diameters and OS ones (often between steel and Al frames)

4- Why not determine the current crankset's chain line and how that worked for you before trying to "paint by numbers"? If the chainline was good just duplicate that spindle length. If at all possible it's better to use real life info before any published guidelines.

5- See the above. I have installed what i thought would be a good spindle length just to find out a slightly longer or shorter one would be best more than a few times. Andy

In my limited experience, mainly working with donated bikes at non-profits, an incorrect spindle length is often manifested by the front derailleur not being able to reach the needed limits, up or down. On closer inspection, there's often chain rub against a larger chainring, or autoshifting off a larger chainring when cross-chained. This usually happens when someone slaps on a new crankset without checking the spindle length. We keep a (very heavy) bin of salvaged spindles and it's usually trail-and-error to get the right one. We also keep a pegboard full of salvaged cranks and sometimes we get lucky with a different crank.

It probably also depends on what type spindle and crank you have. Square taper cup and cone you have to pay lots of attention and there are offsets thrown in too sometimes. Cartridge BB's with square taper you have to pay some attention more closely than ISIS, Octalink or other. With a two piece crank, more common on road bikes, there is even less need to worry as long as you get the compatible BB for both your crankset and BB shell.

With two piece cranks, as long as you keep everything within the proper group and you aren't building a franken bike or such then spindle length and chain line is something the entire group of components take into account by design and aren't something that needs to be in the forefront of the purchasers mind. If you get mixing new and old components it might be something to be aware of. But in my conversions of square taper cup and cone to modern 2 piece road cranks, the only need was to know the BB shell width, diameter and threading. In all cases these were BSA threaded shells on the bike's that I converted.

Problem is the bike came with no f/r der. It is an old road frame, with rear dropouts of 126mm width. I've manage to found a rear hub of the same width and a 7sp cassette. Before I move any further, I want to ensure I am on the right path.

Nico BB are relatively cheap, I bought few of them, with different lengths and will try them out. It seems that's the most viable approach.

What should I be looking at exactly -- is it enough to eyeball if the "wheel plane" is more or less parallel to the "chain plane"?

Forget the ‘planing’ stuff; the wheel and chain will always be parallel-ish to each other regardless of hub width or spindle length. In an ideal world, the measurement to watch is the distnance between the center of the downtube and the outer chain ring. Depending on whether you are running a double or triple crank, there are are standards for this- Sheldon Brown is your friend here.

In my universe, where friction front downtube shifters reign, I simply strive to get the inner-most ring fairly close to the chainstay- within a couple mm. Sometimes this is the result of experimentation using one or more of the handful of square taper BB’s on hand; sometimes it is a lucky coincidence. If using STI indexed front shifters, things need to be more by the book.

It’s not clear whether you are using the same crankset that came on the bike and are just replacing the spondle that was destroyed during removal. If you are, and you know the previous BB was a 122, then just buy another one. The good news is that 7 speed setups are remarkably tolerant of this like this, so it’s a good setup for a first timer and will likely work fine no matter what you do.

That's what happens with too long a spindle. If the spindle is too short, the chainring will scrape on the chainstay, and/or the crank arm will drag on the bottom bracket cup.

[QUOTE)
In my universe, where friction front downtube shifters reign, I simply strive to get the inner-most ring fairly close to the chainstay- within a couple mm. Sometimes this is the result of experimentation using one or more of the handful of square taper BB’s on hand; sometimes it is a lucky coincidence. If using STI indexed front shifters, things need to be more by the book..[/QUOTE]

This! Except I run old pointy Ergos that have a not really indexed ft shift (thankfully so). Andy

If this crankset had worked well on your frame with a BB having a 122 mm spindle, why not just buy another BB with the same spindle length?

spindle lengths are not something you can calculate easily

each crankset has it's own requirement and these can vary wildly... is it for a double or a triple, is is for a road or MTB BB shell, is it an asymmetrical spindle?

best best is to look up what was on your bike and crank originally and use that, and if changing out the crank, use what the crank's spec are

Since there are no standards, you almost have to guess. I’m not sure if Sugino or SR made cranks for Suntour.

FWIW, eBay has a Suntour Radius crank and bottom bracket listed. The bottom bracket listed is a cup/cone with a 118mm length. It doesn’t look asymeyrical and I have no idea if it is the correct one.

John

https://www.sheldonbrown.com/chainline.html

Use this to get the right chainline.

On my bike with 130mm rear spacing and a TA Specialties Carmina I use 107mm bottom brackets to get a 43mm chainline

Velobase indicates the Radius was made for SunTour by SR. I'd guess that would means the spindle uses JIS taper.

While Velobase lists some other info about that crankset, unfortunately two pieces of info they don't list are the BCD and required spindle length.

Others have nailed it - it's all about the chainline. Germany_chris posted a link to the Sheldon Brown article. You need to know what the chainline should be for your bike. It's potentially one of the most important things to get right on a bicycle. If the chainline is wrong, you're setting yourself up for shifting problems, noisy drivetrain, compatibility problems, and other related issues. Unfortunately it's not just the BB that determines that - it's the combination of BB and crankset. Change the crank and you often need to change the spindle length to get your correct chainline back.

There are two different SunTour company versions and different tapered square standards they used. The current (and for a couple decades) ST is owned by SR (if I have this right) and is but a branding product. SR's factories make the ST stuff to current JIS taper specs. Ther ST of my youth (1970s) was an independent company and in the 1970s used pretty much the Campy taper spec. (The Mighty Comp crankset as example).

While both the JIS and the Campy tapers are of the same degree of taper the Campy is slightly smaller and has a slightly different length of the flats. They can be interchanged but how far onto the taper the crank arm will sit is different and sometimes the spindle will "bottom out" at the end of the arm taper or sometimes the arm won't have enough spindle in it to best support the arm.

So, care and experience can be a help in judging what BB fits which ST crankset. How far up the spindle's taper the arm fits directly effects the chain line (and inner ring/chainstay clearances). Another aspect of this is where within the RH crank, arm with respect to the chain rings, is that tapered hole. during the 1980s the design trend was to locate the tapered hole further inboard that in the past, resulting in a shorter spindle to achieve the same chainline. I know of no spec chart or published data that speaks directly to this. (Shimano has families of this spec with their "Low profile" and "Super Low Profile" arm shapes). Instead, and at best, the companies would list spindle lengths for a chainline. This spindle length could be different for a frame made of traditional steel tube diameters or for an Al frame with its larger diameter tubes (remember that the ft der needs to sit and work between the rings and frame, too little room here and the ft der might not swing in enough before contacting the seat tube). These are some of the reasons why choosing a spindle length that works well is less a paint by the numbers and sometimes a best guess and see if it works effort.

During the 1980s and early 1990s ST was the contract factory for the Specialized cranks. Andy

The solution: I bought a new crankset for pennies of which I actually know the spindle length so here we go!

Good decision!

John

I'm fairly knowledgeable about SunTour's corporate history. I know that pre-1990 and post-1990 SunTour were different entities.

However, if I'm reading Berto's "Sunset for SunTour" correctly even during it's heyday SunTour never made their own cranksets in-house; they obtained them from JEX partners. JEX included Sugino; I believe explains why many of SunTour's better groupset cranksets used Campy/ISO taper. I'm almost certain that the Mighty Comp was a Sugino product. (Per Berto, in the 1980s SunTour also obtained some of their cranksets from Dia Compe, another JEX partner.)

SunTour was bought out by Mori Industries in mid-1990 (Mori had acquired SR in 1989). After they were bought out by Mori, it would be only logical for SunTour to use "in-house" (e.g., SR) cranksets. I'm pretty sure by 1990, SR was producing JIS cranksets virtually exclusively.

The crankset we were originally discussing was the SunTour Radius. Per Velobase, the SunTour Radius groupset was sold circa 1990-1992. That means that the Radius crankset was very likely an SR product. I've also seen references (possibly erroneous) to the crankset as being branded SR as well, so it may not have been exclusively sold under the SunTour brand.

Per my usual I combined Sugino and SunTour and confused a bit. Your are right in the time line and the sourcing. But I think you agree with my point about spindle fit and how it can be different on ST cranksets over the years. Thanks for the correction. Andy

PS- Do you have any info on the Shimano/Takagi connection. Mu understanding was that Shimano sourced their 1970ish cranks from them and bought Takagi out to fold it into the growing Shimano empire.

Fully agree on the spindle fit issue. ISO/JIS mismatch can in theory cause significant issues, especially if one tries to "mix and match" and doesn't take the differences into account.

My understanding is that most Japanese/other Asian crank manufacturers were pretty much exclusively JIS - except for Sugino, who produced a fair number of ISO/Campag-taper cranks. But I could be wrong about that.

What I've read leads me to a similar understanding as yours re: Shimano and Takagi - e.g., that Shimano at one point used Takagi as a source for cranks, then later bought the company to bring crank production in-house. I've seen various dates for that, ranging from 1980 to the "mid-1980s". Beyond that, I don't know much at all. Perhaps @T-Mar might be able to shed some light on that subject, if he has the time.

Does that mean you bought a crankset that recommended a certain spindle length? Those recommendations are sometimes accurate, sometimes not. You still need to measure your chainline once you have it installed.

Hmm, guess why I am here. Yes you are right, bought a frame without a spindle, sigh (with Swiss threads to add a little spicy challenge!).

I have taken my best guess and bought a spindle. I based my guess from this web site below.


Spindle Length for vintage Peugeot Mercier Motobecane


This made me think. Does this site have a spindle data base? Perhaps this is a good thread to build upon the velo collective idea. It at least gives you a starting point.

Not sure this site will provide the info you need but take a look. Sheldon Brown's Bottom Bracket Size Database

Thank you. Yes Sheldon’s website is a Legend over here as well. Why is it that the ones I am looking for are always missing! Lol. I found that velo collective quite helpful. I have a frame and bearing caps but wanted a spindle to try and get measurements from and it gave me a size to stab for.

For instance, 118mm spindle seems to be for a lot of triple cranks. On the velo page he has listed 118mm for a 1975 Team Champion with double cranks. I have just bought a 1977 C4 (a similar frame for Europe). Are they the same? Listen this is the French we are speaking about (I love them for their sense of engineering adventure, just like the French language, you have to learn the verbs lol), so I don’t know! It gave me a start so I have found a cheap 118mm spindle on line to try. Oh yes, but 56mm as the normal 52mm will not close up enough, use Italian spec (info again curtesy of Sheldon)…..

You should care about spindle length because poor chainline will cause inferior drive efficiency and faster component wear. Chainline is observed with the chain in the middle of the cassette, not in the most commonly used gear. 130 vs 135mm dropout spacing does indeed affect the chainline.

This is one of the most annoying and difficult to figure out areas of bike building. If you have an existing crank you should use the old part to help you choose a new part. If you are building up a new frame, you'll have to just do your best on the calculation.