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splined BB or square taper?(13 posts)

splined BB or square taper?karlooz
Apr 16, 2002 9:10 PM
i can understand the need for extra strength in mtn biking but is it really needed for road bikes?
re: splined BB or square taper?Rusty Coggs
Apr 17, 2002 5:10 AM
It depends.No right answer for evryone.Campy eems to be doing ok with it.
Needed? Nope.jw25
Apr 17, 2002 5:15 AM
Even on mountain bikes, a properly set up square taper BB/crank interface is plenty strong and reliable, unless you're hucking off 10 foot cliffs, and even then, plenty of people were doing that before splines were popular.
The biggest benefit to splines, IMHO, is the repeatability of crank/BB spacing. When you remove and remount a square-taper crankset, the tapers stretch a tiny bit, for a solid interference fit. Repeat this often enough, and the crankarm (and rings) end up closer to the frame, and eventually, you'll be left with too little taper to keep the cranks in place.
Splined cranks, in contast, should have no deformation of the crankarm, and should remount to the same distance each time, as well as being more repeatable. I say should, because this assumes proper torquing of the mounting bolts.
So, nope, it's not really needed, but I like it. I do wish Shimano could lose a few grams from the splined Ultegra BB, but compared to a UN-72, it's comparable, and the larger diameter spindle should be stiffer under power, though that's small percentages at best.
Incremental difference.`Spoke Wrench
Apr 17, 2002 5:35 AM
Guys with nicknames like "Cannibal" and "Badger" pretty much demoralized everyone else in the bicycling world while using square taper BB's. It would be pretty arrogant of me to say they are aren't adequate for a guy called "Spoke Wrench."
Ahh, you're selling yourself shortNessism
Apr 17, 2002 5:46 AM
What about the effect of repeated remove-install-remove... cycles on the square hole in the crank arms? Don't the crank arms streach out over time?

From an engineering standpoint, the large diameter thin wall spindle seems like a nice improvement. Most industral applications for mating parts like these use splines of some type.

most industrial applications need itSpirito
Apr 17, 2002 6:07 AM
the transfer of power and actual torque from our legs to the crank is on industrial terms very small.

industrial machinery also needs to spin much faster and remain smooth and requires closer toloerances at much higher rpm than any of us actually use (ie much faster than 120 rpm).

if using theory splined makes sense but looking at the data when applied to cycling and the force generated its apparent that its not really needed and over engineered.

did somebody say inbuilt obselescence by a component manufacturer again?
Apr 17, 2002 6:21 AM
I agree with much of what you say.

But consider these advantages to the Shimano design:

- Larger spindle can be made stiffer
- Larger spindle can be made lighter - not sure about actual application
- Splined attachment will not go out of shape with repeated removals

Disadvantages include:

- Obselescence of older parts - not such a big deal considering costs involved (in my opinion)

- others???

fair points but it doesn't apply to me.Spirito
Apr 17, 2002 7:48 AM
bb refurbished every 1 1/2 to 2 years.

ive never held onto a crankset for longer than 8 years.

whats the bid deal?
all up costs are bearings and some grease. if the crank is bolted on properly there is no real wear where they join.

splines are a great idea but i dont think they offer any real world improvement.
Oh yeah they do!!!MrCrud
Apr 17, 2002 8:06 AM
Last season, i broke 2 square axles and deformed a Race Face crank at the square hole where it meets the BB axle ( on my MTB ).
In terms of pure strength, there is a definite advantage. Where you have a lot of strength, you can alwasy reduce the weight to come down to a better balance between over and under-engineering a part. I'm not sure why Campy isnt using this interface, but i am sure they have their very valid reasons. Probably developing their own system...

Speaking of Campy, has anyone seen their new Carbon Record Crankset!!!! The definition of a sexy bike part!


It's all relativegrzy
Apr 17, 2002 9:29 AM
Your points aren't really valid since you don't take into consideration that if you make something light enough even a grasshopper could break it. You don't need "industrial forces" to fail things on a bike - it's all relative. The tollerances and "over engineered" designs are there for a reason - we the end users demand it. We want lighter parts that can handle more force that will last longer and are cheaper. As a mechanical engineer with design and analysis experience I don't think you're qualified to say the splined BB is "over engineered". If the forces and speeds were higher then the designs would change to accomodate this.

It would've been much cheaper for Shimano to keep selling the same time tested design rather than invest the time, effort and tooling in developing a new product. it was also risky, but shrewed from a business perspective.
Needed? Nope.xxl
Apr 17, 2002 12:13 PM
Not to put too fine a point on it, but wouldn't the deformation of the square hole in the relatively soft alloy crank be a more likely cause of "bottoming out" one's crank? (I've never seen the situation you described, but that certainly doesn't mean it couldn't happen.) And, couldn't the deformation of the crank occur even with a splined hole (maybe even more likely)?

I guess I'm also in the "it's not needed" camp, though from Shimano's POV it certainly helps add to compatibility problems.
re: splined BB or square taper?sprockets2
Apr 17, 2002 8:46 AM
I doubt it. The old design served us very well even when the crank arm material was inferior to what we use today.

I like the ISIS design, but the Shimano road spindle seems like a dopey design to me. It may work but it is counter intuitive, at least for me. The actual contact area is only on the outer extremity of the spindle. DUH
re: splined BB or square taper?xxl
Apr 17, 2002 12:21 PM
I forgot to mention this in my earlier post, but would the added machining of the crank mounting hole on a splined system lead to more stress risers? I throw this out because there are some engineering types out there that'd have better insight on this than me.

Frankly, I've only seen the design in photos, but it does seem like overkill at best. I mean, how much is "flex" in the crankarm reduced, due to the mount? Are we talking hundredths, thousandsth of an inch? Angstroms?