Tapered spindle vs hollow tech

[Justin]

Hi guys

 

 

 

Why is there the big hoohaa about hollowtech?

 

 

 

What was wrong with the old tapered spindle? It was easy to maintain, simple to assemble and very durable.

 

 

 

Any thoughts?

[jmaccelari]

I'm not an expert on this one, but I believe that Hollowtech

is more rigid per gram and also overall lighter...

 

[Justin]

So, what do you need to get to convert to hollowtech... The crank and cups? What else?

[jmaccelari]

I think that's a "depends on what you have question". Your frame would

need to be able to accept a Hollowtech compatible external BB.

 

I certainly can't answer this one authoritatively.

 

Maybe Johan B can help?

 

[Justin]

When buying the crank, say on CRC, do you get the BB as well?

[jmaccelari]

 

Typically no - they are usually sold separate...

 

Should check first!

 

I see CRC do include the BB bearings with some cranks...

jmaccelari2009-12-30 03:29:27

[Christie]

As far as I know, Shimano hollowtech refers to the crank. The crank is forged in 2 pieces and welded together, forming a hollow on the inside.

 

With the hollowtech 2 crankset, the bearings of the bottom bracket was moved out of the BB, and housed external to the frame in cups. The theoretical advantages of external bearings are:

 

1. Larger diameter BB shaft can be acommodated. the shaft can be made lighter(hollow instead of solid) or stiffer (larger diameter bends less easily) because of this. Some testing done by fairviewbikes.com have showed that shaft diameter has a big influence on crankset stiffness.

 

2. The wider spacing of the BB bearings (vs narrower spacing of bearings inside old-style BB) gives more bending stiffness - like a person standing with feet together is easier to push over from the side than a person standing with feet further apart)

 

Disadvantages are:

1. Wider Q-factor, meaning in the end that your pedals are further appart - some riders don't like this.

2.  Perhaps more difficult to seal

[Justin]

Cool, thanks. Bang for buck it seems that I will stick with tapered spindle. About half the price of upgrading to hollowtech.

[Johan Bornman]

Shimano Hollowtech is a confusing trademark. At first Shimano used it to brand the hollow cranks that Chrstie talks about.

Nowadays I see they use the same nomenclature to brand what is generically known as two-piece cranksets. The "hollow" here referring to the hollow axle, not hollow crank.

 

For the engineering benefits of a hollow crank and axle, see Christie's post.

 

The problem with square taper axles is weight. To get it strong, it has to be solid and thus heavy. It can be made lighter and stronger by using a larger diameter tube. Unfortunately, BB shells are standard and there wasn't enough space to put a fat hollow axle and substantial bearings inside. Nevertheless, they went ahead and we had the Octalink and ISIS disaster. Octalink was a huge flop (splines too sort and lash managed to loosen the crank bolts for certain riders). Octalink II saw longer splines but the tiny bearing squashed between the BB shell and fat axle remained, causing bearings to fail prematurely.

 

The only way out of that dillemma was to either make the BB shell bigger (only Cannondale had the balls to do this with BB 30, but much later than when the problem presented) or move the bearings outboard. It was easier to market compatible components than try and redesign the frame and this brought us the external BB adapters as we see on today's bikes. Unfortunately the bearings are still too small for the job and the only real solution is a larger BB shell. These will prevail simply because it is a good idea.

 

As Justin said, the square taper is easy to maintain, very durable and simple to work on. Unfortunately weight is king in this industry and high-end bikes cannot afford the extra 100 grams of a square taper axle.

 

My hopes are on BB 30 and 40. These are open standards and founded on proven engineering principles, unlike Octalink and ISIS.

 

 

[GoLefty!!]

Only thing I would correct about Christies post is the bit about Q-factor.

 

External bearings do not limit q-factor at all. What limits Q-factor is crank design i.e. how strong yet thin the manufacturer can make the crank arms, and frame design, i.e. how much heel clearance is practically possible within the confines of <41cm long chain stays and 130mm wide hub axle spacing.

 

the BB bearing being further apart only impacts the crank design very minimally wrt Q-factor therefore there is little reason to not adopt an external BB crank based on this factor.

 

[techguy]

A note about JB's post, Hollowtech from Shimano refers to hollow cranks, mostly found on the Octalink BB systems as they were introduced at the same time, 1996/7 there abouts. Hollowtech II is the new system with the integrated axle (hollow) and the cranks too are hollow...

[Johan Bornman]

A note about JB's post' date=' Hollowtech from Shimano refers to hollow cranks, mostly found on the Octalink BB systems as they were introduced at the same time, 1996/7 there abouts. Hollowtech II is the new system with the integrated axle (hollow) and the cranks too are hollow...

[/quote']

Thanks, that clears that up. I just hope there aren't any two-piece cranksets in the Shimano range with solid cranks and hollow axles. That would really confuse me.

[GoLefty!!]

not any more, even Deore now has a Hollow crank arm.

[Guest Big H]

We have Hollowtech (1) cranks on our MTB Tandem. I shopped around to buy a new MTB crankset for the tandem. It was way to expensive and rather stocked up on a supply of Octalink BB's. Since we bought the bike in 2005 I have replaced two in total.

 

I just do the old wiggle test on the crank arms after each ride.