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ISIS Drive vs. Octalink vs. Square Taper(10 posts)

ISIS Drive vs. Octalink vs. Square TaperTrek Racer X
Dec 2, 2002 9:57 AM
Among ISIS, Octalink, and square Taper, which systems are the stiffest, and strongest overall?
From rumors I've heard, ISIS drive is used in DH bikes and MTB, due to their extreme stiffness and efficient power transfer.
Second in line is the Octalink, which I've heard is great, but not as efficient as the ISIS.
And thirdly, the old workhorse of the decades, square taper, it was good for it's time, but not as efficient as ISIS. Although Campy is still using the square taper system.

-My question is: Is there any truth to these statements? Do I have the rankings out of order?

(Primarily the BB/ crank combination would be used for road training and racing)

Any help is appreciated.

ISIS more efficient than Square Taper?? Weld them on!!Spunout
Dec 2, 2002 10:27 AM
I'd think that any of the above in a correct implementation is as good as all else.

Some are easier to remove, but that is not a functionality of the joint. I've never heard anyone wrecking a campag crank because it was improperly installed (ISIS: yes). I've never heard of a campy crank coming loose (ISIS, OCTA: yes).

Just my two bits.
too small to measure, or at least to feel?cory
Dec 2, 2002 12:05 PM
There may be differences in CRANKS that could affect efficiency (if by efficiency you mean power transmission with the least loss), but I doubt the crank-spindle interface makes a meaningful difference. For there to be a loss of power, there would have to be flex or slippage somewhere, and it's just not there. While there might be demonstrable differences in some quality or other if you stressed them until they broke, in normal use they don't approach that point, so it wouldn't matter.
re: ISIS Drive vs. Octalink vs. Square Taperlaffeaux
Dec 2, 2002 1:09 PM
Supposedly the splined systems (Octalink and ISIS) are stiffer and lighter than the tapered BBs. However, having used both for many miles, I can tell any difference whatsoever. I'd imagine that a test of deflection would show ISIS and Octalink to be about equal. ISIS is the standard that allows companies to produce a BB and crank that are compatable. Shimano owns the Octalink patent and for others to be in the game, a similar product needed to exist.

The big advantage of the splined systems (IMHO) is that the BB spidle does not deform everytime cranks are installed (as is the case with tapered systems). If you are someone that removes your cranks often, this extends the life of the BB. Also this ensures that when you reinstall the cranks it sits in the exact position it was in before removal - the front deraileur limit screws do not need to be touched when reinstalling cranks.
Oh Yeah!!grzy
Dec 2, 2002 5:09 PM
Those DH boys are just *known* for their pedaling prowess and raw power!! Why they need a dang ski lift to get their 50 pound tanks up the hill b/c their skinny legs get all wobbly when they push.

The reason why they're using ISIS is so they can use some Gucci crank which happens to be non-Shimano. Since Shimano owns the patent they either have to use the square taper design or go to ISIS. Once you pull a square taper crank enough times you start having problems with the chainline since the tapered hole in the alloy arm wears out. It might have something to do with stiffness, but given that many of these guys haven't finished high school let alone an engineering program you can bet they aren't making decisions based on actual data. The funny thing is that a few years ago when some cranks were actually measured the ones that everyone thought were da'bomb actually turned out not to be very stiff.

In the end efficiency isn't really the right word since, by definition, efficiency is defined as power out over power in. In other words energy loss. I can assure you that all of the power going into a crank/BB connection is being transfered since even with deflection (i.e. a spring) you get the energy back, baring deformation and catastrauphic failure. Now the actual bearings might be a different story since energy is lost due to friction and not recovered. In any event none of this matters one wit when you consider the orders of magntide involved here. Pro level racers prove this point everyday. You can gain or lose more through tire inflation pressure, how much rest you got, and how smart you ride than your type of BB/crank interface.

Campy started to use a splined system and was quickly shut down by Shimano's lawyers for patent infringement. Shimano is licensing it's splined design to certain manufacturers - just not ones it doesn't like. If you really want to see stiff and light then check out the new '03 XTR integrated crank & BB design - pretty bomber stuff. The bore through the BB is so big you can just about pass a dime through it. Should get both the DH and XC boyz all worked up (when was the last time that happened?). What do you want to bet it shows up in the DA lineup in a year or two?
Oh Yeah!! Oh yeah?Trek Racer X
Dec 2, 2002 5:35 PM
I suppose you are correct, that the energy/power loss difference is negligable, in comparison to the fitness of the rider, as well as other variables. But what's with spaming on the Downhillers, and the MTBer "Boyz?" We're all cyclists here, and the least helpful thing to do is to divide cyclsts. There doesn't need to be "us vs. them." (Considering all of the @ss hole car drivers out there.)

Yeah, I agree there is alot of marketing involved, as alot of hype for products is a marketing ploy. (Although, in many aspects it progresses cycling. ie., disc brakes, full suspension, STI shifters, and the invention of the quick release.)

-Anyway, thanks for the insight. I think I'm going with a FSA Ultimax Ti BB ISIS, with a Truvative Elita 53/39 ISIS crankset.

But Why?!grzy
Dec 3, 2002 11:34 AM
If stiffness was your stated objective then a ti BB is counter productive!

BTW - "spamming" is unsolicited email to a wide audience for a product or service that is marginal at best. A marketing ploy is the deliberate mistatement or misrepresentation of the benifits of a product or feature. Everything you mention are actual technical advancements.

Get your terminology straight and stop tossing around buzzwords and rumors. Now think about this: do you drive a car? Have you ever made a mistake while driving? If so you're also an @sshole car driver - just like the rest of us.

I guess my big point would be this - try to engage your brain before hitting the "reply" key.
D-Hiller clarificationrockbender
Dec 2, 2002 6:19 PM
While it may be true that downhiller's may not exert the same pedaling force as Lance - I don't think typical roadies go huck off 10' drops, either.

I don't think the DH crowd is looking for stiff and efficient so much as strong and burly - two similar but not identical design parameters.
Oh Yeah!!JFST
Dec 2, 2002 9:27 PM
Those downhill boys might not do much uphill pedaling but you can bet that the impact from doing 10 and 20 foot drops at extremely high speeds (yes downhill mountain bikes do go pretty damn fast) is easily more than enough to brake a crank and BB spindle into pieces. The advantage of a splined design is that the force is spread evenly around the spindle. Taper cranks eventually weaken and begin to crack around edges. Its not as common on road bikes due to the lack of impact compared to mountain bikes. The wider spindle of spline designs also makes it stronger. Square taper is smaller in diameter and easier to crack. The major issue with splined setups is that they must be properly torqued to specifications or the can loosen up or the splines can start to strip. Installed correctly though they will not be going anywhere. ISIS is currently the strongest *standard* design there is. It was designed mainly by Chris King and Race Face, two companies known to be obsesive about perfection and making things that work right. The 2003 XTR bottom bracket system (or lack of) is nothing new. They basically adapted the system thats been used on BMX bikes for ages to mountain bikes in a very clever and well designed way.
re: ISIS Drive vs. Octalink vs. Square TaperJofa
Dec 2, 2002 5:54 PM
As virtually everybody else has said in their replies, efficiency is not the issue. Durability is. The original square taper design is flawed in that the crank can squirm up the taper. This leads the attentive user to diligently tighten the crank bolts thinking they have come loose. The process repeats until the crank develops fatigue fractures and eventually fails.

The Shimano design appears preferable but I am worried by its lack of taper. There doesn't seem to be enough to preload the interface enough. The ISIS, does at least have a significant enough taper - from what I have seen - and a larger contact area. In theory I'd say this should be the best, but of course time, and marketing, will tell.

Now if only somebody would do something about the crank / pedal axle interface, which is the worst of all.