Fairwheel Crank Test

[ITTY]

Nice review/comparison. Although as an engineer, I found the strain energy analysis a lot more interesting. Theoretically, almost all of the energy stored in the cranks will be returned to the drivetrain. The only time I think stiffness is actually a real benefit is for very hard efforts and sprinting, which happens a lot in road racing. However, I don't think stiffness is really a big deal for something like a time trial bike.

Also, IIRC, there is a pretty simple equation for strain energy due to torsion. In order to get the total strain energy, you can just add up U_bending+U_torsion. I suspect quite a bit of deflection from most cranks is due to torsion (due to tall+thin cross sections), so focusing on bending probably wouldn't be a very accurate model.

[djconnel]

Lightning has deflection of around 8.5 while Praxis is 6.9 but the old Campy crank which was used by the best riders in the world for over a decade is 10.4.

I conclude the stiffness difference between the Lightning and the Praxis for a light rider is negligible. Riders vary by a lot more than the ratio 8.5/6.9 in applied torque, so for a light rider a Lightning is significantly stiffer than the Praxis would be for a heavy, powerful rider.

On the other hand, the weight advantage (if you care, and if not, why are you here?) is substantial.

Lightning's pricier than it used to be, but I love my old Lightning crank once I realized I needed to lube the spider interface to break the creaking problem. Additionally, I now know 2 top-end tandems which use Lightnings. They really have a nice, versatile system.

[eliflap-scalpel]

why not Hollowgram tested ?

[dereksmalls]

Because I'm assuming the Hollowgram may be in in the BB30 test to come later?

[bm0p700f]

Good to know my old record 10 speed chainset are not really slowing me down. I really want a THM chainset though!

I wonder how the Campagnolo over torque chainset compares?

[solarider]

Over Torque presumably fits in the 'non standard' test to come.

What would also be interesting is to include flex at the chainrings. This is where flex is going to be most noticeable for most people in the form of front mech rub.

The test only looks at the crank arms themselves. As a Campagnolo user, I only mention this because I would like to understand whether the new 4 arm chainset is stiffer when all aspects are considered. It appears to be no better based purely on the crank arms, but the new rings to appear at least to be stiffer.

Before I rush out and buy one, it would be good to know. Otherwise the only benefit is the rarely used ability to switch to different sized chainrings!

[lechat]

Curios as to how the S-works version of the Lightning crank would have fared. A little heavier with its carbon spider, but probably stiffer. The alloy spider the tested crank uses only weighs 36gms and is fairly thin.

[jooo]

Itsacarr, the S-Works crank should be very similar to the Lightning crank...IIRC, Specialized licenses the design from Lightning. That said, any differences would be really interesting, especially if they implied a different layup. The Hirth joints in both cranks should be similarly stiff, so I expect that wouldn't be a factor in any stiffness delta between the Lightning and S-Works cranks.

Cheers,

Jason

Curios as to how the S-works version of the Lightning crank would have fared. A little heavier with its carbon spider, but probably stiffer. The alloy spider the tested crank uses only weighs 36gms and is fairly thin.

I really don't buy this 'almost the same' line much at all. Have a look at the size and shape of the arms. Especially on newer versions of the S-Works crank, they are quite different. They are also manufactured by completely different companies.

I'm sure it doesn't make much difference to stiffness provided they're manufactured and installed correctly but the Hirth joint is also quite different on newer road cranks and all of the MTB cranks. Early versions of the S-Works road cranks used large teeth like Lightning but the new road (and all MTB) versions use a much finer tooth pattern, similar to Campagnolo UT.

The finish on the S-Works cranks also appears to be nicer so given a choice, they'd be my pick any day of the week.

[itsacarr]

Yes I was speaking more towards the newest version. I do know the history of the Specialized crank and lightning - all great stuff.

I have to say I run the newer s-works crank with an SRM spider and praxis rings and have trouble figuring out if it's the stiffest crank I have ever ridden or the Cannondale SRM crank was. Both are pretty amazing compared to just about everything I have touched. Which is just about everything shy of a THM ... which can only really mean that THM SRM .... unlikely though haha

[youngs_modulus]

I really don't buy this 'almost the same' line much at all. Have a look at the size and shape of the arms. Especially on newer versions of the S-Works crank, they are quite different. They are also manufactured by completely different companies.

The designs are quite similar regardless of whether you "buy" it. The newer mountain bike version of the S-Works crank (with an integrated spider) is indeed different, but I haven't been able to find a similar integrated-spider version of the S-Works road crank. The crank arm sections are quite similar, and while they probably have different layups, crank arm section is the primary driver of stiffness for this design. So yes, there's some difference, but the difference between the Lightning and S-Works cranks will be much smaller than, say, the difference between the Lightning and Campagnolo Record cranks.

I'm sure it doesn't make much difference to stiffness provided they're manufactured and installed correctly but the Hirth joint is also quite different on newer road cranks and all of the MTB cranks.

It makes no difference to stiffness. Strength and fatigue life are separate questions.

The finish on the S-Works cranks also appears to be nicer so given a choice, they'd be my pick any day of the week.

We're in complete agreement there. I own the Lightning crank, and its finish quality is barely OK. I hope they've improved the finish as they've raised their prices.

Cheers,

Jason

[jooo]

I'm ignoring the new MTB crank because it is something altogether different, but there was a definite change to the road crank arms in the last year or 2. Maybe called Fact2 or something? The change to the MTB style hirth coupling on the road cranks happened another few years before that IIRC. The old arm shape was much more like Lightning but the new shape is different.

old


new


Lightning


The Lightning arms seem to neck down quite considerably when they enter the spindle. I've often found it aesthetically strange and it seems like you'd like to have the largest cross section there

[kgt]

IMHO it's a fail the new Campagnolo cranksets are 'uglier' without being stiffer or lighter.

[ferrarista]

how come no Campy Over-torque crank? It would be nice to see how much stiffer it is than ultra-torque.

[youngs_modulus]

Nice review/comparison. Although as an engineer, I found the strain energy analysis a lot more interesting. Theoretically, almost all of the energy stored in the cranks will be returned to the drivetrain. The only time I think stiffness is actually a real benefit is for very hard efforts and sprinting, which happens a lot in road racing. However, I don't think stiffness is really a big deal for something like a time trial bike.

For what it's worth, I agree completely. I actually don't think it's a big deal for sprinting, either. And even if it was, all riders experience similar losses, so it's hard to tell.

Also, IIRC, there is a pretty simple equation for strain energy due to torsion. In order to get the total strain energy, you can just add up U_bending+U_torsion. I suspect quite a bit of deflection from most cranks is due to torsion (due to tall+thin cross sections), so focusing on bending probably wouldn't be a very accurate model.

Yes, indeed. But this article was intended for non-engineers, and, in terms of accessibility, I thought even a single strain energy equation was pushing it.

You could simply use superposition to combine bending and torsional strain energies and get a decent approximation. But that implies that you're riding a prismatic crank, and very few cranks out there have the same cross sections along their lengths. (Maybe Rotor is an exception).

Of course, you could just take an integral to capture the shape change along the length and plug that into your strain energy equation. But the crank's shape is three-dimensional, so you'll need at least a double integral (and maybe a triple integral, depending on how rigorous you're being). On top of that, the math isn't the hard part; rather, it's finding an equation for the line(s) describing the cranks. And a composite crank would add several layers (ha!) of complexity on top of that.

Very quickly, it becomes clear (to me, at least) that (a) all of the above is too complicated for a non-engineer, non-physicist audience, and (b) that FEA is a faster way to quantify strain energy than hand calcs for any real-world crank shape.

Cheers,

Jason

[youngs_modulus]

I'm ignoring the new MTB crank because it is something altogether different, but there was a definite change to the road crank arms in the last year or 2.

[snip]

The Lightning arms seem to neck down quite considerably when they enter the spindle. I've often found it aesthetically strange and it seems like you'd like to have the largest cross section there

I see what you mean, and the pictures you posted correspond with what was looking at when I said the two cranks looked similar. As I mentioned before, the Lightning crank and the latest rev of the S-Works road crank are much more similar in design to each other than they are to most of the other cranks in the test. They should still be pretty close.

That said, the Lightning's "waist" above the pedal eye is just as strange to me as it is to you. I'm not sure that it's a critical area for cross section compared to the area closer to the pedal eye or closer to the BB axle. But it does look like an afterthought to apply some "styling."

Specialized's composites engineers are no fools, and the revised cross-section almost certainly makes the crank a bit stiffer and a bit stronger. I just don't think that the new S-Works crank would be radically stiffer than the Lightning crank. If someone put a gun to my head and told me to make a number up, I'd say the new S-Works crank would be 10-15% stiffer than the Lightning crank.

I strongly suspect that Specialized's engineers know exactly how their crank compares to Lightning's, and we (consumers) will never see those numbers. But that's the wonderful thing about Fairwheel's tests: they're actually quantifying these things rather than speculating about them, as I do.

(I wrote the engineering commentary for the article, but the guys at Fairwheel did all the testing and recording of results. They also wrote the article except for my bit. I used to live in Tucson, and I've seen their testing setup. It's pretty good, and not at all different from what I would use for similar tests at work).

If Fairwheel tests a new S-Works crank, I'd be very interested to compare the results with those of the Lightning crank.

Cheers,

Jason