Rotor cranks

[Uba Tracker]

G'day all, has anyone seen or heard anything about http://www.rotorcranks.com.au/index.html

[mikesbytes]

This is a question for toolonglegs

[Birdman]

Doesn't look like a bad idea. Improvement in pedalling efficiency and output. Can always be handy.

Mitch.

[sogood]

Poll on how long would 2Long take to destroy a rotor crank... Bear in mind all the extra gearing within the unit.

[toolonglegs]

I love em but I am thinking of getting back a set of 177.5mm cranks for my race bike,so will put my 180's onto my trainer.So they are for sale if anyone would like a pair.They are in great condition as I pull them to bits quite often for a lube.They are 180mm Ti model...apparently you can run longer cranks with rotors than normal.Not sure how you set them up on a bent thou,you loctite the bb in instead of lubing it and have to have bb in the right place to get timing right.

[Hotdog]

I've heard quite a bit about them on the recumbent forums, some riders swear by them. Apparently the way they help smooth over the dead spots is particularly helpful for climbing on a recumbent.

Even more popular are the Q-ring ovalised chainrings from the same manufacturer, they claim a lot (but not all) of the benefits of Rotorcranks but at lower cost (and weight). I believe Graeme's got at least one Q-ring on his bike.

[Kalgrm]

Not sure how you set them up on a bent thou

Many 'bent riders are looking for cranks in the 150mm to 160mm length (including me). 180mm is WAY too long for me and my 'bent.

Try the Q-rings when you go back to normal BBs. I reckon you'll like them.

Cheers,
Graeme

[toolonglegs]

I like the principle of the Q rings,they haven't really taken off thou in the racing circles...i know bobby julich was a keen user but not sure how many other use them.
150/160mm cranks are rather short...why do you use shorter cranks on a bent?.I always thought as they dont climb that well that the long cranks would help...maybee thats why rotor cranks are popular as you can run a standard length crank but get the benifits of a shorter one.

[Mini Man]

The short cranks are used on speedbikes, usually with a very short axle to get a smaller frontal area , they also help to keep the knees lower which helps to keep them away from the steering etc . John.

[Kalgrm]

I like the principle of the Q rings,they haven't really taken off thou in the racing circles...i know bobby julich was a keen user but not sure how many other use them.
150/160mm cranks are rather short...why do you use shorter cranks on a bent?.I always thought as they dont climb that well that the long cranks would help...maybee thats why rotor cranks are popular as you can run a standard length crank but get the benifits of a shorter one.

The answer's a complicated and somewhat vague one, I'm afraid, but I'll try to explain as I see it.

The first thing you notice when you get on a bent is how much longer the cranks feel. It feels like the knee is being bent up quite severely. I don't know why this is. Richard commented on it and I certainly felt the effect, even though the cranks on my 'bent are the same length as on my MTB. (The reverse happens too: when I get back on my MTB, I feel like my cranks have been shortened.

Anyway, that is "the perception" part of the answer. Physiologically, the idea is that since you can't stand and grind on a 'bent, you must spin. The faster you spin, the more power you can output. Short cranks facilitate spinning because each rotation needs less "foot travel" to complete the cycle.

The other physiological reason is the reduced angle of bend in the knee. It lets the leg be in it's optimum position to fully utilise the quads for power generation throughout a proportionally longer segment of the stroke. By that, I mean you can start applying power when the upper crank is at (say) 10.00 o'clock instead of (say) 11.00 o'clock*.

Now, this is all theory as far as I'm concerned. However, many 'bent riders claim a definite improvement in overall speeds when they reduce their crank lengths and reduce their gearing appropriately (ie they increase their cadence for any given speed.) Placebo? Who knows, but I'm going to give it a go when I can.

Mini Man's points about reduced wind resistance are also valid reasons as to why shorter cranks might be providing improved speeds.

As for world class riders with Q-rings: I know that Ned Overend uses them for his MTB World Cup events. Then again, he is over 50 and still winning, so maybe he's just a freak .....

Cheers,
Graeme

(I should note that the bloke behind Rotor cranks is a regular contributor to the Bent Rider Online forum. Rotor cranks are very popular amongst bent riders, as are the Q-rings.)

*where 12.00 is a vertical crank and 3.00 o'clock is the dead spot.

[europa]

The other thing to note from crank length threads on bent forums is that some people do better by going shorter and others go better by going longer and some don't notice what length they're using. It's a bit like taking a group of riders into a chocolate factory and asking them which one they prefer. The hooman animal is a tad more complicated than we give it credit for.

Richard

[Uba Tracker]

I dunno fellas these 'Q' rings remind me of the old Shimano Bio-Pace items, even uttering Bio-Pace in the mid nineties was akin to pulling out the 'F' word while at confession

[Hotdog]

Q-rings are almost the anti-Bio-Pace though. Bio-Pace had the largest effective diameter at the dead spots, whereas Q-rings (while adjustable) are intended to be positioned with their smallest effective diameter near to the dead spots. Whether either is a good idea is an entirely different matter but they're certainly very different.

[Kalgrm]

I dunno fellas these 'Q' rings remind me of the old Shimano Bio-Pace items, even uttering Bio-Pace in the mid nineties was akin to pulling out the 'F' word while at confession

Maybe, but Rotor cranks, Q-rings and Bio-pace are/were trying to achieve the same thing: reduce the effect of the "dead spot" in the stroke. On a 'bent, that dead spot seems more pronounced, so doing something about it makes sense.

Bio-pace never took off for bent riders because the dead spot is located some 90 degrees away from that on a wedgie relative to the crank position. Bio-pace rings can't be rotated to allow for that. Q-rings and Rotor cranks, on the other hand, allow much more flexibility for the positioning of the long axis of the "lever arm ellipse".

Is there any difference from a circular chain ring? For me, yes. I've only changed my middle chain ring. The other two are standard. I swapped a 42t std for a 44t Q-ring and noticed I could stay in the middle ring on a particular hill that had me changing to the small ring previously. So I found it easier to climb that hill, even though my tooth count had increased. Could be placebo effect though .....

Some time soon I'll swap out my small & big rings for either Q-rings, or home made versions. (I'm off now to find the downloadable program which lets you design and print an elliptical chain ring drilling template. Found it once before but lost the link.)

Cheers,
Graeme

[Uba Tracker]

If you need help with a drilling template Graeme, let me know the number of teeth you want and the mean major and minor elliptical axis dimensions and I'll see what I can whip up for you.
cheers
Harry

[Recycler]

Kalgrm, I think you can use Biopace chainrings on our bents. All you have to do is rotate the chain ring forward one bolt hole position. PS I have not tryed it myself ,but will do . Good Luck TWO BENT

[Birdman]

I read all of the information on the site and i think i got my head around it...

So basically the principal is you have an oval shaped chainring. You put the chainring on as normal (sort of), in a vertical position like this ...0.

Then as you are riding instead of being a fluant circle motion the end of the oval being at the top and bottom of the revolution reduces resistance, so your pedal stroke isn't in the deadspot as long.

Correct me if i am totally off the mark.

Mitch.

[rdp_au]

When I built my 'bent, I used the running rear from a mountain bike, including a set of biopace chainrings. Advice was to rotate the rings 90 deg and they would work fine. On reflection, this didn't make sense to me. All of these systems (biopace, rotor, Q-rings) are designed to interact with the biomechanics of pedalling. This has nothing to do with how you are oriented on the bicycle frame - the 'dead spot' is still at the same location relative to your pedalling action.

So I left them in the standard position. Didn't like how they felt. Against my better judgment, rotated them 90 deg. Still didn't like them. I needed to raise the gearing anyway, so replace the crankset with a conventional 53-42-30 setup.

Rds,

David

[Recycler]

Kalgrm, Why not make your own crank set? Obtain a used crank set then measure from the centre of BB axle up the crank, centre punch at 150mm or 160mm. Drill holes and fit a Re Coil thread . Then you can try it one crank set. If you need more info PM me .. Good Luck. TWO BENT.

[Kalgrm]

I read all of the information on the site and i think i got my head around it...

So basically the principal is you have an oval shaped chainring. You put the chainring on as normal (sort of), in a vertical position like this ...0.

Then as you are riding instead of being a fluant circle motion the end of the oval being at the top and bottom of the revolution reduces resistance, so your pedal stroke isn't in the deadspot as long.

Correct me if i am totally off the mark.

Mitch.

Mitch, you're close to the mark regarding the oval chain rings - rotor cranks are a different concept.

Think of the distance between the chain and the BB spindle as being a lever arm.

In the power position for a rider on an upright bike (crank arm horizontal) the lever arm length (X1 in the "technical drawing" below) is longer to take advantage of that power you can apply. At the dead spot position, the lever (X2) is shorter so it takes less power to get through that part of the stroke. Because the lever is shorter, your stroke speeds up a little through that segment if the "chain speed" remains constant.



David,

There is a big difference in the position of the dead spot when you're on a bent. The dead spot occurs when the crank is near horizontal (depends on how high the BB is relative to the hips). In the "technical drawing" below, you can see where the power position is and why the rings must be rotated 90 degrees compared with an upright bike.



The reason Q-rings are popular with bent riders is the fact that the position of the long axis of the ellipse is customisable in increments of 7.5 degrees ( ? ), so it suits all bikes, not just uprights like the Bio-pace rings did.

Cheers,
Graeme

[Kalgrm]

Kalgrm, Why not make your own crank set? Obtain a used crank set then measure from the centre of BB axle up the crank, centre punch at 150mm or 160mm. Drill holes and fit a Re Coil thread . Then you can try it one crank set. If you need more info PM me .. Good Luck. TWO BENT.

Much more easily said than done, I'm afraid. At no time in my life have I had the training to use (or access to) the equipment I'd need to do the job.

An additional problem is that with today's lightweight cranks, there isn't enough metal to utilise at 150mm from the BB spindle (and some are even hollow at that point). I would need to get myself a square taper BB to use an old crank set. I can get myself some shorter cranks from a place here in Perth. I will need to get another BB anyway, since my current one is one of those new-fangled 2-piece jobbies .....

Luckily, shorter cranks are down on my list of upgrades to be done. The first thing on the list is a very cheap disc wheel (a polycarbonate wheel cover.)

Cheers,
Graeme

[Hotdog]

Luckily, shorter cranks are down on my list of upgrades to be done. The first thing on the list is a very cheap disc wheel (a polycarbonate wheel cover.)

Turning into a bit of a speed demon, eh? Deep section rims with skinny 23mm tyres already and wheels covers on the way, soon your bike will be so aerodynamic you won't have to pedal at all

So is your wheel cover going to be a DIY job or something off the shelf?

[Kalgrm]

..... soon your bike will be so aerodynamic you won't have to pedal at all

So is your wheel cover going to be a DIY job or something off the shelf?

It's a DIY job. You can buy 1mm polycarbonate sheeting from Bunnings for $24/m. I'll be putting my business name on them as advertising. Next job will be a tail fairing from the same material. (Anybody else want to sponsor the "Scene by Hird Flyer"? )

Cheers,
Graeme

[Recycler]

Kalgrm Sorry about that. I use old second hand stuff, plenty of meat on those. Good Luck.

[Birdman]

Thanks Graeme, i sort of get the description with the pic.

But you said the foot goes through the dead spot alot faster due to something being shorter??? But would that not make your spin revolution a little mashy??? Or ..I'm a bit confused.

Mitch.