The only Crankset that truly eliminates the dead spot, ( the top crank is 15 degree past upper dead spot when lower crank is at dead spot) Rotor Cranks are the best solution available on the market to prevent and alleviate knee injuries.
Available in MTB, Road 2 and Road 3 versions
Results in 10% more power in climbing and acceleration, and a reduction in lactates.
Weight: 1270 g (cranks + chainrings + bb assembly)
Similar Products Used: used Q rings and standard cranks
Bike Setup: The set up is very critical, should have an expert who has done them before.
a Cross Country Rider
from Trondheim, Norway
Date Reviewed: January 25, 2009
Strengths: Indeed improves performance and reduces lactate levels. High quality.
Weaknesses: Kind of pricey, a PiTA to install (see below), weighs more than regular cranks (even cheap ones), requires proprietary chainrings
Let's take the good things first. Rotor claims their strangely looking crankset will improve your power output by more than 10% and reduce the buildup of lactic acid in your muscles by 9%. I don't have neither a wattmeter nor have I done lactate testing on my bike with/without the Rotor crank, but I can assure you that the difference is both notable and measureable in means of minutes/seconds shaved off longer climbs.
Effectively eliminating the deadspot of the stroke - contrary to the Q-rings (which I've also been using) that will only reduce the effect of the deadspot, not eliminate it - it also allows me to remain on the pedals across a lot of tricky climbs I had to walk/carry my bike through earlier.
Another plus for it's VERY knee-friendly side effects - being primarly a middle-distance runner, my knees are frequently in need of some relief from the hammering they're being exposed to when running long workouts on hard surfaces. A short (or longer) ride with my Rotor-fitted bike provides perfect restitution.
Now for the downsides. Since it's function is to vary the angle between the crankarms throughout the stroke, it's rotary position inside the crankhouse needs to be fine-tuned with tolerances of less than a couple of degrees for optimum performance. To fix it in this position, you will need to hold back the right crankarm while tightening the left BB cup to 70 NM - it really needs a couple of attempts to get it right. If you're using blue Loctite (which you should, as stated in the instructions. A small bottle sufficient for at least two installations comes with the set) and tighten it hard enough, it should stay in position virtually forever (mine came loose a couple of time due to insufficient tightening).
Some may argue that it's costly and heavy - In my opinion, the amount of engineering, machineing and amount of independently moving parts easily justify both of these points. I do, however, think it's a shame that it requires special, proprietary chainrings available from Rotor only. These rings are not Q-rings, just plain, round chainrings with an eccentric bolt circle. Why not make the spider itself eccentric, with a standard 104/64 BCD?
Bottom Line - The Rotor RS4x definitely works for me, it improves my riding experience and as far as I can tell, it keeps what it promises. If you're not concerned with the added weight and price, it's a well-worth upgrade to nearly any bike meant for going uphill (including XC, AM and road bikes) and even some who aren't. Clearly five chilis for it's function, four value chilis for it's good, but not outstanding value for money and possibly added chainring cost.
Similar Products Used: Bontrager Race with Q-rings, different regular cranks with regular chainrings
Bike Setup: Klein Attitude, RS4x cranks, Look Quartz pedals, XTR deraillers, Yaban chain, XT cassette
a Cross Country Rider
from Sacramento, CA
Date Reviewed: August 5, 2008
Strengths: Machined works of art that seem to do their, job. see rest below
Weaknesses: heavy as hell, a bit of a pain to set up, proprietary bolt circle diameter. Expensive, but not much more than xtr. Everyone you ride with will ask about them
I can't really comment on the racing performance gains, or knee friendliness of these cranks as I don't time my rides or have bad knees, but I definitly know they give me better traction by evening out my pedal stroke, and they make it easier to stand and pedal over uneven turrain. They don't feel awkward for decending, unless you try to back pedal a full rotation. I love them, but not so much that I couldn't ride without them, but I'd definitly recomend them over any other cranks.
Similar Products Used: regular cranksets kind of compare
Bike Setup: 6" travel sinister all mountain bike, about 31 lbs
a Weekend Warrior
from Nokomis, FL, USA
Date Reviewed: April 19, 2008
Strengths: Does work as advertised... but
Weaknesses: Very High maintenance. Bearings very small and O-ring seals are poor at their job. BB position slips even with thread locker.
My wife has a bum knee. We got these to help that issue. They did and do help her knee. She uses them about 100 miles/wk. and they are a maint. pain in the arse. Bearings are small and not well sealed. I have replaced them and o-rings after about 18 months of my wife's neighborhood riding. Cannot see how they would possibly hold up off road. About every 4 - 5 months I find that the BB position has slipped and my wife's knee is hurting. I have cleaned BB threads, used blue thread locker and same story. This weekend I am replacing bearings again and will try the red thread locker. If her bike was not a 3 spd. I would try their rings and not these cranks.
a Cross Country Rider
from Colorado Springs, CO USA
Date Reviewed: May 17, 2006
Strengths: Amazing while climbing, more comfort on long days on the trail, more traction on loose terrain.
Weaknesses: Weight, but the first time I had to go uphill, I didn't mind it at all, specially when climbing.
These things ROCK! I didn't believe the claims at first, but decided to give them a try and was blown away at the actual increase in performance. I originally got these because I have bad knees, and not only does it help with my knees, it also helps me go faster at the same effort.