Blenkinsop's Modified Norco AurumWe usually see the most interesting bikes, components, and modifications during the World Cup season, but that doesn't mean that teams have taken the winter off from tinkering with anything that might allow riders to go down the hill quicker. Photographer Cameron Mackenzie spotted Norco's Sam Blenkinsop running this interesting looking idler pulley and chain guide setup on his Norco Aurum, presumably to change the amount of anti-squat that's built into the Aurum's 200mm of A.R.T. suspension design.
In the Aurum's stock form (shown in the photo of Sam's 2015 race bike to the right), the bike's main pivot looks to be just slightly above the top of the chain ring, depending on the size of the ring. But the custom idler pulley on Sam's bike routes the chain well above the main pivot, a modification that would make the bike have less anti-squat and, therefore, allow the suspension to be more active while Sam is pedalling hard.
The tradeoff is possibly less pedalling efficiency, but they may not matter to Sam if the bike pedals well regardless of the change, or if the track puts much more of an emphasis on bump absorption than all-out sprinting speed.
The setup on Sam's bike is clearly a homemade device, with the upper unit being from MRP's AMg chain guide and a pulley wheel that's held in place with a large bolt and some washers. Note that not only is the upper guide adjustable height-wise, but there appears to be another mounting hole for the pulley wheel that's considerably lower than where it's located in this photo. All of this looks like it's attached to a fin of aluminium that's been welded onto the chain stay. Owen Pemberton, Norco's Senior Design Engineer, had this to say when questioned about Sam's bike: ''
What you are looking at is just a part of our ongoing Norco Race Development program. That setup on Sam’s bike is purely an information gathering exercise at this time.''
Title photo Cameron MackenzieInset photo Dave Trumpore
Also I don't see the owners of any of the big companies actually racing the bike's. as far as I know anyone who has ridden one has loved it and if they sold it they regretted it. lots of companies are following canfields footsteps with the idler pulley, so it obviously means something
www.pinkbike.com/photo/1852607
The only way to aleaveate pedal kick back, is by adding an extra pulley, like Sam did, because he rides at WC speeds, and most of the time on flats. And ride with a larger chainring. Considering every bike design is different, each bike has different amount of pedal feedback. Adding a pulley is usually for bikes that have the most pedal kick back in the market. If yours has only a little bit of pedal kick back, you can take care of it with a 36+ chainring.
For the banshee legend guy, all u need to so is use a 36 or 38t chainring and the pedal feedback would completely dissapear. I can almost bet u are using a 34t arent you?
So what this article tells us is that at WC speeds, the Aurum has too much pedal kickback to be a competitive bike for the podium. Hence the moddification.
It has to to with pedaling because placing the point of tension force higher on the frame means there is a greater "up" horizontal force acting on the rear casset, rather than it pulling it down when its trying to work up. Very similar if you have ever ridden a two chainring setup. Having the chain in the smaller ring makes the world of a difference and you can feel it keeping the rear end in place, but having it in the bigger ring (greater horizontal force up) and the bike bobs up and down more since the suspension is more active.
Give it a try then argue
Don't argue, listen and learn.
Also, Levy, can we stop talking about the location of the main pivot in relation to the chainring for multi-link setups? sure on an FSR it may have slightly more relevancy than on a short link set up but still, the virtual pivot/IC is the real issue and the main pivot location is only one small part of that.
You're arguing for the point here, not against it.
The BIGGEST negative of the JEDI.......It shrinks your local mountains and constantly requires you to be on the move for bigger hills!
what were we talkin about?
Ever tried doing a "quick chainring swap" with a dm ring?
Some of those dm rings don't look the stiffest either...
@gabriel, no I have never needed to do a quick chainring swap, but I can't imagine it being more simple than unbolt 8mm to remove crank, then use a bb tool to remove chainring. Two bolts. Less than the 4 needed for standard chainring. You ever try to do quick ring swap with seized chainring bolts?
Yes RaceFace's arm/axle interface is subject to wear. Infact as a pressfit item, it is extremely susceptible to wear through excessive fitting/removal. I have had many Raceface cranksts. They get noticably easier to fit and remove each time. After maybe 20 times, they are no longer "tight" and I would say essentially worn out...
It all depends on where the virtual pivot is. If idler is higher it will cause squat as the chain can pull the rear wheel up, if idler(or chain line) is lower, it'll increase pedaling induced anti squat.by pulling the wheel down.
It's also probably travel dependent as the VPP will move through the travel.
and not sure if idler is mounted to swing arm, this also would have some effect, but probably very little due to it's location to pivot.