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Pedal feedback: Coming full circle

4K views 26 replies 10 participants last post by  le_buzz 
#1 ·
Pedal feedback: Coming full circle

A disturbing trend seems to have reappeared on my rides lately: right knee pain (the knee I injured in a OTB crash back in '05).

My first full susser in '06 was a blur xc. You know the story by now; backward crank tugs on granny climbs followed
by aching knee for the next couple days. Couldn't wait to get rid of that.

So I played it safe on my next couple bike purchases, sticking to the tried and true horst link flavors of suspension design.
Fast forward to 2011, and I realize that I'm avoiding long climbs on my Knolly Delirium due to how winded you get when things get steep.

But while Knolly's 4X4 may be the most efficient HL design on its face, I'm realizing that for AM riding it's just not the ticket.
(Unless you're one of the guys featured in one of gthose North Shore videos on the Knolly site.) Still a great bike , though.
Just not my cup of tea as an all rounder.

While I was still leery of dual link designs due to the potential for pedal feedback (and how hard that is on your knees),
a couple of Firebird demos that featured technical climbs without a hint of noticeable pedal feedback convinced me to give the
Firebird a try. So I sold the delirium frame and picked up the Firebird frame a few months later.
Everything went well at first as far as the pedal feedback goes. (Although I did have to ditch the rp23 that the bike came with
for a DHX air to get some plushness out of it.) The DHX air started drooling oil a few months back, so I sent it back on warranty,
and while it was there at Fox they retuned it for the Firebird spring rates and my weight- I was told - in addition to the warranty work.

I thought, WOW, splendid and dandy, but I still wanted a bit more plushness out of it, so I've decided to go for a fox DHX RC4 coil.

Now (finally) we get to my question: While I really want to make this mod, will going coil possibly have a negative impact on the
overall pedal feedback issue ? The suspension was apparently designed around an air shock, which are inherently progressive.
So would going coil help flatten out the spring rate curve a bit in the middle, perhaps lessening the overall amount of
pedal feedback that goes into my knee ?

I should add that while I'm not feeling the classical symptoms of pedal feedback, i.e., backward tug on the cranks, herky-jerky pedaling
in the granny/tech, etc., I'm pretty sure my knee pain is due to the chain growth that goes along with dual link designs.

Thanks for reading.
 
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#2 ·
Sorry not quite getting the connection between pedal bob and knee pain. I can't comment on the coil, but, I'm curious about the knee pain and maybe there is a better solution. Personally I have patellar chondromalacia and have never noted any connection between sagging and knee pain, but, that means nothing because different injuries cause different mechanical limitations.

- What exactly is your knee injury? (ACL/MCL/LCL/PCL/Patellar Chondro... )

- Are there pending muscle/strength/stability issues from the injury? Does your physical therapist agree you're 'done'?

- What is it about pedal bob that aggravates the knee? Is it that the bob results in sagging to a lower position? I've never had a bike sag that far under hard pedaling (that it changes the knee motion significantly). Is your sag set correctly? Have you tried going a little stiffer than the recommended sag?

- If its not the sag/position change that bothers the knee, what is it? Are your RPMs too low on your climbing? Just the fact there is a little 'squish' during pedaling shouldn't really cause pain. Its just extra resistance at the pedal - its taking some of the force on the pedal and putting into heating shock oil instead of delivering it to the wheel. The knee doesn't 'care' whether the resistance is coming from the tire or the piston trying to move through shock oil, right? I don't see how chain growth would do it either - its just taking resistance at the pedal.

Have you experimented with the spin-bike at the gym and seen if you can draw any relationship between resistance, RPM, position (matching your fore-aft position, and full leg extension position exactl), and knee pain? This serves as your 'control' for the experiment :p.

- Is your seat set correctly when climbing? At the bottom of your stroke you should have only a minor ~3-5degree bend in your knee. Too low (too much bend) and knee pain is a sure result. People hate riding with their seat this high because you have to keep stopping to drop it on downhills, but its worth it. The magic of the dropper obviates this. How about fore-aft seat adjustment - have you done the plumb-bob test to make sure your knee is directly over the spindle?

(see here: Bike Fit: Set Your Bicycle Saddle Height | Bicycling Magazine)

- Do you use clipless? What kind? Do they have enough float? Adjustable tension?

Regardless, to your question: I have not tried a coil on my firebird, I would think an RP23 with pro-pedal would be better for pedal feedback than a coil, because pro-pedal basically kicks up the low-speed compression with the flick of the switch, limiting pedal bob on climbs. Even then though, on my Firebird with RP23, propedal engaged, I still get some very minor pedal bob on steep seated climbs where I'm grinding at max torque.

Some other things you might look into:
- Shock with full lockout
- Go 2x10 or 1x10 so that you're forcing yourself to use a higher gear, which will have less pedal bob than the granny. You can experiment with this by forcing yourself to stay in the middle ring next ride. However, careful because it could have the opposite affect, if you find yourself bogging down and hammering up those hills at low RPM in middle ring, you can really aggravate your knee.

Hope that helps!
 
#4 ·
Perhaps you are trying to climb hills that are too tough on your knees? Or hills that are too steep for the Firebird? Perhaps you should reinvest on a middle grounds platform that will climb well AND descend well? Or perhaps you should just shuttle to the top?
 
#8 ·
Though Ive never noticed pedal kickback on my bird, according to the suspension graphs on bike cad the bike has significant pedal kickback in the granny.

my browser translates for me:

Linkage Design: Pivot Firebird 2010

Chain elongation is like 30mm or so near full travel. I would say my firebird climbs tech rock allot better in the middle ring if ive got the motor to keep it going. That about the only time I ever notice anything but spectacular climbing.
 
#9 ·
Granny gear?! That's your problem-dont use it! :)
I don't use my granny gear much at all, so I;ve never experienced any sort of feedback.
Most of the time even after almost 2 yrs I still marvel on how well the bird pedals.
I would also concentrate on your pedal stroke. Make sure its not herky jerky due to compensation for knee pan. just a thought.
 
#10 ·
Honestly, this sounds a little crazy but is 100% spot on. I went from a Titus ML to a Turner 5-spot and it took me a while to figure this out. On the old ML, you needed to spin, as being in too big of a gear would cause you to bob up and down like crazy. Sitting and spinning was the key. On the 5-spot, the granny does feel weird but you can stay in the middle ring and lose nothing. There will be no bob and you can even stand and hammer up the hill. Both designs work well but require different ridding techniques.

My solution, ditch the granny.
 
#11 ·
I run a RC4 on my bird and I understand the exact feeling you are getting through the pedals. The RC4 in my opinion is well worth the money, weight and 'perhaps' an increase in pedal feedback (not spent enough time on air to compare).

For me it's only a concern on more technical climbs when choosing a line and putting some power down at specific points is important. When the pedal feedback occurs the entire bike feels ungainly, for lack of a better word. It's not the same type of feedback I've experienced on other bikes.

Strangely enough, the pedal feedback has increased dramatically after I installed a RWC upper bushing kit - the kit is awesome if you like small bump compliance and I highly recommend it, but pedal feedback has increased a lot. Perhaps a little stiction in the bushing was helping?
Not sure If i should just run more LSC for technical climbs? would this adversely effect traction?

For me, not using the granny is not an option, the hills are steep around here, while I could muscle up them on a 32t+ on the front, I think traction would be compromised and I'll be not having a whole lot of fun... I got old and unfit :D.

I have a PhD in knee rehabilitation and I have been pondering your problem for a few days. I can't see that pedal feedback would have a significant or measurable impact on you knees. ddprocter has nicely outlined some other potential areas that may be worth investigating - particularly strength training in increase joint stability around the knee.
 
#14 ·
If feedback is your number one priority i'd go something with less travel and not dw link(or similar small link). Ellsworth ICT perhaps and if you want travel the Moment is a capable bike that climbs wells.
On today's ride i'm going to try granny gear, before i remove it soon, and see if i notice anything. You have me curious as to the effect your talking about.

I was just about to order the RWC kit because i figured it will be more durable and last longer than the bushing.
 
#16 ·
That question depends on many variables. Type of bike and intended use.
XC bikes typically have 3 chain rings which give you lots of gearing options and lock out.
Enduro/Freeride/AM typically have 1 or 2 ring set ups and depends heavily upon rider input/fitness level and how you build up your ride.
And yes you can change cassettes for different gear ratios, but changing sprockets is cheaper.
Not sure why you would want to lock out the suspension on the bird ;) it climbs anything you have the power & skill to climb :)
 
#18 ·
Not sure why you would want to lock out the suspension on the bird ;) it climbs anything you have the power & skill to climb :)
Because apparently the pedal feedback is causing knee injury to the OP, and locking out the rear sus would eliminate it. If this is something the OP doesn't want to do, then other solutions are necessary. (Such as increasing chainring size to reduce pedal feedback and change the cassette to keep the overall ratio closer to what he had earlier.)
 
#17 ·
I have a PhD in knee rehabilitation and I have been pondering your problem for a few days. I can't see that pedal feedback would have a significant or measurable impact on you knees. ddprocter has nicely outlined some other potential areas that may be worth investigating - particularly strength training in increase joint stability around the knee.
Trust me it does. When I went from my old blur to a HL bike,
the difference wwas spectacu;lar
 
#20 ·
If you say it's causing knee pain, I'll accept that.

It's a shame you probably live thousands of kilometers away, would be interesting to somehow attach a dynamometer to the pedal / shoe interface (a few different ways this could be done). Even some EMG to measure muscle activity and co-contraction. It would be interesting to see what sort of forces may be spiking during the pedal feedback.
 
#24 ·
Thamnks for all the helpful replies Saul and ddproctor.
Some rear susp.designs are more prone than others
to pedal feedback. The designers try to reduce the amount
of antisquat toward the end of travel to alleviate this as much
as they can, but some always seems to sneak through.
My Santa Cruz blur had the worst pedal feedback of all the
bikes Ive ridden,; I would have knee pain after rides and
it drove me crazy until I sold it. My next bike was a
Chumba XCL. It wasw a relief to be able to pedal up rocky
climbs without knee pain.

Some knee pain has come back on the Firebird. Right now
Im trying to monkey with the rebound and such. I think
there's things I can do with the setup to mitigate it more.

The best thing I think, would be to go the route that Saul mentioned:
Go to a 1X9 setupl, with a single 30 tooth abd a 38 or 40 large
cog in back. I also want to go coil for some extra plushness.
Do you think that would have a beneficial effect ?
 
#26 ·
Pulling the upper chain should not cause the linkage to compress, because during compression the rear hub moves away from the BB. I think the cause of pedal bob is simply downward force from mashing. As soon as the suspension starts to compress, the rear hub tries to move back - away from the BB - and the tighter the upper chain is, the less pedal bob you get. So a small chainring is more effective against pedal bob. (Another way to reduce pedal bob is to spin the cranks rather than just pushing them down at the front. The effect is immediately noticeable.)

A large chainring reduces pedal feedback, because the cranks rotate less for any amount of chain the rear of the bike pulls during compression.
 
#27 ·
I agree that I should try the taping. I'm actually getting more knee pain at certain times of the day than while
biking, but my rides have been relatively short lately, usually about 40 minutes due to lack of daylight.
I instinctively favor my left leg at times during really rocky climbs and try to time my pedal strokes
so I'm not in that 3 oclock position during the point of highest flexion.

By the way Uphill, are you sure the rc4 is causing more pedal feedback than an air shock ?
I wanted to go that route as I can't seem to get the amount of plushness that I would like from the DHX Air.
 
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