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adjustable fork causes drag?

slyfink

slyfink

Turbo Monkey
Sep 16, 2008
9,331
5,086
Ottawa, Canada
Hey guys, I've often felt this, but have always thought I was just imagining things. Until I read about it in MBA that is.

Essentially, on my XC bike I have a 36 TALAS, and when I drop the travel to climb, it feels like the brakes are dragging. It's really annoying, to the point I don't bother using the travel adjust, and at this point, I feel I probably would have been better off getting Floats for less money and less weight.... :think:

But then I recently saw this on MBA's website: http://www.mbaction.com/ME2/dirmod.asp?sid=&nm=&type=news&mod=News&mid=9A02E3B96F2A415ABC72CB5F516B4C10&tier=3&nid=36AE7CB13BEE4B0EB022AD811B740B42 describing the same thing.

Basically, in their review of the Remedy, they said they noticed "drivetrain drag" when they lowered the forks. So I'm not alone! But in the on-line discussion of that comment, RC doesn't really offer an explanation, or nothing conclusive anyways. So I'm not sure what to think. Any suspension kinematic "experts" out there care to elaborate or hypothesize?
 
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S

slowitdown

Monkey
Mar 30, 2009
553
0
In 2001 Doug Curtiss built me a hardtail around a Marzocchi Z1 fork. The bike rode great with the fork fully extended. When I used the ETA and punched down the fork, the bike felt like the brakes were dragging, just as you described -- except when I was climbing a steep grade, then it felt fine.

I never figured out why, I just know it happened.
 
rockofullr

rockofullr

confused
Jun 11, 2009
7,342
924
East Bay, Cali
I have been using forks with RS U-turn for years now (pike and lyric) and have never encountered "drivetrain drag".

To me this seems pretty strange.
 
Bicyclist

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
I can't think of any reason for this to happen. Sure, the head angle is steeper, but it's not like it will drastically change the geometry. Brakes are a closed hydraulic system and I don't think the lines get kinked or anything like that. Seems like it's maybe just a placebo effect - the bike might handle "strangely" but I don't think that the brakes/drivetrain is actually effected.
 
Sandwich

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,076
5,989
borcester rhymes
I'm guessing it's in your head...I can't think of any other explanation than that.

Try timing yourself through a section with the fork up and then the fork down...give it a few runs so that you aren't just getting faster through it. I bet you'll find that the times are pretty similar.

I wonder if you lower the bike, leave it for a day, then go ride it the next without raising it, and report back how you feel. I bet you won't notice the "drag" that you're describing.
 
Biffff

Biffff

Monkey
Jan 10, 2006
913
0
There's some physics involved with this but it basically creates the sense of harder pedaling caused by the weight shifting forward. I have sensed this before on bikes with adjustable travel. Its one of those thing.....if you don't like it, don't lower the fork.
 
slyfink

slyfink

Turbo Monkey
Sep 16, 2008
9,331
5,086
Ottawa, Canada
Biffff said:
There's some physics involved with this but it basically creates the sense of harder pedaling caused by the weight shifting forward.
Click to expand...
if this were the case, wouldn't pointing the bike up hill negate that sense?

I've been meaning to test my theory out by doing a very unscientific test. I think finding a hill with a slight downslope, marking a start and a stop point, and starting from a dead stop, then doing a few passes with the fork up, and the same number of passes with the fork down, might help determine if the effect is real.

any chance you could elaborate on the "physics involved with this"? In his response, RC says Dave Weagle has looked at this phenomenon, so I would imagine it's not "just in my head"...
 
sanjuro

sanjuro

Tube Smuggler
Sep 13, 2004
17,373
0
SF
I have a Z1, Marathon XC, and a TALAS, and I have never noticed drag on the lower travel setting.
 
Bicyclist

Bicyclist

Turbo Monkey
Apr 4, 2004
10,152
2
SB
Seems that the steeper seat tube angle makes people think that they're experiencing "drag"...more of a biomechanical thing than just a mechanical thing.

edit: is it just me or is "ask RC" not completely retarded now?
 
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punkassean

punkassean

Turbo Monkey
Feb 3, 2002
4,561
0
SC, CA
seems to me this phenomena would depend a lot on seat angle. If the bike has a decently steep SA to begin with then I could see some loss of power from it becoming too steep with the fork lowered. However on a bike with a relatively slack SA, increasing the steepness should make for more efficient power transfer. I imagine it has more to do with simply changing than it does specifically with more forward lean. Changing the seat angle, whether it be steeper or slacker, from a position your body has conditioned itself to be most efficient at, could very easily have perceptible, negative implications. Why do you think top-level pros pay so much attention to all aspects of bike fit?
 
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slyfink

slyfink

Turbo Monkey
Sep 16, 2008
9,331
5,086
Ottawa, Canada
Bicyclist said:
edit: is it just me or is "ask RC" not completely retarded now?
Click to expand...
I too was surprised by his answer. He just bought himself a little more goodwill. I might even buy the magazine for my next plane trip...

Interesting about the seat angle. I'm on a 2005 Enduro. I can't remember which shuttle I have in there now, but I'm 90% certain it's in the steeper setting, which would place my seat angle at 69.5*. I think that's a pretty standard seat angle isn't it? whatever. I usually would only lower my fork for long grinding climps, but I've taken to turning the rebound damping right up practically locking the fork out. the rest of the time I ride it full height.

I should have bought a Float and saved the weight and cost. oh well, live and learn.
 
al-irl

al-irl

Turbo Monkey
Dec 9, 2004
1,086
0
A, A
Ì've definetly notice this but don't think its the forks or anything like that. Its more about your position shift I had an old 04 specialized enduro sx (the 4x one ) which suffered badly when i lowered my 36 talas down to the lowest setting. However I now have the same parts on a Morewood shova frame and it doesn't make a difference
 
4130biker

4130biker

PM me about Tantrum Cycles!
May 24, 2007
3,884
450
I have an enduro with a talas and I know the feeling you're talking about. Here's what I've found: I usually pump my tires to about 40 for climbing, then deflate them to descend. Well, if I forget to re-pump my tires, the and drop the fork, I think my weight on the font makes the bike feel extra sluggish. So maybe check your tire pressure. That being said, I think the enduro feels a bit sluggish on flat ground with the fork down. Could be that it's simply putting me too far forward for flat, because it climbs awesome on steep climbs.
 
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