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Bike feels like it's "twisting" on bottom out

Wa-Aw

Monkey
Jul 30, 2010
354
0
Philippines
Disclaimer: I didn't post this in the M9 thread because I notice how the landings hit me when I get this sensation and I realized I see this in a lot of other bikes/riders, too.

On my previous bike (Banshee Scythe, slightly under sprung), when I landed from drops I would feel it ramp up but the bike would remain solid and straight as it neared bottom out, even when landing sideways on flat drops (when I notice this on the new bike most). These drops usually give me a little headbob at worst when bottoming kinda hard

On the M9 (feels slightly over sprung), when I hit the same drops it's a lot harder to bottom out, I don't feel like I'm quite reaching the end of the travel, but when I near it (this is hard to describe) I feel like the bike twists or at least the symptom is my body not being quite straight when I come out of it or a sensation of instability. No head bob bottom out stuff though, I feel like it soaks it up fine just with a little too much almost-sideways motion.

Theories:

Flex: I know the scythe is *probably* stiffer than the M9, it's rear end is pretty damn solid with enormous bearings but heck what do I know, it's hard to tell with so much more travel on the new bike.

Shock tune: Not enough rebound? Too little HSC? (RC4 by the way)

Spring's too hard? Too much force going into the bike than my body weight can account for?

Something to do with adjusting my riding style to the slacker head angle and how to land bike accordingly?


Curious thing is, this doesn't happen on hard rough hits on, say a fast rough DH course. This bike is the ducks nuts on that stuff and just plows through and stays calm and straight even through some pretty hard bottom outs. No sensation of instability or flex. This only seems to happens on drops or jumps with sideways landings, mostly relatively low speed.

I know this happens to a lot of guys out there, I now understand what that squirmy feeling on landing feels like!

e-engineers, do your worst! :weee:


TL;DR: Fancy DH bike does weird **** when bottomed old skool FR hucks.
 
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Just a guess, but it seems in the last stages of wheel travel the leverage on the rear triangle is enough to let you feel a noticeable twist or sideplay of the whole frame. Of course, that adds to the "twist" caused by other elements such as wheels (loose spokes), tyres, forks, bearings (esp. when worn out), etc. which should be checked every once in a while.

When landing at slow speeds, the forces on the bike are mainly vertical and sideways. However, when going fast (and esp. over rough terrain) the forces pushing backwards on the bike gather importance and may "cancel out" to some extent the effect of other forces acting on the susp. which, let's not forget, rougly moves "up and away" from the bike.

As a curiosity, a fellow had a similar problem to you. His bike had a noticeable sideways play (you could grab the wheel and the handlebar and feel it), but we weren't really aware of it's magnitude until we caught him crashing on a slo-mo video. Then we realized his bike was made out of pudding!!
Same thing goes for forks; taking a slo-mo vid of a friend skidding the front wheel (brake lock), you could see the fork bending and skipping over the terrain. Scary!
What I mean with this is, if you have the chance to be taped slo-mo, you might discover interesting things! :D
 
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k1creeker

Chimp
Mar 11, 2008
40
0
any chance your rear wheel is not tensioned properly or perhaps rear tire pressure is too low?
 

Wa-Aw

Monkey
Jul 30, 2010
354
0
Philippines
Hmmmm, I'll take note never to watch a super slo-mo clip of me hitting anything harsh. :D I like my faith in my bike where it's at! But you make lots of good points there. But I'm not a very heavy rider (150lbs), I can only imagine what the majority of you guys feel when the forces on the bike build up.

K1creeker, wheel is from my old bike. The M9 is just a month old, so I don't think much has changed. Actually, just remembered having it re-tensioned after a race the other week.

But I'll be playing around with shock settings as I find it hard to imagine I push the limits of this bikes rigidity as much larger people ride it harder than I do.
 

P.T.W

Monkey
May 6, 2007
599
0
christchurch nz
Does it allways feel like its twisting in the same direction??? If so it could be something as simple as uneven weighting on your pedals, try switching your lead foot left for right and see what happens:thumb:
 

IH8Rice

I'm Mr. Negative! I Fail!
Aug 2, 2008
24,524
494
Im over here now
the back end of the M9 is a bit flexier than other bikes that ive ridden. if you grab the rear wheel and flex it side to side, you will see the little bit of play.
you need to also make sure that the box link bolts are tight as well. some frames have had issues with the bolts not fully bottoming out when torque to spec which could cause the issue you are having.