concrete slab "bucking"

[sethjs]

I test rode a 696 today and *loved* the bike. My biggest issue with it was that, on concrete slab highway between 60 & 80 MPH, the bike bucked around a fair amount when driving over concrete slab surface.

Is there a way to get the bucking under control with any adjustments to the suspension?

I'd imagine anyone in LA or certain parts of SF Bay area would have experienced this.

Thanks!
Seth

[Raux]

how much do you weigh?
the bike is setup for i think about 160lb rider.
i had the same problem when i forgot to dial it back down after riding 2-up.
there are 16 clicks of adjustment in the rear for the damper and the spring is easily changed as well.
the front you are stuck unless you replace parts.

[the_Journeyman]

My first thought was the suspension needed to be sorted for the rider.  Sounds a bit soft/underdamped but I'm far from an expert on boingers ~

JM

[Raux]

the bucking i think he's talking about occurs on my bike when i have the damper cranked all the way up for a passenger "like the manual says" it does make a difference. on bumpy roads it would feel like the ass end wanted to throw me off. i weigh around 160 (depending on the meal) so right in the middle of the 16 settings is where i keep it for everyday riding. BUT now that i live in Germany i expect i may have to play a bit since i live on a mountain side with tons of twisties.

[Shazaam!]

What you’re experiencing is described in the following article as “amplified damped harmonic motion” (fig. 4-a.) Lowering your road speed will help by changing the timing of the bumps, carrying more weight will affect the natural frequency of the system, but changing damping or spring rate will only make your bike handle worse overall - unless of course, your springs and shocks are not properly set-up for your body weight in the first place.


http://www.ducati.com/bikes/techcafe.jhtml?detail=article&value=theory&part=general&artID=5

[ScottRNelson]

The shorter the wheelbase the more you'll notice the bucking sensation on the freeway.  The stiffer the suspension, the more you'll notice it.

My solution is to avoid riding on the freeway as much as possible, but that's probably not an option in L.A.  I sometimes can't avoid the few miles of I-680 between Pleasanton and Livermore, so I just put up with it.

I definitely would not adjust the suspension to be optimized for the best ride on cement freeway slabs.  I have mine optimized for best behavior on twisty roads.  It turns out that the local suspension expert, Phil Douglas at Aftershocks Suspension, prefers softer settings for compression and rebound, which improves the freeway ride as well as back road behavior.  Softening the compression damping will make it smoother, just make sure you adjust the rebound to match.  Sorry that I can't offer settings to work from (I have them for ST2 and 888, though).

[somegirl]

There's a certain part of 101 by South San Francisco where it always feels like I'm on a pogo stick.  Other parts of the freeway are fine.

My 695's suspension is set up for me, but there's only so much it can do.  It was even worse with the stock set-up (I weigh far less than 160 lbs).

When I rode MrInc's S4R (suspension has never been adjusted since it was bought) over the same stretch, wow what a difference.  There was far less pogo-ing.

[Ivan]

With some suspension work, you can have both a good ride on the slab and good handling in the twisties, it only takes money.

My 3-way adjustable damping Penske shock rides great on some of the worst stretches of freeway that you could imagine, yet it doesn't give anything up in the twisties.  Once you get the correct spring rate, its a matter of dialing in the correct amount of high and low speed compression damping.  You want the low-speed damping to be kinda firm, to prevent the bike from squatting too much when you get on the power coming out of the corners.  This really helps you hold your line.  If you go too firm on the low speed damping, you'll find the front wheel wanting to leave the ground in those situations, you have to experiment to find the right balance.  At the same time, you need the high-speed compression damping to react quickly to the bumps.  Good shocks can be set up to do this.  The stock shocks cannot.

[clubhousemotorsports]

some of the answer to the problem was given in the question.

"the bike bucked around a fair amount when driving over concrete slab " this sounds like two probable scenarios.

1.  Too much high speed compression in the shock (not bike speed but shaft speed) when you hit bumps that spike the suspension the damping is too restrictive and locks up. when this happens the suspension becomes solid for a short period of time making your bike a rigid. high speed needs to be fixed internally on most components. If it is the concrete seams that are the problem look here.

2. The spring/s are wrong for you and to get them close  they have been over preloaded, as you increase preload you increase the force needed to start the suspension moving. Too soft a spring (common) and too much preload can give a jarring ride, changing to a spring that is the right rate for you and your bike your comfort AND handling improves.

Or three just do like I do on our motocross track like roads in NH , get off the seat and grab the tank with your knees. [moto]

[Shazaam!]

Quote: "When I rode MrInc's S4R (suspension has never been adjusted since it was bought) over the same stretch, wow what a difference.  There was far less pogo-ing."

Different bike weights give a different natural frequency of the suspension, so the response to a given bump rate will differ. Note that the S4R weighs 425 pounds, the 695 weighs 370 pounds.

[sbrguy]

i had speeddog put in adjustable forks on my 620 with them sprung for my weight of around 160, and big difference.

the stock 620 forks we found out that they were actually a bit too soft for me.  so what happened was that they made the ride harsher in a way or just less smooth, i know trhat with the new forks its a much more even ride.

of course if you are going over a really bumpy area, its going to feel bumpy noway around that.  but its definitely more comfortable now.

[Capo]

Tire Pressures ?

[somegirl]

Also, just a reminder that you will feel more comfortable if you can hold on with your legs and keep your arms as relaxed as possible.  Tense arms/hands will make the bucking feel much worse.