What could cause a vertical oscillation from the front at a certain speed range? | GTAMotorcycle.com

What could cause a vertical oscillation from the front at a certain speed range?

jc100

Well-known member
Bike is a KTM Super Adventure still under warranty with active suspension and OEM Conti Trail attack 2 tires.

Front rim has been balanced and trued on a digital machine. No side to side wobble but there's a vertical oscillation between 40-60km/h more pronounced on smooth Tarmac. Bike feels like it's on rough road or even a similar feeling to lugging in a higher gear (it's not lugging though). Feeling goes away after 60 and is pretty smooth. I have a warranty recall in on the front rebound cartridge of the bike which is going to be replaced, however some other owners report the same effect even after cartridge replacement.

Any idea what this might be due to? Current owner theories are:

Bad OEM tires (although it seems some owners have the same effect on after markets)
Bad OEM rims. Seems a rim can still have defects after balancing and truing. Is this correct?
Road reading suspension software error. This is my current theory but I can't exactly back it up with hard facts. Just my gut feeling as the oscillation doesn't vary in frequency and is only present at a narrow speed range.

Im going to have the shop look at everything again but would just like some of your expert input before I do.

this is more of a niggle rather than anything else but this did happen in a corner recently and the bike felt pretty unplanted as you can imagine.
 
Likely some kind of weird harmonic in the tire.
Some coarse tread dual-purpose type tires can develop quite a 'hum' at certain road speeds.
If its not hindering performance, short of trying a different set of tires, live with it.
 
Likely some kind of weird harmonic in the tire.
Some coarse tread dual-purpose type tires can develop quite a 'hum' at certain road speeds.
If its not hindering performance, short of trying a different set of tires, live with it.

I'd consider living with it if it didn't make some low speed corners a little dicey. This bike has a fancy dancy suspension set up and I'm wondering if it maybe gets confused or something at this particular range and starts compensating when it doesn't need to.
 
I have heard many good things about John. From other riders, GTAMERS and dealers. Mostly because of my height, almost everyone says he can make pretty much any bike rideable for me, while keeping near stock shock performance. That sounds like a guy I would trust.

Sent from my custom Purple Joe Bass mobile on Tapatalk
 
I appreciate the tip, I know about John. I'm looking for things I should mention to the techs when I take my bike in for other warranty work.
 
It is probably the rim it usually is when this happens.

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Is this a used bike? Maybe previous user messed with the settings
 
I would try the easiest fix first and assume it is the tire. See if they will replace the tire under warranty and go from there.
 
I would try the easiest fix first and assume it is the tire. See if they will replace the tire under warranty and go from there.

Ill have them look at that too. Some owners have had their front OEMs rplaced under warranty
 
Met a guy who had a similar issue on a different bike today. His was caused by a badly seated bead on the front tire.
 

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