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General => Technical | How To => Topic started by: Neil955i on April 30, 2020, 10:24:13 AM
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An enquiry / request for advice.
Now this is not something I do normally, but this morning whilst snapping my flip-front helmet chinbar shut on the move, I took both hands off the bars momentarily. Speed was about 30 mph. Dear Lord what a sphincter-tightening moment that was! The bars began to flap about alarmingly and though I couldn't honestly describe it as a full on tank-slapper, it put the wind up me.
Tentative tests at different speeds show this only to be an issue sub-40 mph. At those speeds I do not feel any oscillation through the handlebars. Which makes me wonder, do I have a (front?) wheel balance issue or could it be down to a 35l top box on the rear upsetting the balance - it only had around 1 Kg of stuff in it at this point?
Any thoughts appreciated or any similar experiences / resolutions* would be of interest.
(* Other than "Keep yer fool hands on the bars!" of course.)
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Yes, that is one of those Doc Campbell things where he says, "Well, stop doin' that!" It will probably diminish when you change your front tire.
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Doubt that Karl, the front's only done just over 1,500 miles? I can live with it, just wondered if anyone else had any thoughts / experience of it.
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Top box can be like tying rock to rear end of arrow------My XTown works with both small box and Givi e-46 box......as long as I keep hands on bars! Possible steering head bearings....but I just think nature of beast. Bikes used to come with steering dampers....but thing of past now
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I came across the exact issue on my agility 125 reminding me of a shopping cart caster how it developed a self accentuated flutter. I'm wondering if it might be a rake to wheel size ratio issue. The trail lessens for any given rake as the wheel diameter decreases.
Now for some weights, dampeners, and a notepad to make my messing around scientific.
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I made the mistake of removing both hands from the bars on my People S200 once....will never do that again! Wobbled like a drunk man on amphetamines. It was actually frightening. Of course, I've always felt like my scooter's frame is made of rubber. I know I can't do it but when riding it feels like I can push forward on the bars and it will move a few inches both forward and back...just a very 'rubbery' feeling.
Always wondered if there is a ton of built in flex with a step through scooter design compared to a typical motorcycle frame?
Is is the flex that contributes to the steering wobble?...
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forgot to mention that my front tire has about 400 miles on it...Pirelli MT 75...and it was mounted and balanced at my local motorcycle dealer so I would like to think my 'hands off bar' wobble isn't tire related. I deal with mine by just keeping my hands on the bars at all times!
Does our funny front end design contribute? By 'funny' I mean the short little forks, connected to a taller steering stem that eventually connects to the bars....as opposed to a motorcycle fork where the forks go all the way up from the front axle to the bars.
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Thank you all for your thoughts, exactly what I've come to expect from this forum; expert opinion laced with good humour! I reckon the sum total of these obsevations is that I should remember to keep my hands on the bars AT ALL TIMES!
Explanations vary, but I do like IaHawk's description of the steering geometry inherent in a step through scooter. I suspect you may well be onto something with that.
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OEM Maxxis tires are the worst! I will retract my statements if yours have real tires! Har, har!
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Thank you all for your thoughts, exactly what I've come to expect from this forum; expert opinion laced with good humour! I reckon the sum total of these obsevations is that I should remember to keep my hands on the bars AT ALL TIMES!
Explanations vary, but I do like IaHawk's description of the steering geometry inherent in a step through scooter. I suspect you may well be onto something with that.
Go much faster - remove hands - if it tosses you - report back. (Edited by: "DoWeeCheat'Em & Howe" legal firm)
Stig
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(Edited by: "DoWeeCheat'Em & Howe" legal firm
Gotta love a 'Car Talk' reference!
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I do wish to find a solution as I take hands free Tennessee seriously. Any thoughts on a possible damper system?
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Finally figured out the Agility's deceleration wobble.
Balancing issues were ruled out after using 1.5oz of Dynabeads with the wobble persisting apparently unaffected. After installing 8oz bar-end dampers the wobble progression was slowed until the bars reached 12 degrees from straight then proceeded as usual. The wobble only occurred with the bike vertical. When I counter weighted the bike and leaned past 6 degrees on a straight the issue repeatably disappeared which narrowed the problem to a cyclic force imbalance in the contact patch.
When a tire is new the profile is a continual radius. Due to riding primarily on straight roads the center of the tire wears a flat spot in the otherwise round profile. The driving force behind the wobble on my bike is that with no input to break the natural resonance, when the tire leans to one side the edge of the flat strip is non-coplanar with the stem and the force imbalance pulls the bar to that side. When the wheel is turned to let's say the right, the bike leans left(counter steering geometry) which grabs the edge of the opposite side of the flat which coupled with the straightening force of the trail throws the wheel the other way and the process continues with ever-increasing force=WOBBLE!
In other words even normal wear can cause the steering wobble. My front tire needed replacement due to age and the wobble disappeared with the old tire. Your case may differ. Hope this info helps.
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Having been riding long enough since no rear susupension/Spring fork/hand shift Harleys-----these bikes while ruff riding at times, would track down the Highway straight as an arrow, hands off. My experience with scooters, going back to 125 Vespas in the 60's----scooters never have nor will never be good to go down the road hands off! Don't like it, get something else.
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TBR125 you have spent a lot of time analysing this clearly and I'm sure tyre will be a major factor for you. In my case however, I'm rarely upright round the twisty Cheshire roads so can confidently rule out front tyre flat spot. Karl, they are Maxxis tyres though! Can't justify dumping them for PowerPures just yet...
Iahawk, I think you have a point taken to its logical conclusion by John, if you don't like it, get summat else! I can live with it, especially as I don't think anyone does a steering damper for a scooter.
Finally, Stig, you made me laugh with the spoof lawyer firm - the equivalent in the UK is a company called "Sue, Grabbet & Runn"
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I understand every case is different but also minor cupping has a similar effect although your tire shouldn't have that issue yet.
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Gotta love a 'Car Talk' reference!
Actually I believe it was a referance from the late Jonnie Carson.
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(https://i.postimg.cc/GhVxQSNt/image.jpg)
Major Tom
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Use them? What could go wrong?....
;D
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(https://i.postimg.cc/GhVxQSNt/image.jpg)
Major Tom
I stand corrected, thanks.