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 Front Wheel CASTER/WHEEL FLOP anomalies?

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SmileAtYourStomach




PostSubject: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 1:45 am

I've bought 3 folding bikes from DAHON over the past 20 years and only once did I encounter an issue regarding straight tracking of the front wheel, or caster/wheel flop.  The way I have always tested this is to ride the bike with "no-hands."   If there's something wrong with the forks, ie; been run into a wall or something, bent forks, etc., the bike will drift biasly either left or right - in my case this bike would aggressively FLOP either left or right making it not only impossible to ride "hands-free" but also I could feel the strong tendency for the steering to want to turn while holding and strong resistance to bring back to straight.  I tried to explain this to the bike shop and they argued with me saying 'you're not supposed to ride hands free.'  I ultimately had to contact DAHON and they got it a little better, sent a new bike to the shop problem solved - I was able to ride the bike hands-free at just about any speed.  There was definitely something wrong with the forks on the other bike.

This brings me to my brand-new WR250r.  I thought of it a little late (1 week later) and started to see how the bike feels hands free.  It pulls a little to the right!  Not real strong but I have to shift my body to keep it on track.  I've tested at different speeds, different surfaces and even out of gear but still.  I started to think ' is it just because the pipe is on the right?'  Nah, I'm sure they would have engineered this weight imbalance out a long time ago.

My question to you all is has anyone experience the same?  How does your bike ride hands-free?  Could this anomaly be possibly rectified with those independant fork adjustments?

Thanks!

From WIKIPEDIA:

WHEEL FLOP


Wheel flop refers to steering behavior in which a bicycle or motorcycle tends to turn more than expected due to the front wheel "flopping" over when the handlebars are rotated. Wheel flop is caused by the lowering of the front end of a bicycle or motorcycle as the handlebars are rotated away from the "straight ahead" position. This lowering phenomenon occurs according to the following equation:

Because wheel flop involves the lowering of the front end of a bicycle or motorcycle, the force due to gravity will tend to cause handlebar rotation to continue with increasing rotational velocity and without additional rider input on the handlebars. Once the handlebars are turned, the rider needs to apply torque to the handlebars to bring them back to the straight ahead position and bring the front end of the bicycle or motorcycle back up to the original height.[23] The rotational inertia of the front wheel will lessen the severity of the wheel flop effect because it results in opposing torque being required to initiate or accelerate changing the direction of the front wheel.

According to the equation listed above, increasing the trail and/or decreasing the head angle will increase the wheel flop factor on a bicycle or motorcycle, which will increase the torque required to bring the handlebars back to the straight ahead position and increase the vehicle's tendency to veer suddenly off the line of a curve. Also, increasing the weight borne by the front wheel of the vehicle, either by increasing the mass of the vehicle, rider and cargo or by changing the weight ratio to shift the center of mass forward, will increase the severity of the wheel flop effect. Increasing the rotational inertia of the front wheel by increasing the speed of the vehicle and the rotational speed of the wheel will tend to counter the wheel flop effect.

A certain amount of wheel flop is generally considered to be desirable. In the magazine Bicycle Quarterly, author Jan Heine wrote, "A bike with too little wheel flop will be sluggish in its reactions to handlebar inputs. A bike with too much wheel flop will tend to veer off its line at low and moderate speeds."[22]

22.  Heine, Jan. "Bicycle Quarterly -- Glossary". Vintage Bicycle Press. Archived from the original on 21 May 2010. Retrieved 3 June 2010.
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23.  Foale, Tony (2002). Motorcycle Handling and Chassis Design. Tony Foale Designs. pp. 3–11. ISBN 84-933286-1-8. Retrieved 3 June 2010.
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blusmoke




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 3:38 am

See if both forks are the same height in the triple clamp.

My forks were uneven by a little less than a half inch, though I did not notice any odd behavior and lol I did manage to try coasting hands free on my test ride wink .

Its always a great Idea to go over every single little thing after any vehicle purchase.

Also it could just be the symmetry of the wr250r/x, There are multiple cables, wires, and a hydraulic line all pulling on the bars. Plus there is a lot of weight on the right side including but not limited to a heavy exhaust, radiator/fan, and everything under that engine case like the clutch and water pump.
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SmileAtYourStomach




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 4:11 am

blusmoke wrote:
See if both forks are the same height in the triple clamp.

My forks were uneven by a little less than a half inch, though I did not notice any odd behavior and lol I did manage to try coasting hands free on my test ride wink .

Its always a great Idea to go over every single little thing after any vehicle purchase.

Also it could just be the symmetry of the wr250r/x, There are multiple cables, wires, and a hydraulic line all pulling on the bars. Plus there is a lot of weight on the right side including but not limited to a heavy exhaust, radiator/fan, and everything under that engine case like the clutch and water pump.

I did look at the settings at the top of the forks and they're both set the same. Perhaps one nut-flat incremental adjustments at a time to test but which side, eh? Yes, I forgot about the radiator also being on the right side. So your's rides dead straight no hands yah?
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waltermitty




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 5:20 am

Couple of things to check:

Forks can be misaligned, twisted in triple clamp. To check this you can lay a surface plate across the fork tubes below the lower triple clamp. A piece of 3/8" plate glass 4"x12" will work.

Rear wheel can be misaligned. Check that the axle alignment mark is the same on both sides. You can also get more accurate by using the string method to align with front wheel.
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blusmoke




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 6:05 am

I was wondering about the height/alignment of the forks in the triple clamp like in the picture. When I got mine home I noticed one of the forks was clamped nearly half an inch higher than the other, I then reset them both to some acceptable amount of an inch,measuring just the gold part of the fork because I'm short. Then I think there is a part of the process about undoing the axle and spinning the wheel then hitting the brakes while your tightening the forks or something to make sure the forks are not binding.



As for straightness I don't experience enough of a tendency then or now towards any side really its just as likely to "flop" towards either side but the bike does feel heavier to me on the right and that might be the pull you feel when you were, "shifting your weight." how does it feel at higher speeds, better or worse?

The rear wheel is great place to start I could really imagine that kinda steering the bike.
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YZEtc

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PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 7:16 am

Could be due to the crown of the road (road, itself, is not flat but curved for water drainage).
If I let go of the handlebar on practically any bike I've had, this could happen.
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rarepartbuilder

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PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 12:28 pm

with the speed things are rammed together these days.. maybe the swing arm pivot bore is not perpendicular to the bore of the main triple tree /steering head . lurk

there is no end to how far one would  could reach for "out of  tolerance" accumulation ...
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4play

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PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 2:10 pm

YZEtc wrote:
Could be due to the crown of the road (road, itself, is not flat but curved for water drainage).
If I let go of the handlebar on practically any bike I've had, this could happen.

Plus 1
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SmileAtYourStomach




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 2:32 pm

Wow, thanks guys, these are all excellent places to start. Good to know there are a number of adjustable aspects of this bike.
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Old Blue




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 3:24 pm

I would start with the front end first.  The bike comes shipped with the forks, handlebars and front wheel disassembled.  Could be the forks were twisted while being assembled at the dealer.  I found on my bike that some of the triple tree clamps were loose.
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zestymac

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PostSubject: Flip flop   Mon Mar 09, 2015 3:35 pm

EZ fix. Just run a set of trials tires. Much squarer shape than oem and then it's hello hands free motoring...
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SmileAtYourStomach




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 3:38 pm

Old Blue wrote:
I would start with the front end first.  The bike comes shipped with the forks, handlebars and front wheel disassembled.  Could be the forks were twisted while being assembled at the dealer.  I found on my bike that some of the triple tree clamps were loose.

Makes a lot of sense. By "twisted," how do you mean? How many check points are on the forks to inspect?
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SmileAtYourStomach




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 3:41 pm

Okay I just found this good thread here I will look into:  help"Suspension Setup Help"
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Old Blue




PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 5:09 pm

What I meant by twisted is like on a pedal bike when the handle bars are pointing in a different direction than the front wheel.  This can happen on a MC as well in a fall, especially if the triple clamp bolts are not torqued to spec.  Even if the bolts are properly torqued, it can still twist if the fall is hard enough.  The link you referred to is great for setting the compression and rebound on the forks and maybe you will find that they are not set the same on each side. I think you have to turn them all the way in till they "lightly" seat, then back them out to the desired setting.
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TwoBuells

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PostSubject: Re: Front Wheel CASTER/WHEEL FLOP anomalies?    Mon Mar 09, 2015 7:33 pm

YZEtc wrote:
Could be due to the crown of the road (road, itself, is not flat but curved for water drainage).
If I let go of the handlebar on practically any bike I've had, this could happen.

classic lurk
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