Stiffy or fork flex

[mossrider]

Things appear to be plenty stiff in the front end but have a look at this;

There is 2" of minimum clearance between the bodywork and the front tire at rest. Bodywork can't move, it's fastened to the frame/motor.

Yet look at that tire rub on the fairing chin from hard braking. You can feel it flexing but it does so in a controlled manner. I would guess most of it comes from the forks but I can feel the frame/head stock moving too in the clip ons. 

Just thought this was interesting. 

 

 

 

[Pursuvant]

That contact patch, it's an oval. So does that means contact is made before forks are fully compressed and as the compress more/move under compression, they drag the patch upward into oval bite mark?! And the forks reach max compression leaving that perfect oval "top" to the bite mark?! Why isn't the bottom of that bite mark have more of a "streak" upward that opens into the oval ?!

Forks must be reaching max compression under braking first, then they complete the flexing to make contact, and that nice oval patch?!

From this pic angle it looks a little "un-possible" because suspension is resting/extended, that makes tire look impossibly far from contact. Maybe a direct side pic at axle height would let my mind understand that oval mark and why nothing above is affected/why not even a taller oval bite.

A lot of little things adding up to this? Raised forks, tire profile, quantum entanglement?

Is anything in that bodywork moving? Ok it's not, my mind wants to hop on the denial of reality train here...

Not sure I really want to know this, you're messing with my karma b4 my morning ride

Edited September 30, 2020 by Pursuvant

[stickshift]

Does the front tyre grow slightly in diameter at higher speeds? This might account for some if it?

Edited September 30, 2020 by stickshift

[Pursuvant]

That morning ride cleared my thoughts, all 3 of them.

Downloaded pic and zoomed in. It changes my ideas a bit, the shape isn't a perfect oval, it does start a little narrower at bottom and bite mark seems to drag upward while it was making contact.

Looks like it's been doing it for awhile? Looks like the contact is "additive"?

And those 2 partial outer rings that wore deeper an quick (one from about 7 to 11 on a clock face, the other starts even higher and from about 12 to 3)? Could you have been turning slightly when you bury those brakes, and maybe you brake harder on entering left turns than right? Or simply fiberglass is not shaped perfectly relative to tire? Wild guesses all, you could speculate endlessly.

There must be some serious forces involved here. How many Dunkin Donuts did you say you were carrying at the time? 

Edited September 30, 2020 by Pursuvant

[mossrider]

I prefer to think of any special forces I generate as a function of my speed more than of the mass carried inside my race suit. So I'll thank you not to refer to them as mere donuts but as traction enhancement from now on.

You're correct in that the fiberglass is not perfectly shaped nor equi-distant from the tire. The amount of flex varies dependant on the track layout. There is certainly some deflection on turn in as braking forces are released in favor of lean angle causing the rub to be ovoid as opposed to centered, and keep in mind the tire's contact patch is 3 dimensional, not flat making the rub truly odd shaped.

Remember all front ends flex, even Moto GP forks and frames are designed for a certain amount of controlled flex to aid turning, traction, braking and acceleration. 

Some more than others thank you Dunkin'.

[seven]

Slightly off topic, but I am always amazed at how much body panels move when I watch videos of cars at autocross. The first time I saw panel gaps almost disappear and then expand under the hard braking and cornering was shocking. You need some flex in a system, too rigid and things just break.

[Pursuvant]

I know flex it keeps lots of things from disaster, but I still get a funny feel watching that airplane wing bouncing in a storm.

A stock bike like MT-07, how much deflection in the fork tube under braking force (ignore lower leg, steering head, just tubes). Does a 41mm tube deflect a heavy 1/2"? An inch ? What's the practical reality here, when tubes are clamped / tree?

I've never heard anyone who knew say... Whatever it is, I sleep ok with it, never consider it, curious. Leads to another thought, is there any significant lateral deflection under turning? Just one more component force making up experienced "turn in" or insignificant relative to rake, wheelbase

Edited October 2, 2020 by Pursuvant
Clarify clamped

[DewMan]

1 hour ago, Pursuvant said:

 I still get a funny feel watching that airplane wing bouncing in a storm.

You ain't the only one. 

[shinyribs]

I vote Moss mounts a GoPro so we can watch this in action

[mossrider]

3 hours ago, shinyribs said:

I vote Moss mounts a GoPro so we can watch this in action

Now there's a thought...

[br4nd0n]

You have me curious as well and having video would be real beneficial to see what's actually going on. Good idea @shinyribs 

[mossrider]

We'll have to wait till next season now. While we're at the racetrack in Brainerd this weekend goofing off, we're not running my bike because it's loaded up and ready for the Indianapolis round of MotoAmerica next weekend. MotoAmerica does not allow camera's on track.