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Do anyone else have concerns that, after a full day of riding, an hour after parking you'll feel the need to ride again?
 

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Discussion Starter #63
Well, this picture turned me off on the AK550. Great review of power, handling and electronics but made for the Asian market. Looks a little cramp for tall riders.
 

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Good eye Uncle, sort of a Squatty Potty seating position. He seems perched atop the seat vs inside the “comfort cabin” of the B650. No forward “kick-back’ foot rests. His knees and the upper fairing protrusion looks like a major pain waiting to happen.
 
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Well, this picture turned me off on the AK550. Great review of power, handling and electronics but made for the Asian market. Looks a little cramp for tall riders.
Look at that coilover position with just one person on the bike 🤭. It’s almost dead sideways. It’s almost 90 degrees from the swing arm movement direction. That makes for poor bump control. Definitely an aesthetics over function decision. Think I’ll keep the Burger and buy parts for it as needed.
 

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Look at that coilover position with just one person on the bike 🤭. It’s almost dead sideways. It’s almost 90 degrees from the swing arm movement direction. That makes for poor bump control. Definitely an aesthetics over function decision.
I built a vehicle for myself with horizontal springs and dampers front and back (to give a super low profile) and didn’t have any bump control issues. Went +/- from horizontal between loaded/unloaded and super comfy ride.

I also did some work on a hub centre steering bike design with a near horizontal damper that static sag took to roughly horizontal.

Riders legs do look cramped (some bike riders like to have their feet under them rather than forward, I can’t tell if he’s got the butt stop full forward? Has 3 or 4 inch)
 

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The best bump and rebound control of a wheel is when your coil over assembly is at as close to a 1:1 motion ratio. Unless you design in mechanical pivot points, like say, in an F1 front end for example, your motion ratio will be far less than 1, and will require a stiffer spring, and higher shock damping. Unless I’m missing something from this photo, I don’t see a pivot, and it appears the coil over is probably achieving somewhere between a .3 -.5 :1 ratio. It’s just physics, that the shock rod won’t travel as far, or fast because of this, thus can’t precisely dampen small suspension movements as well as if it was closer to 1:1.
 

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I still think in the "Moment of Arc" of that shock and spring, it will give a good spring rate past level. As the shocks pivot points are not in the same plain as the swing arm. See the frame cut away below. The frame mount is higher than the swing arm mount. Swing arm's do not go up and down, they swing in an arc and as it goes up it closes the gap between the two mounting points in a near linear fashion.

AK550_Frame-762x456.jpg
 
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In the case of the Burgman 400, they had to do a lever to get the shock plain of angle different from the shock's angle.

For the AK550, here is the plains of the two. The swing angles of A-B and A-D are the same as A is pivot locked and can not move. But as D arc swings up it goes froward too and the distance from C-D gets shorter. C-D distance will continue to get shorter until the A-D angle gets to 90 degrees and goes over center.

Trig hurts my head.

Bikereview-2019-Kymco-AK550-071-1024x683.jpg
 

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Hmm, we are translating car characteristics to bikes and it doesn’t always work (eg bike has 2 front shocks and only one rear and messes up any car spring type calculation)

I do understand the kinematics and while a standard damper does work better at high velocities it is not unusual to have motion ratios less than 1:1 (take a look at R1, Sv650 etc shocks). Obviously that means a different spring rate and preload.

The rate isn’t quite linear as we are talking about arcs, but I see Dave just posted on that while I’m typing.
 

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Hmm, we are translating car characteristics to bikes and it doesn’t always work (eg bike has 2 front shocks and only one rear and messes up any car spring type calculation)

I do understand the kinematics and while a standard damper does work better at high velocities it is not unusual to have motion ratios less than 1:1 (take a look at R1, Sv650 etc shocks). Obviously that means a different spring rate and preload.

The rate isn’t quite linear as we are talking about arcs, but I see Dave just posted on that while I’m typing.
True, when a cars left rear wheel gets lifted in a bump it trys to compress the right front but due to weight and the right rear countering this pivoting it is suppressed. We combat this on reverse trikes a lot.

On a two wheel when the rear wheel is lifted in a bump it will try to compress the front springs due to the rider and bikes frame weight causing a pivot point. Very complex math involved.
 

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In the case of the Burgman 400, they had to do a lever to get the shock plain of angle different from the shock's angle.

For the AK550, here is the plains of the two. The swing angles of A-B and A-D are the same as A is pivot locked and can not move. But as D arc swings up it goes froward too and the distance from C-D gets shorter. C-D distance will continue to get shorter until the A-D angle gets to 90 degrees and goes over center.

Trig hurts my head.

View attachment 92168

Yeh, after looking more closely at it- good job with the cg link arms- I can see the motion ratio isn’t as bad as I first thought when I gave it a quick glance.

Still think I’m one and done with Kymco though
 

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Motorcycles are limited on space and weight compared to cars so smaller shocks have ab advantage, ie motion ratios less than 1:1

Linkages do often take advantage of levers (or double levers like the pro-link where the maths really fries your noodle) but the ratio of shock travel is still well below 1:1 (I’ve seen 0.5:1 on sportsbikes and big BMWs)

There are also direct (no linkage) suspensions where the spring is close to the centre of the bike (KTM) where the swing arm moves far less than the axle and scooters where the shock is beyond the axle takin the ratio beyond 1:1 in the opposite direction

(steeply angled shocks also give a maths headache).
 

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Oops, missed off the reason for my last post -
On a scooter the suspension can cut into the underseat storage so their is a very practicle reason to rearrange it at the drawing board stage.
 

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you are able to extend your feet on the ak. not like the b400. its a bit smaller than 2007+ b400 body wise. the seat and rears widest area is wider on the b400. but the ramp on the b400 is much much better implemented for comfort. there isnt a height jump like it has on the ak.
its a good bike the ak. its not meant for comfort. it has some convenience of a scooter but mostly for performance. the burgmans offer more all around. they have good performance and tons of comfort and convenience.

but I cant understand these designers and engineers who cant make it a tad larger for storage and longer for a more variable seating position at least for the driver. yes they want faster steering but sheesh, youre already in the middle between motorcycle and touring scooter. just add some comfort.

and whats so hard to implement fold down foot rests over pegs? I can tell you that they are not comfortable. instead of swing out, make them fold down from the body.
 
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