Author Topic: Instability at high speed...  (Read 10430 times)

Offline estrasil

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Re: Instability at high speed...
« Reply #60 on: January 11, 2018, 07:05:59 pm »
Just because it is a big box, doesn't mean it is weighted incorrectly.
Would you have the same opinion if the box weighs 8 lbs and is empty? 
The vibration is always happening when the box is empty.  I only fill it with a motorcycle jacket once I get to work.
And I have a fairing, so I don't see wind slamming it being much of an issue...
Panniers are also empty.  And no passenger.  So should not have anything to do with weight.
I am sorry however I didn't post the picture early on. 

Offline RhodeTrip

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Re: Instability at high speed...
« Reply #61 on: January 11, 2018, 07:26:49 pm »
Nothing to do with how it s weighted; what do you think airflow over that thing will do at speed.  ::007::

Offline estrasil

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Re: Instability at high speed...
« Reply #62 on: January 11, 2018, 07:28:14 pm »
I think the windscreen really protects it even at speed.  I wouldn't stake my life on it, but then again once I get to 105mph it's fine again.

Offline WJBertrand

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Instability at high speed...
« Reply #63 on: January 11, 2018, 09:11:02 pm »
Yeah, my concern was aerodynamics not weight when I saw that photo. I don’t think the windscreen can ameliorate that.


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-Jeff-
Ventura, CA
2015 Yamaha Super Tenere ES
2005 Honda ST1300A

Offline estrasil

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Re: Instability at high speed...
« Reply #64 on: January 11, 2018, 09:32:56 pm »
If they can get away with this on a motorcycle, I should be able to have my 16 x 16 x 16 box.

Offline Dogdaze

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Re: Instability at high speed...
« Reply #65 on: January 12, 2018, 12:24:03 am »
If they can get away with this on a motorcycle, I should be able to have my 16 x 16 x 16 box.

That's a trike and they are probably maxing out at 30kph! Not 105 mph.  And of course you can have the coffin on the back of the bike, but don't then whine about instability issues that are caused by rider error.............
As I get older, I am no longer surprised at what I know, I'm surprised at how much I don't know.

Offline Checkswrecks

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Re: Instability at high speed...
« Reply #66 on: January 12, 2018, 10:22:08 am »
I've done 100+ on the Gen2 with the top box a number of times. With three boxes also.
Got the Gen1 to something like 117 mph loaded down when it had the side boxes and Givi 52L Maxiaa.
Never had an issue with either bike.


[Not admitting what State or States that may have been in.   ;)   ]
Damascus, MD
XTZ1200, KTM 690R

Offline RCinNC

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Re: Instability at high speed...
« Reply #67 on: January 12, 2018, 01:14:16 pm »
I think once you're talking about triple digit speeds, there are aerodynamic factors at play that aren't noticeable at lower speeds, and something as simple as the shape of your body can create issues with one guy that another guy doesn't experience.  Everyone's body is different, and just like boulders in a fast running stream, one guy is going to create different airflow and turbulence than another guy.  Our bodies, especially sitting upright on a bike, are most definitely NOT aerodynamically efficient; for that matter, neither are our bikes with their big square boxes.  One guy might experience buffeting and turbulence because of the size, shape and placement of a top case, where I could ride the same bike and not experience it at all.  The windscreens are designed as a compromise to move air up and over an average rider, but the designers can't account for every variable as far as rider size and shape, passenger size and shape, or size/shape/placement of every type of topcase out there.  All of our bodies create turbulent air behind us as we pass through it; it wouldn't surprise me at all if that dirty air was reacting poorly with a top case.  And, like a lot of aerodynamic issues, you could move that top case forward or back or up or down by a very small amount and find that the turbulence was abated. 

It doesn't surprise me at all that a large square top case would cause vibration and sketchy handling at high speed, any more than it wouldn't surprise me that another guy could ride the same bike and not experience the issue at all.
2014 Yamaha Super Tenere
2012 Suzuki DL650 (traded)
2004 HD Road King Custom (sold)
2000 Yamaha Road Star 1600 (traded)
1994 Yamaha Virago 1100 (traded)
1982 Honda V45 Sabre (traded)
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Offline WJBertrand

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Instability at high speed...
« Reply #68 on: January 12, 2018, 01:21:19 pm »
Agreed, it’s mostly about aerodynamics. My ST1300 feels a vaguely loose above about 60 MPH as soon as I mount the top box, even if it’s empty. If I put something on the pillion seat between me and the box, as small and light as a sleeping bag or all the way up to a 160 lb. passenger, the bike immediately feels stable again. I think the gap between the rider and the top box is really important aerodynamically. The taller the box the worst the effect.


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Ventura, CA
2015 Yamaha Super Tenere ES
2005 Honda ST1300A

Offline HeliMark

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Re: Instability at high speed...
« Reply #69 on: January 12, 2018, 01:48:15 pm »
By beefing up the box, you reduced the stress cracking, but not the overriding stress/vibration causing it. I would bet like has been said, the airflow is the primary cause. Somewhere in that sweet zone where you were getting that vibration, the way the air was getting disturbed by going around your windshield and you, that disturbed air was hitting the box. Stiffing it would not eliminate it, your box is tall enough (longer arm), that any vibrations from the top will have significantly more effect on the bike. The amount of stress from a top box just normal riding is pretty significant. I have a Jesse top box, and had to replace the mount due to stress cracking. Bags are generally not a problem that high, as they flex and do not transmit the vibration.

I bet if you cut that box in half, you would not have a problem.

I am sure a lot here remembers when the police departments in England went from the ST1100 to the ST1300 and had high speed stability problems. Supposed to have been caused by the light on the pole they have on the back.

Mark
« Last Edit: January 12, 2018, 01:51:57 pm by HeliMark »
2013 S10

Offline Juan

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Re: Instability at high speed...
« Reply #70 on: January 12, 2018, 02:11:48 pm »
The attached statistics with Givi V46 top box and 2 OEM side cases. No issues whatsoever.

Offline estrasil

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Re: Instability at high speed...
« Reply #71 on: January 12, 2018, 04:42:14 pm »
I just picked up the bike from the shop today.

Today on my ride I reached back at speed and tried holding the box various ways.  I could feel it vibrating and I could make it go away by pushing up hard on the box from the bottom, using the side seat handles to resist against.

I've ordered 4 McMaster-Carr vibration mounts, PN 9232K18.   I will try to install the box on those when they come in.

When I had it in the shop, they found a loose swing arm linkage bolt and missing washer.  They thought for sure that that would be the issue.  They also tried all sorts of things before we stumbled on the box being the issue.
The top of the front shocks is clamped about 3/8" above the clamp... they thought maybe that or the torque on the clamp bolts was it at one point.   And they tried various shock setting, both front and rear.

This vibration starts at 90mph as indicated on the speedometer.  That is about 84mph actual.  Speed limit on my commute is 65mph but the common speed at 10am is 80-85mph.  So if I want to keep up with the flow of traffic, I'm right in that zone.  I would rather be in the fast lane at common speed where I have some outs than buried in the middle lanes where I have threats from both sides and less outs. 

I had the box built on purpose to that size.  None of the commercially available boxes were roomy enough.  I see zillions of bikes and pictures of bikes with sleeping bags and stuff strapped on the back.  I just wanted all that stuff to fit in my luggage boxes and have nothing outside. 

I do a lot of ultralight backpacking, so when I go motorcycle camping with my girlfriend, the tent, sleeping bag, pads, cook gear all fit in the box.  All that gear weighs about 10lbs. 

You know how when you ride you can stick your hand out and immediately feel the force of the wind?   I reach my hand around anywhere behind the windscreen, even to the box and don't feel that pressure. 
I'm not ruling out aerodynamic effects...even though it goes away above 105mph indicated/99mph actual...

The Tacoma Narrows bridge fell apart due to wind effects, so I do get it, however maybe it hits a resonant frequency during those speeds due to some other dynamics.


Offline Sierra1

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Re: Instability at high speed...
« Reply #72 on: January 12, 2018, 06:05:04 pm »
I think once you're talking about triple digit speeds, there are aerodynamic factors at play that aren't noticeable at lower speeds, and something as simple as the shape of your body can create issues with one guy that another guy doesn't experience.


I was surprised to learn, years ago, that motorcycles are not as aerodynamic as one would think; even the sport bikes.  And, apparently there aren't very many cops around San Jose.  Between the traffic and the Troopers, ya' can't do 105m.p.h. around here for very long.
In the stable: Me-'17 TENERE ES & '86 FJ 1200; Wife-'01 TW 200; Son 1-'16 R6; Son 2-'14 FJR ES
Out to Pasture: '77 XS 360; '81 SECA 550; '00 KZ 1000P; '04 BMW 1150 RT-P; '11 ST1300PA; '11 KLR

Offline Cycledude

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Re: Instability at high speed...
« Reply #73 on: January 12, 2018, 10:20:13 pm »
Mine equipped with all the Yamaha luggage has shown 100-122 a bunch of times without any kind of vibration issues, I hope you have good luck getting things figured out.
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Offline Thrasherg

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Re: Instability at high speed...
« Reply #74 on: January 12, 2018, 11:13:30 pm »
I know a few years ago they discovered large vans would tip over due to high cross winds, it was found that if the edges of the van where rounded instead of right angles, the wind had a drastically reduced effect, that is why most modern vans now have rounded edges between the roof and any side panel. I notice your box is very square, I dont know if you have any way to round the edges on the top, but it might be worth a try, it might have quite an impact to how the air reacts and reduce your problem. Most after market top boxes are a lot more rounded than your box, so maybe that is why others with after market top boxes have not seen the same issue?

Just an idea..

Gary

 

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