Do hard cases cause instability?

[AZPI]

At the same time I installed the Shinko 804/805 I installed SKB hard cases on SW Motech racks. The bike was noticeably tipsy and I assumed the tires just need 100 miles or so. Well 150 miles came and went and the instability was still there so on the advice of a coworker I removed the cases....it was a clear improvement and the tipsy had virtually disappeared.

My question is is this common with hard cases?

Is it the aerodynamics that causes the feeling of instability or is it the weight? I had very little weight and well balanced between cases.

Is this just a "feeling" of instability or is the bike actually less stable? Thanks in advance.

 

[scott123007]

Instability is such a broad word it is hard to determine what exactly you mean. Shinko's, especially the 705's, but the 804 and 805's also, are "twitchier" than other tires, especially when they are first installed. They react more to inputs and feel tipsy, but are a great handling tire both on and off road. DO NOT inflate them to the owners manual recommended pressures. Not that they will explode or anything like that, but there is no advantage in doing so. Over inflating "could" be a cause for instability at higher speeds because they are designed to run with a maximum of 33 psi, both front and rear.
I have never noticed much of a difference with or without side cases, but many manufacturers warn of excessive speeds with cases on, and high speed instability is probably why.

 

[Checkswrecks]

There are one or two threads in which people talk about TOP cases and debate whether they cause issues, but I can't think of any concerning side boxes. If you did an ON-OFF-ON-OFF test and they made a difference, then I guess the answer is that there is an issue for your bike with at least those tires.


Tires are basically pneumatic and rubber springs, so they can lead to interactions with suspension, airflow, and rider inputs differently on different bikes of the same model. Not common but possible.

 

[AZPI]

Instability is such a broad word it is hard to determine what exactly you mean. Shinko's, especially the 705's, but the 804 and 805's also, are "twitchier" than other tires, especially when they are first installed. They react more to inputs and feel tipsy, but are a great handling tire both on and off road. DO NOT inflate them to the owners manual recommended pressures. Not that they will explode or anything like that, but there is no advantage in doing so. Over inflating "could" be a cause for instability at higher speeds because they are designed to run with a maximum of 33 psi, both front and rear.
I have never noticed much of a difference with or without side cases, but many manufacturers warn of excessive speeds with cases on, and high speed instability is probably why.

Thanks! I have both front and rear at 33psi cold. Yeah, I understand now that instability is a broad term, your use of "twitchy" is definitely a better descriptor. Mine was a top heavy side to side twitchiness type feeling.

 

[RhodeTrip]

I would take the pressure up to 38psi and see if there is any change.
Jim

 

[Sierra1]

Another question is at what speed did it feel twitchy? Aerodynamics will only come into play as speed increases. If it's twitchy as soon as you start moving, it HAS to be the tires. I think every OE equipped side bag I've seen have warnings of not exceeding 80ish mph with the bags attached. ) Yeah, like THAT'S not going to happen. ::26::

 

[AZPI]

I would take the pressure up to 38psi and see if there is any change.
Jim

Thanks Jim. May I ask the logic behind increasing the pressure?

 

[AZPI]

Another question is at what speed did it feel twitchy? Aerodynamics will only come into play as speed increases. If it's twitchy as soon as you start moving, it HAS to be the tires. I think every OE equipped side bag I've seen have warnings of not exceeding 80ish mph with the bags attached. ) Yeah, like THAT'S not going to happen. ::26::

I believe my exact speed when I noticed the twitchiness was 68mph. And right up to that moment I remember thinking "wow these tires feel great." Then I adjusted my body weight and and felt the twitchiness. Today I removed the cases and hit 73mph for a mile or so, little to no twitch.

I realize I'm answering my own question, I guess I'm disappointed the cases feel this way. I was really looking forward to loving them. I guess I'll just have to adjust to the feeling and do some experimenting with maneuvering to identify the true level of instability.

 

[Checkswrecks]

Like I wrote earlier, a tire is a spring. Before you give up, do like the others wrote and simply run up the pressure. It will stiffen the spring and change the dynamics.

 

[bob dirt]

I doubt if it's the panniers. I over stuff mine on longer rides with enough tools to build a new bike and it never rode any different than with them off. The only time I had a twitchy bike is when I changed tire brands. I quickly got used to them or they "broke in". You need to put some miles on it with it loaded up.

 

[Propsoto]

I've never felt the top or side cases are a major problem with handling. But I do notice every time I put on new tires, my bike is "twitchy". It feels like it dives into corners. I always assumed my old tires were worn kind of flat. Either it goes away, or I don't notice it after a few days.

 

[bnschroder]

Could the racks or cases not be 100% tightly fit to the bike. They are after all after market and from 2 different manufacturers.
I have Pelican cases, so a very similar setup, but mine are on Hepco Becker racks and nothing twitches.


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[AZPI]

Like I wrote earlier, a tire is a spring. Before you give up, do like the others wrote and simply run up the pressure. It will stiffen the spring and change the dynamics.

Ok I will try that. Thank you!

 

[RhodeTrip]

Thanks Jim. May I ask the logic behind increasing the pressure?

If the side walls are non-rigid, low air will result in significant flex.
Jim

 

[old1959]

I hit 89mph today with mine and didn't notice any instability compared to before I installed the cases.

 

[RCinNC]

I hit 89mph today with mine and didn't notice any instability compared to before I installed the cases.

Your right side case is bigger than my first apartment.

 

[Topcop45]

I’ve maxed my bike out at an indicated 131 MPH with 10inch Jesse’s including the top case. I also run 705 Shinkos front and rear at 35 PSI. It was rock solid. Awesome bike

 

[Madhatter]

tire pressure the first and most important item to affect your motorcycles handling . weight distribution or balance can effect handling in a dramatic way ( what you have in those panniers ) . suspension preload is another factor that alters the handling dynamics . weather conditions ,say lots of wind to push you around . and if I may add , what's the point of extreme high speed all loaded down with boxes , they sell hayabusas for that ( just curious ) . the type of tire you run also can change handling (feel for sure ) dynamics . my suggestion is slow down and enjoy the ride. or not..... I have toura tech hanging off my bike , no issues except for previous factors listed......

 

[Buelligan]

I've never experienced any handling issues with my Jesse bags installed, the Tenere is rock solid. I would check tire pressure, and wear.

 

[old1959]

RCinNC, you are correct about the 46 liter case being huge. You're comment had me laughing. I'm still debating about getting a 33 liter case for the right side; wish Givi made a Trekker case between the 33 and the 46.