Stability, rucksacs, weight & science

So today my morning cycle started with a rucksac weight of 11.1kg, I weigh 79.2kg, that's almost 15% more, high-up on my back - the wrong place for stability.

How heavy, is too heavy, when it's a rucksac....?

And, for the physics/maths gurus'... is there any science that could help with a definitive answer?

I have to say, I always preferred having the weight on my back, and stuck to my back. When I have a messenger bag I find I have to compromise my balance on the bike to balance it on my shoulder, and don't get me started on what panniers do to a ride!

I ride with a Berghaus Freeflow 50L fairly heavily packed every day.

Contains work (lots of files), tools and tubes, 3 days of clothes and on the way home - shopping.

It's probably ruining me but like citygent, I've always perceived it to be more comfortable and a more 'balanced' ride than with a courier bag or panniers.

I have toured lightly with the same set-up as well but wouldn't relish doing it again. I'd love to get a set-up like Scotts narrow touring kit from the camping thread but until then, a 15 mile each way commute with a backpack is just fine.

and don't get me started on what panniers do to a ride!

they make it slower and less sweaty and more work on hills (weight is on the bike). the only weird balance thing i find is when i tilt the bike a little to swing my leg over to get on. if its loaded heavy then it feels like it wants to tip. oh and same when you lean the bike against a wall. i love panniers and if had a commute i'd use them everyday for it.

bags are great in the winter though, they help keep you warm.

as for the maths bit... N+1...thats all i know.

3 days of clothes, every day? what do you do with it all?

give them to the naked.

It's expensive but makes me feel fucking warm inside.

ah. how very kind of you.

I find I can usually get by with just a change of underwear..... ;-)

Bearing in mind, three days of clothing for me is basically a spare t shirt and socks. Maybe a thong.
But I often have to go away at short notice so it's good to be prepared.

I find with a decent pair of CK's, you can always turn them inside out and get a couple more days of wear in an emergency.

i've been trying to guess what your job is... i think its more fun guessing than knowing.

Spy.

Shit. There goes my confidentiality clause no-claims bonus.

Being a peeping tom isn't the same as being a spy.

I should know.

How heavy, is too heavy, when it's a rucksac....?

If you can't get on your bike without falling off, it's too heavy.

How heavy, is too heavy, when it's a rucksac....?

I'd hypothesize that an expectable weight of a backpack is proportional to the inverse of the time or length of journey spent wearing the backpack.

I would say anything over 15kg - get a trailer
Otherwise if its for a journey of <1hr I would go with courier bag - I cant stand the lack of visibility and discomfort of cycling with a big rucksack - proper rucksacks are designed to support 80% of your weight on your hips rather than your shoulders and consequently dont work very well when in a cycling position (bent too far forward). Thus I find having weight high up on my shoulder blades much more comfortable.
Anything over 1hr I would go with (big - ie carradice) saddle bag followed by panniers for lighter bulkier items.
You want to keep the weight as close to the center of the bike when using bike mounted luggage, as it affects the handling a lot less - this is why I prefer big saddle bags as you can get loads of heavy stuff in between the wheels - rather than centered on them.
Fully loaded tourer wobble is SCARY when carrying big loads - the big starts to pendulum back and forth and the more you fight it the worse it gets.

Spy.

you need a thong for this?

a peeping tom

a thong makes more sense here..

Spies need thongs; commandos don't.

Spies need thongs; commandos don't.

this isn't the movies you know. come, get real. Everyone needs thongs now and again.

this isn't the movies you know. come, get real. Everyone needs thongs now and again.

When your heart ith filled with thorrow,
Thing a little thong.

Thats heavy to cycle with. You should get panniers.

For walking with a rucsac, the bulk of the weight should be as high up as possible, and as near to your back as possible, so that the weight is balanced over your centre of gravity.