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Kawasaki Jimbo
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PostPosted: 20:24 - 06 Nov 2019    Post subject: Weighing a bike. Reply with quote
If you wanted to weigh your bike, how would you go about it?

Asking because the three bikes I've owned have all allegedly weighed 170-180kg and that's enough for me. I'm aware that manufacturers fudged their figures back in the day, so perhaps modern bikes aren't really as heavy as they sound?
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Sister Sledge
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PostPosted: 20:34 - 06 Nov 2019    Post subject: Reply with quote
I suppose the easy way would be bathroom scales? Under one wheel then the other and add together?
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P.
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PostPosted: 20:42 - 06 Nov 2019    Post subject: Reply with quote
With or without fluids.

They will probably weigh them dry. I'd say add 10kg, then 1kg for every litre of fuel.
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RhynoCZ
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PostPosted: 20:49 - 06 Nov 2019    Post subject: Reply with quote
Paddy. wrote:
With or without fluids.

They will probably weigh them dry. I'd say add 10kg, then 1kg for every litre of fuel.

U2?
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yen_powell
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PostPosted: 21:19 - 06 Nov 2019    Post subject: Reply with quote
Go and find a scrap yard with a weighbridge and ask them to tell you.
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Kawasaki Jimbo
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PostPosted: 21:25 - 06 Nov 2019    Post subject: Reply with quote
yen_powell wrote:
Go and find a scrap yard with a weighbridge and ask them to tell you.

I thought about weigh-bridges but wondered how accurate they are at the relatively low weights of a bike.

Sister Sledge wrote:
bathroom scales? Under one wheel then the other and add together.

Again, is that accurate?
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chickenstrip
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PostPosted: 21:32 - 06 Nov 2019    Post subject: Reply with quote
Kawasaki Jimbo wrote:


Sister Sledge wrote:
bathroom scales? Under one wheel then the other and add together.

Again, is that accurate?


No, because it misses the middle bit.
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Kawasaki Jimbo
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PostPosted: 21:41 - 06 Nov 2019    Post subject: Reply with quote
chickenstrip wrote:
Kawasaki Jimbo wrote:


Sister Sledge wrote:
bathroom scales? Under one wheel then the other and add together.

Again, is that accurate?


No, because it misses the middle bit.

Could be true if weight distribution isn't 50:50.
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stinkwheel
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PostPosted: 21:58 - 06 Nov 2019    Post subject: Reply with quote
Kawasaki Jimbo wrote:

Could be true if weight distribution isn't 50:50.


All the weight is pushing down on the wheels so if you measure how hard the wheels are pushing down, you'll get the weight.

If it's a 100kg bike with 60:40 weight distribution, you'll measure 60kg on one wheel and 40kg on the other.
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doggone
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PostPosted: 22:04 - 06 Nov 2019    Post subject: Reply with quote
If you had two bathroom scales at the same time it would be accurate, with only one you'd have to make both ends level when on the scale or a triangle in the middle would be missed.
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xX-Alex-Xx
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PostPosted: 22:06 - 06 Nov 2019    Post subject: Reply with quote
Set of scales maybe? Put front wheel on and measure. Put back wheel on and measure. Add them up.
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Kawasaki Jimbo
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PostPosted: 22:08 - 06 Nov 2019    Post subject: Reply with quote
stinkwheel wrote:
Kawasaki Jimbo wrote:

Could be true if weight distribution isn't 50:50.


All the weight is pushing down on the wheels so if you measure how hard the wheels are pushing down, you'll get the weight.

If it's a 100kg bike with 60:40 weight distribution, you'll measure 60kg on one wheel and 40kg on the other.

But given only one bathroom scales and a bike with a 60:40 weight distribution, would weighing the front and then the back be an accurate summation?
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chickenstrip
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PostPosted: 23:48 - 06 Nov 2019    Post subject: Reply with quote
Why not strip it down to individual parts, then weigh each one? Winter hobby Very Happy
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Nobby the Bastard
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PostPosted: 23:52 - 06 Nov 2019    Post subject: Reply with quote
stinkwheel wrote:
Kawasaki Jimbo wrote:

Could be true if weight distribution isn't 50:50.


All the weight is pushing down on the wheels so if you measure how hard the wheels are pushing down, you'll get the weight.

If it's a 100kg bike with 60:40 weight distribution, you'll measure 60kg on one wheel and 40kg on the other.


Provided that you get the Wheel bottoms horizontal.
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G
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PostPosted: 23:59 - 06 Nov 2019    Post subject: Reply with quote
Bathroom scales with a block under the other wheel; as above.

I've got some parcel scales that do up to 180kg or so with a remote display, which as it goes I do use as bathroom scales (no, not for the max weight!)... have used them in the same way; phone book or wood etc under the other end. Remote display makes it slightly easier (and it has a 'hold' function too.)
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Sister Sledge
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PostPosted: 08:19 - 07 Nov 2019    Post subject: Reply with quote
Wait until you see VOSA doing checks on HGV axle weights and slip the bike on..

Best and most accurate way is two sets of scales as doggone states: one will miss a relatively small triangular section of the mass and will throw the true weight out by a few kg.
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bugeye_bob
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PostPosted: 08:59 - 07 Nov 2019    Post subject: Reply with quote
Google make and model specs?
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UnknownStuntm...
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PostPosted: 10:36 - 07 Nov 2019    Post subject: Reply with quote
G wrote:
Bathroom scales with a block under the other wheel; as above.

I is disappoint. So many replies before the right one.
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steve the grease
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PostPosted: 11:34 - 07 Nov 2019    Post subject: Reply with quote
I popped to our local quarry and asked to stick it on their weighbridge. 180kg wet with tool roll. Offered the guy a couple of quid , but he wasn't bothered. Asking politely always helps too.
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Sister Sledge
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PostPosted: 17:26 - 07 Nov 2019    Post subject: Reply with quote
Jump on it, ride it around fast and shout "wehey" (weigh?).
I'll get my coat..
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stinkwheel
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PostPosted: 17:56 - 07 Nov 2019    Post subject: Reply with quote
Nobby the Bastard wrote:


Provided that you get the Wheel bottoms horizontal.


I doubt it makes much difference because the angle is so slight. But let's do some maths? (I'll stress my trig

So googling a CBR600RR. It's 192kg wet. and 50.5:49.5 Front to back. So pretty much equal. Say 96kg per wheel

1370mm wheelbase.

So assuming our scales are 100mm high we land up with the bike at an angle of 6.5 degrees. As we approach 180 degrees, weight transfer approaches 100%. 6.5 is 3.6% of 180. So it would weigh 3.5kg less.

Ok, more than I thought.
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Stalk
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PostPosted: 20:12 - 07 Nov 2019    Post subject: Reply with quote
stinkwheel wrote:
As we approach 180 degrees,
.


Should that be 90 degrees? 180 and the bike is on its seat and bars?
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yen_powell
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PostPosted: 08:42 - 08 Nov 2019    Post subject: Reply with quote
Kawasaki Jimbo wrote:

I thought about weigh-bridges but wondered how accurate they are at the relatively low weights of a bike.

When I worked in a scrap yard we got a couple of unnanounced visits from weights and measures. A big lorry hove into view with lots of weights on the back and they proceeded to check our weighbridge at various weight ranges before giving us a receipt for the accuracy and vanishing again.

I once visited a mate who was working as a security guard at some battery place and he was on the gate with the weighbridge on a quiet weekend. I put my FJ1200 onto it and he said it was about 295Kg or similar. I used to proudly boast it was a third of a ton that I was holding up with my skinny legs.
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weasley
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PostPosted: 10:10 - 08 Nov 2019    Post subject: Reply with quote
stinkwheel wrote:
It's 192kg wet. and 50.5:49.5 Front to back. So pretty much equal. Say 96kg per wheel

1370mm wheelbase.

So assuming our scales are 100mm high we land up with the bike at an angle of 6.5 degrees. As we approach 180 degrees, weight transfer approaches 100%. 6.5 is 3.6% of 180. So it would weigh 3.5kg less.

Ok, more than I thought.


And me, so I did some maths too. First off I believe a 100mm rise will create a 4.2° angle:

Code:
sinϴ = (100/1370)
ϴ = sin-1(100/1370) = 4.186°


Next, the change of weight with angle will not be linear (which a % calculation will give you). It'll be sinusoidal. I believe that the relationship will be cosϴ × the nominal weight.

Code:
cos(4.186) = 0.997


So I surmise that the measured weight will be 0.3% off of the actual weight.

Of course all this goes away if you put a 100mm block of wood under the wheel not being measured. And all of this requires you to balance the bike without affecting the weight.
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Old Thread Alert!

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