David Jenkins
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| posted on 12/5/06 at 08:49 PM |
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Weighed at last!
I finally got round to getting my car weighed today, at my local weighbridge - I've been driving it for over a year and a half!
Considering that it's a standard chassis with a car engine, steel floor, and no special effort to keep it light, I was very pleased that it came
out at 600kg ( +/- 20kg) with a half-tank of petrol.
David.
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Surrey Dave
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| posted on 12/5/06 at 08:52 PM |
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What was the axle weight at SVA ? , does that not relate to the total weight?
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iank
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| posted on 12/5/06 at 09:48 PM |
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quote:
Originally posted by Surrey Dave
What was the axle weight at SVA ? , does that not relate to the total weight?
Not by simply adding them no, if you do that I think the weight comes out rather lower than actual weight.
I think if you could figure out the exact COG of the car you could theoretically work it out with lots of trig and simultaneous equations, but
practically speaking it's far easier to go the the weighbridge.
600kg sounds a good weight for a CEC.
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welderman
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| posted on 12/5/06 at 09:49 PM |
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Bloody strange that, had my MK Blade on the scales today too. 500 kg +/- 20kg, full tank of fuel.
Strange that eh!.
Thank's, Joe 
I don't stalk people
http://www.locostbuilders.co.uk/forum/23/viewthread.php?tid=172301
Back on with the Fisher Fury R1
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flak monkey
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| posted on 12/5/06 at 10:29 PM |
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quote:
Originally posted by iank
I think if you could figure out the exact COG of the car you could theoretically work it out with lots of trig and simultaneous equations, but
practically speaking it's far easier to go the the weighbridge.
600kg sounds a good weight for a CEC.
All you need is the location of the CoG between the axles. Then its just moments. Pretty simple stuff, but most people wont know where the CoG
lies.
Weights are around what I would expect, some of the weights quoted recently in another thread worried me somewhat!
Sera
http://www.motosera.com
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iank
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| posted on 12/5/06 at 10:52 PM |
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quote:
Originally posted by flak monkey
quote:
Originally posted by iank
I think if you could figure out the exact COG of the car you could theoretically work it out with lots of trig and simultaneous equations, but
practically speaking it's far easier to go the the weighbridge.
600kg sounds a good weight for a CEC.
All you need is the location of the CoG between the axles. Then its just moments. Pretty simple stuff, but most people wont know where the CoG
lies.
Weights are around what I would expect, some of the weights quoted recently in another thread worried me somewhat!
Yep, knowing the CoG is the hard bit. Doing moments would probably tax this old brain for a while, not done any significant maths since I left school
Were the weights too high or too low? I suspect a lot of people just add the axle weights.
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MikeRJ
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| posted on 12/5/06 at 11:42 PM |
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Adding the axle weights should give the total car weight unless they were not measured properly (e.g. car not perfectly horizontal when measured).
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DaveFJ
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| posted on 13/5/06 at 07:51 AM |
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The total of the axle weights will give all up weight. from the two axle weights you can calculate the CofG easily (longitudinaly anyway). If you want
lateral Cofg you need the weights at all 4 wheels.
Dave
"In Support of Help the Heroes" - Always
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DaveFJ
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| posted on 13/5/06 at 08:00 AM |
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to calculate CofG just remember
Wt =W2+W1
measuring from W1 you ignore the weight at W1....
therefore
a x WT = (a + b) x W2
as you know what a+b equals and what Wt, and W2 are you can solve for a and thus b as well....
 
Description
Dave
"In Support of Help the Heroes" - Always
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flak monkey
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| posted on 13/5/06 at 08:49 AM |
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Total of the weights at SVA will give you a weight less than that of the whole car. i believe they are measured seperately so...
The car can be modelled as a beam. The CoG being the load, one axle being a pivot point, the other being the force measurement point.
The load is not directly above the point where the force measurement is being taken so moments come in to play, which as far as i can see will always
reduce the total weight of the car.
Theres a bit about it in the SVA manual IIRC laid out slightly differently though.
Of course if both axle weights are measured at the same time then the total weight is that of the car.
Sera
http://www.motosera.com
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Dave Ashurst
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| posted on 13/5/06 at 08:54 AM |
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So how does the axle weighing machine know whether the other end of the car is on a set of scales or not?
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flak monkey
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| posted on 13/5/06 at 09:04 AM |
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Actually it doesnt make the slightest bit of bloody difference does it? The sum of the reaction forces at each wheel will always equal the total
weight of the car.
Jeez you can tell I havent done any real maths for 2 years.
Sera
http://www.motosera.com
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David Jenkins
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| posted on 13/5/06 at 12:10 PM |
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quote:
Originally posted by welderman
Bloody strange that, had my MK Blade on the scales today too. 500 kg +/- 20kg, full tank of fuel.
Strange that eh!.
When I typed my meggase I just KNEW that some BEC builder would under-cut me by a mile! 
I don't care... I'm happy with my result!
BTW: At my SVA the design weight was listed as 800kg on the forms - 350kg axle 1, 450kg axle 2.
David
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welderman
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| posted on 13/5/06 at 10:51 PM |
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quote:
Originally posted by David Jenkins
quote:
Originally posted by welderman
Bloody strange that, had my MK Blade on the scales today too. 500 kg +/- 20kg, full tank of fuel.
Strange that eh!.
When I typed my meggase I just KNEW that some BEC builder would under-cut me by a mile!
I don't care... I'm happy with my result!
BTW: At my SVA the design weight was listed as 800kg on the forms - 350kg axle 1, 450kg axle 2.
David
No offence there, i meant that it was strange we both had ours done.
Joe
Thank's, Joe
I don't stalk people
http://www.locostbuilders.co.uk/forum/23/viewthread.php?tid=172301
Back on with the Fisher Fury R1
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NS Dev
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| posted on 14/5/06 at 12:18 AM |
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quote:
Originally posted by flak monkey
Actually it doesnt make the slightest bit of bloody difference does it? The sum of the reaction forces at each wheel will always equal the total
weight of the car.
Jeez you can tell I havent done any real maths for 2 years.
Was getting worried there, you are doing engineering aren't you???
(only kidding!!)
Simplest way is if there is a level run up to your weighbridge, park the front on an weigh it, then the back, then the whole car as a double check,
job done.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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cossey
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| posted on 14/5/06 at 08:33 AM |
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if it isnt on a perfect level then the 2 axle weights if measured on the same scales (ie measure front the turn the car round and measure the back)
wont add up to the total weight but it would have to be seriously of level to make any real difference (ie enough to be out of the +-20kg)
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David Jenkins
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| posted on 14/5/06 at 06:04 PM |
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quote:
Originally posted by welderman
No offence there, i meant that it was strange we both had ours done.
No offence taken, Joe!
It is nice to know exactly how much your car weighs, isn't it - I've been saying "Oh, it's about... whatever" but never
really knew for sure.
With a bike engine instead of my xflow & Mk9 gearbox it would probably be 75kg lighter.
Mabye sometime in the future... 
David
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