anyone have free time this weekend and want to do something for me?

[cam98aro]

I found a way to measure the weight of a car without using scales that is said to be accurate within 5%

it shouldnt take long, but it will be raining here so i cant try it out.. maybe multiple people can do it and we can compare.

anyways, i have a few rules:
1. you must have a stock weight car (or close to stock), or know what the weight of your car actually is if you did any weight reduction (this is just to see how accurate this method is)
2. the car has to be on flat ground

tools needed:
1. tape measure
2. spray bottle of water, or a hose with a nossle so you can spray a mist around the tires
3. tire PSI gauge

the method:

1. Park your car on the flat surface, and spray the water around all 4 tires where the tire contacts the ground
2. Move the car so you can see the dry spots on the surface where the tire was on it
3. Measure the dry spots, and find the area (length x width) for each tire, and write them down
4. measure the PSI of each tire, and once again write them down
5. Add up the areas of the 4 tires, and the PSI of the 4 tires, and multiply them
6. You should get a number that should be the weight of your car

Im interested to see how accurate this method is, and see if it is really within 5%

edit* I just found a website explaining this with a slightly different method: http://www.exploratorium.edu/wsw/pro...ght/index.html

Thanks for anyone who takes the time to do this!

[LETZRIDE]

Re: anyone have free time this weekend and want to do something for me?

this is interesting...I'll wait to see some results...its all rain here this weekend as well...

[zlexiss]

Re: anyone have free time this weekend and want to do something for me?

I remember doing this in science club in middle school :p

[cam98aro]

Re: anyone have free time this weekend and want to do something for me?

this is interesting...I'll wait to see some results...its all rain here this weekend as well...

same here, i hope to get at least a few takers

I remember doing this in science club in middle school :p

i have actually never heard of this method until the other day, and kinda blew it off until i thought about how it worked and how it could potentially be fairly accurate

[dashboardrunner]

Re: anyone have free time this weekend and want to do something for me?

**** it.. im on vacation all next week.. i'll try to find some time to try this out... sounds interesting...

[savagecamaro96]

Re: anyone have free time this weekend and want to do something for me?

how the hell does that work?
would it work on other stuff? like a bike?

[TheGr8Schlotzky]

Re: anyone have free time this weekend and want to do something for me?

The physics makes sense, so I'd be very interested to hear how accurate it is. My car is in storage and weighs a good bit more than stock I'd think, though, so I wouldn't be much help. Also it's raining. Maybe I'll try it with my Buick and compare to the GVW.

[cam98aro]

Re: anyone have free time this weekend and want to do something for me?

how the hell does that work?
would it work on other stuff? like a bike?

basically you take the area footprint of the tire on the ground, which measures how much the weight of the car pushes down on the tire, and compare that to how much the air pressure is in the tire

for instance, if the tire pressure is low, it will push the tires down more and make a bigger footprint, meanwhile when the pressure is really high the footprint will be smaller, but when you do the math, it should give you the same number

I could imagine it would work on a bike as long as it doesnt have an innertube

The physics makes sense, so I'd be very interested to hear how accurate it is. My car is in storage and weighs a good bit more than stock I'd think, though, so I wouldn't be much help. Also it's raining. Maybe I'll try it with my Buick and compare to the GVW.

nice

[TheGr8Schlotzky]

Re: anyone have free time this weekend and want to do something for me?

Well the basic physics makes sense; x PSI (pounds per square inch) multiplied by the area in square inches would, with some basic cross multiplying, yield an answer in pounds. I thought about it though, and decided it would not be as simple as multiplying everything, but rather calculating the area one tire (LxW) multiplied by the PSI of that tire, repeating for all four tires, and then adding the results together.

But in practice, it doesn't seem so bullet proof. I calculated my car, which has a GVW of 3,563lbs by this calculation to be 8960.59lbs. Given a half inch margin of error in length and width measurements, this allows for about +-1,000lbs. Neither come even close.


I thought of several flaws in this experiment:
Namely, this would seem to be more accurate if the cars were sitting on slicks, but the fact is all street tires have a tread pattern, meaning the actual area of the tire making contact with the road is not as simple as the LxW of the contact patch, because you have to account for the empty space between tread sections, as well as the smoothness of the area you are measuring on.
In my case, assuming 63% of the contact patch area is actually rubber making contact with the road, we get an answer of 3,540.3lbs. This is a much more reasonable number, but a completely ridiculous assumption to make.

Other smaller factors include evaporation of the water on the road and water seeping under the tread due to a rough road surface.

It's a cool idea, but not conceptually sound.

[savagecamaro96]

Re: anyone have free time this weekend and want to do something for me?

^that's kinda what i was thinking
different size rims and tires cant have the same properties i would think.

[TheGr8Schlotzky]

Re: anyone have free time this weekend and want to do something for me?

The contact patch area should not be dependent on diameter and width, all other things equal. I.E. 700lbs on a single 185/70/15 tire at 28psi should have the same contact patch area as 700lbs on a single 315/20/19 tire at 28psi. These tires will obviously have a different sidewall heights and amounts of sidewall flex (as well as other factors like cooling properties) and contact patch shape, which would lead to significantly different performance, but the patch areas should be the same.

What I'm talking about though is the tread patterns, and how much tread is actually making contact with the road vs. the area of empty space within the "contact patch." If the tires were completely bald, or otherwise had no tread (ie slicks), I think the idea could hold some water.

[cam98aro]

Re: anyone have free time this weekend and want to do something for me?

Well the basic physics makes sense; x PSI (pounds per square inch) multiplied by the area in square inches would, with some basic cross multiplying, yield an answer in pounds. I thought about it though, and decided it would not be as simple as multiplying everything, but rather calculating the area one tire (LxW) multiplied by the PSI of that tire, repeating for all four tires, and then adding the results together.

But in practice, it doesn't seem so bullet proof. I calculated my car, which has a GVW of 3,563lbs by this calculation to be 8960.59lbs. Given a half inch margin of error in length and width measurements, this allows for about +-1,000lbs. Neither come even close.


I thought of several flaws in this experiment:
Namely, this would seem to be more accurate if the cars were sitting on slicks, but the fact is all street tires have a tread pattern, meaning the actual area of the tire making contact with the road is not as simple as the LxW of the contact patch, because you have to account for the empty space between tread sections, as well as the smoothness of the area you are measuring on.
In my case, assuming 63% of the contact patch area is actually rubber making contact with the road, we get an answer of 3,540.3lbs. This is a much more reasonable number, but a completely ridiculous assumption to make.

Other smaller factors include evaporation of the water on the road and water seeping under the tread due to a rough road surface.

It's a cool idea, but not conceptually sound.

hm, thanks for trying it out, hopefully someone else can also, but its not looking too good

[TheGr8Schlotzky]

Re: anyone have free time this weekend and want to do something for me?

I'll try it on another car if I have some time tomorrow.

['97RedBird]

Re: anyone have free time this weekend and want to do something for me?

Maybe I'm missing something but I don't see how this could ever work. Lets say I do everything, measure my tires, and take the PSI. Then I go to the garage and get the air compressor and add a few PSI to each tire. I don't think the contact area will change that much and Ill have a completely different number.

[TheGr8Schlotzky]

Re: anyone have free time this weekend and want to do something for me?

Maybe I'm missing something but I don't see how this could ever work. Lets say I do everything, measure my tires, and take the PSI. Then I go to the garage and get the air compressor and add a few PSI to each tire. I don't think the contact area will change that much and Ill have a completely different number.

Because it's an area, a very small change can make a huge difference. Like I said, an error or .5 inches in length and width measurements allowed for 1000lbs of fluctuation. I did it in the driveway, I do think a garage floor would be much better suited, but I'm still unsure whether it will work better than my trail.