It made me wonder... how about if you were to ink your tire treads, roll the car onto plain paper, draw a couple of marks at the leading/trailing edge of each tire (so you know what to ignore when rolling the car back off the paper), flat bed scan the results, and work out the contact area based on the number of dark pixels in the image (you could get the image scale from the scan DPI)
Hello. Thanks for the article. Looking for a little clarification.
You wrote "The grooves going around the circumference of the tire were deeper than the ones going across the tire. I redid the calculations only accounting for those grooves"
Which "those" grooves do you mean. The ones ground around the circumference or the ones going across? Also does "only accounting for those grooves" mean you discarded the area modification for "those" grooves, or that you only kept the area modification for those groves and discarded the others?
It's been a while since I did this, so not 100% certain of what past me was trying to say there. I think by "those", I meant the ones going around the circumference. And I believe I only kept the area modification for those particular grooves and discarded the others.
Any scrap yard will have drive in scales, I've weighed my truck that way before. I called beforehand to make sure they were ok with it, and they said it was fine for a one off use.
Though there's also nothing stopping someone from driving in and immediately driving out the exit without unloading anything
That's a lot less fun than using tire pressure as a scale, though
So sometimes tires are filled to higher pressures. And then there are different size tires both in width and diameter causing different contact patches. This is not a way to measure car weight. I thought you were going to measure tire pressure on jacks. And then remeasure with the car on the tires. Unfortunately i think this will also not work due to the elasticity of the tire
That's an interesting alternative. Certainly could work. I think the different size would be offset by a different pressure, so that shouldn't be an issue. As you said, the stiffness of the tire is the real culprit for the inaccuracies here.
On threads manufacturers provide % tread/space ratio as that to traction on various surfaces and weather conditions. For your purpose the sidewall wouldn't matter as you're dealing with static load, not dynamic.
I didn't realize that for the tread, could be a time saver. I think the sidewall does have some contribution despite it being static load. You could think of it as a spring of a sort too. It has some stiffness/springiness and it's certainly deformed a bit. So it is providing a force upwards (F=kx). Good discussions on it here: https://news.ycombinator.com/item?id=23683259
An enjoyable read!
It made me wonder... how about if you were to ink your tire treads, roll the car onto plain paper, draw a couple of marks at the leading/trailing edge of each tire (so you know what to ignore when rolling the car back off the paper), flat bed scan the results, and work out the contact area based on the number of dark pixels in the image (you could get the image scale from the scan DPI)
That's clever. I like it! I suspect the tires would be dirty enough that you wouldn't even have to add ink.
For what it's worth, this works on much larger vehicles as well, but the sidewall stiffness becomes more of an issue because of the scale. https://www.komatsuamerica.com/equipment/trucks/electric/980e-5. Great work!
Very cool, thanks for sharing that.
Hello. Thanks for the article. Looking for a little clarification.
You wrote "The grooves going around the circumference of the tire were deeper than the ones going across the tire. I redid the calculations only accounting for those grooves"
Which "those" grooves do you mean. The ones ground around the circumference or the ones going across? Also does "only accounting for those grooves" mean you discarded the area modification for "those" grooves, or that you only kept the area modification for those groves and discarded the others?
Thank you.
It's been a while since I did this, so not 100% certain of what past me was trying to say there. I think by "those", I meant the ones going around the circumference. And I believe I only kept the area modification for those particular grooves and discarded the others.
Thank you.
Any scrap yard will have drive in scales, I've weighed my truck that way before. I called beforehand to make sure they were ok with it, and they said it was fine for a one off use.
Though there's also nothing stopping someone from driving in and immediately driving out the exit without unloading anything
That's a lot less fun than using tire pressure as a scale, though
So sometimes tires are filled to higher pressures. And then there are different size tires both in width and diameter causing different contact patches. This is not a way to measure car weight. I thought you were going to measure tire pressure on jacks. And then remeasure with the car on the tires. Unfortunately i think this will also not work due to the elasticity of the tire
That's an interesting alternative. Certainly could work. I think the different size would be offset by a different pressure, so that shouldn't be an issue. As you said, the stiffness of the tire is the real culprit for the inaccuracies here.
On threads manufacturers provide % tread/space ratio as that to traction on various surfaces and weather conditions. For your purpose the sidewall wouldn't matter as you're dealing with static load, not dynamic.
I didn't realize that for the tread, could be a time saver. I think the sidewall does have some contribution despite it being static load. You could think of it as a spring of a sort too. It has some stiffness/springiness and it's certainly deformed a bit. So it is providing a force upwards (F=kx). Good discussions on it here: https://news.ycombinator.com/item?id=23683259