Hello people! I really need a help with a Car project using Arduino mega to measure RPM, distance etc... I already did the main part of it, but now I need help to know how much does the tire size can variate regarding its pressure variation on the road. For example I'm using a 305/30ZR19 tire, which has 19 in of diameter, and supponsing that it initiates with 33psi, 19.0 of diameter, and an ambient temperature, then on the road the tire heats, so the pressure increments to 40psi, how much can diameter be affected? For example from 19.0 inch to 19.5 when gets 40 psi.
Take a tire, inflate it, measure the diameter. The exact brand and type of tire will matter.
Of course the tire gets bigger when inflated more but I don't think it's much. What will change more is how deep the weight of the vehicle compresses the tire.
I'm surprised the stackexchange mods haven't cr@pped on him, they're quite strict over there, and tyre size has nothing whatsoever to do with OP's project being Arduino based.
kenwood120s:
I'd be inclined to measure the circumference, to take account of the flat bit at the bottom, and maybe any other out-of-roundness.
The only reliable way to measure the distance traveled per rotation would be to put the vehicle on the ground and move it by one wheel rotation forward, and do so at different pressures and so. The flexing of the tire makes it hard to know "the" circumference.
I recall reading many years ago that the rolling circumference of a radial ply tyre is the same at all inflation pressures (apart from deflated, I presume).
And for the flat bit at the bottom, recall how the flat bit works for a bulldozer
Come to think of it, that sounds pretty plausible indeed! (assuming an ideal tire: no slip or longitudinal compression of the material, which should be quite close to reality).
All rubber tyres slip against the ground - without some slip there can't be any force. Maybe "creep" would be a better word than "slip"
I have no idea whether, or to what extent, it affects the distance traveled per revolution. Perhaps there is less movemen per revolution when the force is high (acceleration) because there is more creep.
For those who may be interested it is the sudden transition from "creep" to true slipping that means that the maximum braking (or cornering) force is just before the tyre slips. Also, a tyre can generate a certain amount of force and that must be shared between cornering and braking - so there will be much more braking force available when moving in a straight line.
That's why I said: ideal tire, I know real tires are not like that. They deform, flex, slip and creep and do all kinds of things that are not ideal. But slip should be very small and can probably be neglected unless indeed breaking or accelerating fast (with wheel lock / burnout being the extremes of course).
I have a friend who works for Ryanair as a maintainance engineer ( A B1 - he says if an aircraft can fly or not) and he told me that 737 tyres are filled with nitrogen.
Hi,
Because not all tyres are created equal would this sound plausible.
You have a test vehicle, fitted with GPS.
For different pressures and temperatures you do runs in the car and compare car speedometer and GPS speed.
A smart bloke, Newton I believe, the apple and gravity character, many many years ago invented a thing called calculus that would help calculate the expanded wheel diameter.
If you have a chassis dyno or rolling road, then the difference between speedometer and road roller speed.
There are several compelling reasons to use pure nitrogen in tires.
First is that nitrogen is less likely to migrate through tire rubber than is oxygen, which means that your tire pressures will remain more stable over the long term. Racers figured out pretty quickly that tires filled with nitrogen rather than air also exhibit less pressure change with temperature swings. That means more consistent inflation pressures during a race as the tires heat up. And when you're tweaking a race car's handling with half-psi changes, that's important.
Aircraft would have N filled tyres because of the temperature extremes in flight.
A very cold tyre being asked to take a jumbo's mass on landing would need to have the sort of pressure it will have after warming up on the tarmac.
Tom...
First is that nitrogen is less likely to migrate through tire rubber than is oxygen,
Aircraft would have N filled tyres because of the temperature extremes in flight.
A very cold tyre being asked to take a jumbo's mass on landing would need to have the sort of pressure it will have after warming up on the tarmac.
I think a quick squint at a physics text book would help. The pressure of all gases is affected by temperature in the same way PV = MRT
I believe it is the oxygen that is the problem - partly because it escapes and partly because it oxidizes the rubber (or whatever it is that tyres are made from these days) and shortens the life of the tyre.
Another advantage of using nitrogen is that it is dry whereas air can contain moisture that can evaporate or condense with huge pressure changes. I suspect nobody ever went to the trouble of putting a mixture of 80% nitrogen and 20% oxygen into a tyre to see if it performs better than standard "air".
And, to be honest, I would like to see a more authoritative statement about the relative migration of oxygen and nitrogen. I don't think there is a huge difference in the sizes of their molecules. Hydrogen on the other hand can escape through the walls of a steel tank.
Robin2:
I believe it is the oxygen that is the problem - partly because it escapes and partly because it oxidizes the rubber (or whatever it is that tyres are made from these days) and shortens the life of the tyre.
Oxygen molecules barely smaller than nitrogen (15.2 A vs 15.5 A) so escaping shouldn't be an issue. It may indeed oxidise the rubber, especially when the tyres are hot.
I'd guess that the biggest variable is tire wear, which could be a few percent over the life of the tire.
. I suspect nobody ever went to the trouble of putting a mixture of 80% nitrogen and 20% oxygen into a tyre to see if it performs better than standard "air".
I was once working on a biotech machine with lots of valves & connections and we tested for leaks with a tank of nitrogen. (We did pressure leak-down tests and we'd find the leaks with soapy water, looking for bubbles.) I asked the gas-supplier about "clean dry air" and he said it's more expensive than nitrogen.
For leak tests in the lab helium is used (but beware: rubber hoses will not contain helium, the molecules are so small they go right through). Then you can use special sniffers to test for leaks, He is not normally present in air so any He detected means a leak.
If He doesn't leak out, nothing will leak out as it's the smallest molecule out there.
