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Where are pneumatic R/C tires? - The sins of John Dunlop.

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Where are pneumatic R/C tires? - The sins of John Dunlop.

Old 07-17-2018, 11:48 AM
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Default Where are pneumatic R/C tires? - The sins of John Dunlop.

So, it's been bugging me. We have foam inserts, we have stiff tires, we glue sidewalls, some tires are even belted, we do all these things to r/c tires.

.... but nobody is using a full carcass pneumatically supported tire yet.

Yeah yeah, they're specifically outlawed in some rules sets. But hear me out.

The advantages of pneumatically supported tires are numerous. By providing a very large, nearly constant rate spring, they cover changes in the road surface real well. They also load up better than foam inserts, as you apply load, the amount of force per unit aera is even across the tread entirely, and to compensate, the tread squishes, leaving you with more consistent tire and rubber loading. Pneumatic tires also provide an easy tuning aid, in that unlike foams, their pressure can be changed on a whim.

The challenges are pretty numerous though. The current tire out there, typically doesn't have a whole lot of structure to work with. The early car tires were called "baloon" tires, as they literally looked like baloons. You'll notice modern car tires are mostly square. That comes from a strong bead, a belted outer diameter, and a plan for the sidewall construction that doesn't leave to much, or to little sidewall in play.

Some of the technology we have, belted tires "are a thing" and are necessary if you want to keep good carcass shape under pressure. But then so are beads, and sidewall construction.

Finally, tire sealing. Would these be a tube type setup? A tubular tire? or would it be a tubeless, depending on the carcass of the tire to do sealing.

Given there's rules, I expect this has been tired. But by who? And when? Why was it specially called out in the rules?
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Old 07-17-2018, 12:17 PM
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Originally Posted by Nerobro
So, it's been bugging me. We have foam inserts, we have stiff tires, we glue sidewalls, some tires are even belted, we do all these things to r/c tires.

.... but nobody is using a full carcass pneumatically supported tire yet.

Yeah yeah, they're specifically outlawed in some rules sets. But hear me out.

The advantages of pneumatically supported tires are numerous. By providing a very large, nearly constant rate spring, they cover changes in the road surface real well. They also load up better than foam inserts, as you apply load, the amount of force per unit aera is even across the tread entirely, and to compensate, the tread squishes, leaving you with more consistent tire and rubber loading. Pneumatic tires also provide an easy tuning aid, in that unlike foams, their pressure can be changed on a whim.

The challenges are pretty numerous though. The current tire out there, typically doesn't have a whole lot of structure to work with. The early car tires were called "baloon" tires, as they literally looked like baloons. You'll notice modern car tires are mostly square. That comes from a strong bead, a belted outer diameter, and a plan for the sidewall construction that doesn't leave to much, or to little sidewall in play.

Some of the technology we have, belted tires "are a thing" and are necessary if you want to keep good carcass shape under pressure. But then so are beads, and sidewall construction.

Finally, tire sealing. Would these be a tube type setup? A tubular tire? or would it be a tubeless, depending on the carcass of the tire to do sealing.

Given there's rules, I expect this has been tired. But by who? And when? Why was it specially called out in the rules?
ipanema made some belted tires for 1/10th scale year back i had a few sets , they were ok but they took over 20-25 runs for them to break in not sure if they still make them, i think they may still make them for 1/8th gt cars
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Old 07-17-2018, 12:18 PM
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I’ve seen them used in large scale, 1/4 and 1/3. Simple answer is money. No company would, or has seen enuff demand to even consider the investment.
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Old 07-17-2018, 12:41 PM
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The short answer is that pneumatic tires are unnecessary and would provide no benefit, and that which works in the larger scales and speeds does not translate well into small scale and vice versa due to the interaction of inertia and impact forces being proportional to velocity squared instead of being linear. I disagree with the assertion that advantage of pneumatic tires would be numerous or even occur at all, air in full size tires is there to support the weight of the vehicle by fighting deformation of the tire, and in so transferring the weight of the vehicle from the rim to the ground via the sidewall, and the force that a fully inflated pneumatic tire applies to the road is very much not even over its contact patch, with the middle and most deformed part of the tire providing the most pressure. Most of what you consider an advantage we already have in our flexible sidewall tires with belts in the main carcass and foam insert that gives a spring rate when in contact with the inside of the tire.

A 1350g touring car has a TINY ground pressure. On the order of a fraction of one PSI, but for its weight it has a huge lateral force and impact force when rolling over even small imperfections in a racing surface. A tiny amount of air pressure in our tires would not be useful.
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Old 07-17-2018, 12:50 PM
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air filled tires would be of great benefit .it would cut down our tires needs on a changing tracks surface,so instead of having 5 sets of tires for a day .all I would need is 1


I think it is just to costly
would cut down on a tire makers profits bigtime
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Old 07-17-2018, 01:29 PM
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I'm amused. In four posts we have two different "in short" answers, three calls of "it's to expensive", one post saying it would be good, and another saying it's useless. This sounds like it's going to be a fun discussion.

.... I've got a lot to say, but I need to finish working first. :-)
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Old 07-17-2018, 01:33 PM
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It is almost like someone is dipping into the pharmaceutical brownies.
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Old 07-18-2018, 09:55 AM
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Originally Posted by Nerobro
I'm amused. In four posts we have two different "in short" answers, three calls of "it's to expensive", one post saying it would be good, and another saying it's useless. This sounds like it's going to be a fun discussion.

.... I've got a lot to say, but I need to finish working first. :-)
Is your name Greg?
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Old 07-18-2018, 10:21 AM
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Imagine what happens when a full size car drives into the curbing or hard against a barrier... tire goes flat, rim gets bent.

Now think how many times you hit/graze in a day at the track with the RC.

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Old 07-18-2018, 11:18 AM
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Funny thread.

Air filled tires need vents. With vents and belted tires you need aluminium rims. And then you have to balance the weels. That's already with normal rc tires a pain in the...
Not to mention the weight.

Before air filled rc tires are coming, I want hydraulic disc brakes in my 1/10 TC...with adjustable brake-balance of course...
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Old 07-18-2018, 12:53 PM
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Originally Posted by DesertRat
I disagree with the assertion that advantage of pneumatic tires would be numerous or even occur at all, air in full size tires is there to support the weight of the vehicle by fighting deformation of the tire, and in so transferring the weight of the vehicle from the rim to the ground via the sidewall, and the force that a fully inflated pneumatic tire applies to the road is very much not even over its contact patch, with the middle and most deformed part of the tire providing the most pressure. Most of what you consider an advantage we already have in our flexible sidewall tires with belts in the main carcass and foam insert that gives a spring rate when in contact with the inside of the tire.

A 1350g touring car has a TINY ground pressure. On the order of a fraction of one PSI, but for its weight it has a huge lateral force and impact force when rolling over even small imperfections in a racing surface. A tiny amount of air pressure in our tires would not be useful.
The air in full size tires provides a whole lot of things. Least of which is "fighting deformation". The air transfers the weight, and ground pressure to the entire surface of the tire. The middle, and most deformed part of the tire, (not accounting for carcass stiffness) has the same ground pressure as any other part of the tire in contact with the ground. That's the magic of pneumatic tires. Your contact patch with the ground is defined almost entirely by the pressure of the tire divided by the weight applied. Things start to get a little different with high hysteresis rubbers and such.

a 1350g touring car... has 1350g of weight on the tires. I'll do a test tonight, and we can calculate the contact patch. (might as well bring some real data to this thread,shouldn't we?)

Given the speed we roll across the ground, I bet air pressure is a significant factor. The air has to go in, and out, though a single hole, and often that's spec'd by the rules. Foam makes sure our tires have "some starting shape" and then any fast transition in tire shape is going to temporarily pressurize the tire. That's testable, too. On a fairly rough track, drilling 3-4-5 1/4 inch holes in the rim would completely eliminate that factor. I bet someone has done that. "maybe we are running pneumatically supported tires, and don't know it".

What going to a tube or tubeless type tire would do, is lose the lateral support that we get from the foam inserts. Lateral load on the tire... is trying to sheer an inch wide piece of foam, instead of crushing a 1/4" of it. That takes a lot more force. Bah, this is bringing up a lot more questions than answers, isn't it? hah.

Originally Posted by R3VoLuTiOn
Imagine what happens when a full size car drives into the curbing or hard against a barrier... tire goes flat, rim gets bent.

Now think how many times you hit/graze in a day at the track with the RC.
How is that any different from now? I've shattered rims, with foam and rubber based tires too. I think the durability would be about the same.

Originally Posted by Tom1977
Air filled tires need vents. With vents and belted tires you need aluminium rims. And then you have to balance the weels. That's already with normal rc tires a pain in the...
Not to mention the weight.

Before air filled rc tires are coming, I want hydraulic disc brakes in my 1/10 TC...with adjustable brake-balance of course...
Vents? Dodge sold an Omni with plastic wheels... so plastic wheels are ok. Bikes, planes, and "other things' Use plastic wheels with conventional pneumatic tires too. So that's not a concern. Really, given the abuse r/c cars take, we never want to leave the "soft" plastic wheels we have. People balance the current tires out there, if you're not doing it, you probably won't need to do it with pneumatic tires. (I don't balance the tires on my motorcycle...anymore)

I think a tube could be put into a conventional r/c wheel and tire combination, right now. You'd lose the lateral support of the foam. Which means the sidewall construction would need to be beefed up. And you'd need to be more careful about gluing them on the rim.

.... I think people are right saying that it would be more expensive. But... there's a good chance the tires would last longer.

Oh yeah, brakes, have been done. A guy with a 2wd off road buggy did it. With modern touring cars, the whole belt drive in the middle does a great job of it, and more or less automatically adjusts brake bias. (this is one reason why subarus, and audis have bigger rear brakes..) Now for one of the 2wd classes, you have something to think about.
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Old 07-18-2018, 01:33 PM
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Originally Posted by Nerobro
The air in full size tires provides a whole lot of things. Least of which is "fighting deformation". The air transfers the weight, and ground pressure to the entire surface of the tire. The middle, and most deformed part of the tire, (not accounting for carcass stiffness) has the same ground pressure as any other part of the tire in contact with the ground. That's the magic of pneumatic tires. Your contact patch with the ground is defined almost entirely by the pressure of the tire divided by the weight applied. Things start to get a little different with high hysteresis rubbers and such.


a 1350g touring car... has 1350g of weight on the tires. I'll do a test tonight, and we can calculate the contact patch. (might as well bring some real data to this thread,shouldn't we?)


Given the speed we roll across the ground, I bet air pressure is a significant factor. The air has to go in, and out, though a single hole, and often that's spec'd by the rules. Foam makes sure our tires have "some starting shape" and then any fast transition in tire shape is going to temporarily pressurize the tire. That's testable, too. On a fairly rough track, drilling 3-4-5 1/4 inch holes in the rim would completely eliminate that factor. I bet someone has done that. "maybe we are running pneumatically supported tires, and don't know it".


What going to a tube or tubeless type tire would do, is lose the lateral support that we get from the foam inserts. Lateral load on the tire... is trying to sheer an inch wide piece of foam, instead of crushing a 1/4" of it. That takes a lot more force. Bah, this is bringing up a lot more questions than answers, isn't it? hah.

.

The method by which pneumatic tires support weight is ENTIRELY based on putting tension on the tire carcass to fight deformation! The weight of the car sits entirely on the bead of the tire and rim, due to how the uniform air pressure pushes both on the top and bottom of the rim it cancels itself out completely. As a pneumatic tire has weight put on it against a flat surface, the sidewall deforms and through the rigidity of the belts and rubber pushes the tire off-center from the axis of the rim, and the internal pressure counteracts the deformation by trying to pop that deformed area back into its natural shape. Also, a tire that is deformed into a contact patch that is some 6" x 4" each does not have exactly even tire pressure over that area as the rubber and construction plies have a spring coefficient, so the weight it exerts on the ground for each small section of tread is not exactly the same. A point on the tire comes into contact with the road surface with an initial load of zero, experiences progressive loading as it gets under the rim, and then progressive unloading as it rolls behind the car and is lifted off the ground.





In summary, air does not transfer weight it is a medium used for putting tension on the tire carcass. Its the same principle by which if you squeeze a balloon or racquet ball it pops back into shape.


So, in what way is it different in RC? Well, in a touring car we use a closed cell foam insert inside of the tire. Closed cell foam is rubber and air, the foam matrix holds the air in the correct shape and gives some strength and importantly some hysteresis to its spring action, a bit like a shock absorber. There is also an air gap in the tire between the foam and rubber, so the tire deforms a little then it touches the foam, which then deforms somewhat as it supports the tire via the rim. In a touring car we may not have a perfect low-high-low pressure contact patch as we have in the pictures above, but its probably closer than you think.


Also, the air breather ports we have in our tires are only there to even the pressure with the outside world, and air exchange during a run is minimal and not intentional. The tiny amount of air inside the tire is not under tension and just lightly swirled around as the tire rotates and compresses and uncompresses during a revolution, moving back and forth very slightly and not experiencing much actual displacement. Drilling big holes in your rim will do nothing good for you, this isn't offroad where a tire can experience a large internal volume change after coming down from a jump. We are not running pneumatic tires without knowing it.
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Old 07-18-2018, 01:45 PM
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I'd be really interested to see the equipment you would need to accurately and consistently set air pressure in rc car sized tires.

This idea would make setting up a car nearly impossible. The loads we put through cars are asymmetrical, so the temperatures of each tire under load will be different. This means the pressure in each tire will change independently, making the cars handling inconsistent and unpredictable.

We use foam inserts and super soft sticky rubber because that is what works best for a car of this size and speed.
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Old 07-18-2018, 02:17 PM
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Originally Posted by DesertRat
In summary, air does not transfer weight it is a medium used for putting tension on the tire carcass. Its the same principle by which if you squeeze a balloon or racquet ball it pops back into shape.
I believe our understanding of what's going on with tires, is the same. The image you posted, agrees entirely with the understanding I have with how contact pressure, tire pressure, and vehicle weight relate.

So, in what way is it different in RC? Well, in a touring car we use a closed cell foam insert inside of the tire. Closed cell foam is rubber and air, the foam matrix holds the air in the correct shape and gives some strength and importantly some hysteresis to its spring action, a bit like a shock absorber. There is also an air gap in the tire between the foam and rubber, so the tire deforms a little then it touches the foam, which then deforms somewhat as it supports the tire via the rim. In a touring car we may not have a perfect low-high-low pressure contact patch as we have in the pictures above, but its probably closer than you think.
My USGT tires, VTA tires, Tamiya tires, and Sakura tires all come with open cell foam. So did my Losi truck. I know closed cell foam is out there... You might be right, how might we test the pressure of the contact patch of a r/c car tire accurately?


Also, the air breather ports we have in our tires are only there to even the pressure with the outside world, and air exchange during a run is minimal and not intentional. The tiny amount of air inside the tire is not under tension and just lightly swirled around as the tire rotates and compresses and uncompresses during a revolution, moving back and forth very slightly and not experiencing much actual displacement. Drilling big holes in your rim will do nothing good for you,*snip* We are not running pneumatic tires without knowing it.
Drilling big holes would only prove the point, definitely not improve things. I doubt it's an important point from wheel revolution to wheel revolution, but it ~might~ be a point when you hit the transition between seams in the carpet, a screw someone lost, a corner dot, or during corner turn-in. There are rules defining vent holes, so it serves to reason that it's been used an a tuning tool. Air has interesting behaviors when going fast, and passing through holes.

Originally Posted by urnotevenwrg2
I'd be really interested to see the equipment you would need to accurately and consistently set air pressure in rc car sized tires.

This idea would make setting up a car nearly impossible. The loads we put through cars are asymmetrical, so the temperatures of each tire under load will be different. This means the pressure in each tire will change independently, making the cars handling inconsistent and unpredictable.

We use foam inserts and super soft sticky rubber because that is what works best for a car of this size and speed.
You may be on the biggest problem. Consistently dealing with small volumes of pressurized air, in a leaky bag. Heck, my bicycle tires will lose 10psi overnight, and those are nearly the thinnest practical air bladders.

The equipment to check the tire pressure, is out there, a manometer is common tool that can handle the pressures we'd be dealing with. To stop from losing to much air during checking, there would need to be a thing or two done to replace the tested air, or return the test air, but none of that is really tricky.

For a long time, we used foam, because it's what worked best for a car of this size and speed. Too.



Just so we're all clear here. I don't think I have a better bread slicer here. Ideally, I'm hoping to flesh out the reasons why, why not, and maybe find some of the history behind it all. :-) If I thought I had something magically better, I'd be sitting at my dining room table with sheets of latex, nylon, glue, and clamps, making this stuff.
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Old 07-18-2018, 02:51 PM
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I'll just leave that here. The year is 2001

http://www.overrc.com/news/news2001/...32001/CRF4.jpg

Complete article (in French) on OverRC.com, le site de la voiture radio-commandée électrique. ... but not able to post link
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