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Why would "best diameter" be different at different speeds ? |
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I did a version of this one.
Tire diameter changes torque and could act as an automatic transmission of sorts to give you gear ratios between the existing gear ratios. (+) |
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Wheels and tyres are always a compromise between many factors; grip, rolling resistance, wear and unsprung mass, amongst others. |
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A thin wheel resembling a bicycle is best for high speed straight running on even surfaces; a wider wheel with a smaller diameter is better for twisty roads. |
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A variable geometry vehicle wheel is an excellent idea - indeed, we use them - but beyond the current primitive state of your technology. |
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^ A close analysis of the electrons used for the above post shows the typical wear marks of a Babbage Engine 14.12 D. So who's fooling who? |
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In a "free" society, everyone gets to fool themselves. |
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That's why we don't have one. |
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No-one's fooling who. That would be ungrammatical. |
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^ <Immediate award of bonus Pedant Points/> |
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Your ride would be rough, and forget cornering. |
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Tire sidewalls take a great deal of sideload that they have to
cope with. I have no idea how an overstuffed turkey tire
would manage this. |
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I would suspect that the extra complexity (and therefore weight) of the gubbins required to modify the diameter on-the-fly would offset any gains made. |
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I don't think changing the tyre's diameter will have much
impact on efficiency. A bigger wheel should always be more
efficient, because it doesn't respond as dramatically to bumps
and dips. Also, the contact area with the road (which must
have an impact on efficiency) will be the same regardless of
wheel diameter (ie, the contact area is vehicle mass divided
by tyre pressure). What might make a difference is variable
tyre pressure, to adapt to dry, grippy roads or wet, slippery
ones as needed. |
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// Your ride would be rough, and forget cornering.
Tire sidewalls take a great deal of sideload that they have to cope with. I have no idea how an overstuffed turkey tire would manage this.// |
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Decreasing the diameter of the tires on only one side of the vehicle while turning will cause the vehicle to 'bank' into turns with less stress in side-walls than if tires remain the same diameter throughout a turn. |
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...or at least in my head they do. |
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// I would suspect that the extra complexity (and therefore weight) of the gubbins required to modify the diameter on-the-fly would offset any gains made. // |
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Dynamic on-the-fly adjustment of tire diameter could be a simple function of controlling air pressure if the geometry of internal banding structures within the rubber were a double-iris like a toroid pantograph so that the smallest sidewall size would correspond with the widest tire size. In this way robustness could be maintained even with air pressure at its lowest. |
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As for those funky new tubeless military tires that can withstand a land-mine with 80% integrity intact... them puppies are just screaming to be made dynamic on-the-fly just by tweaking the design slightly and adjusting rim size.
Minimal addition of weight for a far smoother ride over rough terrain. |
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//I don't think changing the tyre's diameter will have much impact on efficiency. A bigger wheel should always be more efficient, because it doesn't respond as dramatically to bumps and dips. Also, the contact area with the road (which must have an impact on efficiency) will be the same regardless of wheel diameter (ie, the contact area is vehicle mass divided by tyre pressure). What might make a difference is variable tyre pressure, to adapt to dry, grippy roads or wet, slippery ones as needed.// |
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The impact will be huge!
Yes. Larger diameter tires will always deal with cracks and dips better, but a smaller one will deal with bumps and rocks better... if the vehicle could anticipate these obstructions and compensate accordingly it would have to be more efficient than one stuck in one-size-tire-mode. |
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It will be a thing, oh yes, it will be a thing. |
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I think you need to trust your head less. Do you have the
paperwork on its manufacturer? Do you even know where
it came from? Is it an authentic one or a back-alley
knock-off? |
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You seem to be under the impression that tires consist of
nothing but stretchy rubber. Nothing could be further
from
the truth. Take it from a belt engineer, allowing any sort
of
sliding delamination to occur inside the tire wall between
the steel belts and the rubber will basically destroy it. |
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Searching for Baja trophy trucks and Jeeps with "small
tires better equipped for rocks" came up nil. Upon
anticipation of a bump or rock, what is the vehicle going
to do? Lift up its skirt and tip-toe over? There is a small
matter of gravity to deal with. |
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I sincerely bow to your greater knowledge. I just see things in my head and keep having them proven out over and over again. This is one of those things. |
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hmmm what do I 'really' know about tires?... not much.
I've worn enough of them down to physically see the grain of several brands of cross-belting.
I can inflate a tire to a remarkably accurate psi if I have other correctly inflated tires to judge from.
Todays tires seem to be made to programmed-obsolescence specs so that the tread wears down at a predetermined rate and things like walnut shells are now being touted as superior to the all-season worn out pieces of shit I could once take over the Rocky mountains in winter. |
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Could be total bullshit, (what the hell do I know?), the proof will be in the pudding as usual. |
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I just see future tires being able to dynamically flex in ways that don't ever let side-walls come in contact with terrain, (unless that terrain was already very previously tire-shaped).
Tires won't just change diameter on the fly, they will be able to independently change their... angles-of-attack, (for lack of a batter word) without having to twist their rims. |
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Those military tires I mentioned are begging to be pantographed right now. They could even be made to extend and retract secondary treads using only centripetal force when one hub spins faster than others. |
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As for materials composition, and stretch factor ratios, and previous experiments... <shrugs>, that's not my department.
I don't know any of those things.
I see and play with funky shapes in my head, and one of those shapes is this cool double counter helix thingy that can... expand and contract like a quad-nested Hoberman sphere, but toroidal instead of spherical, and can flex one side or the other just like... |
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<only shrugs one shoulder and then the other> |
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I don't have the skills to show you what I see in my head. Picture an Hoberman sphere torus. Now twist it clock-wise. Make another one that would fit inside that first one but twist it counter clock-wise. slice them in half. Nest them, and connect the junctions of those two shapes to their nested half-partner. Then connect the two half-toroids to each other with another pantograph the width of the tire... and you've got the steel belted framework of something which can, by swapping air pressure between the two hemispheres, be able to twist dynamically on the fly if the sidewall material used can take the stretch. |
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<shrugs independently one more time for effect> |
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The dual hoberman thing makes sense. |
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Also, if they embed metal chunks in the road you could go nearer frictionless (like railways) if you synchronize metal areas on the tires to the road. ...Wheg? |
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//but a smaller one will deal with bumps and rocks better//
Ah yes, this is why skateboards are so favoured as all-terrain
vehicles, whereas mountain bikes are limited to smooth
tarmac. |
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The problem is that something had to take the
force. If a tire is that stretchy, then it is easily
deformable under load. Presumably your
Hoberman-style contraption would be what you
intend would take the load. But these things just
aren’t designed to be strong; they’re all wrong for
that, with loads driven into the middles of
connecting rods and such, at least the ones I’ve
seen. |
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Mileage isn’t significantly affected by tire size
anyway. You’re still trying to provide the same
amount of torque either way. |
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What does affect it is the tire rolling
resistance. Harder tires=better mileage but poorer
traction.
Keep on with the visions, though. If you can see
how it fits together you’re a good deal better with
your mind’s eye than I am. |
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How about an array of differently-sized wheels, like the letters on a daisywheel print head? Whichever wheel is preferred for the current terrain can be rotated into place, and the other wheels retracted. |
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//I can inflate a tire to a remarkably accurate psi if I have other correctly inflated tires to judge from// - it's surprising how many concepts for superheroes and their associated super-powers the big comic publishers came up with before they eventually settled on Superman, Batman, Wonder Woman, etc. |
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I must only use my powers for good. |
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//Ah yes, this is why skateboards are so favoured as all-terrain vehicles, whereas mountain bikes are limited to smooth tarmac.// |
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What I meant is that if tires could rapidly and independently shrink slightly as they pass over an obstacle, and then re-inflate on the other side, or inflate slightly when passing over a pot-hole then almost no deviation would be felt by the shocks making for a smoother ride. |
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// If a tire is that stretchy, then it is easily deformable under load. Presumably your Hoberman-style contraption would be what you intend would take the load. But these things just aren’t designed to be strong; they’re all wrong for that, with loads driven into the middles of connecting rods and such, at least the ones I’ve seen.// |
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You're probably right.
Excessive optimism is my Kryptonite. |
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Ah, one of my brethren. I have similar powers of
measurement estimation on pressures and lengths--
unfortunately they register in units of psi and inches.
Once I parked the car in a multi-level car park. My
passenger was concerned that I was coming a tad close to
the barrier wall in front. I assured him that I had four
inches
to spare. He doubted and went to look. After noting that
it
seemed to him that I was spot on, we checked it against
an
8.5 x 11 sheet of paper folded in half. I was easily within
an 1/8". |
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//an 8.5 x 11 sheet of paper// - I continue to be mystified by the USA's reluctance to adopt ISO paper sizing (e.g. A4 paper, with its elegant sqrt(2) relationship between length and breadth and
easy-to-calculate area, where AX paper has an area of 1/(2^X) m^2). |
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We would have to change the size of our folders, filing
cabinets, envelopes, mail slots, mail room sizes, etc. And by
no means are we going to take it from a region of the world
where proper electrical outlets can't be agreed upon. |
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Exactly when have you needed to use that fact in your life? |
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// I assured him that I had four inches to spare. He doubted and went to look. After noting that it seemed to him that I was spot on, we checked it against an 8.5 x 11 sheet of paper folded in half. I was easily within an 1/8".// |
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Nice.
Pretty much everything in my head is based on visual estimations with no numbers to back them up.
Fresh out of school I got a job as a swamper, (manual labourer moving oil rigs with gin-pole trucks), and after about a year of working for the same company without getting shipped out in a whambulance I would be the head swamper on a lot of the moves. This meant that I was the doofus who would have to line up three separate trucks on three different kilters to three sections of derrick... and then have to be the poor bastard who would have to climb up there and pop that last top pin on every section and decide to ride it out or bail based on my gut feelings on the level square and plum of the trucks I had visually estimated the loads of.
Did that crap for about three years or so without losing a single body part. |
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Sorry, I digress. uh, I've always had to estimate everything without numbers and often guessing wrong would cost my skin or someone else's so that now that life is somewhat more stable I can't really turn off that life/death physics estimation look at everything eight-ways-to-sunday overcompensation thing... and so far it's proven fairly accurate. Nowadays I just take things mentally to their outer extremes for fun. I've worked like thirty some odd years with my hands, daydreaming, so friggin bored you can't imagine and I play with physics and geometry on a prisoners'-cinema level without words for much of what I play with.
We might not have the materials now to make tires that flex and change size, but someday, tires will just morph to accommodate changing terrain. |
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