Solid verses pneumatic

OP
B

Biker man

Well-Known Member
And if they don't like the tyres, there's always the rider.
I've ridden in Canada there are bears about and they will eat you.
 

andrew_s

Guru
Location
Gloucester
Solid tyres seem like an excellent idea - but no-one has yet found a material that can be used with any reasonable level of success for a normal bicycle
There is no such material.

Pneumatic tyres work because there is a single air chamber that distributes any change in pressure round the whole wheel. Take a tyre, and squeeze an inch of it down to the rim, and the volume of the air chamber, and hence the pressure, will only change by about 1%. The force required to get the last 10% down to contact with the rim is almost the same as to get the first bit of movement.

In any non-pnematic tyre there is no mechanism for distributing the change in resistance round the wheel, and all changes are limited to that part of the tyre between the rim and the road. If the tyre is pressed half way down to the rim, the force required to move the tyre is double what is was to start with, at 3/4 down the rim it's 4 times, and at the start of the last 10% it's 10 times.
Since there's a minimum pressure equivalent under steady riding on a smooth surface, from a handling perspective, it's inevitable that any non-pneumatic tyre will give a harsh ride. It doesn't matter whether it's foam, a fancy elastomer, or some arrangement of springs, it's all the same.

I'll give a half excuse to HLaB's bike with the gun. If the tyre is rigid, it's the same as a solid steel wheel with 1" or 1.5" travel suspension.
I dare say the gun gets you more road space tho' :smile:
 

andrew_s

Guru
Location
Gloucester
A futher point would be that, because non-pnematic tyres give a harsh ride, they are slow.
All the vibrations that get through to your body are lost energy, human flesh not being noticeably springy, and that lost energy must be replaced from somewhere (i.e. your legs), or you'll slow down.
 

Ajax Bay

Guru
Location
East Devon
Take a [pneumatic] tyre, and squeeze an inch of it down to the rim, and the volume of the air chamber, and hence the pressure, will only change by about 1%.
Show workings please or I'll assume Andrew, that you have plucked this figure from an orifice where the sun doesn't shine.
If the non-pnematic [sic] tyre is pressed half way down to the rim, the force required to move the tyre is double what is was to start with, at 3/4 down the rim it's 4 times, and at the start of the last 10% it's 10 times.
You are assuming that the tyre's material is elastic in that complete range, which I assert is most unlikely. This latter observation is (agreeing with you - no such material) nugatory (and the deduction you make from this erroneous quantatitive approach is entirely valid), but let's stay within science's bounds.
 

figbat

Slippery scientist
I saw a demonstration once to prove that applied load to a tyre makes no difference to its pressure. A car was on a workshop life, tyres in the air. A tyre pressure gauge was attached. The car was then lowered onto its wheels - the gauge needle stayed put.
 
OP
B

Biker man

Well-Known Member
I went to canada once to do some bear hunting
As i was driving along i came to a road sign which said "bear left"........so i went home :whistle:
😃😄😃
 

lazybloke

Lying in the grass looking at the clouds
Location
Leafy Surrey
I saw a demonstration once to prove that applied load to a tyre makes no difference to its pressure. A car was on a workshop life, tyres in the air. A tyre pressure gauge was attached. The car was then lowered onto its wheels - the gauge needle stayed put.
Seems wrong but I need to think about reasons. Relatively low pressure of car tyre with large contact area and inaccurate gauge: that's my gut feeling.
 

newfhouse

Resolutely on topic
I saw a demonstration once to prove that applied load to a tyre makes no difference to its pressure. A car was on a workshop life, tyres in the air. A tyre pressure gauge was attached. The car was then lowered onto its wheels - the gauge needle stayed put.
Surely the pressure will only be higher at the contact point, where the tyres bear the weight. What would happen if you carefully rotated the wheel so that the valve was at the bottom before measuring?

I base my question on the observation that when I pick up a puncture - twice at the weekend - the tyre only deforms near to where it touches the road.









:wacko:
 

Alex321

Über Member
Location
South Wales
Surely the pressure will only be higher at the contact point, where the tyres bear the weight. What would happen if you carefully rotated the wheel so that the valve was at the bottom before measuring?

I base my question on the observation that when I pick up a puncture - twice at the weekend - the tyre only deforms near to where it touches the road.
:wacko:
The pressure is even all across the inside of the tyre, because said tyre is a single chamber.

The fact it compresses where it is in contact with the road just means the rest of the tyre expand to compensate - but the fact there is so much more not in contact with the road means that expansion is imperceptible to the naked eye.
 

figbat

Slippery scientist
Scientifically though, in order for the pressure to change then one of two things must change: volume or temperature. Assuming temperature remains constant then the only vector to increase pressure is a volume change. Does deforming a tyre change the volume, or simple reshape it? The air pressure does not, itself, bear the weight of the vehicle (like, for example, in an air fork) - the pressure provides rigidity to the tyre carcass which bears the weight.
 

lazybloke

Lying in the grass looking at the clouds
Location
Leafy Surrey
Not necessarily inaccurate as such, just with too coarse a scale.
Yes, having considered various scenarios for the area of tyre contact patch on a unicycle with light & heavy riders, I reckon I agree with you Alex.

Possible next steps are : mathematical modelling, followed by practical experiments with my unicycle.
 
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