# Solid verses pneumatic

#### Ajax Bay

##### Guru
Possible next steps are : mathematical modelling
And that 'modelling' (as you put it) will determine that the pressure in a pneumatic tyre (cycle or motor) experiences a negligible increase when a load is applied. Do not trouble the gauge: any change will be less than the instrument error.
Don't be a lazybloke; think about it.

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C R

#### mickle

##### innit
Their manufacturers never mention that 'solid' tyres wear out more quickly than pneu tyres. In theory you could run them until nearly worn to the rim, but the flat top which characterises even a lightly used foam tyre puts you on a pronounced edge in a corner, reducing the contact area when you need it most. The other worst thing about foam tyres, after the terrible rolling resistance, added rotating weight, propensity to spin on the rim under hard braking and often enormous challenge of fitting them is that they absolutely destroy rims. The inch or so depth of tyre does nothing to disperse impact forces.

#### mickle

##### innit
Who's up for a discussion on the pros and cons of the Scott Oiler?

#### andrew_s

##### Guru
Show workings please or I'll assume Andrew, that you have plucked this figure from an orifice where the sun doesn't shine.

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.
The circumference of a 700c tyre is about 210 cm, and an inch is 2.5 cm. 2.5/210 = 0.0119, which in my book is "about 1%".
Not difficult is it?

In fact, that's an overestimate, as the tyre sidewalls will bulge outwards where the contact patch is pressed inwards, offsetting the loss of volume to some extent. The cross section of an undeformed tyre is circular, and a circle encloses the maximum area for a given perimeter, so any deformation involves a loss of volume, but it's not as much as it would be if the rest of the tyre stayed the same shape.

I allowed elastic over the full range because that's the best case.
Any deviation from "elastic over the full range" is most likely to either being a sudden increase in resistance over what a simple elastic proportionality would give, or it's going to involve a permanent or near permanent deformation or failure.
Bear in mind that the energy spent compressing the tyre tread has to be recovered somehow, otherwise the rolling resistance will be horrendous. I'd contend that that means that only elasitic materials will be usable.
Unless, of course, you have any suggestions?

#### andrew_s

##### Guru
The other worst thing about foam tyres, after the terrible rolling resistance, added rotating weight, propensity to spin on the rim under hard braking and often enormous challenge of fitting them is that they absolutely destroy rims. The inch or so depth of tyre does nothing to disperse impact forces.
Not just rims.
One comment I do remember from an ex-user was that he'd had more broken spokes than he previously had punctures.

#### lazybloke

##### Lying in the grass looking at the clouds
And that 'modelling' (as you put it) will determine that the pressure in a pneumatic tyre (cycle or motor) experiences a negligible increase when a load is applied. Do not trouble the gauge: any change will be less than the instrument error.
Don't be a lazybloke; think about it.

#### Smokin Joe

##### Legendary Member
Who's up for a discussion on the pros and cons of the Scott Oiler?
I remember that from the C+ days. A new poster would occasionally come on with a post about Scotoilers that read just like an advert - which it was. It stopped when every reply they got was a stream of abuse.

#### nickyboy

##### Norven Mankey
It seems the current solid tyres are a poor alternative to pneumatic. But consider that the bicycle industry has been extraordinarily poor at innovating. Take for example tubular and tubeless tyres. Automobiles moved off tubular in the 1950s as tubeless was better. But tubular tyres are still a regular fixture on bicycles with all the puncture and pinch flat issues associated

Maybe it just needs a properly funded innovative approach to overcome the issues with current solid tyres

#### figbat

##### Slippery scientist
It seems the current solid tyres are a poor alternative to pneumatic. But consider that the bicycle industry has been extraordinarily poor at innovating. Take for example tubular and tubeless tyres. Automobiles moved off tubular in the 1950s as tubeless was better. But tubular tyres are still a regular fixture on bicycles with all the puncture and pinch flat issues associated

Maybe it just needs a properly funded innovative approach to overcome the issues with current solid tyres
I assume you mean tubed vs tubeless, rather than tubular, which are stick-on tyres that are not that widely used and are essentially treaded tubes.

But some of it comes down to convenience - it is relatively easy for the lay person to replace a bicycle inner tube, should it be punctured. It is somewhat more tricky for a motorcycle (where they are still common in offroad bikes) and even harder on a car wheel. Hence the case for change is less compelling. that said bicycle tubeless is a growing sector.

#### Alex321

##### Über Member
It seems the current solid tyres are a poor alternative to pneumatic. But consider that the bicycle industry has been extraordinarily poor at innovating. Take for example tubular and tubeless tyres. Automobiles moved off tubular in the 1950s as tubeless was better. But tubular tyres are still a regular fixture on bicycles with all the puncture and pinch flat issues associated

Maybe it just needs a properly funded innovative approach to overcome the issues with current solid tyres
Maybe. But automobiles haven't yet made any move in that direction

TBH, I think the differences inherent in going from a single air chamber to any sort of solid or foam construct are such that it is unlikely they will ever manage to get the same ride quality, although the other issues are probably solvable.

#### Ajax Bay

##### Guru
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 circumference of a 700c tyre is about 210 cm, and an inch is 2.5 cm. 2.5/210 = 0.0119, which in my book is "about 1%".
Not difficult is it?
Thank you. I agree that pneumatic tyres are superior than solid ones for nearly all uses.
I took issue with (and invited you to explain) why depressing a tyre to its rim for one inch means the overall volume of the air chamber reduces and the pressure increases "by about 1%". Your explanation is unconvincing.
I suggest that such depression would merely displace the air to other parts of the toroid, which would expand slightly to make up; that the "volume of the air chamber" would stay the same (not decrease); and the pressure would be unaffected.
I think we agree (on the topic headline Q) but your random 1% was worth a 'chat'. Difficult? No. Pub ride - just back from it .

C R

#### biggs682

##### Smile a mile bike provider
We use solid tyre's on the wheelchair and wouldn't go back to pneumatic ever .

#### andrew_s

##### Guru
I suggest that such depression would merely displace the air to other parts of the toroid, which would expand slightly to make up; that the "volume of the air chamber" would stay the same (not decrease); and the pressure would be unaffected.
I disagree.
What causes the rest of the toroid to expand?
If it expands, it's because the walls have stretched to enclose a larger volume, and the only thing that can cause that stretch is increased pressure in the tyre. In the case of a balloon, there would indeed be an increase in volume in the rest of the balloon that would partly offset the increase in pressure, but tyres are designed not to stretch significantly.

#### figbat

##### Slippery scientist
As I said before, the volume is reshaped rather than changed. The tyre bulges to the side of the depression, which can easily be seen on a car tyre when viewed radially.

#### andrew_s

##### Guru
But the bulges are smaller than the depression, so there's an overall reduction in volume.
I explained why in post 94 up above.