Why ride pneumatic tyres indoors?

[ironhanglider]

Whenever the question of tyre pressure for indoor velodromes comes up, the usual response is 5psi less than what would cause failure, or words to that effect. Pressures in tubulars of over 200psi is common.

The justification is that there is no need to rely on the suspension effect of the tyre on a wooden velodrome because the surface is close enough to perfect, so therefore a harder tyre will yield less rolling resistance. Surely to take this to the logical extreme, why wouldn't you just make a wheel with a convex surface, and simply glue a rubber 'tread' to it to provide traction?

We have seen lots of innovation at the elite level to reduce aero drag, with many countries spending lots of money to come up with better aero solutions. This seems like an opportunity to reduce the rolling resistance a little (and presumably aero with no tyre/rim junction). It might also have other benefits when it comes to preparing for racing too. No glueing, pumping etc, which reduces the number of things to go wrong. Not being an expert in wheel manufacture it seems to me that changing the moulds wouldn't be too difficult.

Yes, such wheels wouldn't be suitable for less than perfect surfaces, but lots of racers have dedicated race wheels that only get pulled out when it counts.

I have actually spend some time looking up the rules and there is no requirement for pneumatic tyres, except for junior racing.


Cheers,

Cameron

[Danter]

It has been tried. In the late 90s I was shown a purpose built disk wheel with rubber tread glued on to the carbon. Similar to what you described. I think it was built in the early 90s. It was as an experiment by some of the people that went on to build the Australian super bike of the mid 90s. It is a long time ago but I recall I was told at the time it didn't work because vibrations shook the rider too much. I don't recall the exact superlatives but some given!

[Thoglette]

I''ve just chucked two "airless" tyres in the bin. For good reason.

Pneumatic != solid. Or even foam or gell or whatever.

[foo on patrol]

Solid tyres for racing would be crap = unless the surface was without joins then they would be like ridding on a corrugated surface. You need some deflection in the tyre.

Foo

[ironhanglider]

It has been tried. In the late 90s I was shown a purpose built disk wheel with rubber tread glued on to the carbon. Similar to what you described. I think it was built in the early 90s. It was as an experiment by some of the people that went on to build the Australian super bike of the mid 90s. It is a long time ago but I recall I was told at the time it didn't work because vibrations shook the rider too much. I don't recall the exact superlatives but some given!

Do you know if that was a result of testing on an indoor track? In the 90's there were no wooden tracks in Melbourne (the super-bike team were based at RMIT) and the nearest would have been Adelaide or Launceston. The two best tracks in Melbourne at that time were Northcote and Coburg, and they would be generously described as 'smoothish except for the bumps'. I'm not surprised if the ride was unacceptably harsh on them. Both the Melbourne Arena and DISC tracks were built in the early 2000s.

I''ve just chucked two "airless" tyres in the bin. For good reason.
Pneumatic != solid. Or even foam or gell or whatever.

Yes, I'm not talking about those horrid squishy foam things, just a layer of tread glued onto a carbon disc.

Solid tyres for racing would be crap = unless the surface was without joins then they would be like ridding on a corrugated surface. You need some deflection in the tyre.

Foo

How much deflection do you get at 200psi? That seems to be a typical pressure the tech weenies use at DISC. The wooden tracks sure feel smooth to me, but I'm not riding a solid wheel. I'd like to know more about the the wheel Danter saw.

Cheers,

Cameron

[foo on patrol]

My top tyres go to 290psi and I ride them at 220-230psi so they are not at full pressure but even if they were, you'd still have a percentage of deflection.

Foo

[Thoglette]

How much deflection do you get at 200psi?

How much do you weigh? There’s your answer.

I'm too lazy to explain why, but here's a pretty good explanation as to what's happening at the contact patch and why pnuematic tyres are (nominally) completely different to steel (rail) wheels
The contact patch

There's more there than you might care to know about, but the bit you want to visualise is this: what happens to a (nominal) balloon as you push down on it

[ColinOldnCranky]

Solid tyres, even if of foam, would have extra mass.

But it's even worse than that. In a wheel where the mass of the whole wheel is on the rim, the rotational inertia would be double the linear inertia of that same mass (I proved that when I was a student excelling at calculus.) Now clearly such a wheel is a theoretical construction only but even a real wheel would still have most of it's mass in those tyres and rim.

Bottom line - a solid tyre will decrease the competitive performance by a large amount.

[P!N20]

Solid tyres, even if of foam, would have extra mass.

The question wasn’t so much about a solid tyre, but a convex rim (which you have anyway) that has a rubber lining.

Anyway, from what I understand even at >200psi the shock absorbing qualities of a pneumatic tyre are beneficial.

Still, it would be an interesting experiment.

[ironhanglider]

How much deflection do you get at 200psi?

How much do you weigh? There’s your answer.

I'm too lazy to explain why, but here's a pretty good explanation as to what's happening at the contact patch and why pnuematic tyres are (nominally) completely different to steel (rail) wheels
The contact patch

There's more there than you might care to know about, but the bit you want to visualise is this: what happens to a (nominal) balloon as you push down on it

Thanks Thoglette,

I understand all that but my point is that as pressures increase, tyres behave more and more like solid wheels. Foo's numbers would suggest that at full pressure he's already down to less than 1" of total contact patch, split between two tyres. I expect that there are elite pursuit riders who would weigh considerably less, who are using tyres at full pressure too and are therefore even closer to the limit. (Not casting aspersions at Foo's weight )

Given the limits of human sensitivity there will be some point where a convex rim with a rubber tread bonded on, will be indistinguishable from a pneumatic tyre. Clearly the general opinion is that we haven't got to that point yet, but I do wonder where it is.

The whole marginal gains vs diminishing returns thing means that we'll continue to go to greater and greater lengths, for smaller and smaller benefits. I'm sure that the next Olympic velodrome to be built will claim to be smoother and faster than everything before it. As tracks approach perfection, wheels will too in order to take advantage of it.


Cheers,

Cameron

[Thoglette]

I understand all that but my point is that as pressures increase, tyres behave more and more like solid wheels. Foo's numbers would suggest that at full pressure he's already down to less than 1" of total contact patch, split between two tyres. I expect that there are elite pursuit riders who would weigh considerably less, who are using tyres at full pressure too and are therefore even closer to the limit.

I've thought of a simple experiment to see just what is the difference between pnumatics vs solids

a) pump your tyres up to your favourite pressure. Load the tyre up to your normal weight (say 40kg on the front bars). Measure the floor-to-axle distance.
b) add another 40kg or so. Remeasure. Distance/weight is your spring rate

c) take a wheel without a tyre. Repeat steps a) & b)

I'll buy you a beer if the spring rates aren't different by at least a factor of ten

[Danter]

It has been tried. In the late 90s I was shown a purpose built disk wheel with rubber tread glued on to the carbon. Similar to what you described. I think it was built in the early 90s. It was as an experiment by some of the people that went on to build the Australian super bike of the mid 90s. It is a long time ago but I recall I was told at the time it didn't work because vibrations shook the rider too much. I don't recall the exact superlatives but some given!

Do you know if that was a result of testing on an indoor track? In the 90's there were no wooden tracks in Melbourne (the super-bike team were based at RMIT) and the nearest would have been Adelaide or Launceston. The two best tracks in Melbourne at that time were Northcote and Coburg, and they would be generously described as 'smoothish except for the bumps'. I'm not surprised if the ride was unacceptably harsh on them. Both the Melbourne Arena and DISC tracks were built in the early 2000s.

I''ve just chucked two "airless" tyres in the bin. For good reason.
Pneumatic != solid. Or even foam or gell or whatever.

Yes, I'm not talking about those horrid squishy foam things, just a layer of tread glued onto a carbon disc.

Solid tyres for racing would be crap = unless the surface was without joins then they would be like ridding on a corrugated surface. You need some deflection in the tyre.

Foo

How much deflection do you get at 200psi? That seems to be a typical pressure the tech weenies use at DISC. The wooden tracks sure feel smooth to me, but I'm not riding a solid wheel. I'd like to know more about the the wheel Danter saw.

Cheers,

Cameron

I don't know the extent of their testing. Almost certain it would have included Northcote but not sure about indoors. But they went to the trouble of building it so I am guessing they gave it a fair chance.
This wheel had no give other than the thin rubber tread. The carbon fibre disc was built convex like a normal tire would have been.