Pressures for larger tyres

[dollythelw]

John, the tins are in reasonably good condition and Ive tried to keep them stored off the ground on small stands. Should they be moved clockwise or anticlockwise?

Fridge - its Whitworth, looks totally unused, I dont think it needs a compressor as the label says pre-compressed... I think you just stir it and pour it in, wouldnt a funnel and pipe do?

Same sized tyres, same type of ground, 408 was using 12 metres of air but 402 only had half a bushel, I think thats pretty conclusive proof if ever its needed........ (Im just not sure what of...)

more tyre tech..?

cheap grades of air wear out quickly

Ari and Make concluded that an emulsion of marine grade air and Leos special Dutch "Organic" air reduced ground pressure

how many moles are we talking about?

[Guest otchie1]

Otchie, if you need a BSc you can borrow my MEng for a bit until you get your own (or will swap for a calibrated tyre pressure gauge).

Oo Oo Oo, I've always wanted a MEng...is it still shiny and will a gauge calibrated in candela do? It says on the side that as more air means more cooling so a cooler tyre radiates less light.

[Guest otchie1]

.

Be careful using old canned air. If not regularly stirred in can separate. Here Lars clearly has all the hydrogen in the front tyres causing a certain lightness of steering

[LR90]

Applying the calculation from the link I need 17psi per tyre based on a gestimation of vehicle weight, which sounds about right. Off to buy some chalk and see if we were close?

Alleluia

[Turbocharger]

cooler tyre radiates less light

No no, a lighter tyre radiates less heat, an easy confusion to make. You can borrow my MEng for as long as you need it, but if you want the (Hons) too I'll swap for a boggo tyre gauge and a speedo calibrated in furlong/fortnights (with conversion chart in original condition).

Jez - obviously there's no hard rule to decide if you rotate the tins clockwise or anti-clockwise, it depends how they were filled (although interim stirring can confuse this). There are a number of rumours about this, the only way to be sure just be sure to turn the tin upside down if you meet any stiff resistance to conserve the gyroscopic motion.

Going off-topic (oh, NOW he's going off-topic) would I need to alter the pressure in my tyres if I filled them with helium? The mass of gas would be different but the stp volume would be the same - what is the effect on ground pressure?

[glaggs]

Depends on the Fish.

[BogMonster]

cheap grades of air wear out quickly

Tut. That is what happens when you rely on cheap East European air

Ladair perhaps?

[dollythelw]

I think it was imported (rumour has it, that is ex-Branson balloon air recaptured and relabled), the Russian stuff is rationed and only available on the black market in brown paper bags from men in beige coats, easy to spot - its a tell tale green colour..

[Guest otchie1]

No no, a lighter tyre radiates less heat, an easy confusion to make.

Of course, silly me. As it has less mass it has a lower heat capacity and therefore radiates less once its warmed up to regulo 4.

So, what we're saying is if you over inflate your tyres, all that extra pushiness in the tyre pushes downly at the road and, as every action has an equal and opposite, when you move off the road pushes back to much and you leave little hills behind. Is that it? And when you lower the pressure to go off road that effect is lost so you make ruts?

All makes sense now sensei MEng(Disct) TurboCharger

Oh and be careful with helium tyres, you can put so much volume in that you'll damage your hearing.

[dollythelw]

helium filled tyres sound different when you spin them up outside Mcdonalds, a bit like tyres from a Smurf mobile

[Guest otchie1]

Fridge - its Whitworth, looks totally unused, I dont think it needs a compressor as the label says pre-compressed... I think you just stir it and pour it in, wouldnt a funnel and pipe do?

"..just pour it in"

:hysterical:

[Corrode Finger]

Ooooooh......... i am really confused, can someone explain this tyre pressure/ air/ volume thing to me ?

Also, as my air comes from a non defined source, will the co2 in my breath have an effect on the performance?

[sheeppimp]

can someone please help - i have a choice of tyres for my 1952 80in, obviously standard air for the 6.00 tyres would be whitworth clockwise air, however if i fit the 205 tyres on disco rims do i need metric air? or would whitworth air still work as the vehicle is still the same age? might need another compressor to ensure no cross-contamination?

Jez - can i have two pounds three ounces of your air please to top up my tyres ( just pop it in a jiffy bag and post it)

[glaggs]

Try hot air, there seems to be plenty of that freely available.

[dollythelw]

PM me an address and I'll sort some out - Stig spilled some on the floor but I can hoover it up, run it through an air filter to get rid of any impurities though?

[Exmoor Beast]

I see nobodys mentioned Exmoor Air. There seems to be some strange property in Exmoor Air that enables it to sneak between a BFG tyre and the wheel rim and escape.

I am very glad its Friday, I am going to need a drink come the end of this thread today

Will

[Guest otchie1]

can someone please help - i have a choice of tyres for my 1952 80in, obviously standard air for the 6.00 tyres would be whitworth clockwise air, however if i fit the 205 tyres on disco rims do i need metric air? or would whitworth air still work as the vehicle is still the same age? might need another compressor to ensure no cross-contamination?

Jez - can i have two pounds three ounces of your air please to top up my tyres ( just pop it in a jiffy bag and post it)

With the real early air it's probably wartime military air which was double-helix handed and super heavy. If you start to run low an old gunner's dodge was to take the tyre off (saving the air natch), remove the inner tube, fold the inner tube in half and refit to the bottom of the wheel. You've got to make sure it stays at the bottom otherwise it won't work. Then just put it all back together and you can sell the other half of your air ration on the black market.

It works because you only need air at the bottom of the tyre and the super heavy air natural flows there. Good for speeds up to about Mach5.4

You can tell if it's real double-helix air as it should whistle as you pour it back in.

[Escape]

Sure is some interesting reading here...

My 2cents:

For a given load, the contact area depends only on the pressure and sidewallstiffness.

Assuming the latter is constant, with larger tires having a stiffer construction but also larger deformation lengths, that leaves only pressure.

Pressure, as repeatedly stated here, is force/surface. The load is given, so the force is known.

However, larger tires tend to be wider as well, meaning for the same load and pressure, the contact surface would be identical to that of a smaller tire, but as it is wider, the contact length will be smaller, thus allowing for less pressure.

The contact lenght is what determines the 'unroundness' of the tire, in turn causing sidewalls to deform to allow the round tire to adopt a flattened stretch.

My conclusion would be you can decrease the pressure as the tire gets wider, and in turn it is more important to air down wide tires when offroading to create sufficient contact length, allowing the thread to grip.

I also read some comments about pressure to the sidewalls keeping the tire up. In my view, the primary force accomplishing the load bearing is that resulting from the pressure on both the thread in contact with the road and the resulting reaction force. In fact, if the sidewall is not stiff enough, it will allow the tire to deform sideways under the pressure inside, so decreasing the height of the tire.

[Corrode Finger]

Try hot air, there seems to be plenty of that freely available.

As i said, i am really rather confused by this thread, can someone do a pop up picture explanation?

Here's another conumdrum, Hot air, hot does that affect the performance in a tyre!!

This is a topic i had never even considered, it appears to be very improtant!

Its good to see we have some experts on this forum!

[Guest otchie1]

I see nobodys mentioned Exmoor Air. There seems to be some strange property in Exmoor Air that enables it to sneak between a BFG tyre and the wheel rim and escape.

That'll be because when they fitted the tyres they used to much lubricant. Makes it easy to slip the tyre on of course but also easy for the air to slip out. Take it back and complain if I was you.

[dollythelw]

Here's another conumdrum, Hot air, hot does that affect the performance in a tyre!!

a lap and a half at Pembrey with cut slicks at 18psi makes em good an gooey

not sure about bigger tyres having stiffer sidewalls Escape - big boggers (after they've been broken in) have the sidewall stiffness of my wifes gravy, it makes them nice on meat but can leave unpleasant stains during high speed feeding frenzies

interesting point about Exmoor air - wonder what Finnairs like?

[glaggs]

Sure is some interesting reading here...

My 2cents:

For a given load, the contact area depends only on the pressure and sidewallstiffness.

Assuming the latter is constant, with larger tires having a stiffer construction but also larger deformation lengths, that leaves only pressure.

Pressure, as repeatedly stated here, is force/surface. The load is given, so the force is known.

However, larger tires tend to be wider as well, meaning for the same load and pressure, the contact surface would be identical to that of a smaller tire, but as it is wider, the contact length will be smaller, thus allowing for less pressure.

The contact lenght is what determines the 'unroundness' of the tire, in turn causing sidewalls to deform to allow the round tire to adopt a flattened stretch.

My conclusion would be you can decrease the pressure as the tire gets wider, and in turn it is more important to air down wide tires when offroading to create sufficient contact length, allowing the thread to grip.

I also read some comments about pressure to the sidewalls keeping the tire up. In my view, the primary force accomplishing the load bearing is that resulting from the pressure on both the thread in contact with the road and the resulting reaction force. In fact, if the sidewall is not stiff enough, it will allow the tire to deform sideways under the pressure inside, so decreasing the height of the tire.

OK if this was true why not just run' solid tyres and leave out the air altogether. You could engineer them to deform to give the right contact patch on the road surface and even offer some help by deforming over bumps etc. Answer because they would over heat because the air pocket is an aid to keeping the tyre at the optimum temp. Adjusting the amount (mass/volume -delete as you wish) of air inside the tyre will influence the operating temp of the tyre. Temp. of the tyre is crucial to the tyres performance, ever heard about warming up the tyre?

[honitonhobbit]

I have some very rare Heavy Air. Designed for use in the front wheel of a 1200 Bandit. I found that there was no need to use it after I had fitted (and used the NOS) as I had developed a keen sense and understanding of shear terror.

As it is so rare and very concentrated I only have a very small amount (about .3 of a Troy ounce) but it wil dilute down easily.

TurboC would you swap an FRGS for a month of your MEng? Or maybe an FRSA?

[Exmoor Beast]

interesting point about Exmoor air - wonder what Finnairs like?

I know Alpine Air at 4164metres above sea level is bloody thin, I should think its a devil of a caper getting that stuff to stay in tyres, it would sneak through the smallest of gaps.

I would think nice cold Finn air would be great for shoving through an intercooler but hopeless for tyres.

Will

[Turbocharger]

Tractors sometimes run water in the tyres for extra weight (or mass) - could they get extra performance from knowledge partnering with the nuclear industry and use heavy water for even more traction?

Although you're my Dad you can't pull the "blood's thicker than water" card. I'll trade you an associate membership of the IMechE and a 25-metre swimming certificate for your FRGS, six quarts of (uncompressed) Exmoor air and a digestive biscuit. Final offer or it's all going on Ebay.