Current and Proposed New-Builds

I think it may be a smaller proportion of the wheel surface for a larger wheel, but somebody with a better understanding of the relevant maths will have to confirm.

 

The difference would be so small that it would make no difference to performance.

 

All those powerful Schools Class 4-4-0s with 6'9" driving wheels quietly plying their trade round Yorkshire, Hampshire and Sussex need withdrawing forthwith! Not to mention a large-wheeled T9 down in Cornwall ...

Tom

 

The contact area between wheel and rail is independent of wheel diameter and is dependent on the material properties of the wheel and rail. It is essentially an elliptical patch. It is perhaps most easily understood by considering a car tyre. If (say) the tyre is inflated to 30 psi and carries a load of 600 lbs the tyre will deflect until the area in contact with the road is 20 sq inches. If the pressure is reduced to 15 psi the tyre will deflect until the area in contact is 40 sq inches. You will all be familiar with this effect of an under inflated tyre, I’m sure. It is the same with a loco tyre; the steel deflects until the compressive stress ( the tyre ‘pressure’) of the steel is in equilibrium with the load on the wheels.
The above is a slight simplification; if you want more then there are plenty of research papers to be found on the ‘net.

 

I tried once, but managed to put the tablet down before my brain ran out of my ears... I submit that folk like me simply have to accept that, contrary to what that deceiver common sense tells us, wheel diameter is irrelevant to contact area and leave it there.

 

So who's going to tell the Tornado owners, they simply need to pump the tyres up a bit?

 

Everything with a low enough axle load for the K&ESR struggles on Tenterden Bank!

 

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Nicely put Steve, better than I could have done, especially with being a one fnigered tyspit.
Now go to the car and bike forums to explain that low profile tyres and big tyres on bikes just changes the shape of the contact patch.
Bigger tyres means more rubber on the road! Innit?
You might be some time...

 

Or try a normal bike forum ...

For years, the prevailing wisdom was that skinny tyres were faster, on account of less aero drag. Until someone did the measurements and discovered that for a given pressure (and therefore tyre contact patch area), a wider tyre deformed its carcass less along its length; and it is that deformation that contributed to rolling resistance. (The deformation absorbs energy inelastically, so it doesn't come back). Cue a fairly rapid transition about ten years ago to wider tyres. When I was racing 19mm was common; 22mm "if the road was rough". Now everyone on the road uses 25 - 28mm tyres, which we would have thought of as tractor tyres. It's only on the track where speeds are high enough that the aero gains of narrow tyres win; and they use ludicrously high pressures to minimise the contact area, which isn't feasible on the road for comfort and puncture reasons.

Tom

 

So Tom , what oil is best in my steam loco?
I'll get my coat, it's the one covered in oil.

 

Speaking on behalf of myself, insufficient to remove my duvet


Sent from my iPad using Tapatalk

 

Can someone please explain what that was a reply to?

 

"Imagine the pull [i.e. draw to enthusiasts - TJ] it would have if the E class and P class double headed a Wealdon Pullman??!!", that is a new build Wainwright E and existing Wainwright P pulling a dining train on the KESR.

To which @Sheff replied "speaking on behalf of myself, insufficient to remove my duvet " in other words, of insufficient interest to him to be worth getting out of bed for. Heathen ...

The bit I was drily amused by was the concept that if a hypothetical loco which hasn't yet been built did actually get constructed by the labours and funds of one particular railway, it should then automatically go and be used somewhere else altogether!

Tom

 

Thanks Tom. @MellishR - you can track a quote back by clicking on the little up-arrow next to the OP’s name.

 

I often do that, but I see no such quote in post #4511. Were you quoting post #4485 on the previous page, which is missing for me, presumably from someone I'm ignoring?

 

Yes, it's from someone I think likely is on your ignore list! Which is why I don't bother doing it, it makes some threads non-sensical.

 

Ditto

 

Resurrecting something I started a while ago, what do we think will be the next newbuild to steam?
Betton Grange is looking very good, but do they have a tender for it (and will the panel consider it complete without a tender of their own?)
The Brighton Atlantic is also looking good.
I still maintain a cheeky sidebet on the G5.

 

I would dearly love to say that it will be the G5 - but I think the Grange or the Atlantic are the two most likely candidates.

 

Ditto. Gonna say that 6880 will be next, considering the boiler cladding and pipe work is almost complete. Coat of paint and borrowing a tender temporarily will see Betton Grange steam next….if the Beachy Head group doesn’t tease us with lowering the boiler into the frames….