Rail & wheel design

[DJL]

I was pondering earlier today - how did we arrive at the current rail and wheel design?

I expect a lot of thought has gone into it over the years and that it remains the correct design to use.

However, with all the poor adhesion lately I can't help but wonder whether alternatives might be more suitable.

Thinking about car tyres - having grooves on the wheels or rails would presumably help with grip. I can't believe no one has thought of this before therefore I assume there must be a good reason why it can't/shouldn't be done.
Maybe to do with wear+tare (tear?), noise, or maybe it just slows trains down too much in good conditions.


But then I got thinking - if indeed grooved wheels *is* a good thing, but only in certain conditions, what if we were to devise a way to have both smooth and grooved wheels available as and when required?

i.e. lower the correct wheels into position and retract the undesired ones.

Now obviously, assuming that any such system were safe to use at speeds above 0.5mph there would probably be a cost, and a huge one at that, to implement such a system - not to mention the added maintenance cost.

But if, and I emphasise the if, it were possible (and desired) - might the benefits actually outweigh the costs?

I'm no money expert but just thinking about the amount of money lost due to poor adhesion alone - late running fines, cancellation fines, delay repay, lost revenue from delayed/cancelled services causing passengers to look elsewhere.
Does all this add up to be enough to counter the outlay?


I think I know the answer, but thought I'd throw it out there for discussion anyway...

 

[John Webb]

I'd have thought that the money would be better spent on cutting back lineside growth to avoid 'leaves on the line' in the first place. BR used to do such pruning in the days of steam to minimise the risk of lineside fires; it also had the effect of minimising slippery rails. It would be a lot simpler than changeable wheel sets and possibly cheaper?

 

[eMeS]

Having read several of the recent discussions here about poor wheel adhesion, I was amazed to see Michael Portillo riding up Snaefell on an electric tramcar which relied totally on adhesion for its grip. Quote from Wikipedia: "uses a Fell Incline Railway System centre rail for braking on the steep gradients". No mention of anything other than wheel grip for the ascent. 600m rise in 8,000m - something like 1 in 13. The conditions when Portillo was being filmed were heavy rain, so perhaps the leaves get washed off!

 

[Ploughman]

Installing a groove or tread in the wheel would create more problems.

It would create vibration due to the tread pattern.
Probably create more stress faults in the rail as wheel flats do now.


The amount of the wheel actually in contact with the rail would reduce further.
The actual amount of wheel in contact with the rail is approximately the size of a 10p piece per wheel.
Would this increase delays due to poor adhesion?

 

[DJL]

I'd have thought that the money would be better spent on cutting back lineside growth to avoid 'leaves on the line' in the first place. BR used to do such pruning in the days of steam to minimise the risk of lineside fires; it also had the effect of minimising slippery rails. It would be a lot simpler than changeable wheel sets and possibly cheaper?

As has been pointed out before - leaves on the line is not the only cause of poor adhesion.
apparently light rain is also really bad. And recent experience would appear to corroberate this.

So pruning trees is only a partial solution

 

[Nick W]

Is there any evidence that trains aquaplane?

 

[L&Y Robert]

I remember reading an article years ago in 'Modern Railways' (I think it was), by-lined "Plasma torch can cure adhesion problems". What happened to that technology, then?

 

[DJL]

Installing a groove or tread in the wheel would create more problems.

It would create vibration due to the tread pattern.
Probably create more stress faults in the rail as wheel flats do now.


The amount of the wheel actually in contact with the rail would reduce further.
The actual amount of wheel in contact with the rail is approximately the size of a 10p piece per wheel.
Would this increase delays due to poor adhesion?

Hmm. Again I am not claiming to be an expert but my understanding of why car types have a tread, and why F1 change to treaded types in wet weather is bevause it allows the water to move put of the way resulting in more of the (remaining) tyre to actually contact the road rather than the water.

That said it Is likely that rubber behaves rather differently than solid metal wheels...

 

[David Barrett]

Oddly enough modern bogie design and brake equipment has played a part in the adhesion problem. With more recent designs the tendency for the wheelsets to hunt (yaw) and impart a scrubbing action to the railheads has been damped out leading to a better ride but with the loss of the conditioning effect that this motion had on the rail. Likewise the use of disc brakes in some cases instead of the traditional cast iron tread brake blocks has lead to the loss of the same conditioning effect on the wheel tread area.

Whilst there have always been known areas of poor adhesion, recent events and design improvements highlights the ever present problem of one man's solution leading to another's headache; maybe, in this light, it is time to look at lineside husbandry once more.

 

[razor89]

Having read several of the recent discussions here about poor wheel adhesion, I was amazed to see Michael Portillo riding up Snaefell on an electric tramcar which relied totally on adhesion for its grip. Quote from Wikipedia: "uses a Fell Incline Railway System centre rail for braking on the steep gradients". No mention of anything other than wheel grip for the ascent. 600m rise in 8,000m - something like 1 in 13. The conditions when Portillo was being filmed were heavy rain, so perhaps the leaves get washed off!

Possibly the tramcars are too light to crush the leaves into the form found on heavy rail? Also they won't produce a draught behind them like heavy rail trains, which tends to suck leaves onto the track.

 

[CalderRail]

On the "one solution becomes the next problem" theme, remember that vegetation along rail routes helps cut down on the noise. If you cut it all back, be prepared for complaints and campaigns for reinstatement.

 

[boing_uk]

Actually, vegetation cutting noise is a common but very mis-informed myth.

When I was studying Traffic Engineering, foliage actually reduces incidental noise from traffic very little - it isn't dense enough.

Sometimes, in windy conditions it masks noise by the action of wind interacting with the foliage, but it does not *reduce* noise levels at all.

 

[Trog]

Thinking about car tyres - having grooves on the wheels or rails would presumably help with grip. I can't believe no one has thought of this before therefore I assume there must be a good reason why it can't/shouldn't be done...

Such grooves would be stress raisers, broken tyres the likely result. Also as has already been said with metal wheels the vibration and impacts would also be detrimental to both track and stock.

 

[fowler9]

Actually, vegetation cutting noise is a common but very mis-informed myth.

When I was studying Traffic Engineering, foliage actually reduces incidental noise from traffic very little - it isn't dense enough.

Sometimes, in windy conditions it masks noise by the action of wind interacting with the foliage, but it does not *reduce* noise levels at all.

I certainly didn't notice any difference in the noise from the railway when the trees behind ours were cut back, in fact removed completely. We do get infinitely less leaves in our garden (And I imagine on the railway line), we get lots more sunlight and the view is improved, from upstairs at least.

Back on subject, aside all the other reasons wouldn't cutting groves in train wheels make them really noisy as well (Due to the increased vibration).

 

[Bald Rick]

There is a very noticeable increase in rail defects (and thence speed restrictions) when we have autumn, almostr certainly down to a higher incidence of 50p wheels. One can only imagine the rail damage that steel wheels with a tread on would cause.

(The contact patch between rail and wheel is approx the size of a 5p piece, so a treaded wheel would knock hell out of the rail.)

As has been said above, the answer is to cut the trees down.

 

[Moonshot]

On the subject of track design, I came across this the other week

http://www.hud.ac.uk/news/2013/october/15millionprojecttorevolutioniserailwaytracks.php

 

[edwin_m]

I remember reading an article years ago in 'Modern Railways' (I think it was), by-lined "Plasma torch can cure adhesion problems". What happened to that technology, then?

That was one of the more batty BR Research ideas from, I think, the early 70s. Which only goes to show that the problem pre-dates modern stock.

I also saw a TV programme a few years ago saying that the Italians sometimes have bad adhesion problems on the causeway to Venice because at a certain time of year the rails are swarming with some kind of crawling insect which make a very slippery paste when crushed under the wheels.

Sand probably has quite a bit to do with the grip exerted by trams - modern ones dispense it automatically whenever wheelslip is detected and older ones have manual dispensers. I recall some years back being part of some tests on a Croydon tram where my collegues tried to make it spin its wheels by dispensing soapy water from an onboard tank. At the time some of the TOCs would send a Sprinter out on a line that didn't matter much, fitted with similar dispensers to give their drivers "skid pan training", but it was virtually impossible to make the tram lose its feet.

Most units now have sanders of some sort, as mentioned on some recent threads, and that certainly helps.

 

[Mugby]

One thing I've noticed painted on the solebars of many wagons and perhaps coaching stock too, I can't remember, is a cross section of a wheel and flange with something like 'P5' or 'P8' printed against it.

Anyone know what this means?

 

[HSTEd]

Trams tend to be all wheels motored though.

Which certainly helps since the entire weight of the vehicle is usable for generating adhesion.

 

[David Barrett]

One thing I've noticed painted on the solebars of many wagons and perhaps coaching stock too, I can't remember, is a cross section of a wheel and flange with something like 'P5' or 'P8' printed against it.

Anyone know what this means?

There are different tyre profiles in use, the diagram that you see indicates the profile applicable to that particular item of rolling stock and is for the information of the maintenance staff.

 

[edwin_m]

Trams tend to be all wheels motored though.

Which certainly helps since the entire weight of the vehicle is usable for generating adhesion.

Most have two thirds of axles motored, which allows a maximum gradient of about 6.5%. Sheffield and Nottingham (don't know about Blackpool) do have all axles motored allowing gradients of about 10%.

 

[DJL]

Ok so it sounds like grooved wheels is a bad idea.

What else?

It did occur to me - the old steam engines used to have rather huge wheels for putting down the power.

With a larger diameter wheel there would be more of the wheel in contact with the rail at any time.

Of course this would have the negative effect of increase the distance between the rail and the axle which would then raise the carriage body up as well

Also wider wheels would produce a larger surface area too but I assume there is a very good reason why this can't be done - probably to do with curve radius and/or the flange scraping on the side of the rail?


Perhaps simply directing the power to more of the already available wheels would help?
But then does a 2car EMU (DM+DM) already deliver power to every wheel?

 

[bronzeonion]

Makes me wonder why they got rid of tread brakes in the first place? Even with disc brakes you can still have tread brakes quite happily working alongside them! Near enough all modern Japanese EMU's use both on the same bogie and I think I spotted both on the new bogie for the Desiro City.

 

[W230]

With a larger diameter wheel there would be more of the wheel in contact with the rail at any time.

It would be minimal. I'm sure there must be other reasons they moved away from such large wheels.

Also wider wheels would produce a larger surface area too but I assume there is a very good reason why this can't be done - probably to do with curve radius and/or the flange scraping on the side of the rail?

Again though, it would be minimal. The main reason there are adhesion problems is that you are trying to move/stop a very heavy object with a very low coefficient of friction between its wheels and the rail head (F=µR and all that). Most of the time there are not low adhesion problems and they do not occur everywhere. Your suggestions would be expensive and make very little (if any) noticeable difference.

Perhaps simply directing the power to more of the already available wheels would help?
But then does a 2car EMU (DM+DM) already deliver power to every wheel?

The shortest EMUs are 3 cars (such as the 313). They do have more driven axles (although still not all) but I think this is more to do with improved acceleration for short stops. Again, when low rail adhesion strikes I just don't think it would make much difference.

 

[hwl]

Makes me wonder why they got rid of tread brakes in the first place? Even with disc brakes you can still have tread brakes quite happily working alongside them! Near enough all modern Japanese EMU's use both on the same bogie and I think I spotted both on the new bogie for the Desiro City.

From memory of the Thameslink train spec the motored axles of the Desiro City have tread brakes to help reduce adhesion issues

 

[pablo]

The contact patch must be tiny, rather less than the 5p mentioned.

As some rolling stock gets lighter, does that improve or detract from adhesion?

 

[eMeS]

I recall the Paris Metro back in around 1963 having rubber tired wheels on some of its stock. No idea whether it's still in use.

 

[fowler9]

I recall the Paris Metro back in around 1963 having rubber tired wheels on some of its stock. No idea whether it's still in use.

Was fairly recently on the Santiago metro in Chile and the stock on 4 of its 5 lines is rubber tired, some of it brand new stock.

 

[jopsuk]

Wikipedia article on rubber tyred metro systems- goes into pros, cons and lists installations.

 

[507 001]

Sand probably has quite a bit to do with the grip exerted by trams - modern ones dispense it automatically whenever wheelslip is detected and older ones have manual dispensers. I recall some years back being part of some tests on a Croydon tram where my collegues tried to make it spin its wheels by dispensing soapy water from an onboard tank. At the time some of the TOCs would send a Sprinter out on a line that didn't matter much, fitted with similar dispensers to give their drivers "skid pan training", but it was virtually impossible to make the tram lose its feet.

Most units now have sanders of some sort, as mentioned on some recent threads, and that certainly helps.

I've found that it's actually quite easy to make a tram lose it's feet (M5000), especially on street running sections. I spent an entire evening last week fighting a tram all the way to Ashton and back (twice) every time I went for a bit more than the first notch of power the thing was spinning its wheels.
Braking can also be quite interesting at this time of year.
We're always slipping and sliding around.