-
Our new ticketing site is now live! Using either this or the original site (both powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!
Pacer track wear
- Thread starter TWPacer
- Start date
- Status
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R
RailUK Forums
northwichcat
Veteran Member
I'd be very surprised if tyre profiles on Pacers didn't need doing more frequently. The squealing that comes off them on sharp bends makes you wonder how they don't need a new set after every journey on curved track.
They were actually removed from the Cornish lines because they needed replacing too quickly but since then have had a modification so they don't wear out as quickly.
I've also heard that frequent Pacer use affects the track so it becomes a less good ride for other types of rolling stock. Apparently, this is also the reason for the poor ride on the M5000 trams on the old BR lines in Greater Manchester, the T68s have affected the track so it's less good for the M5000s.
They were actually removed from the Cornish lines because they needed replacing too quickly but since then have had a modification so they don't wear out as quickly.
I've also heard that frequent Pacer use affects the track so it becomes a less good ride for other types of rolling stock. Apparently, this is also the reason for the poor ride on the M5000 trams on the old BR lines in Greater Manchester, the T68s have affected the track so it's less good for the M5000s.
Ploughman
Established Member
On jointed track they do cause joints to dip or existing dipped joints to become worse.
DaveNewcastle
Established Member
Here are Networks Rail's charges for the various classes of vehicle and freight: Track Usage Price List - 2009/10 prices
I would say that these costs are intended to reflect the impact on the network of each class of vehicle, and the 14x seems to get off with the lowest charges.
I would say that these costs are intended to reflect the impact on the network of each class of vehicle, and the 14x seems to get off with the lowest charges.
Speaking of Pacers and track wear...A mate of mine linked this to me the other day...
Not so much as Bouncey Bouncey...
http://www.youtube.com/watch?v=ya1hG7F_EPg
Not so much as Bouncey Bouncey...
http://www.youtube.com/watch?v=ya1hG7F_EPg
northwichcat
Veteran Member
Somewhere on YouTube there's a video of a Merseytravel 142 leaving platform 6 at Chester bouncing a lot more than a child on a bouncy castle.
Actually proportionally Pacers are charged higher rates.
A pair of 156s (92m) is roughly the same length as 3x142s (93m.)
The track access cost for 6 x 142 carriages is 23.7p per mile
The track access cost for 4 x 156 carriages is 21.68p per mile
Actually proportionally Pacers are charged higher rates.
A pair of 156s (92m) is roughly the same length as 3x142s (93m.)
The track access cost for 6 x 142 carriages is 23.7p per mile
The track access cost for 4 x 156 carriages is 21.68p per mile
Old Timer
Established Member
The Pacer series units were constructed using a long wheelbase wagon frame.
The light weight of the vehicle together with the spring suspnsion to the two wheelsets mean that they are susceptible to responding to very small imperfections in the alignment of the track. Basically they respond to the geometry of the track in the same way as a lightly loaded or empty wagon will.
It is unfortunate that the wheelbase of the units also coincides with one of the vertical response frequencies associated with jointed track (60ft lengths) which means that the vehicle will "bounce" up and down" at a periodicity which will at intervals coincide with the rail joints, this then making the vehicle respond further to the rail joint dip thus increasing and continuing the vertical response. Think of the vertical response as being like a wavewith highs and lows.
The lack of bogies means that the vehicle will respond like a wagon in terms of the lateral response, even on perfect track at maximum speed. I seem to recall that 60 mph was the best speed ride-wise but it has been my experience only to ride these on poor track. The long wheelbase also causes problems with regards to the vehicles passing through tighter radius curves.
With regards to track damage, over time the vertical response will cause the track to display what is known as "cyclic top". This manifests itself as a series of dips in the rail top over a length of track. The distance of the dips is related to the length of time that the fault has existed, the speed and the weight of the vehicles using the line. Cyclic top frequencies (the distance between the higher and lower points) are directly related to vehicle length in that they can be caused by one wagon type only.
When the vehicle bounces off the rail head (at the top if the cycle) there is little or no force on the railhead, however when the wheel impacts again, the theoretical point of bottom of the curve is inside the rail itself, which means that all the downward track forces are destroyed over the top of the rail, which in turn means that they are transmitted through the sleepers into the ballast. Over time therefore the track dips down into the ballast to correspond with the low point of the bouncing motion - if I have made myself clear. Apologies but I am a poor teacher.
Lateral response is transmitted to the track in a similar way but because the track is more resillient to lateral forces, this is seen as flange wear and ultimately as "rolling contact fatigue".
This is a very much simplified response intended to explain the basic principles. If anyone wants to go into greater technical detail then I suggest a separate topic is created in the Infrastructure section rather than dog this one down in academic technical debate.
Here is an example of what cyclic top looks like.
The light weight of the vehicle together with the spring suspnsion to the two wheelsets mean that they are susceptible to responding to very small imperfections in the alignment of the track. Basically they respond to the geometry of the track in the same way as a lightly loaded or empty wagon will.
It is unfortunate that the wheelbase of the units also coincides with one of the vertical response frequencies associated with jointed track (60ft lengths) which means that the vehicle will "bounce" up and down" at a periodicity which will at intervals coincide with the rail joints, this then making the vehicle respond further to the rail joint dip thus increasing and continuing the vertical response. Think of the vertical response as being like a wavewith highs and lows.
The lack of bogies means that the vehicle will respond like a wagon in terms of the lateral response, even on perfect track at maximum speed. I seem to recall that 60 mph was the best speed ride-wise but it has been my experience only to ride these on poor track. The long wheelbase also causes problems with regards to the vehicles passing through tighter radius curves.
With regards to track damage, over time the vertical response will cause the track to display what is known as "cyclic top". This manifests itself as a series of dips in the rail top over a length of track. The distance of the dips is related to the length of time that the fault has existed, the speed and the weight of the vehicles using the line. Cyclic top frequencies (the distance between the higher and lower points) are directly related to vehicle length in that they can be caused by one wagon type only.
When the vehicle bounces off the rail head (at the top if the cycle) there is little or no force on the railhead, however when the wheel impacts again, the theoretical point of bottom of the curve is inside the rail itself, which means that all the downward track forces are destroyed over the top of the rail, which in turn means that they are transmitted through the sleepers into the ballast. Over time therefore the track dips down into the ballast to correspond with the low point of the bouncing motion - if I have made myself clear. Apologies but I am a poor teacher.
Lateral response is transmitted to the track in a similar way but because the track is more resillient to lateral forces, this is seen as flange wear and ultimately as "rolling contact fatigue".
This is a very much simplified response intended to explain the basic principles. If anyone wants to go into greater technical detail then I suggest a separate topic is created in the Infrastructure section rather than dog this one down in academic technical debate.
Here is an example of what cyclic top looks like.
Nym
Established Member
To add slightly, if you want to see an example of this vertical response damage, not caused by pacers but caused by standard 2.65m bogies, go have a look at some of the platforms at Piccadilly where the track is jointed, 9 is a good example, you can see a depression in the rails either side of the joint where the concussive force has transmitted over the bogie and back down into the ballast, shattering it and lowering the track. If you look carefully you can actually see the difference in size of ballast.
To hear it just listen to how much of a bang a 185 or bogied freight makes through 13/14
To hear it just listen to how much of a bang a 185 or bogied freight makes through 13/14
- Status