Poor ride quality on IETs: is it caused by the track or the trains?

[RPI]

I have noticed over the past two or three years that the general ride quality along the Berks and Hants route has deteriorated and also between Reading and Paddington, I thought it was the IET'S being rough riding but I dont seem to remember them being so rough when new, certainly they were always more lively than MK3's but certainly has deteriorated in thr past 18 months

 

[43096]

I have noticed over the past two or three years that the general ride quality along the Berks and Hants route has deteriorated and also between Reading and Paddington, I thought it was the IET'S being rough riding but I dont seem to remember them being so rough when new, certainly they were always more lively than MK3's but certainly has deteriorated in thr past 18 months

The IETs have had an abysmal ride from day one. They have all the rude qualities of a drunk staggering home after kicking out time. I don’t think I’m the only one unsurprised at the cracking as the ride quality will be imposing additional stresses to the yaw dampers and the area where they are attached to the body.

Of course the Mark 3 was that good it didn’t need yaw dampers on the BT10s…

 

[coppercapped]

I have noticed over the past two or three years that the general ride quality along the Berks and Hants route has deteriorated and also between Reading and Paddington, I thought it was the IET'S being rough riding but I dont seem to remember them being so rough when new, certainly they were always more lively than MK3's but certainly has deteriorated in thr past 18 months

Already back in 2018 — three years ago — there was correspondance in the GWR Class 800 thread about the ride quality. In June 2018 Pete_uk in post #7,720 wrote that:

I had the sensation of feeling the tracks more, as if a bit more damping is needed somewhere.

and in post #7,727 @Gallentvent replied:

I'm inclined to agree on this point. I find it particularly noticeable at high speed with a lot if “jiggling”, rumble, and sudden realignments. Feels much less “flowing” than an HST. Since this could of course all be in my imagination … I wonder if anybody has used a nice accelerometer / data logger to compare the ride of an 800 with that of an HST over the same piece of track at (as far as possible) the same speed … it would be very interesting to know the results, if so! Likewise the noise levels (in the middle of a coach, say).

My experience then was the same. In the same period on straight level track near Maidenhead in the Up direction there was a sudden crash and jolt as if the suspension had hit the bump stops. They have never ridden as well as an HST in their early days or a Class 158 in spite of being two or three rolling stock generations later.

Frankly I am not surprised that they are broken, but I am very disappointed.

 

[Doomotron]

The IETs have had an abysmal ride from day one. They have all the rude qualities of a drunk staggering home after kicking out time. I don’t think I’m the only one unsurprised at the cracking as the ride quality will be imposing additional stresses to the yaw dampers and the area where they are attached to the body.

Of course the Mark 3 was that good it didn’t need yaw dampers on the BT10s…

I always found Mark 3s to have terrible ride quality (quite frankly impossible to walk through one at high speeds!) so the Class 800s must be dreadful - or perhaps a case of rose-tinted glasses, but I won't know until I actually travel on one.

 

[stuu]

My experience then was the same. In the same period on straight level track near Maidenhead in the Up direction there was a sudden crash and jolt as if the suspension had hit the bump stops. They have never ridden as well as an HST in their early days or a Class 158 in spite of being two or three rolling stock generations later.

Frankly I am not surprised that they are broken, but I am very disappointed.

Me neither. The ride has always seemed far more twitchy and jolting in the 800s, like being in a sporty car with low profile tyres, where you feel every bump. The HSTs rolled about and made annoying squeaks but it took a big bump for them to actually jolt

 

[Wilts Wanderer]

I always found Mark 3s to have terrible ride quality (quite frankly impossible to walk through one at high speeds!) so the Class 800s must be dreadful - or perhaps a case of rose-tinted glasses, but I won't know until I actually travel on one.

Mark 3s always had a tendency to bounce vertically at high frequency but the actual ride quality and bogie steering was excellent. In later years the availability of appropriate dampers changed and the replacement components were of varying quality. Anecdotally the LNER vehicles deteriorated noticeably whereas the GWR examples remained very good.

The 800-family bogies seem to be lacking in stability; the lateral ride is very prone to excitement and the tight suspension (due to the gauging restriction imposed by 26m vehicle length) means much of the force is transmitted through the suspension into the passenger compartment. They do also seem prone to hunting which is rather more concerning, presumably when the wheel conicity becomes suboptimal through wear.

 

[fgwrich]

Mark 3s always had a tendency to bounce vertically at high frequency but the actual ride quality and bogie steering was excellent. In later years the availability of appropriate dampers changed and the replacement components were of varying quality. Anecdotally the LNER vehicles deteriorated noticeably whereas the GWR examples remained very good.

The 800-family bogies seem to be lacking in stability; the lateral ride is very prone to excitement and the tight suspension (due to the gauging restriction imposed by 26m vehicle length) means much of the force is transmitted through the suspension into the passenger compartment. They do also seem prone to hunting which is rather more concerning, presumably when the wheel conicity becomes suboptimal through wear.

I was going to mention this in the 800 ride quality thread but you’ve pretty much picked up some of what I was going to say anyway. To be honest, the only vertical bouncing I’ve felt while travelling on a Mk3 has either been in the much heavier Caledonian Sleeper vehicles, or those within the East Coast Fleet. The reason for the latter comes down to the Pegasus Dampers fitted to the East Coast examples - David Horne was certainly well aware of their poor riding and put out a number of tenders to replace them, seemingly to little avail. However, all the dampers saw replacement with new ones from SV upon their arrival at Neville Hill and were certainly very smooth riding towards the end.

And yes, those GW MK3s remained smooth until the end! Much missed, that’s for sure.

 

[43096]

They do also seem prone to hunting which is rather more concerning, presumably when the wheel conicity becomes suboptimal through wear.

I don’t think it is wear that causes the hunting as they have done it from new. Just an appalling design.

 

[GC class B1]

Mark 3s always had a tendency to bounce vertically at high frequency but the actual ride quality and bogie steering was excellent. In later years the availability of appropriate dampers changed and the replacement components were of varying quality. Anecdotally the LNER vehicles deteriorated noticeably whereas the GWR examples remained very good.

The 800-family bogies seem to be lacking in stability; the lateral ride is very prone to excitement and the tight suspension (due to the gauging restriction imposed by 26m vehicle length) means much of the force is transmitted through the suspension into the passenger compartment. They do also seem prone to hunting which is rather more concerning, presumably when the wheel conicity becomes suboptimal through wear.

I travelled on a LNER class 800 yesterday and confirm bogie hunting occurred. With regard to whether wheel wear and conicity was the reason for the bogie hunting, I was very surprised when I travelled on a LNER class 800 about two years ago when the set was pretty new and just after leaving KX I noted bogie hunting so it doesn’t seem to be related to wheel profile specifically - they are P8 profile.
Yesterday I noted the ride was not as bad north of Peterborough and I also noted south of Stevenage that severe bogie hunting occurred when braking at fairly low speeds.

With regard to Mk3/HST ride quality, I would add that vertical bounce occurs on poor track, especially MML and I believe is due to limited vertical secondary damping as this damping is purely provided by the air suspension and BT10 bogies don’t have secondary vertical hydraulic dampers. BT10 bogies are the last to be designed with a conventional secondary suspension of bolster and swing links in the bogie and the bogie is self steering by virtue of a rubber bush in the centre pivot avoiding the need for yaw dampers.

 

[D6130]

I'm not an engineer, but presumably any prolonged bogie hunting and/or vertical bouncing causes a deterioration of the track quality, which then causes further bogie riding problems and sets up a self-perpetuating circle of decline.

 

[coppercapped]

The IETs have had an abysmal ride from day one. They have all the rude qualities of a drunk staggering home after kicking out time. I don’t think I’m the only one unsurprised at the cracking as the ride quality will be imposing additional stresses to the yaw dampers and the area where they are attached to the body.

Of course the Mark 3 was that good it didn’t need yaw dampers on the BT10s…

Ah! But the BT10s did have yaw dampers. But there was only one of them per bogie and it used an earlier technology.

It was a disc of resin-bonded friction material around the centre pivot which sat between the bogie bolster and a steel disc around the centre pivot pin attached to the coach underframe. The same idea was used in the earlier B4 bogies and both cases it was perfectly adequate.

In later bogie designs the use secondary air springs permitted both the lateral motion of the bogie frame without the use of spring planks and swing links as well as rotary motion about the central vertical axis so the bogie frame had no separate bolster any more. This meant that a simple rotary disc could no longer be used and the external telescopic yaw dampers became essential to control the bogie's rotary motion at higher speeds.

 

[GC class B1]

That is not my understanding of the BT10 bogie arrangement. There is one damper on the centreline of the bogie but ii operates between; the bogie frame and the bolster to provide lateral damping. The centre pin has a flat on it and this engages with a rubber and steel bush in the bolster to centralise and steer the bogie. The bogie sits on low friction PTFE side bearers and not on the centre casting as B4 bogies. BT10 bogies do not have yaw dampers.

Ah! But the BT10s did have yaw dampers. But there was only one of them per bogie and it used an earlier technology.

It was a disc of resin-bonded friction material around the centre pivot which sat between the bogie bolster and a steel disc around the centre pivot pin attached to the coach underframe. The same idea was used in the earlier B4 bogies and both cases it was perfectly adequate.

In later bogie designs the use secondary air springs permitted both the lateral motion of the bogie frame without the use of spring planks and swing links as well as rotary motion about the central vertical axis so the bogie frame had no separate bolster any more. This meant that a simple rotary disc could no longer be used and the external telescopic yaw dampers became essential to control the bogie's rotary motion at higher speeds.

As I mentioned BT10 bogies do not have yaw dampers. The B4 bogie arrangement was not as stable as BT 10 bogies and they were prone to bogie hunting at mileages above about 200,000. To achieve the 600,000 mile bogie overhaul interval required two intermediate wheel reprofilings. It is therefore not strictly correct to state that the B4 bogie arrangement was adequate.

 

[coppercapped]

That is not my understanding of the BT10 bogie arrangement. There is one damper on the centreline of the bogie but ii operates between; the bogie frame and the bolster to provide lateral damping. The centre pin has a flat on it and this engages with a rubber and steel bush in the bolster to centralise and steer the bogie. The bogie sits on low friction PTFE side bearers and not on the centre casting as B4 bogies. BT10 bogies do not have yaw dampers.

Oops, sorry, yes, you're correct... I was looking at the wrong drawing.

However I would suggest that 'low friction' does not mean 'no friction' and the side bearers together with the restoring force of the centre pivot arrangement was sufficient to damp any hunting at the speeds reached. The point I was trying to get across was that although there were no telescopic hydraulic dampers controlling yaw there is yaw damping - but supplied by other means. The conclusion has to be that the stiffnesses in the primary suspension were very well selected.

As I mentioned BT10 bogies do not have yaw dampers. The B4 bogie arrangement was not as stable as BT 10 bogies and they were prone to bogie hunting at mileages above about 200,000. To achieve the 600,000 mile bogie overhaul interval required two intermediate wheel reprofilings. It is therefore not strictly correct to state that the B4 bogie arrangement was adequate.

Again I stand corrected. But the B4 was streets ahead of BR's first bogie attempts and reaching 100,000 or 200,000 miles before reprofiling was a huge advance on the 30,000 or so miles reached by the Mark 1 bogies. That was my baseline for my 'adequate' statement.

 

[GC class B1]

Thank you to coppercapped for replying. The information I provided for B4 bogie mileages was not entirely the complete picture. The 600,000 mile bogie overhaul interval was significantly extended from the original overhaul interval of about 200,000 miles and required a new wheel profile P11 to improve conicity and therefore stability at higher mileages and required two ground wheel lathe reprofilings at 150,000 and 450,000 miles with an intermediate wheelset light overhaul and damper change at 300,000 miles. From memory the original P1 profile was prone to bogie hunting at mileages in excess of 100,000 and the P11 was a significant improvement.
The BT10 bogie arrangement was more stable as discussed above but also had a new profile designated P8 to improve conicity when worn. It is also of interest that the ECML HSTs had a different wheel profile designated RD9 but I don’t know whether this continued after privatisation.

The self aligninging arrangement on the BT10 bogies has the disadvantage that when curving the ’straightening’ force increases the contact force between the flange root and the rail gauge corner and can be noisy. This was a particular problem with the sprinter dmus which also have self aligning bogies (T3 I believe). As gauge corner cracking of the rail has been a problem and maximum noise levels are now specified I understand this is why the higher speed class 158 dmus were fitted with yaw dampers. It is also of interest that the class 158 yaw damper assembly had to be modified Very early on.

 

[greyman42]

What is bogie hunting? I did google it but did not understand the technical definition. Could someone put it in layman's terms.

 

[GC class B1]

Bogie hunting is when the bogie rotates from one end of its travel to the other contiinuously and usually fairly rapidly. It occurs when the bogie becomes unstable and doesn’t run in straight line. It begins to rotate across the track horizontally until the rotation is stopped by contact between the wheel flange and the rail and then rotates in the opposite direction until again being stoped by the opposite wheel contacting the other rail. The bogie stability is achieved by the self centering forces of the wheels on the rails. In a perfect situation the wheel profile holds the wheel roughly central on the tread and the flanges don’t contact the rail. The extent to which the wheel is centralised on the rail depends on the relative ‘fit’ of the wheel on the rail and this is called the conicity. A close fit of the wheel and rail head profile will result in an unstable situation . The P1 profile, the original wheeel profile is a 1 in 20 cone and centralises the wheelset on straight track very well when new. Wear of the wheel tread and rail can reduce this centering effect to the extent that the bogie becomes unstable. The revised profiles such as P8 are designed to wear to a profile that retains the centralising effect for longer as the wheel profile wears.

 

[danielnez1]

The old quotes from forum members and discussion about the quality of the bogie makes me remember on my first LENR Azuma ride from York to Newcastle shortly after their introduction. I particularly remembered the rough riding as well as the loud ding/bang/scraping sounds (which stood out from the HSTs and 225s) coming from what seemed to be the bogie under my seat.

 

[Wilts Wanderer]

There is a very good explanation of the dynamics of hunting in the current Modern Railways magazine edition.

 

[Allwinter_Kit]

Or if you're ever in Manchester and ride the tram out to Altrincham, I have been told the rather "shoogily" ride on the former railway is a result of it hunting around on the track there at higher speeds.

 

[Wilts Wanderer]

Or if you're ever in Manchester and ride the tram out to Altrincham, I have been told the rather "shoogily" ride on the former railway is a result of it hunting around on the track there at higher speeds.

I recall reading that trams have quite a different wheel profile to better suit tight curves involved with street running; consequently the performance on higher speed sections is pretty abysmal.

 

[D6130]

Or if you're ever in Manchester and ride the tram out to Altrincham, I have been told the rather "shoogily" ride on the former railway is a result of it hunting around on the track there at higher speeds.

It's pretty bad on the Bury line too....especially on the longer 'fast' stretches between Whitefield, Radcliffe and Bury.

 

[XAM2175]

Or if you're ever in Manchester and ride the tram out to Altrincham, I have been told the rather "shoogily" ride on the former railway is a result of it hunting around on the track there at higher speeds.

I recall reading that trams have quite a different wheel profile to better suit tight curves involved with street running; consequently the performance on higher speed sections is pretty abysmal.

Yes, pronounced hunting on higher-speed sections is pretty common with trams wherever you go.

 

[rebmcr]

Or if you're ever in Manchester and ride the tram out to Altrincham, I have been told the rather "shoogily" ride on the former railway is a result of it hunting around on the track there at higher speeds.

The ex-BR tracks were relaid in the '00s, the route from Timperley to G-Mex Deansgate-Castlefield is now 100% freshly laid tram tracks, and the M5000s still hunt like mad.

 

[Bikeman78]

What is bogie hunting? I did google it but did not understand the technical definition. Could someone put it in layman's terms.

Do you remember the EPBs? When they hurtled down the gradient from Ockley to Warnham at goodness knows what speed the bogies used to rock from side to side. The 4CEP motor bogies did the same. This was especially noticeable if sitting in the middle of a pair of units where the bolt that held the gangway door open was worn. The heavy door would clatter from side to side. The 387 on GWR hunted quite a lot in some places when they were going 110 mph to Swindon.

 

[Goldfish62]

Yes, pronounced hunting on higher-speed sections is pretty common with trams wherever you go.

And the DLR. In fact that's got some of the most extreme hunting I've ever experienced.

 

[RPI]

Do you remember the EPBs? When they hurtled down the gradient from Ockley to Warnham at goodness knows what speed the bogies used to rock from side to side. The 4CEP motor bogies did the same. This was especially noticeable if sitting in the middle of a pair of units where the bolt that held the gangway door open was worn. The heavy door would clatter from side to side. The 387 on GWR hunted quite a lot in some places when they were going 110 mph to Swindon.

I remember class 117 DMU'S at high speed bouncing

 

[stuu]

And the DLR. In fact that's got some of the most extreme hunting I've ever experienced.

The section East of Shadwell used to be genuinely alarming on some trains, I believe something was done to reduce it as its not as bad now

 

[GC class B1]

It is worth noting that poor ride can increase the stresses on the bogies, vehicle bodies and track.

 

[507 001]

The ex-BR tracks were relaid in the '00s, the route from Timperley to G-Mex Deansgate-Castlefield is now 100% freshly laid tram tracks, and the M5000s still hunt like mad.

No it isn’t. There’s a few sections of old track on the Altrincham line. Dane Rd to Stretford inbound in particular wasn’t touched, and is now subject to a long standing 40mph TSR due to hunting.

 

[Bikeman78]

I remember class 117 DMU'S at high speed bouncing

Oh yes happy memories of classes 101/117/119 hammering down the bank into Deepdene with the speedo pointer off the scale! The blinds were nearly always up so it was possible to see into the cab. The ride could politely be described as lively.