Are Top Speeds Really Just the Recommended Speed?

[hexagon789]

Downhill ..anything is possible. Class 86s were tested at 120mph+ with a streamlined nose at a time they were limited to 100mph commercially.
I'm told 80 to 90mph was achieved with A stock downhill from Amersham to Rickmansworth back in the day when 'speeding' didnt matter..probably ECS.

It's more did they have the power to do it and indeed the distance to do it?

 

[Railperf]

It's more did they have the power to do it and indeed the distance to do it?

Haha exactly.

 

[Wychwood93]

The 442s brakes are indeed excellent..and they needed to be. I recall a trip to Poole where going downhill near Fleet, i could sense we were going very fast indeed. I walked to the interconnecting gangway between the two 442s where there is a window into the drivers cab. Speedo appeared to be showing 115mph!! Shame there was no GPS to corroborate this.
Onboard data recorders, TPWS and changes in driving policy have all made this sort of event a thing of the past!
Clearly the maximum service speeds for stock and track are based on many operational factors rather than the absolute maximum speed that can be achieved by apiece of rolling stock over a stretch of track. Signalling, brakes and passenger safety and comfort are key.
I guess if you locked peoples luggage down and ensured people were sat down and seatbelted up- as on the airplanes - then faster speeds could be possible?

In the early days they could easily brake at 2 mph/sec - sort of from 90 mph at Milepost 98 into New Milton for a stop. A regular happening at assorted locations. Somewhat more exciting was 100 mph down towards Winchester in a 4-VEP!

 

[Peter Mugridge]

I'm surprised that they could do 120 with 4REPs, 100 or so seems likely enough but 115, 120? Seems unlikely to me somehow.

I had a REP once where the speedo needle was jammed against the stop; I think I may have a photo of it somewhere, albeit not a very clear one.

 

[hexagon789]

Haha exactly.

Mind you, since I posted that, I've since come across a report of one touching 123mph when brand-new!

I think it just goes to show, where speed is concerned it can be quite difficult to footer out the accurate reports from the inflated ones!

 

[hexagon789]

I had a REP once where the speedo needle was jammed against the stop; I think I may have a photo of it somewhere, albeit not a very clear one.

And they go up to 120mph I'm guessing?

 

[70014IronDuke]

Downhill ..anything is possible. ....

Oh dear. There speaks a non-engineer.
And probably a no physics GCSE.

 

[Railperf]

Oh dear. There speaks a non-engineer.
And probably a no physics GCSE.

Haha ..your negative comments don't exactly reveal your engineering expertise. Please enlighten us.

Mallard achieved 126mph 'downhill'. I am not sure that was possible on the flat. And it exceeded the normal permanent way and loco operating speeds of the time.
You don't need a physics degree to understand that lol.

 

[Railperf]

A

Mind you, since I posted that, I've since come across a report of one touching 123mph when brand-new!

I think it just goes to show, where speed is concerned it can be quite difficult to footer out the accurate reports from the inflated ones!

As accurate as when my mate reckoned his 1.1 Fiesta would do 125mph. Although to be fair..some car speedos were over reading way more than 10%. In those days GPS wasn't available to verify these claimed speeds.

 

[Railperf]

A

As accurate as when my mate reckoned his 1.1 Fiesta would do 125mph. Although to be fair..some car speedos were over reading way more than 10%. In those days GPS wasn't available to verify these claimed speeds.

Talking of over reading speedos..good to see that the problem afflicting DVTs has been solved. Now on the ECML at least - reaching 125mph with a DVT is the norm - where some years ago it was generally 121 to 122mph maximum.

 

[hexagon789]

A

As accurate as when my mate reckoned his 1.1 Fiesta would do 125mph. Although to be fair..some car speedos were over reading way more than 10%. In those days GPS wasn't available to verify these claimed speeds.

Well considering what I've read about speedometers reading inaccurately I wouldn't be sure an indicated 120mph was actually 120mph.

 

[Railperf]

Well considering what I've read about speedometers reading inaccurately I wouldn't be sure an indicated 120mph was actually 120mph.

Of course when drivers tell you that the speedometer indicated speed is different to the speed being indicated on the TMS that says it all

 

[Greetlander]

When they took the centre car out of the Class 110 DMU sets, they must have theoretically been capable of a fair belt over the 70mph limit.

 

[70014IronDuke]

Haha ..your negative comments don't exactly reveal your engineering expertise. Please enlighten us.

My engineering expertise (or lack of) is irrelevant. You wrote:

Downhill ..anything is possible. ....

While possibly ok for The Sun's science correspondent, it is, simply ... twaddle

 

[Deepgreen]

Wasn't the fastest an HST reached something like 147mph on Stoke Bank? Granted it only had 5 coaches. 91's can do 140mph as can pendolinos

A 91 reached 162mph on test (with DVT leading!). An HST hit 148mph. Both were on Stoke Bank.

 

[Deepgreen]

To address the OP - I think the term 'top speed' reflects the designed service speed, comprising a number of issues such as gearing, power at rail, current service performance requirements (including signalling capabilities), etc. The 'Pendolinos' were designed for 140mph operation, suggesting that their actual possible maximum speed would be somewhat higher (say 160mph), but they remain limited to 125mph. Gearing is an area where differences can be made to the top speed which can be attained reliably. Many SR units had their gearings altered to change their performance - e.g. 2HAPs were re-geared to get to 90mph to run with CEPs, CIGs, etc. A number of CIGs were re-geared in their last years to improve acceleration on the Portsmouth route and were nicknamed 'Greyhounds'.

 

[43096]

A 91 reached 162mph on test (with DVT leading!). An HST hit 148mph. Both were on Stoke Bank.

That is incorrect. The world diesel speed record was set between York and Darlington on 1st November 1987 by 43102/159. The actual record was set just south of Northallerton.

 

[GLC]

The 'Pendolinos' were designed for 140mph operation, suggesting that their actual possible maximum speed would be somewhat higher (say 160mph), but they remain limited to 125mph.

Do the Pendolinos have an actual limiter on them to keep them to 125, or some other restriction that keeps them from hitting their 140mph design speed (I mean in terms of the unit itself, not the lack of the supporting infrastructure)?

 

[PudseyBearHST]

Do the Pendolinos have an actual limiter on them to keep them to 125, or some other restriction that keeps them from hitting their 140mph design speed (I mean in terms of the unit itself, not the lack of the supporting infrastructure)?

In order to do EPS 125, you’ll need to have speed supervision. A few mph above 125 it will be okay but any higher, you’ll upset TASS and it’ll start screaming at you (TASS warning)

 

[hexagon789]

Of course when drivers tell you that the speedometer indicated speed is different to the speed being indicated on the TMS that says it all

Very much so!

Though of course the 4REPs didn't have such a luxury.

 

[hexagon789]

When they took the centre car out of the Class 110 DMU sets, they must have theoretically been capable of a fair belt over the 70mph limit.

First gen DMUs gearing topped out at around 65.5 and some classes had overspeed trips at about 68mph. Downhill you could privacy do 70+ though.

Do the Pendolinos have an actual limiter on them to keep them to 125, or some other restriction that keeps them from hitting their 140mph design speed (I mean in terms of the unit itself, not the lack of the supporting infrastructure)?

As stated the TASS will warn of an overspeed. I believe the brake intervention is at 128mph; it varies between 221s and 390s iirc.

 

[Peter Mugridge]

And they go up to 120mph I'm guessing?

The ones fitted went up to 110 indicated then the needle stop; in this case it was very firmly against the needle stop with no wavering.

 

[hexagon789]

The ones fitted went up to 110 indicated then the needle stop; in this case it was very firmly against the needle stop with no wavering.

I would accept ~110mph - 120, even downhill, seems a little dubious.

 

[Ash Bridge]

When they took the centre car out of the Class 110 DMU sets, they must have theoretically been capable of a fair belt over the 70mph limit.

Many years ago (1973 or 74) a friend and myself were offered the chance to ride back to Manchester Piccadilly from Sheffield Midland in the cab of a 3 car BRCW Class 110 DMU. This was an early evening service during either the late autumn or early spring so under the cover of darkness. During that time the 110s operated the fasts which of course in those days still ran via New Mills and Romiley etc. the Hope Valley stoppers were in the hands of ER Class 114s IIRC. One thing I'll never forget though is that most of the journey from roughly Hathersage to Cowburn Tunnel the speedometer needle was hard against the stop suggesting a speed of between 75-80 mph. It is of course possible that the speedometer was slightly overeading but it still felt damned fast nonetheless.

 

[whhistle]

As accurate as when my mate reckoned his 1.1 Fiesta would do 125mph. Although to be fair..some car speedos were over reading way more than 10%. In those days GPS wasn't available to verify these claimed speeds.

It amazes me that people seem to think GPS is more accurate than a car speedo.
Not saying [GPS] isn't accurate at all but I wouldn't trust it any more than my car reading.

 

[Railperf]

It amazes me that people seem to think GPS is more accurate than a car speedo.
Not saying [GPS] isn't accurate at all but I wouldn't trust it any more than my car reading.

Yes and that's perfectly fine to do so. But a car speedo like a train speedo is never going to be 100% accurate because it is usually designed to measure wheel rotation and that is dependent on wheel diameters tyre diameters and tyre pressures. I don't think any car manufacturer claims that their speedometer provides a 100% accurate Reading they do have a duty to ensure that the speed displayed is accurate to within 10% of the car's true speed and definitely not under Reading.

 

[coppercapped]

Yes and that's perfectly fine to do so. But a car speedo like a train speedo is never going to be 100% accurate because it is usually designed to measure wheel rotation and that is dependent on wheel diameters tyre diameters and tyre pressures. I don't think any car manufacturer claims that their speedometer provides a 100% accurate Reading they do have a duty to ensure that the speed displayed is accurate to within 10% of the car's true speed and definitely not under Reading.

Hmm!

Does tyre pressure affect the tyre circumference and so the indicated vehicle speed? The body ply cords and stabiliser belts under the tread fix the circumference - they flex but don't stretch as they prevent the tyre expanding due to centrifugal forces at high rotational speeds. Tyre pressure will certainly affect the amount that the side walls flex, and so the rolling resistance; the biggest effect on the circumference will be the wear of the profile.

 

[hexagon789]

Yes and that's perfectly fine to do so. But a car speedo like a train speedo is never going to be 100% accurate because it is usually designed to measure wheel rotation and that is dependent on wheel diameters tyre diameters and tyre pressures. I don't think any car manufacturer claims that their speedometer provides a 100% accurate Reading they do have a duty to ensure that the speed displayed is accurate to within 10% of the car's true speed and definitely not under Reading.

The original HST overspeed worked off wheel diameter, so on new tires it would cut power at 132mph, on fully worn at 128mph. I believe most (all?) power cars are now 132mph cut-out regardless, certainly those with Knorre Bremse WSP are. Presumably the way speed is measured is no longer fully dependant on measuring the rotation of the wheels?

 

[DJ_K666]

A

As accurate as when my mate reckoned his 1.1 Fiesta would do 125mph. Although to be fair..some car speedos were over reading way more than 10%. In those days GPS wasn't available to verify these claimed speeds.

Some did have Weber carburettors on them. One friend of mine had one and managed to out accelerate a 2.8i Capri. To be fair I think it had been re-jetted and a couple of other modifications. Not sure about the top speed though as you'd need to uprate the gearbox to get that sort of top speed. Not to mention the brakes...

 

[DJ_K666]

Here's a hypothetical question for you. I understand the 350 Desiros had substantial modifications to allow them to run at 110 on the WCML. Could another 10mph feasibly be wrung out of them or are they screaming on the limit at 110? Just asking out of vague interest before anyone bites my head off.