Traction speed maximums

[PlexiDriver]

Hey all,

Does anyone know what some of the major things are when reducing the maximum limit of a traction unit?

Examples:

387 are limited to 110
Elizabeth line trains are limited to 90
While 800s are 125mph.
And so on.

What are the main reasons trains are limited below this threshold?

Maybe we could make a list of traction, top speeds and why they're limited (if they are!)

 

[Snow1964]

Some are from age and fragility (or to reduce maintenance from a previous quality level) , eg the A60 Metropolitan line trains were reduced from 70mph to 60mph in later years

Some similar classes have more or better dampers, or different springs for higher speed than similar vehicles. Have been some classes of EMU with various sub-classes with different top speeds

Then there is gearing, most modern trains are designed to work about 10% over speed (with new wheels), turned wheels are smaller diameter and this can knock 2% off. General wear and tear can knock bit off speed too as not as free running. Back in days of trains with dc motors, could take eternity to get that last few mph as motor magnetic field was 'pushing against' rotating faster. They often couldn't reach top speed on rising gradient. Nowadays with ac motors top speed is electronically limited, so not maintaining top speed is not usually an issue anymore.

 

[PlexiDriver]

So with something like the 387 it's limited to 110 on generally 125 track. It's not that old, in the sense that it has AC motors. It has tri-part suspension but yet its still limited haha.

 

[Snow1964]

So with something like the 387 it's limited to 110 on generally 125 track. It's not that old, in the sense that it has AC motors. It has tri-part suspension but yet it's still limited haha.

But there are other standards, which apply over certain speeds, there are higher standards for crashworthiness etc. There are speed thresholds for driver only and cab signalling too, which prevent going above these thresholds unless train is equipped.

 

[nmsq]

Driver only trains do 125 mph between Paddington and Didcot.
I believe there is a rule that units with a front fly door are limited to 110 mph

 

[Halish Railway]

Driver only trains do 125 mph between Paddington and Didcot.
I believe there is a rule that units with a front fly door are limited to 110 mph

There’s also the requirements to have a streamlined front end above 110mph, as well as shock absorbers and a crumble zone between the cab and passenger saloon.