0–60: CLASS 755/4

Just how nimble are today’s locos and units, and what’s the quickest off the mark?

A Stadler bi-mode in diesel operation is put through its paces on the gentle gradients of East Anglia.

A trip from Ipswich to Cambridge between lockdowns in 2020 allows Neville Hill to sample a new Class 755/4 bi-mode as it glides over the gentle gradients of rural East Anglia under diesel power.

SCHOOL geography lessons rang in my ears as I crossed from the London-Norwich main line to its Cambridge equivalent: “East Anglia is undulating, not flat.” The Haughley

Jct to Coldham Lane Jct link has gradients averaging 1-in-100 and six pronounced summits in its 40 miles. I had considered the route as unsuitable for reaching a representative 0-60mph time, but took detailed timings while I pondered the problem.

Away from ‘the wires', four-car bimode Stadler ‘Flirt' Class 755/4s use a four-engine body-mounted ‘power pack' in the middle of the unit, that also allows passengers brave enough to move from one half to the other, usually with their hands clamped against their ears. On the other hand, diesel aficionados can nestle in a comfy seat against the engine compartment wall and enjoy the noise level they used to experience in a tunnel standing by a draughty open droplight in the first coach behind an English Electric ‘Type 4' (Class 40). The bi-mode ‘Flirt' concept is similar to a Class 206 Hastings ‘Tadpole' DEMU, but on steroids. The 163tonne weight unit can draw on 2575hp when on diesel, giving a power/weight ratio of 15.8hp/ tonne, three times that of a ‘Tadpole'.

Using diesel down the 1-in-159 from Elmswell, No. 755404 managed 60mph in 0.47miles and 53sec. From Thurston up 1-in-418 the figures were 0.53miles and 58.42sec. Added to evidence from Baard Covington on an unusual diesel southbound start from Stowmarket, an estimate of 0-60mph in 56sec appears justified. That would put the bi-mode Class 755/4 on diesel second only to a Class 220 Voyager in the DMU table.

The Class 755/3 three-car bi-modes are differently configured on diesel, but not so on electric, giving scope to assess comparative acceleration. More in future issues, lockdowns permitting.

Keith Partlow Greater Anglia Class 755/4 No. 755406 leaves Thurston on April 8 working 2W15 11.47 Cambridge-Ipswich. The telephoto lens draws attention to the ‘tadpole' effect of the mid-unit ‘power pack' which is clearly visible here.