The 10A Allocation

As I say that’s quoted from David Smith that 4767 can do 75mph in the latest Trackside

 

Is that a typo for 65 mph?

RSSB RIS 4472 states the following:
G D 1.6 The steam speeds formula takes into account:
a) Wheel diameter rotational speed of 6 revs per second.
b) Piston stroke and oscillation speed of 1600 ft per minute.
c) Number of cylinders (see G D.1.8 b)).
d) Presence of leading pony truck or bogie to add steering and derailment resistance.
e) Age of original design (see G D.1.8 a)).
G D.1.7 Derivation and application of the steam speeds formula is overseen by RSSB, to whom requests for access may be addressed.
G D.1.8 The following general criteria have been applied to the speeds derived:
a) The cut-off for age of design (by which a lower speed is allocated) is 1923. This date is suggested partly because it is the date of the post WWI ‘grouping’ (that created the London, Midland and Scottish Railway (LMS), London and North Eastern Railway (LNER), Great Western Railway (GWR) and Southern Railway (SR) ‘big 4’) but also due to the landmark bridge stress committee work, begun in 1923 and reported in 1928. The output of this work, including the determination of the hammer blow effect, influenced locomotive design philosophy thereafter in a manner beneficial to track force considerations.
b) 2-cylinder locomotives are those most prone to display the ‘hammer blow’ effect as there is no natural balancing to the effect, with piston sequence at 90 degrees. By contrast, 3-cylinder (120 degrees) and 4-cylinder (180 degrees) locomotives are naturally better balanced and exhibit a less pronounced effect.
c) The additional rear wheelset on the 4-6-2 pacific types, although adopted mainly to spread axle load, generally offered additional benefit in ride quality; conversely, certain 4-6-0 types displayed deterioration in ride quality as speed increased. This has therefore been taken into account in setting speeds for the two generic design types.
d) A marginal increase in maximum speed (75 > 80mph) has been allocated to certain pacific types with 6' 8''driving wheels or greater, on the basis that this is a significant increase over 6' 2'' (the basis for the previous maximum limit for 75 mph when operating on the GB mainline railway). One consequence of this is the requirement for fixed rather than portable headlights, as set out in 3.7 where operations are proposed at that speed.

 

I don't believe so Steve, I've heard it said a few times that 75mph will be permitted. Perhaps the owners have had discussions with their vehicle acceptance certification body and made out a technical case as to why 4767 can be treated differently to the other LMS 5s? There was clearly a case made for 45305 20 years or so ago, as a test run was carried out. Presumably WC was the operator of 45305 in 2005 at the time of the 75mph trial?