The 10A Allocation

Indeed, as an example a Britannia and rebuilt Bulleid are both 75mph but the former has rollers, the latter plain whilst both have 6' 2" drivers and are Pacifics.

 

But you’ve read the magazine so you’ve read what it says. You don’t argue with some content but do with others

 

Eh?
I'm not arguing with the magazine report, I'm agreeing with the technical analysis others have made vis bearing/driving wheels differential on permitted max mph.
As you said David Smith says 4767 can go faster because it has rollers and that's what the magazine reported. He obviously has a different understanding.

 

The criteria for 75mph running is driving wheels over 6’ 1” diameter, the fact they are Pacifics is irrelevant.

 

Yes I know, I was simply pointing out John that there was no difference in max speed using 2 otherwise very similar designs, dimensionally where one has rollers and the other does not.
The analogy being that black 5s are all 60mph so the addition of rollers to 4767 would not, in itself, seem to be why a higher max speed would be permitted.
Having delved into the memory, didn't Bert get 5231 approved for 75mph or am I misremembering?