1923 sports rear axle

[Stuart Giles]

Hi Tony, I make no pretence to expertise on rear axles but, if it were a "sports" back axle of that period, shouldn't it be a 10/44 giving a 4.4:1 ratio??

Were they 10/44 in the Brooklands? I'm sure I read somewhere that they were 9/40 giving 4.44:1 Probably academic if no original CW & P pairs have survived; I think this ratio would be hideously overgeared in an unblown car on 19" wheels whichever it was.

[Marcus Ling]

According to the March 1926 road test of the Brooklands, the rear axle was 4.4 to 1, but it doesn't any further details but we could assume 44/10. I have always understood that 4.4 to 1 was the standard ratio for a Brooklands but they could be had on special order at 4.09 to 1 which is the axle fitted to the car in the February 1925 road test. The only sensible ratio I can come up with that gives 4.09 is 45/11

The 1925 car was the earlier model with the dropped waist line, while the 1926 test was on the later model with the straight waist line

Cheers

Marcus

[Mark R]

I seem to remember Steve Hodgson telling me many years ago that early sports parts were marked with SP prefixes, may be worth asking him as he seemed to be familiar with earlier sports parts.

I suspect it's too early for a 9C (Ulster type) part number, wasn't the Ulster cylinder head 9C1 which due to lack of priming cups and chamber shape couldn't (my thoughts not fact) have been originally fitted on a 23 car, why in this case would you have any other 9C part numbers if you hadn't started. Perhaps you weren't thinking this was a part number Tony?

My reading of it would be S6368, not sure that helps much but I'll add my thoughts anyway.

Just looking at the cards on the archive shows various ratios including 10-54 for the earliest cars, I would post a picture if I knew how but it makes for interesting reading! Pages 15,16 and 17 give various ratios but either 9/44 or all others have 50 or more teeth with  10 or more on the pinion. There is no mention I can see of a 4.4 ratio, was there definitely one produced?

[Ian Williams]

Marcus I believe that 4.09 is a myth brought about by a journalistic error that should read 4.9.

[Marcus Ling]

Hi Ian,

You may be correct, I am only going on the information given in the Road Tests at the time. I guess everything is open to  speculation as no cars exist.

The 1925 report says " The gear box is quiet in action and by the use of a special crown wheel and pinion in the rear axle, the following ratios are provided:- First speed, 14.5 to 1: second speed, 8.17 to 1, top speed 4.09 to 1"

The 1926 report says " A special crown wheel and pinion are fitted to the rear axle, which gives the following gear ratios:- First gear, 14.5 to 1: second gear, 8.17 to 1, and top gear 4.4 to 1"

As they give the same ratio for 1st and 2nd, they cant have different back axle ratios. So there clearly is an error.

The final ratios given in the 1926 test are more or less correct with a 4.4 to 1 rear axle and standard ratio 3 speed box. If it had a 4.89 (9/44) rear axle, 1st would be 15.9 and 2nd 8.9.

Cheers

Marcus

[Ian Williams]

They would never have pulled a 4.09 ratio either Marcus.

[Marcus Ling]

I guess we will never know the exact story.

GE held the record at Brooklands in 1924 for the half mile flying start at 83.64 MPH.

He held a total of 22 different records at Brooklands for the 1924 season. The longest was the 200 mile record at 76.84 MPH, if he was running a 4.4 to 1 axle that would mean almost 3 hours at nearly 5000rpm with the inch and an eighth crankshaft. A very impressive performance by both him and the machine.

[Ian Williams]

I would like to see you achieve an average speed of 76.84 MPH for 3 hours with 26" BE rims with a 4.09 axle Marcus thats all I can say, bearing in mind also that this is an average speed not a maximum. Agreed that is was an impressive performance but lets not forget he was fully works backed and I don't believe responsible for the mechanical other than final set up in the cars he raced, I believe he had ideas and suggestions, but with full factory mechanical development. A brand new i 1/8" crank at constant speed may well survive three hours close to 5000 rpm. I have personal experience of a 1 5/16" surviving many many hours at those speeds, I would sit on the motorway a good hour and a half each way to and from Beaulieu year after year at those RPM as well as many road miles sprints and several races before it finally let go after approaching 10'000 miles of abuse. This was a crank of unknown parentage so I can fully believe a new 1 1/8" would survive a fraction of this.

[Damian GT]

Good point about the SP numbers.  Supersports bits were SP and I think maybe some later GE castings too (e.g. the front timing chest castings for the Brooklands - the one with the tacho take-off).  9B & 9C were obviously later, following on from SP, and applied to works TT components then production sports bits.  S was usually stamped on the gearbox for EA 'Usters' and Nippies but as far as I know rear axles have no specific markings to denote Sports (someone might correct me on that).

[JonE]

Surely there must be another early-ish car with an early-ish axle which could perhaps provide another evidence clue to the serial number line at the time?