Ariel hp

[nevhunter]

The "rated HP " was based on capacity ie CC's displacement. Brake Horsepower is determined on a dynamometer, usually in those days on an engine dynamometer. Today it's often measured at the driving wheel(s) The last two will give different outcomes, as the wheels situation has the figure after all transmission losses. The "usual " sized British bike needs about 32 HP to achieve 100 MPH (unfaired) Those BHP figures seem conservative, which is an ethical approach rather than claiming figures many would not achieve in practice. Nev

[leon.mitchell]

RAC horsepower is calculated as follows: If D is the bore and L is the stroke, both in inches, and N is the number of cylinders, then:
H.P. (RAC) = D x D x N ÷ 2.5
It was used for cars, but never for bikes, from around 1910. In the UK, the cost of road tax was based on the RAC hp, and since the RAC hp depended only on the stroke [edit: Woops - I meant bore!] there was an incentive to build cars with small bores and long strokes.
For bikes the "two power" notation was often used. For example a racing JAP twin from the late 1920s was described as "8/45" - 8hp being the rated hp for 1000cc, 45 the actual (brake) hp.
Leon

[Leejm]

Cheers Leon, most interesting! It's just another way for the government to tax us. that figures!! They are still coming up with ideas to free us of our money. Not much as changed really.

[john.mitchell]

When I was an awful lot younger I had an early 50's Wolseley 15/50. I guess that would also be the ratio but would reflect a greater power output.

[PeterW]

I was told that originally the HP matched the cc so a 1400cc car was 14hp but then they decided to just use the cylinder bore to work out the cc and as hp had tax implications the manufactures started making more long stroke motors of larger capacity but the same nominal horse power. No idea if it has any basis in fact.

[leon.mitchell]

Hi Peter,
What you were told is a mix of fact and fiction - the small-bore tax part is correct, but before this came in (around 1910) manufacturers usually just labelled their car by a "nominal" hp. 14 hp would have been a large car, much larger than 1400cc.
Paul's 14/28 Standard and John's 15/50 Wolseley would be "nominally" 14 and 15 hp, with "actual" power of 28 and 50 hp, just as the 1000cc OHV JAP 8/45 twin in the 1920s was nominally 8 hp 45 hp actual.
Usually (but not always!) the "nominal" hp would be more-or-less the RAC hp, so both the Standard and the Wolseley would have bore around 3" (3 x 3 x 4 / 2.5 = 14.4 hp RAC). Confusing!
At least bikes didn't use the RAC system - just nominal horse powers as I outlined above until capacity in cc became the universal way of describing a motorcycle engine.
High order Anoraks can read more here: http://earlymotor.com/serpolettes-tricy ... cle-02.pdf , page 7.
Cheers
Leon

[nevhunter]

One fact is that the bore size and total piston area was the basis of the tax and affected the general design direction. Long stroke engines like the 16hp? Vauxhall in the mid 30's were common. This caused a design feature that limited certain development in Britain that is higher revving engines with more power /cc of capacity to some extent.. It also caused excessive ring wear due high piston speed. With motor cycles some attention was paid to the weight as a determinant of the level of tax. The size of engines in both the USA and the UK was to some extent also related to racing categories, existing at the time though the widespread use of the sidevalve configuration which was developed more than UK generally in cars and bikes. The Ford V8 and Hudson Terraplane being good examples of that. Nev

[adrie.degraaff]

My father learned at scool that 1 HP was; lifting 75 kilo's in 1 second 1 meter of the ground, if i remember it well.

He also learned that; Salomon de Caus was the inventor of the steammashine, the story was; there was a battery of steam apperatos worked by several man, the guy who worked it the best got a bonus, the plant of Salomon was working the best but he wasn't on it, just some connecting wires running over wheels, this invention was later taken from him and given to the more useble (modern) system of James watt.

There was always a dispute between England and France over being the first, see the invention of the differential, the open diff (Starley) was given to England and the closed diff to France based on an old drawing.

The invention of maching V spockets (see the grill of the car) was give to Adré Citroën but it's proven to be stolen of a Russian guy who couldend pay for the rights.
André was basicly a Dutch man named "Limoenman" (Lemonman) his father renamed it to Citroen (lemon) becouse it was better on the social scale, André was renamed to Citroën becouse it was easier for his teacher in Paris.

But this is way of topic.

[simon.holyfield]

But this is way of topic.

Interesting though Adrie. Thanks for sharing.

[IanSlade]

Given the way a SV 550 pulls in top I reckon they are Shire or Clydesdale horse power!