Renold Chain Facts & News

Helpful information and requests for assitance and advice
Posts: 1
Joined: Tue Jan 07, 2020 2:52 pm
Location: Wales, UK

Re: Renold Chain Facts & News

Postby ClassicChainGuru » Mon Jan 06, 2020 9:46 am

Thanks for your help so far folks, much appreciated.
Quite an eye opener looking at your archives & great that such information is still available, especially for the pre-WW2 stuff.

I'm making good headway in my AJS listings from these & many other sources but I do have one question regarding the published figures on the old adverts.

Many of the early bikes were published with a HP figure of say 2.49HP whilst having a CC of 249CC. Same goes with 3.49HP for a 349CC, 4.99HP for a 499CC & 9.96HP for 996CC

Is this purely a coincidence or just advertising nonsense ?

Member
Posts: 643
Joined: Thu Feb 27, 2014 9:27 am
Location: Kent, England

Re: Renold Chain Facts & News

Postby JimFitz » Wed Jan 08, 2020 9:18 pm

If I remember correctly this was how the RAC (or was it the AA) rated vehicles and it may have been something to do with the cost of road tax or purchase tax.
Using your examples it looks like they rated each 100cc at 1 HP.
Perhaps it was different for cars because my 1938 Wolseley 14 HP has an 1818cc engine.

Jim
Too old to Rock and Roll but too young to die.

1952 G80 rigid, 1960 G12 DL / Watsonian Monza, 1954 G80S.

Member
Posts: 95
Joined: Fri Oct 29, 2010 11:03 am
Location: CO. GALWAY EIRE

Re: Renold Chain Facts & News

Postby gotoole » Thu Jan 09, 2020 5:13 am

JimFitz wrote:If I remember correctly this was how the RAC (or was it the AA) rated vehicles and it may have been something to do with the cost of road tax or purchase tax.
Using your examples it looks like they rated each 100cc at 1 HP.
Perhaps it was different for cars because my 1938 Wolseley 14 HP has an 1818cc engine.

Jim


The RAC rated HP was calculated on the surface area of the piston(s). The formula was
Bore^2 x number cylinders
_______________________
2.5

Stroke , and therefore cubic capacity, was ignored. Its' affect was that long stroke engines were taxed lower than short stroke engines of the same capacity.

Member
Posts: 1276
Joined: Thu Jul 04, 2002 12:00 am
Location: NORMANDIE FRANCE

Re: Renold Chain Facts & News

Postby Groily » Fri Jan 10, 2020 12:04 pm

For the old HP rating - using Inches for bore diameter - that's right (except it's not surface area, it's the diameter squared).
In millimetre terms, the equivalent is "Diameter of Bore squared x number of cylinders, divided by 1613".

So a 4 cyl engine with a 2.5" or 63.5mm bore would be rated at 10HP.
While stroke didn't come into things directly, the typical limit back in the day of, say, 2,500 ft per minute piston speed, meant there was something of a constant at work.

The difference between, say, a 2 litre 4 cyl engine with 76mm bore and 110mm stroke (14.3HP), compared with an oversquare 89mm and 80mm motor (19.7HP) in taxation terms meant 'quite a darn lot'.

The old Treasury or RAC Horsepower tax was introduced in 1904-ish and not abolished until 1947. Abolition freed up designers and thereby unleashed considerable increases in performance for a given swept volume as engines became 'squarer' without tax penalties. Lower piston speeds, bigger valves & higher volumetric efficiency & improved fuel consumption, higher compression ratios . . . and, by stages and no doubt necessity, higher octane fuel!

Just for fun . . . the Treasury ratings for one of our 650 twins, with a 72mm bore, and a 650 Notrun twin at 68mm, would have been 6.43HP for the AMC, and 5.73HP for the Norton if I haven't messed up the sums. And a 'cooking' 650 Beesa twin would have been in the middle, at 70mm bore, with a lot fewer horses.

All a bit academic, but it shows how far Engineers have brought us, with outputs way past 100bhp per litre these days, even in not-very-exciting cars. Let alone large two-wheelers. The past is indeed another country!

Member
Posts: 95
Joined: Fri Oct 29, 2010 11:03 am
Location: CO. GALWAY EIRE

Re: Renold Chain Facts & News

Postby gotoole » Fri Jan 10, 2020 2:42 pm

Groily wrote:For the old HP rating - using Inches for bore diameter - that's right (except it's not surface area, it's the diameter squared).
In millimetre terms, the equivalent is "Diameter of Bore squared x number of cylinders, divided by 1613".

...


Not to be pedantic, but that is what I said.
Bore ^2 ( which is the diameter squared). Surface area is directly proportional to Bore^2 (Pi * Bore/2 ^2)

Previous

Return to Help

Who is online

Users browsing this forum: No registered users and 13 guests