• Welcome to the forum website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Online Forum Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this forum website.

    If you have previously registered to use this forum website, you should log in now. CLICK HERE.

    If you have never registered to use this forum website before, please CLICK HERE.

BHP measuring

Howard

Well Known and Active Forum Website User
VOC Member
I've got lots of queries just lately - Egli very very nearly back on the road again, and my brain is getting back into being a Vincent owner (ok half Vincent).

Question - How did the Vincent works measure the power of the bikes? Did they have their own dyno? Did they measure at the wheel or crank? etc

55 bhp is not a lot of power to push a heavy, unfaired bike to nearly 130 mph (probably wearing a Barbour jacket) when my 125 bhp lighter, faired Fireblade is only good for 165 mph. I know all (some of) the theory about diminishing returns, and the faster you go the more power you need to go a bit faster, but even so, there seems a big dicrepancy.

H
 

Albervin

Well Known and Active Forum Website User
VOC Member
Power

Brighter lights than me can give more detail but I believe the answer is Torque. A Vincent develops similar torque figures to my BMW R1100RT (but at lower rpm than the BMW). Given BHP is a figure derived from torque & rpm I have no doubt that those raised on 15,000 rpm Jap machines find it hard to comprehend a Vincent was/is capable of 120 mph. Some road going Vincents I know of have been dyno tested at well in excess of 60 bhp (at the rear wheel) so I am sure the original bikes were in the ball park of 55 bhp at the rear wheel. For day to day riding though, it is the torque you use as ultimate BHP only comes into play as you approach 5,500+ rpm.
My little Aprilia RS250 has a claimed max bhp of over 50 but that is at 11,000 rpm & below 6,000 it won't pull the skin off a rice pudding! It will pull close to 115 mph though!;)
 

ogrilp400

Well Known and Active Forum Website User
VOC Member
Power Measuring

Torque is what does the work. Yes Vincent did have a Dynamometer test house In it was a Heenan and Froude water brake that measured torque directly off the crankshaft. Quite a simple apparatus actually that could do these measurements for hours or days at a time.

Phelps.
 

david bowen

Well Known and Active Forum Website User
Non-VOC Member
water brake

Yes Ken you are correct on the same brake they run the MOD marine engine for weeks, the test house was at the top of the yard at vincents Great North road factory
 

Howard

Well Known and Active Forum Website User
VOC Member
Ok, first part answered, Vincent had a Heenan Froud dyno, I suspect it was probably chain driven from the final drive sprocket, not the crank, so Albervin's thoughts that 55 bhp is a rear wheel power is probably right. Probably around 60 at the crank allowing for losses in the gearbox, primary chain etc.

55 bhp = 125 mph but 125 bhp = 165 mph is still a puzzle for me. Like other subscribers to this thread I used to tell myself that it's because of the torque, but by definition torque cannot do the work, because there's no time factor involved in torque measurement. It's got to be power measured in ft.lbs/sec which determines the speed in ft/sec not the torque which is only measured in ft.lbs (Sorry if ft and lbs are the wrong way round, I use metric units these days).

Torque may be part of the answer, but I don't think it's engine torque. If more torque is needed at the rear wheel we change down a gear and rev the engine more, the engine produces more power, and the gearbox converts it to more torque at the wheel.

I've worked for a long time with industrial electic drives including 0.25 kW electric motors geared down so far they produce 100,000 Nm of torque, but they turn so slowly you can't see any movement.

Any more for any more? My brain must be missing something.

H
 

ogrilp400

Well Known and Active Forum Website User
VOC Member
The dynamometer was driven directly off the crankshaft. That is, there was a double universal jointed shaft between the drive end of the crankshaft and the dynamometer. No gearbox.
100,000 Nm of torque!!!, strewth, that is impressive.

Phelps.
 

Tom Gaynor

Well Known and Active Forum Website User
VOC Member
Power and speed

The answer is that the power required increases +/- with the square of speed, given a constant Cd - aerodynamic drag factor. To go from 100 to 120 mph (120/100 = 20% increase in speed) requires a 44% increase in power (120 x 120 / 100 x 100).
About 36 bhp is enough to push an unfaired bike to 100 mph, and 55 bhp to take an unfaired bike to 125 mph or so. The speeds (110 and 125) claimed for Rapides and Shadows suggest that PEI and PCV knew that.
However if the 55 bhp bike has a Peel fairing, it'll clock 145 mph. Peel faired Manx Nortons (about 55 bhp...) were pulling over 150 mph at the NW 200 30-odd years ago. And a full dustbin fairing was the reason the 70 bhp Moto Guzzi V8 was clocked at 178 mph in 1956.
 

Howard

Well Known and Active Forum Website User
VOC Member
Tom

I think you must be the same generation as me, what you write is what I always understood to be the case.
BUT
By your (our) calcs 98 bhp should be good enough for 165 mph (unfaired) and the 125 Fireblade horses should take it to 185+mph. I'm sure things like rolling resistance change with speed, but 27 lost bhp seems a lot to account for - not including the fairing, and about 80 lbs less weight.

Is this what I've suspected, Vincents work on horses big enough to carry Knights into battle, but the Japanese industry use racehorses.

Phelps

Oh well, I suppose in top gear, we'd only lose about 5% on the way to the rear wheel.

As an aside, the biggest gearbox we built would transmit 500,000 Nm and was used to turn a swing bridge. Our fitter was big on attention to detail, and liked to despatch all his drive units with the keyway on the output shaft vertical (at 12 o'clock) - he went for a coffee break while it was turning into position, when he got back the keyway had turned too far, so he watched it for an hour to make sure it didn't overrun next time. He said it was because he had pride in his work, but I have my suspicions.

H
 

Tom Gaynor

Well Known and Active Forum Website User
VOC Member
Horsepower at crank vs horsepower at rear wheel

The common assumption is that 50 at the rear wheel is 55 at the crank - or at least it is in classic racing circles. Seems a lot in top gear, as has been remarked. However since all I and other racers are only interested in maximising bhp, rather than establishing an absolute number, I don't know of anyone who has investigated the assumption. It wouldn't be terribly easy to do, since all dynos (even of the same basic design) give different results. Stories abound of people seeking the dyno that over-reads most so as to sell their 190 bhp GSX-R for a higher price than a 180 bhp ditto would fetch.
(In passing, "my" dyno man had never tested anything with "only" 50 bhp at the rear wheel, and we had to develop a technique to get the drum up to speed without burning out the clutch. I had to accelerate the Norton through the gears into 6th. A big Japanese bike just does it in top!)
I've always assumed that Vincent did enough brake testing to establish that a reasonable Rapide should put out 45, and a reasonable Shadow 55, and those were the numbers attached to all. I expect that in reality Rapides varied either side of 45, and Shadows either side of 55, and that there must have been "good Rapides" and "poor Shadows" that were indistinguishable in performance.

Tom

Tom

I think you must be the same generation as me, what you write is what I always understood to be the case.
BUT
By your (our) calcs 98 bhp should be good enough for 165 mph (unfaired) and the 125 Fireblade horses should take it to 185+mph. I'm sure things like rolling resistance change with speed, but 27 lost bhp seems a lot to account for - not including the fairing, and about 80 lbs less weight.

Is this what I've suspected, Vincents work on horses big enough to carry Knights into battle, but the Japanese industry use racehorses.

Phelps

Oh well, I suppose in top gear, we'd only lose about 5% on the way to the rear wheel.

As an aside, the biggest gearbox we built would transmit 500,000 Nm and was used to turn a swing bridge. Our fitter was big on attention to detail, and liked to despatch all his drive units with the keyway on the output shaft vertical (at 12 o'clock) - he went for a coffee break while it was turning into position, when he got back the keyway had turned too far, so he watched it for an hour to make sure it didn't overrun next time. He said it was because he had pride in his work, but I have my suspicions.

H
 

Tnecniv Edipar

Well Known and Active Forum Website User
VOC Member
55 bhp = 125 mph but 125 bhp = 165 mph is still a puzzle for me. Like other subscribers to this thread I used to tell myself that it's because of the torque, but by definition torque cannot do the work, because there's no time factor involved in torque measurement. It's got to be power measured in ft.lbs/sec which determines the speed in ft/sec not the torque which is only measured in ft.lbs (Sorry if ft and lbs are the wrong way round, I use metric units these days).

Torque may be part of the answer, but I don't think it's engine torque. If more torque is needed at the rear wheel we change down a gear and rev the engine more, the engine produces more power, and the gearbox converts it to more torque at the wheel.

Any more for any more? My brain must be missing something.

H

You are correct , torque is effort , the push down the road , but power which is torque x RPM is work done , is the factor that allows the bike to develop speed. There is another factor though , power band. Any engine can produce an impressive PEAK power at a given RPM but if that is only a spike a few hundred RPM wide the vehicle is unuseable unless it has a 20 speed gearbox ! Vincents have a wide power band , that is , if the torque and power graphs are examined you would see alot of area under the curve instead of a tall mountain as tends to be the case with modern multi's. This means there is a constant thrust at the drive wheel to develop and maintain velocity.
 
Warning! This thread is more than 4yrs ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Top