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Bike Weights and Weighing

Little Honda

Well Known and Active Website User
VOC Member
I have read differing views on the following method. Bathroom scales under front wheel, back wheel on block same height, balance bike with steady hand on handle bar after pulling upright from slight lean on wall. repeat for back wheel. Add two totals. The question is, can the result be true?
If u check yr bathroom scales by say 5, 10, 30 kgs plus all weights, each time u use yr scale for yr bike, u will
know the deviation factor or "bathroom-factor". What I found out by weighing my Norvin: It had the same
weight distribution, like my Honda RC31 (650 Hawk), which - in my opinion - is the best road holding bike
in the 60hp class. These bikes have a lighter front wheel load, than rear, and this seems to be for the changing
load with braking. If u study modern superbike tests, like BMW 1000RR, Honda CBR1000RR, etc. , they all have
heavier front wheel loads. I asume, that this is for compensating the aerial lift at speeds over 140mph, to keep
these bikes steady at full throttle on the motorway. As we do not have this kind of lift with our bikes, they
should not have the same weight distribution, like modern Super Bikes, to submit an enjoyable ride at lower
speeds, even on track. In other words, a good Vincent, on road or on track, should have abt 40% load on the
front and 60% on the rear. Original brakes in good nick are fine on a Comet, but will need some improvement
on the front with twins.
 

Little Honda

Well Known and Active Website User
VOC Member
I bought 2 sets of el cheapo bathroom scales, the old school type with the rotary needle, make up some simple ramps and wheel the bike on. Hold the bike upright with your fingertips on one bar end and read the scales.......On my current single racer the front was 65.5 kg's and the rear 64.5 kg's........that's near enough to 130 for me.......With oils, no fuel.
Try again with rider on.
 

Little Honda

Well Known and Active Website User
VOC Member
Impressed Greg. Makes it 10kg lighter than a standard Manx, with all the fancy magnesium engine parts and throughdrilled bolts. Still some 15 kg heavier than a Yamaha TZ though.
A modern MotoGP racer has a minimum weight of 157 kg.
The 500cc single cylinder ohc Moto Guzzi works racer of 1939 weighs 90kgs at 47hp.
 

greg brillus

Well Known and Active Website User
VOC Member
I am surprised a Manx is that heavy........Mind you i only read the other day that a Manx engine is 35 Kg's on its own.......In spite of the majority of magnesium parts the engine is quite bulky. When I removed the ESO 500 engine on the scales it showed 30 kg's, this including the oil pump and magneto, plus the special sump I made for it. Because my racer is completely striped down at present, I will carefully measure the weight of the main parts as it goes back together....... I know on these bikes the 2 wheels generally come in at 30 kg's the pair, and this is difficult to do anything about. The modern belt drives save a considerable amount of weight, especially on a twin, I think when i built the twin racer years back the weight saving over the stock primary drive and clutch was at least 3.5 Kg's. I think a Comet engine is around the 30 kg mark as well........anyone know for sure.......
 

oexing

Well Known and Active Website User
VOC Member
Would you believe that these BMW RS 54 dohc twins were about 10 kg lighter than the Manxes ? Well, handling was a bit special which many racers never really got used to. My guess, the wheel base was a tad too short for these speeds. Nevertheless Walter Zeller gave the Manxes and MVs hard times. The engines were more successful in sidecar racers with decades of world championships.

Vic
BMW-Rennsport-RS500-Type-256-Left-Side.jpg
 

Mike 40M

Well Known and Active Website User
VOC Member
Wonder what I miss, having Norton engines in all four Nortons?
One problem with the AMC box is that it's a short distance (not much meat) between layshaft bearing and the sleeve gear bearing. Make them prone to crack when abused.
 
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davidd

Well Known and Active Website User
VOC Member
I think a Comet engine is around the 30 kg mark as well........anyone know for sure.......
Greg,

I weighed the completed engine for Dave Tompkins racer and it was 95 lbs. It had a new BT-H ignition on it. My racer was 280 Lbs. Dave's racer I believe is in the 285 lbs. area. I don't have any titanium on mine. Dave has a lot on his. The Godet racer is 267 Lbs. with a lot of titanium and magnesium cases.

All the casting weights are different amounts, so you cannot be very precise from one bike to another, but I think 275 to 285 lbs. is a good target for a Comet racer.

David
 

Glenliman

Well Known and Active Website User
VOC Member
A couple of years ago I had my 850 AMC trans apart for replacement of the layshaft bearing, which was about to fail completely.
After a good look around in there I decided to take things a little easier in the future. No more powershifting!

For something that was originally designed to cope with 20 HP or less, then marginally upgraded, it does amazingly well. There is a limit though, and the stock 850 Norton seems to be about it. That might be about the same torque output as a stock 1000 Vincent, or a smidge more.
The 850 Norton is a torquey motor.

There is the TTI that will slot right in- expensive but by all accounts an excellent product.

Glen
 
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Glenliman

Well Known and Active Website User
VOC Member
Greg,

I weighed the completed engine for Dave Tompkins racer and it was 95 lbs. It had a new BT-H ignition on it. My racer was 280 Lbs. Dave's racer I believe is in the 285 lbs. area. I don't have any titanium on mine. Dave has a lot on his. The Godet racer is 267 Lbs. with a lot of titanium and magnesium cases.

All the casting weights are different amounts, so you cannot be very precise from one bike to another, but I think 275 to 285 lbs. is a good target for a Comet racer.

David
I am surprised a Manx is that heavy........Mind you i only read the other day that a Manx engine is 35 Kg's on its own.......In spite of the majority of magnesium parts the engine is quite bulky.
I was surprised to read that the magnesium Manx engine is 28 lbs heavier than the aluminium 500 Dommie engine.
This was one of the reasons that Doug Hele wanted Norton to put more money into development of the twin for racing. They ignored his logic.

Re the TTI box fit on a Commando. A friend recently fitted one to his Maney 920 Commando. It required a few minutes with the die grinder to go in. A bit of steel on the cradle had to be removed.

Glen
 
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Pushrod Twin

Well Known and Active Website User
VOC Member
TTI boxes are great, I visited the factory a couple of years ago, they are 80 miles away from me. Bruce is a nice guy and his team are enthusiastic. I too would fit one if my Commando boxes wear out.
 

greg brillus

Well Known and Active Website User
VOC Member
Thanks for the figures David, the numbers are quite amazing. My racer runs a 6 speed TTI box which is just the best......I can shift up through the gears as fast as I like with no issues at all, it is entirely predictable. I have sold the original engine and ancillary parts to a fellow Vincent man and racer, he is also interested in the gearbox which I would replace with a 5 speed in magnesium for the small extra cost. As Roy said, Bruce and the team at TTI in Nelson New Zealand are very helpful. The gearboxes are very strong, they run their own specific output sprockets which are not interchangeable with the AMC style boxes, I think the spline is larger. My frame comes back from the paint shop hopefully this coming week, then the reassembly will begin, this is a genuine Slimline frame with a later swing arm. I use longer back shocks and use a 30 mm spacer under the top yolk, with a longer steering stem to change the steering angle. This helps the bike to "Turn in" on corners much better.
 

Bill Cannon

Well Known and Active Website User
VOC Member
If u check yr bathroom scales by say 5, 10, 30 kgs plus all weights, each time u use yr scale for yr bike, u will
know the deviation factor or "bathroom-factor". What I found out by weighing my Norvin: It had the same
weight distribution, like my Honda RC31 (650 Hawk), which - in my opinion - is the best road holding bike
in the 60hp class. These bikes have a lighter front wheel load, than rear, and this seems to be for the changing
load with braking. If u study modern superbike tests, like BMW 1000RR, Honda CBR1000RR, etc. , they all have
heavier front wheel loads. I asume, that this is for compensating the aerial lift at speeds over 140mph, to keep
these bikes steady at full throttle on the motorway. As we do not have this kind of lift with our bikes, they
should not have the same weight distribution, like modern Super Bikes, to submit an enjoyable ride at lower
speeds, even on track. In other words, a good Vincent, on road or on track, should have abt 40% load on the
front and 60% on the rear. Original brakes in good nick are fine on a Comet, but will need some improvement
on the front with twins.
Don't forget friction is directly proportional to load, so weight on the front gives extra front tyre grip allowing more cornering power and stronger braking.
Cheers Bill
 

Glenliman

Well Known and Active Website User
VOC Member
Yes, that keeps cropping up. Mine is a "standard" Rapide, maybe 8:1CR, 28mm Delortos, Mk III cams, nothing at all spectacular.
However, I took the opportunity to support the outer end of the sleeve gear in a bearing as I believe the factory racing Commandos did. It only needed a few thou of hard chrome and a precision grind to fit into a half inch wide ball race which in turn lives in the 1/2" engine plate.
You can see in one of the pics above that I used a Vincent slipper chain tensioner.
I dont go with the folklore regarding the "heavy Commando clutch" I dont see why the weight of the clutch would have any influence at all. It is simply the force generated by the power of the engine which pulls on the wee spindly shaft.
There are other separate g/boxes which are up to it. Roy Robertson's race bike runs a box which looks like a Triumph and that motor makes plenty grunt. I recall him telling me it has 5 speeds.
Roy told me that he has blown up more than one of these Triumph 5 speeds. They are said to be a lot stronger than the AMC .
One of the fellows on the Norton site runs a modified 850. It's 910 cc and makes maybe an extra 15 bhp or so, which he uses.
He has broken stock AMC transmissions with that one. He's got a TTI in there now, it's holding up.

On the question of weights, how does the 280lbs of a Comet racer compare to the weight of a roadgoing Comet?
Would the racer be approximately 100 lbs lighter than the roadbike?

Glen
 
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davidd

Well Known and Active Website User
VOC Member
Glen,

I think that is about right. The Flash was billed around 330 and it was probably around 340. The street Comet was 390. I weighed a stock street Comet once and it was 400 lbs.

David
 

Glenliman

Well Known and Active Website User
VOC Member
My next question is, how does one reduce the weight by 120 lbs while retaining Vincent frame members and Gridraulics?
I have an ulterior motive. I would like to chop some weight from my Rapide but still have it look like a Rapide. Surely some of the tricks used on the Comet racer could be applied to a Rapide?
Here's my list to date. Some of it has already been done but hasn't amounted to much weight reduction.

-Alloy head brackets- big weight saving possible here.
-Armours silencer to replace Spares Co Spiral baffle- done
Alton to replace dynamo- done
-Replace rear stand with Alloy version s that will only be a fender brace ( Dave Hills stand in place)
-Alloy rims- done
-Lightweight horn to replace heavy Altette - done
-Newby belt drive
-Alloy engine plates
-Remove front stands- done
-Lightweight ignition housing instead of magneto- done
- Alloy fuel tank
- remove ss crash bars
- replace ss and steel fasteners with titanium
- replace ss fenders with alloy version

I'm sure there is more low hanging fruit, but that's the easy stuff that comes to mind ( other than the Newby drive!)

Glen
 

Robert Watson

Well Known and Active Website User
VOC Member
Titanium oil tank
Keep the side stands but drill them up the middle.
Make almost all your fasteners from alloy
Alloy brake drums with cast Iron liners
Alloy brake arms.
Alloy brake rods
Alloy fender stays
Alloy spoke flanges
Drilled and tapped hubs with socket head cap screws and no nuts
Get a new set of lightweight leathers
switch to a beanie helmet
Notice I have said nothing personal here
 

Glenliman

Well Known and Active Website User
VOC Member
Way past that Mike, I'm using a digital hanging scale now. And it's painfully accurate!
My Rapide with the rack and Top box is 507 lbs with 1 gallon of gas in the tank. That includes travelling tools.

Glen
 

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