Building a race bike

Hi Guys,
Drive sprocket and bits, and holes in clutch basket etc, even adding another clutch plate still almost 1.2kg lighter and still not quite finished.  Fingers crossed for a significant amount more to come off.

Rods are Arrow,  need to finalize my final length and then they can be finished.  Remember these are a LOT longer than std so not compatible with normal  engine parts.

Jockeys or skeletons may apply  :LOL: :LOL:  makes my life easier  :P

J
 
KERMIT1200 said:
Hi Julian,
I think you need to aim for the bike to weigh towards 120kg to meet overall weight of bike&rider = 200kg.

Titanium rods I assume specially made?  By who ? Just very interested something to keep in mind for my own race engines.

Very interesting thread,
Andy
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80 kg is a sidecar pair.

Paul
 
chrisk said:
I know right. Here I was looking at yellow feet, trying to work out what yellow feet and Germany flora hand to do with race bikes. But, then I remembered flying into Frankfurt in the early 90?s and asking what all the yellow fields were. Age has wearied my memory, and the fact that I had been drinking the whole flight, but I think it was sun flowers or soya, or something. Those crazy German farmers.
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Rape, or rapeseed, Chris.

Product is rapeseed oil, edible and used in quite a few products, also recently being used as a diesel fuel alternative.  Driving behind an old Merc 200D running on the stuff smells like driving through a rotty old fish'n'chip shop that hasn't renewed the frying oil for months!

piet
 
Thats about the weight of one of my legs, would love a spin in maybe handicapped races. That doesn't sound right at all
 
That weight target is ambitious - but worth aiming at.

In perspective, one of my customer Aermacchi replicas weighed in at 102kg with battery and about 2 litres of fuel.
No enormous effort to reduce weight, but alloy pegs/pedals/rims and bolts drilled out etc. 35mm Cerianis and lightened road Macchi brakes.

The best tuning tip has always been - find a skinny kid to ride it....
 
GregT said:
That weight target is ambitious - but worth aiming at.

In perspective, one of my customer Aermacchi replicas weighed in at 102kg with battery and about 2 litres of fuel.
No enormous effort to reduce weight, but alloy pegs/pedals/rims and bolts drilled out etc. 35mm Cerianis and lightened road Macchi brakes.

The best tuning tip has always been - find a skinny kid to ride it....
Click to expand...

If the rule of thumb of 1kg of weight chews up 1hp. If a 130kg rider gets on a 102kg bike, does it mean the bike is in fact the equivalent of -30hp  (dunno)
 
Simple maths simplified.

If a bike has 100hp and weighs 180kg it has a power to weight of 1000 / 180 = 5.5555  - 5.555 x 100 = 555.5 hp/tonne  with a 70kg rider (250kg ready to race) = 400hp/tonne

If we have 100hp and a ready to race weight of 200kg and therefore a power to weight of 500hp/tonne  that would be the equivalent of the bike above having

1000/500=2    250kg/2:1 hp/kg = 125hp    so my imaginary 50kg weight saving has gained me the equivalent of 25hp  (all other things being equal)

I have just saved another 720g by the way,  Look!!

Jules

 

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Laverdalothar said:
I can do even better: 50 Kilos (well - 50 to many, at least...  :-[)
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Sounds like me Lothar  :LOL: :LOL:

I worked round the clock for a couple of days last month and am now under 80kg for the first time in almost 40 years!  Always hovered between 81 and 85 depending on eating and working, and suddenly whoosh! 78.2  but back to 79.5 now.  Still to old and too slow and too heavy for racing, and maybe too wise  ;) :LOL:

Jules
 
Grant said:
Pedrosa weighs 50kg allegedly...
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Weight wise my teenage son would be a better candidate than me or even Pedrosa as he makes him look positively obese. The only problem I see with this plan is that my son would only be interested if he could participate from the comfort of his computer desk.  :(
 
julian said:
Simple maths simplified.

If a bike has 100hp and weighs 180kg it has a power to weight of 1000 / 180 = 5.5555  - 5.555 x 100 = 555.5 hp/tonne  with a 70kg rider (250kg ready to race) = 400hp/tonne


In regards to the forks.  Was there anything specifically that made you choose the supplier you chose ?  Looking about there seems to be a few people doing similar things ?  I?m guessing because the copyright in them have passed ?  Are there other options out there. ?

Thanks in advance

If we have 100hp and a ready to race weight of 200kg and therefore a power to weight of 500hp/tonne  that would be the equivalent of the bike above having

1000/500=2    250kg/2:1 hp/kg = 125hp    so my imaginary 50kg weight saving has gained me the equivalent of 25hp  (all other things being equal)

I have just saved another 720g by the way,  Look!!

Jules
Click to expand...
 
julian said:
Simple maths simplified.

If a bike has 100hp and weighs 180kg it has a power to weight of 1000 / 180 = 5.5555  - 5.555 x 100 = 555.5 hp/tonne  with a 70kg rider (250kg ready to race) = 400hp/tonne
Click to expand...

Simplified? Blimey, if that's simplified, I must be a dunce.

How does 100 HP suddenly become 1000, and then the resulting number multiplied by a mysterious 100 to get the right answer?
It's not rocket surgery. To get HP/tonne, divide the HP by the tonnes.  100/0.18 = 555.6. Somehow you got the right answer  ???

I have no idea what you're trying to do with your second equation (1000/500, 250/2, etc.)

The weight of a bike + rider combination mostly affects acceleration. It's Newton's Second Law, F=m.a  (HP/tonne is a crude analogy of F/m, so it gives a yardstick for acceleration).

So for a given force shoving the bike along, increased mass will give lower acceleration (and deceleration under brakes). However, it's not that simple in reality. Increased weight gives more traction, so you can increase the force that the bike applies to the road to get itself moving (apply more throttle), at least in the lower gears where loss of traction could be an issue.

Getting back to your assumptions: 100 HP with a 200 kg bike/rider combo (0.2 tonnes), you get 500 HP/tonne (so far you're correct).
Reduce rider's weight by 50 kg and you have 100/0.15 = 667 HP/tonne.
Now, to work out what HP would give the same 667 HP/tonne ratio with the 200 kg combo, it's simply 667 HP/tonne x 0.2 tonnes = 133 HP (Not 125).

I'd give you 2/10 for maths, and that's only because you somehow got the first bit right (555 HP/tonne) even though your method was flawed.  :D
 
chrisk said:
If the rule of thumb of 1kg of weight chews up 1hp. If a 130kg rider gets on a 102kg bike, does it mean the bike is in fact the equivalent of -30hp  (dunno)
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Have you found a picture of me somewhere Chris ?

These days I only test ride them. But there's a line of skinny kids wanting to apply, LOL
I thin down the line by holding auditions alongside the local ATM - proof of ability to pay is required....
 
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