How much extra horsepower would a rider get for each kilo of weight shed?

[Nathan S]

I guess if a factory has spent billions on the carbon fibre and titanium weight reduction program it is nonsense for them to put an old fatty behind the wheel or on the seat.

If the old fatty can get the lap times, the team won't care that they're fat.
The issue is that 125 GP bikes, and Formula Fords are built for short-arses.
Maybe a tall rider/driver would screw up their power-to-weight ratio and/or aerodynamics - but they'll never get the chance to find out because they simply don't fit...

[Lozza]

I reckon Stefan Dorflinger would disagree, he was a tall lanky German racing against jockey size Spaniards and e was still a 4 time world champion on 50 and 80cc GP bikes.That was in a class where riders eschewed sew on lettering on the back of their leathers just in case it slowed them down.  He was very careful to never be photographed standing next to the bike.
 

[Nathan S]

Just to confirm: the best example you can find is a bloke who won his last championship a quarter of a century ago? 

[GMC]

Acknowledging that weight saving doesn’t increase actual horsepower so then if we look at actual power to weight ratios then according to…

Geoff’s second law of Virtual physics

H divided by (R + B) = PWR
H = Horsepower
R = Rider weight in kilograms
B = Bike weight in kilograms
PWR = Power to weight ratio

Examples…
If horsepower is 40, rider weighs 95Kg and bike weighs 105Kg therefore…
40/ (95+105) = 40/200 = 0.2 PWR (0.2 horsepower per Kilogram)

If horsepower is 41, rider weighs 95Kg and bike weighs 105Kg therefore…
41/ (95+105) = 41/200 = 0.205 PWR

Therefore to gain a PWR of 0.205 from a 40 Hp engine then…

If horsepower is 40, rider weighs 95Kg and bike weighs 105Kg therefore…
40/ (95+100) = 40/195 = 0.2051 PWR

Thus, in this example a weight saving of 5Kg has a benefit of 1 Hp to create the same power to weight ratio.

It was stated earlier that there are greater benefits to be had from the rider losing weight in the form of general fitness and wellbeing but this isn’t altogether true.

If a rider loses 5Kg then he will probably be walking around the pits hungry. If he happens to walk past someone else who has a bucket of hot chips he will develop a craving for them. If the track happens to go past the food stand and he smells hamburgers cooking then this could easily destroy his state of mind giving the opposition a psychological advantage.

It is much wiser to lose weight from the bike, for example if you can save ¼ Kg in weight by the use of $500.00 in Titanium fasteners then this will give you a psychological advantage knowing that your bike is closer to being ‘state of the art’
This smug feeling though can easily disappear when you realize that you lap times haven’t increased one iota.
To fully gain the advantage of Titanium fasteners you must tell all and sundry that you have them. Others will then realize how cool and determined you are to win and will probably pull over for you and wave you by as they won’t consider themselves worthy.


Also to be considered is the equation…

(H/2) / (R + B) = PWR

H/2 = Horsepower as stated in the manufacturers brochure.
R = Rider weight in kilograms
B = Bike weight in kilograms
PWR = Power to weight ratio

And to keep in line with Walter the wise…
When the start gate drops the bullshit stops.

[holeshot buddy]

ha i am with brad i have dropped from
94 kg down to 84kg
and my kx 500 still feels fast
must admit i feel fitter on bike and can stand a lot more

[Rossvickicampbell]

Geoff - I hope $500 worth of titanium doesn't increase my lap times?

[GMC]

Geoff - I hope $500 worth of titanium doesn't increase my lap times?

Bloody…
Trust the Louse from Laos to pick up on a typo in my well thought out Thesis
 

[Lozza]

Just to confirm: the best example you can find is a bloke who won his last championship a quarter of a century ago? 

yep, but still a 4 time champion.Would have continued but FIM cut the 80cc championship. When Cathcart tested a 80cc GP he couldn't even tuck under the screen, he was told to brake when you feel the tyre rolling off the rim.
50/80cc was where a lot of technical innovation came from, cassette gearboxes, dual curve ignitions etc etc. Apparently the smaller the capacity the later at night you had to be up revving them

[Mike52]

Gavin McLeod could beat KTM EXC 250's on his XR200 in enduro's ,winning the Australian 4 day in the 250 class.
He also won the Weipa croc run on an XL500 .

Horsepower to weight was not a factor.

[Tom Laird]

Weight is a factor in Dirt Track (Flat Track)Racing. Approx. Ten pounds equals one HP.in real life. That's why there are no huge Flattrackers. They do kinda good on  Short Tracks and smaller TTs but lose on the 1/2 mile and Miles. One,they are giving away HP. Two,They are not Aerodynamic enough (Wind Resistance)   Three ,that being said,There were several National Number Riders'here in the states that won on Short Tracks and TTs a lot. Enough to keep their points up to Nat.Standards. Randy Cartell from Amarillo,Texas  and Eddie Wirth From California being two most notable.both weighing over 200 Lb (100 KG ?) and were over 6 feet tall. On the longer tracks and Road Racing  is where the difference really shows. Anyway enough blathering. See Ya             TCL
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