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

[worms]

I thought that wieght was not revilant to a motors horsepower, ie a 47hp motor produces 47 bhp, just because a fat bastard tries to ride it dosnt mean it has any less hp?


cheers worms

[Marc.com]

I think he is meaning power to weight ratio. I would say the gain is heaps as all the top riders in both MX and road racing tend to be Hobbit size dudes who weigh 60-70kg ringing wet.

We had this theory it also effects what injuries you get and your career end with big guys going out with backs and knees from the downward force and leverage of their bulk and little guys finishing because of breaking their bird like bones.

[paco]

Take the bike to a dyno and start adding weight,take note of the difference per kilo.Or get your gps and take the bike somewhere that has a long straight and check top speed,then start adding weight and take note.ps.Gps set to speed reading.p

[paco]

o have missed the point.{as usual] Horse power is horse power no matter what weight it is asked to carry.p

[Tahitian_Red]

Isn't a horsepower moving 550lbs one foot, in one second?

I'm not a math wiz, but if add weight or increase horsepower you change the equation.  Bottom line is it takes more horsepower to drag our fat asses around a track.  Horsepower costs money and lowers reliability, better to lose 10-15Kg.
 

[Taka 100]

power to weight  mmmmm   might affect a 125 and maybe 250 in certain conditions but not a big bore  power ,(i tested this theary once in my board shorts and thongs on a gravel road aboard a machh 111 kwaka  forward thrust (ooohh thats sounds good) , more like whiplash ,there was an old say that you dont punch a railway spike with a panel hammer   no extra horsepower anywhere except in motor design and modification , maybe it should read how much extra performance for each kilo shed. i am willing to undertake the mission under strictly controlled monitered conditions maybe at the witsundays in a beachside bungalow with controlled diet and riding manicured tracks , but only for 6 months any longer you know what they say " its mango season" quick hide here he comes now

[Nathan S]

I think he is meaning power to weight ratio. I would say the gain is heaps as all the top riders in both MX and road racing tend to be Hobbit size dudes who weigh 60-70kg ringing wet.

Yep.

Mostly, they're fit short-arses - I reckon their weight is a by-product of being both short and fit, rather than the main goal.

Look at the start line of any pro dirt bike race, and the average height is noticably lower than the average of the general public.
Yes, there's guys like Toby Price, David Knight and Joel Smets out there, but they're the exception among pro dirt bike riders.
I'm pretty sure that being short has a weight distribution advantage, that's way more important than the weight itself... Matt Phillips is short, fit and surprisingly not-skinny - and is way faster than anyone on these forums...
The taller blokes are always strapping young lads who (have to) manhandle the bikes, because their height screws up the balance - a tall, skinny pro-level rider is virtually unheard of.


Glen Bell was reported to be comfortably in the 80kg weight range when he was winning lots of 125 races... You'd reckon that if weight really mattered for dirt bikes, that his extra weight at the very top of the national level would have made the difference.

[Marc.com]

Glen Bell was reported to be comfortably in the 80kg weight range when he was winning lots of 125 races... You'd reckon that if weight really mattered for dirt bikes, that his extra weight at the very top of the national level would have made the difference.

But what if Glen had come up against a lighter guy of the same ability, if a 125 weighs say 100kgs plus Glen is 180, say a rider is 60 kilos drops the weight the bike has to haul by what little over 10%. On a 125 thats like gaining 4-5hp. Not sure what Ricky Carmichael weighed but he was a very short dude.

[bazza]

Then in some situations the xtra wieght would mean more traction= more go forward and speed

[vmx42]

I think he is meaning power to weight ratio. I would say the gain is heaps as all the top riders in both MX and road racing tend to be Hobbit size dudes who weigh 60-70kg ringing wet.

Yep.

Mostly, they're fit short-arses - I reckon their weight is a by-product of being both short and fit, rather than the main goal.

Look at the start line of any pro dirt bike race, and the average height is noticably lower than the average of the general public.
Yes, there's guys like Toby Price, David Knight and Joel Smets out there, but they're the exception among pro dirt bike riders.
I'm pretty sure that being short has a weight distribution advantage, that's way more important than the weight itself... Matt Phillips is short, fit and surprisingly not-skinny - and is way faster than anyone on these forums...
The taller blokes are always strapping young lads who (have to) manhandle the bikes, because their height screws up the balance - a tall, skinny pro-level rider is virtually unheard of.


Glen Bell was reported to be comfortably in the 80kg weight range when he was winning lots of 125 races... You'd reckon that if weight really mattered for dirt bikes, that his extra weight at the very top of the national level would have made the difference.

All very well... but the question is about how a reduction in mass affects the performance of a theoretical bike and rider. You can point out anomalies, with riders of all sizes and shapes, till the cows come home, but none of those actually address the original question.

The simple fact is that, in isolation, less mass makes it easier for an engine of a given power output to accelerate that mass [with all other variables being constant]. The question is by how much? And the second inferred part of the question is: do you chase horsepower or mass reduction, or both?

Then in some situations the xtra wieght would mean more traction= more go forward and speed

In the real world that is of course true, but at what point do you reach diminishing returns... an extra 5kg or 10, what about 100?

That is the great thing about dirt bikes, with the enormous number of variables, there is no perfect answer. Which gives all competitors a chance...

[Nathan S]

All very well... but the question is about how a reduction in mass affects the performance of a theoretical bike and rider.

On tar, or even smooth, hard-packed dirt [ie: Dirt Track], then the usual rules apply.

But on an MX track, the original question is a LOOOOONNNG way down the list of things that affect performance - if the rider if fit and competent, then his/her weight is only a bit more important than the colour of the chain joining link.
Even if they're on a 125.

[Taka 100]

ahhh well back to being a numbskull im sick of being a professor, it hurts my head too much i hope to get a bigger helmet soon so i can fit more in, i will make it a full face with a visor next time it keeps me from eating so many snacks whilst on the computer on rainy days , its sorta like calorie control , you can only consume so much through a straw

[Lozza]

A interesting note is gymnastics, at an olympic level all the competitors are all Doc's size and weight, they are incredibly strong for their weight, there would not be a competitor over 70kgs in that level. Now if you take Dani Pedrosa or Toni Ellias (or Kevin Schwantz)for instance whom are tiny jockey size blokes but have the strength to punt a heavy and very powerful motorcycle around for 45mins flat out. Then the late Super Sic was over 6ft and fairly average build (though very fit) that didn't seem to matter much in overall performance. When Dani first went to MotoGP many said he was too small and not strong enough to ride one and last year he was 'to light and should have to carry ballast'.

If in doubt , always go flat out and  go to the front and stay there , Thats two most important rules in racing . Wait,  wait there is another one ( mainly for the chrome trolleys ) . If the front wheel fits through , the rest will follow .

[Nathan S]

GP bikes and F1 cars favor short blokes because the feeder series favor short blokes.

And - like I said before - the rules of power-to-weight actually apply on tar.

[Marc.com]

GP bikes and F1 cars favor short blokes because the feeder series favor short blokes.

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. Its a bit like basketball where it favors a certain body type and you only have fraction of a second spreads between racers so every tiny edge counts.

I am not sure power to weight has such a big influence off road, to support this idea there have been plenty of times at MXd Nations and other events where 125s have shut down the 500s with top level riders on both. Shane Watts was a good example he could alternate between 125s, 200, 250, 450 on consecutive weekends in the States and still win.