Interesting facts

[KTMphil]

On a 1/4 mile drag race, adding 3.2 KG to the vehicle and driver/ rider combination is equal to losing 1HP in engine power. It does not have a material effect on top speed.

 

[Lone Rider]

That is very interesting - do you have a source for that information - URL?

 

[bill]

https://www.youtube.com/watch?v=eTQjRZ84nG4

 

[KTMphil]

That is very interesting - do you have a source for that information - URL?

It was from a guy that was into drag racing that stopped by today, no URL.

 

[Kawboy]

That 3.2kg = 1hp figure is dependent upon the weight of the bike/rider- basically, it would be a change in the power-to-weight ratio, and that 3.2kg would mean more of a change in PTW to a 200kg (+rider) bike that makes 100hp as opposed to the same set-up making 200hp. By top speed I'm assuming you mean 'trap speed' and that is actually fractionally affected by a small amount of added weight, but not by any major margin unless the weight difference is very significant.

 

[KTMphil]

From:

http://www.clubhotrod.com/drag-racing/45857-effect-weight-1-4-mile-times.html



The old rule of thumb was, for every 100 lbs you remove from a car you pick up one tenth second et, so 1000 lbs less equals 1 second faster time. Beyond that, my mathematical skills run out.

...............................................................................................


To address the original thought experiment of 7.6lb/hp in 3300lb car vs. a 4300lb car... assuming perfect or identical traction and ignoring any aerodynamic differences, the two cars will run the same ET at the same speed... 11.45@117mph according to one racing calculator. (BTW: 3300/7.6 = 434.2HP, 4300/7.6 = 565.8HP)

"horsepower" or "power" in general is a measure of "work" over "time". "work" being movement of a mass (weight) over distance. If both cars have 7.6lb/hp doesn't matter if one car is 1000lb and the other is 10,000lb, the answer will be the same.

Now I'm talking about HP to the wheels with ideal traction... not HP at the crank. In the heavier vehicle, you may expect higher losses through the drivetrain.

As mentioned above, a good rule of thumb is that removing 100lbs will reduce ET about a tenth.

Here's the racing calculator I used this time (there are several out there):
http://www.wallaceracing.com/et-hp-mph.php

 

[Kawboy]

Right, but the above example isn't the same as what was posted in the OP- it's simply an example of two cars with different weights but identical PTW ratios running the same times under the same conditions.

Adding 100lbs to the 3300lb/434.2hp car will have greater (negative) effect on the PTW than it would on the 4300lb/565.8hp car (obviously 3.2kg is such a small weight increase that it would be negligible in a car, but it means something on a bike, and it would be way more significant for a 360lb/26hp CBR300R than a 580lb/180hp Hayabusa). Just like the rule-of-thumb '100lbs = 10hp' has been used forever for cars, there is also an equivalent rule-of-thumb for bikes.

Basically, adding 100lbs to the 3300lb car in the above example drops the hp/lb ratio from 0.1316 to 0.1277, where doing the same to the 4300lb car drops it from the same 0.1316 to only 0.1286. If you add more weight, the difference becomes more significant, and would have different effects on the respective ETs. Of course, there are traction factors, aerodynamics, etc to consider.

You can't make a general rule that says 'this much weight' is equal to 'this much horsepower'- it's all relative. If the OP had said 'is approximately equal to' I wouldn't have an argument (though it would be way off in some cases). Sorry if I'm being pedantic.

 

[Pounce]

So, have a decent shit before the race & you'll get a better time.

 

[papa al]

On a 1/4 mile drag race, adding 3.2 KG to the vehicle and driver/ rider combination is equal to losing 1HP in engine power. It does not have a material effect on top speed.

So rider @ 90 kg, reduces power effective by 28HP.
Since my bike has only 18HP to begin with, that is going to be a slow 1/4 I guess.:RE