Ducati Monster Motorcycle Forum banner
1 - 9 of 9 Posts

·
Registered
Joined
·
1,523 Posts
Discussion Starter · #1 ·
So I was just having a discussion with my friend about this topic. If I take my stock bike with xHp and then put on an exhaust system that (hypothetically) gives me 5hp I now have x+5HP. That 5HP makes a tremendous difference on my bike in terms of acceleration time and feel. I understand the concept of power to weight ratios so heres my question:

What is 5hp on a 400lb bike equal to on a 3500lb car? is it just 3500/400x5=(43.75hp)?
 

·
Registered
Joined
·
8,800 Posts
You've basically got it, but you have to add in the rider or driver weight, IE my 430 lb motorcycle is part of a 600 lb package when I'm riding it.
 

·
Registered
Joined
·
132 Posts
Heh, your bike has a package. Heh.

Yeah, you basically have it right. You can also think of it as percentage increase in HP. 5 hp on a 50 hp engine is equivalent to 20 hp on a 200 hp engine.

-Danimal
 

·
Registered
Joined
·
979 Posts
How I do it is car weight divided by bike weight (with me). Mulitply that by the hp increase.


Just went to lunch, was in a 3,000 lb car. My bike with me is just over 500 lbs, so my 63 hp x 6 is like the 3,000 lb car having 378 hp. It might only be a 620, but it's still pretty damn quick. (I think it's listed as a 12.5 second 1/4 mile.)
 

·
Registered
Joined
·
1,660 Posts
12.5? Sounds a bit slow ;D I thought we were faster than that. [laugh] HP/lb is a good way to do it just like torq.
 

·
Premium Member
Joined
·
697 Posts
yeah it's all about power to weight . just use the actual weights of bike and rider, car and driver...and all the **** you might have in the trunk..lol. i'm driving a rental grand marquis this week on a business trip out to nebraska. it's heavy but it has a lot of power. not particularly fast but does nice burn outs and is comfortable as all hell.
 

·
Premium Member
Joined
·
84 Posts
I always like to think of hp in a standardized way. I like to compare cars to bikes with HP / Ton

so a 80hp 424lb bike puts out

(80 / 425) * 2240 = 421.65 hp/ton

a stock mustang puts out 390hp and weights 3650lb

(390 / 3650) * 2240 = 239.35



It's always fun to see how much hp a car would need to equal the hp/ton ration a bike puts out.

421 = 2240 ( x / 3650) x= 686 hp
 

·
Premium Member
Joined
·
2,952 Posts
Actually it's not quite that simple to compare.

If you are talking acceleration rates, then it is mostly HP/WT ratios.

But as speed increases and aero drag comes into play, then frontal area and drag become more and more important. And that starts happening at surprisingly low speeds and becomes a real factor as you go faster. Any vehicles top speed is limited not by its weight but by its drag (rolling resistance + aero resistance). And aero factors overlap into the acceleration part of the equation.

And when you talk "performance", there are so many other things to consider, too. Carroll Shelby came up with what is the best and simplest way to quantify a vehicles basic bare-bones "performance". Zero to 100 mph and back to zero again. Given his credentials, it is hard to argue with what he says.
 
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top