GS Terminal Velocity

[Twism86]

Awesome replies! Thanks! So it appears a GS would fall faster than u can ride it, kinda figured.

[bombsquad83]

Now if we could just get someone to try it. 

[Twism86]

Now if we could just get someone to try it. 

Im someone has a spare GS Ill ride it until about 6,000 ft  Then Ill pull my chute and watch it fall haha.

[burning1]

What are you planning? Riding straight up a wall? On level ground, the weight only matters to acceleration. Maximum sustained velocity the engine has to overcome friction, like drag. It doesn't have to "lift" any weight at all, so heavy or light, two bikes with the same frontal area & frictional drag will have the same max velocity.

I agree. Looks like the back-of-the-envelope calculation confirms falling is faster than riding.  Cool. 

Well, look at it this way... On the ground, the force of the engine at the rear wheel is being used to overcome the wind resistance of the bike. Falling, the weight of the vehicle is being used to overcome the wind resistance of the bike. If the force of the engine at max speed is greater than the weight of the bike, it will go faster on the ground than in the air. If not, the opposite is true*. I attempt to explain my logic...

* Again, assuming that the bike is falling perfectly nose-down.

This is not true because the weight of the bike has any bearing on max ground speed. It is true because the weight of the bike has a massive impact on falling speed.

Remember: Gravity applies a force to the motorcycle equal to the object's weight. The engine also applies a force to the motorcycle. At the engine, this force is measured in foot pounds. We can take the force, multiply it through the various gearing ratios of the transmission, and compare it to the rear wheel size to determine how many pounds of force the engine is actually applying to the rear wheel, at top speed. If the engine is applying 380lbs of force to the ground on a 380lb bike, the bike is capable of accelerating exactly as hard as gravity is capable of pulling the vehicle. The vehicle achieves exactly 1G forward force, but it is being met by exactly 1G of wind resistance, exactly as if the vehicle is falling perfectly nose-down.

Top speed is independent of acceleration, as you point out, and the weight of a vehicle isn't terribly important when trying to reach maximum speed on the ground. However, when falling, maximum speed is determined by the coefficient of drag to area vs the weight of the object. That's where the vehicle weight is important.

If you compare two objects with the same size/shape/etc, but different weight, the heavier object will always have a higher TV.

As a side note: It's very difficult to measure the Coefficent of Drag for a vehicle, or the forward area of a vehicle. But using the above information, it's actually possible to calculate the CdA of any vehicle that has a published dyno chart, gearing ratios, wheel sizes, and listed top speed.

[cbrfxr67]

great thread!  loving it

[dropitlow88]

Awesome replies! Thanks! So it appears a GS would fall faster than u can ride it, kinda figured.

unless it's cbrfxr's bike 

[burning1]

BTW, from a previous thread, here's the driving force curve for a stock GS500.



With most bikes, a wheelie occurs around 1G of acceleration... If you take the weight of a stock GS500, add a rider, gear, and gas, you see that even at peak torque in first gear, the bike probably doesn't have enough grunt to lift the wheel through throttle alone.