Yuku free message boards

GA,

I am sorry to inform you that that formula does not work. The reason that production vehicles can rarely reach top speed in top gear is the actual limiting point is when the vehicle's available power matches the road power, which is the combination of tire resistance and air drag power. At low speeds tire resistance provides most of the required road power (up to 15 to 20 mph), but beyond that speed air drag dominates. Air drag force goes up with the square of the speed. The power to overcome the air drag force goes up with the cube of the speed. For example, at 55 mph a typcial mid-sized sedan only needs 15 HP to match the tire resistance and air drag, but at twice that speed the power required to keep the sedan moving forward is 2 cubed x 15 HP = 120 HP.

The other side of the equation is where the engine has the available torque and power. Note that the speed at maximum torque and at maximum power are two different speeds with the maximum torque occuring at a lower speed. If a bike or car is inching up in speed against an air drag and subsequent power that goes up with the cube of the speed, at most it will not go beyond the maximum torque point in top gear if it gets to that point. It may not get even that far because the torque in top gear is not going up with the cube of the speed like the air resistance power is, so bottomline is wherever the engine's available power meets the wind resistance power that is all she wrote and the vehicle will go no faster.

The T's drag is probably not as great as a mid-sized sedan, but it's limiting speed depends a lot on the air drag. When my T had an oversize Rifle windshield on it that was +3" taller and +6" wider I could not get my T over 102 mph. At least one other Forum Member stated that he saw 115 mph on his T's speedometer, but also remember that Honda speedmometers are typically 3% to 10% optimistic, meaning that most likely the actual motorcycle speed was 103 to 111 mph.

You may know that sportbikes took over from muscle bikes as the fastest production motocycles (back in the late '70's/early '80's). It was because riders could not hang on unfaired motorcycles beyond 135 mph and also because faired cafe racers/sportbikes have lower drag than muscle bikes/naked sportbikes. Suzuki's Hayabusa got the fastest production bike crown because it was the first motorcycle to be designed for lowest air drag using a wind tunnel and because the Japanese motorcycle manufacturers decided to limit the top speed to 186 mph (after the 'busa already achieved 194 mph) so that government authorities would not make even lower speed limits for production bikes.

The T's rev limiter is set at 6600 rpm. As far as I know that is the same in every gear. Per the formula you found I believe that would make the T's top speed be 127 mph. I doubt any T owner will claim reaching that speed with a stock T, but I may be wrong. Anybody?

GA,

If I remember correctly, at 70 mph, according to the mounted Drag Specialties tachometer, my T's engine is running close to 3500 rpm with a Valk-sized tire on the back. That tachometer agrees with the dwell-tachometer I bought from J.C. Whitney some years ago.

Tony,

Back in 1997 Motorcycle Consumers News published the T's dynamometer results indicating that the maximum power obtained from the T engine they tested was 53.9 HP. If we assume that Gary's top speed of 110 mph (161.3 fps) is the most accurate representation of our T's capability then since Air Power = 1/2 x air density x coefficient of drag x T frontal area x velocity cubed I calculate the combination of frontal area times coefficient of drag to be 3.028 assuming Gary was riding on a 59F day when the air density was 0.075 lb/ft^3. That being the case what do you think the frontal area of a T is? For the sake of argument, if it is 9 ft^2, then the coefficient of drag is 0.33. What would be your best guess?

Gary,

If your head is not hurting too much, can you tell us what was the air temperature on the day your glorious T triumphed at 110 mph without the police slapping you to the brig?