top speed?

M

masterx1234

New Member
so if the honda gx35 gets a top speed of 30 mph and with only 1.5 HP on a bikemotorparts kit then a dax titan xc50 with 2.5 HP should get up to 40 MPH correct?
 
If you are using the same bike, same wieght, etc., twice the speed you will not get. Ratio's come into play here.
 
marts1 said:
If you are using the same bike, same wieght, etc., twice the speed you will not get. Ratio's come into play here.
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Marts1 is correct,
and add to his words, torque, advertised horsepower verses actual, combustion effeciency, etc etc. You cannot simply take a given horsepower, add a value to it and compute speed. Many factors come into play before an actual figure could be derived. That being said and to give you some answer, you can generally always expect an increase in speed by adding horsepower but its just not simple addition. Good luck, and ride safe at any speed.
Tom
 
I believe you will get the same speed but it will pull more weight and go up hills better.
A smaller rear sprocket will get you more speed.
 
I roll with the 44 sprocket. I can go up more than 45 degree hill going faster than 15 mile per hour.
 
just to be a voice of dissention here, a 45 degree hill would be a 100% grade.

the steepest street in the world is Baldwin Street, in a suburban part of New Zealand's southern city of Dunedin, at 19 degrees, or 35%.

Superior Hill, in Newport Beach, California, is a 6% grade, which is about 3.5 degrees. the reason i know this, is i got a ticket for riding my skateboard down it in the 80's. there's a law in california saying you can't skate down anything steeper than 6%.

my first bike, a 26" with a 36 tooth sprocket, would clear the hill without pedaling, but just barely. like 5mph or so at the top.

now, if you had a very short ramp at 45 degrees, you might go over it at 15mph. or, you might stop abruptly and flip over the bars.

in case you're interested, wheelchair ramps are usually 4 degrees or less...
 
Elmo said:
I think I have seen a tv commercial for insurance or something with that house. Parked the car, walked off and the car took off downhill.
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Ive heard of that commercial somewhere before too.. parking brakes failing and the car rolling down the hill with that same house in the background..

Id roll down that hill only with the full safety gear on.. knee and elbow pads, thick riding gloves, the works. Imagine stacking the bike at speed .bf.
 
I thought they were just going to start "Blocking" these threads about top speed.
Who really cares about top speed on a Motorbike anyway! Like I have said before, if you want to go fast why not buy a motorcycle. These were never intended to "Go Fast"

John
 
It's not so much that we want to just "block" any thread that makes a reference to speeds - after all it IS one of the major thoughts that occupy almost any gearhead... It's just that every time it's brought up someone insists on making outlandish, unsubstantiated claims and/or wild "guesstimates" based on armchair engineering alone and when disputed - gets irate. Then the drama starts on all fronts and we gotta shut it down.

While it's not possible to prevent people from posting such, nor fair to ban anyone for it - if we could manage to just ignore it or politely request some actual proof of any claim significantly outside the norm then we could actually keep the discussion going.

Most folks would proudly show proof if their speed is even a little higher than normal and it's pretty obvious to all who actually ride these things what "normal" is. With these machines major advancements are still often measured in fractions of miles per hour - a couple at most. If you call them out for proof yet remain civil, then they freak out and act the jerk - then we can clearly see who's in the wrong and take action.

I've often wished such threads could survive - we've quite a few skilled members whose input would be invaluable, even if it's a mere 2mph gain.
 
Just keeping up to city traffic would be acceptable to me. I'd like it much better if I could do that for $200 as opposed to $5000. Also the faster these things are made to go the sooner they will be toast. Find your happy medium.
 
masterx1234 said:
so if the honda gx35 gets a top speed of 30 mph and with only 1.5 HP on a bikemotorparts kit then a dax titan xc50 with 2.5 HP should get up to 40 MPH correct?
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The short answer is YES! That is about right.

There are two components to drag. The rolling resistance is proportional to speed. The aero drag rises with the square of the speed. Once over 30mph, the aero component is by far the dominant factor for most bikes. So to keep it simple, I will ignore the rolling resistance:

Sqrt((2.5hp/1.5hp) x 30mph x 30mph) = 38.73mph

Or, assuming that 1.5hp gets you 30mph, how much power is required to do 40mph?:

1.5hp x (40mph x 40mph)/(30mph x 30mph)=2.67hp

In order for this to be true, the gear ratio must be chosen so that your speed corresponds to the peak power rpm of the engine.

The reverse of this is true. If this bike has a 2.5 hp engine but you gear it so low that it only goes 30mph steady state, then the motor is past it’s power peak and is only putting out 1.5hp steady state.

I tried to make this point in another thread on California law when discussing the 2hp, 30mph laws but it got off track for that thread. This seems like the better thread to make the point since it answers your question.
 
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