Put Up Or Shut Up


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Johnie12341

New Member
Wow thanks for all the info guys, I knew drag played a roll but I didn't know it affected everything that much haha it's really pretty interesting
 
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dx2killa

New Member
I'm gona just state my experience. I recently went on a large bike run that had a closed course (monitored by police and ambulance whole nine yards). I currently only have tbr exhaust and no pcv. I hit 130 at 12k . I also am only 5'6 140lbs so yea. Would never attempt on reg/open roads as its illegal and would be a bit scary anyways.
 

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UselessPickles

New Member
jspansel said:
Not unless you changed your gearing. HP does not = more top speed.
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Kinda...

At any given speed, you will accelerate if your bike has more power at that speed than the power of aerodynamic drag at that speed. When you get to a speed where the bike and drag have equal power, no more acceleration, so that's your top speed. The power of drag is proportional to the cube of speed (speed x speed x speed), so it takes a lot of horsepower gain for a small top speed gain. For example, a 10% gain in power (typical of full exaust + power commander mods) is only capable of giving you a 3.2% gain in top speed (if you adjust gearing to be 3.2% taller).

If the bike is currently limited by drag (like the FZ6R is) and you increase power throughout the entire RPM range, then the top speed will increase without a gearing change. You will now have more power available at your old top speed, which means you'll be able to overcome the power of drag at that speed.

But your top speed is now moving higher than the speed at which your bike makes peak power (assuming the bike isn't geared retardedly), so you're not making full use of your power gains toward top speed gains. Based on the peak power of your bike, you can calculate the speed at which the power of drag is the same. If you adjust the gearing so that your engine is at peak power RPMs at that particular speed, then your bike will be gear for max possible top speed.

Assuming that you don't gear the bike to the point of being limited by redline for top speed, the difference between best gearing for top speed and worst gearing for top speed is not very much - 3-4 mph at most on the FZ6R.

More details here: http://www.600cc.org/forum/f89/effects-changing-sprockets-23986/

Marthy said:
I'm quite sure I can brake the 130-135 without the baggage and a small screen. But like you said... I have nowhere to give it a fair legally shot!
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Assuming stock gearing and stock aerodynamics, and assuming a stock top speed of 125mph, you should be able to get ~133mph on your bike. If you geared it perfectly to make use of your peak HP to get top speed, you could get ~135mph (with 17 front, 43 rear sprockets).

I still need to finish putting together some results based on the torque data you sent me, but there's your first nugget of info :)
 
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