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Theorectical top speed of a bike

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Whosthedaddy
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PostPosted: 12:19 - 01 May 2006    Post subject: Theorectical top speed of a bike Reply with quote

Is there an equation or calculation that can be done to estimate the theoretical top speed of any bike given the engine size and capacity, wheel diameters, dry weight, riders weight etc
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0ddball
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PostPosted: 12:52 - 01 May 2006    Post subject: Reply with quote

There are plenty of good flash ones on the net where you just plug in the numbers. Try motorcyle top speed calculator in google.

The theoretical speed is independant of bike and rider weight, and even engine power. It is purely a product of max engine revs and gear ratio's.

To get a pretty accurate idea of a true top speed you have to factor in engine power and resistance factors. But weight is still irrelevevent.
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simonthepiema...
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PostPosted: 13:00 - 01 May 2006    Post subject: Reply with quote

I've never understood the whole weight is irrelevant although I think its true. what if you have a 600 bike with 90bhp and 180kg weight against the same engine and gear ratios but weighing 1 ton. The 1 tonner wouldnt have the poqwer to reach its max speed surely? Assuming they're both the same dimensions but maybe the second bikes made of lead or something

Anyone explain?? I should have paid more attention during those physics lessons at school Question
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NSR-Rulez
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PostPosted: 13:07 - 01 May 2006    Post subject: Reply with quote

https://www.cosportbikeclub.org/misc/SpeedCalc.html

Dont use that one, apparently the top speed for my NSR is 217.2mph

Twisted Evil Great, i have the fastest NSR 125

I think not.


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cagiva gezzer
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PostPosted: 13:17 - 01 May 2006    Post subject: Reply with quote

Here is mine for the mito. Just subsitute your gearing information.

Also, someone elses tzr chart, which makes pretty graphs. Not sure about the marcos in it though.
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Andy C
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PostPosted: 13:24 - 01 May 2006    Post subject: Reply with quote

you can work out how fast the bike be going redline in 6th if you know the gearing and wheels. Like my SV (RIP) would go 150mph BUT the bike couldnt redline in 6th only 7k rpm so reached 130mph
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Jack_Cheese
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PostPosted: 13:31 - 01 May 2006    Post subject: Reply with quote

Andy C wrote:
you can work out how fast the bike be going redline in 6th if you know the gearing and wheels. Like my SV (RIP) would go 150mph BUT the bike couldnt redline in 6th only 7k rpm so reached 130mph


Spot on Thumbs Up maximum rpm at the crank X overall gear ratio in 6th (crank speed/wheel speed) then multiply that by the circumference of your wheel Thumbs Up that should give you the same top speed that a dyno would.

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Whosthedaddy
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PostPosted: 13:40 - 01 May 2006    Post subject: Reply with quote

I know that the theoretical top speed is gonna be different from the actual top speed achievable, need to get a pen and paper out to work out the various numbers needed to crunch.

Thanks fellas Thumbs Up
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McJamweasel
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PostPosted: 15:08 - 01 May 2006    Post subject: Reply with quote

Whosthedaddy wrote:
I know that the theoretical top speed is gonna be different from the actual top speed achievable...


That depends on the bike. Using AndyC's example, his SV is (was) geared for 150 (theoretical) but would only pull 130 as it didn't have the power to pull through to the redline in top. However, if he downgeared it for a top speed of 140, it is entirely possible that the lower gearing would mean that the power was enough to pull to the redline. If you get my drift.
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lilredmachine
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PostPosted: 15:16 - 01 May 2006    Post subject: Reply with quote

On my 4t 125, the long 6th gear is good for 90-95 MPH, of course the most i have ever seen on the clocks is about 87 down a large hill. It doesn't get to within 2 k of the 11.5 k redline.
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0ddball
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PostPosted: 15:17 - 01 May 2006    Post subject: Reply with quote

simonthepieman wrote:
I've never understood the whole weight is irrelevant although I think its true. what if you have a 600 bike with 90bhp and 180kg weight against the same engine and gear ratios but weighing 1 ton. The 1 tonner wouldnt have the power to reach its max speed surely? Assuming they're both the same dimensions but maybe the second bikes made of lead or something

Anyone explain?? I should have paid more attention during those physics lessons at school Question


Weight is irrelevant within reason. Top speed is reached when the driving force in one direction (bhp) is equal to the resistance in the opposite direction (wind/mechanical resistance). So if speed testing on a perfectly flat surface only horizontal forces need to be considered. Weight does come into it in the mechaincal resistances part. With a 1 ton bike there would be much greater weight on the tyres changing the tread pattern, loading the wheel bearings more ect hence the rolling resistances would be bigger and more energy would be converted to heat and sound energy. So yeah, when the weight is that big a difference it has to be accounted for to be truely precise. But even then, when you are talking about speeds over 100mph the rolling resistance makes up a much smaller part of the total resistance. Air resistance being the biggest part of it. And aerodynamic drag increases with the square of speed. So the faster you go the less relevant rolling resistances become.

As to explaining why it is irrelevant in a scientific way when comparing 2 similar bikes, say a 100bhp 100kg bike and a 100bhp 200kg one. It's a long time since i did it as uni so i couldn't say with confidence. Sure it's on the net somewhere though.
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0ddball
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PostPosted: 15:27 - 01 May 2006    Post subject: Reply with quote

McJamweasel wrote:
Whosthedaddy wrote:
I know that the theoretical top speed is gonna be different from the actual top speed achievable...


That depends on the bike. Using AndyC's example, his SV is (was) geared for 150 (theoretical) but would only pull 130 as it didn't have the power to pull through to the redline in top. However, if he downgeared it for a top speed of 140, it is entirely possible that the lower gearing would mean that the power was enough to pull to the redline. If you get my drift.


Doubtful. Even downgeared to top speed would still most likely be 130mph. Though i suppose it is possible given the non linear power delivery of a bike engine. If with the higher gearing the bike would just about pull 7000 rpm in top gear but the power band didn't start untill 8000rpm, lowering the gearing a bit could just about get it into the band.
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BanditsHigh
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PostPosted: 15:32 - 01 May 2006    Post subject: Reply with quote

Here's my version, displays in both MPH/KPH and displays graphs as well (hover over points on graphs for exact values).

Hope it's useful Smile

All the best ... Barry
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McJamweasel
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PostPosted: 15:37 - 01 May 2006    Post subject: Reply with quote

SpannerMonkey wrote:
Doubtful. Even downgeared to top speed would still most likely be 130mph. Though i suppose it is possible given the non linear power delivery of a bike engine. If with the higher gearing the bike would just about pull 7000 rpm in top gear but the power band didn't start untill 8000rpm, lowering the gearing a bit could just about get it into the band.


I'm just using that as an example, and although the figures are not exact (hell, I just plucked 140 out of the air to demonstrate a point really), the principle is sound. Like you say, the power graph is not linear, and the power does drop off towards the redline. Move that redline closer to 140mph and it may now have enough speed to pull to it.
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