Top Speed

Originally Posted by Sid Squid

SV speedos are extremely generous - anybody who believes their 70 horse, 360+ pound bike will do 140, (or anything like it), is wrong.

Dude...I hate to break the bad news to you but its all down to whats known as the 'power to weight' ratio. The ratio for a GSX750F in a good state of tune is 2.37 kg/hp thats with a dry weight of 211kg and a generous power of 89hp at the back wheel.
The SV650S with a dry weight of 165kg and a generous 70hp in top tune gives 2.35 kg/hp now by the time you've added petrol, oil and a dollop of hefty humanoid the figures are going to get a bit mixed up but all things remaining equal i.e., same rider weight, same amount of petrol etc., the power to weight ratio of the two bikes is almost the same.

I can pis* 132 on the GSX without trying on a smooth flat disused airfield and 140 is easy enough at which point the invisible brick wall appears!

On paper I see this bike attaining very similar figures, in reality I don't see any change!

May I apologise if it appears I was blinding anyone with science. This was not my intention, I only wish to enlighten and empower people with accurate knowledge, if I projected anything to the contrary I apologise most profoundly!

When it was faired, standard gearing, downhill and me tucked in....140ish just, on the Suzuki clocks.

These days it's one tooth down at the front and one extra on the back, no fairing, several kilo's lighter same hill....127.5mph.

Now you might think i'd be disappointed, but I'm not at all. The extra acceleration is way more useful (all the time), than maxxing at the top end. And I'm using the Acewell clocks and sensor on the back wheel. Definately more accurate, while bolt upright at least. The old clocks would be reading about 135 i suppose??

If I lived where you do Haggis I doubt if I'd go above 50mph anywhere...take in all that clean air and peace and rainbows and buttercups and dolphins and.....6 more bleedin' weeks to wait! by then it'll be September...the start of the rainy season!

How many times do you think you'll hear the immortal phrase?

"You shoulda been here last week, it was sooooo nice last week!"

[yorkie_chris]

Originally Posted by RhythmJunkie

Dude... etc., the power to weight ratio of the two

What does power to weight ratio have to do with top speed?

Same power + more weight = less speed.
Same power + less weight = more speed.
Less power + same weight = less speed.
More power + same weight = more speed.
...but what you have to remember is 'everything is relative'.

Example...200lb rider on 360lb streamlined bike with 70hp top speed for arguments sake 138mph. Tuning mods bring horse power up to 73hp with same bike and rider on same road in similar weather conditions will gain speed.

Basically to double the speed for a given weight you need four times the power....you do the math!!

So a heavier bike with more power can have the same top speed as a lighter bike with less power or the same power to weight ratio.
Its just such a coincidence that the GSX750F and SV650S have very similar p/w ratio's considering their different specifications!

thats why my sv1000 is so fast with my lill 72kg frame on it

[yorkie_chris]

Originally Posted by RhythmJunkie

Same power + more weight = less speed.

No, weight only affects acceleration, top speed is decided by power vs air resistance.

[yorkie_chris]

Originally Posted by RhythmJunkie

Basically to double the speed for a given weight you need four times the power....you do the math!!

The force of air resistance is proportional to the square of velocity, so think about it P = Fv hence power is proportional to velocity cubed.

= to double the speed you need 8x the power

(look up the Rayleigh equation if you want to prove it yourself)