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Fuel Weight


bond_yzf
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ok guys making my thru, twist of the wrist 2 and have just finished reading throttle control and a idea pop into my head about an ever decreasing weight on the bike (fuel) the bike is constantly getting lighter, ok i understand that the difference between one and the next lap its going to be very small, but mid-way thru a race/track day or on road 8 litres of fuel difference is quite a bit surely it alters:

 

contact patches 40/60 rule

lean angle rate/steering (id say it quickens it slightly)

alters the sag on the suspension ( lighter bike means less rider static sag)

 

this is just something that made me curious, may be nothing but got me thinking !!

 

cheers jim

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I doubt it will make enough difference for most to notice; 8 litres = 5.5 kg or 12 pounds. If you ride a 125cc GP bike with a combined weight of 300 lb, you may sense a little. But since most bike/rider combinations at track days are around 600 lb upwards, 12 lb or even 25 lb isn't going to make a dramatic impact.

 

Top rank racers, however, are highly sensitive and so are their bike setups, and they will notice. Remember 1999? Doohan struggled during the first 2 races, finishing 4th and 2nd. All year, throughout pre-season testing and during them races, he complained that the bike wasn't right. Despite the team insisting the bike was unaltered since 1998, Doohan persisted that the bike had to be different. Turned out they had altered the fuel tank and moved it 20 mm horizontally and 5 mm vertically, which for him made a huge difference! For his final race, the old tank was back and he dominated until he touched the white paint and fell into retirement.

 

Talking of Doohan; how good was he? Well, 3 months after his accident, at Phillip Island, with two damaged legs forcing him to be lifted onto the bike, and with a hand and shoulder so weak he had to have help to pull the clutch for start-up, on Criville's bike that had been altered (more peaky power delivery, among other things, plus set up for Criville), on unknown tyres and on the first flying lap he was only 4 seconds slower than the new lap record set by Roberts! Asked if the positive time made him reconsider coming out of retirement, Doohan replied "that's not racing, that's just cruising". If he couldn't win, he wouldn't bother.

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I can tell a difference, but it affects my riding only a bit. I like throwing the bike around when it has more fuel in it. It's such a small difference that I only think about it when I fuel back up after my light comes on though.

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