Salt top speed GST?

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internetscooter
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Salt top speed GST?

Post by internetscooter »

I had someone mention to me that you lose 10% of your power riding on salt, is the correct? i.e. if you can only do 110mph on the road, you'll only do 100 on the salt.

For my first attempt I don't want to push my engine too hard (if you can call increasing the hp 400% not pushing), so I need to factor in this 10% increase if it is indeed true.
Marty Hicks
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Post by Marty Hicks »

The percentage of traction loss will be less or more depending on the power driving the vehicle forward vs ( and i'm guessing ) the air drag against you....

Something like Gregs 'Busa will have a greater percentage of loss than my old clunker, which would have greater loss again than the BigBlock postiebike.

I'm sure there be a loss at your terminal speed, but as you've finished acelerating at that point the loss should be well less than 10%.

There will be someone who has SOME sort of formula regarding the infinite variables.........ya know, a boffin... but in essence :mrgreen:

NOT LONG NOW MATE.......
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gennyshovel
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Post by gennyshovel »

The Postie bike dropped about 10 k's in top speed on the salt , in relation to my testing on the road (honest officer, its only 17 k's over the limit !).
This was in '06 when the salt was less than perfect and the big boys struggled to gain traction.

Tiny ('08's looking like a non postie bike year :( )
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Lynchy
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Post by Lynchy »

I'm not sure how that works because if you have no change in aero/engine power/drivetrain and 100% traction then you should go the same speed.

I've read that salt has a traction coefficient of 0.6 and asphalt is about 0.7 so maybe this is where the 10% comes in but again if you have the same car/bike/thing and are not wheelspinning then you are doing the same speed. The lower traction coefficient means you are more likely to wheelspin, therefore you can compensate by adding weight.

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gennyshovel
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Post by gennyshovel »

Lynchy wrote: if you have the same car/bike/thing and are not wheelspinning then you are doing the same speed.
Lynchy

Shifting the "grainy stuff" to gain forward motion will always result in less that perfect traction, no matter how low the available horsepower is , 'specially when your about as aerodynamic as a besser block, like me :oops:
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Lynchy
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Post by Lynchy »

OK. I can understand a reduction, but only with slippage, especially at the top end.

Lynchy
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Post by Dr Goggles »

..the amount of forward force your vehicle can exert is related to the amount of traction it can attain .There is a relationship also between the downforce(weight) and the forward force which is called thrust. The traction coefficient is a given , maximizing thrust is a combination of the psi exerted and the material used in contact with the surface.

For a fixed downforce the rate of thrust declines at the rate that air resistance and combined frictional losses mount. so, at some point , for a given Cd and weight you will go no faster no matter how much power you have ....add more weight = more thrust.....more speed 'til the same equilibrium is reached...you will always need more "thrust" if you want to go faster.....a low traction coefficient and wind resistance are working against you....a low Cd is working for you AND weight will help BUT Accelleration =Force/Mass.......hmmmmmm...how long have you got?

imagine trying to push a pallet on a greasy floor.....with a hurricane blowing toward you...... :wink: :wink: :wink:
...few understand what I'm trying to do , but they vastly outnumber those who understand why..
internetscooter
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Post by internetscooter »

Thanks for the feedback - I guess that I will have to factor in some salt traction loss...

and if the speed reduction is due to traction loss rather than increased rolling resistance, I'll also have to keep an eye on gearing so I don't run out of rpm.
internetscooter
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Post by internetscooter »

The Postie bike dropped about 10 k's in top speed on the salt , in relation to my testing on the road (honest officer, its only 17 k's over the limit !).
This was in '06 when the salt was less than perfect and the big boys struggled to gain traction.


Just an after thought... where was your road testing? I have found that motorway roads up the top speed quite a bit even if cars are far away. My thinking is that even though you don't get a direct slip stream, they disturb the air and disturbed air gives less drag (like pointing your exhaust at the rear wheel).

My experience with high gearing (in hindsight higher that practical as peak power was at 130km/80m)...

130Km/hr (80 M/hr) Monash Freeway = 105Km/hr (65 M/hr) open road (no cars around).

So is it possible that the 10Km/hr difference was "lack of passive slip stream" rather than salt traction loss or were you on a road with no one around and no tail wind?
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gennyshovel
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Post by gennyshovel »

[
So is it possible that the 10Km/hr difference was "lack of passive slip stream" rather than salt traction loss or were you on a road with no one around and no tail wind?[/quote]
No.
It's a good idea to make SURE nobody's around when testing (easy enough to to out here)
I must have done 60 k's testing, on different stretches of road, up and down hill, no wind , head wind, and tail wind, moderate revs, insane revs, and oops a few times before I got an average top speed.
My speedo is front wheel driven, so wheel slippage has no bearing on indicated MPH, but I also gained a few RPM while loosing a few MPH on the salt,enough extra revs to enable the 'rod to stretch, or crank to flex ? .050" and let the piston crown polish the combustion chamber.

Always learnin' Lambert :lol:
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