normal force a weighty issue

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hawkwind
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Re: normal force a weighty issue

Post by hawkwind » Tue Nov 05, 2013 7:44 pm

G'day Pete.
here is my reasoning why ...take it with caution as im far from being an engineer.....I believe that decreasing the rotational inertia frees up power to increase acceleration in a vehicle that is NOT traction limited by power and that suspension setups help keep the contact patch in contact with the surface you are on BUT in the case of the high powered bikes this is not the case.....I personally set every thing up to a target speed and due to the cubed power factor in overcoming the drag high speeds need very high power levels...now this is where all the juggling starts playing off each effect against another ...its rather pointless if you cannot get that power to the ground........the formulae F=L x Cp where F is traction force L is load or weight on the tyre and Cp is coefficient of friction.........in the case of very powerful bikes we have an excess of F and way to little Cp so we are left to play with L ....increasing the physical weight ie lead or such allows us to place more tractive force to the salt ....... in my case I need a lot of weight to use the power I produce....im limited by the constraints placed on the tyre ie load rating ......then add in the greater than recommended speed ....the tyre has a finite ability to accept the abuse we dish out to it .......we can play with suspension settings and even use traction control but this only allows use to get the best results from the numbers we have ....its all about robbing peter to pay paul and crossing ones fingers ...without all the data it is like playing Russian roulette.


cheers
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Financed by.................Nickles & Dimes.
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internetscooter
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Re: normal force a weighty issue

Post by internetscooter » Tue Nov 05, 2013 9:38 pm

Sorry, I am going to repeat that I think pressure is still a major factor. If you want a simple test, next time you do a dyno run try low and high tyre pressure. You'll find you get a higher HP value with higher pressure, the reason you get a lower HP reading with lower pressure is all the missing energy is going into destroying the tyre rather than pushing the drum.

While you are at it, see if you can run full speed. Dyno's are worse on tyres than flat earth, I know my tyres can handle 110 mph, regardless of what the R&D at Sava tell me, because I now do all my runs in top gear. My tyres have done 110mph several times with higher load (due to being strapped down) than what I will be running on the salt.
Paul
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hawkwind
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Re: normal force a weighty issue

Post by hawkwind » Wed Nov 06, 2013 8:18 am

Pressure to where Paul????........Maximum pressure specified by the manufacturer.....50 psi ....100psi ....1000psi??? yes increasing the pressure will allow more weight to be added,it also decreases the contact patch and places a greater strain on the seating bead .....we have reliable and repeatable data to what the manufacturer recommends after that you are on your own......to give you some idea the most powerful bikes are trying to lay down the power of v8 supercars through a single rear tyre and my rough calcs say you need north of 1800kg's ballast to do that .......this problem is the major limiting factor to bikes going any faster
cheers
Vehicle......................A new creation.
Designed by................Troglodyte.
Engineered/ built by......Rustic.
Financed by.................Nickles & Dimes.
Rider......................... Tardus Vetus Inflatio

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internetscooter
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Re: normal force a weighty issue

Post by internetscooter » Wed Nov 06, 2013 8:54 am

tyre pressure - if you recall from the letter I got to allow me to race, the tyre pressure which was recommended was greater than that on the side wall (I'll PM the details as you have seen them already and I don't want them public).

At your higher speeds where you are loosing traction I don't know the effect but I do know the damage caused by tyre deflection is reduced. All I am saying is that it is a variable that needs to be considered.
Paul
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AuotonomousRX
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Re: normal force a weighty issue

Post by AuotonomousRX » Wed Nov 06, 2013 9:01 am

The question I am asking is about the location of the weight. Sprung vs Unsprung weight. :?:

I am curious as to why the weight ie Ballast is predominately located directly on the Swing Arm and is Unsprung weight.

This then leaves the Tyre to be the Suspension and maintain Contact. ( F1 cars do this but the F1 Tyres are designed to do this. M/C Tyres aren't.)

As opposed to Placing Ballast on the Bikes Chassis and using Suspension to maintain the Contact Patch.

I am not saying what right or wrong I am simply trying to understand why things are done the way they are in LSR.

Pete :D
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Pete :shock:
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hawkwind
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Re: normal force a weighty issue

Post by hawkwind » Wed Nov 06, 2013 9:45 am

Pete easy to answer in my case ...I run zero suspension out back ( a hard tail rear end)...why the swing arm also easy to answer for maximum benefit you need the weight over the rear tyre or as close as you can get to it....though weight distribution is to be considered....im running 60/40 bias now and no ill effects yet.....though im placing another 50kg up front if I can work out a way to do it ( ie space ).........but wether its sprung or un sprung it is still going to load the tyre.

Paul I agree
Vehicle......................A new creation.
Designed by................Troglodyte.
Engineered/ built by......Rustic.
Financed by.................Nickles & Dimes.
Rider......................... Tardus Vetus Inflatio

Team Waterbottle
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Re: normal force a weighty issue

Post by Team Waterbottle » Wed Nov 06, 2013 1:09 pm

Hi Guys
I am also trying to add ballast to the front but having trouble finding space.... it would be easy to add weights to the fork tubes, but I'm unsure of handling problems.... any advice on that option??

Finny
#739

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Greg Watters
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Re: normal force a weighty issue

Post by Greg Watters » Thu Nov 07, 2013 7:17 am

Like Hawkwind i'm not an engineer ,not even much good with formulas, just observe what others are doing and draw my conclusions on whats working and why then test ,

i think unsprung weight works better in this instance esp at very high speed ,as the time normal suspension goes through its travel and returns after hitting a salt ridge you will have traveled a long way with no traction, limiting your speed, wheras lots of unsprung weight would cause the tire to deflect more than suspension move giving more total time in contact with the surface

were not dealing with much suspension movement in general, no quick acceleration to transfer weight, no hard braking or cornering, and no undulations
also no real penalty for adding weight, the tractive force gained makes up for the acceleration force you would perceive to have lost

Finny i would be very carefull about adding weight to your front suspension , all my comments about unsprung weight would apply to the drive wheel,
in this instance i would think about adding weight at the front of the motor at about the centreline of your motors mass

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AuotonomousRX
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Re: normal force a weighty issue

Post by AuotonomousRX » Thu Nov 07, 2013 8:49 am

Greg

I am not an engineer either and what you said makes sense to me.

Hi Finny I am with Greg on that one.

Pete :D
Metric Target 250 on a 250 on a Red Bike

Pete :shock:
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