normal force a weighty issue

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hawkwind
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normal force a weighty issue

Post by hawkwind » Tue Oct 22, 2013 8:37 pm

Busy in the shed again mostly ...but I am doing some research regarding traction or to be more precise the lack of it ...especially on the more power endowed motorcycles.....whereas the car blokes have it made relatively speaking ...purpose made speed rated tyres and acres of room to add extra "normal force".

After lots of searching the only way to generate traction practically is down to increasing weight over the drive tyre..... this is where we have a problem some calcs show for 250 rwhp with a coefficient of friction of 0.6 I need close to 400kg's over the rear wheel and from there it only goes up with more power and /or lower CoF ....... we bikers get a choice of DOT or race tyres and in both cases they are speed limited AND load limited ( for what we do to them)..... mine are rear 75W ( 387kg max) and front 58W (236 max) so even trying to put down 250hp I'll exceed the load rating of the rear tyre................so do we run the risk of over heating the tyre with excessive spin ... regardless of how carefull you are with the right hand you will have traction problems either from torque or drag ...or exceeding the load rating of the tyre which in itself increases the temp of the tyre .......I know that the makers of the tyres build in a safety factor so the rating is a conservative figure ...we have tested that safety factor in regards to speed ( 311mph on dot tyres ) ...it makes me wonder if the load rating is as generous as the excess speed safety factor? .......is it wise to exceed the load limit? probably not ...is it wise to exceed the speed rating same answer but we do . Your thoughts
cheers
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internetscooter
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Re: normal force a weighty issue

Post by internetscooter » Tue Oct 22, 2013 9:23 pm

A few points from my investigations - which is a bigger problem than yours - or should I say smaller ;)

Hunt down the Australian standards for tyre tests - you might find them here: http://www.comlaw.gov.au/. I have a horded old copy here: http://www.vespalabs.org/@api/deki/file ... ALFRLI.pdf

Here are some points from my memory (but you read it yourself as this is old memory)... oh and let us know if you find a motorcycle set...

1) you are missing pressure in your calcs - increase it and you can increase the load (it is the tyre deflection that causes the grief)
2) I would be wary of "safety factor", the tyre standard tests look to me that the speed rating is the absolute limit as "After completion of the high speed test specified in Clause 23.3.5 no tyre shall have ‘Tread Separation', 'Ply Separation', 'Cord Separation', 'Belt Separation' or 'Bead Separation', 'Chunking' or 'Broken Cords'.". So the only "safety factor" in my opinion would be covering variation in production quality, so you "could" get a tyre that is on the lower bound of quality with not much over the speed limit "in it". Race tyres though my be different - I know scooter tyres get flats more easily over the limit.
3) Having said point 2) the speed rating test is for 10 minutes, I doubt very very much that you would be doing your top speed for 10 minutes :D . So I wonder if that can be taken into consideration

Cheers,

Paul
Paul
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dave leaney
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Re: normal force a weighty issue

Post by dave leaney » Tue Oct 22, 2013 9:53 pm

Centrifugal force is the dominant force in an LSR tyre. Do the sums on a contact patch size chunk of rubber at the aforementioned 311MPH. Scary. This force loads the entire tyre radially yet the actual contact patch itself is effectively being unloaded slightly by the ground pushing towards the axle. Personally, I'd be more worried of over revving than overloading a tyre.
Cheers.

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Greg Watters
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Re: normal force a weighty issue

Post by Greg Watters » Wed Oct 23, 2013 7:20 am

yep get it right
Image

after this episode at 256mph we switched brands and now have all tires shaved , one on the front of the busa has seen many runs on Richard Assens bike then mine and probably 20 or more passes above 250 in total


varying trials with the car type LSR tires have been less than successful , worked great on a streetbike busa running 184mph , but the profile even with shaved corners was only good in perfect conditions, and side wind that caused a lean put you onto a very small contact patch on the edge of the tire and gave both wheelspin and weave

hawkwind
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Re: normal force a weighty issue

Post by hawkwind » Wed Oct 23, 2013 5:54 pm

Paul ...had a read of the standard .....all Australian standards set a "MIMIMUM" requirement for the makers to produce.....my argument is based on the fact that the manufactures always have a safety factor built into their products ....because people will always exceed the ratings they publish and to protect there collective arses from law suites...so my guess is that the load and speed limits they specify are on the safe / conservative side ...by how much is an unknown......take for example a Z rated radial is speed rated at 240kph+ A w is 270 kph and a Y is 300 kph (Y) is 300+ most high performance motorcycle tyres are W rated ....but its a well established fact LSR racers routinely exceed that rating by 100kph + mostly without harmful consequences and in the case of Bill Warner he ran two (DOT)conti race attack tyres to 311mph or 500kph and continental tyres actually used this as a selling point.....as far as im aware most of the chunking and other tyre failures are a result of excessive spinning due to lack of traction and over heating the tyre (rear)....except in Greg's case (front)where it appears by his own words the tyre chucked in the towel after much abuse well over the makers recommendations. So to limit the excessive spinning from lack of traction we can add as much weight as is physically possible but how much do we dare ? because we are already exceeding the speed ratings so if we start to exceed the load ratings to the same extent how much will this bring us to the ragged edge of the tyres limits ( its real limits not the advertised limits)

Dave this discussion is about overloading on top of over spinning ( which is what we do already) because there is no motorcycle tyre made that meets our demands and adopting a car tyre built for these speeds and loads to date is not satisfactory

Greg what was the brand that failed ? what are you using now ? AND where are you getting them shaved as I cannot find any one in Aus that does motorcycle tyres??????

Cheers Gary
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Greg Watters
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Re: normal force a weighty issue

Post by Greg Watters » Wed Oct 23, 2013 7:42 pm

Gary that was one of the Dunlop GPa, it was well outside its normal area of use and i would not avoid these for a track bike

now using BT003 , they look to have less rubber on them , and we had them shaved in Cali , and was watching and helping setup mine when Acks guy Butch did them .
I have talked to Stuckeys in Melbourne about it last year ,so i'm pretty sure i could show them how if needed , it was a car jig used, and some carefull setting up and measuring involved
all to do with the narrow motorcycle tires and the arc of the cutting tool
Basically, you setup and cut one side, then measure that sides position in the machine, then move the tire so its the same position from the other side and cut the other side, then centralise it and cut the middle
gives a flat bottomed v shape that feels fine and seems to work well
we cut to just short of reaching the wear indicators , and did a few different depths in case there was an issue with perceived going too far

may have to mount the tires on a 17" space saver rim yet , mounting jig is one of the hurdles to cross

oh and i'm just over 500kg with me on it and loaded up with fuel and ice
57% rear, 43% front , nearly weighs as much as a bagger ;)

GeeTee
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Re: normal force a weighty issue

Post by GeeTee » Thu Oct 24, 2013 10:59 am

dave leaney wrote:Centrifugal force is the dominant force in an LSR tyre. Do the sums on a contact patch size chunk of rubber at the aforementioned 311MPH. Scary. This force loads the entire tyre radially yet the actual contact patch itself is effectively being unloaded slightly by the ground pushing towards the axle. Personally, I'd be more worried of over revving than overloading a tyre.
Cheers.
At 311MPH the 'footprint' (section of the tyre on the ground) is actually standing still so there is no centrifugal force acting on its adjacent sidewall.

But the top of the tyre is doing 622MPH. This is where the problem lies and why tyres fly apart and why high speed tyres are light in construction - the lighter weight (shaving would be a good idea!) reduces the centrifugal forces

dave leaney
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Re: normal force a weighty issue

Post by dave leaney » Thu Oct 24, 2013 11:59 am

Going to have to disagree with you there.
Yes, the contact patch is stationary and the top of the tyre is at double speed however that is in relationship to the ground.
Nothing to do with centrifugal force which is the result of angular velocity. My original post was merely pointing out that the ground pushing the contact patch towards the axle is actually opposing the centrifugal force. The contact patch is therefore the 'supported' part of the tyre and less loaded.
Cheers,
Dave.
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AuotonomousRX
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Re: normal force a weighty issue

Post by AuotonomousRX » Thu Oct 24, 2013 5:43 pm

I have been wondering about Tyre Temperature's and the effect this might have in a Land Speed setting.

I found this explanation of a Cold Tear of a Motorcycle Tyre. http://www.youtube.com/watch?v=izaxhNfMnog

Is that what is going on here as well or at least contributing to the failures??

Pete
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Greg Watters
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Re: normal force a weighty issue

Post by Greg Watters » Thu Oct 24, 2013 9:46 pm

not quite relevant as there is just no temp in the tire whatever the pressure , we start cold and the surface sucks heat out rather than contributing to heating

saw some logs of an internal tire temp/pressure sensor last yr , it just reached 100c at the 6 1/2 mile at 264mph but the heavy accelerating areas in lower gears were very cold

i have an infrared sensor to try this yr that will interface with my logger, not ideal as it only measures surface temp , but may get some info from the tire surface just besides the contact patch ,

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Re: normal force a weighty issue

Post by GeeTee » Fri Oct 25, 2013 9:48 am

dave leaney wrote:Going to have to disagree with you there.
Yes, the contact patch is stationary and the top of the tyre is at double speed however that is in relationship to the ground.
Nothing to do with centrifugal force which is the result of angular velocity. My original post was merely pointing out that the ground pushing the contact patch towards the axle is actually opposing the centrifugal force. The contact patch is therefore the 'supported' part of the tyre and less loaded.
Cheers,
Dave.

Sorry, by 'load' and that shredded tyre pic I thought you were discussing reasons for tyres destructing

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Re: normal force a weighty issue

Post by Stayt`ie » Fri Oct 25, 2013 10:48 pm

hawkwind wrote:.......I know that the makers of the tyres build in a safety factor so the rating is a conservative figure ...we have tested that safety factor in regards to speed ( 311mph on dot tyres ) ...it makes me wonder if the load rating is as generous as the excess speed safety factor?
actually, i think you will find that, at the moment, the jury is out, rethinking, the 311mph on dot tyres,,
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Re: normal force a weighty issue

Post by internetscooter » Sun Oct 27, 2013 10:40 am

Here are some interesting links:

Motorcycle standard tests:
http://www.tc.gc.ca/eng/roadsafety/safe ... e-1280.htm

A review of tests for car tyres:
http://www.nhtsa.gov/cars/rules/rulings ... adeII.html

I have only skimmed them (I am not yet at the stage of worrying about speed rating as much as you) - things I noted are that the tests are at 35 degrees (not good) and they dropped considering a test that actually took the tyre up to it's speed rating as it was too stringent (more tyres failed that test).
Paul
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hawkwind
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Re: normal force a weighty issue

Post by hawkwind » Sun Oct 27, 2013 5:43 pm

[quote/ actually, i think you will find that, at the moment, the jury is out, rethinking, the 311mph on dot tyres,,[/quote]

Yes I did read that Bills accident was a result of a tyre and or rim failure........our problem is that there is very little / zero published information out there from the manufactures in regards to there destruction testing
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AuotonomousRX
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Re: normal force a weighty issue

Post by AuotonomousRX » Tue Nov 05, 2013 8:25 am

I find this stuff intriguing.

I was always led to believe that you try and reduce unsprung weight and use the Suspension to "control" traction.

Can someone explain why this is not the approach used in Land Speed Racing?

Pete :?:
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