Can Modified Cars Achieve 1.5G on the Skidpad?

[xxChrisxx]

It says the lateral force, also known as friction, is prop to load^0.8

well, Friction = Coef x Load
.'. Coef of friction is prop to Friction/Load.
ie [load^0.8]/[load]
ie Coef is prop to load ^ -0.2
OK ?

You said said the bike has around 1/5 or 1/6 the contact patch area of a car tyre.
And I said the car has around 5 or 6 times the weight of the bike all balancing on 2 wheels just like a bike. Therefore the 'loading per unit area' is the same...

Mentioning that adding stickier tyres gives more grip doesn't prove anything - by definition it's obvious anyway.

Jeff beat me to the point, it sates a clear range. If a range is stated it's not correct to simply take the middle value and declare everything is that.

Also I'm calling ******** on your Porsche claims of 100% weight transfer at 1.5G. Please note that you can tip a car without steady cornering on 2 wheels first, there is no arguing that you have to trasistion from 4 to 2 wheel during the tipping motion, but you wouldn't really call this scenario cornering. It would be having an accident.

You made the claim, state your assumptions and show your reasoning/working. If you read it somewhere, post the source.

 

[rcgldr]

Contact area isn't just a function of pressure, it's also related to other tire parameters (like sidewall stiffness). Once contact area is beyond some optimum value, then higher pressures can make a car more responsive. An example article about Hoosier DOT R6 (race) and A6 (auto-cross) tires:

http://www.racetire.com/products/tctips.htm

List of Road Racing tires at Hoosier. Note that the softer compound road racing slicks - radial - are only available with 13 and 15 inch diameter wheels, and the road racing slicks - bias ply - don't have any sizes larger than 16 inch wheels. Click on this link, then "specs" in the left menu:

https://www.hoosiertire.com/rrtire.htm

Note, the guys who race modded Porsche 911's, generally run 18 inch wheels, and these are harder compound tires, that won't pull 1.5 gs in turns. If such tires did exist, and 1.5g's did cause 100% weight transfer, then the car wouldn't be safe. Cars generally roll because they get sideways, and dynamic compression forces (perhaps a dip or curb) on the leading side of the car are enough to create enough grip to roll the car. This amount of dynamic force isn't possible with normal turning. Most of the time, cars will spin without rolling.

 

[YellowTaxi]

Note, the guys who race modded Porsche 911's, generally run 18 inch wheels, and these are harder compound tires, that won't pull 1.5 gs in turns. If such tires did exist, and 1.5g's did cause 100% weight transfer, then the car wouldn't be safe. Cars generally roll because they get sideways, and dynamic compression forces (perhaps a dip or curb) on the leading side of the car are enough to create enough grip to roll the car. This amount of dynamic force isn't possible with normal turning. Most of the time, cars will spin without rolling.

Jeff that's funny. Modified Porsches can pull more than 1.5G and they're modified for precisely that reason - they would would tip if they weren't modified. Even a stock porsche 911 will pull well over 1G on a race circuit, since there's more grip on a racing track than out on the street.

ps. I don't know why you sent me a pm claiming that only rally cars on rough surfaces can tip in a curve, and some other such nonsense. Was that a joke ? There's plenty of videos on the net showing cars like BMW M3's tipping purely due to G forces. I have videos of my own where cars tip purely due to pulling sufficient G to lift the inside wheels. This discussion is getting stranger with every post..

As to the other posters , if you're so smart and so disbelieving of what I say, then I suggest you go work it out for yourselves and show your reasoning on here. Instead of chanting childish "Oh no it isn't"s. You people should probably be in a pantomime somewhere.

http://en.wikipedia.org/wiki/Pantomime

 

[xxChrisxx]

Jeff that's funny. Modified Porsches can pull more than 1.5G and they're modified for precisely that reason - they would would tip if they weren't modified. Even a stock porsche 911 will pull well over 1G on a race circuit, since there's more grip on a racing track than out on the street.

ps. I don't know why you sent me a pm claiming that only rally cars on rough surfaces can tip in a curve, and some other such nonsense. Was that a joke ? There's plenty of videos on the net showing cars like BMW M3's tipping purely due to G forces. I have videos of my own where cars tip purely due to pulling sufficient G to lift the inside wheels. This discussion is getting stranger with every post..

As to the other posters , if you're so smart and so disbelieving of what I say, then I suggest you go work it out for yourselves and show your reasoning on here. Instead of chanting childish "Oh no it isn't"s. You people should probably be in a pantomime somewhere.

http://en.wikipedia.org/wiki/Pantomime

Burdern of proof lies with the one making the claim. I find it hard to believe that it is phyiscally possible to get even close to 50% load transfer without the car spinning out first. Even if it were possible (which I have doubts about) as Jeff said no one in their right mind would set up a car with enough grip to roll itsself. It's for this reason I have never ever seen a roll from a steady cornering. There has ALWAYS without fail been some dynamic force at work.

You may find some older cars with floppy chassis that lift the inside front, the the rear's tend to always be planted.

Could you please link some videos that show the phenomenon of a roll caused by steady cornering?

 

[rcgldr]

Modified Porsches can pull more than 1.5G and they're modified for precisely that reason

What I meant was stock 3000+ lb Porsche modified for track use with suspension tuning and DOT tires, as opposed to a FIA racing Porsche at 2500lbs. Note also that lateral grip decreases with load transfer. A race car might be able to pull 1.5g's with a 50% load transfer (cg height = 1/3 track width), but a stock car with with a relatively higher CG won't be able to achieve that because the higher load transfer reduces the effective grip.

Some actual skidpad numbers:

http://www.modified.com/news/0708_sccp_lateral_g_skidpad_testing/skidpad.html

http://www.motortrend.com/features/112_0706_americas_best_handling_car/photo_20.html

Peak lateral acceleration (banked turn) at Laguna Seca exceeds 1.5g's, none of the cars roll:

http://www.motortrend.com/features/112_0706_americas_best_handling_car/track_conclusion.html