Stock tire testing

["N8"]

Deep breath... Gasp...

Ok it took a lot more research than I thought, but I am confident I can explain why we are having this discussion. And as a bonus I can almost wrap my head around some of these awfully confusing equations.

So when you start scouring the internet for this information the first thing you find are a ton of forum posts asking exactly about why the coefficient of friction would lead you to believe that area of contact has no factor. Then when you search a bit farther you figure out that the coefficient of friction only truly holds water for solid objects. And that for soft or elastic objects its a little more in depth than just normal force and applied force.

So when choosing a tire compound for a race car (or suposedly when you are trying to engineer a tire) you turn to the Pacejka formula. Also referred to as "Pacejka's magic formula"

Pacejka's magic formula is refered to as such becouse, it doesnt seem to be based upon emperical evedience. More it looks like Pacejka ran a bunch of tests and made a formula that kinda fit a situation. But its not really said to be baised on any physical propertys.

This is interesting in that it would seem that something as common place as a tire sould have had all its numbers crunched back in the 40's with all the balistics data. But in point of fact, its still an open subject of study for the scientific comunity.

So in school in stead of teaching students about the open study of elastic active friction coefficients, they just teach students about the coefficent of friction that they can proove with emperical evedience. (they just dont tell you it doesnt pertain to everything(pricks))

Tire and vehicle dynamics, Hans Pacejka's book is still widely used today the second edition published in 2002 can be viewed here for free for some reason??? : http://books.google.com/books?hl=en&...age&q=&f=false

But to be honest I dont know if he even backs me on the area affecting traction argument. (meaning i didnt read his book yet)

With help from some very smart people I found a harvard publication by
this guy B.N.J. Persson. It was published in 2006, and I had to purchase it to get at the information. But it does empericaly express area as a function of friction and force. Here is a link to the paper: http://scitation.aip.org/getabs/serv...ifs=yes&ref=no

Now where I respect sale of information, I am not willing to just cut and paste his findings in this thread, but bray d Im just going to send you some of it into you im box. Anyone else can feel free to ask me personally if they want to learn this stuff aswell, but I just dont feel right pirating this guy's work on an open forum.

[93firebird]

I personally like the ridgeline tires because they represent more closely something you would see in 1:1 tires. I may be wrong but I don't think that tires like the hb rovers or the losi lcc stock tires exhist in the 1:1 realm. I think the tires add more of a challenge to crawling after all has any one seen a 1:1 crawl up a vertical face.

[Bray D]

Thanks for the info Nate, I look forward to the read.

93 - There's some sticky ass tires in the 1:1 world. The general public doesn't really have an interest in them so you don't hear about em much. I read where a lot of guys run "red label" Krawlers. Red label being the manufacturer's "sticky" compound.

Here's a good 1:1 pic of a damn near vertical face (already posted in another thread so I may as well do it here too)

[Simon.O.]

A couple of things here.
The ridgelines are ok but can only be cut and pushed so far before it is clear that the Lizzard is the better tire.
Yes I am keen to push the low end rubber to exhaustion and learn about tires and suspension along the way.

That shot of the RedBull crawler is great as we can see that 3 wheel action happens in the real world too when a rig is pushed hard.....upwards

I still get a bit of 3 wheel time but the most of it is when it is really bound or close to vertical.

The (axial) Lizzards are now on borrowed time as I am looking for new rubber, anything but Rovers.

Chisels, Jconcepts, Claws, Grabbers.......just not Rovers.

[93firebird]

Originally Posted by Bray D

Thanks for the info Nate, I look forward to the read.

93 - There's some sticky ass tires in the 1:1 world. The general public doesn't really have an interest in them so you don't hear about em much. I read where a lot of guys run "red label" Krawlers. Red label being the manufacturer's "sticky" compound.

Here's a good 1:1 pic of a damn near vertical face (already posted in another thread so I may as well do it here too)

My point is not so much about tire compound as it is tread pattern. I am well aware there are "sticky" tires, just have not seen tires with lugs like those found on rc crawler tires

[Bray D]

Originally Posted by Simon.O.

The (axial) Lizzards are now on borrowed time as I am looking for new rubber, anything but Rovers.

I love how you're taking the time to understand what's going on to build a super capable rig that's different from the norm.

Originally Posted by 93firebird

My point is not so much about tire compound as it is tread pattern. I am well aware there are "sticky" tires, just have not seen tires with lugs like those found on rc crawler tires

Ah, I see. I agree you don't really see tires that resemble RC tires. Maybe the closest I've seen (tread wise) is the Pitbull Rocker:



I think the reason people don't groove tires to the point that they have super spaced lugs like a Rover is due to the weight of the vehicle and how soft the rubber is. I think you'd be ripping lugs off.

Mud guys on the other hand aren't afraid to cut some rubber. Here's a pic of a Jimmy Dean cut Bogger, gnarly tire:

["N8"]

My my my those rockers sure are sexy.

also: