Alright, I'll confess, it's something I've always wondered.... Why do wider tires have more grip?

Friction to slide an object is (coefficient of friction) * (normal force). Contact surface area doesn't matter in a perfect world where surfaces don't deform. But tires don't behave that way. Why?

Just one of those random things I've always wondered about but never heard a decent explanation.

 

this video provides some information related to your question - and also shows real world tests:

 

Tractive vs traction force. It's mind boddeling. I took a dynamics elective that was solely on vehicle performance and this was one of the more interesting topics. Sandbags in the back of the pickup reduces tractive force but increases traction force. A lot depends on compound too becuase most radial soft tires "paddle" vs roll at launch. The launch is everything. I'll see if I can find my old notes. That was, uhm, a few decades ago.

 

coefficient of friction is different across the tread width.

a wider tire provides more contact area away from the stiffer sidewall.

there are other factors involved as noted above.

t'would be an exciting vocation to be a tire designer.

 

When I brought CTW Motorsports wheels to the market, I had used telemetry and track times from a few CMC racers using the wheels with the same tires as prior and it gave some predictable results. This is moving from a 255-50-16 tire to the exact same one in 275-40-17, having more tire weight, less sidewall, and a 20mm wider contact patch with a 1.5" wider wheel (9.5" vs 8").

Data showed in the case of the typical 3rd gen (slightly front biased, RWD, with a "square" tire setup, you will pick up about 40% of the additional tire width (in %) in terms of more grip in all 4 directions. So if your car pulls 1.00g on your Toyo race tires in 255-50-16, moving up to a 275-40-17 will give you around an additional .035g increase in grip. 0.035g additional grip may not seem like much, but a great driver taking advantage of the extra grip may lower lap times by 1s to 2s with no other changes as proven by track results I was given. I also have one additional data point that blew me away - another racer (who does not run in CMC) had changed his wheels from steel 17" x 8" to CTW 17" x 9.5", lowering wheel weight by 12lbs/wheel and also spreading out the section width/sidewall by 1.5" total per corner. With the same 245-45-17 tires, he ran between 2 to 3 seconds faster per lap without the wider 275 tire, not to mention he did not chew up tires as fast due to the tires being ultra stable in terms of unwanted sidewall flex.

 

So I think what you're saying is the dimensions of the tire change the adhesion coefficient between tire and ground? Basically one tire is able to apply more force to the ground than the other.

 

Huh? Isn't it simply more surface area between tire and road touching?

Is this a troll?

 

friction (side force resistance) is a factor of the coefficient of friction and the normal force (weight)

surface area has no effect for a body with uniform coefficient of friction. increasing the surface area simply decreases the normal force for the area under consideration.

think of it this way. 144 lb over one square inch of contact area becomes 1 lb per square inch when we increase the contact area to one square foot.

physics is the most awesome thing in the world, read it, learn it, live it

 

Nope, I just have a little better understanding than you and know enough to know that I don't know.

 

 

Lol

Sure thing, Pal.

 

That snippet you posted says the coefficient of friction changes with the shape of the contact patch. That's just a reword of wider tires get more traction. The question though is why? Why does it behave that way?

 

A troll that's been a member here for over 20 years with almost 3k posts? Who's the troll?

 

http://ffden-2.phys.uaf.edu/211_fall...n/physics.html

it doesnt make sense by the friction force equation alone lol clearly there is more to it, because as you may know, larger wider tires of same compound have been tested and shown to be faster on a given surface. Like radial tire racing 235, 275 and 315 tires. All suppose to be same compound and all on same track surface, the 315 can take more power than 275 which can take more power than the 235.

that normal force can vary with suspension setups, torque converters and weight balance imo. A really well set up suspension and chassis can apply more force down on the axle, especially radial cars that separate the rear. The maximum eventually reaches limit when considering max engine output i guess and full weight transfer of the car. That downward force that can be applied really depends on the surface and tire compound and size.

i guess its not a static environment like that link says, its dynamic and more tire patch area ensures maximum friction force is applied. I guess its kinda like if you step on to a glued surface track with your tip toes of your shoe, its easier to unstick yourself. If you flat foot it, lot more surface area glued to it, should be more force to remove your foot. My physics was always rusty but something about cars and racing that sometimes seems to defy standard mechanics and enters quantum field haha

 

I did a quick search on frictional properties of rubber. Seems it's maybe a strange little beast.
https://nvlpubs.nist.gov/nistpubs/jr...n4p439_a1b.pdf

Would be nice to find more info targeted at how tires work.

 

It would be interesting to see these tests preformed with modern tire rubber compounds and have a comparision of a modern tire compared to a 1942 tire.

 

So I'm trolling??

He didn't say anything about softness of tire, tire pressure, sidewall height etc

Just... "wide tires"

Which the correct answer would be, more contact area. Good Lord...

 

That's the question reworded, not the answer. It was an observation already built into the question. You're not connecting the dots and not listening to what multiple people have explained to you. You're trying to preserve your ego and looking dumber in the process. We're just going to leave you behind if you don't get with the program.

Also, your expert reference is a student doing substandard work in an entry level college course. Meanwhile, I can count 5 engineers in this thread of various background and you're wasting an opportunity to bend their ear to maybe learn something. Personally, I'm not going to waste that opportunity.

 

Moving this thread forward....

Apparently friction coefficient of tire rubber is not constant with weight and this is a huge part of the answer. The friction coefficient declines as weight is added. Wider tires result in lower contact pressure where the rubber has a higher friction coefficient. But then at some point the friction coefficient will become fairly constant and that's where wider tires may no longer benefit.

Search for the terms Tire Load Sensitivity if you want more info.

 

lower static weight but what about the effects of suspension and aerodynamic downforce that can apply more load to the axle? It would seem more weight over the tires improves traction, its why guys add big wings and see downward force on sensors mounted to the suspension and shocks. And why guys add weight to the back of the car on street or no prep races. It seems to improve traction and be contradictory to the friction explanation

 

"The more that I see, the less that I know for sure"
John Lennon

While reading up on Load Sensitivity I came across a term I hadn't heard before, Relaxation length.
"Relaxation length is the distance a tire travels after you turn your steering wheel but before the tire is actually able to grip the road and turn the vehicle."
Relaxation Length: What Is It & What Impacts It? | SimpleTire

 

This is correct and one of the only things I remember from that elective dynamics course I took way back in my undergrad. I have yet to uncover my notes, but if I recall, tire style also came into play, bias ply, R compound, radial, etc. I remember the big lecture on tractive vs traction force. Unfortunately, i'll need to find my notes since that was so many beers ago.

 

Good question, and I'm not sure yet. I haven't seen a real grip curve yet, just theoretical for discussion purposes. In the theoretical curve the overall grip increased with weight but the rate of increase declined. Basically the curve was laying over. So there was more grip with more weight on tire, but the amount of grip per unit mass of vehicle got worse. But aero puts more weight on tires without adding extra mass.

A real curve is probably non-linear. I found some curves done during studies on ice and it was non-linear. But that has phase changes of materials and all kinds of jazz going on.

And this is just one factor of many, but I think it's maybe a pretty strong factor.

 

Does this all take into account, the durometer of the compounds used to build a particular tire? I might have missed it in the conversation.
FYI Durometer being hardness of the tire compound for those that might not know.

 

Same rubber compound. Better rubber is a quick win as always, but beside the point for this discussion.