What are the benefits of having bigger tires?

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BALIstik916

BALIstik916

Senior member
Jan 28, 2007
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My professor asked us to find out why bigger tires are more beneficial. He said that half the internet lies and tells you it reduces friction and he claims that "traction force" is a made-up idea by Tire companies...Anyone have any idea?

Any input is appreciated.

EDIT: To clarify, bigger meaning wider.
 
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AndrewR

Lifer
Oct 9, 1999
11,157
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0
More surface area = more traction = better acceleration, better cornering

I wouldn't want a tire that "reduces friction" since tires are designed to maximize friction to keep you going where you want to go. I don't think the "Goodyear Hydroplanar XT" would sell all that well!
 
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DanFungus

Diamond Member
Jul 27, 2001
5,857
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wider tires have the same amount of rubber on the ground as skinnier tires, but the difference is in the shape of the contact area. Read this
 
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se7en

Platinum Member
Oct 23, 2002
2,303
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Wider will help with acceleration, traction and cornering to a certain extent. Too wide and obviously cornering will be more difficult and the acceleration needed will also go up once you reach a certain point.

Most passenger vehicles have around a 185-195 width while my mustang has 245's on the front and 275's on the back. Step up to a corvette and they come standard with like 330's on the rear last I looked. Wider on the rear to help that power actually reach the pavement rather than getting spun off. Also depends on how much air you have in them that iwll determine if they will actually help as it can go either way.

They are quite a bit more expensive so I would have to ask him to define beneficial hehe.
 
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mattpegher

Platinum Member
Jun 18, 2006
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There are three components of traction to consider, but I don't know the answer.
Comparing tires of similiar tread pattern and rubber makup and appropriate inflation, you could consider the tire to be like a slick used in drag racing to simplify

1. the amount of rubber touching the road
Which is affected by shape at road but should be porportional to size therefore if tire a is twice as wide as tire b then the amount of tire on the road should be twice, in theory. Realworld studies have shown that it is less than twice

2 the amount of weight per square inch of touching rubber is lessened thus decreasing the friction with the road.

in theory these two equations should cancel each other out

However for dragster the final equation is at what point does the tire loose traction and begin to spin for them traction is either an all or none situation

As far as I understand it a wider tire has more surface to grab and therefore less of a chance at slipping. However when as the surface becomes more slick such as ice or rain then the lower force per square inch become more important.

So in theory he's right but given a dry road that is not uniform with real world tires a sort of automotive quatimechanics come into play. Its becomes not the friction of any square of rubber but the statistical chance that enough squares will slip to loose the whole tire.
 
DrPizza

DrPizza

Administrator Elite Member Goat Whisperer
Mar 5, 2001
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Well, of course, you learned in physics class that the force of friction = frictional constant times the normal force. Thus, surface area has nothing to do with friction. Double the surface area, and you have half the pounds per square inch. I have my students do a lab and I do a few demonstrations in front of them to prove this.

However, when you're talking about rubber tires on the road, it's not as simple as saying "it's only friction." Traction is a bit more involved. If it wasn't, tire companies wouldn't be hiring engineers to design better tread patterns, as the tread patterns would be irrelevant. They'd just make pretty designs and claim they work.

It's a pita to explain within 1000 words, but I'll try:
Traction isn't just a synonym for friction. Friction makes up part of it, but not all of it.

I think a good analogy that can be understood is this:
Imagine a really slippery linoleum floor. Now, imagine a linoleum floor that's just as slippery, but is dented all over the place with little quarter inch deep depressions.
Lay down on that floor and pull yourself across the floor, but keep your hands perfectly flat. That's friction. Now, pull yourself across the floor, but allow your fingers to bend to try to get a hold on those depressions. That's traction. If you allow your hands to change their shape to fit into the irregularities, you can "grip" the floor.

On a road, over a wider area, there are going to be more of those spots to grab by the rubber tires. However, if it's over too wide an area, there's not enough pressure on the rubber to get it to thoroughly dig in. Too hard of rubber and the tires will take a lot longer to wear out, but they won't "dig in" as much. Too soft of tires, and they'll give you much better traction, but will wear out a lot quicker due to more shearing.
------

Here's another mental exercise to show why you can't just say "surface area doesn't matter":
forget about the rubber tires for a moment. Imagine a road covered in packed snow. You have 4 tires on the car. Put chains on the two drive tires and see how much they "grab" the snow to help push (rear wheel drive or pull - front wheel drive) the car forward. Now, somehow extend your axle to allow for 4 drive tires. Put chains on all four of the drive tires, essentially doubling the surface area of chain/snow. Think you're going to get more "grip" i.e. traction? You betcha!
 
DrPizza

DrPizza

Administrator Elite Member Goat Whisperer
Mar 5, 2001
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It's also important to point out that unless the tire is skidding, the type of friction it's using is static friction, NOT kinetic friction. You would NEVER want to reduce static friction. You always want to maximize the amount of static friction. This has no bearing on the fuel efficiency of the car.

What affects the fuel efficiency is the type of friction that acts as a drag force on the car: rolling friction. I have no idea, but it is possible that a larger tire deforms less as it rolls, but still provides a sufficient patch area. Thus, the larger tire *could* have less rolling friction, allowing for better gas mileage.

Again though, I'm not certain. One area where many of the people here are more familiar is with bike tires. If you compare the rolling resistance for mountain bike tires vs. racing tires, it's night and day. The racing tires have far less deformation than the mountain bike tires (120psi vs. 40psi) and thus have much less rolling resistance.


But again, this is another perfect example to prove your prof wrong if he insists that tire size doesn't matter. Find a relatively steep incline and try to ride a bike up it with road racing tires on (1/2 inch wide) You'll spin the tires in place. Then, try to ride your bike up the incline with knobby mountain bike tires on. You'll easily have "traction." However, on the road, those racing bike tires, even on the same bike, are going to blow away the mountain bike tires. Too much rolling resistance for the mountain bike tires. Hit a few bumps though, and the mountain bike tires are going to give you a more comfortable ride. Hit a few decent bumps with the racing tires, and you're going to feel it through your body.

In car tires, there's a lot of engineering to find the perfect balance between traction/safety, wear, and riding comfort. Not to mention channeling water on wet roads, etc.

i.e. your prof is full of shit if he says that "traction" is a made up term by the tire companies. Force of friction = mu * normal force. That's friction. The example with the two types of bike tires on a dirt hill (or you can do it on other surfaces) shows that there's more to the interaction between tires and roads than just simply friction. Traction is much more complex.
 
alkemyst

alkemyst

No Lifer
Feb 13, 2001
83,769
19
81
Originally posted by: swtethan
the internets lies!
Click to expand...

QFT, if it weren't for the GREEDY CORPORATE tire companies...we'd see all race cars on bicycle tires at $2.50 a corner.

Damn those CAPITALISTS!
 
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dougp

Diamond Member
May 3, 2002
7,909
4
0
Originally posted by: swtethan
Originally posted by: DanFungus
wider tires have the same amount of rubber on the ground as skinnier tires, but the difference is in the shape of the contact area. Read this
Click to expand...

what are you smoking?
Click to expand...

Read his link, it explains it perfectly ...
 
N

NeoPTLD

Platinum Member
Nov 23, 2001
2,544
2
81
Wider tire reduces stress per square inch to safe/reliable range. The keyword is width should be appropriate for vehicle.
 
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GoatMonkey

Golden Member
Feb 25, 2005
1,253
0
0
I would assume that this professor is going to come back with some basic formulas showing that the mass supported by each of the 4 tires is the same no matter how wide the tire is. He's going to say that the force going down on the road is the same no matter how wide the tire is, it's just spread across a wider area.

He's wrong.

The distribution of the force across the tire is in a better pattern on a wide tire. The mass is supported width wise instead of length wise if you see what I'm saying. The contact patch with more of the width wise contact patch will handle the force applied going out from the wheel in a turn better.

If he was right we could all walk around normally on ice skates or high heels just as well as running shoes.

I may have not explained the reason well enough to satisfy an arrogant professor, but he's still wrong. Does he really think race car drivers haven't tried this? It would save a lot of weight to run skinny tires.

Edit: this also depends on his definition of "wider". If it's wider by an inch or two over a standard passenger car tire then yes it will handle better. If it's wider by an impractical amount, then it's probably not worth it.
 
C

conehead433

Diamond Member
Dec 4, 2002
5,568
901
126
To use more gas so big oil can make more money, so your professor can make more money. Can't think of anything else except for better braking with wider tires.
 
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