I am about to buy a new tire for my truck. The previous owner had upsized to 220-65/15 tires from the standard skinnier tires for 14" wheels. Only one tire is well-worn so I considered buying four cheap used standard wheels to save money on the tire cost, but four cheap wheels plus cheap tires is always going to run more than one pricier fat tire.
That is what got me thinking about a number of tire and traction questions:
If two different sized tires are driven at the same pressure and driving styles/speeds does the wider tire wear more slowly? My thinking is that since the contact patches are the same for both tires (patch area = load/tire pressure) The larger tire is exerting a lower pressure on the pavement and thus wears at a lower rate. Do wider tires wear more slowly?
Why do wider tires give better traction? Traction forces are approximately given by C[sub]f[/sub] x weight. C[sub]f[/sub] depends on tire compound and pavement composition and surface. What does the wider tire have going for it that makes it de rigeur in racing?
The tire on my truck that needs replacing is the driver’s side rear. I would have figured that the passenger’s side rear would have worn faster. I picture the frequent wheel spin you get when pulling away from a stop sign making a right turn at the same time. But this phenomenon seems weird if I have a functioning differential in the car. Why should the inside tire pulling away from a stop be prone to spinning. It seems to do it even if there’s no water or dirt next to the curb, say in a dry clean parking lot. My first guess would be the load shifting to the outside wheels from centrifugal force, but starting from a stop there is no such force. Any ideas?
Rubber can only hold so much before it starts breaking off pieces. A larger contact patch (from a ‘larger tire’ means there is less force per unit area of tire, so it can ‘hold’ when a smaller contact patch will excede the breaking point of rubber and start to slip.
Also snow tires are typically narrower, and usually downsized for max performance. The reason, you want that tire to ‘dig in’ you want a small contact patch with lots of force driving it down to hold (either in snow or getting right down to the pavement).
But that’s the rub. As I pointed out, contact patch is the same for wide tires and narrow tires. If there were no difference in compound or tread pattern where does the advantage for wider tires spring?
Wider tires are usually stiffer on the sidewalls, as a greater % of the rubber is in the tread (relative to the tire it is replacing in a given application). The lower ratio of sidewall to tread = more stiffness (when cornering, this keeps more tread contact patch on the road).
A 225/50 r15 tire can be stiffer than a wider tire that is used in a completly different application. It is the ratio of sidewall to tread for specific applications that these rules apply.
If you have a 205/75 15" tire and plus size to a 195/70 15" tire, this is a direct swap out, as the diameter retained is almost identically, but the sidewall is now stiffer, and the sidewall is now a lower % of the tire mass. This keeps the contact area in better contact with the road during lateral acceleration,** relative to the tire it replaced. **
I believe you’re thinking of just the front-to-rear size of the contact patch. The wider tire will have more of a contact patch measured from side-to-side. Thus, more rubber actually contacting the road.
Sorry for the kludged-up diagram, I had to put something in so the spaces weren’t compressed. These are the dots. The stuff between the vertical bars is just meant to look something like a treat pattern as seen from below a clear glass “road.”
If the vehicle is equipped with a limited slip or posi-traction axle, then both the inside and outside tires are forced to spin together. The inside tire will notoriously chirp as the tire slips a little over the pavement, trying to keep up with the faster spinning outside tire. Right hand turns are usually a tighter radius, meaning that the inside tire is almost just a pivot point as you turn right, yet it needs to spin as it is pretty much locked to the outside faster spinning tire.
While this alos happens on left turns, left turns are of a greater radius and the inside tire is actually alllowed to track over the pavement.
Posi traction cars with bias ply or old glass bias ply tires constantly chirped and squealed around most turns. Newer tires mask the sound, but unusuall wear patterns still pop up. Depending on tire pressure, driver habits, freqently travelled routes and what not, different tires will wear differently.