I feel that beyond the more subtle context hints here- an almost certain forensic sign this tire was not intentionally shaved with sand paper or otherwise- is that it exhibits uneven wear that is almost certainly due to alignment conditions- on a tiny phone screen it’s hard for me to say with certainty- but looks like camber and possibly toe wear. Tiny screen- but I believe the inner shoulder is corded, and you can still make out the outer tread blocks on the opposite shoulder. So the only way this was “shaved” would be if the person doing it was completely incompetent, ran through the rubber on the inside, and then said “better not go so aggressive on the other side..” but highly doubtful.
Fun fact: “shaving” tires is a real thing. You likely wouldn’t use sand paper- unless it was on a small race car like an RC or slot car. On real race cars, new tires are often shaved- put on a machine and having several mm of tread removed- to improve the break in, longevity under high performance driving, the dry track grip performance of the tire, balance, and weigh. Many tire retailers (especially those catering to racing and performance customers) offer “pre shaved” tires when you order a new set.
For all intents no tire is “perfectly round” from the factory, and no two tires are exactly the same in how “round” they are alone- or compared to each other. The construction of most tires complicates this. You have probably heard of “wheel balancing.” This is where a wheels is spun (or otherwise measured) around the assembly (tire mounted to wheel) and small weights are added to offset imperfections or less than perfect roundness of the wheel and or tire.
This is done primarily because as a rotating assembly, having an unbalanced assembly- or for this discussion consider a non round assembly as the same thing- will cause vibration. To picture it in extremes- picture a toy car with wheels shaped like an egg. As it drives it will bump along rising and falling. When “climbing” the curve of the egg it will be harder to push, and when “falling” down the slope it will be easier.
The faster the assembly rotates- the more pronounced the effect of an imbalance like this will be. In a real car- you won’t usually encounter such an extreme- but most people will be able to actually feel the slight vibration caused by a wheel more than .5 ounces out of balance- generally it is more detectable in front tires and you may also feel the steering wheel vibrating side to side.
These vibrations do impact the cars ability to stay in contact with the road, but slight vibration like this will really only effect the contact to the road and thus the performance of the car at the limits of its traction- like in racing or in regularly driving- times like emergency braking or quick maneuvers to avoid an accident- the tires you likely need all the grip you can get most.
But the BIG issue beyond these things is that these vibrations are constant and magnified by speed. They can loosen connections of parts on the car such as causing bolts and fasteners that hold the suspension or major components together, as well as causing interior components to work loose air rub causing squeaks and rattles in the car that will annoy most people.
By nature most wheels and tires won’t just be perfectly balanced without some effort because you have a valve stem (the thing you use to put air in the tire) which means one side of the wheel has a hole and a little rubber or metal tube and the others don’t. A very well designed wheel can be made with this in mind- but not every valve stem weighs the same so they can’t be perfect for every one- as an example that’s easier to visualize for those not able to picture a deconstructed wheel and tire in their mind.
So our tires come from a mold much like gummy candies or M&M candies. Picturing these candies- they are all mostly identical- but not completely right? You probably haven’t ever taken painstaking measurements and true of a bag of candies- but you’ve certainly had “mutant” gummies or M’s that were obviously not identical to the others. Again- an extreme for illustrative purposes- but that’s the idea.
Lastly, when you put the tire into the wheel (mounting) the tire has its own “trueness” or how actually round it is- and so does the wheel. They both have their own balance to where and how weight is- so even if they are balanced alone- when combined they may not be. If you ever notice- tires usually have a little colored dot on the sidewall. This shows (without getting too deep into how tires are made) where the tread of the tire overlaps when it is constructed. This dog is supposed to be lined up to the valve stem by the installer for optimal balance.
Now that we’ve explained a bit about round and balance- back to shaving. When you shave a tire- you can make it as round as you have the time, tools, and skill to do. By removing material- you can make it so that the combined wheel and tire together are near perfectly round around the outside radius- the part that touches the ground and effects how the car rides and performs on the road. This (combined with Balancing) has benefits for race and street cars when it comes to handling, but also in preventing vibrations that can harm the car, evening out the load on the vehicle on turning the wheels, and in ride comfort/noise.
More for racing- tires come with mold compound and other chemicals/oxidation that can affect performance in grip to the road which are removed by shaving for one thing. For another- the removed tread reduces weight of the tire. It may seem silly- but it isn’t a silly thing to worry about at all- even for those who do not race.
Physics. The first force to look at is rotational inertia. It is much harder to take a heavy disk and spin it than a light one right? A heavier disk will want to KEEP spinning once it is moving- so
It is also harder to slow it down. That means the heavier your wheels/tires are- the harder it is for your car to accelerate. It uses more fuel, works the engine and other vehicle systems more. When you brake, it makes it take longer to slow down and stop and places more stress on your brakes- meaning likely more frequent replacement and also possibility of excess heat build up when you are constantly braking or braking hard in bursts close together. The overall effect of reducing the weight of each wheel and tire by just 10lbs can be related to reducing the weight of the body of the car by 100-200lbs in terms of performance and wear and tear. Lighter wheels also stay in the road better- meaning you will generally maintain better traction with lighter road wheels.
The second factor we won’t go deep in the physics of is something called “unsprung weight.” Your car is held up by a suspension. Usually “dampers” aka shocks or struts, and springs (or air bags.) the spring literally holds the car up. If you vanished them with magic- most cars would smash into the pavement. Everything ABOVE the spring is carried by the spring. Wheels and tires are below the spring (they are part of the assemblies that help hold up the spring in addition to providing you contact to the road). Unsprung weight has a more pronounced impact on vehicle performance. I’ll leave it at that because it is complex. But heavier wheels and tires make a car ride harsher, stop and go worse, grip the road worse* in general- and cause more stress on suspension and steering components. In racing- every little bit counts but even road cars benefit greatly from lighter wheels and tires.
From there- many of the reasons BOTH race cars and street cars might shave tires diverge. A tire made specifically for race track use is called a “slick.” These tires are usually made of VERY soft compounds that would last maybe a few thousand miles of street driving, but cost 2-4x more than most street tires of the same size. The term “slick” refers to the fact they don’t really have “tread.” Like the tire in the picture (but made that way) they are usually completely flat or may have a groove or a few grooves running their circumference.
This is because of something called “contact patch.” The only thing between your car and the road is the tire right? But only one tiny part of the tire is ever touching the road at once in normal operation. So your whole car is held to the road with 4 patches generally no larger than a piece of paper- usually smaller than. For turning and speeding up etc- that’s it.
So the bigger this contact patch is (up to a point) the more your vehicle is connected to the road- the more traction you have to brake and steer and accelerate (a “burn out” or that chirping when turning or braking hard is simply the tire loosing contact with the road.)
So if you picture a near “perfectly” flat road- the tire that will have the most contact to that road is going to be... also nearly perfectly flat. The “tire print” you’ve seen maybe on the road or sometimes in art shows you where the tire is touching the road (the black parts) or not (the parts that make the “tire pattern”) think of your finger prints. The parts that don’t show up are parts that aren’t touching the surface right?
In fact- while it isn’t advisable for MANY reasons- on a smooth flat surface- a bald tire actually grips better to the road than a brand new tire! A slick looks kinda like a bald tire- but it comes that way brand new. This maximizes contact to a flat surface. So why don’t we all drive on slicks?
Well- race tracks are controlled private spaces that are meticulously maintained. Most roads are not. So right away that is a problem- since of the road isn’t smooth and flat- there will be parts of a smooth flat tire not touching the road at all anyway. But what really matters is when we ADD something to the equation that isn’t the road surface or the tire.
Sand, dirt, and especially... water. The primary purpose of grooves on a tire is to deal with these things. When it rains, race cars pull in and change to rain tires. The pro race drivers have the skill to control the car and the skill to not exceed the grip they have until they come in- but on a normal car you can’t easily just change tires and even if YOU are a highly skilled driver- not everyone else on the road is. So street cars need tires to cover a host of weather and road conditions all in one tire.
If you spill some sugar on the counter and place a business card on top of it- the card will easily slide on top of the sugar. More easily than if you run to slide the card on the counter without the sugar. Water, sand, etc on. Road act like this- and the tire is the business card. Anyone who’s ever slipped on fine dust or mud or water knows this first hand.
The treads and grooves on a tire act to carry water or other barriers way from under the path of the tire. They “evacuate” the substance, and the protruding knobs of the tread keep contact to the actual road so that you aren’t just riding on top of water or other substances on the road. (In general) The more pronounced these knobs- the more capable they are of handling more extreme levels of road barriers. So for example- if you’ve seen construction equipment tires for off road reactors and such- the tires have very few but very large Knobs and grooves like paddles.
Trucks- especially off-road trucks have very large and conspicuous knobs on the tires- and truck off road folks already know about rock tires and mud tires and so on. The trade off to these extreme condition and terrain tires is that they offer less contact with dry and relative flat/smooth roads. In other words- staving slicks and off road tires and snow tires and so forth are all specialized tires that excel in certain conditions but do more poorly in others than an “all season” tire.
Snow living folks probably know this well. Tires rated as “mud and snow” do a better job when things get a little wintery than a “summer” or “all season” or “touring” tire- but don’t cut it when it’s SNOW. Snow tires make a big difference when it gets very snowy- but if you run them in the off season or keep them on and drive where there isn’t snow- they suck. Loud, wear out faster, harsher ride, etc.
So back to shaving- on a race car- not all race cars or race classes use slick tires. Many use “street tires” which are usually still- purpose made performance tires that most folks beyond owners of high end sports cars or performance enthusiasts wouldn’t actually use on the street. These tires have tread- but not as much or as thick as a “regular tire” and they are very expensive and generally very soft and will quickly wear out in street driving.
The physics is again- too much for this already long post- but due to how a car actually turns- the physics of what makes that work- slip angle and other factors- when a car corners and maintains grip- the tire deforms- it twists and compresses and does all sorts of interesting things to watch on a high speed camera.
If you picture running your fingers over the bristles of a hair brush- this is what happens with your tires are you drive- your fingers are the road and the bristles are your tread blocks (the knobs that stuck up on the tire.) this deformation puts stress on the tire itself- picturing our hairbrush- let’s say for simplicity it has plastic bristles- if you bend the bristles too far they snap right? And at some point with age and use- from all the bending, the bristles will break eventually. But this deformation also causes imprecision in making the car go where you want. Like walking on a bouncy castle- it’s harder to go where you mean to when your contact point to the ground is unpredictably moving under you.
So shaving tread a bit can also help with this- physics. A simple lever. The shorter the bristles on your brush- the more force it takes to move, and the less distance the tip will travel when you bend it compared to a longer one right?
On street cars- you can get some of these benefits for “normal driving” but they are of course generally not as necessary, and most folks want their tires to last longer, not shorter. Shaving down tread also reduces your vehicles ability to cope with water on the road or mud etc. so the compromise and the economics already make t uncommon to shave street tires- even if we don’t factor in that most people aren’t that invested in getting optimum performance for their drive to work.
Back to our sugar and business card. It’s easier to push the card on the table when we spill sugar right? Because less of the card is touching the table if any. Well- it turns out that while our smooth “slick” tire on a smooth surface offers great traction- it also offers something called “rolling resistance.”
The more of a tire is in contact with the road- in general- the better it will grip, but that also creates more friction. That friction needs to be overcome by the engine of the vehicle doing work. That work requires more fuel for the engine to use. Meaning that our fuel mileage or ev/hybrid charge range will go down in general as our static grip- contact with the road- increases. More heat will also be generated in the tire- which on a long freeway drive can actually cause a tire to fail. If you’ve never touched a race car tire/wheel right after it came back from a race, or touched a road car wheel/tire after a high speed interstate long distance constant trip- they can get HOT. Hot enough to burn you. That’s primarily friction (but a few other things too..)
If you’ve ever heard the “adjust your tire pressure for better gas mileage/the environment” line- that’s why. An under inflated tire saga under load and more touches the road- picture a fully inflated beach ball- a very small spot of the ball touches the ground and rolls easily. Deflate the beach ball- let’s say all the way for extremes- and it is much harder to push along and more touched the ground. Same basic deal.
So for performance and (dry) traction- reducing pressure (to a certain point and within safety limits) will generally increase grip- on a street car this gives you better braking and emergency swerving. But it also will cost you gas. You’ll see the largest impact in fuel in steady state high speed driving like a freeway. Inflating tires to higher pressures will generally decrease dry grip- but increase fuel economy. DONT TAKE THAT AND RUN OFF A CLIFF WITH IT. Tires have a maximum safe pressure beyond which they can blow out and cause loss of control. But even if you don’t hit that limit- over inflating tires is like our beach ball- they “balloon” and the contact patch to the road becomes smaller. This means that beyond reduced traction in the dry- you’ll see uneven tire wear.
The center of your tire isn’t designed to be the only contact to the road. So you buy a new set of tires, and then long before they should need replaced- you have to replace them again. The rest of the tire looks fine- almost new. But the center is totally worn. This will likely cost you more money in reduced tire life than you’ll save in gas.
Beyond the reduced grip being potentially unsafe- the odd shape you’re forcing the tire into and the uneven wear it gets can and likely will effect your vehicle alignment, the aforementioned wheel balance, and of course- cause odd and undesirable behavior in handling- even when driving straight. Your best bet on air pressure is to stay inside the manufacturers specs unless you or someone you know is a tire engineer or bonafide expert who’s actually had years or decades of experience under the most demanding and extreme conditions on that specific set up.
You also have to remember that tires are filled with gas. Usually “air” but sometimes nitrogen and very rarely other gasses. As stated earlier- even just driving on the freeway or windy roads and mountains normally- tires get HOT. Heat makes gas expand. Nitrogen expands less than “air” with heat- but still does.
So if you check your tire pressure at 6am on a cold desert morning, it may seem low. You increase it to “perfect” and let’s say you don’t even drive it. You come back at 2pm after its sat in the desert sun at 100 degrees all day. Now it’s super high. You bled or down to “perfect” and drive 60 miles on the interstate at 75-80mph. You get there and check again. Your pressure is slightly high. You bleed it. The next morning 6am you check and your pressure is SUPER low now.
This is normal, and for most people- you shouldn’t check and adjust your pressure that often- and if you did- this is what you’d see. Your tire pressure can change greatly through the day. In a race car- a single lap session can be enough to raise pressure 2-3psi or more just from the heat of all that high speed driving. Take your cars pressure when you get gas, or once a week, or at least once a month. Try to check it when conditions are the closest to when you do most of your driving- or close to the “average” of the range you are likely driving in for the season. Decide and stick to either reading the pressure when the car hasn’t been driven much or at all- or when the tires are “warm” (the latter is less advisable as without taking tire temps each time it’s hard to be consistent.)
The manufacturers range is designed with it in mind that weather and other factors will affect pressures, so if you go outside that range you may likely find yourself regularly operating in a range the engineers didn’t intend. But it is a range- to allow variance as well as personal taste. Beyond handling- higher pressures generally offer a “harsher” more “rough” ride while lower ones (to a point) offer a more comfortable ride.
Back to the subject of tread- the tire compound and tread design, the depth of the tread and the tire wear- these all contribute to something called “road noise.” Cars make a variety of noises- and their tires do too. The road condition plays in to this- but some tires on some cars drive some folks crazy. A constant hum or whine or “wob wob wob” or other ambient noise while driving. This is tire noise, and the largest controllable factor affecting it is your choice of tires. Some tires have little or no appreciable road noise while others are like a persistent moan or a rhythmic heart beat. Only way to know is to drive a car like yours, with those tires, on the roads you drive on or as similar as possible.
But another factor comes into play- tire technology has improved lightyears since the mid 20th century. Starting around 1970-1980 we started to see “modern tires” and the compounds, designs, engineering, and manufacturing technology of tires has greatly improved off the shelf performance of the “average tire” to well beyond what even many race tires of the 70’s were capable of- while being far more versatile for road conditions. Well designed tires work to fight road noise, increase traction across all conditions or within a special range, last longer, and even incorporate features like increased safety/reliability, aesthetics, more uniform tolerances, or even novel features like “colored smoke” from burn outs or colored tread marks- “run flat” or “self sealing” properties- and more.
The increasing sophistication of tires has put many time tested methods of “improving tires” in near obsolescence or total obsolescence. Shaving or sipping (cutting more grooves) in street tires are almost unheard of now days- and more often than not can make a great tire do a WORSE job. Cars and their suspensions have also improved to make better use of their tires while the factory stock sizing of tires has continued on average from the 1980’s to place tire sizes once only found in performance cars as factory spec for regular sedans.
There are many wonderful “budget” tire options- but in general as with most things and up to a point- you get what you pay for. The tire is then ONE part of your vehicle that touches the ground unless you’re having a very bad day. It’s is a very complex piece of engineering that this long ass post has barely scratched the surface of. Most folks don’t need race tires or super sport car tires on their daily cars, and not everyone can afford to use the tire their car came with or whatever the top offering from the biggest names is. But if you buy a $25 tire- you are getting a $25 tire. Be wary of these “no name” tires like “Tiger paws” and “land sails” and such.
Be wary with tire discounters and big chains running automotive shops on the side. Costco or Walmart etc can have some good deals but I’ve also seen people get hosed. Expired tires (yes. They expire.) and I knew a guy that went tire shopping on price and was so proud he found tires for suspiciously cheaper than anywhere else... until he found out the guy at the tire place sold him no name snow tires. In a place that NEVER sees any snow. And his car ride like a tank and he wore the tires down inside of a year- meaning he spent more in the long run than if he’d bought the modest extra for entry level all seasons from a respected brand.
The amount of comments on this has passed a @mialinay selfie! Sometimes I do hope for a friendly discussion I have come to expect to see a novel by guest_
It is also harder to slow it down. That means the heavier your wheels/tires are- the harder it is for your car to accelerate. It uses more fuel, works the engine and other vehicle systems more. When you brake, it makes it take longer to slow down and stop and places more stress on your brakes- meaning likely more frequent replacement and also possibility of excess heat build up when you are constantly braking or braking hard in bursts close together. The overall effect of reducing the weight of each wheel and tire by just 10lbs can be related to reducing the weight of the body of the car by 100-200lbs in terms of performance and wear and tear. Lighter wheels also stay in the road better- meaning you will generally maintain better traction with lighter road wheels.
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