Gadgetory

now I could do a half an hour on this subject alone and put us all to sleep but instead I want to touch on four high points about tires that I think you can keep on your mind as you go shopping for them first thing to know is the big concept which is your tire isn't this big blob of rubber there's a lot of engineering going in here a structure that is built to operate a certain way not just hold air and unlike just about any other part of your car this one changes shape rather dramatically when it's working that's an amazing thing to keep in mind as well now the first concept is the contact patch or the footprint that's where this tread here sits and meets the asphalt and it varies in width and length if you will kind of this way depending on the tire design pressure and your cars weight what happens at the contact patch is amazing that footprint allows three major things to happen first of all for power to be applied to the road as the wheel is turning one way in relation to the car and for braking to happen as the wheel is being resisted kind of in the opposite rotating direction in relation to the car and then you've got the other two axes which is kind of out and in clatter aliyah cross the tire that's how cornering happens and you get that nice grip and all of those dynamics typically will happen all at once or within a second of each other and the tires got to be able to deal with all of them well the next thing that we all notice very much and you should be aware of is the profile of the tire its height with relation to its width now we love our low profile tires they look great on almost any kind of car it's got a big trend the last few decades to get this sidewall lower in relation to the width of this tread but what does that is the frame inside the tire they're called the belts they're made of either Kali ester or steel and they don't just bring that profile down when you do you change the nature of how the tire operates in two kinds of loads one is radial load the load that comes if you will kind of vertically down on the tread the stiffer this is that may change the ride comfort you get more drumming in the car you get less of a soft compliant ride and this low-profile tire also has a very different behavior for lateral loads which is sort of the side to side load think of it as a cornering load for the most part this low-profile sidewall is stiffer the tires gonna kind of scooch less left to right as you go in and out of a corner that's great for performance but that can also harshing up your ride because there's less give in this overall design it's a trade-off between that sharp performance and that comfortable compliant ride and then of course there's the tread itself that actual intricate pattern that we all know and see on the face of the tire this isn't just here as a random pattern or to look cool big a deal tire to be honest there's no tread if you're driving in perfect conditions on a dry piece of pavement on a summer day like this slick right here it puts the maximum amount of rubber on a dry clean smooth piece of pavement but that's not the real world so our tires on passenger cars you have tread we drive on roads that have gravel that has snow that have rain so your tread is designed to deal with all those to work its way around gravel and find the traction between the actual rocks to get down in snow and find some grip in that material or on a rainy day to take the water in the middle of the tread as you race down the street and evacuate it out the side otherwise you end up flying on the surface of the rain that's called hydroplaning and that's no fun and two other factors about tread design the way that it grips and then releases the road is a key part of how well this thing does in corners is it going to create oversteer or understeer all tires have some slip as they turn but the nature of that allows the car makers that dial in the cornering behavior they want in their overall vehicle and finally tread has a lot to do with quietness of a tire the way these lugs grip and release at the road creates more or less and varying kinds of sound that's where all the road noise you hear from tires comes from and that's a big deal on luxury cars in a different way than on sports cars the last thing I want to bring your attention is rolling resistance what it takes for this tire to roll down the road varies dramatically by its design the really grippy wide sticky tire is going to be great at cornering accelerating and braking but perhaps require more energy just keep the car moving at a set speed let alone to accelerate it and that's not a good guy in an era when automakers are looking everywhere to save even a few drops of gas per mile now used to be that low rolling resistance tires which you'll find on many very high efficiency cars were awful they were like having a three-day-old bagelman on each wheel now they tend to be pretty decent performance tires not extreme but acceptable they're much better at having a quiet ride pretty good performance and actually looking good as well oh by the way if you want to know what all this stuff on the side of the tire means it calls out much of the technology within it and we did a separate piece on this a little while ago about how to read your sidewall so it's important for the tires you've got but especially for the ones you're considering buying I'll put a link into our episode 64 show notes take you right to that piece and that's at CNET on cars comm or carjacking demystified right now at CNET on cars comm click on car tech 101