Tires. For most folks, they’re just an essential part of every car. But to others, tires are a fashion statement. So here’s Pat Goss with the truth about plus size treads.

This time we’re going to talk about tires with our tire expert Matt Edmonds. Matt welcome back to Goss’ garage.

MATT EDMONDS: Pleasure to be here Pat.

PAT GOSS: Alright you brought us an assortment of tires. Tell us what you brought.

MATT EDMONDS: Well I tell you. We’ve brought some plus sizing with us today. On this VW we have a 17-inch tires and wheel package. The original equipment size. In front of you we have an 18-inch tires and wheel. In front of me a 19-inch tires and wheels. So plus one and plus two. The plus being the extra diameter of the wheel as we say, so an 18-inch and 19-inch wheel.

PAT GOSS: Alright, but we see some drastic differences as we plus size these.

MATT EDMONDS: There are. They get a little wider both the wheel and the tire, but more importantly the thing that stays the same on these, the thing we have to make sure stays the same is the outside diameter of the tire or as many people say the height of the tire. That stays the same. We notice the side wall changes though, because if you look at these the side walls have gotten shorter as we’ve gone up in size. Maintaining the outside diameter the wheel has gotten bigger so the side walls had to shrink.

PAT GOSS: Alright, and that’s important. I know out in the field we see all kinds of problems with electronic systems on the car when this is not done properly.

MATT EDMONDS: Yeah if we don’t keep that same outside diameter your anti-lock brake system, your traction control system and your speedometer won’t read properly if those other systems don’t function properly.

PAT GOSS: Another issue we see when its not done right is clearance.

MATT EDMONDS: Absolutely. There are a lot of components behind that wheel. Brakes and suspension components you gotta make sure that you clear those, so it’s very important to work with a reputable wheel shop or an online source where you can go and plug in your make model and year of vehicle and make sure all of those issues are handled and that your tire has the right load bearing capacity.   

PAT GOSS: Alright, now you also brought a minus. 

MATT EDMONDS: We can go plus. We can go minus. And typically when we go minus we do that for winter tire and wheel packages. Where on some SUV’s that have 20 or 22 inch wheels as original equipment they may not have a winter tire option, but you can go down, not only so that you have availability of winter tires but typically when you go down you go to a narrower tire. Since we go wider when we go plus, we go narrower when we go minus. And that’s to make sure the winter tire is going to dig down through the snow and get to the pavement. 

PAT GOSS: So this myth of putting on great big wide tires for snow traction is completely wrong.

MATT EDMONDS: It doesn’t work the same as snow shoes where you want to float up on the snow. We want to get down through that snow because we want that special compound in that winter tire to be able to contact the pavement and do it’s magic and help you stop, start and control that vehicle in winter condictions.

PAT GOSS: OK Matt Thank You. And if you have a question or comment, drop me a line right here at Motorweek.