What's with the new wheel and tire sizes these days?

I don’t think it’s performance, but I’m not sure. My husband loves that look. I find it frustrating, because you are much more likely to damage your wheel on a curb. If you hit a curb with your tire no big deal (I’m talking about at a very slow speed and just a tap) if the curb hits the wheel—scratch. It’s not like I hit every day, but in 10 years I’d say it’s happened 3 times between the two of us.

As far as I know it’s just a style thing, but I might be very wrong about that.

The expression you are looking for is aspect ratio. The newer, flashier tires have lower aspect ratios. Think of them as high heels for your car.

The advantages are: better cornering and better braking IFF (if and only if) the manufacturer used the space to install larger brake disks and tuned the suspension for the tires. The disadvantages are: rougher ride, higher cost, poor performance on ice and snow, and wheels are prone to breakage if you hit a pothole. The biggest reason for them? They look cool, especially if the brake calipers are painted red.

Now let’s look at high heels. The advantages are: additional height offers unobstructed view when walking in crowds; air is cleaner at higher elevations; posture, leg and calf present nicer curves. The disadvantages are: sore feet, tendon damage, poor performance on ice and snow, and ankles are prone to breakage if you hit a pot hole. The biggest reason for them? They look cool, especially if the soles are painted red.

Usually “low profile tires” is the term I’ve heard. It was originally a performance thing. Sort of.

Less sidewall means less flex in the tire and more of the contact patch on the ground. Tires meant to be low profile also tend to have stiffer sidewalls, for example most are in effect “run flat” because the sidewall will support the weight of the car.

So that means the tire retains it’s shape while cornering, but also means the ride is a lot stiffer as you mention. Potholes start to sound and feel like the car is bottoming out, even if that’s not the case.

Up to a certain point, larger wheels can be a performance improvement as well. This gets argued to death on every automotive related website anywhere, so I’ll just add that weight is usually more important than size. You want lighter wheels and tires, if the wheels happen to be bigger and lighter, great.

Another reason why I want to keep my 2006 Sub. Forester forever. The dirt roads here are mostly pot holes with a little bit of connective tissue.

Here is a set of Manolo Blahnik’s for the Forester.

Very funny. Milo fell for it. (I did not).

Both are similarly priced, similarly impractical and ineffective, and are similarly attractive to Y chromosome holders.

“Low profile” is the correct term. Less weight spinning around and having to tote wherever you go aids in giving greater MPG.

I think most of the basics have been covered. However, I do wish to clear one little detail up. It seems that many equate better performance with reduced comfort. I find being isolated from the road dangerous as it can easily lead to loss of control, especially in sub-optimal conditions.

Do you know why JDM and EDM cars perform so much better than USDM cars though? Because USDM cars place such a premium on comfort that they tune the suspension to where road feel is absent, then double-stuff the seats to where you can (and likely will) forget that you’re even driving, and finally slap some 70-profiles on just to make sure you can’t feel the car. Gawd forbid that you feel lateral acceleration in excess of 0.02G, so USDM cars actually “benefit” from excessive sidewall flex by further isolating the driver from the road.

That said, low profile tires can also get a little overboard, but something with a profile in the 45–55 range is generally a good compromise between improved handling and risking rim damage. I’ve see some upsize the rims to where they use a 20 or 25 profile tire, and those cars tend to be “trailer queens”, unable to handle public roads without risking a bent rim.

FWIW, WRC rally cars tend to use 205/65–15 for gravel stages where they jump and hit ruts worse than potholes while switching to 235/40–18 for asphalt stages. As I doubt anyone here drives like this, I think the rim damage aspect is overplayed a little bit. If a 65-profile is good enough for that, then I fail to see how a 40-profile would damage the rim when driven the way most people drive.

And if comfort trumps control on your priority list, please, PLEASE do not drive. It’s not your living room; it’s a 2500–6000 pound hunk of metal that could kill people if you get too comfortable to remember that it’s not your living room.

Ah, yes, sidewalls, aspect ratio and low profile are the words I was looking for.
GA, @LuckyGuy. If I could give you 10 GA’s I would. And thank you, @jerv for your additional insight. Thanks to all others for taking the time to reply.

Intuitively, I could see where the oversize rims could lead to slightly better performance at the expense of comfort and perhaps risk of damage to the rims. but I thought that maybe another reason was “fashion”. They’re fashionable nowadays. Anybody remember white sidewalls?

Low profile! That’s it. I’m glad a jelly said it. I couldn’t think of the term. That’s what my husband calls it.

Here is an excellent comparison study performed by Car and Driver. They compared 15, 16, 17, 18, 19 inch wheels and matched tires on a 2010 VW Golf. The photos are quite instructive.

Please read their report (link above) but here is the bottom line:
“The 19-inch wheels definitely look the coolest. But the 17— and 18-inch setups offer a better compromise of grip, acceleration, price, and ride harshness, so we’re not surprised VW uses 17— and 18-inch sizes on its hot Golf, the GTI. If it’s acceleration you’re after, stick with the smaller, lighter wheels and tires. And remember, unless you believe it is better to look good than to feel good, take our advice and stay away from extremely low-profile sidewalls and massively heavy wheels.”

(Now compare with: 2”, 3”, 4”, 4.5” platform stilettos.)

Aspect ratio is the height of the tire in proportion to the tread width. Tires are listed this way as “series 80, or 78, or 75, 70, 65, 60”, etc. I have 205/70R14 tires on my car. 205 is the height of the sidewall, 70 is the aspect ratio for the tread (to give an indication of the width of the tire) R is for “radial ply” and 14 is the rim diameter.

I had a GTI that had extremely low profile wheels and at least once a month for the three years I had it someone would notice my rims and tires and say something.

@kritiper I had a tire shop try to convince me that the first number was sidewall height and the second was the width, as you state.

The tire shop across the street from them wound up getting my $300 for getting it right.

Your tires have 205mm width and the sidewalls are 70% of that, or ~143.5mm high. Personally, I generally mount tires 10 or 20mm wider than stock, which forces me to go down a profile step or two in order to maintain the same rolling diameter. For instance, my car should take 175/75–13, but I use 185/70–13 instead; that gets me a little extra lateral grip as the tires are almost half an inch wider, but the speedometer is still almost correct as the circumference is nearly the same (0.6% difference). If I wanted to keep that tire width but go low-profile, I would go 185/50–16 and wind up with a circumference within 0.2% of stock.

And yes, it is okay to go with non-stock sizes so long as you have the fender clearance and the diameter is withing about 2% of stock. Of course, modern cars generally require all four tires to match so as not to confuse the electronics; things like ABS rely on having accurate information about the relative speeds of each wheel, and if one tire is different from the others, it will rotate at a different RPM despite being at the same speed, and the poor ECU will lose it’s little mind.

@jerv I’m a little rusty on my tire specs but I wanted to emphasize that the aspect ratio was the height to width aspect. A tire that is a 195/75R14 is the same height as a 205/70R14. But the tread is wider on the 70 series.

@kritiper The way I learned it, 205mm is wider than 195mm, but (205mm*70%) is close enough to (195mm*75%) to yield practically the same sidewall height.

But yes, aspect ratio is indeed sidewall height divided by section width.

For my Integra, I went from 195/60R14 to 205/45R16. Cornering was much better, speedometer was only 0.22% off. I didn’t dare go to 25 or 35 profile tires because that would be higher risk of damage to the rim if I ran over any junk on the road.

I once had a car with 25 profile tires zoom past me because I was too slow. He did not see the speed bump I was slowing for, so hit it at 35 mph. He bottomed out his suspension and sidewalls, so busted a rim. I saw two half cylinders of aluminum (rims) appear from under his car as I drove past him.

Great story, @RocketGuy. Ha, ha.

Relevant for @RocketGuy and @2davidc8

I’m still looking for a certain article from Sport Compact Car titled, “Power, weight, grip! What matters most?”, but the magazine went out-of-print years ago so it;s hard to find that article.