Why would I want (or not want) larger wheels on my car?
November 3, 2014 1:06 PM   Subscribe

Car shopping. One of the variables is the size of the wheels. Apparently, larger wheels are considered a premium feature. What is premium about them?

For example, the entry level Kia Soul comes with "16-inch alloy wheels," the medium gets 17-inch wheels, and the top of the line gets 18-inch wheels.

Clearly, someone, somewhere thinks more metal and less rubber is worth paying for.

What is the basis for this? What is better about larger wheels (and correspondingly thinner tires)? Does it make the car get better mileage? Handle better?

Or is it more to do with aesthetics?

If I think the 16-inch wheels look fine, can I happily save a few bucks there, or would I be giving up performance, mileage, safety, or some other important thing?

Please help me decipher the language of car wheels.
posted by trevor_case to Travel & Transportation (21 answers total) 5 users marked this as a favorite
 
Car and Driver suggests worse mileage and handling for larger wheels/thinner tires.

They do look gnarly, though.
posted by a lungful of dragon at 1:17 PM on November 3, 2014


It is 95% style/curb appeal. The other 5% is a barely noticable (at least on a Kia) improvement in handling. The smaller amount of rubber gives a slightly stiffer, more responsive ride (which you also may not enjoy).

Lastly, I have found that the tires that go on the larger rims/wheels are slightly more expensive. So, over time, you would be paying more money to keep fresh rubber on your ride.

Go with the smaller wheels if you are style indifferent.
posted by milqman at 1:26 PM on November 3, 2014 [2 favorites]


Larger wheel + lower-profile tire results in same overall diameter tire so it still fits in the wheelwell and the final gear ratio isn't changed = less sidewall flex which changes handling characteristics. This is sometimes the opposite of what you want.

Larger wheels have more room on the inside for larger brakes if you for some reason think you'll ever want non-stock brakes.
posted by frontmn23 at 1:28 PM on November 3, 2014


It is predominately to do with aesthetics for road cars to justify the larger sizes, but there are advantages dynamically, although whether those are real to any degree in a road car application is not clear.

You do get some handling improvements with a larger wheel (smaller sidewall on the tyre means a stiffer tyre and greater road holding/lateral g capability) but this is for the most part largely only a factor outside the kinds of speed and loads you'd typically see on the roads. It's also not necessarily an advantage for cars used on the road, either, because with poor road surfaces a smaller sidewall can actually be worse because the large deflections required to overcome (say) a pothole can cause the tyre contact patch to 'bounce' and lose traction. So without the smooth surface you can't get to the higher loads and cornering forces that the smaller sidewall allows, which can mean (as Car and Driver report in the link above) the real world application produces a negative net affect on car handling.

In addition, you will get some more ride harshness with a smaller sidewall/larger wheel as there is not enough 'soft' travel in the tyre itself to absorb bumps and so these get transmitted to the car/occupants. I have 18" wheels on my car and 17" winter tyres and it rides noticeably better on winter tyres than on the 18".
posted by Brockles at 1:29 PM on November 3, 2014 [6 favorites]


What Brockles said. Thinner tires flex less - this means improved handling (and possibly mileage), but at the expense of ride comfort.

Personally, I'd go with the 18s. But I also really like a stiff suspension.
posted by Pogo_Fuzzybutt at 1:38 PM on November 3, 2014


You're also adding "un-sprung" weight. The wheels are heavier (both because of the weight of the wheel and the added weight of a larger tire) which means that the suspension has to work harder to absorb bumps.

It's also possible that they are larger wheels AND a larger tire which effectively changes the final drive ratio (making it taller) so might see every so slightly better mileage and worse acceleration.

The McLaren F1, one of the fastest, best handling cars ever made (and even 20 years later outperforms a LOT of supercars in all three) used 17" wheels which I think says a lot about the performance impact of larger tires.

Our main car is a Toyota Venza which runs on 20" wheels and I can feel it in the ride (especially on smaller cracks, expansion joints and such. But I've seen the models with 18" wheels and it looks a little odd, 16" wheels would just look weird.

It's a "premium" feature in the same way that a spoiler or wing is. Yes, there are some performance implications and there are edge cases where a larger tire is better but the car you're buying isn't one of them. It's all about aesthetics.
posted by VTX at 2:10 PM on November 3, 2014 [1 favorite]


Oh I should add that you probably won't really notice a performance difference between the 16" and 17" wheels (and maybe not the 18" either). The differences are usually pretty small so while I wouldn't pay extra for the 17" wheels if you have to have them to get some other features that you want (if it's part of some options package that you want or it comes with a step up in trim level) I wouldn't let that put me off the upgrade either.
posted by VTX at 2:14 PM on November 3, 2014


You're also adding "un-sprung" weight. The wheels are heavier (both because of the weight of the wheel and the added weight of a larger tire)

This isn't necessarily the case - I am assuming that comparing like for like fitted in a competent manner, therefore the rolling radius (outer physical size of the tyre) would remain the same as would (approximately) the width (because they're comparing two examples of the same model with different sized wheels). So you'd have a bigger wheel, but actually a smaller tyre in surface area to retain the same overall diameter. In that case, it isn't necessarily so that an 18" tyre is heavier than a 17" tyre. It may be that the assembly combined is the same or slightly heavier but it isn't necessarily a significant difference.

Re: McLaren F1 - they were still 45 series tyres, though, so make sure we're talking like for like, here. That was a pretty low profile tyre for the age (and there wasn't the sheer number of 18" wheels that there are now). The overall size of the wheel needs to be considered when comparing 'big' and 'small' wheels. Your Venza, for instance, has a MASSIVE overall tyre size compared to the McLaren F1 (or other normal sized car, even). As these crossover/SUV cars have got bigger the wheel and tyre sizes have increased to retain proportions so it's not a good comparison.

The question itself (bigger wheels on essentially the same car) needs to really be considered as 'are lower profile tyres better than larger profile tyres' or the question gets a LOT more complicated.
posted by Brockles at 2:31 PM on November 3, 2014


My experience was that the larger wheels were less comfortable, more expensive, and tended to need replacing more often (there were a Lot of flats due to potholes that necessitated new tires). Whether all of that is worth the premium for slightly better handling is up to you.
posted by ldthomps at 2:41 PM on November 3, 2014 [1 favorite]


What Brockles said. If you live anywhere with snow/ice/cold weather and the resultant potholes and asphalt patches, get the smallest wheels available. The tires for the 16" wheels, which have a higher sidewall, or "profile," than those of the larger wheels, will soak up bumps much better, improving ride comfort and preserving both the tires and the wheels themselves. We had a terrible winter in NYC, and by March, the roads were in atrocious condition; people were blowing tires and replacing their dented wheels constantly. This was much more common for people with larger wheels than for the rest of us. And these wheels and tires ain't cheap. It was not uncommon for people with SUV's and other vehicles with big wheels to shell out thousands of dollars to replace their busted wheels and tires over the course of the winter.
posted by Leatherstocking at 2:41 PM on November 3, 2014 [1 favorite]


If you have a lot of potholes you can count on a lot more pinch flats with low profile tires. Biggest concern around here and why no one runs them.
posted by fshgrl at 2:41 PM on November 3, 2014 [2 favorites]


The McLaren F1, one of the fastest, best handling cars ever made (and even 20 years later outperforms a LOT of supercars in all three) used 17" wheels which I think says a lot about the performance impact of larger tires.

And actual F1 race cars use 13" wheels, and tires with a much more generous profile than we're talking about for the Kia. Personally, I'd be happy with either the 16" or 17" wheels on the Soul. I suspect the 18" wheels will result in a fairly harsh ride.
posted by Thorzdad at 2:41 PM on November 3, 2014


Note that the width does tend to change as well. For instance, on that Kia, the tire size goes from 205/60R16 to 215/55R17 to 235/45R18. The 18" wheel is 30mm wider than than 16" wheel, a little over an inch.

Wider tires are worse in the snow, in particular.
posted by smackfu at 2:49 PM on November 3, 2014


and tended to need replacing more often

Lower profile tires often have thinner tread depth and wear down faster, as well.

Cars like older subarus(and a few newer ones) that had big fat tires on smaller wheels, instead of big wheels with slim tires ended up having the tires last forever.

It's also worth noting that those low profile tires ALWAYS cost more, sometimes a *lot* more. Tires for my partners nissan sentra with the stock 15in wheels are like, $350 at costco or something. Tires for my friends g35 with stock, but large wheels(18 or 19 i think?) are like $1250 and wear out 3 times as fast.

I'm aware there's different speed/performance ratings and widths and such involved, but those likely apple here too. There's no such thing as economy low profiles really.

I would get the 16in wheels even if i had to have the dealer swap them on. You'll be able to go to costco or $DISCOUNTTIRESTORE and buy totally fine, safe, long lasting cheap ass tires for those wheels. I'd be wary of especially the 18 having that same ability. 16in is like, a staple econobox tire size now. The basic civic, corolla, etc all ship with that size as well i think. You're getting economies of scale and many other things here by getting the smallest size. Not to mention just not replacing your tires as much.

I bet i could also make an argument for the smaller, thinner width-wise tires having lower rolling resistance and giving you a tiny bit more gas mileage too if i really tried and mathed it out...
posted by emptythought at 2:51 PM on November 3, 2014 [1 favorite]


I do remember reading an interview about the F1 with Gordon Murray (I think) where they mentioned that they looked at wheels as large as 20" for the car but couldn't hit the performance targets that they wanted to with anything larger than 17". I think it was in Car and Driver but it was over 20 years ago.

Certainly the larger wheels could be lighter but I'm better that, since these are all alloy wheels that they are all similar construction (either all three options are cast aluminum or all three are forged). I also can't imagine that they're maintaining the same outside tire diameter going from 16" to 18". I think you're answering as a hypothetical with all other things being equal.

I went ahead and looked up the actual tire sizes for this specific car and the options are:

205/60R16
215/55R17
235/45R18

By my calculations that puts the outside tire diameters at 652.4mm, 668.3mm, and 668.7mm with sidewalls measuring 123mm, 118.25mm, and 105.75mm respectively. I can't find anything talking about any differences in wheel construction other than that they're all alloy wheels but it's an economy car so I'd guess that they're all cast aluminum. There might also be differences in wheel design that affect the weight (more and larger spokes in one over the other). For all I know, they designed all the wheels so that all three wheel/tire options are the same weight (IE: The smaller wheels have bulkier spokes to make them heavier) specifically so that the unsprung weight is the same on all three.

So, the jump from 16" to 17" gets you a tire with a larger outside diameter and a lower profile while the jump from 17" to 18" is just a lower profile (called "plus-sizing"). There may be some differences in suspension tuning to compensate but I doubt it. I still wouldn't be afraid of a jump from 16" to 17" (nor do I think it has any value on it's own) but I would probably avoid the 18".

That's about as far as my car knowledge goes. Hopefully Brockles will come back in to give you some better advice about what those differences will mean to the handling dynamics on this car specifically (he is seriously the PhysicsMatt of car related ask.me threads).

And actual F1 race cars use 13" wheels

Those tires also have SUPER stiff sidewalls to compensate. The teams would go to a larger diameter wheel and a lower profile tire in a heartbeat if the rules allowed them to.
posted by VTX at 3:20 PM on November 3, 2014


I'm shopping for snow tires, and the general advice is to go down from the stock wheel size - the narrower profile / higher sidewall tires perform better in the snow. They are also not insignificantly cheaper.
posted by mr vino at 4:19 PM on November 3, 2014


Pretty much purely aesthetics, is my understanding. For example, the engineers on the Lotus Elise, which is all about handling, wanted 15 and 16 inch wheels (for less unsprung weight) on the front and rear, respectively, but the marketing guys made them go with 16 and 17 inch wheels because they "looked better". Lots of people who track that car will put smaller and lighter wheels on it than it came with, because handling is more important to them.
posted by smcameron at 5:07 PM on November 3, 2014


Those tires also have SUPER stiff sidewalls to compensate. The teams would go to a larger diameter wheel and a lower profile tire in a heartbeat if the rules allowed them to.

At the risk of a derail, it's actually not that simple. The tyre manufacturers desperately want to go larger on wheel size (they have tested 18" tyres this year) to maintain development relevance to road cars but the teams don't want to know because the cars are so fundamentally designed around a 13" wheel and the large sidewall movement it produces. They rejected the move to a larger wheel just this past winter. Unanimously...

F1 tyres are (TOTAL guesswork from what I have heard/can find as no numbers are released obviously, plus assuming nominal 18-20psi tyre pressure) roughly 27kg/mm front and 40kg/mm rear (1500lb/inch and 2200lb/inch) effective spring rates. So around 10x the actual suspension spring rates you'd see in a road car but it's actually only about twice as stiff as a road car tyre sidewall (something in the range of 700-900lb/inch from what I can gather) which is probably a huge amount less than you expected. F1 loads are very high, but road cars are very heavy by comparison.

Certainly the larger wheels could be lighter

I wasn't necessarily saying that - I'm not saying you were wrong - more that the larger tyre isn't necessarily heavier. Just the proportions of the wheel (wall thickness etc) may well mean each larger wheel is heavier (most likely). I was just baulking at also necessarily adding a heavier tyre on top of that. The tyre may be lighter or the same. But consider that the 'sportier' 18" wheels are likely a different design and they may even be the same weight as the smaller one as a result. Perhaps as a more complex and costlier wheel (not so cheap casting/forging/material maybe?). Anyway, it's likely that the 18" wheel/tyre is heavier, but not necessarily a slam dunk and maybe not by as much as you initially assumed. But, again, more unsprung weight is crappy for ride/wheel control.

There may be some differences in suspension tuning to compensate but I doubt it.

The 15-16" wheel models likely have no suspension tuning, but the 18 is probably on a 'sportier' package so will likely have slightly uprated damping but the same springs. The difference in unsprung weight may be mitigated by the damping but it is not something the average driver will notice past the harsher ride from the stiffer, smaller sidewall of the bigger wheel option. The damping in the sportier model will be a much bigger factor in terms of body roll in how it is perceived by the driver, but the *bash*crash*thump* over potholes or road surface changes will more likely come from the smaller sidewall than the more stiffly sprung suspension.

So, in summary (as I know I have wandered off all over the place) I guess you can conclude that the main gains for a larger wheel really are aesthetic for normal driving. The gains are outweighed by the downside if ride quality is a high importance parameter for you, or justified if handling is your puppy and you have no issues with a slight gain of harshness over bumps. Also, big tyres cost more. That is a factor.
posted by Brockles at 5:31 PM on November 3, 2014 [2 favorites]


Thanks a lot for the information.

That's a huge help.

It makes a lot more sense now.
posted by trevor_case at 7:55 PM on November 3, 2014


Oh. If you park on the street in a city, you're also far more likely to scuff your rims on the curb with low profile tires.
posted by wotsac at 9:39 PM on November 3, 2014 [3 favorites]


During a brief stint at a scrap yard ( new to town, first job app replied to = quick 1st job in new towne ); I saw A LOT of the tall wheels cross the scales as scrap due to pot hole and curb damage.

Prices for larger tires are flat out bonkers; check the replacement costs tirerack.com discounttire.com etc. Not worth the cost IMHO.
posted by buzzman at 10:58 AM on November 4, 2014 [1 favorite]


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