We pitted a sporty supermini against a big-rimmed, and theoretically more comfortable, premium SUV to find out
30 June 2019

You’ll have read plenty on these pages over the years about how a car’s wheel size affects how it drives. There’s a reason why we bang on about it with such regularity: yes, there may be style benefits to upgrading to the most extravagant rims, but more often than not they have an adverse dynamic impact

Yet it appears our protestations are falling on deaf ears. Wheels are continuing to get larger across every new car category, and buyers keep on lapping them up. The rise of the SUV has also had a marked effect, with most running wheels and tyres substantially larger than their hatchback or saloon equivalents for that chunky look. 

So, we thought the best way to illustrate this was to get two cars together from either end of the spectrum: a Mini Cooper hatchback and a DS 7 Crossback SUV. The latter is running the kind of typical wheel-and-tyre combo that you will find in many well-specced premium SUVs: a 20in alloy shod in 235/45 profile Continental ContiSportContact 5s. The size of the Mini’s, on the other hand, were commonplace a decade ago but are now among the smallest on the market: 15in alloys shod in 175/65 profile Michelin Energy Savers. 

Direct comparisons between the two shouldn’t be fair, as one is a sportily set up supermini and the other is a comfort-focused SUV, but here’s the surprise: by our reckoning, the Mini has a smoother, more consistent and ultimately more comfortable ride.

On our control route, mixing town roads with B-roads of varying speed and surface quality, the Mini’s combination of firm-yet-composed damping and squidgy sidewalls shone through. You’re always aware of the road surface passing beneath you, yet both primary and secondary ride comfort is strong, the body stays level, while even the worst surface disruption or potholes are ably dealt with. How much of that is down to the wheels is open to debate, but we’ve tried Minis with larger wheels and tyres that are much less absorptive over nasty potholes. 

Our Verdict

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The DS 7, on the other hand, is a master of inconsistency. The supple set-up gives the illusion of comfort as you float over speed bumps and bound over crests, yet a tricky road surface (of which there are many in the UK) sees the springs and dampers struggle to control the wheel movements. Around town big bumps audibly shudder and crash through the chassis, while even at speed poor surfaces cause it to thump and fidget. Mid-corner potholes can easily throw the SUV off course, too. (For balance: I’m now running a DS 7 on 19in wheels that is noticeably better in this regard.) 

So why is this the case? David Pook, formerly a vehicle dynamics manager at Jaguar Land Rover who now heads his own vehicle dynamics support firm, VEDynamics, explains. 

“One thing that does change is the unsprung mass,” he says. “Take a 22in wheel and tyre and it could be upwards of 40kg on the scales. Now imagine that 40kg mass hitting ridges and potholes and how much energy it will transfer back to the body, which then needs to be controlled and absorbed.” 

Indeed, we checked the unsprung weight on an unscientific set of bathroom scales, the Mini’s weighing in at around 14kg and the DS 7’s nearly twice that at 26kg. With the DS 7 the heavier car by a mere 235kg, it seems to be the SUV’s substantial extra mass of unsprung weight, alongside inadequate damping to compensate, that has the main effect here. 

Pook claims big wheels aren’t the only factor to consider, however. “It’s never one single thing – not tyre stiffness, nor mass in isolation – but a combination of factors,” he explains. “The tyre is a complex spring-and-damper system all in one, so one will ride worse than the other because of its damping inside. All of this changes depending on the load the tyre is carrying and its inflation pressure. A big tyre or small sidewall doesn’t necessary equal a poor ride, it’s just a different balance or challenge.”

Cars, then, that have been designed to feature large wheels from the off, or those with more advanced suspension systems, can mitigate the influence of the extra size and weight. There may yet be a technical solution that completely offsets the effect, too. 

But there’s more than just ride quality to contemplate. Bigger, heavier wheels often mean worse fuel economy, while the cost of tyres is also worth considering. Using tyre comparison site Blackcircles.com, we were quoted more than £200 for the same tyres on the DS 7, compared with £128 for the 18in wheel option. The Mini’s tyres were a mere £67. Finally, bigger wheels are far easier to kerb, a particular problem for SUVs that get used on rough terrain. 

Is it still worth it? For some, yes. Bigger wheels help offset the sheer visual bulk of modern cars, while the lower tyre profile (in theory) improves cornering stability. But for those who don’t consider that a priority, we would advise thinking again before upgrading.

Smooth operators with snazzy wheels

While some chassis development engineers accept the impact on ride comfort that big wheels have as inevitable, the very best consider it a challenge not to accept. 

And for proof that big rims, big grip levels, sporting handling and good ride comfort needn’t be mutually exclusive, you don’t have to look too far. Cars like the Porsche Macan Turbo, Jaguar F-Type SVR and Volkswagen Golf R all show that rolling comfort needn’t suffer at the mercy of flash wheels. But what they have in common, as high-performance derivatives, is the happy combination of advanced suspension technology, performance tyre technology and extra suspension tuning that tends to be lavished on go-faster models. 

Porsche has yet to launch the Turbo version of the current Macan, but the pre-facelift version rode with a versatility denied by lesser variants. In this case, it was because it represented the point at which adaptive air suspension became standard fit – and without that, the car’s breadth of dynamic ability is much less striking. 

For the Golf R, it’s both suspension technology and fine ride tuning that delivers such an impressively rounded drive. The key here is to make sure you buy a car with optional adaptive damping. 

With the F-Type SVR, it was Jaguar’s wide-ranging suspension overhaul and road-biased priorities, properly executed, that resulted in a sports car that not only handles better and is faster than any of its range-mates but rides better on testing surfaces too. Matt Saunders

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Comments
25

30 June 2019

Car with 45 profile tyres rides worse than a car with 65 profile tyres, its not exactly rocket science, to get a fair comparison, you have to test the same vehicle with different size tyres, not an SUV vs a hatchback. This article is not worth the time it took to write it. 

If you tried the mini on small wheels, and then on large wheels over the same route that would be a fair comparison, and then did the same with the DS7. 

30 June 2019
Citytiger wrote:

Car with 45 profile tyres rides worse than a car with 65 profile tyres, its not exactly rocket science, to get a fair comparison, you have to test the same vehicle with different size tyres, not an SUV vs a hatchback. This article is not worth the time it took to write it. 

If you tried the mini on small wheels, and then on large wheels over the same route that would be a fair comparison, and then did the same with the DS7. 

I, for one, would never,in my wildest dreams, have thought of comparing and contrasting in the manner you suggest.

30 June 2019

Citytiger may be stating the obvious, but he's right, especially in the case of the Mini, where the standard 15" wheels are very much a minority taste, mainly confined to poverty spec Mini One models.  The vast majority of Cooper owners, where it's also the standard fit, seem to have gone for an upgrade.  Our Cooper on 17" wheels (but conventional, not runflat tyres) seems to ride pretty well.

30 June 2019
Citytiger wrote:

Car with 45 profile tyres rides worse than a car with 65 profile tyres, its not exactly rocket science, to get a fair comparison, you have to test the same vehicle with different size tyres, not an SUV vs a hatchback. This article is not worth the time it took to write it. 

If you tried the mini on small wheels, and then on large wheels over the same route that would be a fair comparison, and then did the same with the DS7. 

Exactly, it's called a control experiment. Change only the component in question and leave the rest the same.

30 June 2019
Citytiger wrote:

Car with 45 profile tyres rides worse than a car with 65 profile tyres, its not exactly rocket science, to get a fair comparison, you have to test the same vehicle with different size tyres, not an SUV vs a hatchback. This article is not worth the time it took to write it. 

If you tried the mini on small wheels, and then on large wheels over the same route that would be a fair comparison, and then did the same with the DS7. 

Yes, a proper comparison should be the same car on different sized wheel but as the tyre profile is a percentage of the tyre width, a 45 profile tyre on a wide wheel could in theory have a deeper sidewall than a 65 profile tyre on a much narrower tyre. Of course that wouldn't happen on the same car, but I've been surprised how deep the sidewalls are on some SUVs with relatively low profile numbers.

30 June 2019
Absolutely correct Cititiger. You need to have as many constants as possible to have a valid comparison.

jer

30 June 2019

Try getting a used or deal golf R with adaptive. BMW worse. At least Merc and JLR make them standard on top of the range. Agree its broken road surfaces cracked missing top surface ueven at the same time that low profile tyres struggle with. A factor not mentioned is that heavier 2 ton cars with low profile tyres need stiff side walls to control the mass and avoid damage and its these that you need the big wheel look.

 

30 June 2019

Perhaps I'm missing something. The question is asked "Are bigger wheels ruining ride quality?" and you say "So, we thought the best way to illustrate this was to get two cars together from either end of the spectrum"

I'd have thought the bleed'n obvious method is make everything equal apart from wheel size but the article compares two different cars on two different tyre compunds. WTF? Why not use a DS 7 with different wheel sizes using same tyre models and a Mini with different wheel sizes using same tyre models?

I once owned a 1.6tdi Focus Titanium with 18" wheels (simply because they were easy to clean) having owned a previous generation focus I was disappointed with the fuel economy, and the tram lining which was especially bad.

Due to an accident, the hire car I received was exactly the same car, the only difference being 17" wheels albeit it from a different manufacturer. I drove it for three weeks. Economy went from  50mpg to 57mpg, turning circle improved ( I could drive straight in to our garage now ) and I detected no tramlining whatsoever. Another benefit was reduced road noise but that may have been down to the tyre model in question.

Of course the smaller tyre is better but if you go to the expense of buying a near top-of-the-range or sporty typre looking car, why on earth would you make it look stupid and stick smaller wheels on it?  

 

30 June 2019
scotty5 wrote:

Of course the smaller tyre is better but if you go to the expense of buying a near top-of-the-range or sporty typre looking car, why on earth would you make it look stupid and stick smaller wheels on it?  

Personally, the benefits in ride comfort, steering feedback, road noise and fuel economy, along with the lower cost of replacement tyres and reducing the risk of punctures and rim damage far outweigh any aesthetic benefits of bigger wheels. But then I buy a car to drive, not to impress my neighbours.

30 June 2019

i know someone with an audi Q7 on bigboy wheels, and it keeps getting slow punctures due to the wheel rims cracking; not due to off-road or kerbing, but simply the lack of tyre sidewall and the state of the road surface. Someone else, same problem with a range rover sport. Smaller wheels looked lost in the arches, but they simply weren't correct for the job! I can remember reading an autocar article a while ago (some time in the early 90s) where a Lotus engineer was saying that 65 profile is about ideal for most situations, cars and tyres have moved on since then of course, but i can't avoid thinking it's still about right. Also, the article looking for prices was nice, but something not mentioned (obviosuly) was that some option list wheels can have odd-ball sizes that a lot of shops never/rarely have on the shelf because hardly anything uses them - nissan qashqai 245/40-19, for example

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