Big Wheels, what's the point?

[markjay]

In theory a larger wheel with airy design and with less rubber on it, will be lighter than a small wheel and more rubber.

Wheel weight is important for handling - Google 'unsprung weight'... this is why Alfas had their Calliper on the transmission side of the drive-shaft and not on the wheel

However- I say 'in theory' because it seems that some anoraks actually weighed the different wheels and concluded that bigger wheels are in fact heavier than small wheels...

Presumably this is because the bigger wheels are also much wider thus ending up in having more rubber...

Soooooo - yes, mostly bling

 

[flying banana]

I'm new here, but know a bit about wheel sizes in relation to handling (my other car is a Lotus Elise).

Bigger wheels (which are invariably heavier than smaller wheels, for the same rolling diameter) trash the transient turn in characteristics of a sports car. Mostly through additional gyroscopic effects.

If you take a small gyroscope and spin it up, there will be some resistance to turning it cross-axially - the gyroscopic effect. It will also generally generate a force at 90 degrees to the angle of rotation. If you do the same with a larger gyroscope, the forces involved get much bigger.

This resistance to turning of a rotating body and the secondary forces involved WILL impact steering feel. It's why the Elise has smaller wheels (15") on the front, and larger (16") on the back.

This is important on a lightweight sports car, not necessarily on a big old bus like my E Class.

Secondarily, lower profile tyres (obviously needed to retain the same rolling diameter on a larger rim) have a detrimental effect on ride quality. This is because the tyre sidewall compliance is an integral part of the overall suspension system. The very clever folks in Stuttgart will have spent thousands of hours working out which aspect ratios work best with spring, damper and suspension geometry settings. Changing the aspect ratio will impact that in some way.

Wider tyres will also rob steering feel, although will provide more grip in the dry at least. Again, Elise tyres are 195 wide at the front, 225 at the back to provide lots of steering feel and more rear end grip - they are inherently pointy cars

Which wheels are best for *you* is mostly down to what You think the car is for - I bought my E because I want a smooth, limo like ride to waft me on a wave of torque to and from work and on intercontinental family holidays. My wheel choice is therefore to go smaller than standard - in fact as small as I can get. The car is on 18's currently and the winter wheels I'm putting on in a few days will be 17's. The only reason I'm not going 16 is that having had a quick look, a 16" wheel looks like it might contact the callipers on both axles, so I erred on the side of caution as I bought the wheels over t'interweb.

So if you want 20's on your ride, go for it, but don't expect the car to ride or handle any better because of it, do it because you like the way it looks to your eyes

Cheers all

 

[whitenemesis]

Larger wheels with lower profile tyres (to maintain the rolling circ.) will have stiffer sidewalls, giving less distortion on turns, thereby keeping more tread in contact with the road. Directional stability improves, as does steering response.

All mostly irrelevant to everyday motoring on public roads at legal speeds.

 

[MicB]

Well.....my SL has 17s and they are staying that way.

1. Because bigger wheels and rubber band tyres look silly IMO.

2. Because the car rides well on the higher tyre walls all as intended by the set up defined by the designers of the geometry of the car.

3. I am currently running Conti SC5s which have very supple tyre walls so in conjunction with the higher profile give best grip because the car is less likely to be ''thrown'' on public roads where the surface is less than smooth and very unpredictable

I also note that F1 cars run ''small'' wheels in conjunction with a lot of rubber. This provides most of the suspension and whilst I do not claim to have any insight to the tyre design I do note that slow motion footage shows a lot of tyre wall flexibility when the cars are riding the curbs. Tyres on F1 cars are run at very low pressures compared with road cars. This is no doubt a very specialist area so maybe no conclusion can be drawn from this.

Mic

 

[MBScoob]

I'll post my experiences here.

My car has 18's as standard with, as you'd imagine, fairly low profile rubber. It rides nicely but, being a sport, on the firm side - which I like.

Recently I took these wheels to be refurbished and was loaned some temporary wheels. These temporary wheels were still from a C-Class but were just 16" with taller (but narrower) tyres to maintain the same rolling radius.

Right away I noticed that the ride was smoother, the car soaked up the tiny imperfections in the road more readily - was really quite pleasant. The down side however was that even in moderate bends taken at "normal" speeds there was a LOT more tyre roll, causing the car to feel a lot less planted. Now, I'm not hooning it here, just pottering along as I usually would.

Additionally, despite the smaller tyre technically having probably a slightly larger contact area (narrower but extra squish made it longer) traction felt slightly worse when putting power down in a straight line. During cornering, the tyre roll seemed to add to this.

So, with all else being equal - it was the exact same car, just different wheels and tyres. I'd say the smaller wheel, with higher profile tyre, can make for sublime comfort in a straight line, yet a much less planted feeling during cornering as well as less outright grip - though tyre compound and tread pattern differences might account for that of course.

I suspect car manufacturers could readily design cars with smaller wheels with the same handling characteristics of the larger wheels we're accustomed too. However, I still think they'd need to be fairly low-profile to replicate that planted feeling in bends. Of course styling and aesthetics are a major factor too, but of course very subjective. I personally like larger wheels, though equally I thought the car looked good on the 16's too - they were MB multi-spokes - though friends of mine thought it looked quite comical lol.

Was being driven around in a poverty-spec S-Class recently (poverty-spec and S-Class together lol) which was riding on large 19" wheels but the tyres looked far from "low profile" at least compared to my cars. As you'd expect, the car rode lovely but, once again, cornering even fairly modestly would exhibit tyre roll you could feel.

I'll add that tyre roll isn't necessarily a bad thing, if the car is still planted it's fine when you get used to it. However, coming from my car then having the same car with taller tyres and being in the S-Class, it really didn't feel so planted to me. Weight is of course a factor here too, MB's are heavy, my old Mazda 323F from years ago - running on 13" 165/65's - was under 1,000kg so while it certainly had tyre roll it wasn't as noticable. Note that at the time I was also running an Impreza on 215/45 r18's - quite the contrast, yet the Mazda did not feel that bad in bends by comparison as it was light and designed to run on those 13" bubbles

Interestingly, when I was spec'ing up some Winter Wheels and Tyres I chose to go 16" for the ride quality as well as other factors. Sadly I was unable to make the purchase in the end due to several reasons, but smaller wheels would still be my choice now when combined with winter tyres - plus it's cheaper!

Scoob.

 

[Rashman]

'cause it's straight up gangsta, fam.

 

[MBScoob]

'cause it's straight up gangsta, fam.

Yeah, you're right. I retract my earlier post

Scoob.

 

[John Jones Jr]

I'm another one that is not a fan of large wheels and low profile tyres, the most I've gone is +1. What is worth a little bit of consideration when choosing tyres no matter the size or profile and often overlooked, is the tyre weight. I've found it not uncommon to find a difference of up to 2.5Kg between leading brands for the exact same size tyre, certainly not to be sniffed at, considering the cost of forged lightweight alloys. Even 16'' tyres there can be 1.7kg difference.

Here's the spec I'm fitting to the 230K, as you can see it all adds up.

Standard 16'' alloys 10.0Kg + Bridgestones 9.9Kg = 19.9Kg.
Standard 16'' W208 alloys 6.2Kg + Conti's 8.3Kg = 14.5Kg.

Total saving 21.6Kg plus the multiplying effect of rotation mass (whatever that is, anyone know exactly?). I may not get the outright grip that 17 or 18'' wheels with very low profile tyres offer in the dry but I've reduced the overall weight while not losing the compliance nor the steering feel of 16'' tyres bar upping the tyre pressures slightly in a bid to reduce a little bit of tyre flex - well that's theory anyway

 

[MBScoob]

Yep, increasing un-sprung weight can have a huge effect on handing (even in a straight line) as well as tyre wear, braking etc. It's obviously also working said suspension components that much harder of course.

Used to be fairly common to see cars that shipped with 15's sat on much heavier 17's suffering from various issues. Still, if the car is designed for the wheel size you should be fine. Also of course, it is possible to go to a larger size yet keep un-sprung weight the same - it'll cost though.

Personally, I'd likely not go 19" on my car, 18's look nice and it's what the car was designed for. Same on my Impreza, it's on the same limited edition 17" wheels it was when new, and I'll never change the size of those. Plus they are slightly lighter than a "normal" alloy to start with, so I'd have to spend big money to go larger and keep the weight approximately the same.

It's all down to what people want from their cars really, if someone really want to go big wheels, their will be positives and negatives to this choice but if aesthetics are more important to them that dynamics, then that's 100% - as long as the car remains safe.

One of the first "mods" I did to a car when I was younger was replacing my MR2's standard 14's with some very Stylish 15" 5-spokes - they looked awesome, like the car had been waiting for them for years. Back then, I wasn't really aware of things like un-sprung weight etc, though equally I wasn't one for driving quickly.

It might be interesting to do a comparison of a "normal" tyre vs. the XL (reinforced side wall) version. I run XL's on all my cars now due to them being more ridged & likely to survive potholes more readily.

Scoob.

 

[Borys]

Matter of taste with big wheels but I found swapping from 17's to 20's on my S class car ride is better,airmatic does the job too I guess.
Anyways You will not wear trainers with the suit, why on the street you look around after nice looking ladies?
For me good looking wheels are important the same like personal appearance.

 

[MBScoob]

I do particularly like the AMG Alloys on my car - there's the exact ones I wanted though I thought they'd be the same as those on my friends E350 which I didn't like quite so much. So, rather pleased with that. Plus they've recently been fully refurbished (at the selling dealers expense ) and crystal serum coated so they loot 100% mint

Scoob.

 

[Bamz]

Go faster? There is a 70 MPH max speed limit in this country.

Buts its how quick you get there that counts

 

[Abb]

Putting myself right in the firing line.....I fitted 20" wheels to my 55 for aesthetic reasons, the 19"s I felt looked a little lost. I only have a 25 profile on the rear and 30 on the front, drives fine to me. Guess it would be a dull world if we were all the same!

 

[John Jones Jr]

An old article but worth a read none the less.

Effects of Upsized Wheels and Tires Tested - Tech Dept. - Car and Driver

 

[whitenemesis]

Strange how there appears a massive difference between 16 and 17 inch wheels, less so above that?

 

[John Jones Jr]

Strange how there appears a massive difference between 16 and 17 inch wheels, less so above that?

Compare the 15 to the 19'', performance wise overall the 15'' seem superior. And that's not taking into account 15'' alloys & tyres would offer less drag and better grip in the wet, plus maybe better steering feel also? The only real downside it would seem is from an aesthetic viewpoint the 15'' don't look good at all.

 

[jotter22]

The 15" would probably be superior until you figure in that you will have to remove your AMG brake callipers and discs to get the wheels on!

Tony.

 

[def90cars]

The 15" would probably be superior until you figure in that you will have to remove your AMG brake callipers and discs to get the wheels on!

Tony.

I just cut a slot in the wheel where the calliper was

 

[John Jones Jr]

The 15" would probably be superior until you figure in that you will have to remove your AMG brake callipers and discs to get the wheels on!

Tony.

Clearly you are missing the point of the article for whatever reason which is pity, your loss...

 

[Fudger]

Compare the 15 to the 19'', performance wise overall the 15'' seem superior. And that's not taking into account 15'' alloys & tyres would offer less drag and better grip in the wet, plus maybe better steering feel also? The only real downside it would seem is from an aesthetic viewpoint the 15'' don't look good at all.

From 16" up, they all look fine, IMHO. I'd probably go for either 16" or 17" though as experience has told me that the need for good ride quality always tends to win out over kerb appeal, in the end. Certainly each to their own though