Wheel Size Affects Ride

[Jensen]

Can someone please explain why bigger wheel size effects ride. I've read on this site that 18 inch wheels on avantgarde is harder then 16 inch.
I can't understand how this is so as the 4x4's ie ML, X5 have 20 inch plus wheels that don't seem to effect the ride.
Would this also be as noticeable in Elegance spec.

 

[Blobcat]

The wheel size makes a difference as there is less tyre sidewall, the less sidewall means that there is less absorbed in the tyres and more passed onto the suspension & car. Less of an issue with 4x4's as even though they have large wheels they tend to still have a large sidewall to absorb the bumps.

 

[Jensen]

Thanks, so the solution is to get a tyre regardless of size with a large sidewall. So this being the case I assume it's not a problem/issue?

 

[amwebby]

If you do so your wheel/tyre combination will then have a larger rolling diameter and your speedometer will need to be recalibrated.

http://www.miata.net/garage/tirecalc.html

Altering the rolling diameter will also have an effect on the suspension set up and you may need to make adjustments there as well.

 

[Bolide]

You need to maintain the correct rolling radius whatever the wheel size. If you don't the gearing will be wrong, the speedo will be wrong, wheelarch clearance will disappear so the tyres will catch on full lock and in dips, your gearbox may refuse to change gear and your ABS / EPS & etc may not work properly

As wheel size goes up, tyre aspect ratio goes down and tyre sidewalls get stiffer. There's no getting away from it

I am told that the reason for 20"+ wheels is that the driver's ego exceeds his tolerance for an awful ride

Nick Froome
www.w124.co.uk

 

[Alembic6]

You got me on my subject here - I think its crazy that fashion overrides the engineering. Consider the situation - it takes bucket loads of money and engineering to perfect the suspension and ride of a new car - and its normally based upon 'normal' base model tall tyres. Then the marketing looneys wreck it all by conjouring up the usual model maze that tries to get you spend more than you planned - you know, the base model has everything bar a boot lid, so you have to go for the deluxe model that cost twice as much, includes lots of extra trash, but also the all important sexy low profile alloy wheels. Of course, you probably test drove the base model and was impressed by the smooth ride - and now you find the alloy wheels have wrecked it. Happens all the time, well, to me anyway. Bought a Nissan Micra for a family pool car 3 years ago, after buying found out it has special larger diameter alloy wheels, rubbish ride, and they cost £90 each - on a Micra! Wife's new Fiat 500, just the same - car engineered for base model with nice retro steel wheels, 'Lounge' model has bigger dia alloys that wreck the smooth ride - all for fashion.

Naturally, my two '95 W124s ride on nice compliant original size wheels, and the ride is beyond sublime.... The engineers know best and ignore fashion - I guess that's why they (we) dress so badly!

tim (Chartered Engineer)

 

[Juddian]

I agree completely about the loss of ride quality, but no doubt at all that the 124 will roll noticeably on the original 15" tyres and wheels.

My coupe which has no noticeable suspension wear at all would roll quite badly during spirited cornering.
Its on 17" during the summer period and the difference is astonishing, cornering almost flat at some very high speeds, but you can't have your cake and eat it , the ride is bad compared with originals, but the handling makes up for it.

We are spoiled by the way, i took my son home from work (we work together and still get on, so thats a miracle in itself) a couple of weeks ago, and he couldn't believe just how good the car rode, or how good a proper auto box can be.
He's quite a car nut, but its surprising just how brainwashed the youngsters (27) are by their peers against auto boxes, he was under the impression it would change gear mid corner and upset the handling of the car. (i think they assume these awful automated manual things are true automatics, but you can't tell 'em)

Mind he's got a Subaru imprezza RA superlight, which if you ever get offered a ride in one ...don't... there seems to be no suspension movement at all, and the acceleration and cornering abilities can leave you feeling quite unwell for some time after. Its a little frightening too, i've never been in a car before that can enter a deserted roundabout at 50 and leave it at the NSL for dual carriageways. Just under 300bhp and under a ton, bit too rough for me.

 

[Jensen]

I don't fly around the bends or drive like a raley driver and only put my foot down on the straight. Ride comfort is more important to me, but I prefer the look of avantgarde over elegance. As I fancy an E270/320 W211 I suppose the solution is to buy one with 16" wheels with non low profile tyres.

 

[kid-jensen]

Jensen,

Nice name by the way...

The smoothness of the ride varies enormously between different makes/models of tyres. More so (IMHO) than the difference between, say going from 70 section to 60 section on the same tyre.

If you are thinking about 17 inch wheels on an E-series, but don't want the bone-jarring ride, go for a tyre with a softer sidewall. Japanese tyres tend to be good in this respect ( don't forget that Dunlop tyres are Japanese....and my SP5000's (?) are particulasrly good)

However, some Italian cheapo tyres I have on the front are appalingly hard, but they turn-in well, as you would expect.

The problem with assesing tyres is to get some objective advice, sometimes the Car mags will to a comparitive test, which can be useful to pick out a characteristic that's important to you.

Usually, you have to take a chance and buy them.......it's too late then if they make your Merc ride like an early-eighties XR3.......

My 17 inch wheels have 225x45 tyres and I've had no clearance issues, but I accept that different offsets could give problems.....

 

[MarkCL]

I don't fly around the bends or drive like a raley driver and only put my foot down on the straight. Ride comfort is more important to me, but I prefer the look of avantgarde over elegance. As I fancy an E270/320 W211 I suppose the solution is to buy one with 16" wheels with non low profile tyres.

Actually I'm afraid its not quite that straightforward. I'll try and explain how things work with regard to the wheel & tyre combinations - hopefully it'll help. Basically the wheel related stuff that affects ride comfort and handling are (1) wheel size (2) wheel weight (3) tyre width (4) tyre sidewall height. If you take a base model C180 Classic for example and look at the wheel/tyre combination that comes with it then you probably have something like a 16 inch wheel with maybe a 205 60 tyre on it. The suspension will have been set up to provide a nice comfy ride based on that combination with the shocks and springs supplying some of the comfort and the tyre the rest. The 60 profile tyre has a high sidewall which helps to absorb the bumps etc - however since it is tall it is also fairly soft and therefore when pressing on it will flex during cornering and the handling won't be that sharp as a result. Not a problem if all you want to do is waft around everywhere feeling like you're driving on a mattress but not so good if you want sharper handling and/or the look of larger wheels. Anyway, the important thing about that basic wheel/tyre setup is something called the rolling radius - this is the total wheel dimensions including tyre etc that the speedo, ABS, traction control etc is all calibrated to. You can change the wheel & tyre sizes to be larger or wider or smaller or narrower etc but only as long as you remain as close as possible to that rolling radius.

For the example of a 16 inch wheel with 205 width tyres and a 60 profile sidewall the rolling radius is 2049.58mm. If you decided that you like 18 inch wheels then you need to reduce/change one or more of the tyre dimensions in order to maintain your rolling radius. In the case of 18 inch wheels you could have a number of different combinations of tyre depending on what you're after - for sharper handling a wider tyre with lower profile (shorter and stiffer sidewall) option might be 245 wide but only 40 profile (deep). This would give a lot more grip in the corners, a lot less sidewall flex and overall much sharper handling but at the expense of more tramlining on the road due to the extra width and a harsher ride due to the much stiffer tyre sidewall that would stop the tyre itself from absorbing so much of the bumps etc in the road. To keep a high sidewall and therefore a softer ride even on the larger 18 inch wheels you would need to find wheels that are light enough to not be too much heavier than the stock 16 inch ones so that the shocks & springs aren't too overstressed and then a possible tyre solution could be 195 wide and 50 profile - a narrower tyre than stock (so less physical grip) but still a relatively high sidewall so still a decent level of comfort. To keep the original 60 profile though you would need to drop down to a 165 width tyre on that 18 inch wheel and you would have a lot less grip as a result but still high comfort. All those figures are just theoretical examples to explain the maths involved in tyre & wheel size choice - in reality I don't think you can even get 165 60 tyres for 18 inch wheels as no-one wants that skinny a tyre on a wheel so large, but if they were available they would be the correct fitment if you wanted to retain that high 60 profile for comfort.

The main thing to take from this though is that whatever you decide to do you need to stick as close to the original rolling radius as possible as otherwise not only will your speedo be out/inaccurate, possibly resulting in your getting a speeding ticket etc, but also that your ABS and traction control could be compromised to the extent that they wouldn't work properly, and that could be downright dangerous If you want to figure out your current rolling radius or that of any potential replacement tyre/wheel combinations then you can use this formula: (Rim Diameter (inches) x 25.4) + (tyre width (mm) x (Tyre Profile/100)) x 2) x Pi. Round that to a couple of decimal places and you'll have the rolling radius in mm Stick to within 1% (though I prefer less if possible just to be on the safe side) or so of that figure and things should be fine. Hope that helps clear things up without muddying the waters even further

The easiest thing though is just to ask the MB dealers about the wheel/tyre options for your car as they will already have most of the better/usual options worked out - its only if you want to deviate from those norms that you'll need to get stuck in to the maths

Cheers,
Mark

 

[MBZ560]

Actually I'm afraid its not quite that straightforward. I'll try and explain how things work with regard to the wheel & tyre combinations.

Most informative. At the moment the 560's on deep dish lorinser's wearing Avon 225/50Z/R16 these are due for replacement soon. As I'm ageing fast and simply want to waft around when I can afford the fuel, what's the best tyre to go for a nice smooth ride. Is there a web site that compares ride quality etc

 

[MarkCL]

Hi - glad it was of some help to someone at least As to the tyre choice situation, not sure really but you can try these two websites - might be of some help:

http://www.tyrereviews.co.uk/
http://www.blackcircles.com/tyres_uk

Cheers,
Mark

 

[Tashman]

Actually I'm afraid its not quite that straightforward. I'll try and explain how things work with regard to the wheel & tyre combinations.

Most informative. At the moment the 560's on deep dish lorinser's wearing Avon 225/50Z/R16 these are due for replacement soon. As I'm ageing fast and simply want to waft around when I can afford the fuel, what's the best tyre to go for a nice smooth ride. Is there a web site that compares ride quality etc

205/55/16 has a slightly higher sidewall and the same rolling radius, but may be a bit too narrow if you have very wide rims.

 

[Jensen]

Thanks for all your informative replies, very helpful.

PaulG, I notice you owned a Jensen inticeptor. Thats what I was named after as my dad couldn't afford one. Incidentally I now live in Newcastle upon Tyne but I am from Croydon where all my family still live..........

 

[kid-jensen]

Jensen,

Well, my Jensen is still "resting" in the garage, still shiny and still without an MOT. It's been in that state for about 6 years, so maybe I should look upon it as a retirement project.

In the mean time, the 320 CE is nearly as fast and a lot better-riding (no cart-springs!). Also a lot less rust, though it's catching up..

Spookily, it also does exactly double the mpg: 19 vs 8.5 in the Jensen. With the petrol going up the rate it is, the Interceptor may NEVER come out of the garage. At least it looks pretty.

Really hope the wife never reads this..

Going from Croydon to Newcastle must have been a bit of a culture-shock, I guess the Geordie accent was like a foreign language in the early days.........