low profile tyres

[Decron]

As mentioned, your Roomster should be 10% out. Also, by fitting tyres of a size and type that are not originally inteded for use with the car you will need to inform your insurance company

[KenONeill]

The 205/55 has a lower profile, 112mm compared to the 165/70 of 115mm.

The profile of the tyre has a lot to do with the comfort of the ride, the other thing being of course as you said the suspension, however tyres are the easiest thing to change to give a smoother ride.

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Or "a difference in wall height of slightly less than 3%". If you can feel a 3% change in a spring rate, I'd be most surprised. OTOH I'd also be surprised if you couldn't feel a 33% drop in grip during an emergency stop!

Now consider adding the spring travel, say 200mm, and the 3mm higher sidewall represents a difference of 1% in available suspension movement (assuming the tyre can crush flat, which it can't). I'm sorry, but I just consider all this "lower profile tyres ride much harder" (for given make and model of tyre) stuff to be so much nonsense, based on actual numbers.

[The PM]

I'm sorry, but I just consider all this "lower profile tyres ride much harder" (for given make and model of tyre) stuff to be so much nonsense, based on actual numbers.

So what has changed in the past decade, Ken, that has taken ride quality on normal run of the mill cars from quite good to very harsh...

Other than the widespread introduction of wide, low profile tyres and firmer supspenision...

I'm not basing on numbers I'm basing it on my own experience... I gave you an example earlier, 2001 Fabia Estate, nice comfy ride, same model 2007 version, harsh - difference - low profile wide tyres on the 2007 version... you can say what you want, but, to me, my experience has proved to me, at least, that the tyres have a major bearing on the ride and these new tyres make things worse, and I don't seem to be alone with that view.

[KenONeill]

So what has changed in the past decade, Ken, that has taken ride quality on normal run of the mill cars from quite good to very harsh...

Other than the widespread introduction of wide, low profile tyres and firmer supspenision...

I'm not basing on numbers I'm basing it on my own experience... I gave you an example earlier, 2001 Fabia Estate, nice comfy ride, same model 2007 version, harsh - difference - low profile wide tyres on the 2007 version... you can say what you want, but, to me, my experience has proved to me, at least, that the tyres have a major bearing on the ride and these new tyres make things worse, and I don't seem to be alone with that view.

Well, my experience, based on Citroen Xantia with 185/65R15s and my present Octy with 205/55R16s says the reverse; the Octy is less "crashy" and "fidgity" even on broken surfaces (and lets me carry way more speed through several series of bends that I meet fairly regularly; enough so to make a worthwhile difference to journey times all else being equal).

[Dan H]

Ken,

15's vs 16's on a Roomster I make the wall heights as follows:

205 45 16 = 92mm

195 55 15 = 107mm

SO, 15mm more tyre wall height on 15's

There's no direct relationship that I know of between tyre wall height and equivalent spring rate. I do know that those 15mm make a difference to ride comfort on real roads.

[Gizmo]

Well, my experience, based on Citroen Xantia with 185/65R15s and my present Octy with 205/55R16s says the reverse; the Octy is less "crashy" and "fidgity" even on broken surfaces (and lets me carry way more speed through several series of bends that I meet fairly regularly; enough so to make a worthwhile difference to journey times all else being equal).

But that's not just comparing tyres is it, you are comparing two totally different cars with different suspension setting AND different tyres.

I though you would of known that when making improvements or rectifying a fault it is always best to do things one at a time.

I seem to remember jcblincs buying a Superb II but instead of the OE 18" wheels he had 17" wheels fitted to improve the comfort (which it did) and then went on to fit 16" wheels which improved it even more.

[KenONeill]

But that's not just comparing tyres is it, you are comparing two totally different cars with different suspension setting AND different tyres.

I though you would of known that when making improvements or rectifying a fault it is always best to do things one at a time.

And comparing 2001 and 2007 Fabias is comparing like with like?

The traditional view would be that the Xantia with Hydropneumatic, compressed gas springs, and narrower, higher profile tyres, would ride better.

[Gizmo]

And comparing 2001 and 2007 Fabias is comparing like with like?

No it's not, which is why i didn't use that for reference.

For any objective test the different size tyres need to be tested on the same vehicle (not even one that is 'the same as').

[dibujo]

I think the lower profile tyre wall is not made as soft as the deeper profile sizes so maybe that is another factor in the apparent harder ride.

[ncarring]

I think it's fairly well accepted that tyres with a profile below about 55, have a bias towards "sporty handling" and are intended to stiffen the sidewalls of the tyres, thus giving more precise turn-in, and other such "desirable" benefits.

However they also tend to go hand in hand with larger diameter wheels, leading to an increase in unsprung weight, and wider tyres which although they give a bigger contact patch and thus might perform better in the dry, are more susceptible to aquaplaning and far less efficient in snow or icy conditions.

I have friends who deliberately shun wide/low profile tyres, especially in winter, and who are by no means "comfort queens", but very progressive drivers with skills I wish I had.

I recently changed from an Octavia on 225/45R17 wheels to an Alfa 159 on 225/50R17 and the difference is like chalk and cheese. Far more comfort, and reduced noise and crashing, and yet not really any noticeable loss of "sportiness". The others who've driven it, have loved it as a driver's car.

[KenONeill]

Well, this morning it was light enough for me to actually see where the "new potholes" are! I've been hitting a couple of them (right on a natural line) and can now say that they are "something that happens to other people" in terms of ride and steering kickback. I just hear them like if someone else drove over them whilst I was standing at the roadside.

On the point about wheel mass, well that's true as far as it goes, but if the larger wheel is combined with a lower profile same width, make and model tyre the total unsprung weight could actually go down!

[The PM]

Oh dear, sarcastic as well, eh, Ken (1134 post)... well if thats the way you want to discuss things, then we will just have to agree to differ... as far as I'm concerened its the same car, just several years appart in both ride and age, but you abviously don't. End of as far as I'm concerned.

Edited 3 February, 2010 by The PM

[KenONeill]

Oh dear, sarcastic as well, eh, Ken (1134 post)... well if thats the way you want to discuss things, then we will just have to agree to differ... as far as I'm concerened its the same car, just several years appart in both ride and age, but you abviously don't. End of as far as I'm concerned.

Seriously, I thought the newer car would be a Fabia mk2, so no resemblance to the older one except the name. Even if they were both Fabia mk1s with the same engine (if engines differ, so will front spring and damper rates, even if rears are constant), the older one has 6 years wear on its suspension, and I would not expect a car maker to radically change the wheel and tyre fit without changing the the spring and damper rates as well.

[The PM]

Seriously, I thought the newer car would be a Fabia mk2, so no resemblance to the older one except the name. Even if they were both Fabia mk1s with the same engine (if engines differ, so will front spring and damper rates, even if rears are constant), the older one has 6 years wear on its suspension, and I would not expect a car maker to radically change the wheel and tyre fit without changing the the spring and damper rates as well.

They were both Mk1s and the ride quality I related to was not after 6 years use, but within the 1st year (I had it from new), and as regards engines I have also had practical experience of 1.9 and 1.4 2005 versions which also rode better than the '07 version. The (lack of) ride quality in by Roomster just confirms my view in this matter, if I had the option to be able to change wheels I would... perhaps when it comes to change in about 18 months time I will ask them to see if I have any options in this respect..

Ken, you and I will not agree on this, but I am convinced that the deterioration of ride comfort over the past decade has a direct link with the increased use of bigger, low profile tyres/wheels and nothing you say will convince me otherwise, I'm afraid!

[ruzhyo]

I have 205/40/17 fitted to my Roomster.

The ride is not hard or not comfortable.

But in my next set of tires, I would change to 15 or 16in wheels/tires.

The car just looks funny with low profile tires with large gaps between the tires and fenders.

[Calomax]

The car just looks funny with low profile tires with large gaps between the tires and fenders.

I'll agree with that. There's a picture of one somewhere on the forum with black wheels and very low profile tyres and it looks awful.

Mine rides very comfortably on original 16 inch wheels and tyres, and it's got more grip than I'll ever need.

Edited 4 February, 2010 by Calomax

[KenONeill]

Mine has more grip than I'll ever need.

And here lies part of the problem I think. I feel that grip is the only thing that gets you round that corner you totally mis-judges the acuity of, or stops you short of that pedestrian who walked/tripped off the curb just about under your wheels. So you can never have too much of it.

[The PM]

Proper reading of the road ahead will do much more to ensure that you don't have an accident than any amount of levels of grip... Especially in the examples you have cited.

[KenONeill]

1) Not if an optical illusion makes a corner look less acute that it actually is. If you've never met a corner that looks like this, all that proves is that you're less experienced a driver than you think you are.

2) How does reading the road tell you that someone is going to trip over their feet?

[The PM]

1. You shouldn't be caught out if you are reading the road correctly, there are many ways of telling just what the bend in front is going to do, in addition to the road signs, if you go on any advance driving courses (roads, not racetracks) or Police driving courses they will tell and show you the way to do it, its nothing to do with how experienced you are, its how you read the road ahead... and no, I've not yet been caught out by an "optical illussion", and thats after nearly 50 years driving... I have, however been caught out by driving beyond my capabilities in my younger days, though!

2. It won't tell you they will trip up, but using advanced driving techniques you can be aware of pedestrians and other hazards and what they could do and be prepared for the worse.

I think you and I come from different angles to driving, I used to race in my early days and must have been a pain in the backside on the roads, but nowadays, whilst I do still like to drive fast (100+ on the autobahns for instance), in the main I prefer to make decent progress, but within my capabilities and as economically as possible, driving smoothly and ecconomically are my prime considerations. Both of those two and the long high speed runs I do a few times a year make me apreciate a car whic has decent ride comfort, something I much prefer to out and out handling... regeretably todays manufacturers have been watching too much TG and seem to think that most people want ultimate handling over ride comfort!

Edited 4 February, 2010 by The PM

[KenONeill]

1) By using the word "shouldn't", you're admitting that it can happen. The first time it ever happened to my Dad (that I know of anyway) he was towing a caravan, so claims he was racing are shown to be totally fatuous!

2) If you've never been caught out by someone doing something genuinely unpredictable, you're lucky, not good, and the sooner you at least admit the fact to yourself the better.

3) I'm not so sure. Yes, I like to make progress, but I don't see how that stops me retaining reserves of personal and car talent. What I am saying is that I want to keep a reserve of car talent over driver talent, and compromising available grip in the name of a softer ride compromises the available car talent.

[The PM]

1. The "racing" comment was put in because observation skills on the road are different to those on the racetrack... as I'm sure you know. No-one is perfect and can get caught out, thats why I used the word "shouldn't".... perfectly acceptable use of the word, and not an admission of anything except the obvious that none of us is perfect!

2. I have never said I haven't, in any of my posts, all I've said is that proper observation is worth far more than miles of grip... its best to be prepared and aware and then react than it is to have to rely on the car's grip to get you out of trouble because you didn't observe the hazard in the first place. To turn your comment round, if you don't believe that then perhaps you need to face facts.

3. Believe it or not, you can have very good ride comfort and <safe> handling... but obviously you don't!

Perhaps you drive your car to its limits all the time and need all that grip you seem to think you do, I don't, and I also try to drive well within both mine and the car's limits, a more compliant ride to me is far more important than mega grip, and, driven properly, a car set up that way is no less safe than any other and a lot more comfortable!

Edited 4 February, 2010 by The PM

[Calomax]

And here lies part of the problem I think. I feel that grip is the only thing that gets you round that corner you totally mis-judges the acuity of, or stops you short of that pedestrian who walked/tripped off the curb just about under your wheels. So you can never have too much of it.

Probably what I should have said is that it has considerably more grip than any car I've ever had before. And if all this ultimate grip was essential then tyres would all have formula 1 type compounds.

Edited 5 February, 2010 by Calomax

[KenONeill]

Probably what I should have said is that it has considerably more grip than any car I've ever had before. And if all this ultimate grip was essential then tyres would all have formula 1 type compounds.

You might be surprised just how hard F1 tyres are (have to be to cope with the aero loads).

[Gizmo]

You might be surprised just how hard F1 tyres are (have to be to cope with the aero loads).

Not from my experience they are not