I've read that with the standard 16" alloy wheels for the 20VT, that 2 sizes of tyre can be fitted, either a 205/50 ZR16 or 225/45 ZR16.

In the real world, are their any other benefits in having a wider track tyre, other than a harsher ride with a 45 profile against a 50 profile tyre.

My rears being Conti Sport Contac 3's that are past their best at 2.5mm - 3mm tread left ( 205/50/16 91Y ), further the fronts being Falken Ziex ZE-912 ( 205/50/16 87V ) that I really do not like.
Whatever I decide for the rear in tyre sizes will determine the front as well, which may determine the fate of the horrid Falkens.

Opinions / Advice please. Thanks.

It doesn't make much, if any difference.

The side walls are almost the same, 102.5mm (205*0.50) v's 101.25mm (225*0.45) so there's no difference in ride quality.

There's much more difference between different types of tyre in the same size than between the same tyre in those 2 different sizes.

Thanks Graham, so in reality stick to the size that's already fitted...but choose wisely on the brand / type of tyre.

Fiat switched to the wider tyre size in late '99 so the 225/45 and the earlier 205/50 size are both considered standard fit.

Some tyres are only available in one of those sizes so I'd pick based on tyre make, model (performance) and price, rather than specifically which size.

You'd expect better wheel protection from the 225 tyres, that is sufficient reason to go for these, although they can cost more.

Plus the 225 make the car look nice from behind. oooh err mrs.

Are you allowed to run 225 on rear and 205 on front, till the fronts are worn out and change them to 225 ?

No reason why not as far as I know, it is what I have on mine at the moment.

Yes, but be careful with the differences in grip at one end (caused by the difference in tyre make, NOT the difference in tyre size)

Narrower tyre would mean more sidewall strength as the rim helps support it more. So the steering will feel more direct and responsive with the narrower tyre.

You are fine running 2 different sizes as long as they are the same across an axle and the larger tyres must be on the rear.
I have 225 45 16 toyo t1r and would swear by them. They wear out quicker than I'd like but the wet grip is awesome.

Whilst I would generally agree that the wider tyre on the rear makes sense I don't think it absolutely has to be that way. I did briefly have 225s on the front of mine with 205s on the rear but prefer 205s on the front - and it was only ever going to have the wider ones on the front temporarily.

Pretty sure Audi fitted the last generation RS3 with wider tyres on the front than the rear

Yes you are right. Wider tyres on front.

never heard of this before !

IMHO wider tires gives more grip, no matter what that so often quoted equation about pressure over contact patch said.
Tires provides mechanical grip, and more patch on the road always mean more grip.
However here is different view of this - AutoSpeed link.
There was few tests available from tyre makers proved that that article is not true, Avon was one of the makers.....It's different story that wider tires matters when you stopping, accelerating, and cornering - and there is "weight transfer".....which pushes every corner or side of the car on it's tires.....and this "push" provides more grip from the tires....wider tire provide logically more grip......
However there is downsides as well - less MPG, more power waste, and sometimes bigger or upgraded brake system......because more grip from tires always mean more heat during extreme stops.....and so on.....
It's my opinion only......

No, no, no - wider tyres cannot provide MORE grip - its a physical impossibility - they will provide DIFFERENT grip, but not more.

For the same tyre, there is only one way to provide more grip, and that is more weight. The only way to provide more weight is with downforce, which the Coupe simply can't give (at least not without some VERY serious mods)

If you increase the width of the tyre, the car still weighs the same, so the contact patch will be a different shape, but NOT a different area. Therefore the characteristics of the grip (lateral, longitudinal, slip-angle etc) will change when the contact patch shape changes, but the overall level of grip will remain constant.

If you lower the tyre pressures, the contact patch area will increase, but the weight of the car will remain the same, so the weight is simply spread over a larger area and the overall grip will remain the same

I accept that you can increase grip by changing tyre compound, but that's not what we're on about here

If stationary,a Coupe front axle wheels supports 750kg weight, about 450 rear axle......
When braking hard did front axle still supports 750kg? If not, is that more weight "shifted" from one end to other?

Weight transfer is very different from weight gain.....

With weight transfer, the extra grip experienced by one pair of tyres (whether front to rear, or side to side), is proportionately reduced on the other pair, so overall grip remains the same

So - a stationary Coupe has the same overall grip as one that's moving and hard on the brakes

I've decided to stick with the 205's at the rear, like they are on the front and keep things standard as it is. All i need to do is shortlist some tyre brands / specs to suit the driving conditions that i will use the Coupe for.

If we assume that this is correct, why not wider tires provide more grip?


Newton's laws stops as soon as the car moves.
Here is short quote form "Tune to win" Book by Carroll Smith, a very useful and understandable source:
The racing tire does not follow Newton's Laws of Friction - which are for friction between smooth bodies. It can, and does, generate forces greater than the loads applied to it. Further it can develop an accelerative force, a decelerative force, side force or a combination of either an accelerative force and side force, or a decelerative force and side force.
In case of combined lateral and longitudinal forces, the sum can be considerably greater than the maximum force that can be developed in any one direction.
Here is interesting page shot:

It does not said "wider is better", but for me its more than obvious....and there is no point for me to give any more arguments, below is the link where anybody can download WORD format of this book, and if have free time - to make his own conclusion.
Tune to Win

I've got a copy of that book. IIRC he refers to this as the traction circle.

Newton's law cannot simply cease to apply simply because the car is moving....

The quote above that Newton's law applies only to smooth bodies is simply wrong - Newton's laws apply to any body

Also, to state "it can and does generate forces greater than the loads applied to it" is questioning Newton. I know modern tyres are good, but I rather doubt they have invented a way to overcome physics.

In any event, all of the above is off-topic - we're not talking about friction specifically, we're asking whether friction (grip) increases if you increase a tyre's width. Until you can prove that the pressure/area calculation doesn't work, then it still applies and therefore a wider tyre CAN'T offer any more grip

According to THIS debate on Physics Stack Exchange wider tyres can offer more grip on cornering because of the contact patch and slip angle. Anyhow see link for more, including points already made in the thread.

My money's with Nigel.

However if the wider tyre looks nicer then you can corner at exactly the same speed But - with extra smugness.
I bet Newtons law doesn't take that into account !!

I don't remember enough about physics as it is a long time since I was a school but a simple question for those who do - if a wider tyre doesn't provide more grip why is it being suggested that in F1 they go to wider tyres to reduce lap times through higher corner speeds?

The wider tyre has less of it's circumference in ground contact during each rotation, so the rubber runs cooler and can therefore be run faster. AIUI that's the main reason that F1 tyres are so wide.

Graham has hit the nail on the head - wider tyres run wider contact patches, which means shorter contact patches, which means less tyre deflection from true-round, which means less heat, which means more durability

It can't be ignored that aesthetics also plays a major part - wide tyres give the impression of being there to handle lots of power and as a result, are presumed to be desirable

Forgetting physics and aesthetics, there's one major problem with 225 45 16s I found this weekend. And that is no one carries them.
I spent most of Saturday trying to find a tyre centre with them on the shelf with no luck at all.
That's ok if you can wait a few days and order Them from eBay but if you've a damaged tyre or puncture that can't be repaired its a real problem.

The majority of my local tyre shops can get 225/45 R16 on next day delivery, even Unusual tyres like my like Yokohama AD08R. Worth ringing your locals back, and see what you get offered.

More on the subject of tyre width vs grip - http://www.enginebasics.com/Chassis%20Tuning/Tire%20Contact%20Patch.html