After selling my plus wheels with 225s on a while ago I've been using a set of stock 20vt rims with 205s on.

As soon as I put them on, the car seemed to be far worse getting the power down to the road. Ever since the forged rebuild I'd always thought 'it may only be 315bhp, but I could put every one of those horses down to the road without any problems' I'd just nail it and it was away, yet when I changed tyres all that changed. If I floored it the wheels would spin a lot and then I'd get viscious weaving from one side to the other, losing grip here and there which really took some keeping under control.

So on Friday I swapped back from Pirelli p6000 205/55/16s, to continental sport contact2 225/45/16 and the difference is amazing. I can't believe how much better she grips and puts the power down to the floor. I've also found a lot more grip in the wet. I won't be changing again.

I remember when I made the change on my first coupe running 291bhp. It made a hell of difference......must add that to my list of things to do on my new one.

Funny you should say that I'm just refurbing some wheels with 225/46 16 Toyo T1 rubber - looking forward to fitting those babies soon

You won't believe the difference Mike.

Althought the 205 dunlops you bought from me were second to none of course

I replaced a worn pair of P-Zeros with some Conti Sport Contact 2s recently and noticed a big improvement in Traction and of course a massive improvement in the wet (although you'd expect that with good, brand new tyres). Funnily enough, the ride seems noticeably more compliant as well. However you do pay for all this and it will be interesting to see how they last.
Overall they are certainly the best I've tried so far, from a dwindling choice at this tyre size, and a pleasant surprise from what I always considered to be a German Executive car Tyre.

I've got Conti Sport Contact 2s on myself, amazing confidence in the wet at high speeds, very planted and stable.

I don't realise just how much till I go out in similar conditions in the Ford Ka

Just waiting for Nigel to post on this thread

your probably find the difference is in going from pirelli p6000 to sport contact 2 as much as its is the sizes.

No need - jonone has just done it for me in the post above

Beat me to it.

P6000's? Really? Shocking tyre.

When I went to the track in the HGT I used to put P6000 on the back. Especially in the wet it meant loooaaads of oversteering fun!

I'd had good year eagle f 1s on 205s too and found them equally crap so deduced it must be the tyre size rather than brand.

and 225's definitely fit 20vt alloys?......

...anyone got a pic?

Yes - the Plus's had them fitted as standard from the factory.

Yes, but the plus alloys are a different size......

No, they're not - all 20vt alloys are 7" x 16"



Definitely not - (Jimbo's been waiting for this ) - the width of a tyre has no bearing on the amount of grip

I'd much rather run a good brand of 205 that even a mid-range brand of 225, never mind a budget tyre

Even the high end stuff have noticeable differences between them, just last week i switched from Potenzas to a set of new Michelin Pilot Sport 3's and they are awesome! Highly recommended.

I still don't get this. So you're saying that a Lambo Diablo with 355 wide tyres has no more grip than a 2CV with a 165 wide tyre?

You have done it now.......any minute now.... wait for it

Definitely the same, I had tyres swapped between a set of plus alloys and a set of 20vt alloys - no problem at all.

Annoying as if I'd known I'd have gone for pilot sports rather than toyos

No - what I'm saying is that putting 355 section tyres on the 2CV will not give it any more grip

The Lambo has more grip than the 2CV because it weighs more (and lots of other stuff, such as better suspension geometry to keep the tyre perpendicular to the road, camber & castor settings, trail, toe etc etc)

its simple phisycs, 205 tyre will give better traction than 225 there is no 2 opinions about that. I test some diferent 205 on myne becase of destroyng them in roads of bulgaria.
Conti sport 2 is best for now, barum its cheap crap but eagle F1 disapoited me. Now i have new michelin pilot but i will test them after winter.

the difference in rolling radius between the two tyre sizes suggested is 22.5mm, which is fairly substantial so not great for gearing, etc. the tyre which is smaller in height (the standard 225/45) should technically enable marginally faster acceleration than the taller tyre.
when it comes to handling the 225/45 is the factory fit tyre, so we can assume a certain amount of optimisation was done during the design and testing of the car to make that one more suitable.
yes the wider 225 should theoretically offer better handling, but in reality a difference of 20mm on a car such as a coupe is infantessimal and the real benefits are felt by using a quality tyre specced to the manufacturers recommendation

Surely a wider tyre has a greater contact patch with the road, and therefore more grip? I'm probably wrong but you'd think that'd be the case. If it's not then would anyone explaining why? (somebodys chance to show off)

I wouldn't touch budget tyres in any size. A car with as much power as even a standard 20vt (or 16vt) needs decent rubber under it.

I did notice JBTs coupe at santa pod - 500bhp and mis-matched tyres, some budget ones. Surely not a great idea

Your calculator is broken

The radius of a 205/50 tyre is 305.7mm, with a rolling circumference of 1,921mm

The radius of a 225/45 tyre is 304.4mm with a rolling circumference of 1,913mm

The difference in circumference is just 8mm, or 0.4% - the effective difference on the road is that the wheel will rotate three time more per mile

I defy any one to be able to detect the difference

Yep - very poor for performance. They are a hard wearing motorway tyre - I had them on my coupe when I bought it, and I found lots of excuses to wear them out and replace them.

Oh thank God!! Finally my chance to excel. I do hope I don't blow it!

The grip is lateral resistance to slip: How much lateral force you can exert on the tyre before it skids. The grip is roughly calculated as the total downward force multiplied by the coefficient of static friction (whatever), so the area of surface contact doesn't directly come into the calculation.

In other words, with a larger contact area, the force exerted per unit area is reduced, so the grip per unit area is also reduced proportionately. The total remains the same.

Ok, that makes sense. So the smaller th contact area, the more pressure is exherted on it.

So why do F1 cars have big fat tyres if the width doesn't make any difference?

Also I used to ride motorcycles a lot and the more power the bike has, the fatter the tyres got. Must be a reason for it. If not grip, then what?

Because the SHAPE of the contact patch does have an effect on handling - a wide (but short) contact patch gives better lateral grip than a long thin one

Additionally, a formula1 car can do something that the vast majority of cars can't. There are actually only two ways to increase grip:-

1) increase the co-efficient of friction between the tyre and the road surface - this can be done by using a stickier compound of rubber or changing the road surface
2) Increase the weight of the car so that there's more weight acting on the contact patch(regardless of how big it is)

Its No2 that F1 cars can achieve - they can effectively increase the weight on the contact patch by adding downforce - there is no difference between real added weight and aero downforce

So, I need to stick to the Continentals (must be stickier rubber) or ensure I only drive on race tracks or shellgripped road surfaces