Friends are telling me that if I put 18inch alloys on my Coop, The performance will change drasticly.

The weight of the 18inch rims&tires is 23kg, dont know how much standard rims whey but I changed few months ago from 15->17 didn't felt much performance change.

BTW im fitting Alessio Action 18X8 & Federal SS595

A Punto HGT challenged me to a dragrace...I hope I won

Mine is 20V VIS with sport filter.

It will be close and down to the driver, not the car. If the HGT has good tyres or a good/lucky driver, you may lose

From memory, 23kg is a fairly substantial increase from standard - I believe a 20vt wheel (with tyre) is around 18kg. I'd expect the VIS wheel to be very similar. If so, 23kg represents a 27% increase

If the 18's have a larger outer diameter it could be harder to launch on them and your gearing will be longer resulting in a drop in acceleration.

Only braking performance will be better for sure, if not appropriate rims used handling wont change, but there is room for improvement......

The effective rolling radius is going to be bigger on an 18 inch alloy, no question. Basic physics, there will be a reduction in acceleration and the feel of the brakes will change as you'll be using a bigger lever effectively.

will you notice on a 2 litre engine? Not enough to worry you.

With the correct tyres the rolling radius should remain constant, so the gearing shouldn't change.

However, the heavier rims result in a rotating mass somewhat further from the centre, and *that* acts like an effective increase in car mass; from memory, the effect is worse in lower gears and can be the equivalent of an extra hundred kilos or so.

I did find a web page that discussed this in detail, years ago, but I can't place it now.

Depends on the weight of the rim as well as the weight of the rubber / webbing / ... of the tyre. Some tyres weigh more than lightweight alloys, so the larger rim actually could decrease the total weight.

But going to a larger size rim will most definitely decrease the deformation of the tyre in corners, thus having a more constant contact patch and potentially dramatically increase the grip.

It will change between a 15 and 18 inch. What happens is that the taller side wall of the 15 inch tyre deforms more than the lower profile 18 for the same load. If you measure the height from the ground to the wheel centre (effective rolling radius)for both applications you'll find it greater for the 18 inch alloy. By how much varies massively based on tyre choice and other things such as atmospheric conditions.

I see your point - and I suppose it depends on the definition of 'correct' tyres!

I'd argue that 18" is too big for the car.

.. but Neil, that was a standard Fiat option at the time! Azev E's.

Any increase in unsprung weight will be detrimental to the handling, an increase of 4kg per wheel will be noticeable.

The thing I'm worried are dramatic changes, not small.
The tires I'm fitting are 225/35/18,currently I'm using 205/40/17 with toora rims, the ride is a bit harsh but I think its going to get harsher* when I fit Apex -40mm springs and these new 18".

But in the end, the car will look awesome because the 17" look a bit small(for me), will grip better and won't be wobbly in the corners.

My biggest fear is the overall performance will change dramaticly?, will my brakes be able to handle this (EBC ultimax discs&pads), and will the ride be too harsh for long trips....(around 400km)?

Fit Bilstein B6 shocks (and cut the front bumpstops a little) and it will be ok. The tire wall height of a 225/35 and a 205/40 is similar.

You should be running 215/40/17, not 205/40/17. That said, your sidewall is currently 82mm; on the 18s at 225/35/18, it will be 78.8mm so will be firmer still, but not by much.
Here's a coupe of sidewalls for an idea of how stiff they will be for reference:
205/50/16 102.5mm
225/45/16 101.3mm
215/40/17 86.0mm
225/35/18 78.8mm



Your performance will not change as a result of the wheel / tyre change, even if it gives a different rolling radius. If they are heavier, it will be slower.

Well.....I changed the tires and rims today....i'm very suprised with the results...

The power loss is insignificant,second to none, traction is whoooole lot better (mind that I have brand new tires/ vs. previous 4 year old),and most suprisengly, the ride is softer....YEAH...softer, mush softer than on the previous 205/40/17. Don't know why, but the ride is now superb

I'm lovin it!

It's great to have the feedback and to hear that you're happy

Well after 3000km on new 18 wheels, I must says that performances are affected, also the consumption drasticly changed as I'm now in 10,5L/100km teritory...

I figured that the weight of the alloy is about 12kg, as to previous 10kg, it makes a lot of difference, especialy at high speed, car really stugles over 190km/h so I thought I would change the alloys in spring to
MAK XLR 8,7kg alloys. I think that it will help peformace and fuel consuption .....what do you think?

MAK XLR 8x18

Don't mind the picture, they also have 4x100 and the cost is 145€/alloy which I think is great....hope that for my 18 allesios I should gets at least 300€ as they are freshly refurbished...

And the pics