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MG MGF Technical - Tyre Options

Tyre Options

Ok I know its not an F
but I have a quandary regarding the tyre minded of you all.

Is it possible to change my rears on an overpowered ZT260 from the standard 225/45R18 to 225/40R18? or
to 235/40R18 or 245/40R18?

your comments please?
Neil

Yes you can Neil - but by keeping the profile at 40% you will be increasing the rolling diameter of the tyre - and thus ruining the speedo calibration.

If going for a 245mm wide tyre, then you may want to consider dropping the profile to 35% (this is a guess; I've not worked out the rolling diameter, but there are websites that will do this for you)

The next question is 'how wide are your wheel rims'? Fitting excessively wide tyres can lead to the sealing bead not doing its job properly.
Rob Bell

Yeah I have been considering this. The rolling diameter between the standard
225/45R18 is 3mm more than 245/40R18s

who would be able to tell me whether the 245 will still fit the 225 rims?
Neil

Neil,

Have a look at this site, it has conversion tables that will tell you all that you want to know -

http://www.chris-longhurst.com/carbibles/index.html?menu.html&tyre_bible.html
David Clelland

20mm seems safe enough!

Might go for it!
Neil

How wide are your wheel rims Neil?
Rob Bell

Dont actually know that one Rob

Any out there know size of standard ZT260 rims?

18inch by...XX?

I would have thought it waould have fitted ok I am now a little worried by the lady at mytyres.co.uk helpdesk saying it'll rub the bodywork...??? will have a goood look around the car to see how much space there actually is

Neil

I would have thought that there is plenty of bodywork clearance Neil on the ZT - maybe she's worried about the wheel arch on full suspension compression?
Rob Bell

Neil,
It is quite important, because wheel size (width) will determine the maximum/minimum tyre size.

It should be in your handbook, if you cannot see it embossed on the wheel.

Adrian
Adrian Clifford

got this from Rog of the MG club

My running report on my 260 in the April Enjoying MG included referring to the need to change the rear tyres at 10100 miles, down to the tread wear indicators, perhaps a little into them on the inside edge of the nearside tyre, but mirroring your experience. Richard Monks car has also seen the need for a replacement rear pair of tyres too with a few less miles than mine and most use is with his wife. Then having had time to chat with people at Longbridge and across the road at Sport and Racing seems to indicate that they thought 10k was good! 7 to 8k was referred to as a not uncommon life for rear tyres and double or more for the fronts. Indeed now at nearly 14k I find plenty of life left in the front on mine.

The May issue I report on the driving experience on Dreadnoughts supercharged 260, but in the context of this message I also found some very, very interesting experience with the Toyo Proxes T1R tyres fitted to that car (standard sizes). The ZT135 we went to Scotland in had the standard Continental tyres and I found that the car was less than fully secure on some of the local roads with damp patches. The same roads in the same conditions with the Toyo's with supercharged V8 and traction control off was far better and next to no slip at all. No indication on how long the Toyo's would last bearing in mind that the general rule being more grip - less life!

Further information is that there were several ZT385 development cars running at Longbridge. I am told that they were using standard 18" wheels but fitted with 245/40x18 tyres for a marked improvement in stance and apparently better road grip.

Interestingly this is the size to go for to retain gearing and speedo accuracy as the size difference to standard is just 1%.

SO I BOUGHT TWO 245/40s!!
Neil

This thread was discussed between 09/05/2005 and 12/05/2005

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