Hi all - I know that this has been discussed many times but i'm hoping someone can clarify a few things for me.

I have a set of Michelin 205/80/16's on my Discovery ('91) which need replacing. After looking around for available sizes and using a tyre calculator I see that 235/70/16's will make a 0.14% diameter difference. Can I just put these on and start driving straight away or do I need the gearing rectified? I also saw that 235/75/15 will leave 0% difference or will a 15" not fit at all?

Lastly, as I'm based in Russia and need to take a 1000km round trip out of the country in a week, I want a set of good all season all terrain tyres that will also give me grip on the sometimes icy roads. I'm thinking about Scorpion A/T's as they seem to be a good all round tyre - but concerned that for mainly road travel it maybe less than ideal. Can anyone recommend another tyre? As there is only about 2 weeks of winter left, I do not want to fork out for winter tyres and then another set of summer tyres when the snow melts, which is why I need something versatile.

Any advice would be greatly appreciated.

thanks,

Alex

I can only answere the size question, The number at the end (16) is the wheel rim size so 15's won't fit on your 16 rims. I have as standard the 235/70/R16 on mine so should not make any difference to you.

Thanks James - at least I am now positive about the correct size. Would I need the gearing looked at though?

I would not have thought so, the only thing is that it my change the reading on the spedo however don't forget when you buy new tyres you start at 7mm tread and go down to a minimun of 1.5mm so that in its self is quite a difference on the roling radious of a tyre.

The 15 inch ones would be ok, but you would have to get a set of 15 inch rims to suit. As James says, the larger 235's will have a larger rolling radius but shouldnt affect your speedo too much, after all, there is a built in error margin by most manufacturers, it helps them meet their polution and mileage responsibilities.
Whatever tyres you end up with, make sure that you have all the same size right around the vehicle, including the spare. Different rolling radius tyres can have a detrimental effect for 4WDs.

Theres a very nice gadget here for calculating the difference in your speedo reading
http://www.miata.net/garage/tirecalc.html

I can heartily recommend the Cooper ST discoverer tyres as an A/T. I havn't done any real muddy trips yet but they are good on road, ice and sand. My own ones are 265/75/16 but without wheel spacers or a bigger offset on the wheels they foul the radius arms. Ohyeah, my Disco has been lifted 3" too, so probably not a good idea to use that size on standard suspension!