Hi! Sprackers
Correct tire size for R4 is 135/80/13. or 145/80/13
You can fit 135/70/13 and everything will be alright but it is much harder to find that size and usually they are more expensive than 135/80/13
About your route. That is it. UK to Austria and Germany, no norther part of Europe, Sweden, Norway, Finland?
If that is it than you do not need studded tires. and also they are forbidden in whole europe except high north part of Norway, Sweden, Finland, and even there you can use them if there is big load of snow and ice on the road. Do not know exact law but it is something like that.
Winter tires are mainly made for low temperature (below 7°C) and with lot more small grooves (than summer tires) for good usage on snow and ice as those grooves are dig in snow and ice.
Left is summer tire, right is winter tire
One big difference between summer and winter tire is rubber compound that they are made of.
Winter tire is much softer than summer tire, and that softness is advantage in winter time at low temp.
Bellow 7°C summer tire become more plastic than rubber while winter is still soft.
I live in Dalmacia, south part of Croatia where snow is seen once every 4-5 years and then it is catastrophic.
But winters are also hard with low temperatures that goes below 0°C and lot of rain.
In that conditions you can easily find curve on the road that is icy.
So i am driving on winter tires from start of November till end of March.
Roads are mostly dry or wet from rain, snow is really rare.
I did not feel any difference comparing to summer tires.
Winter tires are little bit louder than summer but you feel difference only first few days. nothing major
If you drive winter tires in summer than you will fill difference, because winter tire rubber compound start to become to soft, like a chewing gum -not that they are sticking all around road - but you can feel that is more wobbly, and not following your steering wheel correctly but with some small delay.
But that will happen if temp is really high - more that 25-30°C (like this days here in Croatia 38 to 40°C)
If you drive it til some 20°C that you still do not feel much.
There is lot more to talk about this topic but i hope you got impression.
From your route, and time of the year, and time period (not more than two months?) i believe you need only 4 winter tires and tire chains (if snow is really big on the road)
practice putting chains on tire while is hot so that you know how to put them on tires when you need then in winter (fingers get really cold really fast when you do that on road side)
Here are my Barum polaris3 winter tires 135/80/13
First one is brand new as i use it as spear tire. 4 others are on the car.
This is how they look after one winter here in Dalmatia
just for fun.