Hi there to you all ; I hope you don't mind me posting this, but I do know an awful lot about tyres & not much about anything else & it really supprises me how people look at buying tyres ; it is without a doubt price driven, which I understand, but honestly, you cannot do better than spend a resonable amount on them, as they really are the defining component on how a car rides, handles, brakes, steers, sounds & uses fuel.
I worked for Goodyear (also owners of many brands (Dunlop, Fulda, Sava & others) as an original equipment test driver for over 30 years & I can assure you that it is a tough business, as even the OEM's don't want to pay for anything !!
So my point is this ; OEMs & suppliers work hard to get the best tyre possible, for several years before any car is launched onto the public. The selection of tyre sizes are an integral part of the initial package & affect may things ; weight, wheel envelope, relating to wheel arch clearance, steering lock requiements, ride height, snow chain clearance etc, fuel consumption to name a few.
We (tyre suppliers) work with them to meet these & other requirements - comfort, NVH, handling braking, wet grip, rolling resistance & so on & finally the 'best' are chosen to be suppliers on a technical level, then the price war begins. The 'best' performers do not always get the business !!
So, basically, my advice is please stick to the OEM tyre sizes & you have a chance of getting close to the OEM performance criteria, to match the vehicle, especially if you stick to the big names - GY Dunlop, Pirelli, Conti, Michelin, Bridgestone to name a few. This is particularly true when a car, such as the A2, uses non popular sizes ; this means that a tyre you buy in the 'correct' size may actually still be the original OE approved construction !!
I understand everyone is on a budget & tyres are one of the highest running cost of a car, but the fact remains, especially in countries that use the Certificate of Conformity (CoC) as a reference for giving a valid MOT pass, it will invalidate your insurance if you do not use the OEM dimensions or have an approved exception to the CoC tyre sizes, eg when the size is no longer made.
If you can't or don't want to stick to the OE sizes, then the things to consider as a minimum are ; The OD should be close to the original for speedo accuracy, the speed index should be at least as high as the OE tyre, the load index should meet or exceed the OE tyre & the rim width you use should be 'legal' - that is to say within the ETRTO allowable sizes for any particular size of tyre. Things such as wheel arch clearance, reduction in steering lock, due to touching on other suspension parts etc. are not 'illegal' as such, but a keen inspector may reject a car for these types of problems, along with exposed wheel rim flanges, due to small tyres fitted on wide rims for that 'cruisin' look'.
As far as the driving experience of the car goes ; tracking under acceleration or on bumpy roads, general steering feel and feedback, comfort, noise and fuel consumption are almost inevitably worse when fitting larger sized tyres, versus the OE sizes & often, even the largest OE approved size works less well than the 'medium' size approved size, but does meet the requirements of the OE Marketing departments need for pretty pictures for the brochures !!
Sorry for the long winded post (not intended as a lecture !), but a tyre makes or breaks the car & often, the people who travel in them !!!
Yours, MartinH
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