Tyre Dilemma

I have always planed to use 13" wheels on my Berkeley project car. My previous car had 13" wheels with 175/50VR13 tyres made by Yokohama. I had always resisted going too wide on my three wheelers on the assumption that the low car weight would not give enough lbs/in squared over the contact patch. I once used a low profile 185 on the back and found that although excellent in the dry and excellent handling up to 150mph but was a bit disappointing in the wet aquaplaning at a lower speed than previous tyres. But that was 14 years ago and tyre compounds have improved since then.

I have now learnt that the contact patch will be the same no mater how wide the tyre, the thing that changes is the contact patch shape and the size is dependant on tyre pressure.

My dilemma is that the new car will be capable of speeds well in excess of 150mph and that would require a rating of "Z", and to my knowledge that rating is not available in 13".

I may be worrying unduly here as the difference in compound between VR and ZR is only slight and the speed rating is based on the ability to withstand higher temperatures and as temperatures are weight related my lighter than normal car may be ok.