Just remember fella's (and talking about c3's here) irrespective of whether your car is a 200hp lo-comp ratio emission era vehicle or hi-comp LT1 or 435hp 427 it is generally going to be capable of 120 mph.
Admittedly only a few of us are likely to achieve that speed (albeit illegally) on our septic isles - perhaps given the right conditions if touring Germany?.........
225/70/15 sized tyres now seem to be used exclusively on vans and commercial vehicles. Only a few of commercial vehicles will be capable of travelling in excess of 100 mph.
Some of the really cheap far eastern/third world tyres are rated at even lower speeds (90 mph) than the ones below.
If you've bought your C3 in the last couple of years and were impressed with the seller 'kindly' putting a brand new set of tyres on for you............ perhaps you need to think about it in another light........
This is arguably a difficult comparison given that our vehicles wouldn't have had tyres originally fitted (when new) that conformed to any form of speed or load rating.
Some of the tyres available (and legal) for use on our vehicles.
BF Goodrich 225/75/15 have an 'S', (112 mph) rating
Hercules 225/70/15 have an 'T' (118 mph) rating
Galaxy 225/70/15 R1 RWL have an 'H' (130 mph) rating
Galaxy 225/70/15 8 ply V2000 whitewall have a 'R' (106 mph) rating
Cooper Cobra 225/70/15 have an 'T' (118 mph) rating
Look 'out of the box' and you'll find these whilst differing sizes an aspect ratios could be used.
Avon Turbospeed 255/65/15 with a 'V' (149 mph ) rating
Or this
Avon Turbospeed 235/70/15 with a 'V' (149 mph ) rating
For those with earlier C3's, perhaps
Vredestein 215/70/15 Sprint Classic with a 'W' (168 mph) rating
I quote this from a UK tyre specialist
The tyre speed rating is clearly displayed on the sidewall of each tyre and indicates the fastest speed that a driver should not exceed when their vehicle is fitted with those specific tyres. The speed rating numbering system run from A1 to A8 in sequence, whilst the letters run from B to Y.
"Can I fit a higher or lower tyre speed rating?
When it comes to changing tyres, there is no problem with fitting new ones that have a higher speed rating than your existing tyres. However, you shouldn’t fit tyres with a lower speed rating than the manufacturer’s original fit, as this can invalidate your insurance."
And we haven't even touched on 'Load Rating' or tyre 'Aging' yet have we?