The car seems beautifully set up with the fixed geometry suspension and stock 175/70-r13s up front and 185/70-r13s in the rear. Am I going to screw up Colin’s beautifully designed suspension geometry if I switch to slightly smaller diameter, wider, sticky Toyo 205/60-r13s rear and 185/60-r13s up front?
Way back in the late 70’s when I first got my S2, it was on the stock steel wheels/tyres. I acquired some genuine 5” width Minilites to install after the rebuild. They came from an Elan and 5” was apparently about the maximum on the rear without bashing spring perches etc.
The Minilites came with Avon 165/60 tyres and those tyres absolutely transformed the car.
I’ll leave out the fact that, over time, the tyres somehow developed an ‘out-of-roundness’ which translated to an increasing vibration which I couldn’t find for ages.
I chased that vibration through suspension joints, U-joints and practically everything till the local tyre guru picked it up while doing the wheel balance yet again.
Anyway, all else being equal, lower profile tyres will cause the car to react faster than a higher profile tyre.
It’s the same with stiffer springs.
Sometimes it’s easier to visualise these phenomena in terms of weight transfer.
While the weight of the car hasn’t changed, lower profile tyres or stiffer springs will permit a faster change of state - e.g. going into a corner.
That’s a good thing on the track but you might not like it if you happen upon a patch of damp leaves on a shady corner of a twisty mountain road.
Caveat: I’m certainly no expert.