Andrew.
5.50/5.60 by 16 were standard tyre for the Ace Bristol and a 15 inch option was available from mid 1957, During the past 12 years I have run dunlop racers on the road and track until Avon and others reintroduced 16 inch tyres. Then the change to Avons proved better on the road in all conditions especially in greasy wet conditions.
John Arnold run 15 inch Avons on his Ace and they were very good on both road and track, however I believe they too were 5.50 /5.60 wide (165mm) some Aces run 175 or even 185mm tread width but I would have thought they would burn the paint off the rear wheel arches asumming they would ACtualy clear, Barrie referes to 205mm lower profile, they would extend beyond the standard Ace bodywork, unless you have modified to lipped bodywork/ arches as per 260/289 Cobra, these were designed to cover the standard 15 inch by 5.5 or 6 inch rims as suppliued by AC Cars " Thames Ditton". 185 x 15 inch with 70% profile.
Andy Shepherd and a few others run 15 inch wheels on their Ace Bristol's, will have a word and pass on their comments.
The Ace requires a softer walled tyre, not sure if the Blockley is the most suitable for the Ace, great on earlier cars and very good with XK 120/140 jaguars, however they are heavier and more touring than Sport..[
]
(Personal opinion. Hopefully not putting noses out of joint)..[B)]
Keith.