Lotus Elan and Lotus Elan Plus 2 Forums

I agree with your theory and figures, Bill.

As I understand it the original tyres were all 80 section and a 145/80/13 would have 116 mm sidewalls on top of the wheel radius of 165 mm. So the 155/80 tyres specified for the later cars should show a 3% increase in speed (per engine speed) over the 145s and a 155/70 should run 3% slower than a 145/80 and 6% slower than a 155/80. 3% is 1 mph at 33 mph.

I swallowed hard and bought four Michelin XAS FF from Longstone Tyres. They have a short video about correct tyres for the Elan on their website. The Wheel Specialist in St. Albans did a resto on the wheels but then struggled to fit the new tyres due to the sidewall stiffness. Turns out you need inner tubes! Total cost ?785 but the car is transformed. Go for it if you can.
Chris