If this space-saver tire's outside diameter is significantly different from that of a standard tire, I wonder how traction control would react.
The manufacturer, K.O.M. Wheels, says that they try to keep the rolling radius difference to below 2.25% to 3% of the OEM wheels. They show how they calculate this using a standard tire size 225/45r17 with diameter of 24.97.
Tire size 225/45R17.
First, multiply section width by profile
Section width (225) x profile (45) = 10’125
Secondly, divide (10’125) by 2540 and multiply by 2 = 7’972
Thirdly, add the rim diameter (17”) 7’972 + 17 = 24.97”
Full sum below:
OE tire size = 225/45R17
1, 225x45/2540x2+17 = 24.97 (“)
Space saver tire size = 145/70R17
1, 125X80/2540X2+17 = 24.87 (“)
Which is a 0.10” or 0.04% difference
Maybe 'space-saver' in this case is a bit of a misnomer - more a light-weight temporary spare
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch Rial X10-i wheels, EVoInnovate EVSE