Purchase a new A-Spec, found it has no spare. Will a 155/90R18 from spare tire.com fit in the slot under the car?

 

The oem spare tire size I believe is 155/85R18, so that one is a *smidge* larger. About a half inch larger in diameter, 29" in total. As long as the bolt pattern matches the oem it will probably fit, but you can always get under there and measure the space to be sure.

 

You might need to get different lug nuts if the rim for the spare is aftermarket and not OEM. Acura use ball (rounded lugs) and a lot of aftermarket rims for Acura use tapered/accorn/conical lugs. They are not interchangeable. I needed to keep a set of OEM ball lugs with my OEM donut spare when I upgraded my pervious vehicles to aftermarket rims with tapered lugs.