I think the plural would be better, but 'motorcycle' is a great keyword in itself. Even though it's a bit long its got alot of potential. Great for a motorcycle sales site or referral to actual sales sites. I would say low to mid $xxx undeveloped with potential for high $xxx.
I'd have to agree that the plural would have been better, as shown on the WordTracker result. But this could work too, I'd say mid to high $xx undeveloped, probably more with an end-user.