I have visited Wheels of Steel a couple of years ago, but he wasn't open that day although it was his advertised times (Monday-Friday 10.30am-6pm). Best to ring Jeff Williams on 020 7629 2813 or 020 8505 0750 to check if he is open the day you want to visit (I presume the first number is the shop number.)
By the way, the entrance to the basement is in Davies Mews off Davies Street at the rear of the building. If you go in the main entrance you have a complex route to follow to get to the basement!
Regards,
John Webb