If you were to switch to 15s your choices are much wider to your choice of tires. The rim I'm on are 15x7 BBS and they work fine for comfort and handeling also changing your supension to a softer or more forgiving. When I injured my back several years ago, riding in a car or any thing with wheels nothing helped, I just had to grit my teeth and hope the pain killers worked
, Changing to a lesser performing tire could help the ride say maybe touring tire, what about your driver's seat is it comfy enough? A wider tire may give you the softer ride, check with your tire dealer they will probly know more than I about tires. Good luck and hope your recovery is soon. Not to get too personal, what, and how injured your back? Mine was a compression fracture of the mid lower back due to a fall rock climbing. All is well now on occasion have a spasm. The recovery was painful and wasn't over soon enough.
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cheers
