Do a search on the darkside/car tire threads and there are some pretty wide ones, but it doesn't take much till you will have to come up with a replacement for the braking drag link. Below are two from the FJR forum that I would NOT recommend, because they are killing the fatigue life of the drag link. (The rod alternates between tension and compression every time you alternate between throttle and brake.)
Flat rod with a bend in the middle:
Hogging out the existing rod:
I'm not sure what's up with that flat rod with a bend in the middle. First I've heard about that variation. And no, it's
NOT recommended. The second is an OEM tension arm that someone cut partway to make narrower at the tire area. The carved it out to the sidewall of the arm only where the tire needed clearance. That is
NOT recommended. The OEM part is
aluminum. I recommend replacing the tension arm with a
3/16" thick steel or
stainless steel flat bar. There have been zero issues of deformation with a steel flat bar. A couple of people have used 5/32" steel or stainless steel, which has not displayed any deformation, but I still don't prefer.
Note that the fracture curve for aluminum is much more finite than steel. If it's continually flexed, it's going to break, it's just a matter of when.
Note also, this is on a FJR. You will not get that wide a tire on the Super Tenere.
-------------------------------------------------------------------------------------------
My wife has a '16 GSA using the tire sizes stated at the beginning of this thread. Some first hand personal experience is that you don't want to run that 170/60/17 on the rear. Not even on the rear of the GSA! The lugs cracked on the knobby tires she has used between the lugs. No tire spinning or heavy off road use and tire pressure at 36F/42R with TPMS in use. After pictures and communication back and forth with the tire manufacturer, it became clear that
THEY don't recommend that width tire for a 4.5" wide rim. They recommend a 150, not a 170. It would be even worse to mount it on a 4" wide rim. The tire carcass is being pinched already on the 4.5" wide rim and causing more stress to the tire. The same tire in 150 width, mounted on the 4.5" wide wheel has shown zero cracking. Same date code. So much for what the manual says from the bike manufacturer.
It is a BMW though.
You're not going to die if you mount the 170 tire, It will probably fit. If it doesn't, it will only rub on the brake caliper tension arm, (what CW is referring to as the drag link). Replacing that with a steel flat bar will give the clearance you need and be as strong or stronger. Just use the aluminum part as a guide for the length and holes.
3/6" thick, 3/4" wide and radius the ends for clearance as the swingarm moves. That said, the wider tire on the narrower rim is NOT ideal. The 170 shouldn't really be run on the 4.5" wide rim, never mind the 4" wide rim. Not only will the tire shape be less than ideal, the tire carcass will be stressed more and fatigue faster in dynamic conditions.