Running 650b on new Specialized Roubiax

I’ve been riding my Roubiax all stock since April and have thought about getting a second wheel set to run a gravel bike set up.
On 700c tires the Roubiax can take up to 33 tires but I was thinking of running a set of 650b for extra clearance and hoping to run something wider than 33s. Has anyone done this or is this a silly idea?


I’ve been mulling it over for my Giant Defy Disc (2016 alu model). I’m not convinced enough of getting clearance to have pulled the trigger on the wheelset to be honest. I’m going to attempt to borrow some wheels and attempt a test.

It really wasn’t on my radar when I did have 27.5 mountain bike! And I can’t even get up to 33mm on it.

It most likely will not work well enough to make it worth the cost/effort. When replacing 700c with a 650b, you need to replace with a large enough tire to make the overall circumference very near to that of the 700c. If you don’t, your pedals will clip the ground in corners because your bringing your bike closer to the ground. You’ll most likely not be able to get a big enough tire in there for the 650b to function properly on that frame is the most you can fit now is a 33mm.


If you do end up borrowing a wheelset I’d like to know how it works out!

I tried 32mm width Gravel Tyres in it last night on the 700’s (Clement Strada LGG Wire Bead). Frustratingly, I had width clearance and it was the height that was the issue this time!

I don’t know whether I’ll get to test the 650b wheels, as I’ve done a deal on a second hand Kona Rove ALthat I’m going to view/ buy tonight. I’ve probably spent a third of the price on tyres trying to get something to fit.

My plan is that this bike will allow me to properly test gravel and cx riding before committing a bike to work scheme to it!

1 Like

Someone at work showed me this video, worth a watch.