I have a newer tarmac S-works and have exceeded 50 mph many times with never experiencing wobbles. Today while Descending Monitor pass I experienced server wobbles at about 40 mph. I checked the bike a few times making sure everything was tight and in alignment. The only thing I changed is I put on S-work Tubeless Tires and have ridden them a few times. But never at high speed. In the past I always rode on clinchers. Additional information: I am 5’5" and about 153lbs. I understand larger riders are more susceptible to speed wobbles.
Before we go any further down of that rabbit hole, answer this question: are you riding exact same wheels as before ?
If not, please describe the differences, i.e. depth, width, etc.
I’ll be interested to hear what the answer is. I have a ride I do 3-4 times a week that I normally hit the low 40’s mph on the decent but have reached as high as 60 with a tail wind. These were all on clinchers with no issues but I just installed a pair Cont. 5000 TL today. Will be doing the ride tomorrow so I’m curious as to how they will handle the speed.
Did you check the tyre pressure? Just asking because sometimes with new tubeless tyres you can get slow leaks, and the pressure drops, which might make it feel weird. I had that once, was surprised that my new front tyre felt so unstable when cornering. Came home, and it’d dropped to 25 psi. With a 25mm road tyre, no longer surprised it felt floppy!
Also check that tires are evenly seated, I had an issue where a part of the bead didn’t seat properly, it’s hard to notice but at high speeds it was wobbling
Yup…this was my first thought as well. Almost a guarantee that one, or both, of tires didn’t get the bead properly set.
What size frame, and what length of stem?