Hello,

I wouldn't want to alarm you, but it's abnormal. I think you should check tyre pressure and shock setting first. With my 50 kg son and my own 70 kg, shock on 3rd (middle) position, 150kph is no big deal ! So at 80, either your shock is on softest position, or your tyre pressure too low or something's really wrong.
By the way, how's the bike when you ride alone ?
I'd suggest to check wheels alignment (you just need to bend a string), rear arm side excessive free movement (I think of used bearings), same thing for steering : put the bike on something hard to free the front wheel, and try to move the fork back and front. If it moves, unscrew up bolt and tighten the steering, with a screw driver and a hammer. Then screw the bolt to keep it tuned. If it doesn't work, get new bearings... And hope the frame hasn't been damaged.
Steering movement must remain easy, to prevent bearing damage and bad steering feelings, so check it before to re-tighten the bolt. I mean the chrome one under the bar.
You could also check rims, spokes (need to be tightened ?) : to check the spokes, try and fold them with your hand : you take two at a time and try to approach them. You do it for each couple of spokes. Maybe one couple will be softer than the others...
Then check suspension. If they are too soft, it could explain the stability disaster you're in.
The most common fork disease is joints failure. Easy to strip the fork and search for oil on the tubes. If there's some, you must change joints and oil. Oil quantity must be perfectly the same in both tubes. So if you loose some, you get two problems : fork too weak and oil quantity different in each tube.
Shock absorbers have joints, too, but if it gets too weak, you'll need a new shock.
Last advice : check wheel weights, sometimes mechanics put flat ones and you loose them.
Try and get the ones that go on spokes. They're more secure. But at 80, I don't think it's the problem.



Have fun !

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