Why do signs warn motorcycles of expansion joints where the joints run perpendicular to the roadway? I mean, it’s not like they have to jump a huge gap! Now, if the joints ran parallel to the roadway (which I’ve rarely seen), then I could see the potential problem. But, so many times the latter is not the case.
Sometimes they cross at an angle. It doesn’t take a lot to get some wheels tracking into the joint. The worst case might be where they fill the joints with some rubbery material that can pop out and cause all sorts of trouble. And expansion joints are good place to find the pavement breaking up.
The bike might become unbalanced and cause the driver to either fall, swerve, or hit something.
The expansion joints, while perpendicular, have teeth that run parallel to the direction of travel. This will cause the bike to wobble a bit as you go over them. The sign is to give bikers a heads up.
Also sometimes the expansion joints have metal plates on each edge. Those are extremely slippery in wet weather.
Ayup. If it’s raining, and you happen to be leaning (e.g. changing lanes or navigating a bend in the road) when you cross over the expansion joint, you can temporarily lose traction. You may recover on the far side, although being startled by a brief loss of traction can make a mess of things. If you happen to be leaned over a lot, it’s possible you won’t recover from that brief loss of traction, and the wheels will continue to slide out from under you, resulting in a Very Bad Day.
I once did such. Though I recovered, it started a not-quite-tankslapper (youtube video) swerve that went about +/- 45 degrees of lean and took 4-5 cycles to damp out. Wild.
Angled railroad tracks can also make for a very bad day. If traffic allows, I will turn so as to hit them square.