I'm going to copy and paste a post from a previous thread. There are lots of factors to consider when re-gearing, the drive shaft is only one of them. But as far as the drive shaft is concerned when you get into those 3,500+ drive shaft rpms the force of any slight imbalances become more and more pronounced. Use the calculator on the bottom of this page
https://4xshaft.com/blogs/faq/diagnosing-drive-shaft-vibrations?_pos=1&_sid=d6ec76a03&_ss=r to calculate your drive shaft RPM at certain speeds, then read the info below.
Okay, I'm back with more math that I may or may not fully understand. I knew that the increase in force (vibrations) couldn't be linear but couldn't figure out how or why. It is not exponential, it is quadratic. I think. When I was first doing the force calculations I was using an overly complicated calculator that also require me to convert units of measure before inputting the values I wanted. I found a simpler calculator which I'll link below. I re-calculated the numbers, based on 1 ounce spinning at 3" radius. The values here are almost arbitrary though, I actually meant to do 3" diameter but entered it as radius but the principal should be the same. I did calculations for speeds in 200 rpm increments from 0 to 4,000. I then created a line graph in excel. Here's what that looks like.
You can see that the increase in force and therefor the increase in vibrations due to minor imbalances or loose parts is not linear. My understanding after reading a bunch is that when speed doubles centripetal force quadruples. You can see in the graph above that at 1,000 rpm the force is around 25. Double the speed to 2,000 and the force is about 100. Double again and to 4,000 rpm and the force is almost 400.
Drive shaft rpm is not the only thing to consider when choosing gears but I think this sheds some light on why many people develop high speed vibrations once their drive shaft rpms get up above 3,000 or so. The faster you are going the more a little increase in rpm is going to have an effect on increased forces that cause vibrations. The amount of force created from an imbalance going from 3,600 to 4,000 is the about the same as going from 1,000 to 2,000. In essence at a certain point 400 rpm can have the same effect at introducing a vibration as a 1,000 rpm increase earlier did earlier on.
Great
Check this centripetal force calculator if you want to estimate the centripetal force acting upon a body in circular motion.
View attachment 349584 www.omnicalculator.com