Vibration through rear rack

[Grape_salad]

I've got an alt-rider rear rack, which I've put a cheap topbox on. I've got a real vibration problem though - particularly on dirt roads a lot of vibration gets transmitted through - anything inside the topbox that isn't well isolated (usually, inside a small backpack that goes in the topbox) gets shaken apart - anything threaded comes apart. I've emptied several water bottles, rattled apart a a tyre pressure gauge, and even lost one of the topbox mounting bolts that had a nyloc nut on it.

Anyone else having these sorts of vibration problems? Any feasible solutions? I've put a rubber mat between the topbox and rack, but it's fairly high density (an old electrical work insulated floor mat cut up, so quite dense rubber about 4mm thick), but I don't think that will solve it. I was thinking of some sort of rubber mounts for the rack, but not sure what would work without being too flexible.

 

[Madhatter]

im thinking the rear of a bike tends to bounce up and down more than the front , so the rear is a bit like a diving board. adjusting the rear suspension might help . ride a little slower in the rough .make sure your tires are balanced . that's all I can think of at the moment. good luck.

 

[Grape_salad]

Ah yes, wheel balance, i hadn't thought of that. Not sure about the "riding slower" suggestion though!

 

[Fordf350]

tire pressure?

 

[Fennellg]

Try making some rubber isolators. Old inner tube or hose. Might help.

 

[Grape_salad]

tire pressure?

Do you think too low, or too high could cause issues?

 

[WJBertrand]

I think those Alt Rider racks aren’t rigid enough and start vibrating at their own frequency. They Might actually amplify vibrations. Maybe that explains the cracking problem those racks seem to suffer.

 

[Grape_salad]

I think those Alt Rider racks aren’t rigid enough and start vibrating at their own frequency. They Might actually amplify vibrations. Maybe that explains the cracking problem those racks seem to suffer.

It does really hang off the back, like a springboard. Maybe I’ll try some high density rubber washers under the mounts?

 

[Tenman]

I had 2 Altrider racks with a Givi v47 top case shatter. When II replaced it with a Givi rack the bolts weren’t very tight. They had been torqued with blue locktite. The Givi feels a lot sturdier. It’s been tested overloaded.