Scandinavian_dirt
I’m about to order a Kona Rove NRB. I like almost everything about the bike, but the 31.6 mm seat post I’m a bit worried about. Wouldn’t that turn out a bit stiff? Have anyone user shims on a gravel bike? I understand it should be avoided on some carbon frames, but in this case we are talking about an alloy frame. The shims I found does look kind of short, just 80 mm.
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HollyBoni
Don't do it! 
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ljsmith
I’ve used shims in mountain bikes with no issues. As long as the shim extends a minimum of 1 inch below the bottom of the top tube/seat tube junction it should be okay. But you probably should check with Kona. It may also void the warranty.
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Konass
An appropriately design shim should be fine. I use a 31.6 to 27.2 USE delrin on my mountain bike with no problem. 
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Scandinavian_dirt
The seat tube on the Rive NRB is prolonged quite a bit over the top tube. So a 80 mm shim may not pass the top tube all that much I am afraid.
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Scandinavian_dirt
Missed the picture in my comment above...
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ljsmith
The seat tube does extend a bit.  The Cane Creek shims I have are about 98mm, I don't know if you will find any longer than that.
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dangle
That's fine. The shim should be at least as long as the 'minimum insertion' of the seatpost. The minimum insertion is usually 80-90mm off the top of my head. I think as long as you have at least an 80mm shim, it should be good.
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