Bike Rack installation problem

I am trying to install a seat-post rack on my Gunnar - I just refuse to install a more traditional rack as I want it to be easy on and off. It is a Bontrager and it is quite simply to install, just 4 bolts. It comes with two shims in case it doesn't fit the seat-post. The problem is that neither DO fit mine, as the attached picture shows. No matter how tight I tighten the bolts - and I took the seat-post out and slid the sleeve over it, it just doesn't fit.

What is the best material to use to fix this? I am thinking about just taking it to my LBS and letting them come up with something - but am I overlooking something obvious and easy? This is the first time I've actually tried to "do" anything to my bike outside of practicing how to change the tube...

I wrapped one with black electric tape. How much space are you trying to fill?
I also sliced some pvc for a big gap. Can you add washers to take up space?

I don't want to wrap the post on my lovely custom Gunnar with tape - just vanity I suppose :o I only intend to use the rack when I am actually commuting or need it for other things, so most of the time it won't be there.

There isn't much of a space, and I tightened the bolts so tight that the sleeve I used is still attached to it after I removed it from the bike - so I know it wasn't a problem of it not being tight enough. It isn't much space...I wonder if a thin rubber sleeve would work - assuming I can find such a thing? It would have the added benefit of protecting the post from being marked by the rack. I think a washer might be too thick but I could be mistaken.

A strip cut from an old inner tube makes a nice non-marring shim. I would think if it's not thick enough you could make a longer strip and wrap it around once, but I wouldn't wrap it more than once since it could make the rack unstable.

Another possibility would be the shims they make to put a narrow seatpost into a larger diameter seat tube. Those would be guaranteed to be the right size. But I think those are metal and might scratch your seatpost.

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Originally Posted by OakLeaf

A strip cut from an old inner tube makes a nice non-marring shim. I would think if it's not thick enough you could make a longer strip and wrap it around once, but I wouldn't wrap it more than once since it could make the rack unstable.

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Good thought Oakleaf and one I hadn't considered. I don't have any "old" inner tubes, but I do have several extra and they aren't that expensive. I hope to FINALLY try my commuting route this Saturday - depending on what the rain does...

You could also try foam pipe wrap. Cheap enough, and won't scratch anything.

That would compress way too much to offer any stability, unless you're thinking of something different from the soft EPS stuff I put on my frame tubes when I pack the bike for shipping.