I have to replace the seat post on my newly acquired Trek Y22 mountain bike. It's the usual Trek/Bontrager 27.2mm diam. Question is, looking on Ebay, some seat posts are sold for road bikes. What is the difference between road and mtb seat posts? I'm looking at a Bontrager Race Lite...how do I know if I can use it? The diameter is right so would fit in the frame ok. Is it something to do with the saddle clamping arrangement that differentiates between road & mtb. Or is there in fact no difference at all?