If I have say 10 1510AP's setup, with 1 RAP and 9 MAP's, with my RAP bandwidth set at 18Meg. Each MAP connects to the RAP, ie no meshing, does that 18 Meg be split between each link, or is it 18 meg per RAP-MAP link.
Easy way to put it is, your bandwidth degrades every hop from rap to map to map to map, etc. In your case, the link is what it communicates at, but the rap and the map still share the same collision domain.
What Scott is saying here is correct. Think of each MAP as a client on a regular wireless network when attached directly to the RAP. Each client competes for the 18mb. I am betting however that some of your MAPs are not directly attached to the RAP due to the ease calculation. If they are all attached then 18mb is the raw data rate achieved. This is NOT the actual throughput rate. Each successive hop cuts the available raw data rate nearly in half. That is why I never suggest more than 5 MAPs to a RAP and never more than 3 hops deep. This is somewhat better with the 1520 series as the raw data rate starts at 24mb and then goes down. Cisco is currently working on a dual radio backhaul solution that should preserve data rates up to 6-8 hops at near full data rates. I am holding my breath and waiting as this will let outdoor MESH finally compete with other technologies effectively.