99_Z_155

Hey guys, i know absolutely nothing about how all this works, but i assume the pcm has a sensor somewhere and then it tells the cluster what to read. Anyway, i have 18" wheels now, and am about to put in 4.10 gears in my m6 car. Is there a cheaper way of correcting the speedo other than a HPP3 or similar device? Also, i am about to put in a cam soon also. I dont think i live anywhere near where i could have the pcm properly tuned. What should i do?

Thanks in advance,
J