Hi! Fairly new guy here… I raced quite a bit in Forza III and have been playing 5 for a month or so. I am not great - consider myself average (maybe a bit below average). As I read through the forums I keep seeing references to grip tracks and power tracks. I think there might be drift tracks too… Can someone enlighten me on all the different track types and be super awesome and tell me what tracks fit into each of those types? Even a couple examples would be good so when I look at the little layout pics I can get an idea what tune might be the best… oh yeah, I buy my tunes, not at the level yet to make my own… yet… 
Thanks!
Chris
A grip track is simply one that a car with grip is more important, whereas a speed track is one where speed is far more important than grip.
To give a more detailed answer: Speed tracks are such as LeMans. It is very long straights with only small curves in between that a wide car can block the road through. For a track like this dump the most engine and power upgrades in the car without it becoming too uncontrollable, you still want to be able to survive the turns ;). A grip track would be a track like Catalunya. It is short with lots of turns of all sizes and only one straight. On a track like this the speed car will beat you off the line but as soon as your car (upgraded with aero and springs and tire compound and all the good platform and handling stuff) hits the turns you will pass the speed cars in no time. I love watching speed cars on small tracks catch up to me on the straights only to have to brake twice as far away from the turn, then I lose them. Some tracks are more unique such as Spa and Bathurst that both have long straight sections but also a fair amount of turns. For these I would say try and find a happy median. For Spa I recommend I Holty I 's tune for the Shelby Cobra Daytona. Good luck, I hope this helps!
I personally classify tracks as grip, medium, speed or niche. Niche tracks to me are bernese alps and LeMans/Road America East because of the unique builds that are needed. Now if you can get a car that can handle bernese, usually you can use the car successfully at medium tracks, but there are many times where a tune set up for a medium track is terrible at bernese.
Lemans and and grip tracks have been covered above.
Medium tracks are ones with some long straights but also plenty of corners. Here acceleration out of the corner is key and this can be accomplished by either added more grip or lightening weight/adding power. The epic grip vs power build battles are common place. Tracks like Silverstone, Indy GP, Spa, all Pragues, Road America West (+ alt version) and most Yas Marinas come to mind here. However, indy GP and Spa do require a little more top end than the others though.
Speed tracks usually mean cars for Sebring, Road America, Road Atlanta, bathurst, top gear loop, and silverstone national where massive acceleration paired with top end is needed. Grip to an extent is needed for road Atlanta, bathurst and silverstone national but you can get away with mostly power builds. Usually a tune with high top end on Spa/Indy GP will do well on these 3 tracks, but not always.
You’d be surprised how some cars at times can bend the rules and others fail miserably at anything other than where it was tuned.
Thanks a lot! This is really helpful. I want to get into tuning my own cars but only have the time to actually race 
This gives me a good idea of what to look for in the tune shops. I have been doing just c class stuff in the first league right now and majority of the racing in two different trueno tunes. I want to branch out a bit and play with some other cars.