How to tell correct class for a championship?

I am sure I have seen this question asked before, but I cannot find the post. How do I tell what is the appropriate class/tuning level for a particular championship? It used to be quite easy in FM4, but I am not sure how to do this without actually going into a race this time.

Thats the only way, go into a race. Then you will get a notification for what you need to upgrade or down grade to.

I use the buy car option from the championship menu. Stock PI for each car will be shown along with PI after auto upgrades. Much easier than loading a race and backing out.

I have found it easier to click on the buy car option, the game then calculates the class needed on the cars in there. Once done click back and select the class needed.

Edit: beaten by a second. lol

Here’s a list of the restrictions for each series in Career:
http://forums.forza.net/turn10_postsm14828_FM5-Events--and-restrictions-list---Career--Multiplayer--Rivals.aspx#post_14828

Thank you very much all, and especially ManteoMax for the useful link.