Your site is fubared at moment with an application error but i'm sure you noticed this or are just working on the site.
The first thing i asked myself was, what is this for?
And then why would i (anyone) want to join?
I understand the idea, the social aspect, forming racing groups, friends groups but how are you providing something that is not catered for yet?
Don't get me wrong, not trying to be an ass, i'm just trying to think with you.
As it is now the main social aspects are allready catered by Leagues, they all run websites, forums, yahoo groups, services or whatever. imo the serious and dedicated drivers are allready in leagues so that shifts the (initial) target group towards pickup racers, serious drivers without time to join a league, friends, and other drifting souls.
In that respect i think you could be more clear and whome you are targeting, pull them in by showing you are providing something those people could realy benefit from because if you are targeting
all sim drivers it might get abit dissapointing?
Shame i can't check the site now but is there a news section as well? sim news? tech news? can members add their own news items to it?
News is all covered anywhere else of course but providing content appart from the social aspect is also something why people return to a site, just the social aspect alone might not be enough. surtainly not for those visiting without an account, they are mearly looking at something they cannot be part off unless they register so there should be more to pull them in.
From memory i think you are also offering blog-space? thats something you could focuss on more, i think thats realy something you can stand out with. there are allot of league-members or otherwise whome are not admins and dont have access to a website, but i know there's quite a few people whome would love to do race-reports etc for their group, stuff like that.
Also -since you appear to want to go big- i would surtainly look into some kind of League-section. you allready got a system going and there are allot of small leagues struggling to stay alive , less sophisticated websites/systems, wanting to grow, not having the tools, thats where you come in.
Providing a system for them where the social part is extended with maybe some nice league-tools (there are many free ones on the web to use) or whatever you can think of.
If you can pull in small leagues that would be awesome i think and those leagues can benefit bigtime using the social site to recruit new members or form friendships with other leagues.
for example we have had quite a few league vs league races in the past and tbh they are a bitch to organise, not in the last place because you have to register to a different league just to organise stuff and half the members have no clue on agreements made (because rules often need to be adjusted as 2 leagues have different outlooks on racing)
Recruitement could be a big asset to this site as it is a contineuous battle for leagues to attract good or dedicated drivers.
Even providing a tool for
all leagues to be able to recruit seems like something worth considering?
Also if possible you could provide abit of server space to special accounts like the leagues so they can share data between themselfes. it realy helps small leagues if they can grow abit by using their own space since they will not have the userbase to rent big serverspace.
Lack of updates (by you or members) is also something you might want to play with, for people to want to become interested the site needs to have new content regurarly so it won't be labeled 'dead' instantly because once thats done people dont return. initialy you gonna have to do that yourself and cheat abit with it and maybe with the help of the first user group.
Oh and add a 'like'and 'dislike' button to the site, no social site is complete without it so it seems, people love to press those buttons and pretent their 'opinion' actualy means something and can bitch about it
All the above is just from the top of my head and little thought has gone into it hehe, but maybe there are a few things you could work with.
URL wise Sim Social makes me think of the Sims. Sim Racing Social network has a nice ring to it imo, explains what its about right away, no questions asked.
Good luck!