Hi Yohann, thanks for reaching out. I did receive your group request. I have a lot of group requests to go through and I haven't had a chance to respond to all of them yet.
Since the Groups functionality is still at a very early stage and we are limited access only, I try to pick groups that are more general so more people would benefit from them and they can become more active. Race car groups sound very specific and I don't know how many other members from the community you would get to join it at this time.