Speaking without any of experience this, id imagine this is where the entrepreneurial side of photography is key. As in any competitive business market you need to promote your product, stoke demand and drive continued sales. The problem is that your customer base is exceptionally niche and your products directly compete with themselves. I.e for karting where the spectator following is small if not tiny, of those spectators fewer still will be willing to buy photographs (simply because unless you are a die hard fan you're not gonna want pictures of cars in your living room).... so that leaves the competitors, they are more likely to purchase... but how many do you reasonably expect they will buy? 2 a year maybe? possibly a few more if you get a few action/crashes.. most people don't have a house full of photos of themselves on the wall, so if you manage to sell one its unlikely they are going to buy another for a while. How much can you sell them for £10 max for an A4 print maybe?... it quickly runs towards a pointless activity at this level.
If I had the time or the offers I would offer photography as a component of a PR drive. If these racers are serious about their prospects, they are going to need sponsors, support etc... I'd imagine someone would be much more willing to pay an annual retainer for a service that could provide them with a promotional website to attract sponsorship, social media management to engage with supporters etc.. yadda yadda you need to ensure you are offering more than just a print service, there's literally too much competition to bother with it.
The higher up the ranks you aim the more spectators and the less interested competitors get, its also more competitive. Grass routes is where the money is for starting out but you have to be a lot more than just a good photographer until you are famous
Just my naive opinion
I'm sure one of the Pros will be able to add to or shoot me down