Hi, I think it's just because when people think of a kit they think Seven or classic touring body hence why Stricker & Stylus / Fury come out on top.
Remember most people have never driven a light mid motor car and don't really know how to get the best out of them.
I love my Riot, easily the most capable kit I've ever own or indeed driven!
Chain tension, same as the bike really, around 15mm slack in the centre of the longest run will be fine.
Tire pressures I have tired several things but I find that 17 front / 18 rear about right for me. As the car is so light the weight of the driver (and passenger if you often have one) will have an influence on tire pressure selection. I'm 77Kgs if that gives you any ideas.
Front springs, softer than the factory supplied that is for sure, I think the factory supplied 300lb/" springs which is a bit on the high side I've currently got 275lb/" springs on the front of mine and it seems spot on, again for the way I drive it, although as you go softer you'll loose a fraction of turn in and gain exit steering so if you are not used to mid motor chassis dynamics it will bite (I must admit to having a lazy spin a combe the other weekend when I was forced to close down the throttle a little more than I'd like mid corner due to the surface being contaminated .. stopped the session a minute later to clean it up).
I've still got the fatory springs on the rear, 200lb/" I believe.
Geo' Neil posted looks good as a starting point, tune to suit your driving style from there.
Build manual / advice ...
http://www.riotcars.co.uk/index.php/build_manualhttp://r1ot.com/Hopefully that will help you out.
If you need anything else just let me know!