[morninggents]

Hi. I raced Lotus Cortinas for about 25 years up until 2015 both to App K spec and to HRSR/HSCC spec which allowed more freedom to engines, brakes and suspension, whilst still using the Lotus twincam engine, standard bodywork and the Dunlop CR65 tyres.


You need to decide which tyres you will use as suspension (and brakes, to a degree) settings differ greatly with the Dunlop crossplies compared to the more modern grippy radial. The Dunlop race tyres are very expensive (around £180 per corner) have very little grip but are a hoot to race on and break away is progressive. Tyre life is reasonable. A modern grippy radial (Yokohama A032/A048 or similar) will cost about £70 per corner, has tons of grip but breakaway is sudden and usually not recoverable. Tyre life not so good as the Dunlop racer.


If you use Dunlop CR65s brakes don't need to be too fancy as the tyres will lock up before the limits of the brake stopping power is reached. With the radials more powerful brakes will be needed for ultimate stopping power. I used vented AP racing discs and 4 pot calipers on the front and non vented 2 pot AP racing rear calipers on my none App K car.


Spring rates for the Dunlops need to be higher than you quote. Around 350/400 lb inch fronts and around 180/200 lbs rears. Spring rates for the radials need to be way higher (I ran 1000lbs inch springs at the front when we could use Yokohama radials in the 1990s before we were mandated to use the Dunlop CR65s). I ran 400 lbs rear coil springs before changing to rear leaf sprigs of around 250 lbs. Dont forget early Lotus Cortinas ran 'A' bracket rear suspensions with coil sprigs in period so that would be a set-up option for you if you want an authentic feel. The coil springs are easier to change than the leaf springs and it's easier to get the correct poundage you need. However, the 'A' bracket needs to be well fixed to the axle case or it will pull the rear diff pan apart and leak oil.


Current thinking for ARBs is the thicker the better. The standard Lotus had a 3/4 inch bar with 7/8 inch bar as a homologated option but 'modern' app K cars run 1 inch bars or even bigger on some I have seen.


As I said at the start - it depends what tyres you opt for.


PS' To make any of it work you will need to seriously strengthen the shell with seam welding and interior roll over bar mountings strut braces and the rear suspension brace bars from turret tops down on to the boot floor and forward towards the door openings are a must fit requirement to stop body flex.


Hope this helps.