Unclejake Posted April 24, 2009 Share Posted April 24, 2009 The application: Mk1 Cortina race car. MacPherson strut front and Hotchkiss rear (leaf and live solid axle). The current task: I am re-designing the suspension. It all has to be same type of suspension as the original 1961 design. No suspension point can be moved more that 50mm from the factory mount. Springs, shocks and swaybars are free but spherical bearings can only be used on the strut top and sway bar. The objective: A low centre of gravity, a sensible roll-center, minimum weight (both spring and unsprung) and a front suspension that gains negative camber on compression beyond static height (ride height). The problems: 1) Right now the front springs are heavy (in actual mass). I want lighter ones which means shorter ones. 2) The camber plates are too deep (vertically) to permit more than 36mm of suspension travel at current ride height. Currently when the front suspension bottoms out the sills (lowest point of the car) are 90mm off the ground, at ride height the sills are about 120mm off the ground. What I need to order: Shorter front springs in a heavier poundage and camber plates that allow more suspension travel. I want to order the shortest possible springs that still give me the suspension travel I need The Question: How far off the ground should the car be (the sills) when the suspension bottoms out? Quote Link to comment Share on other sites More sharing options...
MACKAZ Posted April 24, 2009 Share Posted April 24, 2009 from my racing experience their was no magic compressed height, as long as it didnt hit the ground and slow you down its all good. but in saying that we were only turning left all the time Quote Link to comment Share on other sites More sharing options...
eke_zetec_RWD Posted April 24, 2009 Share Posted April 24, 2009 just shorten the strut is self to suit a shock with a shorter body. that will give you more travel. use a spring thats small in diameter (the bar itself) and has less coils. stiffer isnt always beter-swaybars are where its at. what are rules on swaybars? buy a book called "tune to win" and "engineer to win" both by carrol smith. very indepth book about everything race car chassis, suspension ect Quote Link to comment Share on other sites More sharing options...
OSC Posted April 24, 2009 Share Posted April 24, 2009 ^^^^ definately the most on to it guy i know recommended both those books. can be had from techbooks.co.nz Quote Link to comment Share on other sites More sharing options...
Gaz Posted April 24, 2009 Share Posted April 24, 2009 Goto track and measure height of the bumpities on corners. Then lower car to make lowest point = that + 20mm. Then dont ever crash off track and you will = win. What does yours/Aidens suspension book say? Quote Link to comment Share on other sites More sharing options...
Unclejake Posted April 24, 2009 Author Share Posted April 24, 2009 The book doesn't cover this (probably too many variables). The people driving around with the most stupidly low cars on the planet mainly reside on OS so I thought this would be a good place to get some real world advice How low I permit the car to get on full compression directly influences what springs (leghth) I purchase. Quote Link to comment Share on other sites More sharing options...
Spencer Posted April 24, 2009 Share Posted April 24, 2009 Id say full compression maybe an 30mm you'll be fine. Brads car maybe had 60-70mm (probably less) static height when on his steels around the track was fine. Think he hit a few ripple strips etc as well (which are hell at taupo). HOw often will you see full compression? hardly ever I'd think you're running fairly hard springs aye? JUst going offs the only issue with a low car but who cares Quote Link to comment Share on other sites More sharing options...
Testament Posted April 24, 2009 Share Posted April 24, 2009 I would say you probably want 25-50mm clearance when on the bumps, but I doubt its super critical. Really getting your roll center and camber change geometry right is of much much more importance. What about the front hub carriers? can you change anything on them or do you have to use factory items? Can you use different length custom control arms? Quote Link to comment Share on other sites More sharing options...
Unclejake Posted April 24, 2009 Author Share Posted April 24, 2009 The hubcarriers can't really be changed as the MacPherson strut is unit construction. There is no law against it though. It would just be hard and expensive to mess with them. Longer (adjustable) lower control arms are absolutely possible. I plan on retaining my existing shocks and struts. The only real question is where to set the travel. I will need to change the strut tops to gain more travel and that means a longer spring that has more unsprung mass than the springs I had already ordered (but not paid for so I can change the order easily). Thanks for the suggestions all. EDIT: The struts have already been shortened to accept the shocks. The shocks were about a grand so I don't really want to change them. Quote Link to comment Share on other sites More sharing options...
slipsittin Posted April 26, 2009 Share Posted April 26, 2009 For what its worth (and that might not be much lol) I run VW Golf adjustable gas pressure tokico, koni or kyb in all the early fords I have ever raced and setup for others. They are a shorter travel shock so I mount them at the bottom of the struts with spacers to keep the original struts the same to avoid issues with officials. This allows you to change springs and just make spacers to suit your arrangement on the day. I have usually set these up with aftermarket springs but not adjustable coils as the smaller diameter spring coils alter the bump steer and increase the chance of cracking the strut towers. To alter your camber the easy way you can get a big range of eccentric bushes from BNT or Autolign and the also sell eccentric bolts and weld on camber slotted kits. Racing these days certainly has a heel of a lot more ease of aftermarket parts that we had to make from scratch. All the best with the car UJ, its looking good. Corey Edit: Forgot to add that my setups always bottomed out when the car was 50mm of the gound and that was at full bottom out not just hitting the bumpstop. The rear can be altered in an even easier way also. Quote Link to comment Share on other sites More sharing options...
Unclejake Posted April 26, 2009 Author Share Posted April 26, 2009 ^ Cheers ears! I have removed the springs from the front and don't have bump stops so the bottom out of the suspension is the shock bottoming. I went and looked for some replacement camber plates today. My existing ones take up 50mm of vertical suspension travel and the new ones will be about 15-20mm shallower which gives me more travel - but possibly not yet enough. I need to wait to get a sample of the camber plates in my hand so I can measure them up and make a decision - but I think it is the way to go. Quote Link to comment Share on other sites More sharing options...
Mick Doohan Posted April 26, 2009 Share Posted April 26, 2009 ^ Cheers ears!I have removed the springs from the front and don't have bump stops so the bottom out of the suspension is the shock bottoming. I went and looked for some replacement camber plates today. My existing ones take up 50mm of vertical suspension travel and the new ones will be about 15-20mm shallower which gives me more travel - but possibly not yet enough. I need to wait to get a sample of the camber plates in my hand so I can measure them up and make a decision - but I think it is the way to go. you really dont want the shock bottoming out unless it has internal bumpstops... smashes the internal valving if its a track only car 30-40 mm is heaps but that dependant on your tyre profile and how much that will absorb as well if its a road car and you plant to drive it hard on the road id be wanting 80mm .. Quote Link to comment Share on other sites More sharing options...
Unclejake Posted April 27, 2009 Author Share Posted April 27, 2009 ^ Tis a track car only. I am going to be adding bumpstops, the type that just slip over the shock shaft. Next step is to move the swaybar forward 48mm Quote Link to comment Share on other sites More sharing options...
Mick Doohan Posted April 27, 2009 Share Posted April 27, 2009 just use ya bumpys to limit your bottom travel and develop the shit out of that from there start off woth 60mm bumps and cut them down till you reach what proves to be optimal around the track ... you can be to low .. blade type swaybar jakey ? Quote Link to comment Share on other sites More sharing options...
Unclejake Posted April 27, 2009 Author Share Posted April 27, 2009 The sway bar is just a thicker version of the original bent bit of steel rod. I really thought hard about building an adjustable one but don't want the extra weight associated with it (mountings and brake radius rods etc.). I have become interested in simplicity wrt to the suspension on this car. I plan on testing with the Watts link removed once I have it all as I want it to drive as the Watts is probably close to 5kgs, 3kgs of which is unsprung. Simple, well engineered and light should = reliable and fast IMHO. Quote Link to comment Share on other sites More sharing options...
kyteler Posted April 27, 2009 Share Posted April 27, 2009 I would hazard a guess that Lotus may well agree with you in that regard there UJ. Quote Link to comment Share on other sites More sharing options...
RT Posted April 30, 2009 Share Posted April 30, 2009 mine bottoms out over anything bigger than a matchbox.. Quote Link to comment Share on other sites More sharing options...
car96 Posted May 2, 2009 Share Posted May 2, 2009 Hi uncle, good to see you are still pedaling the mk1. when i racing against you, i kept the front suspenion pretty simple, and light wieght. are you wanting to have a large amount of ajustment for camber / castor?, or just camber?, i'll dig out some photos and post them up. car96 Quote Link to comment Share on other sites More sharing options...
forced Posted May 2, 2009 Share Posted May 2, 2009 I'd have thought the easiest thing to do would be to assemble it completely with no springs. That way you can measure the compressed space available for the springs, measure the travel etc. If you know spring rates and the weight on the front of the car you can also work out how high it should sit... at least theoretically. If you take stock springs and cut say one turn off, the car sits lower but the spring rate is also greater. I'm not suggesting you cut stock springs but it DOES work to a certain extent. That was probably the first mod I did to my first car, while I was at it I drained the struts & filled with hypoid 90, did the same to the lever arms in the back (the hypoid 90). Hard suspension when cold, softer as it got hotter.Yay. Steve Quote Link to comment Share on other sites More sharing options...
Unclejake Posted May 2, 2009 Author Share Posted May 2, 2009 Hey Shane. Simple is my plan too. Up to 5 degrees negative camber will do, with 4-5 degrees of caster. I will never run that much but if it is adjustable to those settings it would be good. Forced - I have taken the springs out and am manipulating things with the jack. New shallower camber plates are on the way Quote Link to comment Share on other sites More sharing options...
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