Does a LIve Axle require rake?

[GordonW]

This question relates to a series 2 if anyone has any experience of them. The front suspension has very little facility for adjustment to balance things out.

I'm familiar with the convention of 15mm (ish) rake for the de dion but I don't recall seeing the live axle discussed.

Any info/experience would be appreciated.

[Golf Juliet Tango]

I think so. I'd have to measure mine.

[GordonW]

Thanks Stephen any advice is welcome.

[rkeywood]

About 1/2" would be the norm on a live axle S3 running standard spring rates. Caterham give the ride height at the front of the cockpit so if going from there it's a bit less than 1/2". On my car for track use it's 120mm front and 130mm rear (about 52/48 F/R weight) and for the road I put 1/2" on F & R (sorry for mixed units!)

[GordonW]

Thank you gentlemen very useful. What are the 'standard' spring rates please and for track use do you use the same?

[Jonathan Kay]

From the 1996 Assembly Guide:

Jonathan

PS: Please let me know if you'd like a copy.

 

[GordonW]

Jonathan, that is brilliant, a copy would be very useful thank you.

[Jonathan Kay]

If anyone else would like these: for live axle cars I have the Guides etc from 1988 and 1996.

Jonathan

[rkeywood]

Just bear in mind that diagram is for the later live axles - IIRC the springs/dampers, ARB, and top wishbone(?) all differ post '95. The '88 manual is probably better for your car and does at least make reference to some of the pre '87 chassis differences. This doesn't give the rake and I'd have thought running over 1/2" between the points on the diagram would be a bit front heavy. Also, I'm not sure if the camber and caster are adjustable on a '96 car or if the figures given just for checking? The advice I got from Caterham when prepping my car for racing in the early '90s was 1/2" measured at F & R axles. The ride height for road use was based on 185/70x13 tyres so will be lower with 60s. For their race series Caterham specified a limit of 120mm at the lowest point on the chassis rail (with driver). If intending track use I'd go by the cornerweights with a front ride height between 120 and 130mm and no more than 55/45 F/R weight.

The standard springs supplied on my car were, I think, 120 on the front and 75 on the rear fitted on awful Spax adjustable dampers. For the track the fronts were normally increased considerably - up to about 300lb - and the rears up to 140lb. I played with quite a few different springs (unfortunately on crap mandated dampers) when racing and settled at 280 F and 105 R finding the softer rear better for traction. I found this a bit stiff for the road and when I made the car a little less track focused a while back I went for 265 F and 90 R on Protech shocks. In hindsight I think should have gone for something softer on the front for the road and just swapped back to the stiffer springs if/when I go on the track. Hopefully others will jump in with their experience - I know Tazio (Alan) for example fitted 225 / 125 springs on his early car recently and it would be interesting to see what he thinks.

Other things to think about, if not already done and will fit on an S2, might be a 5/8" ARB and the addition link that triangulates the front suspension, along with the 1deg (neg) camber wishbones.

[Tazio]

To put it in context, I have a 1985 crossflow that I've rebuilt, and haven't gone for ultimate grip just a nice compliant communicative set up and am using 185/70/13 tyres and I have gone for 225F and 125 rears on Protech dampers, I'm happy with the front end, and though I am still playing with the damper setttings, I suspect i could have gone a touch lower poundage with the rears, 

Alan

[GordonW]

Many thanks rkeywood. Being a series 2 there is very little facility for front suspension adjustment as you probably know. The regs I am preparing the car to require pretty much standard suspension is maintained although overall ride height can be a minimum of 100mm ( to chassis). And steel bodied adjustable dampers are allowed.

Interesting that you settled on f/r spring rates far wider apart than those routinely used on de dion cars and as you say as used by Tazio. If you were competing with that set up I guess you found it to be a good balance?

[rkeywood]

I'm not that familiar with de dion setup but yes, considerably softer on the rear, mainly to help with traction and kerbing. Another thing is weight - a stripped LA car is probably 35-40kg lighter than a typical early de dion and I'm guessing a race S2 will be lighter still. Mine is under 540kg with (light) driver and half a tank. Late on Caterham did supply progressive springs for live axles and that might be worth exploring. Maybe have a word with ProComp Motorsport who have a lot of experience with light (7 type) live axle cars. They may also be able to supply steel dampers in matched pairs valved to suit the weight or dyno and revalve stock dampers. Caterham stock dampers are not, from my experience, matched or sensibly valved for lighter cars. Ride height at 100mm sounds too low - I'd worry about the 'box and sump (if wet) and want to stay well clear of kerbs at that. As you say, no adjustment on the front so there's also the question of rack height and how much you'd need to lift that, particularly if running very low. Can you at least use the negative camber lower wishbone?

[paul_w]

Judging by the way S2 Lotus Elevens run a lot of negative camber in historic racing (when they had positive from the factory with essentially the same set up as the early 7s) I'd guess standard wishbone lengths are not known/checked by scrutineers?!

I'm looking at changing the geometry on my S1 (for road use) and I'm thinking of just getting some wishbones made up to my spec with increased camber and castor, as they aren't particularly complicated items. If I increase the distance between the inner ends I can use washers to adjust castor as on the later cars.

[GordonW]

Thanks all. rkeywood yes I agree 100mm is low but there is an idea afoot to possibly shorten the sump to match the height of the bell housing (which cannot really be changed) as a part of alterations for baffling, since it must stay wet, the modification would include some means of retrieving the lost oil capacity shortening would incur. Even so 100mm will probably be risky low 110/115 being more likely. I plan to have a minimum of 65mm below sump (which is the critical measure) for track.

I'm talking to IG Racing about (limited) choice of steel dampers and he favours Gaz believing these have superior seals  over others. Also he sources them in component form and builds the up to his quality control and your spring/valving requirements.

The HSCC regs require an individual 'passport' issued post inspection, which is a separate issue to regular scrutineering. Rumour has it running over the car with a magnet is to be expected.......

Paul, I like the idea of different wishbones but I fear that would fall foul of the Passport/regs process, I have a feeling the days the 7's cleaning up are fresh in their memory and they don't want it happening again!!