R8 springs et c.
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  1. #1
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    Default R8 springs et c.

    For those who came in late: the story so far:

    Some of you will be aware that I have considerable interest in improving the handling of rear-engined Renaults with fairly minimal interventions. Six elements in this activity have been wheels, tyres, springs, dampers, steering & camber-compensators. I have posted about most of this elsewhere in the past. Two vehicles are relevant, a much-modified 4CV & a more mildly modified R8.

    Each of these is basically standard R8/R10 in suspension but the 4CV has much weight shifted to the front & a turn lopped from standard R10 rear springs. The R8 has, until recently, retained standard rear springs (although always the shortest of what I had available). The 4CV thus had more -ve camber at the rear than the R8. Both had 2.5 turns steering, 4.5 F & 5.5 R rims & 165/65 F & 185/60 R tyres (until recently Continentals) & camber compensator transverse leaf rear springs.

    My favoured 185/60 tyre, the Conti EcoContact3, is no longer available & the R8 needed new rears. I fitted Bridgestone's Turanza T001. Good dry & wet grip but astonishingly sloppily structured (they must develop their maximum cornering force at unusually large slip angles). On the pressures I used with the Contis, the R8 was dangerously "loose" at the rear (& I like a mobile rear, just not like this). I made radical changes to F/R tyre pressure relativities to restore stability but it was but a partial cure as I wasn't comfortable dialling in my usual "neutral to oversteer" balance.

    Independently of this, I have long advocated the use of camber compensators in these cars but, in the decades that I have been using them, it has been with standard coil springs (the R8) or slightly stiffer "chopped" ones (the 4CV). As the leaf acts as a supplementary spring in mass support & in "bump", I have long wanted to try softer rear coils so that more of the load is taken by the leaf (not too much, given the way it's mounted). That way, given the softer rear coils, I'd have less roll stiffness at the rear & shift relative weight transfer forward. This should be a recipe for less work being done by the rear under lateral load, less tendency to get the rears moving to positive camber & more roadholding & more sanitary "limit" behaviour at the rear. I was already hunting for some of the softest springs standardly available for rear-engined Renaults (Dauphine Normale Aerostable type) when the T001 disappointment hit.

    So, a heightened sense of "need", then. The Dauphine springs are not just softer but longer than R10 ones (with the same number of turns but "stretched out"). My plan was to lop a turn (mild stiffening) & end up with an R10 length spring which was still softer than normal & would sag more under load to give more-ve camber. This would have been a good thing regardless of any tyre problem.

    With the T001, my hope was that the greater static -ve would pre-tension the outside tyre sidewall a bit & that the reduced weight transfer would stress the tyres less. A major test would be if I could reduce the large F/R tyre pressure difference I had reverted to & manage a swift left/right "jink" without changing my trousers.

    And now:

    In short, I got my springs, had them lopped & retensioned the leaf to suit them. So, less rear roll stiffness & more
    -ve camber. Functionally, it worked very well & the R8's handling is back to being entertaining despite the tyres (which do grip well). Response is eager & limit behaviour is controllably mobile - and it will now "jink" again.

    The 4CVG & R8 have quite a different feel (the former is go-cart like - & yes, I've driven a go-cart) & each is inferior to the Djet (predictably - there's no going past a mid-engine & wishbone geometry rear-suspension). But the R8 is back to being in a solid third place & a joy to fang. So, I suggest a camber compensator & softer rear coils is a nice option to consider for a road car, even if you haven't put the T001 on the rear.

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    cheers! Peter
    Last edited by 4cvg; 12th November 2014 at 01:49 AM.

  2. #2
    Fellow Frogger! Ross's Avatar
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    Thanks Peter

    Very informative and obviously well thought through.

    So what are the tyre pressures you have ended up with?
    Ross:

    1989 Alpine GTA Twin Turbo
    1963 Renault R8
    1996 Peugeot 106 S16
    1967 NSU Prinz 1200TT
    1989 Peugeot 205 GTi

  3. #3
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    Quote Originally Posted by Ross View Post
    Thanks Peter

    Very informative and obviously well thought through.

    So what are the tyre pressures you have ended up with?
    28 F & 36 R

    So, an 8psi difference compared to the 14 psi difference (24/38) pre spring change (& avec T001) & the 4 psi (30/34) set up with EC3s all round (which was admittedly "tailier" but with controllability).

    When I get around to it, I may swap the 4CVG's EC3s on to the R8 as an experiment & see where the optimum is. I predict that I'll get back to the even pressures all round that I had with a previous set of saggy standard R8 springs. Might even try more pressure in the fronts (as I have in the super-controllable Djet).

    cheers! Peter

  4. #4
    1000+ Posts Frans's Avatar
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    Quote Originally Posted by 4cvg View Post
    (as I have in the super-controllable Djet).

    cheers! Peter
    I like the words you used and this is a demonstration of just that. I think the video should be seen with narrow 15" wheels and that the driver delibarately provokes a drift to show the controllability and the fact that the suspension hasn't been worked, it is factory standard 1965/66 vintage. I have posted this video before and I love to watch it.

    https://www.youtube.com/watch?v=B5YJPnaRWh0

    Regards
    Frans.
    Old enough to know better
    Young enough to do it anyway.

  5. #5
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    Quote Originally Posted by Frans View Post
    I like the words you used and this is a demonstration of just that. I think the video should be seen with narrow 15" wheels and that the driver delibarately provokes a drift to show the controllability and the fact that the suspension hasn't been worked, it is factory standard 1965/66 vintage. I have posted this video before and I love to watch it.

    https://www.youtube.com/watch?v=B5YJPnaRWh0

    Regards
    Frans.
    A lovely video; thanks.

    Three others which I have loved are:

    an R8G one which was on Renault's site for a good while & which I posted here - the camera focused or rear suspension camber dangers in slow motion;

    an A110 one on a dirt traffic-cones course in which the driver deliciously connects the corners so that the finish of one has angled him perfectly for the next; &

    a classic tarmac rally in France which was run in the wet - star of the show was a modern Mustang who was by no means fast but spent the entire rally sideways for the entertainment of onlookers.

    I'd love to be able to drive as well as these guys but in the meantime I'll still have fun.

    The Djet really is special.

    I set up all of my cars on one particular bend which has good sight-lines across a paddock. It's a sweeping right angle bend which each of the four toys is comfortable doing >100kph around. I choose a wet day & play with tyre pressures until the toy in question will four wheel drift around it without any particular balance-unsettling interventions by me. I haven't yet done that with the latest version of the R8's set-up but it & the 4CVG have been easy enough to get this way. The Moke was harder work. Once the front pressures went up, the Djet was easiest of all & by far the neatest & most wired-to-your-instincts intuitive to gather up again at the end of the drift.

    cheers! Peter
    Last edited by 4cvg; 16th November 2014 at 03:44 AM.

  6. #6
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    [QUOTE=4cvg;1301823]For those who came in late: the story so far:

    <snip>

    In short, I got my springs, had them lopped & retensioned the leaf to suit them. So, less rear roll stiffness & more
    -ve camber. <snip>

    Just a small update for anyone who's interested:

    The R8 had an alignment check recently as the adjustable tie rods which I've fitted to the R8 & 4CVG had, in the latter's case, wriggled loose a bit & let the wheels drag into toe-out & so we were checking the R8 - it was fine.

    Using the springs & C.C. combination as per above resulted in a little bit over 4 of -ve camber at the rear on each side. (The 4CVG has a little over 4 on one side & about 3.3 on the other.) 4 is rather more than I intended (2.5-3 was my thought) & about the maximum I'd contemplate an a road car but the R8 is now so nicely behaved that I'm pleased with the outcome of the various causal elements including the 4. It adds another confirmatory footnote to the book of swing-axle wisdom's exhortations about the joys of -ve camber.

    As noted, it's all behaving nicely now; though one can still feel the T001 rear contact patches migrating laterally under cornering load - just not in as feral a manner as before.

    cheers! Peter
    Last edited by 4cvg; 16th December 2014 at 04:00 AM.

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