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  1. #1
    Join Date
    Jul 2018
    Location
    france
    Age
    49
    Posts
    68

    Ride height vs shocks mystery

    On my 1988 IRS DAX full rebuild, time is to choose new dampers to replace SPAX one’s. I’ve found and post some infos in another post (http://www.cobraclub.com/forum/showthread.php?t=10697) but as this is a fully DAX related i've open a new one here.
    My main concern is about ride height vs shocks lengths. I don’t understand why I’ve found that at DAX advised 5.5” front and rear 6.5” ride heights the shocks are nearly on the bumpstops ! So make a temporary rear end suspension assembly with old dampers, lower arm, hub carrier, etc and place the lower side of frame chassis rail at advised height and redo all measures at the rear end. My wheels are 15” so take a 13” radius (taken 255/15/60 and 0.5“ tire compression).

    • Shock full extended to 15” > hub center to ground = 8.25”
    • Shock full compressed to 15” > hub center to ground = 13.2” (same as wheel radius !!!)

    So set ride height as advised conducts to drive on the bump stops ???
    Has the ride height of DAX been modified or are all IRS chassis on the bumpstops when setup at the “nominal” ride height ?
    ShockExtended_.jpg
    ShockCompressed_.jpg

  2. #2
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    697
    Two reasons why I have changed my suspension. 1. The Spax are shot to bits. 2. The ride height was extremely low and caused problems.
    I have fitted my new set up but am yet to put the car on the ground.
    The Dax manual will give you recommended heights. But as long as you are happy you can set the suspension up to how you want it. If you want the arse up in the air then go for it!
    You will find the Gaz give you lots more adjustment so I am hoping to gain an inch or so in ride height. But don’t forget that the old suspension will have naturally settled and set. So new springs will also increase your ride height slightly.
    A couple more things to consider is your geometry. Wheel camber, toe in/out. All that could be affected. And also your headlamp aim.
    Once I have mine on the ground later today I’ll put some more info on this post.
    David.

    Life is driving the Cobra. The rest of the time is just waiting................till I fix it!

    Wessex region caretaker rep.

  3. #3
    Join Date
    Jul 2018
    Location
    france
    Age
    49
    Posts
    68
    My concern is not ride height as dax nominal values please me but why these dax values correspond to ride on the bump stops with initial spax dampers.
    In ideal world you chose spring rate according to desired suspension frequency and set very little spring preload so ride height is mainly set by shocks open length. Effective travel ie closed lenght arts as margin vs bump stops. Perhaps 15" open lenghts are not good lenght for rear ? Some good point nevertheless as protech or avo seems to have shorter closed lenghts for same open lenghts il more travels so Martin vs bump stops.

  4. #4
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    697
    I understand what you mean. I’ve just come in for a break adjusting my Gaz. The length of travel so far is biased to retracted and still the ride height is a little high. I’m about to tackle the rears now but I’ll get them ball park and drive it as is for six months or so to let everything bed in and settle. Then I’ll revisit the ride heights.
    My opinion is that the springs on the Gaz are perhaps a little too aggressive for the car. But time will tell.
    David.

    Life is driving the Cobra. The rest of the time is just waiting................till I fix it!

    Wessex region caretaker rep.

  5. #5
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    697
    It sounds to me that you have either very tired springs or very shortened ones.
    I matched up my Gaz ones to my old Spax ones off the car today to get a ballpark starting point with the Gaz suspension set up. But when I fitted the new suspension I was extremely surprised to see the car looked like it was about to go green laning! All six springs needed considerable adjustment to get the car anywhere near sensible ride height. I have it more or less there now. I’ll put some miles on the car in order to let it all settle down before making final adjustments. But I’m pleased to say that the car has gained some height and given me more ground clearance. Happier bunny now.
    David.

    Life is driving the Cobra. The rest of the time is just waiting................till I fix it!

    Wessex region caretaker rep.

  6. #6
    Join Date
    Oct 2018
    Location
    Shipston-On-Stour
    Posts
    727
    Quote Originally Posted by Darnpistonbroke View Post
    It sounds to me that you have either very tired springs or very shortened ones.
    I matched up my Gaz ones to my old Spax ones off the car today to get a ballpark starting point with the Gaz suspension set up. But when I fitted the new suspension I was extremely surprised to see the car looked like it was about to go green laning! All six springs needed considerable adjustment to get the car anywhere near sensible ride height. I have it more or less there now. I’ll put some miles on the car in order to let it all settle down before making final adjustments. But I’m pleased to say that the car has gained some height and given me more ground clearance. Happier bunny now.
    I did the same as you, set the new ones as the old ones off the car and also found the car was too high when fitted! I have got the fronts as low as the threads allow and it’s still a bit higher than it was.

  7. #7
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    697
    Quote Originally Posted by ChrisP View Post
    I did the same as you, set the new ones as the old ones off the car and also found the car was too high when fitted! I have got the fronts as low as the threads allow and it’s still a bit higher than it was.
    I actually think the cars look better with a little height. Makes them look a little more authentic and period. Next time you are at Goodwood Revival, look how tall the 289 FIA’s are. Lots of room between the tyre and the wheel arch. Especially the rears.
    David.

    Life is driving the Cobra. The rest of the time is just waiting................till I fix it!

    Wessex region caretaker rep.

  8. #8
    Join Date
    May 2016
    Location
    Hockley ,Essex
    Age
    58
    Posts
    482
    Quote Originally Posted by Darnpistonbroke View Post
    I actually think the cars look better with a little height. Makes them look a little more authentic and period. Next time you are at Goodwood Revival, look how tall the 289 FIA’s are. Lots of room between the tyre and the wheel arch. Especially the rears.
    I make you right on that with the ride height ,
    that being I'm a bit biased towards this due to my SR running a bit high in
    some people's opinion.
    It's what ever floats your boat with what we do .
    Chris.

  9. #9
    Join Date
    Oct 2018
    Location
    Shipston-On-Stour
    Posts
    727
    Quote Originally Posted by Chris1 View Post
    I make you right on that with the ride height ,
    that being I'm a bit biased towards this due to my SR running a bit high in
    some people's opinion.
    It's what ever floats your boat with what we do .
    Chris.
    I was looking at an original cobra for sale at Classic Car Hub last year and that was several inches higher than mine. Very noticeably higher. (I wasn’t buying btw, just calling in for a coffee!!!)

  10. #10
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,738
    My measurements DAX SPAX shocks MKiv chassis 15 inch wheels, tyres 235/60 15 rear and 215/60 15 front. On level floor. With weight of the car suspension ride heights with fuel tank at 1/2 full. No added passenger weight. The wheel rim to rim is 16" 1/2 inch.

    Drivers side measurements only.

    Chassis rail bottom Rear in front of wheel = 5" 3/4 inch

    Chassis rail bottom Front in rear of wheel = 7" 3/4 inch

    Rear top wheel arch to top wheel rim = 7" inch

    Front top wheel arch to top of wheel rim = 6" inch

    My rear shock centre hole to centre hole is 13" 1/4 inch .

    I could not measure the front shock lengths yet.

    My car does sit higher as I have underslung exhaust.

    Some people might add your body weight in the seat and re-measure heights.
    Last edited by jon1d; 01-06-21 at 04:46 PM.
    John Desz

    Essex & Herts Area Rep. UKCC

    Dax 351 Cleveland T5 2.88 PL

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