ArAKern
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| posted on 25/10/17 at 10:38 AM |
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Shock lengths road going Phoenix
Hello All
Could anyone give a some advise on the correct shock lengths for a road going phoenix?
The car is an original STR chassis and i believe they had 65mm under the front rail, but after
speaking to RAW they recommend 120-140 cm which would be more road friendly.
I tried winding up the shocks but i am nearly at the end of the travel and have not achieved 120mm
clearance. I am assuming i have race length shocks?
Many thanks
ArA
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Angel Acevedo
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| posted on 25/10/17 at 01:57 PM |
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Regarding Ride height 100 mm would be OK if you drive conservatively and are aware of sleeping policeman.
I am going for 100 mm front 112 mm rear.
You state that you havent reached 120 and are at end of travel..
What is the extended length of your dampers (shocks)?
The length you need will be dictated by your Suspension Brackets and upright Pivot points.
Easiest way to achieve is lifting chassis @ desired ride height, Measuring Length, Decide how much travel you are willing to have, longer will allow
for softer suspension therefore comfier ride, shorter will lead to stiffer ride...
Travel may be limited by suspension components/tyres hitting parts of the chassis or body, or chassis components hitting the ground.
Once you know what you want and can accomodate, deduct this length from Ride height length ad this will be your dampers closed length.
Then you add a similar amount to Ride Height length and you will get extended length.
If you are close to the maximum extended length, you may get some air on droop which is undesirable at best and may be dangerous at worst.
You should attempt to have half the travel for bump and half for droop.
I have gone for two thirds bump and one third droop... My reasoning to do so is that I want to have additional travel before hitting solid...
Hope this helps.
AA
Beware of what you wish.. for it may come true....
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ian locostzx9rc2
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| posted on 25/10/17 at 02:46 PM |
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If you can get 100mm lowest part of car / sump you should be fine .
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rodgling
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| posted on 25/10/17 at 07:14 PM |
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quote:
Originally posted by ian locostzx9rc2
If you can get 100mm lowest part of car / sump you should be fine .
#
Agreed, IME 80mm is about the bare minimum, I get occasional light scrapes of the sump at this height. 100mm ought to be plenty.
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procomp
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| posted on 26/10/17 at 04:09 AM |
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Hi.
Not quite that simple, STM Pheonix chassis where built specifically for racing with suspension pickup points placed in a higher position than JP
cars.
You need to run 80mm under front chassis just in front of front wheels using 185/60/13 tyres on front and a rake of 12 -19mm with drivers weight
taken into acount using 205/60/13 on rear
Simply raising the ride height to 100mm will place the pivot crs at the wrong angles and make camber control and handeling appaling.
If wanting to run a higher rideheight move upto 15" rims to maintain pivot crs angles.
Once you have the rideheight set either with packing under chassis or by use of exsisting dampers and springs measure damper bolt crs to give a static
height then add the extra required for droop travel, usualy 25-32mm.
Cheers Matt
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Angel Acevedo
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| posted on 26/10/17 at 02:57 PM |
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quote:
Originally posted by procomp
Hi.
Not quite that simple, STM Pheonix chassis where built specifically for racing with suspension pickup points placed in a higher position than JP
cars.
You need to run 80mm under front chassis just in front of front wheels using 185/60/13 tyres on front and a rake of 12 -19mm with drivers weight
taken into acount using 205/60/13 on rear
Simply raising the ride height to 100mm will place the pivot crs at the wrong angles and make camber control and handeling appaling.
If wanting to run a higher rideheight move upto 15" rims to maintain pivot crs angles.
Once you have the rideheight set either with packing under chassis or by use of exsisting dampers and springs measure damper bolt crs to give a static
height then add the extra required for droop travel, usualy 25-32mm.
Cheers Matt
What he said...
An educated answer... Compared to mine (amateurish)...
AA
Beware of what you wish.. for it may come true....
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ArAKern
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| posted on 26/10/17 at 04:41 PM |
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Ok please help my ignorance but what is "CRS" angles
so just to add some info my phoenix is a very early STM chassis with box section not round tube some have mentioned it may be an actual JP chassis.
As to having 80cm under the rail would make the car undrivable and the sump hangs under the rail by about 20-30mm cannot measure exactly at the moment
the engine is out of the car. (and before anybody mentions the idea the sump has already been cut and shut  )
Currently the car is running 16" wheels so I hope this will help with "pivot crs angles".
The car will never see a track only some spirited Sunday driving once in a while, all i need it to be is driviable / predictable and comfortable would
be nice bonus.
Will try and get some measurements this weekend and report back. Next questions will be on spring rates think mine are 300 Front 200 Rear....
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Angel Acevedo
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| posted on 26/10/17 at 04:58 PM |
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Where are you located?
That may help you get local help or recommendations to a pro near you...
Again.
Straightforward to driveability, select proper ride Height (with proper, whatever makes you comfortable)
Select appropriate Bump travel according to desired level of comfort -longer travel = softer ride
Based on those two select appropriate Shock Length.
Finally, you may or may not need to change your springs to a usable length.
Sprung weight per wheel may give you a good starting point as per Spring rate, there are several threads addressing this.
Then you will neede to drive the car some to adjust according to preferences...
Lighter spring softer ride/more roll
Stiffer springs harder ride/less roll..
Then you may want to change spring rate balance.... and so on and on...
Beware of what you wish.. for it may come true....
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procomp
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| posted on 26/10/17 at 06:28 PM |
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Pivot crs are the outer ball joint centres on the upright and the wishbone bolt at chassis end centres.
The heights from the floor to the ball centres at the upright will determine what the height of the wishbone bolt centres.
If its a jp chassis you will have a sherpa lower joint and Metro top joint.
If a STM chassis it may have same joints or a few rose joints.
If it is a jp race or stm it will have the wishbone mountings on chassis raised to allow chassis to run a 80mm ride height.
If a std jp chassis it will have std chassis pick up points allowing for a rideheight of 100 - 110mm ride height unde front chassis.
For a start measure from floor to cetre of lower outer ball joint. Height. Then set rideheight so the wishbone chassis bolt centre is a same height IE
level. That then puts you chassis and rideheight into the small window of static ridehight.
Measure the length of damper bolthole centres then add 30mm to give the correct open length of damper for the application.
[Edited on 26/10/17 by procomp]
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ArAKern
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| posted on 26/10/17 at 10:19 PM |
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Many thanks Procomp and AA for the advise so far!
Will get the tape measure out tomorrow 
AA I am based in Southampton. for my road cars I use http://www.wheelalignmentcentre.co.uk (Nick has always been fantastic 25+ years working for
Supertracker)
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ArAKern
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| posted on 27/10/17 at 04:34 PM |
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Ok so I have taken some measurements!
Front Damper Length closed / open 255 - 330mm
Rear Damper Length closed / open 245 - 315mm
Between damper bolt holes max values for Droop and Bump
Front Bump-Droop 275 - 350mm
Rear Bump-Droop 280 – 390mm
So now onto this “For a start measure from floor to cetre of lower outer ball joint”
 
Description
Where exactly am I taking this measurement from?
1) set at 190mm length of damper bolthole centres is 315mm if we add 30mm
open length of damper for the application = 345mm so my dampers are 15mm short
(but form a quick googling dampers come in 13” or 14” 330mm or 356mm)
2) set at 215mm then it ~345mm + 30mm = 370mm which is beyond my max droop….
Also on the rear does the same apply eg set front add rake 12-19mm then measure damper bolthole centres add 30mm?
(this measured at ~340mm + 30 = 370 rear shocks are very short.)
Sorry lots of questions much learning to do 
So what is the recommendation either live with my current dampers or adapt the chassis? Or leave well alone?
Your continued support is much appreciated
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