TRD shocks and springs

[NoHachi]

No you would have to do some calcs on that.
You are planning on track duty no? How much experience do you have? Do you have any laptimes for reference?
Will you be running street tires (0.8G), semi-slicks (1.0G-1.3G) or slicks (1.4G-1.7G)?
Depending on experience choose the lower number for little experience or the higher number if you run close to class record lap times.

You do the same calcs I did. Static cornering load = static load (veh.weight) and cornering load (approx.).
Static load = ~275[kg]
Cornering load = static load * G-force
Needed bump travel = 1.1*static cornering load / spring rate.

So for street tires you need about 1.1(275+275*0.8 ) / 8 = 68mm bump travel
Street = 68mm
Semi = 76mm - 87mm
Slick = 91 - 102mm
(when using 8kg/mm fronts)

Do you understand how to go from that number to the correct length of the strut and the position of the perch?

[NoHachi]

I would chop 60mm's from the piece of the strut above the spring perch (if possible, don't cut into the threads of the top cap). See how that works out for you. You can get away with just 40mms too if you ensure that the rate goes up towards the end of the stroke (aka use a bumpstop!).

80mms will be way to short. Dropping the car a further 40mm (by moving the perch down) will most likely drop you onto your bellypan or close.

[drako323]

NoHachi Wrote:Static load = ~275[kg]
Cornering load = static load * G-force
Needed bump travel = 1.1*static cornering load / spring rate.

Just a small correction:

Static load = weight * 1G(gravity) = 275kgr*9.81m/sec^2 =~ 2.7KN
Cornering load = weight (on axle) * lateral acceleration (depending on type of tire) * center of gravity height (~0.5m) / half track (~0.7m) =(for 1G lateral acceleration) 275 * (1*9.81) * 0.5 / 0.7 =~ 1.9KN

[4000GT]

Yes full track duty, running slicks.

Oddly enough TRD made spacers to go under the shocks for use with the TRD blues.

[NoHachi]

Drako is right offcourse (thanks for joining in dude!). I used the 1G approximation, hence the "~" and "approx".

If you run the numbers on the static+dynamic loads you get the following results. I also plugged in better numbers for sprung weight of a stock AE86 and added a margin of 10% to soak up road irregularities during cornering.

Street = 72mm
Semi = 73mm - 74mm
Slick = 74- 76mm
(when using 8kg/mm fronts)

So about 75mm needed on average.
available travel = 155mm - 75mm = 80mm minimum compressed length of spring. So the strut is about 20mm too long to avoid top hat contact.

To make a long story short -> remove 40mm of material "above" the spring perch. Use a 20mm spaces "under" the shock and you should be golden. Captive springs, decent travel and bumpstops to save your shock towers.

The spacers from TRD have a different reason. Not only the stroke is shorter, but so is the shock body. So you also need some spacers under the strut fill up the space. If they are ~20mm long then they are supposed to work with 40mm strut shortening.

[4000GT]

Good thing those TRD spacers are still available

I get all the principles discussed, but it wont be till Im mucking around with it that the numbers fall into place. In terms of cutting the strut about be perch, where is best to trim it?

[drako323]

drako323 Wrote:

NoHachi Wrote:Static load = ~275[kg]
Cornering load = static load * G-force
Needed bump travel = 1.1*static cornering load / spring rate.

Just a small correction:

Static load = weight * 1G(gravity) = 275kgr*9.81m/sec^2 =~ 2.7KN
Cornering load = weight (on axle) * lateral acceleration (depending on type of tire) * center of gravity height (~0.5m) / half track (~0.7m) =(for 1G lateral acceleration) 275 * (1*9.81) * 0.5 / 0.7 =~ 1.9KN

Heheh, now I have to correct myself also:

It's weight on axle, which is 275*2=550kgr, but it is not half track, it's whole track (1.4m). Result is the same, once again two false = one correct!

[drako323]

NoHachi Wrote:Drako is right offcourse (thanks for joining in dude!). I used the 1G approximation, hence the "~" and "approx".

If you run the numbers on the static+dynamic loads you get the following results. I also plugged in better numbers for sprung weight of a stock AE86 and added a margin of 10% to soak up road irregularities during cornering.

Street = 72mm
Semi = 73mm - 74mm
Slick = 74- 76mm
(when using 8kg/mm fronts)

So about 75mm needed on average.
available travel = 155mm - 75mm = 80mm minimum compressed length of spring. So the strut is about 20mm too long to avoid top hat contact.

To make a long story short -> remove 40mm of material "above" the spring perch. Use a 20mm spaces "under" the shock and you should be golden. Captive springs, decent travel and bumpstops to save your shock towers.

The spacers from TRD have a different reason. Not only the stroke is shorter, but so is the shock body. So you also need some spacers under the strut fill up the space. If they are ~20mm long then they are supposed to work with 40mm strut shortening.

Best is to remove a part of the strut between the perch and the start of the thread, so you can weld this part back on. It's a bit tricky to align it exactly but this way you don't have to make a new thread in the strut, which would require a lathe (or some pretty rare taps I have never seen). One way to align it is to fit the insert in the strut, then the cut part over it, tack weld, remove the insert and then make the complete seam weld (always in steps to avoid too much warp).

[4000GT]

Out of interest, the spacer at the bottom is to ensure the shock is supported and not floating correct? Is the threaded section at the top not sufficient to take the load?

[NoHachi]

No you end up with a strut housing that is longer then the TRD shock (they are in reality AE92 shocks). At rest the shock would be hanging inside the cartridge. The shock doesn't come into work untill the slack is taken up by spring compression. After that the shock hits the bottom of the cartridge with a nice little bang and starts working. No good.
You add a spacer under the shock to make things nice and snug. The shock starts working immediately during compression.

The spacer itself is just a lump of metal, something anyone can make on the quick.