BC Racing Coilovers into MA61

[rdorman]

found out BC cant do 6kg rears in these springs, would it be hard to get them custom made to suit? trying to work out whether to get 10/8kg and get all 4 changed if its too stiff for daily, or 8/8kg and just change the rears.

[82MKII]

Shouldn't be too hard to get them custom made. There seem to be custom spring manufacturers in most states.
Dimensions of rear springs from BC are: Rear 117 mm diameter at one end, 119 mm diameter at other end (ground flat), 200mm free length, 8kg/mm.

So I guess you'd ask the spring guys for: Rear 117 mm diameter at one end, 119 mm diameter at other end (ground flat), 230mm free length, 6kg/mm. Note you will need to ask for a longer free length (as they will compress more). I'm no expert in predicting what length you will need, but given that the springs that come with the kit are only just long enough, i'd go at least 230mm, maybe even 250mm.

There might be enough of us interested to buy a few sets to lower the overall cost as well.

[patrickleslie]

Note you will need to ask for a longer free length (as they will compress more). I'm no expert in predicting what length you will need, but given that the springs that come with the kit are only just long enough, i'd go at least 230mm, maybe even 250mm.

You can always adjust the height shorter anyway. How much height range do you have now?

[82MKII]

The adjustable spring perches are wound up to get as much height as possible now.
I could drop it by about 40mm.

[rdorman]

thanks so much for that 82mkII!

i spoke to a place here in adelaide today, when i get my springs i will take them down a sample and they should be able to make them. they dont usually do tapered springs, however because its only a couple of mm they can expand them or sleeve their tooling to account for the extra couple of mm on the top end.
thanks for the info reg lengths, i didnt even think of that! so you're saying they should have come around 230mm from factory in the first place, to get a little bit more height adjustment? im guessing the 2kg lighter rate will make it sag a little more?

also just a note for anyone reading this, BC can do any rate for the fronts, they are no issue in kgmm increments. the rears are another story, and the only springs BC do for the rear are 8kg. ive seen elsewhere someone thought he got a 9/7 kit, had a look at the photos and they are the standard 10/8.

[Rodger]

rdorman.

Good reading so far and interesting way to do rear set up. Must keep this in mind.

Perhaps the difference in diameters top and bottom is due to the required inside diameters. At the top the combination of spring perch diameter and the wire diameter of the spring means the spring needs the extra few millimeters to clear. Perhaps BC makes a straight spring and expands out the top?
Perhaps BC have other rate rear springs that have the correct inner diameter not neccessarily a similar taper.

Any custom made spring will need to have the correct inside diameters to clear the perch, this could be ok at the bottom allowing a straight spring to be made.

Regards

Rodger

[rdorman]

i thought about that Rodger, and managed to stumble across this pdf which i believe shows most of the springs that BC manufacture.

http://flushstance.ccwheel.com/wp-co...il-Springs.pdf

[82MKII]

Good find rdorman - looks like no other 117/119 combos available from BC.
I crawled under the car this morning and took some more measurements.
The compressed length of the spring is roughly (hard to measure) 155mm, hence it has drooped 45mm. Hence a 6kg/mm spring should droop by 60mm (45x8/6), or 15mm more than the 8kg/mm spring.
Hence you would want the free length to be at least 15mm more in the 6kg/mm spring (ie 215mm).
To put the height 'in the middle' of the adjustable perch range (about 40mm total), I'd add another 20mm to that. ie total of 235mm free length for a 6kg/mm spring.
As I said before, I'm no spring expert, so if anyone else has a different interpretation of how to calculate this I'm all ears.

Regards

Peter

[1G-GTE]

do the rear bc's have adjustable damping like the fronts?

[rdorman]

its not as easy im led to believe, need to take the strut off at the bottom and rotate it to adjust?

[82MKII]

Yes it is adjustable (32 levels, like the front), and no you don't have to rotate the bottom to adjust - just rotate a knob on the top of the shock (like the fronts).

[rdorman]

ah thats nice then! what is the bottom rotation? height adjust of the strut?

[82MKII]

Yep, when you are setting the max length of the shock (to make sure your springs are still captive at max suspension travel), you screw in/out the bottom section of the shock.

[rdorman]

thought i would post it here to keep all this info together:



230mm, 6kg.

will fit them this weekend, and update here with a couple of photos once it settles. if i need to take them back to get them shortened / lengthened i can once for free apparently, but they should be alright. custom made here in Adelaide, if it works out okay ill post up some more details reg the order. wasnt too expensive either

[marvis]

AJPS do rear 6kg springs too.