New bc's installed, now what??

[mmx005]

Hi guys, just few questions from a suspension noob.

I have replaced the 265,000km old suspension in my nb8a with new V1 bc's, and just wonder what hppens now.

Do i need an alignment straight up or later on??

how long will they take to settle, weeks or 0000's of kms??

i also have no idea about the pre load of the springs ie where to set them. The front end feels fine and im happy with that, but my rear end doesnt feel right.it feels quite bouncy when i come off a decent dip or go over a short sharp speed hump unless i crawl it over.

i have kept the dampning at the factory 8 clicks from soft.

cheers,

Ben :-)

[broady]

Go get an alignment.

[Charlie Brown]

Your springs should settle in after about 2 – 3 weeks of driving, then head off for a good alignment. Chris Gough should be able to tell you where to go on the central cast, otherwise get down to Sydney to Spinning Wheel for Stu to do the work.

Preload on your springs should be just enough to capture the spring under full extension unless the manufacturers instructions say otherwise.

To fix the rear bounce you need to harden up the shocks. Go up say two clicks and then test it. If it’s still doing it go up one click at a time until you get the desired ride.

If you’re getting someone on the central coast to do the alignment, I’ll make a stab here and say that as you had big K’s on the old shocks you probably won’t want to do something too aggressive to start with, so get them to set it up as follows: Camber -1.2F, -1.7R, max castor, 2mm total toe in front and 3mm total toe in rear.

[ricky-pinky]

Hey ben,

It's funny you should have issues with your BC rear shocks. I did too. My problem was (in my opinion) insufficient rear damper travel. I posted a thread on this problem about 12 months ago.

If you scroll back through the pages in the suspension topic you will notice quite a few posts on BC racing shocks. Some people put them in straight out of the box and have no problems. Others have had an issue which they have solved in their own ways. I solved my problem by getting a damper with a longer stroke and fitting a taller high-hat to accommodate the longer stroke. I had BR's but I think the V1's are the same geometry.

If you fitted your shocks without moving the lower control arm inner pivot bolts, then you won't have affected your wheel alignment. Let the car settle and get your adjustments sorted before you spend dollars on a wheel alignment. On my car, the rear springs sagged a couple of mm after a couple of weeks, but the fronts didn't move. The rear springs. being shorter and made with smaller diameter steel are more highly stressed.

Ricky

[mmx005]

thank you for the comments gentlemen, much appreciated

Charlie, i thought about what you said with hardening up the shocks. so i went and re deciphered the chinglish instructions and discovered something. i knew i had 30 clicks of adjustment and they come pre set at 8. what i didnt realise is that 0 is the hardest and 30 is the softest, so they are already pretty stiff.
There is no recommondation for preload in the instructions. im not sure where the factory setting was because dad wound up the preload (about 8-10mm) in an attempt to help my hight issue (see below) but then i thought it might just make things really stiff and horrid so i wound it down on saturday arvo before going for my 1st drive. After reading your comments earlier tonight and having a think about it, i wound the preload up 2.5mm according to the verners. Will test drive tomorrow and see.

Ricky, i tracked down your post and a few others. i can sort of understand where you are going, but im no maths or suspension wiz so im on the fence with your issue. i have installed mine straight from the box.

HOWEVER i do have an issue of my own,

i wanted to get the car back to a reasonable hight (i was sick to death of bottoming out etc on my saggy old suspension) so i wound out the hight adjustment on the fronts and took some measurements (with a builders tape measure so its not exactly shop perfect but its pretty damn close) and now have 360mm from the guard to the center of the hub (my research suggests for the front it should be 352 or 345 for an se ) i still have a reasonable amount of adjustment left if i ever wanted to go higher(i DONT). this all good

HOWEVER the rears are another story.

i wound the rears out and then run out of thread. The chinglish instructions say not to wind it out too far as you can damage the thread, but does not state a mimimum amount of thread that has to be kept inside the lower part of the adjuster i.e from the hight locking ring to the end of the threaded shock body. Make sense??? i made an educated guess and have made sure about 10-12mm of thread is in the adjuster. Because of that, my rear measurements are about 350mm but should be 371 or 364 for an se. This made me think i had put the rear shocks in the front and the fronts in the rear but looking at my old ones proved i had installed them correctly. tall shocks in the front, shorter ones in the rear.

Do you see the problem?? if my new stuff settles 5mm im almost back to square 1(the rears had sagged to 330mm befor the change) albeit with stiffer springs etc.

i hope everything makes sense. i have taken some photo's which i might draw on and post to clear things up a bit.

Cheers,

Ben

[Charlie Brown]

Ben,

2.5mm of preload will gain you some suspension height by decreasing sag.

If you have zero preload, when the car is dropped back on the ground it settles to the point where the springs take up the full load of the car.

If you preloading the springs to a force equal to the downward force of the car you end up with no sag. This doesn’t change the spring rate or stiffness which is constant in a linear coilover spring.

There are a number of sites around that explain the principals if you do a search.

I’m not to sure with the NB but with the NC every 1mm change in thread length of the shock alters the wheel height by 1.5mm, so if I want to drop or raise the car 6mm, I move the collar 4mm, so you may still be able to get a little more height in the rears.

The next thing you must do is to make sure that the pitch of the car (check the rail height near the jack points) doesn’t sit lower at the back. Level to 5mm higher at the rear with the car loaded is your target.

Also remember that you can run a little lower than the SE height because the stiffer springs on the coilover will reduce vertical travel on the same given bump.

Good luck.

[Locutus]

i wound the rears out and then run out of thread. The chinglish instructions say not to wind it out too far as you can damage the thread, but does not state a mimimum amount of thread that has to be kept inside the lower part of the adjuster i.e from the hight locking ring to the end of the threaded shock body. Make sense??? i made an educated guess and have made sure about 10-12mm of thread is in the adjuster. Because of that, my rear measurements are about 350mm but should be 371 or 364 for an se. This made me think i had put the rear shocks in the front and the fronts in the rear but looking at my old ones proved i had installed them correctly. tall shocks in the front, shorter ones in the rear.

check this out: viewtopic.php?f=30&t=42337

[Lokiel]

:
so i went and re deciphered the chinglish instructions
:
Ben

The BC coilover instructions ARE complete rubbish and look like they've simply been run through a Google translator and no English speaker read them before they were published.

I found these adjustment instructions somewhere which ARE written in English and may be of help to others:



I'm still driving around with the default dampening (8 from hard), which I like but had to raise the default rear height since I kept dragging my arse over every speed bump.

Keith Tanner from FM recommends the following:

"I'd recommend a ride height around 12-12.5" front and about 1/2" higher in the rear. Raising the car up to 13" in the front will probably take it pretty close to the maximum height on an NB, but as long as you're still on the threads that's not a problem."

[ricky-pinky]

Ben.

There was a post by about this very same problem by 94 clubman perth on 14/06/2010. He got around the problem by switching the front adjusters to the rear and the rear adjusters to the front.

I have BC Racing BR type shocks, but I understand the V1's have the same geometry. The advantage of the BC shocks is that the height adjustment is independant of the spring preload, so it doesn't matter what height you run your car, you still have the same suspension travel. With the BR's, the factory recommended spring preload is 5mm which is TWO-AND-A-HALF turns of the spring collar. However, I run mine with a minimum of preload, ONE-QUARTER of a turn, just enough to stop the spring from becoming loose if the suspension goes to full droop. Also, the factory stated minimum for the adjusters to be screwed on is 25mm. However, when I examined the the adjusters, I saw there was only 20mm of thread anyway, so I figure TEN turns is the minimum amount you should screw the adjusters onto the damper body. The front adjusters can be screwed onto the damper a maximum of THIRTYFIVE turns, so that gives you TWENTYFIVE turns of height adjustment from maximum height to minimum height. The rears can be screwed onto the damper a maximum of TWENTYSEVEN turns, so that gives you SEVENTEEN turns of height adjustment.

My car is a 2002 NB. After I fitted my shocks I had a bit of a play with height settings. At maximum height, ie. with the adjuster only screwed on TEN turns, the front was very close to standard height and the rear was about 20mm lower than standard. So I reckon the rear adjuster is about TEN threads too short! I then lowered the front by FIFTEEN turns, which is 30mm at the shock and, theoretically, 45mm at the wheel, and I lowered the rear by TWELVE turns, which is 24mm at the shock and, theoretically, about 34mm at the wheel. However, the car only settled about 40mm at the front and about 30mm at the rear, because, I think, the compliance of the suspension bushes provides some assistance to the spring in holding the car up. So the car now runs about 45mm lower than stock at the front and about 40mm lower than stock at the rear.

Apparently you are not supposed to lower an NB unless you notify the RTA, but you are permitted to lower an NA. Since raising the car by using the adjusters won't give you more suspension travel, you may as well run it a bit lower because they look nicer lower. If I get caught and have to raise my car, I will be able to get the front up to stock height with the adjusters, but the rear, even at maximum height, will still be about 20mm low, so in order to jack the rear up I will have to increase the spring preload by about SEVEN turns. Increasing the spring preload gives you more suspension BUMP travel at the expense of DROOP travel. In order to get the additional BUMP travel but still maintain the original DROOP travel was why I opted for the 30mm longer dampers, and I fitted the 30mm taller tophats to compensate for the additional piston rod length. With standard BC rear shocks you will only have about 5 to 10mm of piston BUMP travel before the top of the damper hits the bump rubber. In your case, if you want more BUMP travel you will have to increase the spring preload. Rear suspension travel is an issue with the MX5. Mazda made a small diference between the NA and NB, but they increased the NC rear travel using... taller tophats.

As for the shock settings, at first I ran mine on the softest settings, but after things wore in a bit, I increased the stiffness by HALF a turn which is 5 clicks. I think BC shock are a bit soft at the rear, so I may need to stiffen the rear a little more.

I'm quite happy with my set-up, although I reckon out-of-the-box, BC rear shocks leave a bit to be desired. However, as you can see by the responses to the posts on this subject, most people run them out-of-the-box and love them.

Ricky

[ricky-pinky]

Sorry, I misread my data. The car now runs about 40mm lower than stock at the front and about 50mm lower than stock at the rear. It looks a nice height. No rear bottoming issues, even over the nastier speed humps.