Real Fiero Tech

Finally got around to doing a bounce test on my '87 Chump Fiero with the 260# front springs. Disconnected the front shocks and bounced the front end as per this page:
http://www.smithees-racetech.com.au/per ... ctors.html

I did the test several times and the average was 2.05 cycles/second. Has another else done this test, and if so, what were the results? I'm going to see about getting a wheel rate using ballast and scales to add another data point plus I'll get some measured motion ratios.

Okay, step 2 is done: ballast fo find wheel rates.

Front wheel rate is 130 #/in with 260 #/in springs. Works out to a motion ratio of 0.71, very close to the measured 0.69.
Rear wheel rate is 240#/in with 300 #/in springs. Works out to a motion ratio of 0.89, not too far off the 0.86 usually cited (didn't measure this one).

Scale weights are 525 lbs front/corner and 720 lbs rear/corner. I'm assuming about 90 lbs unsprung front and 100 lbs rear, so sprung is 435 front/ 620 rear. Frequency works out to 1.71/1.95 hz.

I don't trust my bounce test because I can't get enough movement of the suspension. A shorter stroke of the suspension would give a slightly quicker cycle rate than the wheel rate calcs indicate, matching what I'm seeing.

With urethane bushings there's also a lot of friction in the suspension, and a lot of goofiness with rubber. I wouldn't trust bounce test results seriously.

I have urethane in the front, but the main issue I see is the amount of scrub that the front tires have as the suspension cycles. I might borrow some wheel alignment plates and try it again to see if that helps.

looks like QA1 does struts again... may be worth looking into, double adjustable coilovers available, a little over a grand for struts and springs, but the springs aren't available in very high rates as part of the package.

Edit: forgot to add the link...

http://www.qa1.net/suspension/street-pe ... ut-systems

I'm about to get new springs for the rear of my car, and thought it would probably be a good idea to update the fronts as well to match them. anyone have suggestions? the car is an 85, with an 88 rear cradle thrown in, and stock front suspension. weight distribution should be about like stock. I'm running 18x8" fronts with 225/40's, and 18x9.5" rear wheels with 285/35's. I was planning on a 400-450# rear spring, but wasn't sure about what to do with the front. I would like to do coilovers, I've seen people convert 88's to coilover, but not 84-87, either that or I haven't looked in the right places. future plans include the anti-dive brackets like Will made for his car, and Fieroguru's lateral link relocation brackets, and if I can find them, drop spindles for the front to bring it back to or slightly lover than stock after the dive brackets.

I appreciate any advice, I don't have alot experience with spring rates and shocks.

Thanks-

Eric

ericjon262 wrote:looks like QA1 does struts again... may be worth looking into, double adjustable coilovers available, a little over a grand for struts and springs, but the springs aren't available in very high rates as part of the package.

Edit: forgot to add the link...

http://www.qa1.net/suspension/street-pe ... ut-systems

Bilstein, Koni and others have universal motorsport struts that would probably be easier to adapt... although not cheaper.

ericjon262 wrote:I'm about to get new springs for the rear of my car, and thought it would probably be a good idea to update the fronts as well to match them. anyone have suggestions? the car is an 85, with an 88 rear cradle thrown in, and stock front suspension. weight distribution should be about like stock. I'm running 18x8" fronts with 225/40's, and 18x9.5" rear wheels with 285/35's. I was planning on a 400-450# rear spring, but wasn't sure about what to do with the front. I would like to do coilovers, I've seen people convert 88's to coilover, but not 84-87, either that or I haven't looked in the right places. future plans include the anti-dive brackets like Will made for his car, and Fieroguru's lateral link relocation brackets, and if I can find them, drop spindles for the front to bring it back to or slightly lover than stock after the dive brackets.

I appreciate any advice, I don't have alot experience with spring rates and shocks.

Thanks-

Eric

IIRC, Steven's running 475's rear and ~700 front, but that's with 1.4:1 mechanical advantage and 2.0:1 motion ratio.

If making your own arms for coil overs in an early chassis, relocate the shock attachment point as far out on the control arm as you can. You'll adjust the spring rate down, of course, so the wheel rate will stay relatively constant, but having a softer spring in a coil over means you don't need as stiff a damper, which means a cheaper damper can do the job.

My plan is to use 2x2 or 2x3 square tubing for the lateral portion of the lower arm from the forward pivot out to the ball joint.
The "thrust arm" from the ball joint back to the rear LCA attachment point can be a threaded sleeve arrangement as it doesn't have to bear any bending loads, just compression from bumps and brake application. This has the added bonus of being able to fine-tune wheelbase side to side and/or add caster.

awesome, thanks for the insight.

The anti-dive blocks eliminate all the caster the stock UCA's can produce. I think right now I have slightly positive on one side and slightly negative on the other.
Fully adjustable UCA's are absolutely required with anti-dive blocks in order to get the caster back and keep the vehicle stable. Negative mechanical trail on the outside front in a corner really sucks to drive.
I think I have a design that's workable and simple to fabricate. I'll whip a set out when I get back.

The Dark Side of Will wrote:The anti-dive blocks eliminate all the caster the stock UCA's can produce. I think right now I have slightly positive on one side and slightly negative on the other.
Fully adjustable UCA's are absolutely required with anti-dive blocks in order to get the caster back and keep the vehicle stable. Negative mechanical trail on the outside front in a corner really sucks to drive.
I think I have a design that's workable and simple to fabricate. I'll whip a set out when I get back.

I remember reading that in your build thread, and was definitely on the list of things to fix. I think the front of this car is about to get turned inside out though...

Not sure what car you're talking about, as Fieros don't have struts in the front.

Are you a bot?

Deleted known spammer.

Cool. Thanks.

Picking up a little where Steven left off... as one gets up into the 1.8 to 2.0 suspension frequencies on the fiero with ~450lb rear springs and stock sway bar the Koni red rear struts start to fall a bit short in their dampening ability. Enter the Koni 8611s or 8610s.

Looking into trying to install a set of koni 8611s or 8610s into the rear OEM Fiero strut housings. I've looked over this site and OE and have found very little info and no one has tried this or achieved a theoretical 'can it work'. Furthermore, this may be a way to obtain high performance rear struts again now that koni has stopped making the fiero rear struts.

Does anyone have any old OEM struts lying around that they could crack open and get the following measurements?

Overall shock length Extended and Compressed
housing ID and OD
Internal housing depth
Gland nut size and thread

draven wrote: ↑Wed Oct 09, 2019 12:35 pm Picking up a little where Steven left off... as one gets up into the 1.8 to 2.0 suspension frequencies on the fiero with ~450lb rear springs and stock sway bar the Koni red rear struts start to fall a bit short in their dampening ability. Enter the Koni 8611s or 8610s.

Looking into trying to install a set of koni 8611s or 8610s into the rear OEM Fiero strut housings. I've looked over this site and OE and have found very little info and no one has tried this or achieved a theoretical 'can it work'. Furthermore, this may be a way to obtain high performance rear struts again now that koni has stopped making the fiero rear struts.

Does anyone have any old OEM struts lying around that they could crack open and get the following measurements?

Overall shock length Extended and Compressed
housing ID and OD
Internal housing depth

I think we'd be better off looking at the envelope and figuring out how to build a shell from scratch that works as an inverted strut. Steven has already crunched the numbers and figured out which Bilstein damper would work. There may be a Koni of similar dimensions.

draven wrote: ↑Wed Oct 09, 2019 12:35 pm Gland nut size and thread

OEM struts are welded. No gland nut, which is yet another factor in building from scratch. Actually... Koni has a PN for an M48x1.5 gland nut. I ran across it in dealings with BMW stuffs.

Oh I have delusions of grandeur about mounting duplicate 88 lateral links, or custom A-Arm, to the frame to a bracket on the rear upright strut holes more or less reproducing the same geometry as the lower links, but with better camber curve, then add any number of shock types to the same upright bracket to the strut tower mounting plate..lots of possibilities there...

I'm just looking for something that may be 'relatively' cheap and reproducible by others and make use of the old housings...

Although the Koni J-body strut inserts are discontinued, the J-body crowd and the Beretta guys utilize the Gen 1 Eclipse/Laser strut inserts with a spacer.

Furthermore I found a vendor in Australia, surely one equivalent stateside, that makes female gland nut inserts/spacers for housings that don't already have them.

draven wrote: ↑Wed Oct 09, 2019 12:35 pm Gland nut size and thread

OEM struts are welded. No gland nut, which is yet another factor in building from scratch. Actually... Koni has a PN for an M48x1.5 gland nut. I ran across it in dealings with BMW stuffs.
[/quote]

Koni Gland Nuts
Thread & Pitch Part Number
M48 x 1.50 73.25.01.003.1
M48 x 1.00 73.25.01.002.1
M51 x 1.25 73.25.01.006.1
M51 x 1.50 73.25.01.007.1
M52 x 1.50 73.25.00.025.1
52.8WW 73.25.01.011.1

After further removing some minor rust scale from my frunk in preparation for paint I obtained some measurements on our OEM strut housings. 2" OD housing, 13" housing length, 20" length with a 5" stroke, if the housing can have an internal threaded adapter for a gland nut then either

8611-1256 Race
or
8611-1257 Race

would work in our housings..

see: https://www.koni-na.com/en-US/NorthAmer ... e_Inserts/

I think I have original struts on my 88.

I just pulled them off the car. I can snap pics if anyone wants.

Shaun41178(2) wrote: ↑Fri Oct 11, 2019 12:04 am I think I have original struts on my 88.

I just pulled them off the car. I can snap pics if anyone wants.

If you could, verify the measurements I have above, extended length, compressed length, housing length, housing width etc...

If you're going to toss them could you snap some pics of the top of the housing where the cap is welded and then cut it off find out the inside diameter/gauge of the housing. Then hold onto them if you might want to duplicate what I'm doing after I pull it off.... short of a readily available female gland nut insert I think it's highly likely...