84-87 stock front suspension wheel rate

[pmbrunelle]

At some point, I figured I would want to restomod the original suspension on my Fiero.

Before doing any mods however, I wanted to record some "baseline" parameters.

I looked online for the info, but didn't find any. Maybe my google-fu is no good. So I did a more "calculation" approach, and a direct measurement approach, to see if the two methods would agree with each other. I present my findings here for reference.

DUT:
1985 Fiero SE
WS6 RPO code on the tag
FJH paper tag on the front springs
NYM paper tag on rear springs

*****Calculation approach*****
A-arm bushing to spring distance: 6.75 in (measured in the car with a measuring tape)
A-arm bushing to ball joint distance: 11.25 in (measured in the car with a measuring tape)

Active coils: 7.25 (guesstimate, I looked for where the rusty zones of contact between the coils started/stopped)
Mean coil dia: 3.875 in (measured in the car with a measuring tape)
Wire dia: 0.504 in (measured in the car with a cheapy Mastercraft caliper)

Modulus of rigidity: 11600000 psi (generic value; I did not measure this)

Wheel rate by calculation: 79.8 lb/in

*****Direct measurement*****
Test procedure:
Ensure that swaybar is not connected
Place feet on bathroom scale
Using a prybar, force the knuckle up to a height of 2.5 in off the droop limiter.
Note the weight on the scale
Now, allow the knuckle to descend to a height of 0.75 in off the droop limiter (1.75 in displacement). As you do this, your body weight will be transferred from the prybar to your feet on the scale.
Note the weight on the scale (in reality, the delta relative to the first reading).

In my case, I measured the displacement relative to the garage floor, not the car body. The car body (rocker panel) moved by 0.075 in during the supposed 1.75 in indicated displacement, so the actual displacement of the knuckle relative to the car is equal to 1.675 in.

Change in load on the bathroom scale for 1.675 in of suspension travel:
Trial 1: 38 lb
Trial 2: 34 lb
Trial 3: 29 lb
Trial 4: 36 lb

Standard deviation: 3.86 lb (for information only)
Average: 34.25 lb

Crowbar hand-to-fulcrum distance: 23.5 in (measured with a measuring tape. I tried to push with my hands on a line drawn onto the bar)
Crowbar fulcrum-to-knuckle distance: 6.5 in (measured with a measuring tape)

Wheel rate by direct measurement: 73.9 lb/in

Initially, I did the wheel rate test with a small movement from 0.250 in to 0.050 in (with a dial indicator stuck on the spaceframe). This didn't work; I got a result of 1150 lb/in. I believe the suspension was still stuck against the droop limiter, which was rather stiff and not representative of normal driving.

[ericjon262]

neat! what are your plans for the suspension? something completely custom? or just improvements on the existing equipment?

[pmbrunelle]

Presently I have 215/60R14 Radial T/As on the stock 14" wheels and a rear sway bar.

So the first step before doing anything is to pick a wheel/tire combo, probably in these sizes:
205/55R16, 16x7, ET+45 (I want the high offset to reduce steering kickback)
245/45R17, 17x7.5, ET+45 (not sure about knuckle/strut clearance, but I want the wheel sunken in to avoid too much of a poke/modified look)

I was thinking of Enkei M52 in Hyper Black (i.e. gunmetal):
https://enkei.com/shop/wheels/performance/m52/

Suspension restoration/mods would follow logically:
Coilovers in the rear for tire clearance
Chop the front springs a bit to look cool
Trim the front bumpstops to avoid bottoming out
Which leads to pulling the front crossmember to do a sandblast + paint job after rewelding the bumpstops
Sandblast + paint the wishbones; install new ball joints + bushings

So no crazy plans... essentially keeping the stock stuff.

I have a spare rear cradle if I want to do some anti-squat mods at a later time; by not modifying the cradle that's in the car, I can roll back the change if it doesn't work out.

For now I just want to get my Fiero running on the stock wheels/suspension. Getting parts may be difficult for a while, so I don't want to dismantle too much of the car and be unable to put it back together due to difficulty in getting parts. I could also encounter cashflow problems due to me losing my job... that would put a halt on any expensive car project activities.

Once I get the car driveable, I'll want to work on the auxiliary gauges project. If there are any delays with the gauge install, the driveability of the Fiero isn't at risk.

I need to do some maintenance on my daily driver (coolant leak from timing cover gasket, clutch master sucks, no parking brake, rust holes), so I want to get my Fiero working so I can take the daily out of service for a few weeks.

[The Dark Side of Will]

Presently I have 215/60R14 Radial T/As on the stock 14" wheels and a rear sway bar.

So the first step before doing anything is to pick a wheel/tire combo, probably in these sizes:
205/55R16, 16x7, ET+45 (I want the high offset to reduce steering kickback)
245/45R17, 17x7.5, ET+45 (not sure about knuckle/strut clearance, but I want the wheel sunken in to avoid too much of a poke/modified look)

I totally get if there's a budget constraint, but have you read my trials and tribulations in fitting a C5 Corvette 18x9.5 to the rear?

viewtopic.php?p=152247#p152247

[ericjon262]

I like those wheels, IIRC, they made the short list before I bought my Enkei Kojin's. I plan to spend quite a bit of time investigating improvements to the suspension of my car once I get is on the road again, I'm honestly thinking of a ground up clean sheet design using off the shelf motorsports parts so that the car can not only perform better, but also more reliably while being easier to service. ideally I'd be able to find off the shelf spindles and control arms, but I don't think that's realistic. when I'm not deep into other aspects of my life, I try to read up on the engineering behind suspension and steering systems, but I still have a TON to learn.

[pmbrunelle]

Yes Will, I saw that wheel-fitting part of your project. It's a good thing for the 84-87 Fiero community, since it defines an envelope that someone could stay within and not ask too many questions with regards to tire clearance.

You didn't have Fiero knuckles for that test, did you? Do you think your results would be transferable to someone running Fiero knuckles?

For this Fiero, I want to stick with narrow front tires for these reasons:

• I expect to do a bunch of cruising on rutted highways. I think narrow front tires will have less of a tramlining tendency.

• Probably less hydroplaning tendency too in case of rain driving.

• I want to keep steering effort down during parking maneuvers.

• Wheels and tires in this front/rear sizing combination can be sourced from multiple manufacturers; hopefully this configuration is robust to future supplier changes.

• And you said it, budget! Not only for now, but for future tire replacements.

The rear tire size follows from the selection up front.

Grip as such is not top priority... I'm not looking for this build of mine to shine in any particular category. It's a general-purpose sports car.

********************************************************************************

I like that these wheels look easy to wash... also offering access to the brake calipers for washing. I'm also done with polished wheel lips... it's a maintenance headache. I prefer all painted. Also faster/easier to blast+repaint when the time comes.

Eric, I saw this thread of yours:
viewtopic.php?f=6&t=21549

I would suggest an engineering degree as your next challenge after your Navy life. You can read books about suspension and steering, but I guarantee that it will sink in 1000% better once you have a better grounding in the fundamentals. A degree in school is not the only way to learn things, but it is the fast/lazy guy shortcut to learning.

[ericjon262]

Eric, I saw this thread of yours:
viewtopic.php?f=6&t=21549

I would suggest an engineering degree as your next challenge after your Navy life. You can read books about suspension and steering, but I guarantee that it will sink in 1000% better once you have a better grounding in the fundamentals. A degree in school is not the only way to learn things, but it is the fast/lazy guy shortcut to learning.

it's definitely something I'm interested in pursuing, I need to start working on a formal plan to do it though.

[The Dark Side of Will]

Yes Will, I saw that wheel-fitting part of your project. It's a good thing for the 84-87 Fiero community, since it defines an envelope that someone could stay within and not ask too many questions with regards to tire clearance.

You didn't have Fiero knuckles for that test, did you? Do you think your results would be transferable to someone running Fiero knuckles?

Yes, the results are transferable. The A-body large pattern knuckles are exact fit for the Fiero knuckles. The hub bearing offset is 42mm for both cartridges. It'll all work with the stock Fiero knuckles.
Now... would I want to run sticky 285's (or wider?) on the stock Fiero wheel bearings? Of course not.

My next step is to wrap up the design of my strut clamp extension plates so that I can test them... I think I can run 18x11-55mm wheels without spacers or adapters once those extension plates are installed. The edge shape to weld to the strut is a little complex, but I think I only have a couple more revs left to get it perfect. I've had other priorities, though.

[The Dark Side of Will]

I like those wheels, IIRC, they made the short list before I bought my Enkei Kojin's. I plan to spend quite a bit of time investigating improvements to the suspension of my car once I get is on the road again, I'm honestly thinking of a ground up clean sheet design using off the shelf motorsports parts so that the car can not only perform better, but also more reliably while being easier to service. ideally I'd be able to find off the shelf spindles and control arms, but I don't think that's realistic. when I'm not deep into other aspects of my life, I try to read up on the engineering behind suspension and steering systems, but I still have a TON to learn.

Select wheels and tires FIRST, then suspension. The whole point of suspension is to take maximum advantage of the tires. No amount of suspension work will make a car fast on crap tires.

I do agree with you on using shelf racing parts for updates, with the caveat that specific production parts (e.g. C7 Corvette rear wheel bearings with 33 spline CVs) should good to add to the mix as well.

Another job I have in the pipeline is to translate the CMM data I have on the '88 Fiero knuckle into a drawing that Coleman can use to build replacement '88 Fiero knuckles, but which accept C5/6/7 Corvette front wheel bearings instead of the '88 cartridges. With a fresh supply of knuckles that accept strong bearings, converting the '84-'87 cars to accept those knuckles is *mostly* a matter of extending the control arms and tie rods. With the offset of the knuckle so much lower, There may be room outboard of the '84-'87 bumpstop for a coil-over that passes through the UCA, making for a bolt-on motorsport-caliber front suspension.

[ericjon262]

Select wheels and tires FIRST, then suspension. The whole point of suspension is to take maximum advantage of the tires. No amount of suspension work will make a car fast on crap tires.

I do agree with you on using shelf racing parts for updates, with the caveat that specific production parts (e.g. C7 Corvette rear wheel bearings with 33 spline CVs) should good to add to the mix as well.

Another job I have in the pipeline is to translate the CMM data I have on the '88 Fiero knuckle into a drawing that Coleman can use to build replacement '88 Fiero knuckles, but which accept C5/6/7 Corvette front wheel bearings instead of the '88 cartridges. With a fresh supply of knuckles that accept strong bearings, converting the '84-'87 cars to accept those knuckles is *mostly* a matter of extending the control arms and tie rods. With the offset of the knuckle so much lower, There may be room outboard of the '84-'87 bumpstop for a coil-over that passes through the UCA, making for a bolt-on motorsport-caliber front suspension.

Paraphrasing a quote I heard a few years ago

"Every discussion on suspension design should start and end with the tires."

it makes sense because as you said, the job of the suspension is to maximize the use of the tire.

C5/6/7 bearings were actually already in my plans, they're built for a heavier, high performance car, so a in a lighter car they should be able to last damn near forever, and be easy to source replacements for. the other perk is built in wheel speed sensors.

this is all a ways down the road still, I have a huge pile of projects to finish before I consider one like this.

[The Dark Side of Will]

Paraphrasing a quote I heard a few years ago

"Every discussion on suspension design should start and end with the tires."

Where'd you hear that?

C5/6/7 bearings were actually already in my plans, they're built for a heavier, high performance car, so a in a lighter car they should be able to last damn near forever, and be easy to source replacements for. the other perk is built in wheel speed sensors.

FYI, the C7 bearings... at least the rear ones, do NOT have built in wheel speed sensors. My guess (hope?) is that they needed so much space inside the cartridge for bigger, stronger, further separated bearings that they ran out of room for the wheel speed sensor. I haven't looked at a C7 front yet.

EDIT: My main consideration for the C7 rears as opposed to earlier Corvette rears was the 33 spline CV joints. The 33 spline outer CVs used in GM FWD large cars (e.g. Dustbuster minivans) from the early '90's on makes those CVs readily available. I need to verify this, but I suspect they spline right on to Fiero manual transmission axles.

[ericjon262]

Where'd you hear that?

some forum on the internet, last I checked about 80% of Fiero owners think it's the gates to hell... LOL.

FYI, the C7 bearings... at least the rear ones, do NOT have built in wheel speed sensors. My guess (hope?) is that they needed so much space inside the cartridge for bigger, stronger, further separated bearings that they ran out of room for the wheel speed sensor. I haven't looked at a C7 front yet.

EDIT: My main consideration for the C7 rears as opposed to earlier Corvette rears was the 33 spline CV joints. The 33 spline outer CVs used in GM FWD large cars (e.g. Dustbuster minivans) from the early '90's on makes those CVs readily available. I need to verify this, but I suspect they spline right on to Fiero manual transmission axles.

The VSS bit is good to know. As far as I'm concerned, the axle shafts between the joints should be easy enough to have any major axle manufacturer produce a set that has the correct inboard and outboard splines. if I were to go this route though, I would have at LEAST 2 sets of each axle made so that in the event of breaking an axle you're not SOL for a month.

[The Dark Side of Will]

DUT:
1985 Fiero SE
WS6 RPO code on the tag
FJH paper tag on the front springs
NYM paper tag on rear springs

*****Calculation approach*****
A-arm bushing to spring distance: 6.75 in (measured in the car with a measuring tape)
A-arm bushing to ball joint distance: 11.25 in (measured in the car with a measuring tape)

Active coils: 7.25 (guesstimate, I looked for where the rusty zones of contact between the coils started/stopped)
Mean coil dia: 3.875 in (measured in the car with a measuring tape)
Wire dia: 0.504 in (measured in the car with a cheapy Mastercraft caliper)

Modulus of rigidity: 11600000 psi (generic value; I did not measure this)

Wheel rate by calculation: 79.8 lb/in

*****Direct measurement*****

I'm pretty sure I've run across the design rates for Fiero springs somewhere over the course of all the junk I've read on the internet. Maybe some strategic googling will help with this effort?

[pmbrunelle]

FYI, the C7 bearings... at least the rear ones, do NOT have built in wheel speed sensors. My guess (hope?) is that they needed so much space inside the cartridge for bigger, stronger, further separated bearings that they ran out of room for the wheel speed sensor. I haven't looked at a C7 front yet.

EDIT: My main consideration for the C7 rears as opposed to earlier Corvette rears was the 33 spline CV joints. The 33 spline outer CVs used in GM FWD large cars (e.g. Dustbuster minivans) from the early '90's on makes those CVs readily available. I need to verify this, but I suspect they spline right on to Fiero manual transmission axles.

The VSS bit is good to know. As far as I'm concerned, the axle shafts between the joints should be easy enough to have any major axle manufacturer produce a set that has the correct inboard and outboard splines. if I were to go this route though, I would have at LEAST 2 sets of each axle made so that in the event of breaking an axle you're not SOL for a month.

I think that with the front wheel speed sensors, and the speed sensor in the transaxle, that should be enough to implement traction control with the MS3.

Do you see any other benefit to having individual rear wheel speed sensors?

I'm pretty sure I've run across the design rates for Fiero springs somewhere over the course of all the junk I've read on the internet. Maybe some strategic googling will help with this effort?

I actually have the paperback version (3rd edition) of the book "High Performance Fieros" by Robert Wagoner:
https://books.google.ca/books?id=M7OnAg ... &q&f=false

He says "Factory spring rates can be found in multiple sources on the internet", but he does not explicitly point them out... I didn't find anything. The 3rd edition of the book is dated March 2006, so it's possible that whatever sources he identified may no longer exist.

If you think you can find something, have at it!

On the page I linked to (76), he states:
Stock Fiero 6 cyl front 208.1 LBS/inch

Using my LCA measurements that I presented in the initial post, Robert's claimed spring rate (208.1 lbs/in) works out to 74.9 lbs/in at the wheel. That's pretty damn close to the value I got by the "direct measurement" method!

[ericjon262]

I think that with the front wheel speed sensors, and the speed sensor in the transaxle, that should be enough to implement traction control with the MS3.

Do you see any other benefit to having individual rear wheel speed sensors?

more data is never bad, but you're right, I wouldn't necessarily need them. that being said, some transmissions also don't have an integrated VSS. IIRC, the F40 doesn't always have a VSS.

[The Dark Side of Will]

I think that with the front wheel speed sensors, and the speed sensor in the transaxle, that should be enough to implement traction control with the MS3.

Do you see any other benefit to having individual rear wheel speed sensors?

more data is never bad, but you're right, I wouldn't necessarily need them. that being said, some transmissions also don't have an integrated VSS. IIRC, the F40 doesn't always have a VSS.

Right. Saab applications get vehicle speed from the stability control system over the CANBus and don't have a VSS. Pontiac G6 transmissions have a VSS that reads the ring gear teeth directly. Buick transmissions have a VSS that reads a trigger wheel on one of the output shafts. Buncha weird stuff.

My point about the 33 spline CVs is that basically ANY C5/6/7 front wheel bearing would be fine. They're mechanically interchangeable, and with the Fiero front end being as light as it is, they'd be fine even with slicks and HUGE aero. The C7 (or SKF/ZO6 C6) hubs are only advantageous to make the cheap plug/play 33 spline CV axle combo work.

[The Dark Side of Will]

I actually have the paperback version (3rd edition) of the book "High Performance Fieros" by Robert Wagoner:
https://books.google.ca/books?id=M7OnAg ... &q&f=false

He says "Factory spring rates can be found in multiple sources on the internet", but he does not explicitly point them out... I didn't find anything. The 3rd edition of the book is dated March 2006, so it's possible that whatever sources he identified may no longer exist.

If you think you can find something, have at it!

On the page I linked to (76), he states:
Stock Fiero 6 cyl front 208.1 LBS/inch

Using my LCA measurements that I presented in the initial post, Robert's claimed spring rate (208.1 lbs/in) works out to 74.9 lbs/in at the wheel. That's pretty damn close to the value I got by the "direct measurement" method!

Claim by FIeroGuru, source not identified: http://www.fiero.com/forum/Forum2/HTML/139002.html
More or less authoritative info from Doug Chase: http://www.fiero.com/forum/Archives/Arch ... 54238.html
The usual spring code listing: http://calgaryfieros.com/OSGdocs/springs.html
Citation of MVMA specs: http://www.fiero.com/forum/Archives/Arch ... 42357.html
More from Doug Chase: http://www.fiero.com/forum/Archives/Arch ... 44403.html

I'm pretty sure I've read the 85-87 WS6 suspension rear spring rates as being about 20# stiffer than the '88's, but I don't know where I read that.

That being said, if you have a pair of ARB '88 front springs or NYJ '85-'87 rear springs, I'll take them off your hands.