Shock Valving, Spring Rates

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Series8217
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The Dark Side of Will wrote: Based on checking things out with a tape measure, I thought that the mechanical advantage for both early and '88 suspensions was 1.4, which puts the motion ratio at 2.0.
You have the number and name right. The motion ratio (MR) is indeed about 2.0. (It's actually 1.886). But the wheel rate is MR^2 * spring rate. If you state that the motion ratio is ~2.0 then you must agree that the wheel rate is is not MR*(spring rate), because that doesn't take into account the reduced spring travel.

I'm not sure where you got the 1.4 mechanical advantage measurement from. The mechanical advantage of a second-class lever is the ratio of the distance from fulcrum to effort to the distance from fulcrum to load.. The spring is ~200 mm and the balljoint is 350mm from the control arm pivot. That's 1.75. The extra 8% of the motion ratio comes from the installation angle of the spring.

Discussion of the actual motion ratio measurements for the '88 Fiero begin in this post of this thread.
The Dark Side of Will wrote: I've read some of the E30M3 Project pages before. He uses the term "motion ratio" differently than the way it was introduced to me. What he calls motion ratio is really mechanical advantage. (I got my def here: http://www.amazon.com/dp/1560918314/ so I'll stick with it...)
I'm sorry, but Dixon is wrong in your print of that book. I have the same author's other book (The Shock Absorber Handbook) and it has the correct definition which is used by the E30M3 guy and the Kaz Engineering source I cited (as well as dozens of others I can pull up if you'd like). Here are some excerpts from Chapter 4, page 135 of The Shock Absorber Handbook by John C. Dixon:
4.2 Motion ratio
At a given suspension bump position Zs from normal ride height, the damper compression is ZD. A small further suspension bump motion (delta)Zs results in a corresponding further damper compression deltaZD, Figure 4.2.1. The ratio of these is the displacement motion ratio for the damper at position Zs.

[...]

Often the spring and damper are fitted coaxially and have the same motion ratio.

[...]

4.3 Displacement Method

One way to obtain the motion ratio value for one nominal bump position is by analysis of a pair of slightly different suspension positions. If the position analysis is undertaken by a drawing method it is prone to inaccuracy because of the relatively small difference of positions. Hence the drawing must be undertaken by an experienced draughtsman at a large scale. With less epmhasis on accuracy, a wide spread of positions will give an average ratio over the movement which may be useful in some cases. Also a sequence of, say, eight to ten positions may be drawn through the bump motion, and the damper compression plotted at a graph against suspension position, with the curve smoothed through the points. This helps to reveal any errors. The motion ratio for any particular position is then the gradient dZd/dZs of the curve.

[...]
You can find a better explanation of the same information in his newer book, Suspension Analysis and Computational Geometry, but I don't have a copy of it. Here's the motion ratio definition from Amazon's excerpt:
The dynamic behavior of a vehicle depends on the on the effect of the spring as seen at the wheel, commonly called the 'wheel rate' or 'effective spring stiffness', and on the damping coefficient effective at the wheel. However, the spring and damper are not installed at this point, but elsewhere on the suspension. The effective spring and damper characteristic at the wheel must therefore be related to the characteristics of the actual spring and damper. On a double-wishbone suspension they often operate abotu half-way out on the bottom suspension arm. On a racing car, often they operate through a linkage, including various forms of intermediate rocker. Basically the effect of the spring and damper depends on the ratio of velocities spring-to-wheel and damper-to-wheel when the wheel is displaced in its bumpa ction. In general this velocity ratio, also known as the 'motion ratio' or 'installation ratio', is not constant, but varies with the wheel bump position.

[...]

One of the ways to obtain the motion ratio value for a given nominal suspension bump position is by analysis of a pair of slightly different suspension positions. [...] The spring motion ratio for any particular position is then the gradient dxz/dzs of the curve at the particular suspension bump position.

Here's another excellent source about suspension design including ride frequencies and spring rate: Powerpoint presentation on suspension design from FSAE Lead Design Judge, Steve Lyman from DaimlerChrysler
(motion ratio information on slide 8 )

The coolest thing about that article is actually slide 6, which has a chart of front and rear suspension ride rates, corner weights, unsprung weights, sprung weights, and frequencies. It includes vehicles of all types including the E36 M3, E320 AWD, '02 Grand Cherokee, VW Passat, and so on. Everything from SUVs to hatchbacks.

EDIT: Merged my recent posts
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Ooops... I guess I got the terms swapped in my head, then.

At any rate, "rate ratio" is the square of either motion ratio or mechanical advantage, whichever way you want to look at it.

As I said, I thought that the MA for the '88 control arm was ~1.4 based on measurements with a tape, which would put the rate ratio at 2.0.
fieroguru wrote:
Series8217 wrote:What's a good way to measure the motion ratio on the front of an '88 Fiero? I'm about to take my shocks out to have them revalved and I want to make sure I get it right.
The distance the lower pivot of the damper moves is 52% to 54% of the lower a-arm ball joint for +/-80mm of suspension travel.
The Lotus suspension analyzer says the ratio is 1.866 for 30mm bump and 1.897 for 30mm droop.
Went back and found this... I would not have expected to be off this far with a tape measure.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

I assembled my shocks last night and charged the gas reservoirs with 200 psi of N2, which produces a preload force of 47.7 pounds based on my calculation (shaft area * charge pressure).

Since my shock dyno is not done yet, I picked a valving by adjusting Bilstein's representative dyno of a digressive valving to match the curve generated using Dennis Grant's dynamics calculator, and picked the closest standard valving from Bilstein's valving manual (available at the bottom of this page). I assembled a 300-160D valving by using the rebound shims from pg 61 (300-100D) and the compression shims from pg 67 (480-160D).

UPDATE 2022-10-30: I'm no longer certain about the intended force curves for the standard Bilstein valvings. Originally I thought the numbers are pounds-force at 10 inches/sec since that is what is stated in the catalog. In other places the valving numbers are described as being 10's of Newtons at 0.52m/sec. So 300 could mean 3000N @ 0.52m/sec (674 lbs @ 20 inches/sec) or it could mean 300 lbs @ 10 inches/sec (1334N @ 0.25m).
The Dark Side of Will wrote:Ooops... I guess I got the terms swapped in my head, then.

At any rate, "rate ratio" is the square of either motion ratio or mechanical advantage, whichever way you want to look at it.
Right. Rate ratio is practically 4.0 for this suspension. Urggh. Suckage.

On a related note, I recently realized that Dennis Grant's dynamics calculator (and his math in general) doesn't take into account the velocity ratio of the shock. He says to set the digression curve to digress to 0.15 times the initial slope beyond 3 in/sec.... however that 3 in/sec is representative of significantly different chassis motion velocity for a motion ratio of, say, 0.8 vs 0.5. It's going to need to be different for the front suspension vs rear suspension on most cars.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

My car has all four shoes on the ground now, with 700 lb/in springs up front (stiffer actually, because I had to cut two coils off to get them to fit), and 475 lb/in springs in the rear. Driving impressions tomorrow. This is all super last minute because I have two track days starting Saturday. Ugh..

I had to chop the QA1 8MB700 springs down to 6 inches or so (I need to measure them again when I pull them back out) to get the ride height OK up front. I'm using stock ball joints because the 1" drop balljoints cause the rotors to rub on the ball joints (yes, I trimmed the control arm back that far to find out). With lower-offset brake rotors and 1" drop balljoints, the springs would still need to be trimmed a bit -- 6.5 or 7 inches is probably OK.

Anyway, I'm only going to run these springs for this weekend, and then get something more appropriate. The upper spring perch is flat, so when I cut the QA1 spring from the top, I ended up with a tangential end. This is far from ideal. Unfortunately I don't have any means of bending the end flat, otherwise it could probably work. Rather than rework the springs, I'll probably order either custom springs, or 2.5" ID 4" length 700 lb/in springs. Unfortunately I'll have to limit droop quite a bit to run the 4" springs, or at least add a lightweight helper spring. 2.5" ID 5" length springs would work, but nobody stocks those. 2.25" ID springs come in 1 inch increments, but 2.5" ID springs only come in 2" length increments.

If I did this again I would either use 36mm shocks (with 2.25" springs) or extend the lower shock pivot another inch downward and run 5" travel ASN shocks. By extending the lower shock pivot further down, the spring perch will be lower on the shock body, which makes it possible to accomodate a longer spring. One problem with the ASN-series shocks is the threads start a good distance from the bottom of the shock, so the spring perch is pretty high up. At the minimum height, it's 1.8 inches from the bottom of the factory spring pocket. 0.25 inches can be gained by eliminating the jam "nut" and modifying the main adjustable perch to lock with a setscrew. That's a decrease in ride height of 0.5 inches -- pretty significant.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Series8217 wrote: At full mechanical bind (not sure what's hitting)
Image
Is your mechanical bind the corner of the pipe hitting the shock body?
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The Dark Side of Will wrote:
Series8217 wrote: At full mechanical bind (not sure what's hitting)
Image
Is your mechanical bind the corner of the pipe hitting the shock body?
I don't think so. When I checked the other side for clearance it looked like the lower control arm was hitting the crossmember further inboard before anything else.
I will double check though. It looks close in the pic but photos tend to be deceiving with those sorts of angles.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

So 700# springs with a 200# wheel rate front and 475# with a ? wheel rate rear. You still running the Koni red struts... or have you revalved them or running something else?

Have you confirmed the wheel rates with ballast?

I have 325# rear springs on The Mule with stock '87 GT front springs. 215/55-16 front tires and 245/50-16 rears. The usual problem with the front end of an early car is brake dive. Most racers have to run very stiff springs to reduce brake dive, as lowered cars can actually drag the chin spoiler under hard braking. This means that they end up having to make compromises to their spring rate balance for cornering in order to deal with brake dive.

However, my anti-dive mod makes brake dive almost non-existent.

Right now the UHMW control arm bushings I made in college are worn out. I need to upgrade to spherical bearings. That involves getting a fairly intricately machined part produced in a quantity of 12 (4 for The Mule's rear, 4 for The Mule's front and 4 for the Storm Trooper ('88 Formula) front) along with 24 spacers in 3 lengths... not fond of doing all that machining myself, so I'm looking at having them made... just not going to happen until I get a job.

Anyway... the stock fronts and 325 rear seems to be a good combo, although the shelf Konis can't quite handle that stiff a rear spring, at least not for my liking.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Originally posted by Steven Snyder:

I'm running 700# springs up front and 475# in the rear. I have custom Bilsteins up front and Koni reds in the rear set to full stiff (but they're not stiff enough).

This results in wheel rates of 175 lbs/in in the front and 293 lbs/in in the rear, and ride frequencies of 1.8 Hz front and 2.0 Hz rear.
Saw this on the other forum...

293/475 = 0.617
cos^-1(0.617) = 51.9 degrees

I know you have Fiero guru's pivot lowering brackets on your knuckles, but I have a hard time believing that the strut axis is over 45 degrees from tangent to the wheel's direction of motion.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

The Dark Side of Will wrote:
Originally posted by Steven Snyder:

I'm running 700# springs up front and 475# in the rear. I have custom Bilsteins up front and Koni reds in the rear set to full stiff (but they're not stiff enough).

This results in wheel rates of 175 lbs/in in the front and 293 lbs/in in the rear, and ride frequencies of 1.8 Hz front and 2.0 Hz rear.
Saw this on the other forum...

293/475 = 0.617
cos^-1(0.617) = 51.9 degrees

I know you have Fiero guru's pivot lowering brackets on your knuckles, but I have a hard time believing that the strut axis is over 45 degrees from tangent to the wheel's direction of motion.
You forgot to square the rate ratio to get back to the motion ratio before you cos^-1'ed it.

My calculation was based on a motion ratio of 0.86 for the rear... but now I wonder if I typoed when I recorded that, and it's supposed to be 0.96? I need to double-check. Stock strut angle is 16.5 degrees according to Bloozberry's drawing. I don't think the lowering brackets change the angle.

EDIT: Oh, right. You need to account for the mechanical advantage of the wheel over the control arm link. It took me awhile took get a grasp of this for strut suspension. Actually I had to make a drawing in Solidworks and move the links around before I could even convince myself of it. I thought that because the strut and knuckle are fixed, that the distance between the wheel and strut are not important. However, that could only be true if the camber never changed with compression. We all that is false... If moving the wheel up increases the camber angle, that means a torque contributes to the compression of the spring, so there is mechanical advantage there. You need to account for the ratio of distances between the lateral link inboard joint and outboard joint, and lateral link inboard joint and center of the contact patch.

EDIT 2: OOPS. I used the wrong numbers on my post in Old Europe. It should be 196 lb/in front wheel rate (using 0.53 motion ratio) and 351 lb/in for the rear wheel rate (using 0.86 motion ratio). What I posted were ride rates. My bad.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

My previous numbers were incorrect. I recalculated them:

I put together a SolidWorks model with Bloozberry's measurements of the stock '88 rear suspension. I placed the lateral link perpendicular to the ground. The motion ratio for the rear is 0.95 for the first 50 mm of compression (at the tire), and 1.01 (yes, more spring motion than wheel motion) for the next 50 mm.

With the outer pivot of the lateral link lowered by 38mm (1.5 inches), the motion ratio for the rear is 0.90 for the first 50mm of compression, and 0.95 for the next 50 mm.

Also I played around with the distance from the outer pivot to the vertical centerline of the tire. Adding 50 mm to the distance decreases the motion ratio to 0.93 for the first 50mm of compression on the stock suspension and to 0.88 for the lowered outer pivots.

So with my wheels, which have a 15mm higher offset than stock, and fieroguru's lateral link relocation brackets, the motion ratio is 0.907 for the first 50 mm of compression and 0.96 for the next 50 mm of compression.

My previous wheel rate calculations used a motion ratio of 0.86 for the rear. That's a rate ratio of 0.74. My actual rate ratio with 45mm offset wheels and the 38mm drop bracket is between 0.83 and 0.92 depending on ride height.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

I experienced some horrid wheel hop during launches at an autocross over the weekend. I really need to get the rear dampers done. I did buy some Bilstein struts (for the Fiero) from a guy on Old Europe, and he finally shipped them this week. So hopefully next week I'll have them in hand to inspect and see what needs to be done to convert them to takeaparts, revalve them, add some coilovers, and get them on the car.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

I don't think the struts have much to do with controlling wheel hop on a Fiero.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

Why not?

I didn't get wheel hop until I upped my rear spring rate from 325 to 475 a couple weeks ago.

The last time I had hop was with my old 88 when I had 325# springs and worn KYBs. The same springs with Konis never had hop.

It sure seems like a spring/damper issue to me...
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

Wheel hop results when components that compress from drive torque and/or tractive loads work with the mass of the drivetrain to create a "relaxation oscillator".

The tractive loads and the jounce/rebound of the suspension only couple via the pro/anti-squat capabilities of the suspension.

Wheel hop typically has much more to do with powertrain mounting than with suspension damping. I've had the same wheel hop problems with worn out Gabriel struts as I do with my current Konis with the same 325# springs. Of course the '87 and '88 suspensions have different squat characteristics, but the principle is the same.

Transverse drivelines tend to wheel hop worse than longitudinal, because of the combination of both mass and torque in one unit. In a conventional longi driveline, the diff reacts to axle torque, but is a fairly light component with a small moment of inertia (MOI of the entire unit around the torque axis, not just the rotating components), so even with soft mounts its natural frequency in a relaxation oscillator is fairly high. The engine and transmission have most of the mass and MOI of the driveline, but their mounts are only exposed to driveshaft torque, so they don't have access to as much energy to store.

A transverse driveline has all the mass and MOI in a unit that is exposed to axle torque... so not only can the mounts capture a lot of energy thanks to the high torque, the large MOI moves the natural frequency down to a problematic range.

Urethane powertrain mounts, for example, contribute to clutch chatter, which is also a relaxation oscillator phenomenon.
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Re: Shock Valving, Spring Rates

Post by bse53 »

Hello,
New to this website, but not to trying to make my 88 Fiero faster.

Currently it's running in XP in autocross.
Weight 2350 with a 4.9 caddy engine. Used to be owned by Tom Hill.
I'm running 600 lb springs in the front and 400 lb in the rear.
275/35x15 A6 tires all around.
I haven't concerned myself with shocks since I'm still trying to finalize spring rates.

Series8217, you didn't post how the car handled with the 700 lb springs up front? Are you going to go stiffer yet?

Ax and road racing are different animals and I'm more concerned about the lack of grip on extremely tight slow Ax corners.
I've been reading Ron Sutton over at Corner Carvers and he's a proponent of soft spring/big bar setups. I understand you're using the stiffer springs to control the dive in braking.

I have some 700lb springs I was going to try out, partly to move some of the weight transfer to the front, but I couldn't get them mounted without cutting them (as you had to do), so I'm toying of changing the upper spring perch to allow taller spring and shocks. I'm in the process of tearing the front apart to figure out how to do that.

As to shocks, I found the Koni 30-5436 shocks have the valving that would work with either the 600 or 700 lb springs. But they are eyelets on both ends, which is another reason to change the upper mount. The car has a tubular lower A arm set up for coilovers now.

Another element I hope to change is how the camber/caster is set. Right now I'm running 2 degrees static negative camber, but that reduces the caster to about 4 degrees. Probably the best option would be to build a new upper A arm that moves the upper ball joint back to add more caster. Another option may be to just increase the depth of the adjusting slot to allow more movement. the drawback to that is it in essence shortens the a arm, which has the effect of adding to the camber gain.

This might be a good subject for a separate post. I've followed Bloozeberry on the Old Europe and his mods to the rear, but haven't found much on the front, which I think is at least as important.

Look forward to hearing more from you and your great car.
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Re: Shock Valving, Spring Rates

Post by Series8217 »

bse53 wrote:Hello,
New to this website, but not to trying to make my 88 Fiero faster.

Currently it's running in XP in autocross.
Weight 2350 with a 4.9 caddy engine. Used to be owned by Tom Hill.
I'm running 600 lb springs in the front and 400 lb in the rear.
275/35x15 A6 tires all around.
I haven't concerned myself with shocks since I'm still trying to finalize spring rates.
Welcome to the forum!

That's a very light car. What are your corner weights?
Series8217, you didn't post how the car handled with the 700 lb springs up front? Are you going to go stiffer yet?
Oops. Can't believe I forgot to talk about that. I just checked and it wasn't in my thread in Motorsports either.

The 700# / 475# combination works fantastic. I had never driven a Fiero with stiff springs and level ride before, and it really is amazing. I can hit massive dips and bumps at high speed at the chassis is not upset. Just keep the steering angle and go through. Roll stiffness is still a problem, but it would be tolerable if I had more camber up front --- I have caster maxed out with as much camber as I can get at that setting; not quite -1 deg. -3 would be better. Turn in is absolutely mindblowing, though I still have mid-corner understeer to deal with (see potential solution below). Also much less dive under braking, and the car transitions off braking much faster, so I can turn in almost immediately. I used to have to wait a second for the car to settle or risk spinning out on corner entry.
Ax and road racing are different animals and I'm more concerned about the lack of grip on extremely tight slow Ax corners.
In stock class they may be different but in XP you're in Race Car territory so you can do pretty much the same stuff I'm doing. At low speed I assume the car pushes? That's a Fact Of Life, but getting some more caster in your front suspension should help a lot.
I've been reading Ron Sutton over at Corner Carvers and he's a proponent of soft spring/big bar setups. I understand you're using the stiffer springs to control the dive in braking.
By "soft spring/big bar" I assume you mean soft ride rate, stiff roll rate? Ok, the car will be slower to transition in throttle and braking, and you'll get more geometric weight transfer under both conditions -- as well as whatever effects a lot of suspension movement has for your car. That's going to be application and vehicle dependent.. What's Ron's explanation for that type of setup?
I have some 700lb springs I was going to try out, partly to move some of the weight transfer to the front, but I couldn't get them mounted without cutting them (as you had to do), so I'm toying of changing the upper spring perch to allow taller spring and shocks. I'm in the process of tearing the front apart to figure out how to do that.
You could use the same control arm modification I did, but adapt the lower perch to accept your spring. Then you can get at least an extra inch of spring in there, although you'll lose the easy adjustment and will have to use shims.
As to shocks, I found the Koni 30-5436 shocks have the valving that would work with either the 600 or 700 lb springs. But they are eyelets on both ends, which is another reason to change the upper mount. The car has a tubular lower A arm set up for coilovers now.
What information do you have on the 30-5436 valving?
By the way those aren't much cheaper than the Bilsteins I'm running, which you can put whatever valving you want in... (and I'll be sharing my valving in this thread shortly).
Another element I hope to change is how the camber/caster is set. Right now I'm running 2 degrees static negative camber, but that reduces the caster to about 4 degrees. Probably the best option would be to build a new upper A arm that moves the upper ball joint back to add more caster. Another option may be to just increase the depth of the adjusting slot to allow more movement. the drawback to that is it in essence shortens the a arm, which has the effect of adding to the camber gain.

This might be a good subject for a separate post. I've followed Bloozeberry on the Old Europe and his mods to the rear, but haven't found much on the front, which I think is at least as important.
Funny you should mention this... I'm actually working on a bolt-in adjustable control arm as I write this. I hope to have my first prototype done by the end of the month. I'll share all the information in a new thread here once I have it ready. It's basically SPC control arm components with a custom ball joint plate and cross shaft.
Look forward to hearing more from you and your great car.
Thanks! I'm happy you've decide to join us.
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Re: Shock Valving, Spring Rates

Post by The Dark Side of Will »

bse53 wrote:Hello,
New to this website, but not to trying to make my 88 Fiero faster.

Currently it's running in XP in autocross.
Weight 2350 with a 4.9 caddy engine. Used to be owned by Tom Hill.
I'm running 600 lb springs in the front and 400 lb in the rear.
275/35x15 A6 tires all around.
I haven't concerned myself with shocks since I'm still trying to finalize spring rates.
Welcome to the forum!
Feel free to start your own build thread if you'd like.

Tom Hill was one of the "Team Python" guys, right? I understood they were in AZ. Is that where you are?

As long as you have a "square" tire fitment with a rear-heavy car, you'll have trouble getting the handling perfect...

I @$$ume you're using a pyrometer to get tire temp and understand how each end of the car is using its tires, right?

Your car is an '88 all around, right? Meaning that it has '88 rear AND front suspension. I know George Ryan used to really like an early front end paired with the '88 rear and he was an influential voice in the "history" of Fiero AutoX.

I'm a stiff spring, soft bar guy. Big bars can be useful in certain specific circumstances (e.g. an extremely low BMW with a roll center 4 feet underground), but I don't like them in general use with decent suspension geometry.

To clarify, are you having problems with PUSH in slow AutoX corners, or with overall GRIP?
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Re: Shock Valving, Spring Rates

Post by bse53 »

That's a very light car. What are your corner weights?
505/501 front, 720/690 rear.
What information do you have on the 30-5436 valving?
Just from the Koni website. I've looked at buying shocks that can be valved, but the bilstein shim kit is almost $300. The Koni's are pretty clost to what I think I need on the front and with the lower perch are about $150 ea.
What bilstein's are you running. One of the things I couldn't figure out was what the valving are on the stock ones. They had 100/300 lb shock, which I assume is the valving at 10 in/sec, but don't have any other specs.
Tom Hill was one of the "Team Python" guys, right? I understood they were in AZ. Is that where you are?

As long as you have a "square" tire fitment with a rear-heavy car, you'll have trouble getting the handling perfect...

I @$$ume you're using a pyrometer to get tire temp and understand how each end of the car is using its tires, right?

Your car is an '88 all around, right? Meaning that it has '88 rear AND front suspension. I know George Ryan used to really like an early front end paired with the '88 rear and he was an influential voice in the "history" of Fiero AutoX.
Yes, I think Tom mentioned Team Python. I'm in Washington State.
The car is total '88.
I used a square setup so I could rotate the tires, in addition to flipping them. Tire temps on the front have been low 120's, rear low to mid 140's. The car is feeling pretty balanced right now, but it's been quite a journey. I knew when I bought it that it wasn't going to be competitive in XP, but I wanted to run at the top of the heap in raw time. FTD for bragging rights.
You probably know the the national champion in XP, Fred Zust, runs a Elise at 1800 lbs pushing 400 hp.
With the 5 liter caddy engine, I have to weigh 2450. So I'm short 100 hp or so and about 600 pounds too heavy.

What I hope to correct is the low speed push mid corner. I think it may be ackerman or camber related. Looking at the geometry of the front, it doesn't look too bad. Right know I'm trying to figure out what the car is doing in compression and drop in terms of camber gain. I was using the suspension points that Bloozeberry had, but with the car lowered most of those coordinates are different.

Hope to have some data soon.

Brian
fieroguru
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Joined: Sun Jan 15, 2006 1:30 pm

Re: Shock Valving, Spring Rates

Post by fieroguru »

bse53 wrote: Right know I'm trying to figure out what the car is doing in compression and drop in terms of camber gain. I was using the suspension points that Bloozeberry had, but with the car lowered most of those coordinates are different.

Hope to have some data soon.

Brian
I should have the readouts for the 88 front suspension lowered 1 1/2" cycled through its motions in bump/compression and roll if that would help.
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bse53
Posts: 33
Joined: Sun Aug 11, 2013 6:42 am

Re: Shock Valving, Spring Rates

Post by bse53 »

I should have the readouts for the 88 front suspension lowered 1 1/2" cycled through its motions in bump/compression and roll if that would help.
I broke down and bought a suspension analysis program from Autoware, which should be here by the end of the week. It would be interesting to see how close it is to your results.

Are your readouts, calculations or did you physically measure the suspension?

One of the ideas I'm looking at is moving the upper mounting points back and inboard while raising them. It looks like that would increase the static caster and reduce the camber gain in compression and loss in rebound. It's what finally got me to spend the money on the program. Hopefully it will give me some good analysis whether moving the upper mounts would help.

The UCA that Series8217 designed looks like a great idea also.

Brian
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