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How do I know if my springs are sagging? by huracan2015
Started on: 05-18-2014 11:25 PM
Replies: 18 (378 views)
Last post by: Bloozberry on 05-20-2014 08:27 PM
huracan2015
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Report this Post05-18-2014 11:25 PM Click Here to See the Profile for huracan2015Send a Private Message to huracan2015Edit/Delete MessageReply w/QuoteDirect Link to This Post
I'm looking into lowering springs, but I'm afraid that when I put them on (if I get them) there won't be a difference since my stock springs have sagged too much. I don't know if they've been replaced, so what do I do?
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Bloozberry
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Report this Post05-19-2014 07:05 AM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
The stock clearance between the ground and the bottom of the engine cradle side rails is 6 inches.
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rogergarrison
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Report this Post05-19-2014 07:09 AM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
As ive seen it, its trial and error. Ive never seen a set of lowering springs be very close to what they advertise. Its always either lower or higher than they say.
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Csjag
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Report this Post05-19-2014 07:16 AM Click Here to See the Profile for CsjagClick Here to Email CsjagSend a Private Message to CsjagEdit/Delete MessageReply w/QuoteDirect Link to This Post
It seems to me that lowering springs would change the geometry of the suspension and adversely affect the handling of the car.
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rogergarrison
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Report this Post05-19-2014 07:25 AM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, to be exactly right, you must do a wheel alignment afterwards. Handling does improve as the center of gravity is lowered. Usually also degrades the ride.
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huracan2015
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Report this Post05-19-2014 09:51 AM Click Here to See the Profile for huracan2015Send a Private Message to huracan2015Edit/Delete MessageReply w/QuoteDirect Link to This Post
Does anyone who has replaced stock springs know how much clearance there is between the fender and tire when the car is sitting level?
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rogergarrison
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Report this Post05-19-2014 12:32 PM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
park it on a flat garage floor and jack it up till the sides are 6" (I think) off the floor and that will make the wheels fit the wells just as stock ...with stock tires. Then when you let it back down, you know how much they sagged.

There is a diagram somewhere that shows the measurements including ground clearances.

[This message has been edited by rogergarrison (edited 05-19-2014).]

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Bloozberry
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Report this Post05-19-2014 01:08 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by rogergarrison:
Handling does improve as the center of gravity is lowered. Usually also degrades the ride.


That's a common misconception... the handling of a Chapman (or MacPherson) strut car does not improve with lowering... it almost always is detrimental to it. The location of the center of gravity is only one element of the complex physics involved.

 
quote
Originally posted by huracan2015:
Does anyone who has replaced stock springs know how much clearance there is between the fender and tire when the car is sitting level?


The most accurate way is by measuring the clearance to the underside of the engine cradle as I mentioned earlier.

 
quote
Originally posted by rogergarrison:
There is a diagram somewhere that shows the measurements including ground clearances.


I can post the diagram but need to know if this is for an '84-'87 or an '88 since they are different. Regardless, none of the diagrams have the height to the top of the fender arch, only to mechanical parts like the underside of the engine cradle that I've already posted.
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huracan2015
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Report this Post05-19-2014 04:04 PM Click Here to See the Profile for huracan2015Send a Private Message to huracan2015Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Bloozberry:


I can post the diagram but need to know if this is for an '84-'87 or an '88 since they are different. Regardless, none of the diagrams have the height to the top of the fender arch, only to mechanical parts like the underside of the engine cradle that I've already posted.


It's an '87 GT. And thanks everyone for the help!
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ranger stone
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Report this Post05-19-2014 06:34 PM Click Here to See the Profile for ranger stoneClick Here to Email ranger stoneSend a Private Message to ranger stoneEdit/Delete MessageReply w/QuoteDirect Link to This Post
Only lower the car using springs if you have good roads,, the ride will be much harsher,as I found out the hard way,, you have to be certain what you want ,if you are young it should be no problem,, I built a fiero rebody & needed a slightly lower look to capture the
sporty racy look of a Lotus .. I hate the harsher ride I have now,,
but the car handles around corners much better which I like

[This message has been edited by ranger stone (edited 05-19-2014).]

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rogergarrison
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Report this Post05-19-2014 07:22 PM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
I dont think ive ever seen a car with the CG lowered that didnt corner better assuming everything else remains the same. Thats pretty much just physics. On my race car, we put everything we could as low as we could, even to bolting lead weights under the frame rails (now they put them inside). Lower the radiator, battery, engine, seat, etc all as low as you could under the rules. Your going to have to explain how thats a misconception to me. My van sure corners way better than the RV does.

[This message has been edited by rogergarrison (edited 05-19-2014).]

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Report this Post05-19-2014 09:01 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by rogergarrison:
Your going to have to explain how thats a misconception to me. My van sure corners way better than the RV does.


Alright... you asked: the CofG has to be changed relative to the location of the roll center, not relative to the ground. The roll center is the point about which the front or rear of the car rolls during a turn and is determined by the angle of the control arms. Many people mistakenly believe a car's body rolls side to side about the tire contact patches, but it in fact rolls about the roll center. Since the CofG acts on the roll center, the greater the distance between the two at any given moment, the greater the moment arm that the CofG has to pitch the car in roll. The more the car rolls in a turn, the more camber gain the suspension needs to keep the tires flat on the ground. The trouble is, adding drop springs decreases the amount of available camber so you lose traction earlier.

To illustrate my point, here is a graph from my build thread that shows the effect of adding drop springs to an '88 Fiero (I assume given the geometry that the earlier cars would be even worse). The blue line shows how the roll center moves away from the center of a stock Fiero rear end as the car rolls through 0 to six degrees of roll. The red line shows the effect of a 2" drop spring on the roll center. It only goes to 4 degrees of body roll since 6 degrees was off the map. At four degrees of body roll, the car with drop springs has a roll center that's 1.45 meters away from the center line while the stock Fiero has the roll center 1.25 meters away. Neither are great, but the drop springs worsen the situation.



There are similar graphs showing the detrimental effect of a spring drop on camber and toe gain, anti-squat, and a host of other parameters... all you have to do is visit my build thread to see. As mentioned above, the reduction in camber gain means that the angle of the tire contact patch can't change enough while the body rolls in a turn to stay flat with the ground, so traction is reduced despite having lowered the CofG relative to the ground.
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Report this Post05-19-2014 09:13 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
Here are the trim height specs for your car huracan:



Measurement "K" isn't particularly legible even in my service manual so it's really not clear in the image above. It reads 186 or perhaps 188 for all tire sizes. Let me know if there is anything you don't understand regarding how to measure.
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rogergarrison
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Report this Post05-20-2014 08:26 AM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you have the front aligned to specs after the drop, dont the camber work just the same as before. The alignment adjusts the camber back to where it was right? I do know that caster changes as the suspension moves up and down, or steering turns the wheel.
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Report this Post05-20-2014 10:11 AM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
No... all you're doing by getting an alignment after lowering a car is resetting the static settings for camber, toe, and caster. The problem is that camber changes as the suspension is compressed and the change isn't linear. So during the first degree of body roll, let's say the camber also changes by 1 degree to compensate. From 1 to 2 degrees body roll, the suspension might only be able to change the camber by an additional 1/2 degree, and from 2 to 3 degrees body roll perhaps only 1/4 of a degree. While the numbers are fictitious, that is how the stock Fiero's camber changes.

By lowering the car, you change the angles of the control arms relative to each other at stock height, which shifts the rate the camber will change for the worse. So in the example above, instead of having a full degree of camber change during the first degree of body roll, you might get only 1/2 a degree. Then from 2 to 3 degrees of body roll, you'll only get an additional 1/4 degree of camber change. So the tire contact patch gets tilted off the ground earlier with drop springs than without. That's why drop spindles are superior because they maintain the stock rate of camber gain per degree of body roll.

The same happens with toe gain as well since the rate that toe changes is also non-linear. The toe is designed to change as the body rolls to give the car either neutral, under-steer, or over-steer characteristics. Lowering the car shifts the rate of toe change away from what the designers had in mind... but this is more of an issue of taste since GM designed the car to under-steer and many people prefer more neutral steering. But there are also many other suspension and handling parameters that are also inter-related.
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rogergarrison
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Report this Post05-20-2014 12:25 PM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
OK, barring all the technicalities, I'll still stick with lowering generally will improve cornering as far as Im concerned...

Going by what you say, as I understand...if you took a jacked up 4x4 Jeep CJ and made different spindles & control arms to follow the original caster/toe specs, it would outcorner a lowered one....

[This message has been edited by rogergarrison (edited 05-20-2014).]

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Bloozberry
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Report this Post05-20-2014 01:31 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by rogergarrison:
OK, barring all the technicalities, I'll still stick with lowering generally will improve cornering as far as Im concerned...


Barring all technicalities?? Really? Suspension design is only technicalities Roger, so if you bar them, all you have is intuition. I prefer my cars designed by people who go on a bit more than intuition.

 
quote
Originally posted by rogergarrison:
Going by what you say, as I understand...if you took a jacked up 4x4 Jeep CJ and made different spindles & control arms to follow the original caster/toe specs, it would outcorner a lowered one.


You're bastardizing my description of what happens to a Fiero and then applying it to a Jeep.

First, you cannot jack-up a Jeep without raising its CofG. That then changes the length of the moment arm between the CofG and the roll centers, which in turn would cause the fictitious raised Jeep in your example to corner worse. If it were possible to raise the Jeep and shorten the vertical distance between the CofG and the front and rear roll centers, then yes, it would possibly corner better than your lowered Jeep, but that would depend on many other factors as well.

But the last time I looked, this thread was about lowering a Fiero with an SLA front suspension and a MacPherson strut rear... not a Jeep with two solid axles sprung with leaf springs. Different suspension systems react differently to various modifications.

[This message has been edited by Bloozberry (edited 05-20-2014).]

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rogergarrison
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Report this Post05-20-2014 07:22 PM Click Here to See the Profile for rogergarrisonClick Here to Email rogergarrisonSend a Private Message to rogergarrisonEdit/Delete MessageReply w/QuoteDirect Link to This Post
I still go with my 'intuition'. Im still going on a lowered Fiero will outcorner a stock one with everything else the same...after an alignment. Rocket scientists can design them for years, and do all the math and solve all the tech issues, and they still blow up. Hell, GM cant even design an ignition switch that works properly. So, ill let you go on that.
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Report this Post05-20-2014 08:27 PM Click Here to See the Profile for BloozberrySend a Private Message to BloozberryEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'll be waiting for you at the finish line.
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