Lamen terms needed (spring rates, wheel rates, etc.)
10-10-2003, 02:00 AM
#1
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Lamen terms needed (spring rates, wheel rates, etc.)
I've been reading over a lot of "explanations" of what goes on under the car when driving. Suspension setup to me is as important as having gas in the gas tank, but I really don't understand a lot of it. My car is tired and is needing a suspension transplant. I've already got an idea in mind, so I'm just asking for explanations on what all of this means and how it relates to the cars reaction from side to side and front/rear to rear/front...
Spring rates - I think I have an idea but I doubt it. When a spring has a 400# rate, what does that mean? I know the higher the rate, the stiffer the ride.
Wheel rates - No clue
T-bar effective diam. - Obviously the bar's OD isn't necissarily the right number I should be interested in.
Like I said, I'm in the process of rebuilding a spare engine I have, and am also looking the entire car over for areas that need the most attention. Suspension/steering is what links me to the road, so it is a high priority. Please give any info on this topic. I know a lot about cars, but suspension is the area I know just enough about to get myself in trouble (aka, very little).
-edit-
I have a manual rack on my car, do these need any kind of reconditioning, rebuilding, etc.? I just don't want something to mess up somewhere and I have to convert to power. I can't find any place that advertises manual steering. Thanks.
Spring rates - I think I have an idea but I doubt it. When a spring has a 400# rate, what does that mean? I know the higher the rate, the stiffer the ride.
Wheel rates - No clue
T-bar effective diam. - Obviously the bar's OD isn't necissarily the right number I should be interested in.
Like I said, I'm in the process of rebuilding a spare engine I have, and am also looking the entire car over for areas that need the most attention. Suspension/steering is what links me to the road, so it is a high priority. Please give any info on this topic. I know a lot about cars, but suspension is the area I know just enough about to get myself in trouble (aka, very little).
-edit-
I have a manual rack on my car, do these need any kind of reconditioning, rebuilding, etc.? I just don't want something to mess up somewhere and I have to convert to power. I can't find any place that advertises manual steering. Thanks.
10-10-2003, 02:06 AM
#2
Spring rates--Without going into indepth physics explanations (because I don't remember the equations and don't want to look them up), it's just how much force the spring produces. The stiffer the spring is, the harder it is to compress and the more force it takes to compress.
Wheel rates--[Taken from Paragon]A wheel rate is the effective spring value when taking into consideration the placement, construction, and type of the sprung materials. It can get pretty complicated, but it's what the end result is when taking into consideration all of the different effects on the suspension.
http://64.226.197.185/Paragon/Info/9...comparison.htm
T-Bar diameter--Don't know
If you want a semi-technical, but very readable and understandable explantion of vehicle dynamics, read one of Carol Smith's "....To Win" series books.
Wheel rates--[Taken from Paragon]A wheel rate is the effective spring value when taking into consideration the placement, construction, and type of the sprung materials. It can get pretty complicated, but it's what the end result is when taking into consideration all of the different effects on the suspension.
http://64.226.197.185/Paragon/Info/9...comparison.htm
T-Bar diameter--Don't know
If you want a semi-technical, but very readable and understandable explantion of vehicle dynamics, read one of Carol Smith's "....To Win" series books.
10-10-2003, 02:11 AM
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LOL, Paragon is where I got confused in the first place, but you clarified some of my confusion, thank you. So the Wheel Rate is a percentage of the Spring Rate, correct? Could anyone shed some light on my Torsion Bars? 
Also, if anyone feels up to it (I know it's late) go into depth on this. Equations are great, numbers don't lie.
Also, if anyone feels up to it (I know it's late) go into depth on this. Equations are great, numbers don't lie.
10-10-2003, 02:13 AM
#4
So the Wheel Rate is a percentage of the Spring Rate, correct?
10-10-2003, 02:20 AM
#5
Race Car
400# means it takes 400 lbs to compress that spring each inch until it is fully compressed. The formula is:
spring rate = force / distance, where distance is the amount the spring is being compressed.
# = lbF/inch
If your spring is compressed 1/4" under 100# of force then your spring rate is 100lbF / [1/4"] or 100lbF * 4" = 400#
If you apply 800lbF of force to a spring with rate of 400# then it will compress 800lbF/400# = 2"
EDIT:
Spring rate Vs. wheel rate:
The wheel rate is what actually affects the balance of your car. On a 944 the THEORETICAL conversions are 0.90 for the front springs, 1.00 for the rear torsion bars, and 0.55-0.65 for rear-mounted coil springs or 'coilovers.'
If you install a 29mm torsion bar then look at Paragon to find the spring rate. Since it's a torsion bar the rate will be the same at the wheels. If you go with 400# front springs to match you will get 400#(0.9) wheel rate at the front or 360#. You want something in the rear that matches 360# but this MATCH is different for everyone.
Porsche made front and rear wheel rates very even so you might want 360# in the rear as well...it's all up to what you like, as some will go with 300# to match, some with 250# to match and some with 400# to match!
If you install rear coilovers in addition to your torsion bars you will have the rate of your 29mm torsion bars [refer to Paragon for the spring/wheel rate] then add 100# coil spring [0.60] you have 60# wheel rate in addition to the wheel rate of that 29mm torsion bar. If it feels good after driving, then great. If too much understeer remove the coil. If too much understeer add 150# rear coil rate, 200#, etc.
spring rate = force / distance, where distance is the amount the spring is being compressed.
# = lbF/inch
If your spring is compressed 1/4" under 100# of force then your spring rate is 100lbF / [1/4"] or 100lbF * 4" = 400#
If you apply 800lbF of force to a spring with rate of 400# then it will compress 800lbF/400# = 2"
EDIT:
Spring rate Vs. wheel rate:
The wheel rate is what actually affects the balance of your car. On a 944 the THEORETICAL conversions are 0.90 for the front springs, 1.00 for the rear torsion bars, and 0.55-0.65 for rear-mounted coil springs or 'coilovers.'
If you install a 29mm torsion bar then look at Paragon to find the spring rate. Since it's a torsion bar the rate will be the same at the wheels. If you go with 400# front springs to match you will get 400#(0.9) wheel rate at the front or 360#. You want something in the rear that matches 360# but this MATCH is different for everyone.
Porsche made front and rear wheel rates very even so you might want 360# in the rear as well...it's all up to what you like, as some will go with 300# to match, some with 250# to match and some with 400# to match!
If you install rear coilovers in addition to your torsion bars you will have the rate of your 29mm torsion bars [refer to Paragon for the spring/wheel rate] then add 100# coil spring [0.60] you have 60# wheel rate in addition to the wheel rate of that 29mm torsion bar. If it feels good after driving, then great. If too much understeer remove the coil. If too much understeer add 150# rear coil rate, 200#, etc.
Last edited by PorscheG96; 10-10-2003 at 02:46 AM.
10-10-2003, 02:23 AM
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Ahhh, that clicked. Muchos thank yous. So now I'm down to figure how the torsion bars play into all of this. I'm wanting to say that they...I don't know what I want to say. 
I need sleep.
I need sleep.
10-10-2003, 02:28 AM
#7
The torsion bars are the springs in the rear. They twist instead of compress like a spring. Work in much the same way I'd imagine.
"Torsion: In physics, the state of strain set up in a twisted material for example, when a thread, wire, or rod is twisted, the torsion set up in the material tends to return the material to its original state. "
I don't know the mathematics behind torsion, but I'd assume that the thicker the diameter and thus more material to twist, the higher the effective rate is.
"Torsion: In physics, the state of strain set up in a twisted material for example, when a thread, wire, or rod is twisted, the torsion set up in the material tends to return the material to its original state. "
I don't know the mathematics behind torsion, but I'd assume that the thicker the diameter and thus more material to twist, the higher the effective rate is.
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10-10-2003, 02:42 AM
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Cool cool...many thanks to both of you. You have educated the ignorant. My friend thought it would be cool (meaning stupid) to put hydraulics on it. He's into that low rider cult thing, I don't know. Anyways, you guys are great help, Rennlist truly is the best.
10-10-2003, 12:27 PM
#9
Race Director
Most have posted some good info, but I'd add what was stated in a few more details
Spring Rate:
400# means it takes 400 lbs to compress the spring 1". So a linear rate spring takes 800 lbs to compress 2". The higher number the more force it takes to compress the same amount so when cornering or hitting a bump a stiffer (higher spring rate) will compress less given the same car. Also a 400 lbs/in spring is twice as stiff as 200 lbs/in spring. Progressive springs are different in that the force to compress changes with how much it is compressed. (example 200 lbs for the first inch and 300 lbs for the second)
Simple right?
Wheel Rate:
This the actual spring rate at the wheel. This is often times not the spring rate due to suspension geometry. This value can be expressed in lbs/in or as a percentage of spring rate. This value is car specific since its dependant on the suspension design and car model specifics like control arm length and things. I'd use the paragon estimates for wheel rate for our cars.
Torsion bars:
They are springs, but not a coil spring. They are straight bar that is twisted. The diameter and length of the bar determine how much resistance to twist there is. This resistance is the the spring rate. Since the suspension is common to all 944's the length of the torsion bar is always the same. (911's have front torsion bars too, but these are not the same length.) Therefore of the two parameters that determine spring rate only diameter is variable. So stock torsion bars are at 23.5 mm in diamter. 29 mm torsion bars are 29 mm in diameter. So how stiff is 23.5 vs 29mm? Well the formula is such that stiffness is a result of the diameter to the 4th power (D^4) so a 29 mm bar is really twice as stiff as a 23.5 mm bar. I do not know the exact spring rate since I would need to know the length exactly and material properties. Now remember wheel rate? Well the number paragon shows for t-bar rate are the wheel rates not actual spring rates. In fact since the t-bar uses a twisting motion spring rate cannot expressed in lbs/in. It all depends on the length of the moment arm. (swing arm in lay terms). So bottomline is that wheel rate of a stock 23.5 mm torsion bar is 126lbs/in in the 944. 30 mm bars are 330 lbs/in.
Now they quote effetive bar diameter since there are things like hollow bars. Hollow torsion bars actually need to physically thicker to provide the same springs rate. So a 30 mm solid bar may be 30 mm, but a hollow bar may need to be 31.5 mm to have the same stiffness as a 30 mm solid. Therefore its "effective diameter" is 30 mm and you can mathamatically treat it like a 30 mm bar. Nice thing about hollow bars is that they can be lighter for the same spring rate. Why is a geometry physics thing.
Rear Coilovers:
These physically are springs just like the fronts, but due the way they are mounted in the car have a wheel rate that is much lower than the spring rate.
Hope this helps.
Feel free to ask more questions if anything was not clear.
Spring Rate:
400# means it takes 400 lbs to compress the spring 1". So a linear rate spring takes 800 lbs to compress 2". The higher number the more force it takes to compress the same amount so when cornering or hitting a bump a stiffer (higher spring rate) will compress less given the same car. Also a 400 lbs/in spring is twice as stiff as 200 lbs/in spring. Progressive springs are different in that the force to compress changes with how much it is compressed. (example 200 lbs for the first inch and 300 lbs for the second)
Simple right?
Wheel Rate:
This the actual spring rate at the wheel. This is often times not the spring rate due to suspension geometry. This value can be expressed in lbs/in or as a percentage of spring rate. This value is car specific since its dependant on the suspension design and car model specifics like control arm length and things. I'd use the paragon estimates for wheel rate for our cars.
Torsion bars:
They are springs, but not a coil spring. They are straight bar that is twisted. The diameter and length of the bar determine how much resistance to twist there is. This resistance is the the spring rate. Since the suspension is common to all 944's the length of the torsion bar is always the same. (911's have front torsion bars too, but these are not the same length.) Therefore of the two parameters that determine spring rate only diameter is variable. So stock torsion bars are at 23.5 mm in diamter. 29 mm torsion bars are 29 mm in diameter. So how stiff is 23.5 vs 29mm? Well the formula is such that stiffness is a result of the diameter to the 4th power (D^4) so a 29 mm bar is really twice as stiff as a 23.5 mm bar. I do not know the exact spring rate since I would need to know the length exactly and material properties. Now remember wheel rate? Well the number paragon shows for t-bar rate are the wheel rates not actual spring rates. In fact since the t-bar uses a twisting motion spring rate cannot expressed in lbs/in. It all depends on the length of the moment arm. (swing arm in lay terms). So bottomline is that wheel rate of a stock 23.5 mm torsion bar is 126lbs/in in the 944. 30 mm bars are 330 lbs/in.
Now they quote effetive bar diameter since there are things like hollow bars. Hollow torsion bars actually need to physically thicker to provide the same springs rate. So a 30 mm solid bar may be 30 mm, but a hollow bar may need to be 31.5 mm to have the same stiffness as a 30 mm solid. Therefore its "effective diameter" is 30 mm and you can mathamatically treat it like a 30 mm bar. Nice thing about hollow bars is that they can be lighter for the same spring rate. Why is a geometry physics thing.
Rear Coilovers:
These physically are springs just like the fronts, but due the way they are mounted in the car have a wheel rate that is much lower than the spring rate.
Hope this helps.
Feel free to ask more questions if anything was not clear.
10-10-2003, 01:58 PM
#11
The manual rack should be good to go. Just make sure the boots at the end of it are in place and in good shape, and the rack should be just fine.
Feel lucky, we don't have to worry about leaky PS racks!
Feel lucky, we don't have to worry about leaky PS racks!
10-10-2003, 02:29 PM
#12
Nordschleife Master
Originally posted by FSTPRSH
My friend thought it would be cool (meaning stupid) to put hydraulics on it. He's into that low rider cult thing, I don't know.
My friend thought it would be cool (meaning stupid) to put hydraulics on it. He's into that low rider cult thing, I don't know.
