findmuck Posted October 22, 2014 Report Share Posted October 22, 2014 I was thinking in class a few days ago and I came to the idea that if you find a set of springs for the rear of your car that are identical to yours (the diameter and amount of springs) but are from a car that is heavier in the back; lets say your car weighs 400 lbs in the back and the car you got the springs from weighs 700. If you put the heavier car springs (that are meant to hold more weight) on your lighter car wouldn't they simply make your ride in the back stiffer? I'm asking because I am gonna lower the back of the wagon by cutting one spring (don't judge me, its cheap and wont affect my drive because no racecar) and don't want my already saggy rear to turn into a jumper house ( I got new coils for the back too). B) Quote Link to comment
MicroMachinery Posted October 22, 2014 Report Share Posted October 22, 2014 Just cutting the existing springs will make it stiffer and lower. Quote Link to comment
findmuck Posted October 22, 2014 Author Report Share Posted October 22, 2014 Just cutting the existing springs will make it stiffer and lower. But will different springs make it even stiffer? Quote Link to comment
MicroMachinery Posted October 22, 2014 Report Share Posted October 22, 2014 Only if they're stiffer springs. 1 Quote Link to comment
datzenmike Posted October 23, 2014 Report Share Posted October 23, 2014 There is a formula for determining the spring rate of a coil. The rate is in pounds per inch or the pounds needed to compress one inch. Two springs that are identical will have he same spring rate. One car may be heavier but if you look when installed it will also be compressed more.The same spring, (same diameter of the coil, same wire thickness and same number of compressible coils) even though from a heavier car will not be 'stiffer' Absolutely, but to be 'stiffer' the coils must be narrower diameter OR thicker wire diameter OR fewer coils. Or any combination of those.Fewer coils will increase the spring rate. I'll give an example. My 710 front coils are...Coils............ 6.5Wire thickness.... .5"Coil diameter..... 5.0625"Spring rate....... 102.5 lb/in.If I were to cut one coil off the spring rate increases to 123.16 lb/in!! Keep in mind the the spring would now sag less under weight, but, it is also shorter by one coil. Setting ride height by cutting coils is at best, hit or miss, and IF you get to where you like the ride height the spring rate may be (and likely is) too stiff or not stiff enough.Lets say you somehow found another identical spring but the wire was thicker by 1/8". Applying the formula we find the spring rate has increased from 102.5lb/in to 254.43!!! BIG difference.Lets say you somehow found another identical spring but the coil diameter was slightly narrower by 1/4". Applying the formula we find the spring rate has increased from 102.5lb/in to 121.31 lb/inIf you take some careful measurements for me on your coil spring I can tell you where you are rate wise. From here you can make an educated guess of where you want to go. Ask other owners that know what rate they have or like and go from there. On my 710 coil I cut 1 and a half coils off (I think) and the rate increased 50% to about 150 lb/in. I find 150 is good for me but its a personal choice. I do have an extra set and may try 175 and maybe 225 and keep my 150 set just in case. 2 Quote Link to comment
paradime Posted October 23, 2014 Report Share Posted October 23, 2014 Wo Mike. The name of this thread is Pothead Moment, Too much math for a Wednesday. Teto, Load me a bowl. 5 Quote Link to comment
JoeCool Posted October 23, 2014 Report Share Posted October 23, 2014 Unless you REALLY know what you are doing, and do your homework on the job, I wouldn't recommend cutting the springs. Even a slight bit off and it can fall out of position which is very dangerous. That happened to a guy I worked with at the Ford dealer. He was a mechanic, but got the measurement slightly off on one spring he cut on his Trans Am. Luckily he didn't crash! Quote Link to comment
datzenmike Posted October 23, 2014 Report Share Posted October 23, 2014 It's covered in the Dime Quarterly. They're held in place with a chain. Quote Link to comment
Charlie69 Posted October 23, 2014 Report Share Posted October 23, 2014 Wo Mike. The name of this thread is Pothead Moment, Too much math for a Wednesday. Teto, Load me a bowl. ROFLMAO Quote Link to comment
Nuclear Water Boy Posted October 23, 2014 Report Share Posted October 23, 2014 Unless you REALLY know what you are doing, and do your homework on the job, I wouldn't recommend cutting the springs. Even a slight bit off and it can fall out of position which is very dangerous. That happened to a guy I worked with at the Ford dealer. He was a mechanic, but got the measurement slightly off on one spring he cut on his Trans Am. Luckily he didn't crash! Peeef!!! ya well it's a Trans Am. The 510 rear spring is snuggly held in place. Best spring height to start at is 10" then 1/4" diameter cut from there until you have you desired ride height. My rear springs are 9 3/4" not as low as some but low enough for me. I believe for every difference in spring height cut it lowers the rear twice that amount. So you go from say 10" to 9 3/4" it'll lower the back 1/2" Quote Link to comment
findmuck Posted October 23, 2014 Author Report Share Posted October 23, 2014 There is a formula for determining the spring rate of a coil. The rate is in pounds per inch or the pounds needed to compress one inch. Two springs that are identical will have he same spring rate. One car may be heavier but if you look when installed it will also be compressed more. The same spring, (same diameter of the coil, same wire thickness and same number of compressible coils) even though from a heavier car will not be 'stiffer' Absolutely, but to be 'stiffer' the coils must be narrower diameter OR thicker wire diameter OR fewer coils. Or any combination of those. Fewer coils will increase the spring rate. I'll give an example. My 710 front coils are... Coils............ 6.5 Wire thickness.... .5" Coil diameter..... 5.0625" Spring rate....... 102.5 lb/in. If I were to cut one coil off the spring rate increases to 123.16 lb/in!! Keep in mind the the spring would now sag less under weight, but, it is also shorter by one coil. Setting ride height by cutting coils is at best, hit or miss, and IF you get to where you like the ride height the spring rate may be (and likely is) too stiff or not stiff enough. Lets say you somehow found another identical spring but the wire was thicker by 1/8". Applying the formula we find the spring rate has increased from 102.5lb/in to 254.43!!! BIG difference. Lets say you somehow found another identical spring but the coil diameter was slightly narrower by 1/4". Applying the formula we find the spring rate has increased from 102.5lb/in to 121.31 lb/in If you take some careful measurements for me on your coil spring I can tell you where you are rate wise. From here you can make an educated guess of where you want to go. Ask other owners that know what rate they have or like and go from there. On my 710 coil I cut 1 and a half coils off (I think) and the rate increased 50% to about 150 lb/in. I find 150 is good for me but its a personal choice. I do have an extra set and may try 175 and maybe 225 and keep my 150 set just in case. Thanks Mike ill get those to you soon! Quote Link to comment
datzenmike Posted October 24, 2014 Report Share Posted October 24, 2014 Need diameter of the coil, center to center. You can go outside to outside if you want, (easier) then all I have to do is subtract the wire width to get the center. Make sure you note which way you measured them. A caliper is good for getting the wire width. Scrape off any paint or loose rust or undercoating. The number of coils are the ones that are actually able to move and compress. Usually the last 3/4 coil is wound tight against the coil above it. Ignore that piece and start where the coil separates. The more accurate your measurements, the better the results. Quote Link to comment
mttam510 Posted November 7, 2014 Report Share Posted November 7, 2014 GD4/8ND3 where G= 11.25x106 D= wire diameter N= number of 'active' coils D= mean spring diameter (ID + wire size or OD- wire size) BTW...a .125" chage in wire diameter is HUGE....Eibach's wire sizes are in increments of .1mm....and yes, wire diameter has a BIG effect on spring rate 2 Quote Link to comment
findmuck Posted November 11, 2014 Author Report Share Posted November 11, 2014 Need diameter of the coil, center to center. You can go outside to outside if you want, (easier) then all I have to do is subtract the wire width to get the center. Make sure you note which way you measured them. A caliper is good for getting the wire width. Scrape off any paint or loose rust or undercoating. The number of coils are the ones that are actually able to move and compress. Usually the last 3/4 coil is wound tight against the coil above it. Ignore that piece and start where the coil separates. The more accurate your measurements, the better the results. Picked these up from rockauto! Inside Diameter: 3.437 Wire Diameter: 0.473 Number of coils: 7 I got these not off of my wagon but off of the the info for parts ! Quote Link to comment
datzenmike Posted November 11, 2014 Report Share Posted November 11, 2014 Well that works out to 168 lb/in but this is not what's on your vehicle. Also the number of coils isn't clear if these are active or some are resting against the top and bottom perches. This is just a replacement coil and all it has to be is the same general spring rate. It may have more coils but thicker wire. Quote Link to comment
findmuck Posted November 11, 2014 Author Report Share Posted November 11, 2014 Well that works out to 168 lb/in but this is not what's on your vehicle. Also the number of coils isn't clear if these are active or some are resting against the top and bottom perches. This is just a replacement coil and all it has to be is the same general spring rate. It may have more coils but thicker wire. Sorry about that ! Ill get you the actual number! Quote Link to comment
datzenmike Posted November 11, 2014 Report Share Posted November 11, 2014 It's OK. I have Maxima struts and the Maxima is built on the zx platform and shares lots of things. The Maxima springs are 150 so I assume the zx is somewhere around this number. PL510............. 89 lb/in 710................ 101 lb/in Maxima.......... 150 lb/in Quote Link to comment
metalmonkey47 Posted November 11, 2014 Report Share Posted November 11, 2014 It's OK. I have Maxima struts and the Maxima is built on the zx platform and shares lots of things. The Maxima springs are 150 so I assume the zx is somewhere around this number. PL510............. 89 lb/in 710................ 101 lb/in Maxima.......... 150 lb/in Is the Maxima spring rate close between the front and rear? Quote Link to comment
datzenmike Posted November 11, 2014 Report Share Posted November 11, 2014 Don't have that info Matt. The struts I have were from an '84 goon and they had rear leaf springs. But I did measure and calculate the front springs at 145 lb/in. Quote Link to comment
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