- :
- 2008 Mazda5 GT
Mazda5 YellowSpeed Coilovers
The recent suspension discussion brought some interesting points and since we have a few members with good first hand experience, figure now is prime to bring this up. Ive had this in mind and taking notes/measurements and put them aside for awhile and have been too lazy to follow through. Winter leads to tinkering time. I hope to get feedback from those with experience or knowledge/understanding and not just hearsay.
I have never used a true full coilover setup. Ive always been a separate spring/shock combo kinda guy on all my previous cars simply b/c DD is #1 priority. Im also cautious about wintery environments. I did try coil over sleeves, once, when I was much younger (stock shocks (silly)). I feel Im a little bit more informed and am very tempted to give a full CO a try and want to see if I am approaching it right.
For now, lets just use rears for discussion b/c I have a set of YellowSpeed (YS) Coilovers (CO) available for measurements. If someone have a rear OE spring lying around, PLEASE measure the total free length, coil diamter, and inner diameter. It would also allow us to gauge a percentage difference.
Basic Info
. Well use the GT specs as the example. If we distribute the 3,475lbs for 43% rear, this give us 1,494.25lbs on the rear axle. Split that in half and we get 747.125 lbs rear corner. Cars are never truly symmetrical so well have to estimate and assume even distribution. Anyone here corner weight their car?? Another assumption well have to make is total unspring weight; weight thats not load bearing on the suspension (tire/rim/rotors/calipers/etc. and some parts of the suspension geometry). Theres no way to tell this exactly but from surfing the web, I get numbers ranging from 70-150lbs (sub compacts to full size). Considering the Mazda5 is built on the Mazda3, which is a compact so on the lower end of the weight scale, Id guestimate ~100 lbs.?. If someone can clarify or add some more, that would be great. 747.125 100 = 647.125 sprung weight on the corner. Since we are estimating, lets round this up to somewhere around 650lbs pushing down on one of the rear corners at rest.
YS rear spring
http://yellow-speed.com/products.php?func=p_list&pc_parent=1&p_front_type=ss&p_brand=MAZDA
I have Yellowspeed DSPs so this will be the example. The rear springs are marked 074 160 008, which seems be 74mm inner diameter (2.91), 160mm height (6.23), 8kg/mm spring rate (447.98 lbs/in). I wasnt sure so I measured them to be sure (still unsure about the spring rate, more on that later). I also the questionable consistency of these low end springs.
Spring Specs per dial caliper/ruler:
Height: 6.4375
OD Top: 4.47 (I think the top coils are wider to mount the stock spring perch as it does not come with one like the BC, which you have to put ontop of the existing OE spring perch)
OD Bottom: 4.5 (ID is smaller on the bottom)
Coil Thickness: .6
Total Coils: ~4.8
Active Coils: totally guessing ~2.8 (or less)?
Material: Listed as SAE9254 steel in the literature. Anyone know what material resembles this in psi/GPa? Google is coming up with silicon chrome steel or chrome vanadium as most commonly used for car springs but I cant get an exact match to that SAE standard. http://www.engineeringtoolbox.com/modulus-rigidity-d_946.html. The spring has a slight tapered design in that you cannot invert it. B/c of these, I cannot get any of the online tools/formulas to accurately spring rate. Can someone here confirm this?
Calculating
So the .6 thickness x 4.8 coils = 2.88 in total coil thickness (height) when the spring is fully bind. 6.4375 total length 2.88 coil thickness = 3.5575 of full theoretical suspension travel. At rest, the corner is already pushing down 650lbs. Assuming the spring is 8kg/mm (=447.979 lbs/in), the 650lbs would be 145% of the 447.979 lbs/in spring, so about -1.45. At rest, the suspension would be 3.5575 1.45 = 2.1 rounded. I have max 3.55 when wheel is in the air or high speed forces and 2.1 in low speed situations. Someone check my math.
Undetermined Variables
Bump Stop
This does not factor in the loss of travel from the bump stops/jounce bumpers! They measure .82 in total height but all is not lost. While these YS stops seem to be pretty much hard stops but Id wager theres a smaller percentage compression in it before you feel the big crush. The top has .37 trapezoid shape so Im going to guess it offers somewhat linear rate (totally guessing). The bottom .45 half is solid.
Shock Travel
Generic promo pic
The total length of the exposed shaft is 5.57 from the top of the base to the bottom of top hat. So, 5.57 free length - .82 bump stops = 4.75. 4.75 3.5575 (unbinding spring) = 1.1925 of shock travel not used by the shocks or spring. Someone check my math.
Of course, this completely ignores the optimal range these shocks are built to operate in. Interesting unofficial test: when cranked all the way to soft, the rears can be compress pretty easily (bound) and decompress at a moderate rate (rebound). When cranked all the way to hard, the compression is slightly harder but decompression is noticeably slower. It leads me to belive the promo chart is somehwhat onpoint but not necessarily to scale.
Conclusion
More questions than answers. With COs, there isnt much as much free travel to work with. However, there seems to be about 1.1925 length of dark space that is physically impossible to reach. Is this necessary to prolog the shock from blowing? Why the aggressive bump stop? The reason I did all this is to see if I can 1) swap out for a lower spring rate, say 6kg/mm (335.984488 lbs/in). B/c of the lower rate, the forces at hwy speeds x weight would prob amplify what the shocks has to manage and need more space to work with. Do we have a physics major in the house? The question Im not sure on is: can I use a longer 6kg/mm spring? It looks like I have free length and the ID of the spring is close to 3, which is common. The sleeve seems to be able to accommodate the length since Im not looking to slam it. Even an extra .5" would do wonders. Im also thinking since the travel will be short, no matter what, how helpful would it be to mitigate the bump at full compression by using a longer and more progressive jounce bumper? This way, the progressive stop (rates in the hundreds of lbs/in) can help manage the compression along with the lower rated spring, sorta like a filler. http://fatcatmotorsports.com/FCM_app_guide.htm
The recent suspension discussion brought some interesting points and since we have a few members with good first hand experience, figure now is prime to bring this up. Ive had this in mind and taking notes/measurements and put them aside for awhile and have been too lazy to follow through. Winter leads to tinkering time. I hope to get feedback from those with experience or knowledge/understanding and not just hearsay.
I have never used a true full coilover setup. Ive always been a separate spring/shock combo kinda guy on all my previous cars simply b/c DD is #1 priority. Im also cautious about wintery environments. I did try coil over sleeves, once, when I was much younger (stock shocks (silly)). I feel Im a little bit more informed and am very tempted to give a full CO a try and want to see if I am approaching it right.
For now, lets just use rears for discussion b/c I have a set of YellowSpeed (YS) Coilovers (CO) available for measurements. If someone have a rear OE spring lying around, PLEASE measure the total free length, coil diamter, and inner diameter. It would also allow us to gauge a percentage difference.
Basic Info
Specs above per Motor trend for a red 2008 auto GT - I just happen to have a red 2008 auto GT
. Well use the GT specs as the example. If we distribute the 3,475lbs for 43% rear, this give us 1,494.25lbs on the rear axle. Split that in half and we get 747.125 lbs rear corner. Cars are never truly symmetrical so well have to estimate and assume even distribution. Anyone here corner weight their car?? Another assumption well have to make is total unspring weight; weight thats not load bearing on the suspension (tire/rim/rotors/calipers/etc. and some parts of the suspension geometry). Theres no way to tell this exactly but from surfing the web, I get numbers ranging from 70-150lbs (sub compacts to full size). Considering the Mazda5 is built on the Mazda3, which is a compact so on the lower end of the weight scale, Id guestimate ~100 lbs.?. If someone can clarify or add some more, that would be great. 747.125 100 = 647.125 sprung weight on the corner. Since we are estimating, lets round this up to somewhere around 650lbs pushing down on one of the rear corners at rest. YS rear spring
http://yellow-speed.com/products.php?func=p_list&pc_parent=1&p_front_type=ss&p_brand=MAZDA
I have Yellowspeed DSPs so this will be the example. The rear springs are marked 074 160 008, which seems be 74mm inner diameter (2.91), 160mm height (6.23), 8kg/mm spring rate (447.98 lbs/in). I wasnt sure so I measured them to be sure (still unsure about the spring rate, more on that later). I also the questionable consistency of these low end springs.
Spring Specs per dial caliper/ruler:
Height: 6.4375
OD Top: 4.47 (I think the top coils are wider to mount the stock spring perch as it does not come with one like the BC, which you have to put ontop of the existing OE spring perch)
OD Bottom: 4.5 (ID is smaller on the bottom)
Coil Thickness: .6
Total Coils: ~4.8
Active Coils: totally guessing ~2.8 (or less)?
Material: Listed as SAE9254 steel in the literature. Anyone know what material resembles this in psi/GPa? Google is coming up with silicon chrome steel or chrome vanadium as most commonly used for car springs but I cant get an exact match to that SAE standard. http://www.engineeringtoolbox.com/modulus-rigidity-d_946.html. The spring has a slight tapered design in that you cannot invert it. B/c of these, I cannot get any of the online tools/formulas to accurately spring rate. Can someone here confirm this?
Calculating
So the .6 thickness x 4.8 coils = 2.88 in total coil thickness (height) when the spring is fully bind. 6.4375 total length 2.88 coil thickness = 3.5575 of full theoretical suspension travel. At rest, the corner is already pushing down 650lbs. Assuming the spring is 8kg/mm (=447.979 lbs/in), the 650lbs would be 145% of the 447.979 lbs/in spring, so about -1.45. At rest, the suspension would be 3.5575 1.45 = 2.1 rounded. I have max 3.55 when wheel is in the air or high speed forces and 2.1 in low speed situations. Someone check my math.
Undetermined Variables
Bump Stop
This does not factor in the loss of travel from the bump stops/jounce bumpers! They measure .82 in total height but all is not lost. While these YS stops seem to be pretty much hard stops but Id wager theres a smaller percentage compression in it before you feel the big crush. The top has .37 trapezoid shape so Im going to guess it offers somewhat linear rate (totally guessing). The bottom .45 half is solid.
Shock Travel
Generic promo pic
The total length of the exposed shaft is 5.57 from the top of the base to the bottom of top hat. So, 5.57 free length - .82 bump stops = 4.75. 4.75 3.5575 (unbinding spring) = 1.1925 of shock travel not used by the shocks or spring. Someone check my math.
Of course, this completely ignores the optimal range these shocks are built to operate in. Interesting unofficial test: when cranked all the way to soft, the rears can be compress pretty easily (bound) and decompress at a moderate rate (rebound). When cranked all the way to hard, the compression is slightly harder but decompression is noticeably slower. It leads me to belive the promo chart is somehwhat onpoint but not necessarily to scale.
Conclusion
More questions than answers. With COs, there isnt much as much free travel to work with. However, there seems to be about 1.1925 length of dark space that is physically impossible to reach. Is this necessary to prolog the shock from blowing? Why the aggressive bump stop? The reason I did all this is to see if I can 1) swap out for a lower spring rate, say 6kg/mm (335.984488 lbs/in). B/c of the lower rate, the forces at hwy speeds x weight would prob amplify what the shocks has to manage and need more space to work with. Do we have a physics major in the house? The question Im not sure on is: can I use a longer 6kg/mm spring? It looks like I have free length and the ID of the spring is close to 3, which is common. The sleeve seems to be able to accommodate the length since Im not looking to slam it. Even an extra .5" would do wonders. Im also thinking since the travel will be short, no matter what, how helpful would it be to mitigate the bump at full compression by using a longer and more progressive jounce bumper? This way, the progressive stop (rates in the hundreds of lbs/in) can help manage the compression along with the lower rated spring, sorta like a filler. http://fatcatmotorsports.com/FCM_app_guide.htm
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. I actually sent Swift an email a few days ago with some questions on availability. It seems their catalog of 3” ID springs start at 12” length –that’s not going to work for me 
. The YS springs are 6.43” so I’d like 7” or 7.5” max. It seems the perch allows a tad more room but not 12”! I’m not sure why there’s 1.19” (this includes the .82 bump stop) of shock travel that’s not used at all so at the moment it leads me to think there is some wiggle room. I need to check with a shock manufacturer. 
