ToplessZ Posted May 23, 2003 Share Posted May 23, 2003 OK Guys I want to get some 8 inch rear coil over springs and want to know what rate to get. This is a mostly street car with mild racing asperations for now. It is also a 280 so it is heavier. Should I look at 220lb should I go more or less. Would like some input. Thanks guys Quote Link to comment Share on other sites More sharing options...
johnc Posted May 23, 2003 Share Posted May 23, 2003 Whatever Dan Baldwin ran for his street/track combo. I think 175 front and 200 rear. Quote Link to comment Share on other sites More sharing options...
auxilary Posted May 23, 2003 Share Posted May 23, 2003 Depends on the weight of your car, how stiff you want it to be, whether it's for street or track. I'm running stock L24 Z with 200lb/in on all 4 corners, the car understeers a bit, but I don't have a rear sway bar on (it's hanging up on the wall). The front rates will drop to about 175 because of the lighter rotary I'll be putting in Quote Link to comment Share on other sites More sharing options...
ToplessZ Posted May 23, 2003 Author Share Posted May 23, 2003 because my car is a 280 and its gonna prob be in the 2800 range should I go with the 220's I want a fairly nice ride and I need a light cushion to allow a low profile tire Quote Link to comment Share on other sites More sharing options...
katman Posted May 23, 2003 Share Posted May 23, 2003 Check the coil bind height with an 8 inch spring, you might want to go to a 10 or 12. Probably okay, but with 220# rates (which I think is too high for a street car, but I'm old) you'll compress the springs 2-1/2 inches or so right off the bat, and you want another 2-1/2 for bump travel minimum. That's 5 inches of squash for an 8 inch spring. Hmmmm. Quote Link to comment Share on other sites More sharing options...
ToplessZ Posted May 23, 2003 Author Share Posted May 23, 2003 Any other input guys? Quote Link to comment Share on other sites More sharing options...
Tim240z Posted May 23, 2003 Share Posted May 23, 2003 I have 225 rear and 200 front in my LT1 240Z. It is not on the road yet, so no driving impressions yet, but that is what the vendor recommended. Since it is very easy to change springs, and they are fairly cheap, it's not a problem to experiment. Tim Quote Link to comment Share on other sites More sharing options...
ToplessZ Posted May 23, 2003 Author Share Posted May 23, 2003 Ok so do I want slightly stiffer springs since my car weighs more as it is a 280? Quote Link to comment Share on other sites More sharing options...
Tim240z Posted May 23, 2003 Share Posted May 23, 2003 No I don't think so. I think stock springs are less than half that rate, so they will be plenty stiff. Tim Quote Link to comment Share on other sites More sharing options...
ToplessZ Posted May 23, 2003 Author Share Posted May 23, 2003 OK one last question the above post about 8 inch springs being too short is that true I was hoping to do that to run a taller wider tire? I thought other guys were doing this also. I should be alright...right? Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted May 23, 2003 Share Posted May 23, 2003 Pete used 8" out back, but used 300# springs so he wouldn't bottom out. Insted the rear would almost bounce off the ground when he hit a dip in the road. http://mywebpages.comcast.net/pparaska/suspensionmods.htm Quote Link to comment Share on other sites More sharing options...
ToplessZ Posted May 23, 2003 Author Share Posted May 23, 2003 uh oh So a 240 pound spring in the rear will not be good enough to hold my tail off the ground. I was hoping to lower the car about 2 inches also if this helps. Quote Link to comment Share on other sites More sharing options...
TimZ Posted May 24, 2003 Share Posted May 24, 2003 Check the coil bind height with an 8 inch spring, you might want to go to a 10 or 12. Probably okay, but with 220# rates (which I think is too high for a street car, but I'm old) you'll compress the springs 2-1/2 inches or so right off the bat, and you want another 2-1/2 for bump travel minimum. That's 5 inches of squash for an 8 inch spring. Hmmmm. katman is on the money with this post. Coordinating the coil bind height/spring free travel with the available strut travel is critical to properly setting up a coilover suspension. Lack of attention to these details is precisely what gives coilover suspensions the reputation of being "bouncy" on many forums. Eibach's 8", 225lb/in, 2.5"id spring has 5.29" of free travel before coil bind (other brands will be very similar), so the 5" number that katman quoted is pretty much all the travel that is available with that spring. It's also worth noting that this spring gives up ~2" of the available strut travel no matter what you do. The best placement of this spring (centered on the available travel) would result in an approximate 1" drop, assuming unmodified struts. Dropping an additional inch would only leave you with about 1.5" of available travel - which would leave you riding on the bump stops pretty much all the time. Not good. Another problem that you can run into when trying to go to a stiffer spring to keep from bottoming out is that you lose droop travel - basically your droop travel becomes only the amount that the spring gets compressed at the static ride height. In Pete's case, there is only about 2" of droop travel available, no matter what he does. So, any bump that causes a rise of more than 2" causes the tire to leave the ground. I do use a coilover setup on my rear suspension, but I opted to use a longer spring that was capable of utilizing the full travel of the suspension. I had to give up about 0.5" of wheel clearance to do this, but it does still give more clearance than the stock spring. With this setup I was still able to fit a 245/45-16 under the stock wheel wells with a small amount of trimming. My struts don't bottom out, and my tires don't leave the ground on bumps. 255's would not have fit. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 24, 2003 Share Posted May 24, 2003 Another problem that you can run into when trying to go to a stiffer spring to keep from bottoming out is that you lose droop travel - basically your droop travel becomes only the amount that the spring gets compressed at the static ride height. In Pete's case, there is only about 2" of droop travel available, no matter what he does. So, any bump that causes a rise of more than 2" causes the tire to leave the ground. I'm confused by this statement. How does spring length limit droop? Are your springs attached to the spring perches? BTW... I assume the spring travel discussion includes shortened struts. Quote Link to comment Share on other sites More sharing options...
TimZ Posted May 24, 2003 Share Posted May 24, 2003 Another problem that you can run into when trying to go to a stiffer spring to keep from bottoming out is that you lose droop travel - basically your droop travel becomes only the amount that the spring gets compressed at the static ride height. In Pete's case' date=' there is only about 2" of droop travel available, no matter what he does. So, any bump that causes a rise of more than 2" causes the tire to leave the ground. [/quote'] I'm confused by this statement. How does spring length limit droop? Are your springs attached to the spring perches? BTW... I assume the spring travel discussion includes shortened struts. When the spring has reached it's maximum extension, any further supension droop is uncontrolled. The suspension might droop farther on it's own, but there is no guarantee that it will. In practice, it won't droop much farther due to stiction (yes that's a real engineering term) in the suspension, and even if it does there is essentially no force on the suspension at that point. So, if your spring only has 5 inches of travel and your suspension has 7 inches, those last two inches of travel don't really "count". Strut sectioning was never mentioned in the oringinal discussion, and I've noticed a couple other posts where people seem to be installing coilovers without sectioning the struts, so I am assuming that ToplessZ was not going to section his struts. I did make that distinction in my post, btw. Quote Link to comment Share on other sites More sharing options...
pparaska Posted May 24, 2003 Share Posted May 24, 2003 BTW, my Z is off the road now for TBI installation (including new fuel lines), and up in the air. I'm going to put 8" 250 lb/in springs on the rear and I'll instrument it to see what the max bump travel used is under normal and spirited driving to see if the coils bind. If not, I may opt for even less spring rate (maybe as low as 200). 300 is too much for me. I did drive from MD to AL (SEZS#1) and back with those and the Tokicos on 5 in the rear, and believe it or not you do get used to it! Even my 40 year old, 220 lb body! But I've gone back down to a 4 setting on the shocks (3 up front with 225 lb/in springs) and it's much better. 3 is too low on the rear, lots of pogoing. Even pogoes a slight bit on 4. If 250 is still to stiff and 200 or 225 lb/in in the rear would bottom, I'll do something to gain length up top, like shorten the strut top isolator or maybe a urethane isolated top mount. BTW, I shortened the struts front and rear by 1.5" and use stock 240Z strut isolators. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 24, 2003 Share Posted May 24, 2003 any further supension droop is uncontrolled. The rebound in the shock would (and does) control droop whether the spring is there or not. In practice, it won't droop much farther due to stiction (yes that's a real engineering term) in the suspension, and even if it does there is essentially no force on the suspension at that point. Usually the weight of the wheel and tire (35 lbs or more) will bring the suspension into full droop, it just doesn't droop at the same rate as when the spring is involved. Happens all the time in race cars - that's why lots of guys run the little helper springs with 8" regular springs. The bump in the shock would also add some measure of control until the spring was re-engaged although this is not an ideal situation. BTW... I'm not disagreeing with you or Keith regarding the choice of spring height for a street car. Quote Link to comment Share on other sites More sharing options...
TimZ Posted May 24, 2003 Share Posted May 24, 2003 any further supension droop is uncontrolled. The rebound in the shock would (and does) control droop whether the spring is there or not. The rebound in the shock will resist movement, but the natural frequency of the suspension will be undefined, as there is no longer any spring rate associated with the suspension (possibly some minimal rate from gas pressure shocks, but this is negligible). As such, the suspension has lost it's ability to track the surface it is moving over. Usually the weight of the wheel and tire (35 lbs or more) will bring the suspension into full droop, it just doesn't droop at the same rate as when the spring is involved. Happens all the time in race cars - that's why lots of guys run the little helper springs with 8" regular springs. The bump in the shock would also add some measure of control until the spring was re-engaged although this is not an ideal situation. For instance, let's say that the suspension did continue to droop from the inertia of the unspriung weight as the car crested a rise. Until the suspension is back on the spring, it will be able to compress at pretty much the rate at which the undulations in the road can push on it, but it can only re- extend at at the rate at which gravity can overcome the suspension's stiction. This isn't very fast, assuming gravity can overcome the stiction at all. The available traction from the tire in this condition is at best highly unpredictable and very likely to be nil. I don't disagree that it happens all the time - I'm just contending that the additional travel does nothing particularly useful, and is not the same as droop travel when a proper length spring is used. Hence my argument that the additional travel doesn't count. Quote Link to comment Share on other sites More sharing options...
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