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01-12-2018, 07:06 AM | #1 |
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Springs
So, I think I am going to get some shocks for my car, and I need to get springs. I have sets of 17x9 Kosei K8r's, and will be running 225 or 245 hoosiers.
I think I have the spring rates figured out, but I would like to confirm the lengths with people that are running 9" front wheels. From what I have read, it is a 9" spring in the rear and 8" in the front. Thanks in advance. |
01-12-2018, 08:35 AM | #2 | |
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Which dampers again? |
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01-12-2018, 08:49 AM | #3 |
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I am not sure how Ryan makes 6" work up front without massive binding unless he is running ridiculously stiff springs.
7" is what you need (depending on coil-over strut length) to keep the spring perch above the tire (I run 178mm springs). That is cutting it pretty close. I have K8R in 17x9 ET45. You need at least an 8mm spacer up front. Preferably use a proper 10mm so that you can get the spacers with a hubcentric lip to mount the wheel on. You'll also need adjustable camber plates. In the rear, you'll need a slight roll too depending on how much camber you run. Personally, I try to keep my rear camber less aggressive than -2*. Multi-link rear suspension does not lose camber under cornering loads like the mcpherson front suspension does. But, the camber can help avoid the fender roll. Also, stack height of the upper mount has nothing to do with the relationship between the lower spring perch and the tire. Stack height of the upper mount just effects ride height. Last edited by bbnks2; 01-12-2018 at 01:13 PM.. |
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01-12-2018, 08:50 AM | #4 |
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AST 5200. Awesome. This is what I was wondering. I saw that the lower perch has to go above the tire to clear a 9"wheel/tire combo, but couldn't find an exact measurement anywhere.
It looks to be a shorter stack height for the camber plate. Am I correct in assuming 9" is good for the rear then? |
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01-12-2018, 09:11 AM | #6 |
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https://www.turnermotorsport.com/p-3...track/?pdk=Awo
These are the camber plates that will be used. |
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01-12-2018, 10:41 AM | #7 | |
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In any case, there's a big difference in corner weight between a 135 and a 128. |
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01-12-2018, 01:08 PM | #8 | |
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01-12-2018, 01:18 PM | #9 | |
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As for travel... I'd beg to differ. Do the math. Cornering loads can exceed 1500lbs on the outside tires. Even at a spring rate of 500lbs/in that's 3in of compression travel (not including the sway bars added roll resistance of a big bar that puts you closer to 800lb/in). People who don't want to run 500lb/in, which is pretty damn stiff compared to say 300lb/in, would all benefit from running the longest spring possible when using the relatively softer springs vs your setup. If you're not already riding on your bump-stops at times, you are probably a hair away from it. Last edited by bbnks2; 01-12-2018 at 02:28 PM.. |
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01-12-2018, 04:20 PM | #10 |
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FWIW, I'm selling a pair of TC Kline 6.5" 400lb-in coil-over springs. They cleared a 17x9 +35 with a 255/40 tires no problem. Message me if interested.
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01-13-2018, 08:10 PM | #11 | |
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I'd like to say, I've zip-tied my shocks and never went to bumpstops. And my car ran pretty damn well... |
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01-14-2018, 08:21 AM | #12 | |
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If you do the math, a 6" 450lb spring will bind at about 2.5% less cornering load than a 7" 336lb spring can handle. The 336lb would just make more use of the struts usable stroke and have more droop travel available for curbing and uneven pavement. If he runs a 6" 336lb spring he will have .5" less usable spring stroke (3.7") and he will reach max usable stroke at only 60% of the cornering load a 7" 336lb spring could handle. Does that better illustrate the point so that op can make a more informed decision about what springs to go with??? 7" springs clear my k8r wheels fine even with a bit of sag in them. But, not all coilovers have the same strut length. The math makes sense. Math is how engineers and race teams build cars. Peoples logic on forums for wanting to run springs that limit their suspension travel to nothing is what doesn't makes sense. Why not just bolt the wheels directly to the chassis? |
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01-14-2018, 09:04 AM | #13 |
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Okay, starting back here.
You're assuming a lot of things. 100% load transfer (doesn't happen). That TOUCHING a bump stop is bad (it's not, assuming you have quality bump stops). That sway bars work in a very different way in your universe than they do in practice. I suppose if there was no sway bar on the car at all, operating on a very high grip surface, and running the mega-soft rates you're suggesting, you'd be correct. The car operates from the factory on the bump stops on both ends. If OP runs a 336lb spring on Hoosiers, he'll have way bigger handling problems to worry about than coil bind... You're right in that math is always right. But you have to utilize all of the factors to ensure your math is correct. You've also completely ignored the effects of roll centers as well. This isn't NEARLY as simple as your'e claiming it to be (nor is it for damn near anyone), which is why real world experience and testing is far more valuable than sitting in front of a computer. |
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01-14-2018, 10:59 AM | #14 | |
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The numbers I presented don't factor in sway bars. I left those assumptions out of it to provide a straightforward example of how spring length plays a roll in how much load a wheel can see before the spring binds. It really is that simple if you understand how much the spring compresses at static ride height and how much usable spring length you then have left over before it binds. It's basic math that I won't lay out for you. Everything else you said makes 0 sense as a rebuttal to what I said. You need to read back up. The only one making assumptions is you. I simply replied to point out to op that the length of spring he needs to clear the tire will vary depending on the strut body length and that the length of the spring is going to have a significant impact on what kind of spring rates he is going to be able to run. I then followed up with an example. You're the one assuming things based off the setup you run and the trial and error that finally got you to a working setup. The problem we have here is that you don't really understand why the setup you run works. Also, I run 275 z214 with 336lb spring... Care to explain why it's a handling problem? As I already said, it just means that my car has more suspension travel. Roll center is a great thing to bring up, but moment arm can only be tweaked so much. Maybe if you tweaked it correctly you wouldn't need 500lb springs? There is only so much you can do to change weight transfer. The cars center of gravity can only change so much and you can only make the car so wide. All you can. Really do is tweak wether the outside front wheels see more load or the rear... Also, It doesn't take "100% load transfer" (whatever that means) to put 1500lbs of Force on the outside front wheel if that's what you were getting at... And, I have no clue what you mean by sway bars work differently "in my world." I am the one usually saying there is no magic to a sway bar in threads. It's a lever that provides resistance to weight transfer. Last edited by bbnks2; 01-14-2018 at 11:39 AM.. |
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01-14-2018, 11:46 AM | #15 | |
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And yes, I know what your point is. But there is math and "sound calculations" and there are real life data points. If you want, feel free to lookup my 128i results from campaigning in STX...on 6.5" 400lb springs up front and 9" 700lb springs in the rear. |
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01-14-2018, 12:04 PM | #16 | |
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01-14-2018, 12:06 PM | #17 |
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Just some food for thought. Lots of people know that the front suspension is different from the rear. What they don't know is that lowering the front and rear does not produce the same affect on the moment arm. I'll let you figure out if you want the rear of the car higher or lower relative to the front... It will depend on wether you want load shifted forward or rearward in lateral transitions, of course.
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01-14-2018, 12:58 PM | #18 |
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Thanks for all the input guys. I am going to start with 450 lb springs in the front with 6” length. Keep in mind that the ast’s have the upper perch on the strut shaft.
For the rear, it will be 800 lb 9” springs. Probably have to play with it a bit, but it seems like a good place to start. FYI- it will be the stock bar in front. Might try a rear bar as well, but I want a torsen lsd, so May leave it off. |
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01-14-2018, 01:02 PM | #19 | |
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01-14-2018, 02:58 PM | #20 | |
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01-16-2018, 02:55 PM | #21 |
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A little late to the party, but I run:
Front Springs: Swift 7.0kg (392lb-in) / 7" length / 65mm ID Rear Springs: Swift 12.0kg (672lb-in) / 9" length / 65mm ID On the front, I have a custom spacer at the knuckle and this combination with the 7" spring works well as I have maximized spring travel (and minimized the risk of coil bind) - the spring is barely preloaded so we have maximum droop travel available. I am thinking about a slight increase in rate - when I do this, if I had the option to do a 6.5" spring I would, but I think I will likely end up sticking with the 7" option which will fit the same as it does now but sit a bit higher on the ride height front. On the rear, I could lower the car another 1/2" to 3/4" easily on my current adjusters so I believe the 9" spring is an ideal length without helper. Cheers, Mark Ride height at rest:
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08-03-2018, 06:13 AM | #22 | |
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What shocks are you running? |
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