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Driving on the street with the new springs feels like you have the sport suspension setting on all the time. It's a subtle change and very driveable.
I was afraid of this because I DD my car as well as make the trek from San Diego as far up to Monterrey for track events. Those kind of SPASM-ish drives would be too taxing for me.
I had left over 60mm Swift mains and helpers from my old M3. I will be adding longer 392#/in mains up front on the GT4 to keep the single spring configuration. It's only 50#/in softer than what Tarret uses so I figure I can dial in my preferences/results with the front sway.
Here's what I'll be installing:
F: Z60-203-070 392#/in
R: Z60-178-100 560#/in, thrust sheets to try to cure rear end noise, and 60mm helpers (don't recall PN)
I was afraid of this because I DD my car as well as make the trek from San Diego as far up to Monterrey for track events. Those kind of SPASM-ish drives would be too taxing for me.
I had left over 60mm Swift mains and helpers from my old M3. I will be adding longer 392#/in mains up front on the GT4 to keep the single spring configuration. It's only 50#/in softer than what Tarret uses so I figure I can dial in my preferences/results with the front sway.
Here's what I'll be installing:
F: Z60-203-070 392#/in
R: Z60-178-100 560#/in, thrust sheets to try to cure rear end noise, and 60mm helpers (don't recall PN)
You have selected 8 inch springs in the front. I think these are too long because the stock springs are around 7 inch (I'm guessing they are 180 mm H&R, if the were any bigger, like 200 mm, there would be tons of pre-load). The swift set uses 5 inch springs in the front with helpers. Without helpers your spring should be longer and Ira at Tarett suggests 6 inch springs (if no helper).
What you really want to match is the compressed length, the length of the spring when the car has its weight on it. Each front corner has around 700 pounds on it so:
stock front compressed length = 7.09 spring length - (700 (lbs) weight/257 (lbs/inch) front stock spring rate) = 4.37 inch
If you use 6 inch 392 pound/inch swift = 6 - (700/392) = 4.21 inches
So you'll get a very close compressed height for the front. By the way, another thing to keep in mind is the bump travel, this is the difference in spring length between having the spring fully compressed, as if you went over a bump, and the static compressed height of the car just sitting there. With 6 inch swift springs you'll have 2 inches of bump travel, just like stock. (BTW you only have 1.5 inches of bump travel with the 5 inch swift springs)
In the rear, use the Z60-178-100 560#/in springs you already suggested, but Tarett uses the 70 mm swift helpers. They are softer, which is what you want because they should be fully compressed most of the time. PN H60-070-008
I might as well give my crazy idea now. I also want to use a Z60-178-100 560#/in main with H60-070-008 helpers in the rear (same as the tarett/swift option). However, I want swift Z60-152-070 392 pound/inch front main spring, 6 inch as you do, but I'm going to put a tiny 9mm compressed eibach helper (or 12 mm KW helper) so that the front springs don't make noise under a big droop. Using another company's helper allows for a shorter helper than the shortest that swift makes. The shorter helper allows for a 6 inch main spring where if you have a longer helper you need a 5 inch main spring. With the 6 inch main spring you don't lose bump travel. The only downside is my stack height (statically compressed by car weight) will be 3mm (spring coupler thickness) + 9 mm + 4.21 inches = 4.68 so I'll loose .3 inch of lowering adjustment (because it's .3 inch taller than stock compressed length), but it seems there is about .8 inch adjustment from stock so I'll still be able to lower by .5 inches, more than enough for me (I like the stock ride height).
Bump travel was a consideration of mine, thus why I was debating between a single 7" or 8" length Swift offered in 60mm 392#/in. These options have 4.5" and 5.2" of max stroke respectively. I ultimately decided on the 8" since I had no definite length of the factory front spring off the shock, it was at least 7" in length, and I have approx 1" of lower thread adjustment to play with. This would limit options of deviating from the factory ride height minimum but I'm not trying to lose my front lip.
The Tarret spring configuration looks like it takes advantage of the lower thread settings when you look at the pics in this thread (for the rears at least).
Were you considering re-purposing the factory rear helpers to the front as your "tiny helper"?
Bump travel was a consideration of mine, thus why I was debating between a single 7" or 8" length Swift offered in 60mm 392#/in. These options have 4.5" and 5.2" of max stroke respectively. I ultimately decided on the 8" since I had no definite length of the factory front spring off the shock, it was at least 7" in length, and I have approx 1" of lower thread adjustment to play with. This would limit options of deviating from the factory ride height minimum but I'm not trying to lose my front lip.
The Tarret spring configuration looks like it takes advantage of the lower thread settings when you look at the pics in this thread (for the rears at least).
Were you considering re-purposing the factory rear helpers to the front as your "tiny helper"?
You should definitely not get an 8 inch free length front spring because your compressed length (not bump, just static weight of the car) will be 8 - 700/392 = 6.21 inches
I'm pretty sure the front free length is 7.09 inches, but even if its free length is 7.87 then its compressed length is 5.146. You wouldn't be able to get the stock height with an 8 inch free length spring that's 392 lbs/inch (6.21 is more than an inch more than 5.146, so at the very minimum you'll be a little higher than the stock ride height with no downward adjustment). You have to go 1 inch shorter than the stock spring, when you use a stiffer spring, simply because for a stiffer spring the compressed length will be longer even with the same free length. (and if the stock spring really is 7.09, you'll end up 0.8 inches higher than stock with no downward adjustment)
So if stock is 7.09 257#, you need 6 inch 392#, without a helper, and if stock is 7.87 257# you need 7 inch 392#, no helper. I understand that the pictures taken on the car were not showing the free length, but assuming the preload is low, it should be close to the free length, which is why I think the front is 7.09 inch.
I did consider using the rear helpers in the front. I think they are 12 or 14 mm fully compressed so they could work with a 6 inch front spring. However, I want to keep as many threads as I can in the front so I'll probably get the eibach 9 mm compressed length helper (60 or 70 mm free length).
I plan to do this setup sometime early next year, I want to get used to the car a little more first
The Swift spring upgrade went smoothly. Install wasn't as easy as I thought since disconnecting the endlinks did not drop the strut rods enough to clear the hats in the rear. DIY here: https://rennlist.com/forums/gt4/9613...l#post13724561
New hardware setup:
F: Swift Z60-152-070 392#/in main, Swift 60mm spring coupler, OEM rear helper, thrust sheets
R: Swift Z60-178-100 560#/in main, OEM spring coupler, Swift H60-60-015 84#/in helper, thrust sheets
Front OEM static length at just under 7.5"
Front Swift combo static length at a hair over 8"
Swift installed at front
Rear spring static lengths nearly identical at approximately 10" using Swift couplers. Retained OEM coupler in the rear to negate delta.
Rear Swift installed
The ride is noticeably stiffer but not as harsh as SPASM on OEM springs.
I'll be setting a track alignment next week and track testing is slotted for 11/19 at Autoclub Speedway.
Last edited by MVEED3; 11-04-2016 at 07:18 PM.
Reason: Added DIY link.
Do you think this exact setup would work but with 448# front springs @ 6" free length instead?
At the same load these springs would compress ~10% less than then 392# ones you used.\
Also, what is the fully compressed height of the OEM rear helper that you ended up using in the front? (less than the 0.75" compressed height of the Swift brand helper, I assume?)
I'm considering piecing my own setup together like this rather than the Tarett for fear of not enough bump travel on the Tarett 5" front spring setup...
Originally Posted by MVEED3
The Swift spring upgrade went smoothly. Install wasn't as easy as I thought since disconnecting the endlinks did not drop the strut rods enough to clear the hats in the rear. DIY here: https://rennlist.com/forums/gt4/9613...l#post13724561
New hardware setup:
F: Swift Z60-152-070 392#/in main, Swift 60mm spring coupler, OEM rear helper, thrust sheets
R: Swift Z60-178-100 560#/in main, OEM spring coupler, Swift H60-60-015 84#/in helper, thrust sheets
You can swap the 6" 448#/in main up front into my setup and still hit the minimum OEM ride height - 0.8" based on similar calculations Yargk posted in this thread and the remaining strut threads I've measured on my car. That's enough margin to account for the front rake consensus on corner balance. The apples-to-apples delta of the two springs are as follows:
6 - 700/392 = 4.2"
6 - 700/448 = 4.4"
FWIW, I have 13~14 lower threads exposed on the front struts post corner balance with the 392's.
The FCH of the rear stock helpers should be the same as the Swift H60-60-015 since they have the same coil count and material thickness. The only delta is the coil spacing which will not affect FCH.
Looking back after the install, I'd opt to run the 7" length 392#/in main and no helper up front. This nets 4.3mm more compressed spring length when compared to my 6" 392#/in main with helper and coupler. Usable stroke is the driving force and the considered 392#/in lengths show:
Usable stroke spec - (free length - compressed length) = GT4 usable stroke from static
3.5" - (6" - 4.2") = 1.7"
3.8" - (7" - 5.2") = 2"
Last edited by MVEED3; 02-01-2017 at 03:59 PM.
Reason: Added detail
This thread has been so helpful! Thank You to the earlier contributors.
In short, I was initially leaning towards a DSC controller. But read that two similarly upgraded cars (even with similar alignment specs), on the same track in the hands of the same driver, netted no change.
Some details, and link to summary. (Hope the OP Doesn't mind the quote) Car A had just the spring upgrades Car B had spring upgrades + DSC
Both drivers felt the spring upgrade improved the handling similar-ish to what DSC did.
That said for some reason. Vividracing is listing these swift springs for about 50% less than other sites. All in i spent about $265 shipped on my parts in green below. If you wanted to spec helpers all round, the total would have been still shy of $350 vs what the list is on other sites that package a kit.
Last edited by hybridporky; 08-26-2021 at 02:34 PM.
...In short, I was initially leaning towards a DSC controller. But read that two similarly upgraded cars (even with similar alignment specs), on the same track in the hands of the same driver, netted no change...
Did they change any of the settings from what was shipped on the controller?
Did they change any of the settings from what was shipped on the controller?
I believe so, if you refer to the thread itself. DSC actually offered him a unit to test. So I think it’s a honest review. His summary was upgrade springs or DSC. But not both.
This thread has been so helpful! Thank You to the earlier contributors.
In short, I was initially leaning towards a DSC controller. But read that two similarly upgraded cars (even with similar alignment specs), on the same track in the hands of the same driver, netted no change.
Some details, and link to summary. (Hope the OP Doesn't mind the quote) Car A had just the spring upgrades Car B had spring upgrades + DSC
Both drivers felt the spring upgrade improved the handling similar-ish to what DSC did.
That said for some reason. Vividracing is listing these swift springs for about 50% less than other sites. All in i spent about $265 shipped on my parts in green below. If you wanted to spec helpers all round, the total would have been still shy of $350 vs what the list is on other sites that package a kit.
I've been looking at this setup, but on paper it appears that using the 7" 448# spring in the front could result in the spring floating when unloaded... Here's my observation and tell me where/if I'm wrong.
My car is currently corner balanced at stock ride height and stock springs and the front (I measured it on the passenger side, driver may be slightly different) shows about 0.5" of preload (i.e. with the wheel off the ground the preloaded spring height is 7", compared to the free height of 7.5"). Given that the compressed height of the 7" 448# is 5.4" Vs the the stocked compressed height of 4.8" it appears that the adjustment ring would need to be loosen by 0.6" to achieve the same ride height. When comparing these two numbers (the 0.5" of current preload and the 0.6" in increased compressed height) I seem to conclude that the 7" 448# will have no preload at my current ride height...
09-16-2016, 01:43 PM
