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Learning how to build Lotus Seven replicas...together!
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PostPosted: May 11, 2022, 5:10 pm 
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Joined: May 11, 2022, 4:51 pm
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Hey everyone! My girlfriend just bought herself a used Locost 7. It was very much an impulse buy, and we are diving head-first into it, and have some suspension questions.

The first thing this thing needs is new coilovers. The ones on it are completely worn out, leaky, and just shot. My game plan had been to just take them off the car, look up the part numbers, and just order identical replacements, but of course it isn't that simple. First off, the shocks are Carrera-branded, which I have learned was purchased by QA1 a few eons ago. Searching their part numbers turns up literally NOTHING on the interwebz. So I went to the QA1 site, and tried looking up custom shocks based on the lengths I measured, but nothing quite matches. Additionally, I know the front springs are 200 lb because they're actually QA1 springs I was able to look up. The rears are unlabeled, but I SUSPECT they're way too stiff because the rear shocks BARELY compress when the car is sitting (less than an inch.)

SO, we've gotten to the point where we're just going to kind of wild-ass guess something and order new QA1 shocks and springs, and figured I'd post here first in case there were any, "JUST MAKE SURE YOU DON'T DO XXX" comments we needed to hear first.

Here are the measurements I got from the Locost:

FRONT SUSPENSION
- EXTENDED: 11.5"
- AT RIDE HEIGHT: 10.5
- COMPRESSED: n/a (need a spring compressor to remove the coil on this one)
SPRING RATE: 200

REAR SUSPENSION
- EXTENDED: 12.9"
- AT RIDE HEIGHT: 12.0"
- COMPRESSED: 10.25"
SPRING RATE: ???

So I'm looking at getting these at all four corners. They're a bit taller than what is currently at the front, but the next step down was too short, and I figure these have some ride height adjustability so...
QA1 DS304
- EXTENDED: 12.75"
- RIDE HEIGHT: 10.75-11.25"
- COMPRESSED: 9.5"

SPRINGS
- FRONT: QA1 9HT220 @ 220 lb (that's the lowest they have)
- REAR: Hyperco Coils 189A0150 from Summit Racing @ 150 lb

Does what we're doing make any amount of sense? It's kind of a SWAG and hope for the best. I'm not unfamiliar with working on cars, but I'm COMPLETELY unfamiliar with working on wild-ass kit cars where everything is custom, and I can't just go to the KW website and order a set of V3s specifically for the car, lol.


Last edited by Stang70Fastback on May 12, 2022, 9:47 pm, edited 1 time in total.

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PostPosted: May 12, 2022, 10:28 am 
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Joined: January 1, 2012, 12:44 pm
Posts: 531
Location: Boise, Idaho
Welcome to the group Stang70FB,
I used the QA1 DS shocks on my locost and my RX7 and I like them. The 150 lb rear rate estimate is reasonable, but you can also take measurements of the coil wire diameter and coil count to use in an equation to calc the spring rate. This all assumes that the resulting wheel rates yield a ride that you both will consider acceptable. Be aware that you may want to adjust them after logging some miles. The hypercoil springs are an excellent brand. They are also available in a 2.25 in ID, which may increase your choices. The perches on the QA1 shocks have enough material to be turned down for 2.25 ID springs (I've done this on mine).

Ron


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PostPosted: May 12, 2022, 11:28 am 
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Joined: December 22, 2006, 2:05 pm
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That is not enough information to make a good decision on what to buy or determine spring rate.

Post pics of the front and rear coilovers with the car sitting at ride height so we can see the active coil count.

Remove a front and rear coilover and the springs.

Using a dial caliper (about $25 at hbf), measure the wire thickness (probably about .300-.430"), the spring inside diameter (probably about 2.5"), and the eye inside diameter (probably 1/2").

Using a ruler or tape measure, measure the uninstalled spring length (probably about 10 inches), the coilover length fully extended and compressed without the spring and bump stop installed.

I made an excel spread sheet for calculating spring rate but there are online versions too.

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PostPosted: May 12, 2022, 4:18 pm 
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Location: Under the weather. (Seattle)
How much do your wheels move for those shock movements. How much are the springs pre-loaded?

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PostPosted: May 12, 2022, 8:26 pm 
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Joined: April 1, 2010, 10:26 am
Posts: 512
Your going to get a million and one answers on this site. I would recommend matching your current shocks as close as you can. GAZ coil overs are a go to shock, check out Jack's web site https://www.kineticvehicles.com/Shocks.html and his spring rate calculator if you want to get fancy, https://www.kineticvehicles.com/Shocks.html

Don't overthink it, there is no right answer, get the car on the road and have some summer fun.

Graham


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PostPosted: May 23, 2022, 3:05 am 
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Joined: July 4, 2006, 5:40 pm
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Location: Novato, CA
Sounds like you're in the ballpark, but it's hard to say for sure without looking at the car. 200# up front sounds a little soft, but if the ride is comfortable and you're not bottoming out, it could be okay. 150# in the rear sounds way too stiff, especially compared to the fronts. In a normal Locost the rear springs are vertical and the fronts are leaned in, so your fronts are always going to be stiffer based on that alone.


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PostPosted: May 30, 2022, 7:03 pm 
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Joined: March 2, 2021, 1:06 pm
Posts: 13
Just to throw as much useless information at you as possible - I have 110 lb springs at the front, but they are vertical at car centerline with 2X rockers and 18” pushrods at a 45 degree angle from the LCA.
Rear springs are 350 lb mounted nearly horizontally with similar pushrod/rocker linkage. I’ve given up trying to analyze the system and would suggest sticking with the known specs unless you are trying to cure a “bottoming” or oscillation problem.
Graham’s advice looks to be the best, but unfortunately more homework!


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