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PostPosted: June 12, 2020, 4:51 pm 
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Joined: May 31, 2019, 12:37 am
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Location: Alberta
Hello again everyone, I need some help now so I can order some shocks. I have my pushrod suspension setup on one side, with. 0.75/1 ratio at the moment. The car at most will weight 300# per corner. I have lots of adjustments available to change my rate, but I’ll have 4” of travel needed on the shocks.

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File comment: Front suspension
9B683966-4EB4-43E4-8900-D4B0448519E9.jpeg
9B683966-4EB4-43E4-8900-D4B0448519E9.jpeg [ 158.61 KiB | Viewed 443 times ]


I can technically fit up to an 18” shock, but I would definitely like a double adjustable option. The car will have 2” compression and 2” droop at the wheel so compressed 1.5” on the shock at ride height. How the heck do I figure out what I need now??? Hahaha

Here’s a video of the movement if anyone is interested.
https://www.facebook.com/1244110147/posts/10217490662798835/?d=n

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PostPosted: June 13, 2020, 12:56 am 
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Joined: March 19, 2011, 10:22 am
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Location: Holden, Alberta, Canada
https://aldanamerican.com/coil-over-shocks-professional-grade/
These are the guys that supplied my coilovers for the TBird 7 build. Shoot them an email, I'm sure they will help you out.

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PostPosted: June 13, 2020, 1:34 am 
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horchoha wrote:
https://aldanamerican.com/coil-over-shocks-professional-grade/
These are the guys that supplied my coilovers for the TBird 7 build. Shoot them an email, I'm sure they will help you out.


Nice looking units, but quite pricey. Slightly more than QA1 as well I think. I’d be into them for almost $2k Canadian by the time I’m done. Hahaha. Our dollar sucks again.

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PostPosted: June 13, 2020, 7:07 am 
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Joined: August 28, 2010, 7:53 am
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Dennis Grants's site is excellent for calculating suspension stuff, inc springs, arb's and shocks. Read through his WS- youll learn a lot

http://farnorthracing.com/autocross_secrets16.html


IF you are not big on math and spreadsheets, I think a good place to start for a street car is as follows:
Wheel rate equals 1/2 SPRUNG corner weight. the ARB rate should be about 1/3 to 1/2 of the wheel rate. ex 400 lb sprung corner, 1:1 motion ratio. 200lb spring, 75 lb ARB This allows the car to turn well and not get rattled over small bumps. A little anti-dive geometry is good too. The weigh calcs are with driver fuel, fat guy in the pass seat, etc.

The rear usually needs slightly softer if the car is 50/50 weight. If its tail heavy it might need more. Straight axles use a lot less. Tune the rear ARB and/or panhard/Watts etc to balance the car

Once you have the springs, weights, ARBs, etc, you can calc shock rates


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PostPosted: June 14, 2020, 3:41 am 
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Without preload, 2 inches of droop is 1/2 wheel rate to corner weight, which runs ~2.2Hz. This is not a bad starting point. Track oriented, but still streetable depending on individual ride tolerance. At 300 lb sprung weight (fully loaded?) and a .75 motion ratio, that technically comes out to 266 lb/in springs. So you'd probably be looking at a 250 or 275 pound/inch spring in that case. Are you expecting it to be the same at all 4 corners, or biased one way or the other? Do you have sway bar plans? If so, personally I'd go with a bit higher frequency rear than front, and then tune it in with the sway bar(s).

It sounds like you're looking for an entry level (cheap) double adjustable shock solution, and have found the QA1 Proma-Star. I've never seen any shock dyno data for them, and have no personal opinion about them, but I think a few people around here have used them. Based on your 18" comment, it looks like you'd be most interested in the 5" (16.375 extended) or 6" (18.75" extended) travel variants. This should leave you enough room to utilize a softer/longer bump stop.

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Last edited by Driven5 on June 14, 2020, 3:53 am, edited 1 time in total.

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PostPosted: June 14, 2020, 3:52 am 
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Driven5 wrote:
Without preload, 2 inches of droop is 1/2 wheel rate to corner weight, which runs ~2.2Hz. This is not a bad starting point. Track oriented, but still streetable depending on individual ride tolerance. At 300 lb sprung weight (fully loaded?) and a .75 motion ratio, that technically comes out to 266 lb/in springs. So you'd probably be looking at a 250 or 275 pound/inch spring in that case. Are you expecting it to be the same at all 4 corners, or biased one way or the other? Do you have sway bar plans? If so, personally I'd go with a bit higher frequency rear than front, and then tune it in with the sway bar(s).

It sounds like you're looking for a cheap double adjustable shock solution, and have found the QA1 Proma-Star. I've never seen any shock dyno data for them, but I think a few people around here have used them. Based on your 18" comment, it looks like you'd be most interested in the 5" (16.375 extended) or 6" (18.75" extended) travel variants. This should leave you enough room to utilize a softer/longer bump stop.


Awesome help man! Actually I’m thinking now that the sprung weight should be lower, but that’s a good starting point. Probably nearer to 260. It is just a bec with turbo.

It should be very close to 50/50 weight as well. I have a second trans in the rear, battery, fuel, ice box and whatever else I can get back there.

I’m actually considering a very cheap alternative as well for shocks, but I’ll wait on the specs and quote before I share a bit more...

Sway bar plans- not sure yet. I haven’t looked into designs for use on pushrod style yet so I don’t know what it would take to build or fit.

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PostPosted: June 14, 2020, 1:16 pm 
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" and a .75 motion ratio," Motion ratio or spring ratio? I think something has to be squared?


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PostPosted: June 14, 2020, 4:32 pm 
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Joined: August 28, 2010, 7:53 am
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Velix - Its easiest to connect ARB to rocker arms in a pushrod setup

Bobber- calculating wheel rate of spring is motion ration squared
ie If the spring is mounted in the center of the LCA (one would be very unlikely to do this) it would move 1/2 as much as the wheel. The wheel would also have 2x leverage on the spring. The MR needs to be squared due to both of these things.


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PostPosted: June 14, 2020, 5:24 pm 
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Sean in CT wrote:
Velix - Its easiest to connect ARB to rocker arms in a pushrod setup

Bobber- calculating wheel rate of spring is motion ration squared
ie If the spring is mounted in the center of the LCA (one would be very unlikely to do this) it would move 1/2 as much as the wheel. The wheel would also have 2x leverage on the spring. The MR needs to be squared due to both of these things.


Sorry, what do you mean by ARB?

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PostPosted: June 14, 2020, 7:55 pm 
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sorry - sway bar = antiroll bar ("ARB")


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