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PostPosted: November 3, 2019, 11:44 am 
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Joined: November 2, 2019, 7:23 pm
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For my Miata-based build, I misread the Saturn plans as having the rear suspension mounted to the upper control arm. It's all welded in, and I have GAZ shocks sized for that short distance (the smallest GAZ model, 7"-9", compared to 9"-13" for the front). Running the numbers through the often-linked Brunton Performance Products excel spreadsheet, I'm getting very high lb/in numbers for the springs:

rear: (GAZ 7"-9", 9.6" wheel-to-pivot, 4.4" shock-to-pivot, 15 deg. off vertical, 4.5" travel, 33% droop -> ~1050lb/in, 2.57Hz)
front: (GAZ 9"-13", 16" wheel-to-pivot, 11" shock-to-pivot, 40 deg. off vertical, 6" travel, 33% droop -> ~550lb/in, 2.22Hz)

A few questions:

1) Is the rear-shocks-on-UCA setup viable, and am I right to just use the Brunton spreadsheet in the same fashion? I'd like to make it work even if it's sub-optimal.
2) Is it pretty normal to vary the travel and droop values between front and rear like this, and any thoughts on how I should tweak things? Giving the rear 50% droop for example gets the lb/in down very close to the front.
3) I found this comprehensive source of 1.9" ID coils: http://www.shock-factory.co.uk/1.9-springs.html but are there state-side suppliers? Would 1-7/8" ID coils work?

Thanks for any advice or direction! Not going for anything close to perfection here, I'd be happy with a reasonable driver, with no concern for maximizing performance or comfort. I'll try to reconstruct my build thread when I get the chance...

-Tom


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PostPosted: November 4, 2019, 8:47 pm 
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Joined: January 11, 2017, 11:06 pm
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Hmm, got any pictures? I think the biggest consideration would be the strength of the upper A-arm and however it connects to the hub. These are usually not built in such a way as to bear the weight of the car so much as to help transfer acceleration/braking/cornering load. That would be my concern.


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PostPosted: November 4, 2019, 9:16 pm 
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ZiG wrote:
Hmm, got any pictures? I think the biggest consideration would be the strength of the upper A-arm and however it connects to the hub. These are usually not built in such a way as to bear the weight of the car so much as to help transfer acceleration/braking/cornering load. That would be my concern.


Here's a picture of one of the rear UCAs:

Image

I think it's pretty over-built: 3/16" plate on the top, which is welded over the tubes, so can't imagine downward force breaking anything there.


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PostPosted: November 5, 2019, 8:34 am 
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Joined: November 2, 2019, 7:23 pm
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How about the spring question, will 1 7/8” fit GAZ, or does it need to be 1.9” ID? I’d rather buy them stateside, but everything’s listed in 1/8” increments.


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PostPosted: November 5, 2019, 9:00 am 
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Joined: August 31, 2015, 2:24 pm
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Location: Delaware
tlippy01 wrote:
How about the spring question, will 1 7/8” fit GAZ, or does it need to be 1.9” ID? I’d rather buy them stateside, but everything’s listed in 1/8” increments.



Eibach springs (https://www.summitracing.com/parts/EIB-08001880350) fit the Gaz 1 3/4" shocks that I bought just fine.


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PostPosted: November 5, 2019, 3:49 pm 
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Joined: November 2, 2019, 7:23 pm
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Thanks! I've gone ahead and ordered springs that seem about right, we'll see...


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PostPosted: November 5, 2019, 5:45 pm 
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Joined: July 4, 2006, 5:40 pm
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Location: Novato, CA
hfmaxi wrote:
Eibach springs (https://www.summitracing.com/parts/EIB-08001880350) fit the Gaz 1 3/4" shocks that I bought just fine.


Pricey. And red.


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PostPosted: November 6, 2019, 4:18 am 
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Location: Under the weather. (Seattle)
Is your stated travel (4.5 and 6) the fully compressed to fully extended shock stroke or the travel at the wheels for the full range of shock motion? Is the travel compression limit when first making contact with the bumpstop, or the point at which bottoming the shock without a bumpstop would occur?

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PostPosted: November 6, 2019, 8:23 am 
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Joined: August 31, 2015, 2:24 pm
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Location: Delaware
nick47 wrote:
hfmaxi wrote:
Eibach springs (https://www.summitracing.com/parts/EIB-08001880350) fit the Gaz 1 3/4" shocks that I bought just fine.


Pricey. And red.



The Eibach coil springs cost about the same as everything else that's offered in 1-7/8" (hyperco, afco, qa-1 etc). Of the handful of springs I've bought they always seem to have the best fit and finish.


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PostPosted: November 6, 2019, 11:07 am 
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Joined: December 29, 2007, 10:41 pm
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Location: Vancouver, BC
From all my research, 1.9 ID springs and 1 7/8" springs are the same (1.875 rounds up to 1.9). As for sourcing springs, Southwest Speed stocks 8" and 10" springs, provided you can use either of those free lenghts:

https://www.southwestspeed.com/?sec=view_menu&cat=Suspension&sub=Springs&ssub=Coilover%20Springs&sssub=!1%207/8%22%20Diameter%20x%208%22%20Tall%20Springs

https://www.southwestspeed.com/?sec=view_menu&cat=Suspension&sub=Springs&ssub=Coilover%20Springs&sssub=1%207/8%22%20Diameter%20x%2010%22%20Tall%20Springs


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PostPosted: November 6, 2019, 11:44 am 
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Joined: September 30, 2005, 1:28 am
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Location: Sunny-Okanagan, Canada, eh?!
I've gotten a few springs from Suspension Spring Specialist, and have been very pleased with their customer service.

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PostPosted: November 6, 2019, 8:56 pm 
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Location: Novato, CA
Eibach is probably top of the line for off-the-shelf springs. I would check with Jack, then Merlin Motorsport, which has a huge selection of 1.9" ID springs at about half the cost of Eibachs.


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PostPosted: November 8, 2019, 10:25 am 
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Driven5 wrote:
Is your stated travel (4.5 and 6) the fully compressed to fully extended shock stroke or the travel at the wheels for the full range of shock motion? Is the travel compression limit when first making contact with the bumpstop, or the point at which bottoming the shock without a bumpstop would occur?


That's the travel at the wheels, and for the shorter (rear) travel, assumes no bumpstop, so right now there can be almost no upward motion before contacting the bump stop. I was wondering if maybe I could/should get a much thinner bump stop (or trim the existing one in situ) from the current ~1" to 1/2" or 1/4"...

I'm OK with this being a few-hundred-dollar mistake if I ultimately have to just redo the rear suspension to use the LCA, but if there's nothing catastrophically wrong with this I might as well try getting it on the road with the current setup and see how it feels.


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PostPosted: November 8, 2019, 4:18 pm 
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Joined: April 26, 2008, 6:06 pm
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Location: Under the weather. (Seattle)
The good: You stumbled straight into a decent f/r frequency balance for 'flat ride'. Your ride rates are also primed for hitting the autox on R-comps or slicks.

The neutral: I see no reason it won't physically run on the road. While you may not need it, it wouldn't be a bad idea to at least make plans for how you might install a front sway bar should the tail need some taming. For the bump stops, unless they're really nice with a soft linear initial travel, I'd start with trimming to ~1/3 of travel to generally try to stay off of them. So down to ~2/3" in the rear.

The bad: Your ride rates are not great for the street. I'm also concerned for the ability of the off-the-shelf GAZ dampers to handle 1000+ springs.

The uncertain: For the 'wheel pivot' are you using the upright pivot or the wheel centerline? It should be the former, but the picture makes the shock mount look more than half way to the upright pivot, not the less than half your numbers would indicate. If your calculations are based on the latter, try rerunning them based on this. Also, are you including driver, passenger, and full load of fuel behind them in your sprung weight? After reverse engineering your numbers, I think you might be light on both rear weight distribution and sprung weight for a finished and fully loaded car. If your calculations are based on an empty car, try rerunning them fully loaded with most of the additional weight being added to the rear axle.

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Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


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