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Street Rail: I need help with rear coilovers!
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di11ard
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PostPosted: Tue Mar 13, 2018 5:18 pm    Post subject: Street Rail: I need help with rear coilovers! Reply with quote

I have a new set of arms going on the street rail. The are 2 inches wider and 3 inches longer.

The rail's previous setup was a pair of air shocks running from the arms to the cage behind the driver/passenger. I didn't care for rebound/compression offered from the air shocks and will be installing a new set of coilovers + anti-sway bar.

I need help determining if I should keep the upper mounting location or not.

Below, I have an image with strings running from the mount in the arm to two locations on the buggy. The right most string runs to the original location of the upper mount. I am wondering if this is too much angle and I should mount the coilovers in a more "vertical" fashion as displayed by the 2nd (or left most) string.

The rail is street only, and long travel is not a concern. The goal is a well sorted, good handling, play toy that may see some autocross in the near future. The rail sits very low and does not need long travel.

Your feedback is greatly appreciated.

Image may have been reduced in size. Click image to view fullscreen.


A picture of the rail for the curious:
Image may have been reduced in size. Click image to view fullscreen.


Build log here:
https://www.thesamba.com/vw/forum/viewtopic.php?t=673451
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mkparker
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PostPosted: Wed Mar 14, 2018 8:58 am    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

Killer street rail! The trailing arm looks to be a Mendeola or very similar. It looks like your stock top shock mount has been deleted, but this is what you would typically need I believe.

Image may have been reduced in size. Click image to view fullscreen.


More info on Mendeola suspensions here:
https://www.coolrydescustoms.com/store/c2/MENDEOLA_SUSPENSION.html
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di11ard
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PostPosted: Wed Mar 14, 2018 9:10 am    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

Thanks mkparker.

Yes, the rear arms are custom length mendeola arms. My original top shock mount is deleted, so I am looking to either use the current upper mount or add in a new upper mount.

The problem... I am not a welder. Confused

So, I am evaluating how the angle of the coilover effects the handling characteristics of the rear arms.

I have been doing as much reading on suspensions as possible, and I understand the vertical angle of a trailing arm has effects on how the spring works.

Many of the tech articles I find, regarding trailing arms, indicate a 90 degree angle at full compression. Many of the buggies/rails are setup with the upper mount at a forward angle as this increases the over all travel of the rear suspension. For me, this is irrelevant as my rear suspension will only be moving a few inches.

So, I think I am answering my own question... I need to mount the rear shock/coilover in a more vertical fashion (possibly with a slightly forward angle to help mimic the arc of travel from the arm).

And while I am oversharing & thinking out loud... Even if I was to have the original shock mounts on the rail, they would also sit too far "forward" due to the added length of the arms.

I think it is time to find a local welder to help. Sadly, the buggy is in a state of disassemly. So I need to find someone to come to my house and help.

Sh!t. Sad

So, here is the final question...
How negatively will using the current upper mount effect handling?
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di11ard
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PostPosted: Wed Mar 14, 2018 9:39 am    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

I did a quick (very crude) mockup of what I should probably do... But I'd still love to get feedback if anyone can provide insight to how the angle will affect the rear suspension based on my current upper shock mount.

Below, white represents new steel & yellow represents the new coilover.

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.
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Dale M.
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PostPosted: Wed Mar 14, 2018 1:25 pm    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

Looks as if chassis setup was intended for extreme long nitrogen shock/coil overs... Not little bitty squat coil/shocks...

Something similar to image below...

Image may have been reduced in size. Click image to view fullscreen.


Instead of making premature frame mods, you might investigate a longer shock option...

Ride looks pretty cool...

Dale
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di11ard
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PostPosted: Wed Mar 14, 2018 1:33 pm    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

Thanks Dale.

You are correct. The chassis was created/setup for long shocks (or coilovers).

I'm just trying to determine what to do as the buggy is 100% street (and not going back).

I appreciate your thoughts!
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Mr. Unpopular
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PostPosted: Wed Mar 14, 2018 2:46 pm    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

The general "rule of thumb" is to have the shock sit 90 degrees to the arm when at full compression. Any other angle and the arm won't have the proper leverage on the shock and the spring rate will actually decrease through travel.
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Dale M.
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PostPosted: Wed Mar 14, 2018 3:09 pm    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

di11ard wrote:
Thanks Dale.

You are correct. The chassis was created/setup for long shocks (or coilovers).

I'm just trying to determine what to do as the buggy is 100% street (and not going back).

I appreciate your thoughts!


Yes on "street" and long shock really look cool on car scene....

Dale
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L5wolvesf
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PostPosted: Wed Mar 14, 2018 6:22 pm    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

One good place to start with handling is this
https://www.amazon.com/How-Make-Your-Car-Handle/dp/0912656468

plus Carroll Smith's books

AutoX is where I started which got me to road racing and off road.

Good luck
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PostPosted: Thu Mar 15, 2018 12:47 am    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

Fred Puhn wrote a fine book way back in the 70s in that "How To Make Your Car Handle. He owned a company that built road race cars called Chassis Engineering. He also invented the 2-piece aluminum wheel that Cragar bought the rights to and became the Cragar Super Trick that was THE wheel for Funny cars as well as road racers. The Sunbeam Tiger I was a crew member on in the late 60s raced on those wheels and Fred was a guy I saw many weekends a year when I was Tech Inspecting his race cars. I have that book stashed away in the book shelves somewhere.

Yes, off roaders like shocks to be at no more than 90° to the axis of the trailing arm at full bump. That is so the shock shaft is never in a bind under load. It's not so much about leverage ratios.

One factor that applies regardless of where the car is used is that the shock mounts should be parallel to the pivot axis of the trailing arm. And the shock should be mounted so the lower end moves in an arc at a radius to the pivot axis of the trailing arm. Since your car is set up with the trailing arm pivots in the same place as stock VW IRS, that means the arms should be pivoting so the hub moves inward as well as forward as the suspension is compressed. So the upper shock mounts should be inboard of the mounts on the arms throughout the travel of the suspension, no matter how short it is.

You should probably be shopping for relatively short coilover shocks much like what is shown in that photo of the Mendeola show display in MK Parker's post. That entire suspension setup in that Mendeola display is intended for street oriented buggies, not offroaders - The trailing arm, the short coilover shock, the torsion delete bracket, and the truss bar setup (that is totally unneeded on your tube frame buggy).

That 3-point structure would be good for the job. You will need to adjust it for the length of shock you decide on. Remember that you CAN have more suspension droop than past the desired ride height. For instance if you want 3" or 4" of bump travel from ride height and that still keeps the belly of the car off the pavement, then a 6" to 8" travel shock would probably be fine and would probably reach the upper mount as you drew it in that side view. You use the adjustable coil seat on the shock body to set your ride height.

A stock length shock would only reach about 2/3 of the way to that mount as you drew it. I suggest taking the same side photo with someone else holding a tape measure on a bolt in the lower shock mount to determine medium shock length, then push the arm up to where you feel full bump should be and do the same photo again to determine compressed shock length. then again at max droop for extended shock length. THEN go shopping shocks.
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PostPosted: Thu Mar 15, 2018 12:55 am    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

On another VW site, there is a forum about handling and suspension for those who like to go fast on pavement.
http://shoptalkforums.com/viewforum.php?f=51
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PostPosted: Thu Mar 15, 2018 1:19 am    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

dustymojave wrote:


Yes, off roaders like shocks to be at no more than 90° to the axis of the trailing arm at full bump. That is so the shock shaft is never in a bind under load. It's not so much about leverage ratios.



Shock shafts have heims on both ends to keep them from binding. What they don't have is the ability to defy physics.
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di11ard
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PostPosted: Thu Mar 15, 2018 7:37 am    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

Thank you, thank you, thank you!

You guys are validating my thoughts and helping provide guidance.

Dusty, you mentioned:
dustymojave wrote:
And the shock should be mounted so the lower end moves in an arc at a radius to the pivot axis of the trailing arm. Since your car is set up with the trailing arm pivots in the same place as stock VW IRS, that means the arms should be pivoting so the hub moves inward as well as forward as the suspension is compressed. So the upper shock mounts should be inboard of the mounts on the arms throughout the travel of the suspension, no matter how short it is.


Looking at a stock IRS rear end, it appears the upper shock mount is at an angle. Possibly 5ish degrees, counter clockwise, away from the car's centerline than the IRS (inboard) pivot point. Maybe it is just an optical illusion. Should the upper mount on the shock be at the same angle as the large bolt on the inner IRS mounting point?

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PostPosted: Thu Mar 15, 2018 5:24 pm    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

shock mounting bolts should be parallel to the irs arm pivot bolt.
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Thu Mar 15, 2018 8:18 pm    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

di11ard wrote:
Thank you, thank you, thank you!

You guys are validating my thoughts and helping provide guidance.

Dusty, you mentioned:
dustymojave wrote:
And the shock should be mounted so the lower end moves in an arc at a radius to the pivot axis of the trailing arm. Since your car is set up with the trailing arm pivots in the same place as stock VW IRS, that means the arms should be pivoting so the hub moves inward as well as forward as the suspension is compressed. So the upper shock mounts should be inboard of the mounts on the arms throughout the travel of the suspension, no matter how short it is.


Looking at a stock IRS rear end, it appears the upper shock mount is at an angle. Possibly 5ish degrees, counter clockwise, away from the car's centerline than the IRS (inboard) pivot point. Maybe it is just an optical illusion. Should the upper mount on the shock be at the same angle as the large bolt on the inner IRS mounting point?

Image may have been reduced in size. Click image to view fullscreen.


You're right. The stock mounts are crappy. And they were originally and all the way to the end of production designed for use with swing axle suspension. Not IRS. Swing axle pivots at 45°. Early swingaxle upper shock mounts are parallel to the centerline of the chassis. Neither is correct. Many things in early VW Bugs are VERY WELL engineered. The rear shock mounts are not included in that.

YES, the large inner pivot bolt is the angle the new upper and lower shock mounts should parallel to.
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di11ard
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PostPosted: Fri Mar 16, 2018 11:45 am    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

You guys are awesome!

Thank you very much for the very detailed feedback.

Dusty, I owe you a beer. Thanks man.
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PostPosted: Sun Mar 18, 2018 4:44 pm    Post subject: Re: Street Rail: I need help with rear coilovers! Reply with quote

I'll drink one and say "Cheers!" to you.

You're quite welcome. Good luck with your project.
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