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Suspension travel, shock towers and maths.

Posted by Paul Buck 
Paul Buck
Paul Buck
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Volvo 242 in progress


Suspension travel, shock towers and maths.
September 27, 2015 03:42PM
So we're just about at the point where we're going to install the towers and we need some guidance. As you can see in the picture we're drilling out the rear firewall for easier access.

Our maths went something like this...

We're planning on putting the attachment points right where the bumpstop is on the 1030 axle, so i got under the car and measured the distance between the bump plate and the huge rubber bumpstop attached to the frame. 4.5" is what i got. Then we measured the slick ass JVABs and got approx 28 3/8" overall and about 19 7/8" compressed. So I figure the huge rubber bumpstop must be meant to compress some, so instead of subtracting 4.5" from the compressed length i take off 6.5" and end up with a tower height of roughly 12.5".

Can someone tell me if we're headed in the right direction or if we're total idiots, which would not be surprising.

Thank you.
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john vanlandingham
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Re: Suspension travel, shock towers and maths.
September 27, 2015 05:26PM




John Vanlandingham
Sleezattle, WA, USA

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www.rallyrace.net/jvab
CALL +1 206 431-9696
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is 3 hours behind Eastern Standard Time.
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Eric Ewert
Eric Ewert
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Location: Calgary, Ab
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Re: Suspension travel, shock towers and maths.
September 29, 2015 01:44AM
12.5 inch tower height... this is a vague number without any frame of reference. I assume your using the floor of the car as a reference/ datum point. Cause that sounds about right. I can check my car tomorrow, keep in mind its just a guideline. You can probably set it up a bit better than what I did.
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Paul Buck
Paul Buck
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Location: Portland, OR
Join Date: 03/23/2015
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Volvo 242 in progress


Re: Suspension travel, shock towers and maths.
September 29, 2015 09:14AM
There is roughly 6.5" of upward travel between the axle and the floor of the car. Beyond that, wheels end up rubbing wheel wells and the axle will smash into the floor. If the shocks have a fully compressed length of 19" because we measured wrong the first time then the tower height, from floor to mounting point is 12.5". I don't see how that number is vague. It may be wrong, but there was thought put into it. My explanations are vague which is what all math teachers used to yell at me about.



Edited 1 time(s). Last edit at 09/29/2015 09:16AM by Paul Buck.
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Robert Culbertson
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Re: Suspension travel, shock towers and maths.
September 29, 2015 10:39AM
Quote
Paul Buck
There is roughly 6.5" of upward travel between the axle and the floor of the car. Beyond that, wheels end up rubbing wheel wells and the axle will smash into the floor. If the shocks have a fully compressed length of 19" because we measured wrong the first time then the tower height, from floor to mounting point is 12.5". I don't see how that number is vague. It may be wrong, but there was thought put into it. My explanations are vague which is what all math teachers used to yell at me about.

This is what I would do... but I'm weird and usually wrong about most things in life, except coffee, I know good coffee. I wouldn't add mounts to the top of the axle, I'd use the stock lower trailing arm with a small bracket to hold the lower shock eye where to stock-spring used to sit. Doing it this way allows you to swap in ANY Volvo 240 axle if you have an issue at an event. There's no custom brackets that have to be fab'd onto the housing, so replacements at an event could be as easy as "borrowing" an axle from a 240 in a parking lot. But onto more pressing issues.

The axle can only move up so far before it starts hitting the floor, or the drive line hits the top of the tunnel, or the suspension links run out of articulation. It could go higher, but then you would have to section out the rear of the car, and that's a lot of work so your bumpers can drag on the ground. I would first remove the original shocks and springs to make it easier to move the axle through it's FULL range of motion.

Well take the collapsed length of the shock and add an inch or so for the compressed height of the bump stops. This may not be enough, but most bumpstops that I have worked with end up with a "block height" of about 1/3 to 1/2 their original height.

Now you get to make a little fixture (faux shock) that's going to represent the shock at full compression. Take a chunk-o-metal and drill some holes in it at the collapsed length+1in.

Now jack the axle up until it's against the floor (remove the stock bumpstops, but don't destroy them. They may be a nice tuning tool later on down the road), install the faux shock into whatever mounts you have on the axle end. The top of the faux shock is where the top mount of the tower needs to be. Let it be so.
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john vanlandingham
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Re: Suspension travel, shock towers and maths.
September 29, 2015 10:55AM
Quote
Paul Buck
There is roughly 6.5" of upward travel between the axle and the floor of the car. Beyond that, wheels end up rubbing wheel wells and the axle will smash into the floor. If the shocks have a fully compressed length of 19" because we measured wrong the first time then the tower height, from floor to mounting point is 12.5". I don't see how that number is vague. It may be wrong, but there was thought put into it. My explanations are vague which is what all math teachers used to yell at me about.

Collapsed length is 17.6"

I envision that at static height, car level that there should be roughly 6" up and 3.7 down and the links more or less horisontal...

So extended is 26.8---make a jig outta a stick or board with 2 holes roughly 23.1" c-c.. slide towers up and down till its groovy when the shock mount is say 2 O'clock looking from driver's side.

OK?



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
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Eric Ewert
Eric Ewert
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Re: Suspension travel, shock towers and maths.
October 01, 2015 11:27AM
mine are 10.5 inches from the floor and im guessing an extra inch or two would has been better. So yes you are on the right track.

John's description of the install is exactly how I did it, can't remember the exact length of "jig" I used but it was very close to the 23.1" number above.
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Robert Culbertson
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Re: Suspension travel, shock towers and maths.
October 01, 2015 12:10PM
Quote
Eric Ewert
mine are 10.5 inches from the floor and im guessing an extra inch or two would has been better. So yes you are on the right track.

John's description of the install is exactly how I did it, can't remember the exact length of "jig" I used but it was very close to the 23.1" number above.

Does your shock bottom out first or does the axle hit the chassis? Setting up for a certain amount of sag/bump/droop travel is a good idea, but if you don't account for full bump you can have issues.

I've made this mistake on a race bike. Setup the rear shocks so they were at 35-40% sag at ride height. Turns out that the tire hit the frame before it got into the bump stops, not exactly fun when that happens.
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john vanlandingham
John Vanlandingham
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Saab 96 V4



Re: Suspension travel, shock towers and maths.
October 01, 2015 01:25PM
Quote
Robert Culbertson
Quote
Eric Ewert
mine are 10.5 inches from the floor and im guessing an extra inch or two would has been better. So yes you are on the right track.

John's description of the install is exactly how I did it, can't remember the exact length of "jig" I used but it was very close to the 23.1" number above.

Does your shock bottom out first or does the axle hit the chassis? Setting up for a certain amount of sag/bump/droop travel is a good idea, but if you don't account for full bump you can have issues.

I've made this mistake on a race bike. Setup the rear shocks so they were at 35-40% sag at ride height. Turns out that the tire hit the frame before it got into the bump stops, not exactly fun when that happens.

Naturally I warn people to jack things up and check... It goes without saying---that's why nobody said anything..
Nothing is carved in stone...tack, check, check again, tack check..weld.



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
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Eric Ewert
Eric Ewert
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Location: Calgary, Ab
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volvo 240


Re: Suspension travel, shock towers and maths.
October 01, 2015 01:29PM
It hits the bump stop on the chassis but i recall it also hitting the bumpstops on the coilovers at more or less the same time so worked out pretty good. Had I made the mounts for the top of the shocks higher (aka bringing the axle closer to the chassis) it would limit travel... I think I got that described right.

I just found the measurement for the length of rod I used to fit these... 22.9''cc. In other words near as makes no difference the same as johns number.
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Robert Culbertson
Robert Culbertson
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Re: Suspension travel, shock towers and maths.
October 01, 2015 01:45PM
Quote
john vanlandingham

Nothing is carved in stone...tack, check, check again, tack check..weld. Realize you had the wrong wheels on the car so the shocks now rub the tire. Move lower shock mounts. Realize now that the springs with the towers... move spacers... realize that the axle shifted an inch to the side and now the driveline hits the tunnel....

Fixed it for ya smiling smiley
It seems that you always forget SOMETHING when doing this crap!

edit: I realized that I just chronicled Kyle's build without even knowing it. That's an odd coincidence !



Edited 1 time(s). Last edit at 10/01/2015 01:46PM by Robert Culbertson.
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john vanlandingham
John Vanlandingham
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Location: Ford Asylum, Sleezattle, WA
Join Date: 12/20/2005
Age: Ancient
Posts: 13,994

Rally Car:
Saab 96 V4



Re: Suspension travel, shock towers and maths.
October 01, 2015 02:07PM
Quote
Robert Culbertson
Quote
john vanlandingham

Nothing is carved in stone...tack, check, check again, tack check..weld. Realize you had the wrong wheels on the car so the shocks now rub the tire. Move lower shock mounts. Realize now that the springs with the towers... move spacers... realize that the axle shifted an inch to the side and now the driveline hits the tunnel....

Fixed it for ya smiling smiley
It seems that you always forget SOMETHING when doing this crap!

edit: I realized that I just chronicled Kyle's build without even knowing it. That's an odd coincidence !

Who is Kyle?



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
Please Login or Register to post a reply
Robert Culbertson
Robert Culbertson
Professional Moderator
Location: Portland , Or
Join Date: 08/15/2010
Age: Party Animal
Posts: 1,208

Rally Car:
MK2 VW GTI



Re: Suspension travel, shock towers and maths.
October 01, 2015 03:08PM
Quote
john vanlandingham

Who is Kyle?

The guy that bought the V8 Volvo project that Charles (safe drives) had, and then Matt Weaver had. It definitely needs some love and a few things worked over.

http://www.rallyanarchy.com/phorum/read.php?5,101052
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john vanlandingham
John Vanlandingham
Godlike Moderator
Location: Ford Asylum, Sleezattle, WA
Join Date: 12/20/2005
Age: Ancient
Posts: 13,994

Rally Car:
Saab 96 V4



Re: Suspension travel, shock towers and maths.
October 01, 2015 04:20PM
Quote
Robert Culbertson
Quote
john vanlandingham

Who is Kyle?

The guy that bought the V8 Volvo project that Charles (safe drives) had, and then Matt Weaver had. It definitely needs some love and a few things worked over.

http://www.rallyanarchy.com/phorum/read.php?5,101052

OOOOooooooooooohhhhHHHH...

Poor thing.confused smiley



John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.
Please Login or Register to post a reply
Paul Buck
Paul Buck
Ultra Moderator
Location: Portland, OR
Join Date: 03/23/2015
Age: Settling Down
Posts: 155

Rally Car:
Volvo 242 in progress


Re: Suspension travel, shock towers and maths.
October 01, 2015 05:40PM
ok. so work has been utterly crazy... but now, with all of you fellows fine words of wisdom, i feel i have enough info and reassurance to go ahead and get this thing done. found some 5" steel tube with 3mm walls and it's $50 for 4ft. Not bad. Going to get on it this weekend while trying to go pick up a 16v motor for Roderick. I told him he'd have to fight me for it when he comes to pick it up. community!
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