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 Post subject: INBOARD FRONT SUSPENSION
PostPosted: Tue Sep 21, 2010 9:24 pm 
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Location: NORTH VANCOUVER, B.C.
HAS ANYONE TRIED AN INBOARD SUSPENSION SETUP. I HAVE LOTS OF ROOM AHEAD OF THE ENGINE FOR A PAIR OF SHOCKS AND I SAW A PHOTO SOME WHERE HERE OF SOMONE WHO WAS GOING TO USE THE SYSTEM BUT LATER PHOTOS SHOWED IT GONE. I HAVE BEEN STUDYING ALOT OF F1 CARS AND OFF-ROAD BUGGIES USING THE SYSTEMS BOTH FRONT AND REAR AND I GUESS IT WORKS. THE THING I LIKE IS THAT IT KEEPS THE COIL-OVERS INSIDE AND EASIER TO KEEP THE CAR CLEAN (CLEANING COILS IS A PAIN)
I STARTED MINE TODAY BY BUILDING THE ROCKERS. THEY SHOULD BE DONE TOMORROW. WE WILL SEE FROM THERE........................


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PostPosted: Wed Sep 22, 2010 12:12 am 
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Location: Just South of Charlotte, NC on Lake Wylie
I am doing it on my car, there is some info in my build log :cheers:

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PostPosted: Wed Sep 22, 2010 11:28 am 
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Caps lock key...


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PostPosted: Wed Sep 22, 2010 12:06 pm 
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I can't understand you when you're screaming! :lol:


Attachments:
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PostPosted: Wed Sep 22, 2010 3:06 pm 
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Location: Denver, CO
CAPS LOCK IS CRUISE CONTROL FOR COOL

EVEN WITH CRUISE CONTROL YOU STILL NEED TO STEER

No, seriously though, quite a few cars are using pushrod suspensions. Just look around the build logs.

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Build Log (not much there yet): http://lotus.reddeth.com
442e frame, 3.4l Camaro donor


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PostPosted: Wed Sep 22, 2010 4:02 pm 
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Location: Under the weather. (Seattle)
Remember that while any suspension requires a certain amount of math and attention to detail in order to determine correct geomety, it is a somewhat more complex solution to design. As long as you understand the details of how everything interacts, including an inboard suspension in your build is certainly achievable.

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PostPosted: Thu Sep 30, 2010 12:25 am 
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Can I use motorcycle coilover mono shocks? I have two off a couple GSXR's and have mocked them up and I like the way they look but not sure how they will work. The springs may be a bit stiff. Trying to figure out if the springs are interchangable or not.

Still trying to figure out how to add pictures, mine are too big

by the way look, no caps................................


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PostPosted: Thu Sep 30, 2010 1:25 am 
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Starman, you can change the springs but if you change the rate more than 20% either way you should have the shock revalved to suit, lest you wind up over- or under-damped.

Inboard shocks are complex, too much to go into on a message board. See if you can get a copy of Staniforth's Competition Car Suspension, where he goes into much detail about how to arrange linkages, calculate leverages and wheel rates, etc. The book's a good investment whether you go inboard or not, IMO.

Thanks for taking the time to shift! You're doing yourself a favor, really, because it's too hard to read more than a few words in all caps; most readers will skip an all caps message.

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PostPosted: Thu Sep 30, 2010 3:25 am 
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How is this?

Image

Image

Image


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PostPosted: Thu Sep 30, 2010 11:14 am 
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Ordered the book, I get it in10 days. I guess I'll hold off for a couple weeks until I read it. Lots of other things to do............................


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PostPosted: Thu Sep 30, 2010 10:49 pm 
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I don't see the inboard system as being that complex. My rocker if you will, is four inches on either side of the pivot point so its as if the shock were outboard without a rocker system at all, as I see it. The angle on the pushrod side in relation to the rocker is the same as the shock is on the other side of the rocker. Therefore, if you have a 500 lb. spring on a shock on the outboard side or the inboard side the load would be the same, in or out. I can see, if you have a different length arm on on side of the pivot or the other, the load on the spring would differ depending on which has the longer arm. Also the longer arm would have a greater travel, ie: one inch travel on a two inch arm would corrispond to a two inch travel on a four inch arm. On that same setup, the four inch arm would have twice the load on the two inch arm. Its a lot of blah, blah, blah when both arm lengths are equal. Maybe I'm not seeing something and I AM NOT a automotive engineer but.......................


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PostPosted: Fri Oct 01, 2010 5:22 am 
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modernbeat wrote:
How is this?

Image

Image

Image


isn't the gusset on the rocker on the wrong side?


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PostPosted: Fri Oct 01, 2010 8:16 am 
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Lumbering Giant
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Starman, you can see from the pictures the leverages that are at work. They are:

1. Percentage of distance between chassis pivot and pushrod mount to distance between chassis pivot and lower ball joint.
2. Angle of pushrod to wishbone.
3. Angle of pushrod to rocker.
4. Relative lengths of rocker legs.
5. Angle of rocker to shock.

Something to watch out for with your angles is that at 90 degrees you have 1:1 leverage, so if you are approaching 90 degrees you have a rising rate, and if the angle is falling away it is decreasing rate.

Guesstimating some values to illustrate using modernbeat's setup, we have:

1. About 0.85
2. Call it 60 degrees, so sin 60 = 0.866
3. 90 degrees; sin 90 = 1.0
4. Looks like about 3:2 or 1.5. With motorcycle shocks the outboard leg will typically be the longer one.
5. Call it 90 degrees for a factor of 1.0

Multiplying these together we have 0.85*0.866*1.0*1.5*1.0=1.104 which would be the motion ratio. In other words, raising the wheel 1" would compress the shock by 1.104".

To relate wheel rate to spring rate, we would divide the desired wheel rate by the square of the motion ratio to get our target spring rate. Let's say we want a wheel rate of 100#/inch; that would give us 100/(1.104^2)=100/1.219=82. So, an 82# spring would provide a 100# wheel rate.

Again, a motorcycle shock setup will have a lot more leverage, where a 1" bump will compress the shock 0.5" or less, to convert a spring rate of 550# to a wheel rate of 100# or so. Also, with a motorcycle shock I think I would want a sturdier, well-braced double shear mounting for the bottom of the shock due to the greater force being applied to it.

This estimate was very rough and intended only to illustrate the principles. In reality, you'd want precise measurements and to model the action in CAD or with a scale mockup, checking your motion ratio in steps from resting position to full bump, in order to make sure that the wheel rate is constant or perhaps slightly progressive.

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PostPosted: Fri Oct 01, 2010 9:01 am 
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flat4 wrote:
isn't the gusset on the rocker on the wrong side?


No.


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PostPosted: Fri Oct 01, 2010 9:32 am 
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modernbeat wrote:
flat4 wrote:
isn't the gusset on the rocker on the wrong side?


No.


I see. So its actually designed to take compression. Nice build!


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