Multiple suspension dimension questions for an e30 based Locost

[r3vmonkey]

Hello guys I'm brand new to here. Looking for some help in working out a suspension that is close to a stock 325e (1984) but it utilizes double wishbone (A-arms) instead of the McPherson strut/upright. Yes it's a long post.

I started this project years ago but it has been sitting in storage for about 3 years. I really want to finish it within a year. The build so far.

http://www.locostusa.com/forums/viewtopic.php?f=35&t=1004&hilit=raven7

Currently the front suspension of my 325e is sitting in my living room with a partial wooden mock up of the frame.

http://www.locostusa.com/forums/viewtopic.php?f=5&t=8759&p=90462&hilit=raven7#p90462

To help get things set right before I dismantle the whole thing to convert the struts I am hoping for some dimensions, and have some questions.

What is the distance from the bottom of the steering rack(center) to the ground?
Are the "tabs" that the ball joint and tie rod attach to perfectly horizontal when parked?
Are the lower control arms horizontal as well or do they angle down? How many degrees?
Approximately what angle does the strut housing angle towards the back of the car?
And since I have no strut towers etc.now to support this. I was going to make a quick wood or metal frame to "float" things at the right distance. What is the distance (center to center) of the strut tower bearings?

I had no idea how important these dimensions were when I tore apart my donor years ago, or I would have kept track then.

I will be making lower control arms from scratch and am hoping someone knows what the taper on a stock ball joint is 7°? 10°? and if there are screw in ball joints and sleeves available like this?

http://www.speedwaymotors.com/Speedw...int,38296.html

http://www.speedwaymotors.com/Steel-...isplayId=38296

I will be chopping the strut off and creating an adapter very similar to this:

http://www.sevenesque.com/assembly/35-converting-struts-to-uprights.html

My lower A arms will be made very similar to this:

http://www.sevenesque.com/assembly/36-lower-control-arms.html

My upper arms will likely be like this:

http://kineticvehicles.com/ControlArms.html

I could do at least the upper control arms with the speedway parts above, but I really love BMW and want to use as many of their parts as possible. And since I am far from a suspension expert (hell I'm not even a novice) I was going to start with stock suspension settings and adjust them to suit my driving as I get to know the car.

Thanks for making it through the post - here's hoping for some good answers.

Eric

[JoeyBones]

not to cramp your style, but why not rob the front from a Miata or Civic? You'll be much cheaper and less fabrication. I know you have the e30 parts, but seems to me there are better/cheaper parts available.

also, there are no "screw in" ball joints...they are all press in style. However if you're custom making a bunch of crap you can use whatever ball joints you want and fabricate to match them.

[r3vmonkey]

JoeyBones - A lot of guys doing these use the Miata as a donor vehicle. If it gets too crazy I may switch to that for the front, but was still hoping to stick with BMW parts.

As for the ball joints - apparently they (US ball joints - no idea about German) usually come with a 7 or 10 degree taper. They sell a reamer to fit each - I could ream the bottom of the e30 upright to fit assuming the current hole isn't too large.

Can anyone else help with some dimensions? I'm especially interested in the center to center of the strut tower bearings and the distance the bottom of the steering rack is to the ground. Designing a suspension is pretty crazy and it would be good to have a few good reference points to try and be close to.

Eric

[r3vmonkey]

Is there anyone here from Mpls. area that I could take some measurements myself? I thought it'd be easy to get a few measurements, but so far no takers.

This is what I'm hoping to figure out -
What is the distance from the bottom of the steering rack(center) to the ground?
Are the "tabs" that the ball joint and tie rod attach to perfectly horizontal when parked?
Are the lower control arms horizontal as well or do they angle down? How many degrees?
Approximately what angle does the strut housing angle towards the back of the car?
And since I have no strut towers etc.now to support this. I was going to make a quick wood or metal frame to "float" things at the right distance. What is the distance (center to center) of the strut tower bearings?

Thanks
Eric

[e3o]

My car is lowered, has Camber plates and an e36 steering rack but I'll try to help you out. As it sits
1) 3-1/2" from bottom of rack to ground
2) "tabs"? not sure
3) My control arms are close to horizontal but depends if or how much a car is lowered
4) If you mean caster 9 degrees
5) distance center to center of struts should be 39.5"

Hope that helps

Is there anyone here from Mpls. area that I could take some measurements myself? I thought it'd be easy to get a few measurements, but so far no takers.

This is what I'm hoping to figure out -
What is the distance from the bottom of the steering rack(center) to the ground?
Are the "tabs" that the ball joint and tie rod attach to perfectly horizontal when parked?
Are the lower control arms horizontal as well or do they angle down? How many degrees?
Approximately what angle does the strut housing angle towards the back of the car?
And since I have no strut towers etc.now to support this. I was going to make a quick wood or metal frame to "float" things at the right distance. What is the distance (center to center) of the strut tower bearings?

Thanks
Eric

[einstein57]

Most of the measurements your asking for vary from car to car based on trim level and modifications. You probably don't want to base your design on the cheapest design BMW could use to make their entry level 316i still affordable. I'd want to use porsche, corvette, lotus, etc dimensions as a starting point. You'd probably be better off reading a couple suspension books and starting from scratch since the e30 will have almost nothing in common with your final design.

What are you planning on retaining from the e30 front? The steering rack ratio sucks, the shocks are to long, the breaks are not that good and track pads are almost double the cost of other cars. A Z3 rack, brakes, and detatchable hub might be a better way to go if you want to stay BMW. If you just want to stay german a VW corrado would be cheap and easy. Tons of cheap brake upgrades available too if desired.

[JoeyBones]

You could also do some look online at FSAE build diaries as they will usually have some pretty detailed pictures of suspensions. I'd find a car you can rob a hub/knuckle from then use tube steel to make an a-arm set up. Again probably cheaper and much easier to use a miata set up.

There are great books on suspension geometry and design available. Spend an afternoon at Barnes and Noble, load up on caffiene and knowledge, then sketch out what you want to do.

Are you using the 325e engine? if not and plans for a more compact light weight engine are in the works, I'd actually fully suggest picking up the monoshock rear from a hyabusa or a gsx-r 750 (highest spring rate), since the chasis of your car will be so light. These are basically fully adjustable coil-overs with short stroke (plenty for the track and probably enough for the road) that can be had for under $100 each on ebay... so if one goes, it's a toss in the hat vs anything worth while you'll buy for a typical car set-up. I know thats the route we went on our FSAE cars. Not to mention if you decide to get real fancy, there are full race versions available for these bikes from the likes of FOX and Ohlins. OH and if you don't like the rates, there are plenty of companies that have different spring rates available too!

I do understand wanting to use what you have as it's already there, but I think you're complicating things way too much

[r3vmonkey]

Thank you guys - been away for a bit. The measurements help considerably as a starting point. I'll also look into the hyabusa coil overs. Adjustability is the name of the game on this build - especially since I'm so inexperienced.

I did pick up some miata parts just in case - very cheap from a local guy.

Thanks,
Eric

[JoeyBones]

Yea i think you did a good thing, even if you dont end up using them, they are good pieces to measure and possibly model your set up off of.

I think the bike coil-overs will be a great way to go for something like this.