Noah Teates - question about your N2's front control arms

[dhs]

Noah,

Do you have any more detail on the contruction of the custom front control arms you show in your N2 project blog thread:

http://www.bmw2002faq.com/component/option,com_forum/Itemid,50/page,viewtopic/t,326460/

I am assembling parts to do a similar modification to move the control into the middle of the subframe to allow uncompromised positioning of a steering rack. As shown in your images, I am hoping to retain the outer part of the arm and join it to a round tube to the heim joint for the inner connection.

This is what i have going so far. Using 1-1/4" chromemoly tubing (.095 thick) with a weld in bung that is rethreaded to accept an heavy duty metric heim joint (M16 with M18x1.5 male threaded end). the joint between the tube and the arm I have yet to decide how to do and would love to get input on.

thanks

[TobyB]

I've been looking at what's 'standard practice' in GT2 cars (heavier

and more powerful than 2002's) and they seem to use the

'oversize' 1/2" rod ends exclusively- like these- http://www.speedwaymotors.com/X-Series-Rod-Ends-Male-LH,7730.html

You have to be a little careful with a rod end replacing a rubber sleeve-

the rod end has no resistance to rolling, and can be damaged by it.

Noah's use seems correct in this pic- the radius arm stabilizes the end.

AND he gets it into double shear, which is a big improvement.

If one were to replace the end of the radius arm with a rod end, then

one would run into trouble, as nothing would prevent the arm from rolling.

The Production car crowd does this sort of thing a lot- we're allowed to modify

our designs, but not necessarily replace it completely.

t

[dhs]

Yeah, i may go one and build a fully solid jointed set of 'race' arms as well. As I bet you are aware the basic design you describe has been used on many a bmw race car in the past, most easily seen on documentation of e30 M3 DTM race cars. The arms on the N2 are unique in that they blend rubber and solid together into one arm (and move the arm up which is really the whole reason for this exercise). I am quite confident in the choice of rod end and diameter/strength of tubing but would be looking for input on the joint of the old arm to the tube. Have any thoughts Toby? I was thinking of decontructing the remnant of the stock arm I was going to attach and then sort of rebuilding it around the tube (basically cut out the middle where the tube would go, put the tube in and then weld along there, maybe box it in a little there

here is a good page of one man's (a very meticulous man) making of fully jointed arms for his m3 for those who are interested

http://www.e30m3project.com/e30m3performance/installs/installs-3/control_arms/index.htm

[ArdenK]

The control arm is cool, looks lighter than the stock arm too

[peteinjp]

DHS- how does this design move the arm up? Are you talking about the inside pivot?

Best,

Pete

[TobyB]

looks lighter than the stock arm too

it's not. Stock arm, inclusive, is only #5. The ends weigh over #1...

t

[Guest Anonymous]

Sorry, it moves forward. If you moved the pickup point on the subframe, you could move it up, just little. Might also be able to lengthen in too, just a little, but would have to check that you did not then limit travel an unacceptable amount. I have not really looked at moving the pickup point and at this point and probably will not. For a racer that can do it in their class, might be worth investigating.

I agree it is a probably similar or a little heavier than stock. The end with the rod end will be heavier _but this end does not matter much, and you are adding weight to attach it to the remnant of the arm, so that would be heavier too. If you were to go to a fully jointed version, completely fabricated, some weight savings could be realized. Or to take it further go to the final design of the aluminum arm from the e30 race cars, and have more weight loss.

[peteinjp]

Given that the heim joint doesn't limit movement for and aft (as compared to the rubber bushing in the stock control arm) do you think it would be a good idea to use a stiffer bushing at the front of the radius rod/subframe?

[dhs]

here are some pics of custom arms for e30

from this thread:

http://www.s14.net/forums/showthread.php?t=16656

a recent interpretation in aluminum here:

http://www.s14.net/forums/showthread.php?t=36627&highlight=dtm+arm

some good pics of dtm front suspension here (early dtm e30 m3 suspensions were out of steel, later the arms moved to aluminum)

http://www.s14.net/forums/showthread.php?t=37172&highlight=dtm+arm

and here is another dtm car with the aluminum arms:

http://www.s14.net/jakesdtmtours/suspension.html

[dhs]

that is an interesting question, one that I don't have a sure answer for. Real world testing will have to say if there will be binding or unacceptable movement. My gut says fore/aft movement is what the strut rod is good at controlling, 'roll' or pitch of the arm is what it is not so good at. My personal recipe for a stock strut rod bushing upgrade would be to only upgrade one of them to poly and leave the other rubber (possibly the turbo busing in the subframe) to help avoid binding. If you go to a fully jointed front arm it is a non-issue.

[peteinjp]

How about eliminating the attachment at the front of the sub and running it to the rear as the e30? any advantage there? But I guess that would get in the way of the steering rack...

[dhs]

Pete,

no real benefit, it is just turned around version of the same basic suspension design. If you wanted to use an e30 or other front steer steering rack, it would be a good way to go. The e30 Struts are stronger by my ey3, and the m3 version of the strut is 5 lug with larger bearings.

[peteinjp]

The radius rod attachment at the front is a high stress point right? It does a lot of work under braking as well. With heim joints at the control arm instead of the bushings it is going to take even more of the loads. The only advantage I could see with mounting them as the e30 is that the area near the frame rails is probably much stiffer location in comparison to the stock 02 locations at the ends of the wings. With all the for and aft loads with modern tires, bigger brakes, and the before mentioned issue of using heim joints maybe it starts making sense to contain those loads at the stronger part of the shell.

[dhs]

the strut rod does a lot of work in tension and compression (inline with the angle of the strut rod) but does not do much in bending

Yes, I believe you are onto something with the location of the e30 rear pickup being a stronger, more rigid location, than the front strut rod pickup on the 2002 subframe.