I'll take some pictures of my suspension when I have time. I was able to
mount an adjustable upper a-arm to the inner frame rail.
When I designed it, I went for a very long IRC/SAL (instantaneous roll
center) (Swing arm length) This gave me very little camber loss through the
travel range. My only angle loss would be from the roll of the car. If I
get to the point where I have to worry about that, i'll add a stiffer sway
bar. It's been a while since I did all the calculations, but my roll center
should be around 4" off the ground, that's just a WAG. I don't know if it
would be worth it to go lower seeing as the rear end roll center is even
with the axle line.
I did not design in any anti dive, but am adding anti squat for the rear
end. I believe adding more antidive would result in a caster change, and I
didn't want to start messing with caster.
And for bump steer, I haven't had time to work it out yet, but should be a
small problem to correct if there is any. I believe they say that the
steering arm should be close to parallel to the top arm.
Mike
> James,
> Thanks for the reply. The upper arms wouldn't have to be
> considerably "longer", per say (or at least there length projected
> against the horizon wouldn't have to be longer (go tell your old math
> teacher, we're using Cosines in real life!!!)), but their mounting point
> on the x-member would have to be lowered. I understand that most
> kit-manufacturers would like to use stock mounting points and therefore
> make a bracket that mounts to where the old Armstrong shock would
> attach, but many of those kits also require you to cut the ends off the
> x-mount so that the coil-over could fit. That being said, it shouldn't
> be too much harder to mount the upper A-arm pivot-points lower on the
> x-member. Ideally, I'd like to buy a post 74 x-member and some mustang
> II parts and just muck around until I get a decent geometry. There are
> some relatively cheap design packages for PC out there, too. One can
> use them to find roll-center, etc. With a little inspiration, we could
> also build in some anti-dive on the front end.
> I've done some welding (even took a course once), but I wonder if I
> would have to do any fancy heat-treating (stress relieving if I made any
> of the new linkages? Thoughts from anyone??? I promise I won't hold
> anyone liable for their welding advice if one of my a-arms flys off at
> 65 mph ;-)
> James J.
>
> >
> >
> >
> >
> >
> >>First, to my DC area friends, my e-mail is now m1garand@speakeasy.net
> >>now that DirecTV has shut down their DSL service.
> >>
> >>Now to the group: (and answer me directly if you think it is off-topic
> >>enough that the group wouldn't be interested) I've been reading up on
> >>suspension design, primarily to see about options for the back-end, but
> >>I also started looking at front-end design. What I noticed, is that
> >>every author that I read said that un-even length, non-parallel a-arms
> >>are the way to go in nearly evey case (so far, so good, for the MGB),
> >>however they all suggest that the upper a-arm should be higher at the
> >>wheel than at the cross-member. The reason being that when a car rolls
> >>to the right (for example) the wheel on the right side also leans to the
> >>right, reducing the size of the tire contact patch. With the MGB, as
> >>that side of the suspension compresses, the upper a-arm travels up
> >>through it's arc, becoming longer relative to the hub, pushing the top
> >>of the wheel even further out and reducing the tire contact patch even
> >>more. If the upper a-arm (in its static position) was angled upward
> >>from the x-member to the king-pin, then any roll to that side would
> >>compress the suspension and make the upper arm SHORTER relative to the
> >>lower arm, and bring the top of the tire back in to reduce the camber
> >>effect of the roll, and increase the size of the tire contact patch,
> >>improving handling.
> >>
> >>First, I wonder what the MG guys were trying to achieve with that
> >>design, and second, I've seen at least four new coil-over designs for
> >>the MGB, where the old a-arms are dismissed with, yet none of them
> >>change the geometry to "fix" the upper a-arm issue. The car can be
> >>designed with some built-in static camber to compensate for this, but
> >>that method increases uneven tire wear on the inside edge. Has anyone
> >>here used a front-end design that corrects the camber issue? Most of
> >>the kit/muscle/street-rod crowd have adopted the Mustang II front-end,
> >>and the parts for this are plentiful and relatively cheap (Including 2"
> >>dropped spindles). (remember that this car was the same platform as the
> >>Pinto/Bobcat.......Kaboom!!!!!)
> >>
> >>So if anyone has any experience, I'd love to hear from them. Also, if
> >>anyone is interested in working with me in trying to adapt the mustang
> >>II front end to the MGB, let me know. When things get a little quieter
> >>around my house this spring, I want to start taking dimensions off the
> >>MGB for the front-end and back end and putting them into CAD, and
> >>playing around with them. TurboCAD is cheap and powerfull. If anyone
> >>has done something similar, and would like to share their files, please
> >>let me know, too.
> >>
> >>Thanks, and my apollogies to those who don't want to read about
> >>suspension design.
> >>James J.
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