Steering, Suspension, & Brakes

So why is it no one uses any of the Mustang II IFS's advertised all over the hotrod magazines for MGBs? Seems like if they can be narrow enough for a '32 ford, they'd be narrow enough for a B. And several companies seem to make them for varying widths. Seems like even starting with one & reworking the control arms to change the ackerman would still be way easier than starting from scratch... but since no one seems to have tackled this, I'm guessing there's a good reason -- it's just not intuitive what it is.

I think there are two Mustang II suspensions in the MGA section of our photo gallery, plus a "Fat Man" suspension (which uses Chevy components.) More Mustang II stuff shows up in the Sunbeam section, and I think there's at least one Mustang II suspended Spitfire...

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This question (or my comments) may stir up a hornets nest. I'm no expert - I've never designed a suspension - but I've been reading a lot about suspension design and tuning over the years.

It's just not intuitive to me why a Mustang II suspension would be a good idea for an MGB. To begin with, Mustang II certainly wasn't a sports car. Traditional American hot-rods (e.g. '32 Fords) have never been about "handling"... instead, they've been about looking flash, boulevard cruising, and straight-line acceleration.

Ackerman isn't a big issue to me, because Ackerman matters more at very low speed than when really carving corners.

I believe that one of the characteristics most associated with Mustang II suspensions is anti-dive, which seems to be a big selling point to some hot-rodders - but it's arguable whether anti-dive is all that important for a sports car. Even if you want anti-dive, a little may be enough.

Certainly camber change characteristics and roll center height are much much more important criteria for judging any given suspension, but I've not seen where the aftermarket Mustang II suspension companies talk about that stuff.

What else would I be concerned about? Bump steer should be very minimal, and it should be easy to integrate the (presumably new) steering rack to the MG's column. Easily adjustable (tuneable) caster, camber, and corner weight (e.g. fine-tuneable ride-height) would also be priorities to me if I were shopping for a suspension. Finally, I'd definitely want simple provisions for attaching and then tuning the anti-roll bar.

Hi Rob,

I've been reading a lot on the locost usa forum over the past year. The mustang uprights/spindles seem like they would work well with a B and are tried and true with locosts (with lots of wheel/tire/brake options, but Curtis hit it about the geometry. I've been playing with some suspension design software to work out a homebrew crossmember. Once you set your hub center - determined by your wheel/tire choice - , track and spindle pivot points it basically will allow you to plug in different pick-up points (double wishbone/coilover set up) and how these points affect various characteristic like bump steer, ackerman, etc - or let you work backwards if you know your target camber/castor - probably along the lines of 7 degrees castor and 0-3 degrees of neg. camber. The locost crowd tries to get the lower control arms horizontal (loaded suspension). Plugging in the track gives you control arm lengths/pick up points. With some general playing around I think some of the optimal upper pick up points are about 6 inches forward and behind the centerline of the hub (a bit wider than off-the-shelf stuff). With bump steer - the relationship of the rack to the lower control arms comes into play and ususally where some compromises start getting apparent. Other popular uprights are out of miatas, thunderbirds (with some mods) and mgbs.

I think mustang II control arms would work well - just not quite optimized for ultimate handling. Adding in curves to the control arms adds a significant amount of complication to the calculations. The locosterers use 7/8s tubing (tapped) with 5/8s fittings and get a lot of adjustability with their designs. It's also easy to do mock-ups with pvc pipe. Makes for interesting, thought provoking reading and interesting to compare the plugged parameter to some of the aftermarket set-ups.

t.lay Wrote:
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>I've been playing with some suspension design software
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Tom, what software? Where did you get it? Sounds interesting and fun.

Rob, while the Mustang II system is reasonably tuneable, with a great many aftermarket manufacturers/suppliers providing parts, you may want to look at the overall weight of the suspension and crossmember. This set-up works well (enough) for cars that weigh as much as twice the GVW of an MGB. As a result, the constituent pieces are sized accordingly.
If you are unhappy with the handling of your B (is that what this thread is about?), you may want to look at what some of the racers are doing to improve things. IMHO there is much to be gained from less compliant bushings but the cost is comfort. Also, remember that if even if you were to fit the best possible front suspension for your particular compromise, there is still a big tube hanging out behind you.
B

I'm trying figure out what would be improved by using a Mustang front suspension. A stock MGB front suspension with a few standard tweaks is pretty good.

I've run my slightly moddified MGB suspension on 3-4 road courses & a few autocrosses. It's not quite a Miata, but I feel like it handles the corners pretty darn well.

[www.locostusa.com]

Freeware of a guy named McDermot - there's some examples on the locost forum under the suspension topic - also some good info on one of the build page - look for "rod's 5.0 build" - he shows the parts/sources/how tos using mustang spindles

MGBV8 Wrote:
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> I'm trying figure out what would be improved by
> using a Mustang front suspension. A stock MGB
> front suspension with a few standard tweaks is
> pretty good.
>
> I've run my slightly moddified MGB suspension on
> 3-4 road courses & a few autocrosses. It's not
> quite a Miata, but I feel like it handles the
> corners pretty darn well.

Well, given your results @ the V8 meets, that logic is hard to argue with... but folks are often talking about updating the suspenstion. Ted's front suspension which looks an aweful lot like a mustang II IFS... I know looks have little to do with function & he put a lot of engineering into his IFS but it got me thinking... what's different. The only variables I can think of are the control arms -- where they mount in relation to the spindle & how long they are which ultimately affect akermen & camber change. I haven't used any of the suspension software packages to see how different from the readily available mustang II units those would need to be, but seems like for someone wanting an updated IFS (say so they don't need to modify the cross member for a 302 as an example), starting with a mustang II unit & modifying it for the MGB wouldn't be that difficult.

Barry Preston uses Mustang II components in both the front and rear of his "Brooklands" MGB conversions.
He retains the Mustang II track and therefore fits his own flares for which he created molds.
Brooklands website:
[www.noisette-software.com]

Rob, I think it's primararly a cost issue. The stock MGB suspension is pretty good and lots of parts develolped for it so unless you really need the additional adjustability for caster and camber why bother. I've looked at the Mustang II crossmembers and I really have my doubts that the bump steer has been considered in the design as the width changes between applications and the steering rack stays the same. At least that's one thing on a B that you don't have to worry about.

Makes sense Bill... My thought process started with the Ford 302. One of the things that folks still struggle with on that install is modifying the cross member. I personally believe if done well, there's no structural concern, but the "formless dread" factor defnitely causes some folks concern. When looking at the options, a front cross member like the FastCars one &/or the Hoyle are common considerations... but they're 2-3x the cost of a Mustang II unit. That just got me to thinking. Then someone mentioned they were thinking about building their own IFS which got me thinking more... The more I've thought about it, the more I've realized that if you're going to go through the trouble to adjust where the control arms connect to the cross member; probably their length, and possibly/probably the steering rack &/or how it's lined up, the cross member itself is probably the least of the concerns.

There is one consideration that has never been properly tested and that is the torsional stiffness of the crossmember. The real question is, "Just how much stiffness is needed?" and I think this depends partially on how much horsepower will be available, whether GT or roadster, type of rear suspension and axle used, and whether or not the car will be raced. The stock unit seems to be gross overkill but it may still be too early to tell. The large tubular section at the front of the car is very effective in resisting twisting of the front frame rails as well as the body tub, but we've no reports so far that this is even a problem. Some people have added reinforcements in key rear locations, usually acknowledged as good insurance, but have we ever heard a report of damage where they were absent? I have not. BMH adds extra body welding on demand for competition bodyshells which reputedly stiffens the car though, and this extra stiffness for improved handling may be justification enough for that, but it still doesn't answer the question.

I have to be honest, I've driven Steve Carrick's car on the track (with the Fast Cars suspension) and it felt very good. But I wasn't trying to outpace an identical car with the stock crossmember so it really doesn't tell me much except that the car felt like it handled well and I didn't notice anything irregular about it. Is it faster? Who knows? There were too many variables to answer that, aside from the fact that I was not pushing the car to it's limits. (Well, maybe on cornering I was a little.)

What I do know, is that if you remove the stiffening effect of the front fenders and do not provide sufficient reinforcement you begin to see stress cracks in the inner fenders, which suggests to me that MG didn't overbuild the bodyshell to the point that you can frivolously remove bracing without looking at the results of it. And I'm not saying we're doing that, but I do think that it's worth keeping the factors I mentioned above in mind, and I do think that if an alternate or modified crossmember is fitted it is simple prudence to periodically inspect the seams of the inner fenders and frame rails for any signs of cracks or flex, especially if a very high output engine is fitted, and even more so if the car is used on the track. Over time I suspect we'll see no signs of damage except possibly in very extreme cases (such as the Roadmaster perhaps) but I always thought the Mustang II front end looked a little spindly compared to stock. Sometimes cheaper is not better.

Jim

You got it on the crossmember Rob. In some respects, the first role of the crossmember is to match the coordinates of your ideal pick up points. On tube frames, this is usually where compromises start taking place because there isn't always a tube where you need it. On a fresh sheet - you can pretty much put things where you want. As for torsional strength - The stock piece is stout. In thinking about a tubed crossmember, I may add an extra 2 x 2 out by the nose for a little extra insurance.

Quote:

What I do know, is that if you remove the stiffening effect of the front fenders and do not provide sufficient reinforcement you begin to see stress cracks in the inner fenders, which suggests to me that MG didn't overbuild the bodyshell to the point that you can frivolously remove bracing without looking at the results of it.

Along those lines, has anyone given some thought to the idea of fabbing a fender to fender brace? I see these modern cars with aftermarket strut tower braces and wonder if something similar might do some good for us in hard cornering situations.

I've got my doubts Carl. Maybe with a Fast Cars IFS it might add something but the stock crossmember is so stiff in vertical flex that I can't see any gain from it. Maybe to control diagonal flex of the front of the unibody, but the pyramid box sections up high on the inner wing seem to do a pretty good job of that. It's a good thought but without the need to control the tops of a set of strut towers.....

Now that does leave the vertical bracing of the forward monocoque itself and I've sometimes wondered if the frame rails might flex the inner wing panel and move up and down in the process. If you look at it there really isn't any direct diagonal bracing to prevent it. But there also really isn't much space to allow a proper diagonal brace to be added either. I suppose you might add a box section running through the dip or bulge above the shock absorber and tie it into the pyramid boxes somehow though. Might be pretty hard to implement as an add on.

Jim

just for illustration - this is the front suspension of a dune-jumper - the tubular shock mount has another tube at the top (with the square flange). A cross-brace fits there for added rigidity. The roll cage is tied in to the frame at many points - it's a surprisingly rigid set-up for a ladder frame. This thing sees ridiculous abuse - thought the frame profile looks similar to the Bs front rail profile - something like a cross tube could be fit on an MG - for that matter, you could tube the entire front (isn't gavin's aussie racer tubed up front?).

OLD BRONCO'S RULE!

Old*
*66-77 year models.

SAFETY FASTER!

Early Broncos, my other obsession. If you can make a 1000 hp bronco rigid, a B should be a cakewalk

Hold my beer & watch this! :)

nice bronco!! i was wondering to the post about flexing, if there is flexing wouldn't there be signs of fatigue and cracking?