home made lower front brace

[johnl]

After the subtle success of my home made upper tower brace, I thought it was worth trying a lower subframe brace, especially since I've read a number of anecdotal reports of lower braces having a greater effect than the upper brace with the 147 (and 156, GT). So I made one today. The reports are true (subjectively...).

Seat of the pants evaluation from as yet only one test drive; the lower brace does have a more substantial affect than the upper brace (I think much more). The front end feels significantly more 'of a piece', the steering is better, the handling improved, the car is more directionally stable and less 'wandery'. Even the shock absorbers seem to be doing a better job (though I still think they are not quite stiff enough). The ride and steering feedback is less 'juddery' on rougher surfaces, the front wheels feel in more consistent contact with the road, the cars' steering and handling is generally more confidence inspiring. Everything feels 'tightened up'.

I think the steering feels more 'linear', i.e. initial turn in is about the same, but not then followed by an overly abrupt increase in steering effect that (previously) sometimes meant you had to back the steering off approaching mid corner. Just about every aspect of the front end feels significantly better controlled.

I have read reports of lower braces causing an increase in general harshness, but not to any significant degree with this brace on my car (maybe other people have had their brace contact the exhaust and / or sump...?). I have also read people saying they have found this kind of brace works very well, but they have ended up removing it because of ground clearance issues. My brace does inevitably decrease ground clearance, but only by 17mm, much less than I've seen in photos of commercially available lower braces. The upper face of the brace clears the lowest part of the sump by about 7mm, with no sign as yet of the sump contacting the brace.

This is because I have used a solid rectangular bar passing under the sump, rather than a deeper section tube (as I've seen in pics of commercially available braces). The bar is 40mm X 10mm (quite stiff in compression), but only in the part of the brace that passes under the sump. Under the gearbox (where there is more vertical clearance) the upper face of the rectangular bar is welded to the bottom face of a fairly thick walled 20mm X 20mm square tube (the square tube being mounted somewhat higher than the rectangular bar). On the engine side the rectangular bar is welded to a vertical tube that houses the head of the bolt (inner wishbone bolt). The top of the rectangular bar is welded to the bottom face of the square tube near the bell housing (just to the left side of the exhaust, i.e. passenger side on a right hand drive car). On the gearbox side the 20 X 20 tube is welded to another vertical tube, again attached to the chassis by means of the inner wishbone bolt. The vertical tubes are welded to thick washers that the heads of the bolts bear against.

Ground clearance is OK, but I haven't as yet measured it so can't give a number. The car is at standard ride height, I doubt any lowering would be a good idea...

Sorry for the poor description, it really isn't all that complicated, pictures would help, but it's a hassle for me to take and then post pics.

Regards,
John.

[johnl]

Surprised there's not a bit more interest in this...

Anyway, after some some days and a few hundred kms driving with this new brace fitted I'm now even more happy with it. It does all that I said above, and I'm now sure it's not a placebo like affect.

Also noticeable is a significant reduction in the cars' tendency to tramline, which I used to find somewhat problematic on roads where longitudinal ruts existed (the kind where there are two 'U' shaped depressions running along the road, caused by heavy vehicles). These used to cause the car to veer from side to side quite badly, which still happens but now a lot less so. The car will now take fast sweeping bends with a lot more stability. Just pick a line and steer into it and the car doesn't need nearly as much steering 'correction' as it previously did, it just sits on and holds the line with far less deviation. There is a noticeable general decrease in 'crashiness' from the front suspension, even if there is a small increase in the degree to which irregularities in the road surface can be felt through the chassis and steering (i.e. you can feel the road more, but the feeling is more controlled and 'firm'). The handling in general is more predictable, and more enjoyable...

So far I haven't scraped the brace on the road, or any bumps etc. Ground clearance is about 12 cm, just over 4.5".

I can only assume that the subframe 'arms' (to which the lower wishbones are connected) are not laterally rigid enough, so when a significant lateral force is placed on an 'arm' it moves either a bit inward or a bit outward. This would cause some degree of uncontrolled camber and toe change. Connecting the 'arms' together with the brace means that any lateral force acting on a given side of the suspension is now resisted by both arms, instead of just one arm. This also means that even if both arms do flex laterally in unison (i.e. equally since the 'arms' are now more rigidly connected to each other), there will be less (zero?) affect on toe (even if both front wheels might still 'steer' equally in some unwanted degree). I'd like to triangulate the brace in some way to a point nearer the rear of the subframe, which I expect would improve it a bit more, but as yet haven't devised a means to do it (without the triangulating members hanging too low).

It's my understanding and interesting to note that Alfa fitted additional lateral bracing to the subframe for the GTA versions of the car (and / or the 156 GTA?), even if these braces do not connect the 'arms' as other lower braces such as mine do (i.e. from photos I've seen the GTA subframe is stiffened in each arm individually with an added plate attached beneath each arm of the subframe). They must have done this for a reason...

Regards,
John.

[Colin Edwards]

Happiness is a stiff chassis!
Alfa made a big deal about how much torsional stiffness the 159 had compared to competitor's cars. 
If your really want a chassis to be predictable it needs to be stiff so the suspension can be looked at in isolation. 
The Toyota Aurion V6 I used to drive was a great car however the chassis seemed to flex like a freshly cooked penne!

[Neil Choi]

John, pictures would be nice, me picturing your description is limited especially after a few JW and dry.
Neil
I really want to make my 156 handle better, though not knowing what is better, I am happy with my bog standard 156 for what it is.

[Cool Jesus]

+1 for photos. Have been watching quietly as I'd like to stiffen up the spider aswell. I'm liking your results...

[johnl]

Happiness is a stiff chassis!
Alfa made a big deal about how much torsional stiffness the 159 had compared to competitor's cars. 
If your really want a chassis to be predictable it needs to be stiff so the suspension can be looked at in isolation.

Agreed. I think the vast majority of newer cars have chassis that are substantially more rigid than their older counterparts. I doubt that improved handling is usually the real driving force here, more like ANCAP test results, and maybe NVH considerations. A rigid 'cage' (with front and rear 'crumple zones') results in a better ANCAP number and a car in which it's safer to crash, with the side benefits of (potentially) improved handling, lower NVH and a more 'solid' feel to the car.

The downside is considerably increased weight, being why fuel economy for newer cars hasn't (until quite recently with direct injection etc.) improved all that dramatically despite all the efforts of the engine and drivetrain engineers to improve it (i.e. more fuel efficient and powerful engines installed in much heavier cars resulting in fairly similar fuel economy and performance). Modern cars do tend to be very porky compared to similar sized cars from a couple of decades ago. A small car of today can weigh as much as a 'family sized' sedan or yore...

The Toyota Aurion V6 I used to drive was a great car however the chassis seemed to flex like a freshly cooked penne!

I find that somewhat surprising. For work purposes I regularly drive a late model Toyota Camry (a car I don't particularly like, though it's an acceptably competent appliance if you don't enjoy driving all that much), but one thing I do find in it's favour is that it does feel like it has a very rigid chassis. I can't say that I have ever felt anything in this car that seemed like chassis flexure, and nothing ever creaks or rattles.

It's a strange car, or at least I feel the suspension engineers have made some odd choices with the set up for what is basically a family hack. To me it feels to have very stiff damping, particularly on the rear end. The dampers transfer a lot of shock from larger bumps into the cabin, it can be quite jarring compared to any other car I've driven that wasn't meant to be in some way 'sporty'. Now I don't really mind this, but as a trade off I do expect the handling to be sharp and precise with minimal understeer etc., which it just isn't...

Chassis stiffness is an area in which I think the 147 is a bit lacking. I do sometimes feel the thing flex, and I can hear creaking from the door latches as it does so. It might be less with the five door versions, but the long doors of the three door version would tend to move more at their rear end (in the latches, causing increased noise from that area). I think part of the problem is that the chassis is like a box in which the rear panel has been removed, common with other hatchbacks and wagons. I recall being a passenger in a Honda Civic and looking over my shoulder to see the lower edge of the rear hatch moving sideways relative to the chassis as the car was driven over uneven ground.

This IMO is a fundamental design problem with hatchbacks and wagons. It's also an issue with sedans that have large apertures in the bulkhead behind the rear seats (the kind intended to allow an increase in cargo space by lowering the rear seat backrests). The only way to address it is for the manufacturer to add lots of metal elsewhere to increase chassis rigidity by 'brute force', which will also add a lot of weight. Alternatively, an owner might add triangulated bracing in the 'open space' left by the lack of a stressed bulkhead behind the rear seats. I did this with my old Honda Accord, and the result was noticeably improved handling and the car did feel more 'robust' in a hard to define sort of way. It's the same reason why rear tower braces work, but taken a step beyond that. In theory this sort of bracing should be especially beneficial in a hatchback or a wagon.

Keep in mind that such rear bulkheads used to be the norm in sedans, i.e. a stressed panel (in shear loading) that lived between the towers of the rear suspension, and added considerably to overall chassis stiffness by 'closing the box'. To some degree a sedan benefits from the 'shear' stiffness of the rear window, which at least partially 'closes the box'. By their nature wagons and hatchbacks don't have a stiffness adding rigidly located rear window (the hatch door won't add much stiffness because its latch won't be rigid enough to prevent movement between the door and chassis). Nor do they have a stressed panel behind the rear seats (or even the remnants of one after a big hole has been cut in it), because it deducts from the potential cargo space which is the raison d'etre of wagons and to a somewhat lesser extent hatchbacks. It was only when the marketing departments dreamt of the sales benefits of increased sedan cargo space that cutting a big hole in these bulkheads seemed like such a 'good idea'. I doubt the  chassis engineers were such big fans...

Regards,
John.

[johnl]

John, pictures would be nice, me picturing your description is limited especially after a few JW and dry.
Neil
I really want to make my 156 handle better, though not knowing what is better, I am happy with my bog standard 156 for what it is.

Neil,
I generally find I prefer single malts (maybe because I'm something of a pretentious booze snob), but JW BL is very nice too. I think adding anything to a fine whiskey is sacrilegious, not that I'm religious about such things. At any rate, I can only rarely afford the whiskeys I like, so that's good for the liver...

It's not that I can't post pictures at all, but I almost never take photos and have to remember how to get the shots onto the computer, and it's a hassle when spare time is precious. I'll see what I can do, no promises.

Regards,
John.