Does anyone know geometry changes behind installing Smart Struts and do they really make the car handle better.

I can't believe that Zora Arkus-Duntov made a mistake that redesigned bracket and rods would correct.

 

Just ask your self how do you set the camber on a stock system? Stock vettes are really pretty crappy machines

 

I don't know the exact change in degrees but I got about 5 degrees total camber change on original struts. On the Smart Struts as I remember it is about 2 degrees over the arc of wheel travel. Yes it provides better handling. You also get poly ends which will give you less deflection.

 

Bean counters contributed as much or more than Zora to the design of the Corvette.

Are you trying to tell me transverse leaf springs and power piston steering assist are crappy? The other car I owned with transverse leaf springs was a 47 Ford -- an autocross dream. You can still find that kind of inexpensive steering upgrade for Ford farm tractors -- makes tilling so much easier.

 

gkull, I have never seen Smart Struts and am under the impression that it changes the angles of travel. I have VB&P urethane strut rods with the outer end changed to a Heim. I am installing Johnny Joints on the trialling arms. The differential ccrossmember will have a rib along the top, all seams welded and the 4 holes to on top will have tubes welded to secure the top half to the bottom half.

All these modifications are to fix the problems that are due to manufacturing cost concerns. The suspension should work as designed. Does the Smart strut change the mounting points or change the arc of travel?

 

The strut itself makes no difference. It's a rod.

The aftermarket mounting bracket lowers the inner mounting point of the strut making it slightly more parallel with the half shaft. This change in geometry reduces the variation in camber angle throughout the range of suspension travel by a few degrees. Whether this is a big deal or not depends on the indiviudal driver and what the car is sued for.

As to this being a 'factory error' forced by bean counters, I think not. This is a very interesting paper from 1963

http://www.web-cars.com/corvette/196...er.php?page=10

 

Smart Struts lower the inner mounting point limiting camber change during verticle wheel travel. They use a threaded rod so it is easy to set the rear camber.

The differential cross member is not really a weak link in the system. If you install large diameter aluminum washers at either end it holds the CM very ridged and inhibits wheel hop

 

This is a Solidworks analysis (not mine) of chamber improvement with Smart Struts. This has been posted before; and, flamed before. The argument seems to be: Is reduced camber on a wheel/tire under load a good thing for performance? You can watch the open-wheel formula cars that are running considerable negative camber. I will probably eventually go with Smart Struts, with Heim or Johnny rod ends to prevent loosening of the jam nuts.

 

The vertical slot in the Smart Strut bracket (available separately, #52000B) facilitates easy camber curve adjustment, or the amount of negative camber gain when the suspension travels into bump or squats. At face value, negative camber gain might seem a bad thing, which leads many to assume it would be desirable to eliminate it, but it must be remembered that when the body rolls over towards the outside rear wheel without a compensatory amount of negative camber gain relative to the chassis (I've actually seen C3's setup with positive camber gain at the rear wheels) that wheel can go into positive camber relative to the road surface during cornering, which greatly compromises traction.

Thing is, modern and/or wider tires don't require as much negitive camber gain as did narrow bias ply tires which were the norm back when the C2/C3 suspension was first designed. (FYI, the C2 had even more camber gain built in than the C3.) So, IMCO most enthusiasts interested in better handling should follow John Greenwood's advice (found in his VIP articles) to lower the inner camber strut links 1/2" below the diff from C3 OEM height, as a baseline. Conveniently, the top of the slot in VBP's Smart Strut bracket achieves ~1/2", which IMHO is no coincidence.

One may well find a different adjustment works with their particular chassis/engine/tire combination, and I urge using a pyrometer to help zero that in. That said, it shouldn't go without mention that minimizing or eliminating camber gain altogether is a good goal for the drag strip, but cornering and drag racing present very different problems. However, the more power available the more likely reduced camber gain will help in putting the power down out of corners (where there's less throttle application in the turns themselves).

Unfortunately, with so many variables at work here (I've only scratched the surface) there isn't really a one-size-fits-all height at which the inner links should be set, and it is for that reason I always recommend the scientific approach of testing deviations from the Greenwood baseline sited above rather than guessing, else just leave it there and be happy.

FWIW, I much prefer camber struts with heim-jointed ends over poly, and camber lock plates to eliminate the eccentrics. Poly is better suited to 2D bushing applications such as anti-roll bars and front CA's, and IMOE the eccentrics just won't hold adjustment under heavy loads. Oh, and unless they've addressed the issue, you'll probably need to bush down the 4 bolt holes in the SS bracket (mine came oversized) where it mounts to the diff. Hope that's worth $.02 to someone.


TSW

 

Thanks for all the info.

Mike Ward's link was very interesting and shows that the set up was not a result of economics but rather a well planned out design. The execution might have a few flaws do to bean counters and a little beefing up is in order.

If it was designed today I think it would be different due to the availability of modern tires as pointed out by Charlie. It would look like a C4.

I will fab up a new bracket 1/2" lower and stronger then stock. I figure this will be an improvement over stock.

Tom

 

Everything Skunk Works said. Also, the vertical slot in the bracket will also allow a lower the rear roll center in addition to changing the camber gain curve. The lower rear roll center increases the rear roll couple and will result in more body roll and weight transfer at the rear. The C2 to C3 strut rod bracket change lowered the rear roll center in the C3 so the dimension in the drawing in the '63 write up is for C2 bracket and tire diameter.

 

Correct. Lowering the rear roll center requires increased rear anti-roll to maintain understeer/oversteer balance. With minor adjustments one might not notice so much, but the further the lowering, the more anti-roll will be needed to a point where spring and/or bar adjustments become necessary. However, a lower rear roll center will yield the benefit of reduced jacking forces which work to lift the rear under cornering loads. Ain't vehicle dynamics fun?

 

TSW
this is further headache stuff...

i have the VB&P smart struts but i placed the inner rod in the middle , not 1/2" lower than oem, because i used some square plates provided in the kit. so better to move to top of the slot anyway?
the Z and D of about 1" suggested by Greenwood in the VIP article are meant to give the best suspension travel?
I'm going to lower the front coils and get 1" Z but can't do that at the rear because I want to keep the 1/2 shaft angled down and I can't raise the diff. would i go into excessive unbalance front-rear? suggestions?

 

Aldo, my take on this in your case would be to suggest you might want to set up your rear ride height first. Then set your front Z height to ~0.750” (+ 0.125”) more* than your rear D height winds up as measured with the rear camber struts centered in the Smart Strut bracket. Given the middle of the SS bracket’s “camber-inclination” slots locate the inner camber strut links to ~0.875” below OEM (C3) from the differential, this should achieve approximately the same rake as that had with the Chevy Power road race prep recommended heights, though your Z may be a little above 1”. That said, from a roll axis standpoint the lower is your rear roll center the more rake allowable, but there are other factors in how much rake can be run without generating detrimental effects.

As for camber gain adjustment, since you already have camber lock plates, I’d evaluate where the above puts you before worrying about the final camber gain setting. Then, should you feel the need to tinker with it, in lieu of going back to the eccentrics it’s perfectly fine to fab up your own lock plates (use hardened steel) with the holes located where you wish. Keeping in mind that the optimum static camber setting can be affected by camber gain adjustments, only affect changes to one or the other at a time so you can best quantify results (yes, you’ll have to reset static camber when adjusting gain, and vice versa). If the sensitive instrument on which you sit doesn’t give clear enough indications, a stop watch and/or pyrometer should help you determine what’s happening, but I’d keep a close eye on tire temps regardless.

This stuff makes my head hurt sometimes too, but hope this helps a bit whether or not you decide to put it into practice.



*For those following along, should the maths above put Z below 1”, I’d raise both D and Z by the amount necessary to bring Z up to 1”.

 

TSW

my D is 1.5" right now( smart strut in the middle of the slot)

you say to deduct 0.75" from that D , but it's too much!

my current Z is 2,3" now !!! I think I'm going to cut away 1 turn out of the front coils and see what happens.
I'll remove the rubber bumper blocks too and go for the VB&P bump steer blocks.

about camber , i have no chance to get a pyrometer and a suitable track to test the tires temperature. so i'm spotting for about 1 deg neg camber both front and rear ( my Porsche Boxster has a bunch of neg camber and no uneven tire wear).I want as much neg camber as possible also to increase the track width ( I'm going to use 1" wheel adapters and so need neg camber to have the tires not sticking out fom the fenders)

 

My front and rear bumper blocks have been gone for years. You can also remove the big headed lower ball joint bolt and replace it with a regular bolt to save a little weight. I do recommend the bump steer kit.

I was never able to run more than about .60 neg camber on the front without burning up the inside of my tires. I run a wider track front and rear. It requires more spring. My big front tires put so much stress on the rear lower A-arm mounting point that it cracked. So I had to weld up the cracks, grind them flat, and gusset over the top of them.

I actually went out and ran my first welds about 100 miles of hard driving to see if my welds held up before gussetting.

 

Any pics of the gussets?

My passenger side mount lower rear mount was twisted and cracked. I thought it was from a previous owner's accident. I cut an old frame and reinstalled the mount but never did not add gussets

 

Rolling on the floor, laughing my *** off. You were joking right.
Bee Jay

 

I often have to apologize for my sarcasm. Only reason I could afford to buy two used Corvettes was because GM made the car "affordable." I owned a 7-series BMW once and discovered the other side of the equation.

 

Sorry, I was apparently more tired than I thought when I posted that reply (see correction), and should have said to add the ~0.750" to your D height measurement. That said, I was not aware your D height was so high (equal ~1.125" above Chevy Power D height), but with that at 1.5" (center of slot) your current 2.3" Z does put your chassis pretty much parallel to that had with Chevy Power D & Z heights. So, I'd give some thought to ~1.5" Z and 1.0" D (center of slot) if you can't get the rear further down.