Bob_H Posted January 8, 2003 Share Posted January 8, 2003 I thought I knew what I was talking about, but have been lead to believe I may be off base. I will post my thoughts, and please post yours if you feel I am out in left field,(well, I am in left field, but tell me if my ideas are in left field...). I contend there is NO camber gain, but camber loss,(or gain in positive or loss of negative, however you want to word it) in the early Z strut assy's. The spindle is attached to a strut, and can only compress. The lower control arm can pivot, but assuming you start at or near level, it will only decrease the effective distance btw the upper mount and the lower part where the spindle is,(i.e take an extreme unrealistic example where the strut is angled out at ~30 degrees, now piviot the lower control arm up and with the two fixed points of the inner lower control pivot and the upper strut mount, the angle will decrease, and lose camber). I'm not sure my explanation is clear. Let me try this. Show me how the Z gains negative camber as it is lowered or the strut is compressed. I am not set in my mind, but I am having a really hard time seeing how it can gain camber as it compresses. A good friend seems set in his mind that I am not of my right mind....and that strut cars like the Z will gain negative camber as they are lowered or are compressed. II not only think he is wrong, but that he looks funny too. I only see it staying basically the same through all travel, having the most negative camber when the lower control arm is perfectly level, losing camber whenever it is above or below that. Bring it on! -Bob Quote Link to comment Share on other sites More sharing options...
Mudge Posted January 8, 2003 Share Posted January 8, 2003 I dont know what car doesn't pickup negative camber when lowering it. Quote Link to comment Share on other sites More sharing options...
74_5.0L_Z Posted January 8, 2003 Share Posted January 8, 2003 A popular modification of the Z front end is to relocate the pivot point of the lower control arm upward by 3/4" to improve bump steer. Other side benefits of relocating the pivot point of the lower control arm is to give lowered cars some camber gain, and to raise the roll center. Further camber gain can be accomplished by adding caster so that the wheels gain camber as they are turned. Quote Link to comment Share on other sites More sharing options...
jt1 Posted January 8, 2003 Share Posted January 8, 2003 Glad to see you're coming to VIR in Feb, Bob. I'll see you there, look forward to checking your car out. I guess you don't want to be my instructor again, huh??? John Quote Link to comment Share on other sites More sharing options...
jt1 Posted January 8, 2003 Share Posted January 8, 2003 Back to the discussion- I am not saying Johnc is wrong, he probably knows more about Z suspensions than I ever will, but isn't the angle between the strut and spindle fixed, with the ball joint below attaching to the LCA? I thought the strut could only pivot at the top-- maybe I just don't understand. John Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 8, 2003 Share Posted January 8, 2003 Originally posted by Bob H:So with my assumption of a level starting point, it will lose camber as it compresses. And a 100% stock Z can't be that much lower than level....of course I haven't seen one in a long time... No flaw in your logic, Bob. This was my whole point in saying that the JTR 'Bump Steer' mod was still useful in improving the camber gain characteristics - it locates the arm such that the camber increases (instead of decreasing) for the first inch or so of suspension compression travel. BTW, I think that the term 'gain' in this instance does not refer to gain vs loss, but rather it refers to a mathematical gain function, like the 'm' in y = mx + b. Quote Link to comment Share on other sites More sharing options...
TimZ Posted January 8, 2003 Share Posted January 8, 2003 Originally posted by jt1: isn't the angle between the strut and spindle fixed, with the ball joint below attaching to the LCA? I thought the strut could only pivot at the top-- maybe I just don't understand. The angle between the strut and spindle is fixed, but the angle between the strut and the ground (hence the spindle and the ground) is not. This is specifically the reason that the strut has to pivot at the top. Remember that the bottom of the strut is attached to the LCA at the ball joint. Since the LCA is constrained to move in an arc, so must the bottom of the strut. Just to bend everybody's brains a bit farther, we must also consider that the arc that the LCA travels in is also constrained by the compression rod. Because of this, the arc is not perpendicular to the body. The arc travels through three dimensions, not just two, and the caster changes along with the camber. I haven't sat down and checked, but this also should explain why the camber doesn't change by the amount that you think it should. Interestingly, when you adjust camber by relocating the pivot point in or out, only about half of the distance that you moved the pivot point results in camber change. The rest results in caster change. This is because the compression rod is at a ~45 degree angle (probably more like 60 deg, but you get the picture) to the body. So, moving the inner pivot point out results in moving the spindle both out and back, decreasing the caster. Anybody's brains exploded yet? Quote Link to comment Share on other sites More sharing options...
johnc Posted January 9, 2003 Share Posted January 9, 2003 > but isn't the angle between the strut and > spindle fixed, with the ball joint below > attaching to the LCA Correct, but also see what Tim posted above. > Just to bend everybody's brains a bit farther, > we must also consider that the arc that the LCA > travels in is also constrained by the > compression rod. Good point. To expand on it further in this camber gain discussion: shortening the effective length of the TC rod can significantly reduce camber gain. Why (someone might ask if they are bored enough to read this far in the thread?) Well... positive caster has a lot to do with the camber gain a suspension might have. Even if your car has lots of static positive caster at ride height, a TC rod with a shorter effective length tightens its arc, which means the positive caster goes away quicker as the suspension compresses in bump. This significantly reduces the camber gain in bump that might have appeared to exist when everything was measured sitting still at ride height. So, you might measure 6 degrees of static positive caster at ride height, but because the pivot point of the TC rod has been move forward from its stock location (via different bushings, special heim jointed mounts, etc.), you might lose all of that positive caster after only 2" of bump travel. BTW... you're guaranteed to lose some no matter how long the TC rod's effective length is. > This is because the compression rod is at a > ~45 degree angle (probably more like 60 deg, > but you get the picture) to the body. So, > moving the inner pivot point out results in > moving the spindle both out and back, > decreasing the caster. Now we're getting to the real subtle stuff. Pushing the rod forward more to get back this lost caster back puts a lot of fore/aft load on the inner control arm bushing and the TC rod bushing. This increase friction (stiction) in the suspension and reduces compliance. One noticeable effect of this is that shock adjustments don't appear to work anymore. Anyone made changes like this to the front suspension and then think their Tokico Illumina adjusters were broke? My hand is in the air! Angle drilling a new set of solid bushings suddenly gave me back ALL of my shock adjustments. Quote Link to comment Share on other sites More sharing options...
Bob_H Posted January 9, 2003 Author Share Posted January 9, 2003 While I apprecaite the thought, it does nothing for explaing why....I know plenty of cars,(and trucks), that gain no camber at all.... Of course I am talking about solid front axles such as my 1930 Ford Model A. And a great example of a car with double arms that gains postive camber as it compresses is the 60's Ford Mustang. At full droop it has some crazy negative camber, at full bump, that top of the tire leans out something fierce. So there are plenty of cars that don't gain negative camber as you lower them...but I am limiting our discussion to the early Z's, i.e. 70-78. So again, show me how, and examples of cars don't show me squat. -Bob Quote Link to comment Share on other sites More sharing options...
johnc Posted January 9, 2003 Share Posted January 9, 2003 Its not that complex Bob. If you lower the front ride height you gain negative camber until the lower control arm goes past level. Have a really fat person sit on the front of your 240 while you put camber guage on the front wheel. Also remember that the strut is attached to a ball joint at the bottom and either the stock, compliant rubber bushing or a spherical bearing up top. The strut not only compresses, it pivots at the top and bottom. Be like a Zen Master: accept! Or, take some poster board and cut out parts to make a 2D suspension. Play with at at your desk on some graph paper. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted January 9, 2003 Share Posted January 9, 2003 If you lower a Z from stock ride height, you will increase negative camber (which is good!). This is because, stock, the inner control arm pivots are above the outer control arm pivots, and the outer control arm pivots are below the spindles/stub axles. Lower the car from stock ride height, and the horizontal distance from inner pivots to outer pivots/ball joints increases, pushing the bottom of the strut outboard. For race Zs already lowered significantly, negative camber is LOST as the car is lowered, because the horizontal distance between inner control arm pivots and outer pivots/ball joints begins to decrease since the inner pivots are below the outer pivots in this case. When I lowered my Z from stock about 1", I gained quite a bit of negative camber. When I tried out 1" bump steer spacers, I lost a lot of that camber at the front, so I removed them. On a more severely lowered car, the bump spacers would INCREASE negative camber at the front. clear as mud? Hey, how goes the RB26DETT progress? Quote Link to comment Share on other sites More sharing options...
johnc Posted January 9, 2003 Share Posted January 9, 2003 BTW... just becuase the suspension gains negative camber that doesn't mean you'll actually see an increase in negative camber on a race track. Body roll can negate any suspension camber gain at the tire itself. The trick is to balance static negative camber and the camber gain in bump against limiting body roll while retaining compliance. Quote Link to comment Share on other sites More sharing options...
Bob_H Posted January 9, 2003 Author Share Posted January 9, 2003 Ah ha. I was assuming starting with a level lower control arm, as mine are nearly level as my car sits,(granted with aftermarket suspension). See: The lower control arm can pivot, but assuming you start at or near level,... So with my assumption of a level starting point, it will lose camber as it compresses. And a 100% stock Z can't be that much lower than level....of course I haven't seen one in a long time... The interesting thing is exactly how much does it change? And I was assuming that the top was not pivoting. But my basic assumption in the last paragraph was correct, i.e. it has the most negative camber when the lower control arm is perfectly level, and has less above and below that. Therefore, I win my argument, ah discussion! So is there a flaw in my logic? I would think with the upper mount pivioting, that it would negate any change overall...but this is with the unknown how much the camber changes through the travel of the Z.... -Bob Quote Link to comment Share on other sites More sharing options...
Bob_H Posted January 9, 2003 Author Share Posted January 9, 2003 Oh, RB progress is moving along. Got the motor right before I left on vacation for christmas. I am ordering things such as the intercooler, radiator, etc... I decided to do the suspension swap to a shell of a car,(see buy/sell for my want ad), while putting the RB into my existing body with suspension, etc.. That gives me time to work out the bugs in the motor, keep getting track time starting with the full course at VIR in Feb, while giving the shop the time it really needs to do the suspension swap. So yea, the project, as all projects, took on a bigger scope, but I'll get it done the way I want. I hope to have the motor in and started,(maybe not running right, but running), by the end of this month. -Bob Quote Link to comment Share on other sites More sharing options...
jt1 Posted January 9, 2003 Share Posted January 9, 2003 I love these suspension dynamics threads. I always learn something. At first glance, I thought johnc was talking about the strut pivoting vs. the spindle; After more consideration & reading the above threads, I realize(!) he meant the strut/spindle pivoting vs. the LCA, which makes perfect sense. Thanks for the great explanations, Tim & John. And thanks to Bob for kicking off a great discussion. John Quote Link to comment Share on other sites More sharing options...
Mikelly Posted January 9, 2003 Share Posted January 9, 2003 Yup this is good stuff... I got into a long discussion e-mailing a potential customer back and forth and the one thing he (And most people) over looked was the fact that the ball joint at the bottom, and the rubber mount/ isolator at the top allow the assembly to move in that arc. The info discussed about the TC rod placement is very interesting. I know our Northern California car is running an aggressive front caster setting at well over 7 degrees, but runs very little negative camber, at less than a degree in the front wheels. Bump steer is a much more critical factor in the Z early suspension design and I'd think that competitors who plan to champaign a Zcar in a series would want to buy three major pieces of equipment in order to set their cars up: Caster/ Camber Gages, Bump travel Gage, and scales. Then learn how to use them effectively and how to interpret the data and apply changes accordingly. This last part is critical to being successfull. Mike Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.