BlackBeaut Posted September 4, 2006 Share Posted September 4, 2006 Thanks for the pics Ron, I agree it looks like this could be an issue for anyone making these commercially, we all love big fat rims! I suppose you could add 2 or 3 different mounting points for the T/C rod clevis on to the LCA to give an option of mounting in stock location over to optimal BJ alignment. Cheers, Rob Link to comment Share on other sites More sharing options...
tube80z Posted September 4, 2006 Share Posted September 4, 2006 It would be better for anyone making these to stop using a clevice. It's far easier to bend where the clevice is than if you use a solid rod end and a double shear mount. My old race car used arms like these and I could bend the dog legs from time to time (braking and jumping FIA curbing). A double shear mount with the clevice stopped this but then I have an extra piece that's a waste. I'd be careful to think about using flat steel for the LCA. With sway bar loads you've introduced an undamped spring. Is it an issue? I don't know. Cary Link to comment Share on other sites More sharing options...
bjhines Posted November 15, 2006 Share Posted November 15, 2006 I am building my own front LCAs right now.... I have a few points I would like to address concerning some of the designs I have seen here... 1: First off... I see some designs lacking jam nuts... WTF??? the threads have to be bound tightly to eliminate slop... 2. the factory arrangement of the inner bushing offsets the LCA to the front... ie. closer to the steering rack... I see a lot of these designs use the same width spacers on both sides.. thereby CENTERING the LCA in the lower crossmember mount-holes... wasn't there some discussion about moving the steering rack closer to the LCA centerline... Shouldn't the LCA be as far forward as possible???? .... Link to comment Share on other sites More sharing options...
tube80z Posted November 15, 2006 Share Posted November 15, 2006 1: First off... I see some designs lacking jam nuts... WTF??? the threads have to be bound tightly to eliminate slop... Agreed, I would see this as dangerous without locknuts. 2. the factory arrangement of the inner bushing offsets the LCA to the front... ie. closer to the steering rack... I see a lot of these designs use the same width spacers on both sides.. thereby CENTERING the LCA in the lower crossmember mount-holes... wasn't there some discussion about moving the steering rack closer to the LCA centerline... Shouldn't the LCA be as far forward as possible???? Moving the LCA forward has the most effect on ackerman. In some ways you have a small amount of tuning available by moving using these spacers. You can also move the crossmember back and forth a certain amount too. Ideally you want the LCA to be perpendicular to the ball joint in plan view to take the majority of the force. Otherwise you'll start putting more lateral load on the TC rods. Cary Link to comment Share on other sites More sharing options...
JMortensen Posted November 15, 2006 Share Posted November 15, 2006 I'm trying to get my LCA's perpendicular to the centerline of the car (they were previously angled forward quite a bit due to increasing the caster. So if you run a lot of caster, that means that the spacer in front needs to be smaller. In my case the spacer in front is going to be pretty darn small, and the spacer in back is going to be longer than stock. I hadn't thought of how that would affect Ackerman before now, but it seems like the further forward the arm is the more Ackerman you would get. Link to comment Share on other sites More sharing options...
JMortensen Posted November 15, 2006 Share Posted November 15, 2006 Actually, shouldn't it be the caster that changes the Ackerman more than the spacing of the LCA? More caster, end of LCA moves forward, steer knuckle is farther forward relative to the rack. Right? Link to comment Share on other sites More sharing options...
blueovalz Posted November 15, 2006 Share Posted November 15, 2006 In regards to Ackerman, the factors influencing it are the angles created from the tie rod pivot at the steering arm end, to the ball joint and back to the tie rod inner pivot (at the rack). You could in theory have the usual Ackerman built into the OEM Datsun steering arm, but with the steering rack moved so far rearward that the above angle was 90º (angle "A" in the drawing). In this configuration, no Ackerman affect would be seen in either turn lock-to-lock. As the rack is then moved forward (and nothing else changed), the above angle becomes less than 90º which results in the Ackerman affect. To continue forward with the rack would be increasing the Ackerman affect. The positioning of the inner CA pivot will have no affect on this. EDIT, this drawing was corrected to show correct Ackerman effect (outward angled steering arms per comments by Jon and Olie05. Moving the inner pivot of the CA forward, without shortening the arm ever so slightly will result in a slight decrease in caster. Moving the spindle rearward would decrease the angle "A", and increase the Ackerman affect. This was one of the reasons I chose to move the entire crossmember forward when I lengthened the TC rod. This helped maintain the OEM Ackerman ratio. Link to comment Share on other sites More sharing options...
joe d. Posted November 15, 2006 Share Posted November 15, 2006 thank you! Link to comment Share on other sites More sharing options...
bjhines Posted November 15, 2006 Share Posted November 15, 2006 ok... so in short... the small(3/4") movement fore and aft that can be achieved with the inner pivot spacers turns out to be barely worth the effort...???? Link to comment Share on other sites More sharing options...
blueovalz Posted November 15, 2006 Share Posted November 15, 2006 If the intention is to change camber or caster, yes. In fact, adding the spacer does much the same thing as the previous discussion about straightening the CA (which in effect makes it longer) in decreasing the amount of caster and camber by a very small amount. Link to comment Share on other sites More sharing options...
bjhines Posted November 15, 2006 Share Posted November 15, 2006 just how much additional length are you guys adding to the TC rod to get the desired caster???? Link to comment Share on other sites More sharing options...
JMortensen Posted November 15, 2006 Share Posted November 15, 2006 I'm not sure about all of this Terry. I mean if you make the LCA perpendicular to the frame, that would LENGTHEN it, right? I mean, it would be farther away from the centerline of the car if it was directly perpendicular to the centerline of the car. That would increase camber. As far as caster, I don't think the caster changes at all by moving the inner LCA pivot. Caster is determined by the angle between the strut top and the ball joint. Lengthen the TC rod and you move the ball joint forward, this changes the caster angle. Maybe as you said, it changes just a gnat's ass. As far as the Ackerman, I think you have that part wrong. My understanding is that the closer the rack is to the crossmember, the more Ackerman you'll get. This is because of the angle of the tie rods relative to the steer knuckle, and the "cam" effect if you want to call it that of the tie rod as it gets pushed and pulled from that angled tie rod. I hope that is correct, otherwise I spent a lot of time and effort screwing up my crossmember adding anti-Ackerman (moved the rack back 7/8" relative to the crossmember). Link to comment Share on other sites More sharing options...
bjhines Posted November 15, 2006 Share Posted November 15, 2006 How much do you guys lengthen the TC rods to get desired caster angles??????? Shifting gears for a second....... ok... try this on for size... I have a crossmember that was redrilled(by the P.O.) to add 1 5/8" track width... with stock control arms.. I have slotted this hole upwards to get the correct setting for bump steer... I am pretty sure the hole spacing is way too wide... I am liable to have to shorten my control arms by 3/4" to get me back into the usable range... which will exaggerate the camber dynamics as the arm moves through it's arc... hold your thoughts.... I can see this(short LCAs) as being an advantage considering the car is going to be stiffly sprung I will get a great deal of camber gain with the shorter travel... as long as I can get the right static angles on the control arms with the car lowered... Link to comment Share on other sites More sharing options...
Mikelly Posted November 16, 2006 Share Posted November 16, 2006 Let me comment for a second on a few things... I showed some pics of LCAs and TC Rods without the Jam nut in the past ONLY to show design of the units... In my opinion, Running any adjustable part without a locknut on ANY of them is WAY Dangerous. Now, BJH, I can't tell you with any degree of certainty what my previously sponsored car ran legthwise, because the car was adjusted to lengths from 4 degrees on up to well over 7 degrees. We employed a 7.5 inch threaded 3/4 inch tube threaded onto a "J" bar that was adjustable from lengths one inch shorter than the stock TC Rod to well over 2 inches longer than the stock rod... We DID unfortunately use a Clevis only because folks wanted a bolt on solution... However, I can tell you all that this whole design will change, and a number of improvements will be made this coming year with my planned testing. Time, Funding, and Resources should allow me to play at the track a LOT more in 2007 and I'm all ears for ideas on things to try at the track. And I must say that I'm truly impressed with the level of technical discussion in this thread folks... Keep up the good work... Many people will benefit from what's being discussed here for years to come... This thread is an EXCELLENT example of why HybridZ is here on the web. Mike Link to comment Share on other sites More sharing options...
bjhines Posted November 16, 2006 Share Posted November 16, 2006 can anyone pull a string and figure out how far forward the balljoint ends of the LCAs are angled...??? pull a string between the BJ grease-nipples... and measure back to the middle of the crossmember opening(forget about the inner LCA offset front/rear, just measure to the middle of the x-member opening) I am just trying to get into a general range... before I start mocking up parts.... sometime soon I am going to get this thing up on the alignment rack and actually set static alignment.. and get a few measurements at extremes... Link to comment Share on other sites More sharing options...
bjhines Posted November 16, 2006 Share Posted November 16, 2006 I might be wrong here.. but I think that keeping the TC rod long and the pivot point even with the inner LCA pivot would get the most A-arm-like response from the front end... It appears that the S-30s could use some more camber gain as the suspension compresses... especially since a track car has very little suspension movement... and typical lowering(flat LCA angles) reduce dynamic camber gain as well... on that note... moving the inner LCA pivots out as far as possible and shortening the LCAs to bring track width back into spec could have some benefits... It may also make it easier to relocate the TC rod pivots(due to the fact that they can move up and OUT... giving more TC rod clearance to the frame rail... Link to comment Share on other sites More sharing options...
JMortensen Posted November 16, 2006 Share Posted November 16, 2006 I think you're barking up the wrong tree. Ideally you would just set it to what it needs to be and it wouldn't change much at all through the motion of the suspension. Making the suspension angles change MORE through the travel is going the wrong way I think. Link to comment Share on other sites More sharing options...
bjhines Posted November 16, 2006 Share Posted November 16, 2006 I could set less static neg camber and rely on neg camber gain in compression... it might reduce trammeling in a straight line a bit... it is unclear how that would affect braking and turn in.. I think it would be an improvement... but I haven't tried it yet.. Link to comment Share on other sites More sharing options...
bjhines Posted November 16, 2006 Share Posted November 16, 2006 Some pics of progress... I have left myself some room to play... The overall mockup of the LCA... It is set at stock length in these pics... I can shorten it a great deal(13/16")... I can lengthen it some(~1/2")... I have relocated the inner crossmember pivots as well... so I won't need to lengthen them at all... I added some 3/16" strips inside to anchor the stud securely... I still have to drill some holes for plug welds in the bottom... I neatly cut the top section off and I can replace that as well... The stud is a grade-8 bolt, 5" long, with 3/4"x16 threads... I cut the heads off flush... It is inserted halfway into the rod end... The rod end is a high strength teflon lined aerospace piece... Aurora... ... Link to comment Share on other sites More sharing options...
olie05 Posted November 16, 2006 Share Posted November 16, 2006 As far as the Ackerman, I think you have that part wrong. My understanding is that the closer the rack is to the crossmember, the more Ackerman you'll get. This is because of the angle of the tie rods relative to the steer knuckle, and the "cam" effect if you want to call it that of the tie rod as it gets pushed and pulled from that angled tie rod. I hope that is correct, otherwise I spent a lot of time and effort screwing up my crossmember adding anti-Ackerman (moved the rack back 7/8" relative to the crossmember). Jon, you are forgetting that ackermann steering can also be achieved by pointing the steer knuckles towards or away from the centerline of the car. I'm kinda new to the whole ackermann thing, but from what I understand, on a car that has the steering knuckles forward of the front axle, the steer knuckles must point outwards in order to achieve 100% ackermann effect, assuming the steering rack and tie rods are parallel. (in a top view) Also, I understand that when the tie rods are perpendicular to the steering knuckles, then 0% ackermann effect is achieved. In the case of the car with forward mounted steering knuckles this would occur forward of the tie rod mounting location on the steering knuckle, assuming the steering knuckles are still pointing away from the center line of the car. So, in your case, moving the steering rack back towards the axle centerline should increase the ackermann effect. note: when I say steering knuckle, i really mean the imaginary line from the steering axis to the mounting location of the tie rod ball joint. I honestly don't see how changing the inner position of the CA front to rear would significantly affect ackermann. Link to comment Share on other sites More sharing options...
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