Tony Posted October 14, 2008 Report Share Posted October 14, 2008 The confusion between the two examples is due to the cambers starting position (positive-negative) in the case of your example it's best we stick with the latter. I don't think you've been given the full picture regarding this cars impact!..... So before any conclusion can be assessed you need to adjust the OSF camber, replace the steering arm/worn bushings and measure again. Also measure "symmetry and set back" from the "make additional measurements" prompt. Ah, I hadn't noticed the positive-negative. So, looks like the wishbone/mounts may be to blame. It doesn't have dedicated camber adjusters, just some movement in the upper wishbone-to-strut link. I'm not expecting much movement (~4/5') and when I tired to free-off the bolts prior they were hella stiff. Either way, seems mute untill the bushes are replaced. Hasn't the strut got two pinch bolts at the hub... like a Golf? Quote Link to comment Share on other sites More sharing options...
CIH Posted October 14, 2008 Author Report Share Posted October 14, 2008 Yes, that's what I meant. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 14, 2008 Report Share Posted October 14, 2008 Yes, that's what I meant. I thought you were talking wishbone bolts .... Anyway the bushings cannot be solely responsible for the camber because they are to far away from the wheel. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 14, 2008 Author Report Share Posted October 14, 2008 Hmn, they're already riding my butt for taking too much time over it. Anyway, so the IA can mean different things if camber is toward excessive positive or negative ? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 14, 2008 Report Share Posted October 14, 2008 Hmn, they're already riding my butt for taking too much time over it. Anyway, so the IA can mean different things if camber is toward excessive positive or negative ? Do they want an accurate diagnostics or stab in the dark and a possible complaint? The IA is dependant on the camber.... As you know the SAI is perpendicular to the vertical and 99.99.9% of the time point inboard toward the car, whereas the camber could be negative of positive. Point is this gives you a mental image of where the SR is, so with a little logic it makes it easy to assume what's bent. I suggest you set the camber... do another swing, if the castor is uneven then check symmetry and set-back and if you can wheel base. If the castor is set back and the wheel base is off then it's a fair bet the cross member is displaced. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 14, 2008 Author Report Share Posted October 14, 2008 I think I should be careful of making diagnosis as I clearly have much to learn. Is there a specific couple between SR and IA ? They're defined by much the samething aren't they (interplay between Camber & SAI) ? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 14, 2008 Report Share Posted October 14, 2008 I think I should be careful of making diagnosis as I clearly have much to learn. Is there a specific couple between SR and IA ? They're defined by much the samething aren't they (interplay between Camber & SAI) ? Diagnostics will always be theoretical despite all the information the machine gives you..... Think of it as triage, where your best assessment offers the best results born from that information. SR and IA are similar things, the only real problem you have is the missing fields like wheel off-set and tyre size? Does you machine measure "roll force lever?". Quote Link to comment Share on other sites More sharing options...
CIH Posted October 14, 2008 Author Report Share Posted October 14, 2008 No idea! I think we should explore SR more thoroughly. Like, how to use the figures to assertain if the SR is correctly placed ? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 15, 2008 Report Share Posted October 15, 2008 No idea! I think we should explore SR more thoroughly. Like, how to use the figures to assertain if the SR is correctly placed ? This won't be easy..... First up let's forget about OEM cars and assume at the design stage everything was spot on. With this "spot on" car the owner wants to fit non OEM wider wheels and tyres, can you see any problem with this? Quote Link to comment Share on other sites More sharing options...
CIH Posted October 15, 2008 Author Report Share Posted October 15, 2008 The static position, and any subsequent migration, of SR would need to change to take into account the extra tyre surface. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 15, 2008 Report Share Posted October 15, 2008 Forgetting offsets "for now". Could you assume that the SAI and camber would be incorrectly placed if the wheel is wider. No: why Yes: why Quote Link to comment Share on other sites More sharing options...
CIH Posted October 15, 2008 Author Report Share Posted October 15, 2008 Camber would need to be reduced (ie moved toward a more neutral position) to accomidate the extra tyre cross section. That's a given. SAI seems more complicated. I would think it may be correct unless it was a dramatic increase in wheel & tyre. Something I've been meaning to check, but always forget, is how camber adjustment affects SAI. Clearly, there must be an impact ? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 15, 2008 Report Share Posted October 15, 2008 Excellent. You are correct about the camber move but the missing point as you have found is the SAI. What you will find is the SAI barely moves if the camber is adjusted above the hub, whereas if the camber is adjusted on the lower arm the SAI is hugely adjustable. Point to note, all the readings you will find Googling will say the SAI and IA are fixed "their not". So we now have a wider wheel and a desire to move the camber so that the SR is moved, but to where? Next stage: what is your understanding of wheel off-sets. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 16, 2008 Author Report Share Posted October 16, 2008 Excellent. You are correct about the camber move but the missing point as you have found is the SAI. What you will find is the SAI barely moves if the camber is adjusted above the hub, whereas if the camber is adjusted on the lower arm the SAI is hugely adjustable. Point to note, all the readings you will find Googling will say the SAI and IA are fixed "their not". So we now have a wider wheel and a desire to move the camber so that the SR is moved, but to where? Next stage: what is your understanding of wheel off-sets. Offset is the difference between the wheel centreline and the hub mounting face IIRC. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 16, 2008 Report Share Posted October 16, 2008 That's correct. By design the SR would fall into the zero off-set, this is why different off-sets or spacers cause such a problem, but.... a change in camber, particually if this is at the lower arm will reposition the SR to compliment the new rims/spacers. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 20, 2008 Author Report Share Posted October 20, 2008 So is there a way to use the Geo readings to determine if SR is correctly positoned ? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 20, 2008 Report Share Posted October 20, 2008 So is there a way to use the Geo readings to determine if SR is correctly positoned ? The IA is the only clue you have.... The IA is just an angle, it's never right or wrong but it's position is gained by the camber and SAI so if the data shows guides for these then you can mentally assume the SR. Historically the tyre wear is a result of the SR being positive or the camber line and SAI line intersecting below ground level. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 21, 2008 Author Report Share Posted October 21, 2008 positive SR ? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 21, 2008 Report Share Posted October 21, 2008 positive SR ? Yep.... If the lines intersect below the ground it's deemed as positive, above the ground it's negative.... If you use your imagination you can image the position of the SR from this. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 21, 2008 Author Report Share Posted October 21, 2008 how does that cause tyre wear ? I can imagine lateral poitioning causing problems but hadn't thought about the vertical plane. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 21, 2008 Report Share Posted October 21, 2008 how does that cause tyre wear ? I can imagine lateral poitioning causing problems but hadn't thought about the vertical plane. You cannot measure this on your machine so trust me.... Example A 225mm wide front tyre, a -30' camber and a SAI of 4 degrees will give you a SR "positive" contact patch of around 90mm. So 90mm of the tyre is within the steering pivotal point, this "safe zone" allows the cars weight to migrate correctly as the steering is turned, but if this position is moved, let's say by lowering the car then the contact patch (still 90mm) will not be within the steer axis then the migration will deform the contact patch and wear the tyre...... as well as handle pants. It's hard to image but let's say the SR is 0, then as the steering is turned left the camber and castor will tilt positive and forward respectively and if the math is correct the SR will remain within the 0 steer axis. The migration is not away, in or out, it's retained at 0 despite the steering yaw. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 31, 2008 Author Report Share Posted October 31, 2008 but would the SR not move because of the camber changes on turn ? Incidentally, it seems my lifting procedure woes stem from the rig prompting me to straighten the road wheels before and after lifting. Doesn't always do it. Any ideas what prompts the rig to do so ? Those idiots at work accused me today of shirking the tyre bay work because my geo sessions are taking longer. "Just track it up" they said, like it's a 20min job. From guys who dissapear every 10mins to have a cig Quote Link to comment Share on other sites More sharing options...
Tony Posted October 31, 2008 Report Share Posted October 31, 2008 Yes but so does the SAI..... Example DA you have -1d camber and 14d SAI, turn left this will migrate to +10' camber 12d SAI (fictitious numbers) but you get my point. As for the lift you need the steering brace on and the toe within spec to make the lift but it shouldn't ask you again after the cars lowered. Does you machine use a virtual screen and or a bar graph screen? As for your work mates do they also use the machine? Quote Link to comment Share on other sites More sharing options...
CIH Posted October 31, 2008 Author Report Share Posted October 31, 2008 Yes but so does the SAI..... Example DA you have -1d camber and 14d SAI, turn left this will migrate to +10' camber 12d SAI (fictitious numbers) but you get my point. how can SR be static if it shifts across the tyre contact patch ? As for the lift you need the steering brace on and the toe within spec to make the lift but it shouldn't ask you again after the cars lowered. Does you machine use a virtual screen and or a bar graph screen? Bar Graphs. Last time I adjusted Toe but only to within tolerance, not spot-on. Perhaps I should check Steer Ahead (not displayed by default) before lifting ? Do you ever use lift axle on the rear btw ? As for your work mates do they also use the machine? Yes, he showed me how to use it first time round. They all think of it like a tracking ie; a quick 15 minute job. Infact KF shows it as a "super track" on the till. If I gave him a completed Summary he wouldn't know any of it beyond the basic camber/castor/toe angles. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 31, 2008 Report Share Posted October 31, 2008 You are learning well.... Yes the SR migrates I have to set the toe within tolerance before i lift..... As for the rear, yes i lift this often, not just for the jap cars but for the heavy cars, 4X4's when camber needs adjusting. Your mates attitude keep me in business... Long may they work in ignorance and i get to repair their poor workmanship..... I went though the same problems when i worked for fast-fit and i found when i had a really difficult car i would ask them for advice even though i knew the answer, over time they stopped mocking me because there was a high risk i would embarrass them Quote Link to comment Share on other sites More sharing options...
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