Paul XE Posted March 29, 2010 Report Share Posted March 29, 2010 Just thought I'd post of a few pics of my slightly adjustable suspension/steering set up on my car! This has been great in one way as everything is adjustable, but a nightmare in another as I have not got any real starting points! I have had a few headaches in trying to get a decent set-up but I think I'm getting there now, slowly! Over the past few weeks I have had the engine out and taken all the suspension apart which allowed me to set all the arms to the same length which has been very very difficult before. The main problem I've got now is straight line stability, corners feel really good for a change, which was the main problem previously. On any straight road, the steering requires constant adjust to keep the car straight. If i let the car coast I can take my hands off the wheel and it travels in a dead straight line making me think, but under any power (even very light load) it pulls one way or the other (normally to the left). I think its down to one of four things: 1. Steering/suspension geoetry. 2. very slight play in steering rack and rose joint in place of track rod ends. 3. Corsa power steering rack giving free play between steering wheel and rack pinion. 4. Plate LSD giving funny feeling through steering. My current front settings are Toe: 0mm Camber: 2 degree neg Castor: 6.5 degree SAI: 13 degree Rear: Toe: 0.75mm toe in camber: 1 degree neg Corsa electronic power steering column, fully adjustable assistance, Gripper plate LSD. Few piccies of the suspension arms: Front tie bars, lower TCA's, top arms, top tie bars Quote Link to comment Share on other sites More sharing options...
Tony Posted March 30, 2010 Report Share Posted March 30, 2010 The cambers are about right but the castor is way to deep as is the SAI..... What offset do the wheels have compared to stock? Quote Link to comment Share on other sites More sharing options...
Paul XE Posted March 30, 2010 Author Report Share Posted March 30, 2010 I got a feeling the wheels have a 10mm pos offset, but with the spacers I'm using it measures around 15mm neg. Will have a double check next time I'm up the garage. Quote Link to comment Share on other sites More sharing options...
Tony Posted March 30, 2010 Report Share Posted March 30, 2010 If you can imagine the position of the upper pivotal point which is inboard compared to the lower pivotal point then project a line through both to the ground, that is the steer axis. Then extend a line through the SAI declination to the ground -V- the actual camber, then you have the scrub radius. A change in the wheels offset can move the actual contact patch outside the steer axis, meaning high speed stability is impaired. The was around this is to either change the offset or change the position of the scrub radius by moving the camber. In addition 6d of castor have given you a very negative castor offset meaning the imaginary line is aft of the spindles position. Quote Link to comment Share on other sites More sharing options...
Paul XE Posted March 30, 2010 Author Report Share Posted March 30, 2010 Ok, I see what your saying. The cornering grip and feel is very good with this geometry and I am a bit reluctant to change it as its never handled this well before! What effects would reducing the castor to say 5degrees and SAI to around 10 with 2 degrees camber?? I was also thinking about a small amount of toe in on the front to increase stability . Wheel offset cant really be reduced as the lower damper mount is already very close to the inside of the wheel. Thanks for your help Tony, I've had many a sleepness night trying to get my head round what is wrong with the geometry and handling! Quote Link to comment Share on other sites More sharing options...
Tony Posted March 30, 2010 Report Share Posted March 30, 2010 Ok, I see what your saying. The cornering grip and feel is very good with this geometry and I am a bit reluctant to change it as its never handled this well before! What effects would reducing the castor to say 5degrees and SAI to around 10 with 2 degrees camber?? I was also thinking about a small amount of toe in on the front to increase stability . Wheel offset cant really be reduced as the lower damper mount is already very close to the inside of the wheel. Thanks for your help Tony, I've had many a sleepness night trying to get my head round what is wrong with the geometry and handling! Castor offset Your jumping before you can walk..... Calm down a little and stop second guessing the overall solution in one hit. Bring the castor back to around 4 degrees, this should give you around a zero offset, keep the toe/ camber and SAI as it is and report back. Quote Link to comment Share on other sites More sharing options...
Paul XE Posted March 30, 2010 Author Report Share Posted March 30, 2010 I have a bad habit of changing more than one thing at a time, even though I know I should'nt! I will reduce castor to 4 degrees on saturday, and let you know how it goes. Thanks again Quote Link to comment Share on other sites More sharing options...
Tony Posted March 30, 2010 Report Share Posted March 30, 2010 I have a bad habit of changing more than one thing at a time, even though I know I should'nt! I will reduce castor to 4 degrees on saturday, and let you know how it goes. Thanks again Evolutionary Geometry needs to be incremental, i can model many scenarios on paper but the real world needs real time, matter of fact results..... Slowly catchy monkey is not a term you would read in any suspension bible. Quote Link to comment Share on other sites More sharing options...
Paul XE Posted April 4, 2010 Author Report Share Posted April 4, 2010 Had a play around with the settings over the weekend and I'm really gutted to say its taken a massive step backwards :laughingsmiley: Sat: adj settings to try and obtain 4 deg castor, 2 neg camber and 13 SAI, but because I was in a rush (had to be somewhere in the afternoon) I only managed to get close to what I wanted (camber spot on, castor and SAI within 1 degree of target settings) and the car felt worse compared to previous settings. Cornering felt ok, but understeer was increased slightly and it lost the "planted" feeling. Straight line the car felt pretty bad, quite twitchy and nervous requiring constant steering input to keep it on the straight and narrow! Went into work today to try and improve on this and ended up with the following settings: Camber = 2 deg neg both sides Caster = 4.25 deg both sides SAI = 13 deg OSF / 12 deg NSF Toe = 0.5mm toe in total. Wheel offset = 17mm plus 23mm of wheel spacers giving -6mm total wheel offset. On the drive home the car felt VERY nervous and twitchy, to the point where I could not take one had off the wheel under any acceleration, even light. Anything over 50mph required 110% concentration and all my driving skill to keep it in a straight line! It almost felt undrivable it was that bad! Cornering felt similar to yesterdays attempt with understeer increasing and a little unsure through the corners. I really dont know what way to turn now I really dont know way to turn now as I am completly lost into whats causing the problem. I know the rack and rose joints have a small amount of play in them but it feels like they are hanging off and turning on their own whenever they feel. I am going to replace the rack and rose joints asap but i dont think that is the problem, but its certainly not helping. All I want is to be able to put my foot down and be able to control it in a straight line, and enter a corner and have confidence I will see the end of it, which i dont have either at the mo. I know I am comparing chalk and cheese, but in my Merc I can take both hands off the wheel at 120+mph and I know it will stay there. In the mini, I cant take either hand off the wheel at any speed (makes gear changes hard!!) Please help!!! Quote Link to comment Share on other sites More sharing options...
Tony Posted April 5, 2010 Report Share Posted April 5, 2010 With those settings there's no way it should drive like that..... Take the spacers off the front and test again.... I really feel the problem you are having is the scrub radius is outside of the steer axis. Quote Link to comment Share on other sites More sharing options...
Paul XE Posted April 5, 2010 Author Report Share Posted April 5, 2010 I'm glad you've said that, as I was only thinking the same thing today. I was up the garage today looking at the front suspension and I did wonder if I could move the wheels inwords at all to reduce scrub radius. Trouble is it will not be as easy as just unbolting the wheel and removing the spacer. They are there because the inside of the wheel is extremely close to the bottom of the coilover so to move the wheels inword I will have to remake/modify the lower coilover mount. But we'll give it a go! I will get some more pics up during the week, and report back when its done. Quote Link to comment Share on other sites More sharing options...
Tony Posted April 5, 2010 Report Share Posted April 5, 2010 Please do. You seem to have grasped if the SC is outside of the SA then the car will handle pants. At the end of the day everything funnels down to that contact patch, if this is in the wrong place no Geo will save you. Quote Link to comment Share on other sites More sharing options...
Paul XE Posted April 14, 2010 Author Report Share Posted April 14, 2010 Sorry I haven't posted in a while, my internet connection is down at home and I've been very busy in work! Anyway, as promised I have a few pics of what I've been doing over the past couple of weeks: Here is the problem I had with moving the wheels in closer to the body (reducing offset) As you can see, the bottom of the coilover is very close to the inside of the tyre, and this was using a wheel with 17mm pos offset and 23mm of spacers. If I move the coilover in too much, it will contact the body at the top due to the arc followed by the suspension top arm So, after carefull measurements, I decided this would work, just! And after a bit of grinding and welding I ended up with two of these: This allowed my to use the same wheels but this time with a 10mm spacer, as opposed to 23mm! This reduced the scrub offset and has improved the driveability if the car. I would not say its all sorted yet, as I need to recheck all the gemoetry again and prob reset to 4 deg castor, 2 deg camber and 12ish SAI with 0 toe and test drive again, but its defo a step in the right direction. Thanks for all the help so far, you've saved me from certain insanity! Quote Link to comment Share on other sites More sharing options...
Tony Posted April 14, 2010 Report Share Posted April 14, 2010 Is the adjuster knob the closest part of the damper to the wheel?..... If yay why not just turn it 180d. Nevertheless it's good to read we were on the right track ( no pun intended ) and shows the importance of maintaining the lesser mythical scrub radius, now you know why i have a dislike of spacers Quote Link to comment Share on other sites More sharing options...
Paul XE Posted April 15, 2010 Author Report Share Posted April 15, 2010 Is the adjuster knob the closest part of the damper to the wheel?..... If yay why not just turn it 180d. I knew someone would say that!! Although it looks very much like that, the widest part of the coilover just above the adjustor is the part that causes problems, although I have turned them 180 deg as every little helps. Am planning to do a recheck on the geo and shake down run on sunday so will report back after then! Quote Link to comment Share on other sites More sharing options...
Paul XE Posted April 23, 2010 Author Report Share Posted April 23, 2010 Will be going up to Castle Combe to try out the new set-up, hopefully it will be loads better than before. Will post up a report and pics early next week. Quote Link to comment Share on other sites More sharing options...
Tony Posted April 23, 2010 Report Share Posted April 23, 2010 Quote Link to comment Share on other sites More sharing options...
Paul XE Posted May 2, 2010 Author Report Share Posted May 2, 2010 well, as promised. . . the report! To be honest, it could have gone better!! On the first warm up lap I lost the back end coming out of the chicane due to cold tyres and the back end too stiff (I think) which resulted in the bootlid flying off and landing on the track. After this I calmed down and got into my stride and I was really pleased with how the car handled and drove. I could not feel any real understeer under any condition and it pulled in a resonably straight line. The only thing that did sort of let it down was the back end. It felt quite loose and not really under control, and this was highlighted by the first lap incident and about half way though the session (lap 4-5) I went into a fast right hander in the wrong gear (4th instead of 3rd) at 95mph and the back end stepped out right the way around the corner! I think this is due to the back is set too stiff (450lbs springs, anti roll bar on its stiffest setting and 18psi in Toyo 888's) so I'm going to leave this alone for the next track day and see if it happens again, then soften the ARB, maybe soften the dampers if that doesn't work and if that still isnt soft enough I have got some 350lbs springs. I just have to be careful not to make it too soft so it induces understeer. Also, unfortunatly on the last but one lap I went to overtake another car on the right and just as I come up to go past he moved over and I had know where to go apart from the grass on the in-field at 100mph which resulted in ripping the front splitter off and bending two of the suspension arms on the front, so not a very happy bunny! Here are some pics that will hopefully speak a thousand words! Quote Link to comment Share on other sites More sharing options...
Tony Posted May 3, 2010 Report Share Posted May 3, 2010 Looking good.... There's some inertia loading at the front on the apex that's lifting the rear paw but i've seen a lot worse.... It looks really good, i'm pleased for you, ok you had an "off!" but that's racing... well done Quote Link to comment Share on other sites More sharing options...
Paul XE Posted May 3, 2010 Author Report Share Posted May 3, 2010 Thanks for the comments Tony, and thanks for all your help. A bit of advice and comfirmation of what I was thinking was right was what I needed to get the car handling like I always knew it could. I still think there is more to come with a bit of tweaking here and there, but the fundementals of the chassis has a good starting point. Just a couple of things to add though: 1) Would be thread be better off in a build diary section as I can carry it on as I change things here and there . . . . and 2) how come only Tony ever replies to my posts??!!!!lol Quote Link to comment Share on other sites More sharing options...
Paul XE Posted May 6, 2010 Author Report Share Posted May 6, 2010 Tony, quick question: What would be the effect of reducing the KPI on my set-up?? Say 4 deg Castor, 2 deg Camber, 10 deg KPI. I can't help thinking 13 deg is too much, although it is helping to reduce the scrub radius. Quote Link to comment Share on other sites More sharing options...
Tony Posted May 7, 2010 Report Share Posted May 7, 2010 10/ 13d KPI is very lazy, steering return would be slow and the scrub radius is suspect depending on the wheels offset...... Sprint/ hill and climb needs a low KPI in an ideal world, i would head for 5d Quote Link to comment Share on other sites More sharing options...
Paul XE Posted May 7, 2010 Author Report Share Posted May 7, 2010 Ok. I have another track day booked for the 29th of this month. I will leave things as they are for the min and try and tweak the rear end to increase grip without inducing too much understeer! After that I am planning to remove the subframe and carry out a couple of mods to it and make some jigs up for the suspension arms to ensure they all start off the same length both sides. Then I will try and get as close to the above settings and see how things go. I got a feeling I am going to strugle to achieve 5 deg KPI with the standard hubs though . . !! Quote Link to comment Share on other sites More sharing options...
Tony Posted May 7, 2010 Report Share Posted May 7, 2010 Yeah you will..... Have you got spacers fitted at the moment? Quote Link to comment Share on other sites More sharing options...
Paul XE Posted May 7, 2010 Author Report Share Posted May 7, 2010 Yeah you will..... Have you got spacers fitted at the moment? Yeah, 10mm ones giving a total wheel offest of 7mm. Its the lowest offset I can run without having to totally re design and make the subframe. The other option would be to make all new suspension arms (longer) moving the hub further into the wheel. Either way, an awful lot of work! Quote Link to comment Share on other sites More sharing options...
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