Commander Posted April 9, 2015 Share Posted April 9, 2015 I have a problem with understeer on my track car - initial turn in and general agility is great, but sustained corners lead to too much understeer. I'm going to dial in more camber because tyre wear is telling me I have nowhere near enough on the front and I already run more caster than standard. If this doesn't fix the problem though, next up is the springs. I'm currently running on 8 & 12 kg/mm springs that came with the BC BR shocks I'm running. If I stick with BC, the next step up in terms of shock stiffness is 14 & 20 kg/mm, but these rates are VERY stiff - race car stiff if my research is anything to go by. Does anybody have any views on this? The car is a stripped out e46 m3, it only gets used for track days, but I do have to drive it there and back. Quote Link to comment Share on other sites More sharing options...
Keyser Posted April 9, 2015 Share Posted April 9, 2015 (edited) How much dive are you getting as you brake and turn in? A lot you need stronger springs - also does she feel like she is trying to push over the front wheels as you turn in - almost a wallow feeling sort of bouncing to the outside of the corner - not sliding just before that point? I ask as if that is the case you may be suffering more from imbalance rather than soft springs, if you take all the seats. the spare and all the crap out of the boot you will have a nose heavy car - yes it is lighter so will go faster in a straight line and accelerate quicker but when BMW spent big bucks on RandD they balanced the car based on it having seats a spare or jack or whatever else in it. Of course if you took it all out and put a cage in you probably restored the balance (pun intended) Just the ramblings of a non BMW track car owner - food for thought maybe Edited April 9, 2015 by Keyser Quote Link to comment Share on other sites More sharing options...
RobPhoboS Posted April 9, 2015 Share Posted April 9, 2015 (edited) It might be worth asking this on the wheels in motion forum as well (they do road/track/drift set ups) Just a quick google brings up: Mid-corner (mid-phase) understeer • Excessive front tire pressure • Excessive relative front roll stiffness • Excessive front toe (in or out) • Excessive Ackermann steering geometry • Insufficient front dynamic camber • Relatively narrow front track width • Insufficient front wheel travel (car rolls onto packers or bottomed shock) • Insufficient droop travel (on non droop limited cars) Edited April 9, 2015 by RobPhoboS Quote Link to comment Share on other sites More sharing options...
Ekona Posted April 10, 2015 Share Posted April 10, 2015 What are your current geo settings? What number of clicks are you running on the dampers? Quote Link to comment Share on other sites More sharing options...
Commander Posted April 10, 2015 Author Share Posted April 10, 2015 Current geo is BMW standard which isn't anywhere near good enough for track use and I'm wearing the outside edges of my tyres too much as a result. New geo will be -3 camber all round, 0 toe at the front and a smidgen of toe at the rear; I'm hoping this will improve things a lot, but only time will tell. Shocks are about 3/4 of the way to full stiff, which seems fine as bump handling and initial turn are good enough for now. Tempted to run full stiff but I think what you gain in initial turn in response, you lose later through more understeer? Again, I need to experiment a bit with this. Tyre pressures are 32psi hot. ARBs are the standard M3 ones and the bushes are fine. BMWs are known to understeer so already running a square setup. Ackerman geometry is unchanged from factory defaults. Suspension / shocks don't feel like they bottom out on any of the stops. Car corners fairly flat, and by the looks of it never lifts the inside wheel. Front/Rear balance of the car is something I had been considering, but have resigned that I can't do much about it. A lot of weight has been taken out of the car, and all of this weight loss is from the windowscreen and rearwards - no carpets anywhere, no airbags, no trims, most of the dash is cut away, lightweight bucket seats, etc. I've deliberately kept the (very heavy!) battery in the boot to keep 'some' weight over the rear and apparently the CSL boot lid I'm running does produce downforce, but no idea how much. All that said, it doesn't feel unbalanced at all and I've only had the rear come round unexpectedly on me once so far. For Keyser's comments; I get some dive, but it doesn't feel a ridiculous amount. Mid corner it feels a bit wallowly, but not skippy or bouncy... just understeery. No cage yet, but it's on the agenda. Quote Link to comment Share on other sites More sharing options...
Ekona Posted April 10, 2015 Share Posted April 10, 2015 You'll want much more toe out at the front, at least 1.5 if not more. Tad of toe in at the rear like about 0.2, then as much camber as you can get at the front and the -3 at the rear should be fine. For the shocks, drop the rears back about 3-5 clicks. Very rarely do you ever want shocks the same stiffness front to rear on a track car, save maybe on a very wet day. If that doesn't sort it, I'll eat my hat 1 Quote Link to comment Share on other sites More sharing options...
Keyser Posted April 10, 2015 Share Posted April 10, 2015 Damn, I was going to say "what he said" referring to Ekona above but I'm not eating his hat I do agree with what he said though back should be a little softer than front, front toe higher - only other thing would be tyres, they can make a huge difference but you haven't said what you use? I know my 888's on track were so much better than my Yoki's, another thing to add into the equation 1 Quote Link to comment Share on other sites More sharing options...
RobPhoboS Posted April 10, 2015 Share Posted April 10, 2015 Last thing, where are you based ? Quote Link to comment Share on other sites More sharing options...
Keyser Posted April 10, 2015 Share Posted April 10, 2015 Last thing, where are you based ? Your not going to tell me the further north he lives the more under steer he will get are you ???? Quote Link to comment Share on other sites More sharing options...
RobPhoboS Posted April 10, 2015 Share Posted April 10, 2015 Last thing, where are you based ? Your not going to tell me the further north he lives the more under steer he will get are you ???? You read my mi... Naa, haha, just that I've had a few mates race their E46's in the 24hr Britcar etc So could point him towards the guy's that set their cars up. 1 Quote Link to comment Share on other sites More sharing options...
brillomaster Posted April 10, 2015 Share Posted April 10, 2015 haha im so glad you're asking all these questions now, will make our setup so much easier when we switch to federals next month! the new beemer currently has terrible understeer, we've got loads of camber on the front, but crap narrow tyres and no idea on the toe settings be very interested to hear how you get on once the toe and camber is adjusted. also an easy thing to try is tyre pressures - standard bmw tyre pressures have a ridiculously high rear, so maybe try something like 31psi front, 35psi rear when hot. but I suspect camber and toe angles will sort you out. Quote Link to comment Share on other sites More sharing options...
Commander Posted April 10, 2015 Author Share Posted April 10, 2015 Car is on Federal 595 RSRs at the moment - R888s are definately a grippier tyre, but I can't justify the cost at the moment, especially while I know my tyre wear pattern is fubar. I'm going to Abingdon on Friday 24th so I'm going to play around with tyre pressures, the new geometry and shock stiffness then and will report back. Thanks for all the suggestions guys. Rich Quote Link to comment Share on other sites More sharing options...
Commander Posted April 10, 2015 Author Share Posted April 10, 2015 Last thing, where are you based ? Didcot Quote Link to comment Share on other sites More sharing options...
RobPhoboS Posted April 22, 2015 Share Posted April 22, 2015 Last thing, where are you based ? Didcot Ok, well if you're still struggling, my good friend John runs: http://www.thorney.ms (only just up the road from you) If you do contact him, just let him know Rob with the 350z recommend you Quote Link to comment Share on other sites More sharing options...
Ekona Posted April 22, 2015 Share Posted April 22, 2015 Does John still have the dodgy dyno that copes with VXT power levels, but lets VX NA cars slip? /old VX.org thread Quote Link to comment Share on other sites More sharing options...
RobPhoboS Posted April 22, 2015 Share Posted April 22, 2015 Does John still have the dodgy dyno that copes with VXT power levels, but lets VX NA cars slip? /old VX.org thread Heh no idea. When was that ? Also, just to add that Wheels In Motion are happy to work/geo on a track only car if you can get it down there. Quote Link to comment Share on other sites More sharing options...
Ekona Posted April 22, 2015 Share Posted April 22, 2015 Years ago when I had the VXR, over on the .org forum there were some claims about John's dyno giving some dodgy power figures on the turbos, which he put down to the dyno slipping when running the NA cars but not the turbos I took my car to TMS though, had great service and I'd have gone back there again. Not cheap, but then good never is. Quote Link to comment Share on other sites More sharing options...
RobPhoboS Posted April 22, 2015 Share Posted April 22, 2015 I'll ask him just to wind him up in a mo Quote Link to comment Share on other sites More sharing options...
docwra Posted April 22, 2015 Share Posted April 22, 2015 Mostly been said but Id add that 20/14 springs are mental hard for anything this side of a Bentley, and if your rear is toeing in I doubt that would be helping either 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.