MIP Posted October 26, 2016 Report Share Posted October 26, 2016 My Z4 (3.0si) has always been quite a tramliney car since I bought it roughly a year ago. It's been modified by previous owners, different wheels (I'd say they fill the arches more so probably have more offset, and the rears are now staggered/wider from 235 to 265, keeping the same rolling radius) and eibach lowering springs, and undoubtedly it's going to be effected by those things, as nice as they look: I've done a few things so far, all have improved it but I'm not quite happy with it yet and want to do more. Here's what I've done - Reduced tyre pressure (from 36 to 31psi) - quite a big effect overall, going lower doesn't have much effect - Changed rear trailing arm bushes to powerflex - made the back end feel quite a bit less wandery - Changed rear tyres (to eagle f1 asymetric 3 from toyo t1s) - didn't have much effect but I needed new tyres anyway - Got the alignment done at a local place - Everything is in spec now, apart from front camber which can't reach spec due to the lowering springs Things are better, particularly at the rear, it felt unsafe on motorway before, it's stable enough now but does still get pulled about (tugging through the wheel) quite a lot more than my previous car (S2000), I'd like to improve it further. Things I'm thinking about doing: - Replace front-end bushes with powerflex - Replace suspension with BC racing or KW coilovers: Then I could adjust the right height up a fraction, not as height as stock but maybe 10mm up to get a bit more travel and maybe allow the front camber to get more in spec - Replace front tyres - Get WIM to customize the geometry to try and improve things I'd like some thoughts on the above, what I should prioritize doing, anything I'm not thinking of? Quote Link to comment Share on other sites More sharing options...
Rich Posted October 26, 2016 Report Share Posted October 26, 2016 What tyres do you have fitted? Some are terrible for tramlining. Quote Link to comment Share on other sites More sharing options...
MIP Posted October 26, 2016 Author Report Share Posted October 26, 2016 They're Toyo T1S or T1 Sport I think on the front (what was on the car when I bought it). Goodyear Eagle F1 asymmetric 3's on the back. Quote Link to comment Share on other sites More sharing options...
Rich Posted October 26, 2016 Report Share Posted October 26, 2016 The Toyos are a directional tread pattern and I have those on my MX5 with no tramlining at all. Asymetrical tyres are the worst for tramlining but if the F1's haven't made much difference it probably isn't the tyres. Although it might be an idea to swap the rear with the front for testing purposes, even though they're wider to see if it helps - I'm sure Tony will say if that's a good idea or not. Can you find out what the difference is in the offset? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 27, 2016 Report Share Posted October 27, 2016 Thanks for a detailed summery...... Changing the suspension will help the drive but not cure the complaint. Personally i would steer clear of the KW because they are more track orientated with harsh coil rates. Same could be said for rated ARB's bushings. Some questions now..... If you dab the brake can you feel a thump on the peddle Does the TL snatch at the steering If yes is it worse on bump The geometry you've had done can you display the numbers Quote Link to comment Share on other sites More sharing options...
MIP Posted October 27, 2016 Author Report Share Posted October 27, 2016 I'm not sure how I'd find out the diff in offset. I know they are apex arc-8's https://www.turnermotorsport.com/BMW-E85/c-348-apex-arc-8-wheels Thanks for the KW tip, maybe more worth looking at BC as they offer a choice of spring rates. It's a tricky thing to buy, I want to end up with good road comfort as I'm only on track rarely and not looking to break any records. I've never noticed any thump from the brake pedal, brakes feel good. The tramlining does snatch at the steering. Going down a motorway, you can often feel it tugging a little around the center left and right (even when not in the rutted slow lane). Prior to the rear bushes (I went for the softer road one's rather than the 'black' track one's), it felt pretty wayward over bumps, almost pivoting around your hips a bit like an oversteer sensation. It's much better now, but still tugging through the steering wheel. I will seek out the last geometry print out when I'm home (hopefully it's not been lost in the recent house move). Quote Link to comment Share on other sites More sharing options...
Tony Posted October 27, 2016 Report Share Posted October 27, 2016 I think that geometry report will revival many options...... When it was done was the car on lowering coils and if yes did they add weight in the car ( ballast ) Quote Link to comment Share on other sites More sharing options...
MIP Posted October 28, 2016 Author Report Share Posted October 28, 2016 I didn't see them do the alignment so not sure if weight was added, but yes the car was lower with the eibach springs (has been since I bought it). Quote Link to comment Share on other sites More sharing options...
Rich Posted October 28, 2016 Report Share Posted October 28, 2016 No caster measured as usual (it's grey), why do so many companies not measure it! Do you have the other report with all of the data, I think Tony would prefer that. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 29, 2016 Report Share Posted October 29, 2016 BMW and Hunter ( the machine ) didn't release the castor target because BMW measure it with the wheels off the ground which machines like Hunter and alike can't do. In this event we look for symmetry and yours is fine in fact the end figures are very good for once. The front lower wishbone bushings need to be inspected now. Quote Link to comment Share on other sites More sharing options...
Rich Posted October 29, 2016 Report Share Posted October 29, 2016 I never knew that but surely the data is vital for the overall picture? After all you always pick up whenever the caster hasn't been measured on any other car. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 29, 2016 Report Share Posted October 29, 2016 Well yes and no? The position has been measured but the target datum hasn't hence the numbers in gray shade, addition the castor isn't adjustable so symmetry is fine albeit in gray shade, Quote Link to comment Share on other sites More sharing options...
MIP Posted October 31, 2016 Author Report Share Posted October 31, 2016 Yea, thanks Tony, I think bushes probably make sense as a first port of call, given the mileage of the car and the effect it had on the rear. Powerflex offer options that are more standard: https://www.powerflex.co.uk/road-series/product-details/Front+Wishbone+Rear+Bush/1304.html Or a stiffer performance variant that adds '+0.5° of caster'. https://www.powerflex.co.uk/road-series/product-details/Front+Wishbone+Rear+Bush%2C+Caster+Offset/11515.html Any good reason I'd choose one over the other? Also what effect (if any) would my out of spec front camber have? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 31, 2016 Report Share Posted October 31, 2016 Any extra positive castor will add steering stability so i would go for them. The position of the camber combined with the extra rates the lowering coils add is fine in fact the chassis is set to a stable position with a hint of understeer. Quote Link to comment Share on other sites More sharing options...
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