John Vine Posted May 30, 2005 Author Share Posted May 30, 2005 Another update.... I swapped the front wheels round yesterday and gave the brakes a good pasting. No difference, but not too surprising really as the tyres are the same make, compound and age, and are worn equally. I hope to hear more from Jon at Millwood soon. (I'm still puzzled by the unequal lift on jacking -- I'm sure there's a clue there.) JV Link to comment Share on other sites More sharing options...
shn7 Posted May 30, 2005 Share Posted May 30, 2005 At least that's another thing discounted as the cause. Steve. Link to comment Share on other sites More sharing options...
John Vine Posted June 1, 2005 Author Share Posted June 1, 2005 More.... I've just had a useful chat with Jon (of Millwoods), who's as puzzled as anyone. The prospect of a twisted chassis would be a first, it seems (no history of collision damage), so I'm now going to undertake a couple of (separate) experiments: 1. Swap the discs/pads over. 2. Adjust the NSR collars upwards (that is, tighter) by, say, three turns in stages. I'll post the results -- but don't expect anything for a few weeks! JV Link to comment Share on other sites More sharing options...
Mr Locust Posted June 2, 2005 Share Posted June 2, 2005 John, Having had the car on a brake roller and showing equal braking force I would expect to see no benefit at all from changing hubs and discs side to side. Have you considered that a dud spring may be giving this problem? i.e characteristic is not as linear/consistent as it should be. Whilst the spring platforms can be adjusted to compensate for any discrepancy in static corner weights a weak spring will not load the wheel up under braking as it should and with lower weight transfer the wheel will lock. Assuming that the spring platforms are set to similar (ish) positions swap the complete spring/damper assemblies side to side and see if the problem shifts. Alternatively, buy some new springs or borrow a friend's dampers for a bit. A pair of new springs are relatively inexpensive (even if it proves not to be them) once you start to consider that you may already be into buying specialist's time to sort these problems. Substitution of springs is going to be as cheap as trying to measure rates unless you have equipment available to test them yourself. A good indicator of the spring condition is that once removed the springs should have (almost) exactly the same free length as they are closed and ground at the ends. A weakened spring will generally be shorter. Ian Green and Silver Roadsport 😬 Edited by - Mr Locust on 2 Jun 2005 11:49:30 Edited by - Mr Locust on 2 Jun 2005 11:50:08 Link to comment Share on other sites More sharing options...
Myles Posted June 2, 2005 Share Posted June 2, 2005 I had hoped that flat-flooring would fix it Erm - just a thought - but won't the camber of the road affect the loading, or have you discounted this? I'd try to find out how much extra force it takes to lock both fronts - there *might* just be a small difference - in which case you are just chasing yourself into the ground. Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
John Vine Posted June 2, 2005 Author Share Posted June 2, 2005 Thanks for the feedback, chaps. Ian: Re the discs, I take your point. Maybe I should consider swapping them around only if all else fails. Re the springs, I hadn't considered them at all. I'll swap the units round as a first step. Out of interest, I've just measured the collar positions: OSF: Number of threads visible below lower collar = 7. Length of compressed spring = 130mm NSF: Number of threads visible below lower collar = 10. Length of compressed spring = 122mm Presumably I should reverse these settings when I swap the units over? Myles: Re camber, I tried to discount it by finding a clear, flat road and conducting my crash stops straddling the white line! Re braking force, yes, that's a good idea, and I'll investigate. I'm not sure I can recall ever getting the NSF to lock up, though. JV Link to comment Share on other sites More sharing options...
Mike Bees Posted June 2, 2005 Share Posted June 2, 2005 Try swapping the dampers over as well in case one of them is duff? This will bugger up your corner weighting of course... but if you just do it for the purposes of the test and swap them back without touching the adjusters then you'll be back to where you were. Mike Link to comment Share on other sites More sharing options...
John Vine Posted June 2, 2005 Author Share Posted June 2, 2005 Mike, Yes, that's what I plan to do (that is, swap the complete spring/damper units). But I also plan to reverse the collar settings to maintain the corner weighting -- or is that a bad idea? JV Link to comment Share on other sites More sharing options...
Myles Posted June 2, 2005 Share Posted June 2, 2005 Yes, it's a bad idea. You're still driving a RHD car... Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
John Vine Posted June 2, 2005 Author Share Posted June 2, 2005 Myles, I don't follow.... What I meant to say was that, after swapping over the spring/damper units, I'd adjust the collars so that they'd retain the same relative position as they had prior to the swap. (This assumes the units are identical in performance, of course.) Is that a bad idea, though? JV Link to comment Share on other sites More sharing options...
Mr Locust Posted June 2, 2005 Share Posted June 2, 2005 OSF: Number of threads visible below lower collar = 7. Length of compressed spring = 130mm NSF: Number of threads visible below lower collar = 10. Length of compressed spring = 122mm Have now got to a 'comfortable' stage in the evening so excuse me for thinking out loud with beer on board but... here goes. If we assume you have standard (ish) front springs. Say 140 lb/in. 8mm is approx 5/16" in old money x 140 = 43.75lb difference in the static loading of the front springs with more loading on the NSF (along the axis of the spring). Were you or your helpful assistant measuring the compressed length of the spring? i.e. were you sitting in the car at the time of measurement as you haven't stated. For information, can we also assume that there is more preload on the OSR than the NSR to maintain the diagonal weighting? Assume the car was laden, examine the front tyre friction to the road. As F=mu * N where mu=coefficient of friction (assume about the same for both wheels unless you like white lines) N= the normal reaction from the ground and also completely ignoring the weight transfer under braking to keep it simple - surely the more highly laden wheel (nsf in this case) will tend to generate more friction and hence be less prone to locking under the condition of the limit of friction. So is the penalty for achieving a 'flat floor' setup?? Can we also assume that the more lightly laden NSR wheel is closer to locking up than the OSR wheel but that this doesn't show due to the brake bias being insufficiently towards the rear to lock the wheel? (Assuming no LSD operation) DISCUSS. (Myles- I make these suggestions as the basis of a potentially interesting discussion on what is happening and not where the driver sits 😬 Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
John Vine Posted June 3, 2005 Author Share Posted June 3, 2005 Food for thought here, Mr L. I'll discuss it (with myself, who else?), and let you know what conclusions we come to! JV Link to comment Share on other sites More sharing options...
Nick Woods Posted June 3, 2005 Share Posted June 3, 2005 I suspect Mr L is on the right track, but.... were those compressed lengths taken with you in the car ? If not then I'd expect the OSF to compress more than the NSF with you in it. If you werent in it I'd get someone to re-measure while you sit in the car and then repost the results so we can all think about it a little more Nick Red and Black 1.6K supersport visit Carrotland.co.uk Link to comment Share on other sites More sharing options...
Mr Locust Posted June 3, 2005 Share Posted June 3, 2005 What is normally taken as a process/method for flat flooring from scratch then? Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Mr Locust Posted June 3, 2005 Share Posted June 3, 2005 here was the thread I was trying to recall but the link doesn't seem to work any more. Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Nick Woods Posted June 3, 2005 Share Posted June 3, 2005 This is how a few of us have been doing it, based on threads on here and other information we've found elsewhere. We start from the assumption that castor and toe-in are already correct although one of us does have a camber gauge so we do check that first. Either get the driver in the car, or ballast to the same weight (4 bags of homebase builders sand and a couple of cans of oil in my case 😳) We prefer the ballast technique as the driver can assist in the setup and we've all learnt more as a result of doing it this way Get the ride heights as close to correct as possible , with 15mm front-rear rake Put the car on the scales, still ballasted, and fine-tune the settings to get the cornerweights correct. We have a spreadsheet to help us with this, which we've developed ourselves from an earlier spreadsheet we got via blatchat, although its quite a straightforward calculation anyway, once you understand it (I'll post a link to it when I can find it) This is where it gets less clear - some people prefer to set the front weights the same to get even braking while others prefer to get the diagonals as even as possible for best handling. The diagonals wont ever be equal without a passenger because the drivers weight is offset. None of us are good enough drivers to determine whether 'equal fronts' is better or worse than 'best diagonals' and in any case we've found the difference is only a few kg , e.g for my car its 'diagonals' 'equal fronts' FL FR FL FR 139.3 147.2 143.3 143.3 RL RR RL RR 177.2 187.3 173.3 191.3 which as you can see is only +- 4Kg at any given corner anyway Nick Red and Black 1.6K supersport visit Carrotland.co.uk Edited by - Nick Woods on 3 Jun 2005 21:27:08 Edited by - Nick Woods on 3 Jun 2005 21:29:54 Edited by - Nick Woods on 3 Jun 2005 21:39:43 Link to comment Share on other sites More sharing options...
Nick Woods Posted June 3, 2005 Share Posted June 3, 2005 Roger Swifts article which includes the basic maths for the 'diagonals' calculation is here. The 'equal fronts' calculation is even simpler :- Take the original FR + FL weights and divide by 2 to get the new weight for each front side You cant move weight from side to side , so the new value for the RR has to be (original FR plus original RR) minus new FR and the LR is (original FL plus original RL) minus new FL Easy once you know how Nick Red and Black 1.6K supersport visit Carrotland.co.uk Link to comment Share on other sites More sharing options...
Mr Locust Posted June 3, 2005 Share Posted June 3, 2005 John seems to be instinctively leaning towards the equal fronts based on the braking at the limit scenario. Off to see what was in Staniforth's Race and Rally Car Sourcebook..... Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Mr Locust Posted June 4, 2005 Share Posted June 4, 2005 Nick, Race and Rally Car Sourcebook puts it slightly differently (simpler) but seems to be the same result. Add all four wheel weights to get the total. Add the fronts to get the front rear split and express the percentage as a decimal. So for your example 55% front > 0.56 Likewise the rears > 0.44 Likewise the N/S wheels > 0.486 Likewise the O/S wheels > 0.514 Then just multiply the total weight by the two factors which apply to that corner so Target NSF = total *0.56*0.486 I don't know what scales you used but your figures are Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
John Vine Posted June 5, 2005 Author Share Posted June 5, 2005 Nick,were those compressed lengths taken with you in the car ? If not then I'd expect the OSF to compress more than the NSF with you in it. If you werent in it I'd get someone to re-measure while you sit in the car and then repost the results so we can all think about it a little moreAh, thanks for pointing this out! My original measurements were indeed taken without me in the car. I've just remeasured (or, rather, my wife has) with me in the car: OSF 123mm (was 130mm) NSF 120mm (was 122mm) Ian,A relatively simple test could be carried out just by equalising the front spring heights and seeing what happens under harsh braking. The main thing is that you have taken a before reading and can reinstate it later if you don't like the result.Good thinking. Many thanks to all of you for your most helpful and knowledgeable input. I'm shortly off on my hols but, on my return, plan to try out your various suggestions. Bearing in mind that this will be a purely empirical exercise (I've no scales), I think the batting order will be: 1. See how much extra braking effort is required to lock the NSF. 2. Tighten the NSR collars incrementally by up to, say, three turns, so as to increase the loading on the opposite (OSF) corner. 3. Equalise the front spring compressed lengths (again, incrementally). 4. Swap front spring/damper units around. 5. Measure the free length of both front springs, and renew if different. 6. Renew both dampers. 7. Get chassis tested for alignment. 8. Sell car to non-member! 9. Order CSR. JV Link to comment Share on other sites More sharing options...
Mr Locust Posted June 5, 2005 Share Posted June 5, 2005 Not trying to find a way to skip to 9 yet then? 😬 Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Nick Woods Posted June 6, 2005 Share Posted June 6, 2005 I'm at the limits of my knowledge about suspension theory here, but I'd expect the compressed length to be shorter if the spring is carrying more weight. I might be wrong about this though so dont take it as gospel. I'm hoping to re-weigh my car this week so I'll do a little experimenting to see if I'm correct. I'd be careful about adjusting just one platform in isolation - IMHO you'd be better to adjust both NSR and OSF by a small amount rather than just the NSR by a larger one. The effect is the same, adjusting one platform up increases the weight on it and on its diagonal opposite at the same time, and reduces weight on the other two diagonals. Dont forget to count exactly how many turns you give each platform so that you can reset it back again if you need to. A better solution would be to try and get the car weighed with you in it, easier said than done though. Nick Red and Black 1.6K supersport visit Carrotland.co.uk Link to comment Share on other sites More sharing options...
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