Spacenut

Excellent! That has narrowed the choice down. In fact, of the two brands left the Toyo T1R isn't available with a 65% tyrewall profile (only 55% which is a bit low), so I think I will give the Vreds a whirl. The bonus is that I can source them locally Thanks again for the advice! Lauren

I could give it a go I suppose - they can only say no

Hi guys - from a previous thread you will know that my front tyres are worn unevenly and will require replacement before the next MoT. The Nova currently has Marangoni Vanto tyres all round, with 185/65HR15s on the front. I need the tall profile to maintain the ground clearance and I can't go any wider than 185 section without fouling the wheelarch. My Nova weighs approximately 900 kg with fuel and driver on board, distributed 46% front, 54% rear. I am looking for a high performance road tyre which provides good all-weather performance and maximum grip in spirited cornering. I've only got 95 bhp so I won't be shredding tyres, but I would like to exploit the chassis potential to the full. Given the constraints listed above, is there a tyre out there that fits the bill? The reviews I have read say that Pirellis are wrong at every level, only the mid-range Marangoni Verso is available in my size, or the Vredstein Hi-Trac, or the Dunlop SP Sport 300, Avon ZV3, Goodyear Eagle NCT5, Toyo Proxes CF1... I quite like the look of the Vredstein Hi-Trac, mainly because it is supposed to be good in the wet as well as dry. But really I haven't a clue when it comes to tyre choice. Help! Thanks! Lauren

Thanks H - not sure there is any magazine out there that would be interested in my paltry chassis engineering efforts "on the cheap", but thanks anyway! The balljoints pop off relatively easily mainly because I have to do it so often, although the Nylock nuts look a little the worse for wear as I use them as packing for the balljoint separator (saves me having to re-dress the threads on the balljoint). Lauren

OK, so things have been a little quiet again of late, so I thought it would be a good idea to bring you up to date on the latest happenings in the world of hurt that is the Green Machine. Being mostly about bump-steer I thought it warranted a separate thread. As you know, I managed to get the new spindles and alloy hubs installed before the AROC Christmas meal in December, and a break in the snow allowed me to get to the New Years Day classic car event at Elsted on January 1st. But in spite of the improvements, the front suspension still wasn't right, so a couple of weeks into the New Year I reversed the Green Machine back into the garage and put the front end back on blocks. This time I would get it right... So, armed with a piece of string I first tackled the wishbone geometry, rebuilding top and bottom wishbones ensuring all the joints had the minimum thread penetration (1.5 x thread diameter for the Rose joints I was using). The only exceptions were the upper wishbone front joints, which have the biggest influence on caster angles – I set these with an additional 3 turns in to pull the caster angles forward. Eventually I got both sides equalised at +2.75°, quite a lot less than the +5° I have been using to date. With everything lined up nicely, it was time to put the springs back on, but while I had the coils off I used my laser crosshairs to check the bump-steer geometry and couldn't quite believe how much I found! Lacking a proper DTI bump-steer gauge, this is the technique I used; The drawing board is used to draw three parallel lines, which represent the nominal ride height, full bump and full droop positions. The laser crosshairs are attached to the brake disc face (magnetic base), and the suspension moved through its travel on the scissor jack under the bottom balljoint. With the suspension at nominal ride height, I set the nominal line on the drawing board to line up with the laser line, then move the jack smoothly up and down. Not as accurate as a DTI, but I was able to take readings down to less than 0.25° - not that I needed that much accuracy to start with! The bump-steer was in fact a massive 2° of toe-out as the suspension moved through its range. What was even more galling was the knowledge that I was responsible for making it that bad in the first place, courtesy of a set of 5 and 6mm steel plate shims under the steering rack. And to cap it all, although the bump-steer is at least adjustable on the Green Machine, access to the steering rack mounting bolts is only possible with the cooling system drained and the fuel tank removed! The direction of toe change suggested that the rack was too high; removing the shims was therefore the order of the day. So, determined to do the job properly this time, I took a deep breath and drained the cooling system, removed the radiator and used the electric fuel pump to siphon the fuel into an empty C16 fuel bowser borrowed from my friend Sean. It's graduated in litres and US gallons, so I was able to determine that my reserve fuel capacity is a handy 11 litres after the gauge reads zero – not bad! With the fuel tank removed I could at last access the steering rack. As you can see, the rack itself is mounted on additional chassis longitudinals. About 15 years ago I determined that the steering rack (its a Cortina unit) needed to be raised up a bit, and welded on these pedestals out of 4mm steel plate. The top plate has captive nuts welded on underneath so that longer rack bolts can be used with spacers. It seemed like a good idea at the time... So, with 3 spacers removed (dropping the rack down a not insignificant 17mm), I bolted the rack down thus and repeated the bump-steer measurement. It was better, but alas still too large, and still in the same direction – the rack needed to be even lower... (Notice the slightly pink colour of the undertray below the chassis – that's the original red gel coat peeking through) There was nothing for it – I took the guard off my trusty Sealey angle grinder, put a fresh 5†grinding disc on and got to work. Two hours later, with my ears still ringing and a grinding wheel the size of a £2 coin, I had managed to remove the tops of the two pedestals, complete with captive nuts, and cleaned up what was left. The pedestals had been reduced in height by 10mm. Not wishing to have to repeat the exercise again, I securely ty-wrapped the rack onto the top of the plates and re-measured the bump-steer on both sides. This time the toe-out changed to toe-in on bump, confirming that I had indeed lowered the rack sufficiently. It was time to get the welder going... So, here are the new, improved mounting pedestals from the front... ...And from the side, looking through from the nearside front wheel arch. I know its very sloppy welding, but the thick metal allowed me to use a really hefty current setting and a fast wire speed, so they are at least strong enough. Also notice how the originally pink tinged undertray has turned charcoal black from all the grinding! I put several coats of Hammerite on the chassis and allowed it to cure for a week before finally setting the rack height. In the end, the best bump-steer geometry was obtained by using 3 x 1mm shims on the offside, and one 5mm plate plus a single 1mm shim on the passenger side. You can see the rack is not exactly level due to the unequal shimming. I can only assume that this unevenness is due to minor variations in the suspension pick-up points on each side. The final bump-steer figures, with the rack centred, were <0.25° toe-out on bump and droop, both sides. The very slight toe-out on bump means that if any effect manifests itself in roll, the outside wheel will tend toward understeer in a corner, which is of course safer than going into oversteer! You can also see my steering damper, which was based around the unit from a VW bus, together with a split alloy clamp which fits around the end of the nearside rack bar, just behind the track rod inner balljoint. I designed it to help counter the kick-back in the steering which (at the time) I thought was mainly due to the poor scrub radius geometry of the Cortina suspension uprights. (Hehe – there's news on that front as well...) I removed the front grille to show the modifications I have made to the stock undertray – I have fitted ABS brake cooling collectors either side of the nosecone, although these connect to the cabin ventilation system, and cut a nice radiused aperture for the radiator cooling. You can also see why I had to fit remote fluid reservoirs for my brake and clutch master cylinders! This is the view looking forwards. That's my radiator in the background, with the twin electric fans (the Alfasud has a single fan, I simply drilled and tapped the upper radiator flange to take a second unit, “just in caseâ€). I rarely have to use the fan override switch, even in the hottest weather. Anyway, back to the story. With the rack now (finally) in the right place, I bolted it down, re-measured the bump-steer (unchanged), reconnected the steering column UJ and clamped everything up, refitted the fuel tank, refitted the radiator and re-filled with fuel and fluids, refitted the coil-overs, put the car back on the ground and very gingerly went for a gentle drive around the block. This revealed that the tracking was all over the place, and the camber was a bit off as well, but the steering effort was markedly improved due to the reduction in caster angles. There was also no pull to the left, which has been bugging me ever since I rebuilt the suspension last year. A second journey last Friday settled the suspension and allowed me to determine how much camber adjustment was required. I removed both front wheels, centred the rack, refitted the steering wheel (it was one spline off to the left), popped the top balljoints off and made the necessary adjustments to the camber (1 turn = 0.25° camber change). With the car back on its wheels I used my trusty Longacre trammel bar to set the toe to zero. Job done A longer drive yesterday confirmed what I had hoped would be the case – a significant reduction in steering effort at all speeds, steering kick-back reduced by half, no pulling to the left and best of all, no instability under heavy braking (because the toe setting doesn't change with suspension travel). Its been a long hard slog to just get this far, but the car feels sooooo much nicer to drive, it really does feel like its been worth the effort! Lauren

That's pretty good. I haven't managed to do that yet, although I have set fire to my hair and put length of red-hot welding wire straight through my finger while trying to extinguish a fire around the fuel tank of my aging Barracuda. Its a wonder I'm still here really Hmm - maybe we could drift away together, on a sea of unresolved angles, in search of a life of perfect alignment Sorry, I just couldn't resist. I've never been propositioned by a chassis alignment specialist before. Its hardly the stuff of Mills & Boon, is it? I hope you don't do this to everyone who screws up their suspension alignment!?

Well, desperation actually, but thanks anyway I've owned a grand total of 6 cars since I started driving, and each time something has gone wrong, I have tried to fix it myself. Eventually I massed enough mechanical engineering knowledge to give chassis design a try. With the Nova I wanted a car that went as good as it looked, which needed a fair amount of effort, as you can imagine! And... well, I've made some mistakes along the way, as you can see Well, I've had a good day today - bump-steered both sides with the rack ty-wrapped down over the captive nut plates, and the characteristic is now the opposite to what I started with i.e. toe-out on bump - its now toe-in on bump, on both sides, so I know I have gone low enough. While the plates were located and all the bolts were in place, I firmly tack welded the plates to the chassis, then removed the rack and seam welded both sides. I like welding thick metal, I keep blowing holes in the thin stuff I managed to get a couple of coats of paint on the exposed metal, cut back the inner wing and reverse the lower front wishbone bolts, so that the threads don't chafe on the steering rack gaitors before packing up for the day. With a single 4mm shim under the OS rack pedestal, the bump-steer is as close to zero as I can determine with my crude measurement. The NS is a bit more interesting, with a 4mm shim it is still quite large, with a 5mm shim its better, and with two 4mm shims it has turned over and is toeing-out again. I need to do a bit more work on this one, but things are looking OK so far - I'm back where I thought I was last weekend Lauren

Unfortunately, yes I knew the rack height had to be raised, but I screwed up the positioning and then welded up the pedestals out of 4mm steel plate. That was 17 years ago - I have learnt a lot since then! This afternoon I turned a brand new 5" grinding wheel into a disc the size of a £2 coin... ...But the good news is, the pedestals are now low enough to eliminate the bump-steer. The actual change in height was less than 10mm in the end. I've been grinding, then re-installing the rack and securing it using ty-wraps, measuring the bump-steer, then taking the rack out and grinding more etc. I need to check it all again tomorrow, but if all is well I can tack-weld the captive nut plates into place, remove the rack, seam weld around the pedestals, paint, reassemble the rack, notch out the fibreglass inner wings where it fouls the gaitors, refit the fuel tank, refit the radiator and recharge with fuel and coolant. Easy life Lauren

Thanks Tony - I had a feeling it was still too large. I did think about some sort of rod end, most track cars use them and you simply ream out the taper in the steering arm... but annoyingly the optimum position for the track rod appears to be in the middle of the steering arm, rather than above or below it! (I've temporarily ty-wrapped the bare end of the trackrod directly to the steering arm on the upright, just to check) I'll take a deep breath and start grinding tomorrow - if I can retrieve the top plate with the captive nuts I can weld it direct to the chassis rail tops if I add some clearance holes. That should retain the chassis strength but drop the rack height by 25-30mm, which hopefully will be enough. At least I won't be leaving the job half-done (again), and it has been a bit embarassing having more bump-steer than a standard VW Nova Lauren

Hi guys - another update on the rebuild thread, because its been a while, and, inevitably, another question! I haven't wasted all the time I was confined to the garage in all that snow, I determined the chassis centreline, and attached some string to the chassis rear centreline. I'm really hi-tech The string allowed me to confirm the front lower balljoint positions each side when I refitted the wishbones. I calculated the minimum thread engagement for all the Rose joints and with the joints in place the lower wishbones were all in alignment. I then built up the uprights and top wishbones from that base, dialling in +2.75° caster each side, with zero camber at the nominal ride height. So far, so good. Then I had a brainwave - with the spring/damper units removed, and a laser crosshair attached to the brake disc face and pointing straight down, I could check the bump-steer geometry! It was TERRIBLE! And toe-out on bump. I have the rack shimmed with quite coarse (4mm thick) spacers, and I thought if I removed them all I might be able to get a better result. So last weekend I drained the cooling system and removed the radiator, drained the fuel tank and removed that (easier said than done, but needs must), removed the bolts holding the rack in place and took all the shims out... and then had to pack up because it was dark! This afternoon I had another measure. With no shims at all, the steering toes out by 2° as I move the suspension from full droop to full bump (about 6" of travel). With a single 4mm shim in place, the suspension toes out 3° over the same range. Bottom line - the rack isn't low enough I can drop the rack down further, but only by grinding off a pair of pedestals welded to the tops of the chassis rails. The pedestals include captive nuts to take the rack mounting bolts. I can drop the rack by an additional 30mm this way, but I would probably have to go back to bolting the rack directly through the chassis rails, which would require longer bolts. So, here is my question du jour - is 2° toe in bump too much, bearing in mind that it will probably reduce to 1° or so for normal road use (I haven't plotted the curve yet, just the extremes)??? Or should I get the grinder out? I don't intend on taking the fuel tank out again for a long while, so I am going to have to live with the consequences if I leave residual bump-steer in. It WILL be better than it was before, but will it be good enough? Your comments (polite please, it was my first, and so far only chassis design) would be very welcome! Lauren

Thanks guys - that's exactly what I'm aiming for. Trouble is, I have to drive the car to WIM, so I need to at least resolve the major issues first. Now that the thaw has set in I can pick up where I left off and re-measure and reset all of the wishbones in relation to the vehicle centreline. I'm pretty sure this will eliminate the pull. If there are any odd suspension or steer characteristics after that then I would have to address those after a session on the geometry rig, otherwise I am just searching in the dark... I just need to minimise the amount of work that will have to be done at WIM - I don't want to leave the site until all of the recommended changes have been made and the geometry re-checked, my plumb-bob camber/caster guage and non-level garage floor (not to mention my tape measure and spirit level) are just too crude to be relied on to effect accurate changes Lauren

Hi H - yes, that's me Lauren

You mean set up an asymmetric caster angle to alter the steering pull? I could do that, but there is clearly a difference in wishbone alignment on each side, so I thought I would sort that out before trying to tune the caster angles. I have approximately +3.5° caster each side - which side do I make more positive to compensate for a left pull? I'm guessing nearside front, am I right? Lauren

Hi Tony - how is this change in geometry made? Is it something to do with the length of the Pitman arm relative to the idler? I can't imagine any other way of doing it :angry: The performance version of my old Plymouth Barracuda was available with quick steering - all Chrysler did was supply the car with a longer Pitman arm! I'm not sure the idler arm length was changed at the same time, so that would affect TOOT wouldn't it? Of course the biggest problem with the AAR 'Cuda was that the back end was jacked up to make way for larger tyres, which messed up the roll characteristics. My European export model could easily outhandle them, not that I ever got the chance... Lauren

Just a quick update to this thread - no progress as I've been snowed-in for the last week :tongue2: ...But before the blizzard conditions set-in, I made a final attempt to take charge of the geometry situation. Using a combination of plumb bob and laser level, I've finally managed to establish a centreline for the Green Machine. I was therefore able to measure, with a reasonable degree of accuracy, the distance from the centreline front to each rear wishbone, and vice-versa for the front wishbones. Although both rear wishbone dimensions were within 2mm of each other (which is about the limit of my measurement uncertainty), the NSF wishbone is 10mm closer to the rear centreline than the OSF. So with the front wheels tracked at zero toe, the effective axle line is steered to the left. Unfortunately, that's as far as I got before the snow started falling. I need to get the car back on blocks in the garage - I will set up a reference for the lower wishbones on each side and build up the suspension again. Hopefully this will cure that pesky drift to the left I've been getting I managed to get to the New Years Day show at Elsted though. I haven't got my pictures developed yet, but my friend Sean (with the AMC Javelin) found this link which gives an idea of the huge diversity of vehicles that turned up! http://www.geograph.org.uk/search.php?i=10073747&page=7 Lauren

I know you are right - but there are limits to what you can do with a tape measure and a plumb-bob I just need to get the car into a state where it can be driven to the alignment shop and adjustments made without too much difficulty... otherwise I'll be at WIM for a week! Lauren

I think I may have found the cause. I measured the wheelbase each side today as accurately as I could and there is a discrepancy - the offside wheelbase is almost exactly 1cm longer than the nearside. Because I set the front tracking at zero during the rebuild (i.e. both front wheels parallel), but the nearside wheelbase is shorter than the offside, the front axle line is skewed to the left... slightly. I'm pretty sure that is the cause of the slow drift to the left. I checked the chassis triangulation after the accident, and I know that the distance between the NSR and OSF, and OSR and NSF frame brackets are exactly the same. So any difference in wheelbase is down to the adjustment of the joints in the wishbones. Looks like my offside wishbones are placing the spindle slightly ahead of the nearside, which is something I can correct without too much difficulty. See what I mean about all this adjustment? I can quickly swap over the front wheels as well, just to eliminate that as a contributory cause. The tyres are going to need replacing very soon anyway, the inner shoulders are close to the wear limit, although the rest of the tread is fine. Thanks for all your good advice, its greatly appreciated. All being well I am going to venture out tomorrow for some fuel before the VAT goes up, and a classic car show on New Years Day. Hopefully it will stop raining by then Lauren

Thanks H - yes, I had noticed I get better visibility of the instruments that way. Nova Nigel was so impressed, he used the same trick. Its a bit different You're right. Straight ahead is straight ahead. But if I let go of the wheel on a non-cambered surface, the steering just drifts to the left. Seems to go only so far before self-centring forces take over. Given that dimensionally everything else about my uprights was equal, I am assuming that the SAI is the standard factory 4.8° both sides. I'm thinking my wheelbase might be different on each side - if front and rear wheels are at zero toe, but the offside wheelbase is longer then the car will steer to the left. I'll check the chassis and wishbone triangulation again... Lauren

Thanks Tony - I'm glad the overall performance looked OK. I did video 2 for the other Nova club members mainly, but the driveby footage (particularly Nova Nigel's car) shows how the suspension deals with some of the bumps along that part of the road... I've just been out and re-shimmed the NSF top wishbone to correct the caster on that side. Both sides now +3.5° near as dammit. Steering still has a very slight pull to the left, I've eliminated brake and bearing drag, tyre pressure and caster. Camber may be slightly asymmetric (I was shooting for zero, NSF may be slightly positive, changing camber thrust), also the wheelbase may not be equal side-to-side (I compensated for this in the post-crash alignment, something else to check... if it ever stops raining ). I suppose the other possibility may be the tracking, I centred the rack and aimed for zero toe, but there may be some crabbing in the geometry somewhere... need to redo the chassis squaring measurements... That's the trouble with having Rose joints everywhere, its infinitely adjustable Lauren

They are? That's good. Subjectively they feel right too. I used the formulas in Allan Staniforth's Race and Rally Car Sourcebook. The corner weights were measured on the Green Machine prior to it getting on the road - 831 kg with reserve fuel and fluids, distributed 46% front, 54% rear. I whistled up a spreadsheet to factor in weight of fuel, driver etc., and used a target CPM of 120 - or 2 Hz. The spreadsheet allowed me to iterate the spring rates to achieve the desired natural frequency - 225 lb/in front and 325 lb/in rear, to give the resonant frequencies quoted above. I just had to do something, this was my third complete set of springs, at £30 a corner. Previous attempts at getting the spring rates right relied on pure guesswork and got me nowhere. I took some in-car video last year, and while I am not one to publicise my amateur efforts to a wider audience, the camera fixed its anti-vibration reference on the horizon, so you can see the movement of the chassis on the bumpy bits. The video shows that there is travel, and the damping is adequate... I used the same spreadsheet to calculate the spring rates for another Nova, this time all VW based, so the owner could decouple the front torsion bars and replace with coilover dampers. He was very satisfied with the resulting ride and handling too, although the video below was acquired when he had 120 lb/in springs on the front (target was 110 lb/in, but 1.9" diameter springs are only available in 20 lb increments). Onboard footage was hand-held in his car, but the ride still wasn't bad. Nigel eventually changed the front springs to 100 lb/in with a corresponding improvement in ride comfort. Both videos are rubbish, but it was my first attempt with a borrowed camcorder... Lauren

I see - hmm. Corner weight plus wheelbase. Not sure what units to use, or which corner weight to take, but I have calculated the natural resonant frequency of the Green Machine: the front suspension is 122.39 CPM, or 2.04 Hz, and the rear is 128.75 CPM, or 2.15 Hz. That's with 1 occupant and reserve fuel, i.e. the highest the frequency is likely to be. I don't know how those numbers tie in to DI, if at all. Lauren

100% human muscle powered. Cortina/Pinto manual rack, with a VW bus telescopic steering damper to take the sting out of the steering kick-back. I basically copied the design used by the Lamborghini Miura. Very true - I just tried to ensure the rack length was compatible with the wishbone geometry, to minimise bump-steer. The wheelbase is certainly different, which has made the already poor Ackermann worse... um, what's DI? Lauren

Cool The Vanto is a passenger car tyre, its just not a performance version. I needed a tyre that was no wider than 185 section, but with a 65% profile and a 15" wheel diameter. Those requirements usually eliminate all the serious rubber - they are considered to be a bit archaic nowadays Without a major chassis re-design I am stuck with the 90mm SR dimension. I've done 13,500 miles with it, I guess I can cope Lauren

Hi Tony - its not as bad as you think... I think. Here's what's available in terms of adjustment... (1) All of the Rose joints are adjustable, with a little bit of work. Both top and bottom wishbones have one at each end. These allow (within reason) the length of each wishbone to be altered, and the caster to be adjusted by adjusting one joint in or out relative to the other - for each wishbone (2) The outer balljoint is threaded and allows coarse adjustment of camber without having to remove the entire wishbone. (3) Because the inner top frame mountings were dropped, there was clearance either side of the joint, which allows axial movement of the top wishbone. I have used various thickness washers either side of the Rose joints to set the top balljoint position relative to the bottom balljoint, i.e. another form of caster adjustment. I used the same track dimension as the Cortina donor, so I am confident that the steering arm radii can be brought into line with the wishbone arcs - that is what they were designed for, after all. I just need to remove some shims under the steering rack to drop it down a bit. That's the next job on the to-do list. The static roll centre height is about 1.5" above ground level. It obviously moves around with body roll, and with the top wishbone half the length of the bottom the lateral movement would be quite significant but for one thing - the overall suspension travel is less than 2" under all operating conditions. So again, I'm hoping it will not be as bad as you think. Look at it this way - if you can sort this one out, everything else will be a walk in the park Latest news is that the spindles are holding up, but after re-checking the camber (as best I can), tyre pressures and ride height I am still getting a slow drift to the left. I measured the caster and the NSF is +4° while the OSF is only +3.5°, which might explain it. I'll see what I can do to equalise the settings side for side. Maybe I will try a lower caster value, the steering is heavy enough as it is - maybe I can reduce the steering effort at the expense of some directional stability... +2.5° perhaps??? Lauren

Thanks for looking anyway Tony. I just wondered if it was possible to eliminate the scrub radius geometry from the equation, as I have chosen to stick with this spindle/wheel offset arrangement. As you say though, its probably a combination of several factors, and 4,500 miles from a pair of tyres isn't considered bad these days - mind you, that is usually with FWD! Lauren