I'm enjoying an old age brain fart and can't remember which way round it works on a fwd car! Googling just confuses me further!! So if I increase my rear track (for sake of argument) what will that do in regard to under/oversteer? TIA Thicko
Increase understeer. The roll moment has a wider track footprint to exert itself over, force x distance. Cue more theoretical grip.
so a wider front track, could in theory increase oversteer? just thinking as I have spacers on the front and not on the rear for since my last suspension revision on the mk1, and might of picked up ever so slight oversteer
it should in theory give understeer,but like all suspension mods it depends on driving style and the car in general (weight bias etc..) Having said that my mate & i have tried this same mod in the last week & at Cadwell on wednesday,it didn't give noticable understeer but did give stability with less turn-in. I guess every one and their cars are different along with driving styles so you have to think things out and give things a try "IF" you think they will improve your car or match/suit your style or car. No RIGHT or WRONG here,its what people feel "comfortable" with or prefer.
If more front grip can be generated, this'll introduce oversteer. So if spacers generates more grip (in theory they will, but there are ET effects to be considered) it should shift the balance of the car rearwards (all in theory mind).
small track changes can make a surprising difference, I did one sprint without my spacers on the back and it felt a bit tail happy, so for the next run I put on 5mm spacers on the rear and it transformed into huge understeer!
I have contradicting information.............. I was messing around with the mk1 on Saturday so went for a short drive around some private roads, loading up the suspension through moderate speed bends and provoking low speed understeer on tighter corners. I mentally noted the feel of the car into, through and out of the corners. I then fitted 10mm spacers to the rear wheels so widening the rear track by 20mm. No other changes were made in this test. I then proceeded to replicate my earlier route with some surprising results! The ride has become a bit more compliant over uneven surfaces but that was expected due to the longer lever forces across the rear axle. But interstingly the turn in became more responsive. The car would turn in earlier with less delay and now the backend felt like it was coming round more too but not in the way harder rear springs would. I started to push harder and found the chassis now had more Oversteer than without the spacers but without feeling dangerous! The rear wasn't loosing more grip but the car just felt much sharper and held it's line with much less steering effort than before. On the low speed corners, I could accellerate harder before loss of grip and on high speed corners, the car felt perfectly planted but very precise to input. Remember, this is all relative to how my car behaved before the spacers were added. So given this, I started to think about why this might be happening and with a bit of reading came to some info of what might be happening. Read posts #18 to #25 http://www.ten-tenths.com/forum/showthread.php?t=92085&page=2 I will have to see how this effects things on a track as this will ultimately determine if the spacers do actually help. Private road tuning hasn't let me down yet... Gurds
I think any change to the beam's ability to twist is limited since the length of the lever has not changed, even if the rotation point is further outwards. So the compliance change doesn't have a straight logic. (I'm not disputing your feedback, just saying I can't explain it, and the answer theoretically lies somewhere else). I wonder what effect the roll stiffness in the beam is having as the track is widened. I'm guessing the roads were damp? If the car is turning in quicker, requiring less steering effort, and enabling you to get on the power earlier, then that has to be progress, at least on corners of that sort. It's really interesting to think about this, albeit rather inconclusively. The ten tenths stuff isn't that clear (on a one-read, anyway!).
Just trying to get some thought and input in this. I am still trying to make total sense of what has been said in the link thread. The conclusion seems to be that the axle that is widetracked will induce more understeer at that end. Just thinking out aloud. At the rear, by spacing the wheel out, hasn't the tyre contact point to the axle pivot gotten longer? Thus longer lever? Maybe I'm wrong. The roads were 100% dry & warm when I went out in both setups on Saturday. Today, driving the car to work in wet conditions shows the car to be good still. Front still turning in better and feels confident and stable although not driven with as much aggression due to being busy public traffic roads. Gurds
Briefly going back to the base theory is force x distance. Put a force in the side of the car at each end (at C of G height) and which end moves first? Clearly a nonsense in isolation as the car isn't moving yet, but in principle a set of rear stabilisers of + 1 metre will reduce the effect of any lateral force, as a car leans on its suspension before it loses grip. Onto reality and the car turns in on the nose, dampers & springs do what they do, car turns, weight shifts rearwards.... and then the litmus test. Then the rear beam, complete with roll stiffness, comes into play. The beam is resisting efforts to twist, increasing grip at the rear wheel. The track is wider, scribing a wider arc than without spacers, binding in the beam as before to generate roll stiffness and grip. It could relate to the front end, if the effect of the beam's stiffness / increased track allows the front to pitch harder as the back resists? - and that's as far as I can take it! Bounce thoughts!
more rear arb shifts balance away from understeer therefore, in theory, if you spaced out the rear, wouldnt you gain rear roll resistance and therefore less understeer??
there's loads of other factors like suspension ratio, castor/KPI etc, roll center heights that will complicate things but fundamentally a wider track = less load transfer (on that axle) and therefore more grip on that axle. One thing to remember, track change has a different effect to spring rates and ARBs. ARBs reduce roll by increasing spring rate and both these and springs will affect the rate of load transfer, where track change changes the actual magnitude of load transfer.
True, but the force acting on it has changed.. as you said, force x distance, meaning the ARB's properties would kick in sooner and also have a more pronounced effect on the rear beam. Suspension may be softer due to the added distance, but I'd also by the same token imagine hte ARB would become more efficient? Just a thought
from VW_Singhs comments it sounds like what you hear stock hatch people talking about... 'controlling roll from the rear'. reducing roll at the rear will also reduce the roll at the front to some extent, this will help front end geometry and might be giving you better front end grip. I'd suggest that it might oversteer more due to gaining some front end grip, rather than anything to do with the rear ARB or beam.
Widening an axle effecively reduces the spring rate by increasing the lever length from tyre to the COG (Center of Gravity) across that axle, not ARB lever length. Well thats what I am seeing in my head. So by widening the axle, the lever to the COG across the axle from the tyre has become longer thus the improvement in ride and possibly the reduction in total load transfer. And this reduction in load trasnfer is why you can now carry more speed because the tyre saturation level has been shifted. But now the arc the axles take through a corner have changed so maybe this affects the understeer/oversteer characteristics? Am I talking b)*&%x? Gurds
Mec82, I did what I could (to my knowledge) to maximise front end grip with KPi, castor, camber, toe and then I balanced the front/rear with arbs/springs. Up until now I had only widened the front track and not touched the rear as I was always under the impression that widening the rear would induce more understeer. However, I kept seeing race bred/inspired cars that have widened rear track along with the front winning races (and yes, FWD golfs too). So I thought there was no harm in playing around with it. And low and behold, the car turns much better with loads of grip and stability (relative of course). The car had a very slight understeer before that I could mostly dial out with damper settings but not enough without making the ride significantly worse. The slight widening of the rear track just seems to have worked in my case and I am trying to work out why rather than just living with it. Gurds
I see where you're coming from, except the ARB bit. It's attached to the rear beam, so it MUST get it's force from somewhere, and it aint the pivot points, ergo the only other place is from the widened rear track, and by widening hte track it's actually become more efficient. Add in my bit to your bit Gurds, and I reckon that sounds at the very least somewhere close to an answer.
And it looks like you've done a good job from the vids but a mcpherson front suspension is always going to have issues with roll, even with a lot of static camber and castor. Thats where I'm trying to help out, I did some vehicle dynamics at uni and I've got some stuff from my projects including a spreadsheet I made for working out load transfer etc. If I can host it somewhere I'll post it up
