Handling woes

[supermono]

I've got a little Peugeot 207 HDI 110, Does 120mph eventually and obviously not all that keen to go from slow->fast.

It does handle quite well though considering, but I really feel like there's a bit more cornerspeed to be had if only it didn't understeer.

I can control the understeer somewhat on the throttle and sometimes a little dab of the brake on the way in gets a reasonable "set" through the turn but ultimately I'm curtailed on very large roundabouts or long sweepers.

Question: Is it possible to adjust the standard geometry to improve front end grip? I don't mind if the limiting factor becomes the rears because I'd rather have a bit of oversteer bias than understeer.

SM

Edited by supermono on Wednesday 24th June 21:17

[GreenV8S]

If you increase the rear anti-roll stiffness you'll reduce the tendancy to understeer and move it back towards neutral. Go far enough and you will get oversteer. Best make changes in small steps to avoid getting caught out.

[GravelBen]

If camber is adjustable then a bit more negative camber should help.

[WhoseGeneration]

Or, drive within the limits of your vehicle.
I doubt there's enough geometry adjustment, as standard, in this one.
If that doesn't suit, change it.
For your own and other's sake.

[StressedDave]

supermono said:

Question: Is it possible to adjust the standard geometry to improve front end grip? I don't mind if the limiting factor becomes the rears because I'd rather have a bit of oversteer bias than understeer.

1) Try going slower...
2) You don't want an oversteer bias - at least hwat I;d term an oversteer bias because it has two main effects:

a) It slows down the response of the car
b) You run the risk of reaching the critical speed for the car and it becoming dynamically unstable - i.e. it'll spin in a straight line without the benefit of you doing something to make it so.

3) Geometry changes aren't going to make much difference (even if you could do them, which I doubt). Manufacturers have to allow for all loading conditions etc. in their design so having plenty of healthy understeer is the norm

4) You can change other components to get a better balance but:

a) Make sure its been designed by a proper ride and handling engineer rather than knocked up out of a parts catalogue. I spend a lot of time trying to sort out -ups created by others.
b) You'll be looking at new springs and dampers on each corner plus new anti-roll bars - t'wont be cheap.

[timskipper]

WhoseGeneration said:

Or, drive within the limits of your vehicle.
I doubt there's enough geometry adjustment, as standard, in this one.
If that doesn't suit, change it.
For your own and other's sake.

What a supercilious cock!

[supermono]

Thanks for the comments so far -- rofl at the driver slower comment, mate I think you're rather missing the point of the thread

I don't want to change anything out so it has to be an adjustment, and I don't want to start getting uneven tyre wear either so wild camber is out of the question.

I'm guessing I can't adjust the rear ARB stiffness but if I did wouldn't that reduce the grip on the rear? I'd obviously prefer to increase the grip on the front.

Camber wise, that sounds promising. Are there any specialists around the Surrey/Berkshire/Norfolk regions who would be able to tune the camber for me? Assuming it's even adjustable.

There's no need to change the car -- for what it is it's really a great little runabout just be nice to dial out a little understeer.

SM

[supermono]

WhoseGeneration said:

Or, drive within the limits of your vehicle.

Naturally, but I want to move those limits upwards a little so I can drive within them and go faster. See?

SM

[supermono]

StressedDave said:

supermono said:

Question: Is it possible to adjust the standard geometry to improve front end grip? I don't mind if the limiting factor becomes the rears because I'd rather have a bit of oversteer bias than understeer.

1) Try going slower...
2) You don't want an oversteer bias - at least hwat I;d term an oversteer bias because it has two main effects:

a) It slows down the response of the car
b) You run the risk of reaching the critical speed for the car and it becoming dynamically unstable - i.e. it'll spin in a straight line without the benefit of you doing something to make it so.

3) Geometry changes aren't going to make much difference (even if you could do them, which I doubt). Manufacturers have to allow for all loading conditions etc. in their design so having plenty of healthy understeer is the norm

4) You can change other components to get a better balance but:

a) Make sure its been designed by a proper ride and handling engineer rather than knocked up out of a parts catalogue. I spend a lot of time trying to sort out -ups created by others.
b) You'll be looking at new springs and dampers on each corner plus new anti-roll bars - t'wont be cheap.

Useful stuff, thanks very much.

SM

[GravelBen]

Not sure what geometry adjustment (camber, caster etc) is available on one of those but it can make a big difference. If (for example) you had front camber adjusted from -0.5° to -1° I would expect a noticeable improvement in front-end grip when loaded up mid-corner. It was certainly very obvious with the MX5, but I'd expect your shopping trolley to be less sensitive.

Any tyre/suspension fitter or mechanic that does wheel alignments shold be able to adjust it for you - whether they're willing to go outside manufacturers spec may be another question, not a problem where I am though.

Edited by GravelBen on Thursday 25th June 10:21

[supermono]

GravelBen said:

Not sure what geometry adjustment (camber, caster etc) is available on one of those but it can make a big difference. If (for example) you had front camber adjusted from -0.5° to -1° I would expect a noticeable improvement in front-end grip when loaded up mid-corner. It was certainly very obvious with the MX5, but I'd expect your shopping trolley to be less sensitive.

Any tyre/suspension fitter or mechanic that does wheel alignments shold be able to adjust it for you - whether they're willing to go outside manufacturers spec may be another question, not a problem where I am though.

Edited by GravelBen on Thursday 25th June 10:21

Ok, that's really useful thanks. We'll have to see if the adjustments can be made and if they are indeed as effective on POS like a 207 as on the other-worldly handling supremity of an MX5.

I'll definitely look into it.

SM

[thiscocks]

StressedDave said:

supermono said:

Question: Is it possible to adjust the standard geometry to improve front end grip? I don't mind if the limiting factor becomes the rears because I'd rather have a bit of oversteer bias than understeer.

2) You don't want an oversteer bias - at least hwat I;d term an oversteer bias because it has two main effects:

a) It slows down the response of the car

...never heard that before.. How is that so?


Id say experiment a bit with tire pressures. Pump the rears up more than the front and see what it is like.

Camber might help, but I doubt it would make that much of a difference on the stock dampers/springs, but I could be wrong. Id say spending money on roll bars and dampers ect.. would be too costly for the improvement possible.

Failing that, might be easier(and cheaper) just to buy a 205gti!

Edited by thiscocks on Thursday 25th June 11:51

[GravelBen]

StressedDave said:

supermono said:

Question: Is it possible to adjust the standard geometry to improve front end grip? I don't mind if the limiting factor becomes the rears because I'd rather have a bit of oversteer bias than understeer.

...
2) You don't want an oversteer bias - at least hwat I;d term an oversteer bias because it has two main effects:

a) It slows down the response of the car
b) You run the risk of reaching the critical speed for the car and it becoming dynamically unstable - i.e. it'll spin in a straight line without the benefit of you doing something to make it so.

...

Meaning oversteer bias in terms of dynamic instability (in the engineering sense)?

I expect you would still agree most cars have a long way to go from factory understeer through neutral balance to reach that point though, which often seems to be missed in threads like this (more so in GG than the AD forum) - dialing out factory understeer is generally making the car more neutral rather than an uncontrollable spin machine.

Edited by GravelBen on Thursday 25th June 12:37

[LeoSayer]

thiscocks said:

Id say experiment a bit with tire pressures. Pump the rears up more than the front and see what it is like.

That's what I'd do first.

[Get Karter]

You can't answer your question until you define when the understeer occurs, and how you drive round corners.

But I suspect it isn't a genuine question.
This is advanced driver baiting at its most obvious.

[supermono]

Get Karter said:

You can't answer your question until you define when the understeer occurs, and how you drive round corners.

But I suspect it isn't a genuine question.
This is advanced driver baiting at its most obvious.

What a funny post. Plenty of others managed to help me no end without needing to know how I drive round corners. And they know I'm not baiting drivers. But even if I was it's hardly an advanced attempt!

SM

[StressedDave]

GravelBen said:

Meaning oversteer bias in terms of dynamic instability (in the engineering sense)?

Yes

GravelBen said:

I expect you would still agree most cars have a long way to go from factory understeer through neutral balance to reach that point though, which often seems to be missed in threads like this (more so in GG than the AD forum) - dialing out factory understeer is generally making the car more neutral rather than an uncontrollable spin machine.

Yes, but IME (the thick end of a decade investigating RTAs and six years doing suspension development work amongst other things) it's very easy for someone with little knowledge of the subject to go too far. There ae sideline issues to do with roll damping which make 'just whacking a stiffer ARB on one end' fraught with unintended consequences. I've driven some 'race prepared' abortions over the years.

[Get Karter]

supermono said:

Get Karter said:

You can't answer your question until you define when the understeer occurs, and how you drive round corners.

But I suspect it isn't a genuine question.
This is advanced driver baiting at its most obvious.

What a funny post. Plenty of others managed to help me no end without needing to know how I drive round corners. And they know I'm not baiting drivers. But even if I was it's hardly an advanced attempt!

SM

Well their advice should perhaps be treated with caution, as there are different causes and solutions for entry, mid and exit understeer.

So, how do you drive round corners?

[StressedDave]

thiscocks said:

StressedDave said:

a) It slows down the response of the car

...never heard that before.. How is that so?

Something to do with the fact that under road type conditions the response is akin to a second order system and the natural frequency and damping is proportional to the amount of understeer. A car with 'lots' of steady-state understeer has a higher natural frequency but less damping which means it reaches the point of steady state quickly, but overshoots before settling down. The more the understeer, the greater the overshoot - hence why when you see a fishtailing car in the movies, it's always American <ducks>

As you reduce the amount of understeer you get slower response but less overshoot, so when you drastically reduce the understeer by fiddling with the ratio of front-to-rear roll stiffness, the car feels less inclined to turn in and takes a little longer to reach a set. Cars used in Autocross in the US tend to run a very understeer bias to get it to turn in quicker because the corners tend to be short duration and they don't really care about steady-state behaviour.

Driver training to make the best use of the cars characteristics is actually key here - which was what I was trying to convey in the post that made SM ROFL... My experience of other drivers is that they're trying to make the car turn quicker than it wants to and all the destabilising inputs tend to do is get you some turn-in at the expense of mid corner behaviour. Hence going a little slower so you can work with the car rather than complaining that it's abilities are outstripped by your god-given driving talent.

Given that one should be driving at a speed hwereby you can stop in the distance you can see to be clear and this is (on a dry road at least) well within the limit of adhesion, I'd suggest that rather than trying to fix the car, some money spent fixing the driver would be better spent.

[HellDiver]

Adding an aftermarket rear ARB on Astras and Fabias helps to bring them towards neutral. As they're pretty similarly set up to the little Pug, you could do worse than fit something along those lines.