How to reduce to understeer? - What suspension mods/tyre pressures work best?

Gibbo

Gibbo

Gibbo

OcUK Staff
Joined
17 Oct 2002
Posts
39,414
Location
OcUK HQ
HI there


After doing so much work on my Mustangs suspension setup, I have got the rear-end so grippy its now really showing up the fact it has more of a tendancy to understeer.

Let me explain, roundabouts in the wet, take it fast with smooth throttle and the front-end will loose grip causing it to run ride, the steering communicates this before it happens and when it happens it is controllable by either easing off gently and steering through it or doing the brave thing and applying power so it turns into oversteer.

However to best improve corner speed it would be best to try and cure this problem, admittedly you do have to go rather fast for it to happen and tend to only see it in the wet.

Still first question, could I dial this out with different tyre pressures?

At the moment 34psi all round, would a lower tyre pressure in the front help things? Bear in mind the front wheels have lower profile tyres as standard.

Secondly what suspension work can help dial out understeer?

Thirdly I assume if I was to loose weight from the front end that would help too?
 
Stiffer front end will = more understeer. Stiffer rear end will = more oversteer.

You can choose between ARBs, suspension or tyre pressures to change the balance around. Not having driven the car myself its hard to say for sure.

Seeing as you say it is communicated through the steering but does not react at the same time i would suggest that you don't want to make the front any softer as the delay will be even worse. So as such i would maybe stiffen the rear and loose a couple of PSI on the front tyres.
 
Basically what GunderscoreD said and you can also try a little toe out at the front.
 
Jonny69 said:
Basically what GunderscoreD said and you can also try a little toe out at the front.
Click to expand...

Would that not change the cars entry into the corner, then depending on the castor angle change through the corner give more understeer?

I was under the impression that toe in gave better front grip coming out of a bend and a little understeer going in.

Neutral toe, neutral.

Toe out, more agressive turning in and little less grip coming out.

Obviously it depends on the rest of the suspension.

Nobody in the states got a suspension setup they used on track or anything?
 
I know less about toe and geometry than suspension setups by my understandings are as follows:

On the front, toe-out (negative angle) helps turn-in and lateral grip.

On the rear you want toe-in to help stabilise the car.

Too much toe-in causes understeer and excess tyre wear. I don't really know how to quantify 'too much' though.


Whilst we are on more specific tuning points you could also increase the font camber and/or decrease the front ride height. However i think we are getting ahead of ourselves now on a road car setup.
 
Hi there


I am no suspension expert, but the rear-end of the car is pretty much as stiff as its going to get, infact the rear is like its on rails.

The front-end understeer is really only seen in wet conditions, in the dry the speeds required to make it apparent are far too high as the car does have very high levels are grip as one would expect from 275 width section tyres.

So what is toe, how does one adjust it?

Seems easiest solution to try at the moment is to drop the front by about 2psi each, giving the fronts 32psi and rear 34psi.

If it helps the gurus on here help me any more the car weighs circa 1550-1600kg, obviously more with me in it. :D
Weight distribution is circa 53/47, so there is a bit more weight over the front wheels....


If want went extreme say with 28psi in the front and 34psi in the rear how would one expect that to effect handling characteristics of the car? I am not gonna do this am just interested to help me understand how different tyre pressures affect the handling of cars.
 
you could play aobut with pressures

or space out the rear end if possible. stronger rear arb (effectively making the rear grip less) or softer front springs.

played about with geometry much?
 
Toe adjusts the degree the front of the wheels angle towards or away from each other. Adjusting it means a trip down to a geometry specialist or if they are happy to change from the normal setup written down in their books where ever you get your tyres fitted can do it.

If you were silly and took all the pressure out the front and blew the rears up like a balloon, you would have to little grip at the rear and you would expect the car to oversteer. Moving the pressures a few PSI here and there wont make huge differences it is more a very fine tune. But if the car is handling well as it sounds then this is most likely the stage you are at anyway. Problem with changing the pressures is you are going the effect the tyre wear which maybe something you are cautious of.

Also don't forget making changes for the wet could negate the currently very good handling characteristics of your car in the dry.

Sounds like the car handles very well and has a good setup and balance. Less speed on the way into the corner and feeding more power on as you go through would have the same effects........?
 
G_D said:
Toe adjusts the degree the front of the wheels angle towards or away from each other. Adjusting it means a trip down to a geometry specialist or if they are happy to change from the normal setup written down in their books where ever you get your tyres fitted can do it.

If you were silly and took all the pressure out the front and blew the rears up like a balloon, you would have to little grip at the rear and you would expect the car to oversteer. Moving the pressures a few PSI here and there wont make huge differences it is more a very fine tune. But if the car is handling well as it sounds then this is most likely the stage you are at anyway. Problem with changing the pressures is you are going the effect the tyre wear which maybe something you are cautious of.

Also don't forget making changes for the wet could negate the currently very good handling characteristics of your car in the dry.

Sounds like the car handles very well and has a good setup and balance. Less speed on the way into the corner and feeding more power on as you go through would have the same effects........?
Click to expand...


The way its setup at the moment I suppose is good because its safe, it does not all of a sudden just loose grip and fall off the road, I can feel when the front-end grip limit is reached and can either hold it there or push into it more causing the car to run wide or give to much throttle to provoke oversteer.

What I would like to achieve is improving the grip at the front end because by increasing the grip on the front-end the result would be great corner speed, especially in the wet.

My car does have heavy duty upper mounts fitted which allows upto 1 degrees of camber adjustment in either direction. At the moment they are set to maximum to give the front wheels this stance / \ hopefully that makes sense. However the front wheels dont have that kind of angle its very minor and front tyre wear is still even. Should I keep them at that setting or try adjusting the camber on the front so the stance is more like | | thanks for any help.
 
Your current camber angle is negative camber and that's what we want. Keeping them at their maximum as they currently are is the right thing to do.

My only worry now about improving the grip on the front is that the rear is going to either need to become very stiff and thus perhaps twitchy and more uncomfortable than is necessary on the road. Equally making the front softer will slow the cars reactions and responses down, which is something that i wouldn't personally want to do especially if you are having the slight delay you mentioned already.

One possible idea to consider would be to have different tyres front and rear, having softer tyres on the front but that is maybe a crude answer that could encounter other problems.

Maybe next bet is to go and get a custom geometry setup done from somewhere. They will, you would hope, know more than we do and could talk you through what they can achieve once they have seen how much adjustment you have.
 
Buy a car that handles decent in the dry to start with is my advice, aka a non us made car they might have the grunt but thats about it

*edit* i love the mustangs but they are what they are, and there certainly no M3 or 911
 
Last edited:
Bradmax57 said:
Buy a car that handles decent in the dry to start with is my advice, aka a non us made car they might have the grunt but thats about it
Click to expand...

Ahh ha, yes that was it! That's what i was trying to remember about toe and camber. If you have some understeer you need to buy a different car....
 
G_D said:
Your current camber angle is negative camber and that's what we want. Keeping them at their maximum as they currently are is the right thing to do.

My only worry now about improving the grip on the front is that the rear is going to either need to become very stiff and thus perhaps twitchy and more uncomfortable than is necessary on the road. Equally making the front softer will slow the cars reactions and responses down, which is something that i wouldn't personally want to do especially if you are having the slight delay you mentioned already.

One possible idea to consider would be to have different tyres front and rear, having softer tyres on the front but that is maybe a crude answer that could encounter other problems.

Maybe next bet is to go and get a custom geometry setup done from somewhere. They will, you would hope, know more than we do and could talk you through what they can achieve once they have seen how much adjustment you have.
Click to expand...


Hi there

Yep thats it negative camber and they are set to maximum. I shall give the tyre pressure thing a go. Will drop the fronts 2psi below the rears and see how it affects things.

At the moment the car is very re-active to any steering input, infact I've never driven a car with faster or more direct steering but it is heavily modified to make it that quick and sharp.

Only last thing that will definetely improve matters is the front tyres will be due for a change as the rear now has brand new tyres on it and am still on the older fronts so this is an obvious answer as to why its a lot more noticable in the wet but even when car is on new tyres all round its always had a tendency to understeer.
 
This is just a guess because obviously I can't make a proper judgement without seeing you drive.

Could it be possible that you are trying to take the corner too fast, so that no matter how good the suspension set-up is it would understeer anyway. You may just be trying to go round the bend faster than physics allows for.
 
Bradmax57 said:
Buy a car that handles decent in the dry to start with is my advice, aka a non us made car they might have the grunt but thats about it

*edit* i love the mustangs but they are what they are, and there certainly no M3 or 911
Click to expand...

HI there

Your either a troll or have no idea of the previous cars I have owned. Simple answer is the car is setup and modified, it handles better than an M3 and yes I have owned an M3 CSL and the CSL was a better handling car than the Mustang, but a CSL is a night and day better handling car over the normal M3 and I have driven several.

Driven Porsches, owned S2000, R34 GTR's and driven some of the best sub 60k cars Europe has to offer and sorry I choose to take the Mustang because whether you like it or not it handles better than most would believe and my god its a whole lot more fun to drive oh and then yes it does indeed have that grunt and rarity.
 
A bit more static castor at the front will also improve mid-corner bite, by increasing the amount of negative camber you will be acheiving whilst steering.

There are so many variables, it depends on how much you want to spend, and what exact handling charecteristics you want.
 
Gaverick said:
This is just a guess because obviously I can't make a proper judgement without seeing you drive.

Could it be possible that you are trying to take the corner too fast, so that no matter how good the suspension set-up is it would understeer anyway. You may just be trying to go round the bend faster than physics allows for.
Click to expand...

HI there

That is indeed a possibility, The R34 GTR I had for a while understeered even more at lower speed and that had 4WD so it is indeed a possibility.

Believe it or not its pretty much just one roundabout its just one I take everyday but saying that nothing has ever kept up with me around it whether it be wet or dry so maybe I am trying to defy the laws of physics as I do have my mad moments but at the same time if I can give the front-end more grip then it would be nice to do so.


paradigm said:
A bit more static castor at the front will also improve mid-corner bite, by increasing the amount of negative camber you will be acheiving whilst steering.

There are so many variables, it depends on how much you want to spend, and what exact handling charecteristics you want.
Click to expand...


Just a bit more front end grip, which getting new tyres will certainly help with, but was just wondering if different front/rear tyre pressures would help more and maybe some other suspension mods to the front or new setup.

Dont get me wrong I do love how it drives, guess I am just trying to tweak that little extra of it now to pretty much make it perfect.
 
Thinking about it, you could also change the ackerman. Giving the outside wheel a tad more lock than the inside wheel seems to be the way forward for most race teams.
 
You must log in or register to reply here.
Back
Top Bottom