understeer issues

[marinetowing]

Hi guys,
had another track day yesterday and managed to better my best time by a second but am experiencing bad understeer..so much so that i have nearly ruined a new pair of semi slicks...a lot of this is possibly caused by my driving style but even after running different lines and powering on later it is still happening.

Sorry for the out there question ..( i am a bit of a noob when it comes to gsr running gear)..but was told today that it may be attributed to the gearbox..and lsd (or lack of it )..the car has the gsr gearbox with a vr4 casing...it has a 2wd/4wd locker bolt,and apparently has the viscous coupling from the vr4 box,
When i had the car on the dyno the mechanic tried the locker bolt but said when 2wd was selected the wheels would bind up..which I since have been informed the cause of this may be mismatched diff ratios?? and mismatched ratios would cause the coupling to fail, any suggestions to where i should start in sorting out the problem?? obviously finding if the ratios are matched will be first on the agenda,but in terms of getting lsd to the front and finding a coupling if mine is ruined??
The car has new drummonds coilover fitted and the mechanic was going to speak to Jamie Drummond today for any tips on suspension adjustments i can make to try and counteract the front end,but really need to sort out the gearing issue i think?

Sorry for the long rant and as i mentioned i dont know the first thing about the drivetrain,any help or suggestions would be hugely appreciated.
Cheers scott.

 

[GSRWRC]

Quite often a simple wheel alignment to the correct specs will dial out understeer. Excessive toe-in will cause chronic understeer so could be one thing to look at.

Another thing to check is the rear swaybar. If your GSR still has the stock 14mm item throw it away and get yourself a Whiteline 20mm swaybar.

 

[DOUGMO]

did you try adjusting the coilovers at all?

and as gsrwrc says, wheel alignments can play a big
part in overall handling.

with the drummonds you should be able to get a decent improvement

 

[marinetowing]

Cheers guys,
I have a 20mm whiteline swaybar in the car and will be putting in a rear strut brace shortly, had a wheel alignment done about 3 months ago but it might pay for me to get it rechecked??
Have made no suspension adjustments since the coilovers were fitted as i wasnt too sure where to start but hopefully drummonds will give me some settings to try, so you dont think the problem is gearbox related?? I was contemplating buying a new coupling from ralliart but $1100 is a big outlay if its not the source of the issue..
Will give the alignment another check,adjust the coilovers..and if the pain persists may have to see the gearbox doctor
Thanks guys
scott.

 

[rob323]

How much camber on the front are you running with the semi slicks and what brand/ model semis are you using?

What pressure were you running in them (hot/ cold)?

If your centre diff was locked (or very limited slip), this will cause understeer. If your viscous coupling is stuffed and no longer limits slip, this will NOT create understeer, in fact it will help with turn in very slightly.

If you have a front lsd, this will create more understeer when turning into a corner.

Edit: I assume that your car is a GSR, is it not?

 

[DOUGMO]

running a ralliart centre diff on tarmac will slow you down

they are designed for gravel cars.

 

[marinetowing]

Cheers again,
yes its a gsr..and still only has a gsr diff, not 100% on camber but will check on this today, running toyo r888 semi slicks with 40psi all round..which i was maintaining all day..
track was reasonably warm all day, was sunny with temp around 17c.

So i gather that all improvements i can make will be suspension related?
the car is fitted out with good gear..whiteline sway bar and bushes,new coilovers etc.
thanks again
scott.

 

[rob323]

Try around 2 degrees negative camber on the fronts (minimum) for semis (otherwise you just chew out the outside edge). 40 psi is also way too high (unless they are 18" diameter tyres. I run 25 psi cold (goes up to 30 when hot) in my 15" A032R semis with 2.5 degrees of front camber. Tyre compound will also slightly determine how much camber and pressure the tyres will like.

Have a chat with the people you got the semis from for an indication of tyre pressures.

 

[Jazz9]

I've been finding a fair bit of understeer with my front LSD - hoping that when i get a rear lsd + camber sorted it will be solved.

Glen

 

[DOUGMO]

try differnt pressures also,

40 is fairly high

 

[marinetowing]

Thanks for the advice guys,
will give it all a try, i spoke to dms this morning and they suggested running the bump adjustment on the front four clicks back from maximum hard and if it helps then increase the spring rate,
the techs said that without a ralliart coupling and an evo lsd the car will wont handle 100% :? ..and to treat the coilovers more as a fine tuning device than a miracle cure for dynamic handling....am a bit unsure on how to take that advice??

will look at changing tyre pressure,adjust camber and stiffen the shocks and see what happens.
cheers again

 

[rob323]

the techs said that without a ralliart coupling and an evo lsd the car will wont handle 100% :?

Which tech's said that and what is their back ground (rally, tarmac etc)?

An lsd does nothing really unless you are losing traction, which at a circuit, rarely happens. No, you may not get 100%, but you will get 90%.

Definately stiffen the bump up as much as you can. Soft spring rates won't cause excessive understeer, just excessive body roll like this:

 

[marinetowing]

Thanks rob, will give it a try, I questioned the tech about the coupling in regards to it only being good for gravel use and he was quite adamant that the car would not handle on tarmac to its full potential without it....I am now taking that comment with a grain of salt...as i know i can find more fact to the questions i have asked on team4g, and do appreciate the assistance.

In regards to tyre pressure...i am running 17s and ran 30 psi for a few laps but the tyres were squealing badly and the car felt very unsteady, would you still consider 35 psi to be too high??after heating up they increase by 2-3 psi and i check them and deflate after each run.

I was also considering getting an evo diff, but the car has no problem with grip on the track so i guess i would gain no advantage from it?

thanks scott.

 

[3zercrowd]

40 PSI is recommended for NORMAL day to day driving(on 17's)

I run 36 PSI in my 15's......

As for track work, deflate by a few psi until you find a nice balance....

Id say 30 PSI is too low for 17's........The airs in there for a reason isnt it :wink: :lol:

 

[DOUGMO]

try playing around with pressures between 36-38psi hot and see how you go,

or alternativley start slightly lowering the pressures from 40psi 1 at a time and test it out

 

[marinetowing]

Thanks guys will give it a shot and see if i can find a good balance,I had the following settings recomended to me by a mate with a track evo just wondering if they sound like a good guideline for my application??............

Personally I would get the fronts set up with approx 3.75 deg to 4 deg neg ( only for the day and get it changed back for the road if you can be bothered,as I ran 5 deg on the road with normal shit tyres inbetween events )Get as much Castor as can be put on as this increases camber in a turn.
Toe on the front I'd have straight ahead or possibly 1 mm overall for turn in.
Rear I'd get as much neg as possible 3 deg if possible with say straight ahead with the toe ....

 

[265T]

just excessive body roll like this:

THIS is excessive body roll

 

[rob323]

I had the following settings recomended to me by a mate with a track evo just wondering if they sound like a good guideline for my application??............

Personally I would get the fronts set up with approx 3.75 deg to 4 deg neg ( only for the day and get it changed back for the road if you can be bothered,as I ran 5 deg on the road with normal shit tyres inbetween events )Get as much Castor as can be put on as this increases camber in a turn.
Toe on the front I'd have straight ahead or possibly 1 mm overall for turn in.
Rear I'd get as much neg as possible 3 deg if possible with say straight ahead with the toe ....

That large amount of front camber may not be easy to achieve depending on how much adjustment you can get from the DMS struts. I could only get 2.5 degrees on my car and it tramlined a fair bit (still liveable though - just) with the semis slicks on the street, I can't imagine what it owuld be like with 4 degrees.

One thing, the more camber you run, the closer to zero your toe should be to minimise edge wear during "normal" driving.

Also, the more front camber you run, the more likely you are to light up the front inside wheel when powering out of a corner (and therefore need a front lsd) and the earlier the front wheels will lock up under brakes.

 

[swellso]

To some extend Scott I think your finding the limit of the GSR chassis. I always had some understeer with the 2, although swaybars etc did sort it out a bit.

The 4 is the other way though. At the moment it wants to oversteer into corners. Hard to compare the two when this one has coilovers and less power but I would say that once I get the AYC sorted and some more time in the car I should be pretty close to your time (and with quite a bit less power :wink: ).

I'd be up for spending a day out at Basker's seeing what pressures, damper settings, etc can do. You can have a go of my car too to see if you think that handles any better.

 

[marinetowing]

I think it may be the case Shane, Had a good chat to Del yesterday and also spoke to Chris Fitzgerald..who was the previous owner of the car and the ralliart mechanic at dj's...he now has a track based evo 4...
Have been given a lot of options to try...mainly camber and toe settings which I have been told will make a noticeable difference,
I will be in a test day for sure sound like a great idea, I wont make any changes before the hillclimb as the car should be right at home in that environment compared to baskerville as corner speed will be way below that experienced on the track.
I am heading up tomorrow to meet Nick re the camera mounts and then will take him to your place..so will see you then