Terminal Understeer

Hi all,

After the sprint on Sunday and thinking about it my car defo has terminal understeer… It was my understanding that the Exige would be very “pointy” and a lot more prone to oversteer!

When I first got it it was awesome! But the geo was very different, it had 45 profile tyres on the front and must have had a ride hight < 90mm, slammed to the deck so to speak But as it was a Rockingham track car I can see this

Since getting the geo redone it wasn’t quite the same. And since it’s been repaired it’s not seemed the same…

Things I’m thinking, I had the suspension changed (standard LSS with A LOT less miles on)… But this could have been put on the wrong way, i.e. rear suspension up front. How could I tell the difference? Is the poundage marked on the springs?

The ARB is set differently? Too still isn’t it? Or would it be too soft?

Tyre pressures are too high up front? Need to have a play with them but I think that’s the last action as it’s like the final bit of tweaking IYSWIM.

Geo is poo? It was done by sinclaires and they normally do a good job (but am suspecious of my “C” service as my oil is still black )…

Any ideas gratefully recived

Rears are WAAAY longer than the fronts so you’d notice.

Since you’ve had the tyres off I’d check those… a lot of tyre monkey places will inflate them to 40PSI or so. :slight_smile:

Cool about the suspension! One load off my mind, so there’s no way they could even remotely be fitted the wrong way round? Phew!

I just went to the petrol station to find they digital air pump thingy is now just a couple of hoses sticking out of the ground and my foot pump is stuck on 20PSI

RemarkLima

From the reports everyone suffered from understeer and traction problems at North Weald last weekend… so maybe you shouldn’t worry too much

As for geo… do you have a note of the current settings ? could you post-up??

Also you are running Toyo’s… without wishing to start a fight… i never reckoned they were any good on my car (T1-S) but you should play around with the pressures… pump em up a bit higher than normal but not too high and start from there. I agree with you that this would be final tweeking compared to some other stuff… like geo.

However, you need to ensure the geo is proper first. I have only ever heard good things about sinclaires but i guess they could have made a mistake or maybe something has loosened. I think our cars are more sensitive to rear toe as well, compared to other cars, so don’t let these be ignored and when the geo was done, did they weight the car down and did it have at least half a tank of fuel ?

Also if the wishbones have been off ?? have they ?.. perhaps the castor isn’t quite right…

The ARB is a possibility… so you could try adjustment.

Whatever you do… only change one thing at a time.

Cheers Rox,

OK, geo brakes down like this:

Before:
Left Front Right Front
Camber: -0deg 47sec -0deg 54sec
Castor: 2deg 40sec 2deg 41sec
Toe: -0deg 11sec 0deg 11sec

Left Rear Right Rear
Camber: -2deg 50sec -2deg 49sec
Toe: -0deg 12sec 0deg 21sec

After:
Left Front Right Front
Camber: -0deg 47sec -0deg 54sec
Castor: 2deg 40sec 2deg 41sec
Toe: -0deg 01sec 0deg 00sec

Left Rear Right Rear
Camber: -2deg 50sec -2deg 49sec
Toe: 0deg 11sec 0deg 11sec


Is this the right kind of geo? Looking at the service notes there’s not enough castor by the looks of things, should be 3.5deg… So that would add more neg camber as the steering turns…

It was weird at N. Welad tho’, I could get any oversteer at all, really had to struggle to get anything, even booting it in 1st just kinda pushed me straigh on

I’ll try the tyre pressures first tho’ (easiest ), you think higher??? I always thought lower would get more grip, the tyre get’s hotter easier and deforms onto the road easier (i.e. the contact patch is bigger)… Or have I got demeted thinking again?

Thanks again!

RL

I guess all your seconds are actually minutes… trivial point but could you confirm that the readings you have defo aren’t in decimal (eg where you say -0deg47sec isn’t actually -0.47deg)

It would be good if someone like MArkA could come along and comment but i think the following…

So assuming they are all in deg, min Your castor is too small - i’m not sure how this hurts turn in but if it adversley impacts -ve camber then that won’t help you either… Also you have almost 1 deg of -ve camber at the front which is quite a lot and will mean that the Toyo’s may not be in optimum contact with the road for their design… i’m not sure how they will like this, they also seem to have a sqwidgy sidewall (which is why i’d say try pumping up the pressure) so maybe they don’t like all the neg camber.? Lower pressure will give more contact patch but at expense of sidewall flex and if the car’s not heavy enough some other weird things will probably happen and the contact patch will prolly deform anyway (you know the classic wear outside edges but not the centre thing… )

Anyway, castor apart… it doesn’t look like geo is your problem, unless its moved… What about the ARB setting and ride height after replacement of your suspension?

Mark, here’s RussT’s old road settings also used by AndyD. I’ve driven Andy’s (Nitroned) car relatively recently (at North Weald) and oversteer was much more prevalent than in my std car, I liked it.

That said, the better I’ve got as a driver the better I’ve found the Exige’s handling to be. Going in faster helps bring the rear biased weight into play, but understeer is still very much there in slow corners.

Ian

Rox,

I’ll scan the Geo sheet this evening. But it was say -0deg (little 0 at the top) and 42’ which on memory is in fact minutes… But could be -0.42.

Looking at it tho’ it seems to be degs and minutes.

Not sure what the ARB is set at. I assume it’s the same but will check over the w/e (not having a garage yet it’s wet and dark when I get home )…

Has anyone tried 45 profile tyres on the front? Dropping the ride hight a little then you have less sidewall to flex. the A058’s (I think) that were on it when I got it were 45 on the front and it was pretty awesome!

Ian, cheers for that, they look pretty standard the settings

I guess at N. Welad it was very slow so no high speed corners to get the rear bias coming into play. And very cold tyres! The development will continue

Mark - If I remember rightly you had new Toyo T1-R’ on at North Weald just like me??

I’ve picked up a load of understeer too so I think it may be down to the tyres. I’m really not impressed with them.

I need to get them on track so I can get a handle on what pressures are best but I used to run 24/26 hot on the T1-s on track and 23/25 on the road.

I’m planning to raise the rear ride height on mine to try to get them working harder. Will let you know how I get on.

Chris, I had the T1-S’ on… They looked new because Sinc’s covered them in that tyre wall [email protected] (that ends up over your body work )

I’ll try those pressures out and see how I get on…

Your review of the T1-R’s isn’t too promising so it may be a case of looking for something else… 38’s just seem to expensive for road driving!

Its the British weather that puts me off running 48’s full time. I like to press on a bit when I’m driving, even if its a bit wet.

I’m planning on going back to 39s on the next change as they have to be the best alrounder. Don’t like the price tag though.

The other option is BF-Goodrich G-profiler. You can get those in 195/45/16 and 225/45/17.

If you go 195/45/16 for the front then the world’s your oyster for tyre choice It’s only the 195/50/16 thats tricky.

Mark A was running 45 profile Toyos at North Weald before changing back to 48s.

Has anybody tried the Goodyear Eagle F1s? They come in the right sizes (I think - see here) and won Autocars tyre test a couple of years ago. Sorta sexy tread pattern too.

[image]http://www.goodyear.co.uk/services/tyreguide/img/tyre_prod_eagle_f1_gsd2.jpg[/image]

Ian

I was running 48’s at North Weald, I had really bad understeer on the first chicane & first hairpin, after that they seemed to warm up & the understeer largely disappeared.

I think some of the trouble with the first hairpin for me was that it was too fast for 1st gear, but the engine had dropped out of the power band in 2nd, hence I couldn’t get enough power on to get the back to move as well. I think a better driving technique, than mine, was needed here.

Anthony, I got the first hairpin kinda right once, 1st gear booted and the back went round (as opposed to pushing me head on to a “3” wheels on the grass ), then into 2nd and with some power…

But N. Weald isn’t the only reason I say this, the car kinda doesn’t have any front end “bite” like it used to… That’s more the case… But need to get to a trackday v. soon!

So far I have been very happy with the 48’s as a road tyre, no grip or aquaplaning problems even in really bad conditions.

I am half tempted to give up my search for a 2nd set of wheels and just use these all year round.

Okay,

I’ll try and catch up a bit.

Understeer at North Weald on Sunday was horrendous, especially as there are tight hairpins on the LH hairpin after the fast LH bend I had to use most of the track on the exit! Speaking to most people they were suffering the same way.

I was running fairly new T1-R’s and they had quite a bit of understeer but then I wasn’t messing with tyre pressures (just running std L:otus pressures) but when I changed to the AO48’s after Lunch it had less understeer but it was still there.

From looking at your geo (it’s in degrees & minutes) the only differences I would make are to increase the castor (you are approx 1 degree less than my car) and I’d also increase the front Camber slightly as well, you are running a lot at the rear (i.e. just under 3 degrees). What setting is your ARB on? as in the wet conditions it may have been too stiff as I believe you still run LSS from comments in your 1st post.

Wait until you have tried the car on a proper track as it will feel quite different.

Cheers Mark, yep standard LSS on there…

Am I right in thinking that adding castor will add neg camber as the wheel turns, that was my understanding

I did find just half a deg of neg camber on the front of MR2 made a world of difference!!!

I’m not just going on North Weald but even just driving there’s just no bite up the front, it feels like there’s some grip then it just let’s go with no loading up to tell you IYSWIM… It inspires zero confidence!

How hard is it to add some castor? Is it shim plates like camber? I’m right in thinking I could add a little neg camber just with some of the correct shim plates?

Although I guess it’ll be another run to Sinclaires too

The camber is easy, just remove another shim (other option could be to reduce the rear camber to keep it balanced and relative to the front).

Castor change is similar but more difficult as the bolts and washers are a nightmare to get out! On the top arm you can see the shims (washers) between the bushes and the chassis.