Solving understeer

[mrsoundcraft]

OK Im finally developing my car. My first track session has shown up a bit of understeer so I would like to try and fix this, allowing me to raise my cornering speed.

The car:
Its fully poly-bushed at the front end and has KYB shocks with 3" lowering springs.
The back has some well used Landrover shocks and 40mm blocks fitted.
I was running some worn (now dead) 155 80 13 budget tires.

Ive got a few things Im going to try out to see if I can improve the grip, although I would appreciate some advice to help me along.

Theories, some might be silly

I need to run lower profile tyres, to reduce the sidewall flex
I need wider wheels, (bigger tire contact patch - more grip, axle weight spread over bigger area)
Need more negative camber, too much wear to the outer edge of tyres
Need bigger blocks at the back, so the car isn't as "nose down"
Need to double leaf the back and get some Spax shocks

[Chris_C]

What pressure were you running your tyres? When I was on 13's I ran 42 front 38 back otherwise she skipped all over the place but that was horrific on the road so standard pressures there.

What do you want out of the car? I've raised the cornering speed of mine and it's become a lot less fun. You can't play with it at low speeds anymore which gets annoying.

I'd suggest sorting out the grip balance rather than trying to dump a load more grip on the car. Do you have the same make of tyres front and back? 3" lowering springs will do horrific things to your toe settings (300's do have "bump steer" style tendancies, look at the rack ball joints in respect to the wishbone pivots. A suspension drop will effectively screw your toe completely which is how a 300 gains it's grip), did you get the car re-tracked when you dropped it? They seem to like nose down when set up right though.

I'd suggest getting good tyres as a first. Not good as in super grippy, just good as in progressive. The only cheap way of doing that is looking at 15"s though, though A539's are available in 13"s for a lil bit longer

[SteveP]

I reckon you'll find fitting 15x7 alloys on 195/50/15's would work wonders. Don't go for A539's though!

You might be right Chris about the lowering affecting toe... but significantly having less body roll (unless you've got bucket seats!) will help no end imo. My old GLT cornering speed was limited by me falling out of the stock seats and not being able to steer before it lost grip

[mrsoundcraft]

Oh I have buckets alright!


so it was defiantly the car that was loosing out in the cornering battle. Have you got some sporty seats now Steve?

As far as my enjoyment of the car goes, I really like the way it drives at the moment but I just want to be able to corner slightly faster, for example at Kames I was nearly coming off the track above 25 MPH going round the hair pin, which is really tight, so not surprising. I would like to think though that If I could increase the speed that I could take this corner, that would allow me to brake less, and later and allow me to progress sooner out of the corner. It would also be nice if I could improve the front to the extent where the back starts to let go a little

I think My 13s were at 27psi front and 30 rear, the front tires are knackered now anyway, the outside edges are completely worn, leading me to believe I need more negative camber.


Although maybe it is down to the fact that the cornering was trying to pull them off the rim due to the side wall flex, or perhaps 27psi wasn't enough??


These were not good tires to start with, I know that pressures and quality of rubber is a basic rule but It was all I could get at the time and I didn't have a big pump at the track with me. 3 of them are Viking and ones a Dunlop, so they're almost a match.
I cant believe you were running your fronts at 42 Chris, I had My fronts at 40 during the winter, the car drove so badly I didn't use it until I realised it was the tire pressure that was the problem.

I have some Volvo 15's but I think they're only 5.5J. The car did feel a bit better when I had them on, but they are heaver than the nice little Borbet 13s. There's always a trade off I suppose, but Im maybe getting some BBS 14s or MK1 MR2 15s that should be lighter and wider.

I had the tracking corrected to 0 degree toe after I lowered the car. Is this enough or should I be fitting adjustable top mounts and getting the car back in for a proper alignment check?
Thanks for the comments and tips your helping me work out what I need to spent my money on first!

[volvodspec]

don't worry about the weight that much

like Steve said, 15x7 on 195/50/15 tires makes a very, very big difference in handling and even keeps the speedo correct. seen the other suspension parts i allmost wonder why you still have the thin rims with monsterhigh tires

the with of those will improve grip both in wet and dry conditions (also depending on tire though) and the sidewall (wich is about twice as small) makes less random movement of the car under steering so much more control in the corners.

i must warn you though, i was fully accustomed to 155/80/13 on 35psi all round with throwing it through corners, bit of drifting etc. when i put on the 15x7 alloys and did the same i allmost folded myself up against a tree because the car handled completely different from what it used to do

[Chris_C]

I agree, on the road those pressures are horrific, don't ask my why it seemed to work on track though.

15's certainly improve things and you get a much better tyre selection! Dropping the fronts already increases negative so I'd suggest the sidewalls were flopping, you should be able to feel that though. Have you polybushed it?

[mrsoundcraft]

Yes its all poly bushed at the front. Was considering changing the top mounts and maybe the leaf spring bushes too. And while Im at it the engine mounts. I think I could sense the tires bending, a lot to take in though.

[SteveP]

You have all the right ingredients! I wholly believe it's your tyres letting you down. Especially if you have fresh suspension all round. Perhaps sourcing a set of GLT rear leafs might help too? I can feel the sidewalls flexing when driving my GLS... and I haven't even been driving it hard. Best bet is to find some 15x7's with a 35 offset and go for some good tyres, even Toyo T1-R's I think will be a big improvement and they're only around £28 a corner.

I never got round to fitting any more supportive seats... I did try and source a set of front RX7 leather seats as they would've matched the rest of my interior, but then the car died of rust anyway

As for ratios, I assume yours is a 1.4 5 speed? Probably the best diff combo for the box really. I forgot how big that hole between 2nd and 3rd was til I got my current 360!

[Chris_C]

F7R torques remove that hole amazingly

I've got 195/50 15's on, running Eagles (not the new assymetrics, the old arrow head pattern) just above stock pressure was awesome. On T1R's I'm running 8 above standard to cure the sidewall flop, they felt horrible on standard pressure but gorgeous now.

Have you have proper supertracker 4 wheel laser alignment? Ask for a set of numbers as to how far out everything is as well as just them sorting out your toe. I don't run book value for toe but that is down to personal preference I find.

[SteveP]

F7R torques remove that hole amazingly

You can't deny it'd be far better with more sensible ratios though!

[Chris_C]

Yeah, it's true. I did work out the ratio it needs a lil while back, all the others are remarkably well spaced.

[Speedy88]

I kinda like that hole as it allows me to give that low rev "boooooaaaaawww" that more powerful cars make for more than 3 seconds

[mrsoundcraft]

Maybe that's what the hole's for then speedy?

Looks like its my tires for sure then? That's an easy fix, this time next week I'll probably have a massive collection of alloys, thats the problem with ebay

Im going to double leaf the suspension too, more stiffness!
As far as power and acceleration goes I'll see if I can help it with weight, I know its not much but it'll make the car feel a bit more like a racer too.
What about changing the cogs in the box, is it possible?

[mat_91]

as said it does sound like tyres ive got old bushes just lowered and stiffened and some decent tyres up front in 195/55/15 flavour
and i get no under steer at all even with a welded diff