I definitely think the locked diff is a big factor there, but I have to ask a question. I'm not sure if I am reading it right. Did the car handle and turn into the corners very well and then slowly started to get worse, or did it start understeering suddenly after a part change (spring, shock, whatever)..

It's pretty difficult to know what to suggest without knowing a little bit more. Do you happen to know the front spring rate (being a mcpherson strut, the wheel rate and spring rate are close enough to be considered the same). Going too stiff will increase understeer but if it is too soft, going stiffer can help. I'd suggest that if the front spring rate was under 150lb/in then you could safely run stiffer.

It might also be that the shocks (original fronts with new oil) have started to get 'sticky' (I wish I could think of a better word) - and they aren't allowing enough movement, and it's making the front easy to slip on initial turn in. Maybe it has slightly blocked/restricted some of the valving on the shocker. Maybe try emptying them and replacing with thinner oil as an experiment (it might end up being too soft then, but it's worth a try).

Very generally you can do a couple of things to help intial turn in understeering. Of course the 'good old' option is to run more negative camber on the front wheels. I think it would be quite hard to get too much front neg camber - there just isn't enough room to move the strut top inwards (unless you run a longer control arm).

The other thing that works, but I have to warn you, it will wear out the front inside edge of the tyres if you run it on the street or very long distances. But the trick is to adjust the front toe-in - you adjust it to provide anywhere from 1-3mm of toe OUT. This typically helps initial turn in but it isn't as good for long distances, and can be a little less stable/smooth at high speeds (compared to 1-2mm of toe-in

About the only other thing I can think of (for now) that might be a factor - is there any chance the front tyres have 'gone off' - this can happen if they are massively overheated during races - even if there is a lot of tread left. Another possible cause would be if they got a lot of oil contamination or something.

Ronald lets make sure I have this right.

The ride height in the rear is lower. You have 155mm wide tires on the back but a welded diff for traction??

Also the tall rear tires (80 series) are going to have a softer / more flex in the side wall.............read softer rear suspension.

Lower rear ride height means weight transfered off the front tires

So you have the triple whammy going on: softer rear suspension / Rearward weight bias / Welded diff.................not surprised your fighting understeer.

I would ask what drove you to this set-up: did you fit the wide fronts after welding the diff to combat understeer? Then Skinny Rear tires in a further effort to combat the understeer?

If your car isn't belting out more than 85-90 Flywheel horsepower ditch the welded diff run an open diff till you can source an LSD.

I'll share with you the budget set up we started with: 185/60-13 Yokohama A008R tires, 7/8th (21mm) front bar, (15mm) 5/8 inch rear bar , cut down 240Z springs front with lower blocks rear dropping the whole car 50mm (2 inches), Cheap gas struts front and KYB shocks rear. The motor was near stock the first year we raced it but the car handled very well.............not as good as the current proper suspension but good enough.

I'd be willing to be getting the ride height equal front to back and four of the same size tires (even with the welded diff) would result in better lap times then the current set up. Don't know what kind of circuit your racing on but I also suspect with an open diff what you gain in corner speed would more than make up for the bite the welded diff offers in slow corners.

Tom

thats similar to my understanding rally twit, just wasnt sure how to explain it- im running a set up similar to what rally twit said, but using coilover front suspension and 240z cheap gas shocks and a rear sway bar- its pretty balanced for what it is.

but im using 165 65 13 rear and 155 70 13 fronts. 165 all round or even 175 on the rear would be ok too as the 155 up front tend to lock easily

Whoah,kinda detail info u all posted...
Actually i used my car for drifting...(but used it for daily too)...
BTW the corner i meant is jus nice flat turn. No bumpy/holes..

Jmac: No understeer when start to turn in,but when i steer more it start to under or if i suddenly steer more(like to evade thing on the road) it will understeer hard...

For the front suspension,i really hv no idea bout the spring rate. But i recall tat is from S14 rear spring(i put in to the frt suspension).

For the tyre,185 int he front help to combat understeer slightly but still i think no enough(normal road tyre).
I tried 155 at the rear n help a bit to reduce understeer.

-2.5deg camber still not enough??(nvr think bout tat b4)

Agree wif u bout the toe-in stuff..

My tires r still fine. Nvr use it on track yet..

Rallytwit: The rear height were juz equal if equip wif frt 185/60r13 n rr 155/80r12. Other than tat,the rear will b slightly higher than frt. 155 n diff is to make drifting easier + combat understeer.

Will try ur set up soon...
But those rear bar is kinda hard to get around Malaysia..
From wat other model u guys suggest?

my rear bar is off a commodore, you dont have them in malaysia- it was heated with an oxy torch by daveman i think and bent into sape to fit. works ok, not as stiff as a proper built sway bar set up but better than none. i estimate about 70% effective compared to previous set up of no sway bar.

Quote:
Ya know what, ...my money is on the welded diff for sure. Typical charateristics is understeer into corners and oversteer coming out. Do yourself a favour and swap the welded centre out for an open spinner or even better a LSD unit.

If you think that you are going to keep the welded diff & still drive it on the street then modify your driving technique to speedway style & throw that sucker into the corner & steer it with the throttle.

Keep a good supply of spare axles on hand too.
Oh yeah, what brand of tyres do you use? I want to buy shares in the company.

Haha,though to throw into a corner b4 but i was too scary...
1 mistake n my car will end up sticking to the divider/drain...
For the axle,is quite lasting for me..
It can last 3yrs(mostly daily drives)...
Im using Retread tyre for the rear most of the time,so is not too expensive for me... :D

When you discussed wider tyres on the front, I was almost going to ask if maybe you run the car in drifting competitions!

What I _think_ might be happening, is you actually _do_ have some turn in understeer, it's just that on big wide/slow turns, you don't turn the steering wheel quickly (don't need to) - and so it's only on tighter corners, or where you turn the wheel quickly at the start, that it starts to understeer. It's probably still mostly diff related.

If I'm reading it correctly, there's no wear on the front tyre tread. I'm assuming you mean two things here - 1. that it isn't worn on the inside or outside edge (like if there was too much toe out or neg camber etc) and 2., at the same time there's no significant wear on the front tyres at all. OK - If I _have_ got that correctly, you might actually be in a situation where the front tyre tread is too hard.

Not all tyres are created equal. And believe it or not, wider tyres (all by themselves) don't grip better. Now of course if you go so narrow as to have a small contact patch, it can overheat and 'go off' . But let's look at a more typical example. If you had a certain tread, 15cm wide and another 30cm, lets say with the same diameter/circumference and the same tread compound. Well grip is a result of two things - the friction co-efficient of the tread and the total downforce. In other words, in a perfect world, they'd both grip the same. About the easiest I can describe it is this - if you double the tread contact area, each small section gets half as much downforce on it so the overall grip 2 x 1/2 = 1 is essentially the same.

OK, so with that established, it would mean that wider/bigger tyres don't grip better. But they do. And the reason is actually pretty simple. the bigger/wider the tyre the softer/stickier they can make the tread compound and still get acceptable life. So those wider tyres can be a bit softer, and have the same life as smaller tyres with a slightly harder tread compound.

So, wider tyres can and usually do have stickier tread. Then you come to certain exceptions. In the 185/60/13 range, there are a bunch of different brands of tyres, and also a few that have many different tyres in that size from the same manufacturer, ranging mostly in tread compound and tread pattern, from pasenger car stuff to semi-race and beyond. Then you have some of the sizes that are becoming rare. Two I can think of off the top of my head are for 10 inch mini rims (A few years back there was only one brand for street tyres for them - falken, not sure currently, but there might be one new one) and the other would be early datsuns (and possibly early corollas, I am pretty sure I had 12 inch tyres on a ke20 about 20 years ago) and their 12 inch tyres. In this range you will probably find some examples (if they still exist) like 'bob jane australian all rounders' - they are/were made in a sweatshop somewhere, that probably made a nike factory look like heaven. A _very_ hard compound and not much grip. On the other end of it, there are tyres like 'hero' - which I think are made in China. I originally got them, to get a roadworthy on my datsun coupe, because they were dirt cheap (about AUS$70 each) - in 12 inch size.

Anyway, I planned to use these tyres for about a week or two and fit mag wheels and 185/60 13s . But the biggest surprise I got was driving the hero tyres - they have (seriously) remarkably good grip. I don't think they will last too long (so far about a year and about 8,000km and they look ok still) but who knows.

So the point is - it's possible that the rear tyres are grippier than the fronts despite the size difference.

Another thing which comes to mind is the front end - is there any chance it is low enough that the control arms have dipped below parallel with the ground. Below that and it can cause the front to sort of 'unload' during a corner due to roll centre and weight transfer issues. If this is the case, raising the front until the control arms are just higher than parallel (allowing them to travel to parallel when they compress slightly when cornering)

When you put the s14 rear springs in, did they go in standard, or did you have to cut them down at all to get the right ride height? I've done a fair bit of swapping of front springs in the last few months (about 1 time every 2 weeks) to try and get the fronts right. A stock spring is too soft, and it will bottom out during corners with good enough tyres. Heavier springs will 'work' but they have to be thick enough (to get suitable spring rate and prevent bottoming out) that by the time you cut them down just to get std ride height, they are about 2inchs too short to be 'captive' which means they'd need a shorter strut insert (or the spring to be wired in for safety)

I'd still suggest trying lighter oil in the front struts.

About the only other thing i might ask about is what tyre pressures are you running? They often write about (mostly for drag racing, but also some circuit racing) lower tyre pressures giving more grip. This is _only_ true for tyres especially constructed for circuit racing or drag racing. On modern radial tyres (esp those for the street) the way they are made, lower tyre pressures actually compromise the grip. At the front you might find that pressures up to and even above 40psi will improve front grip, because it brings more stability to the tread blocks as they are put in contact with the road (esp when undergoing other forces during cornering). Running above 38 or so will tend to wear out the inside of the tyre on a streeter, but sometimes the shorter life is worth it for better, and more predictable/consistent grip.

If you could lower the rear without compromising it, then the alteration of the 'pitch' (to use the aeroplane terminology) of the vehicle actually increases the front caster. This 'would' be good, but you can't do that without altering rear suspension geometry, usually for the worse.

The problem is there are so many things that can cause it it's hard to narrow it down.

Salute to u Jmac...
Really agree wif u both smaller tyre in some case hv better grip than wider. I heard it b4 but nvr figure it out y.

As for the lower arm,i must check to double confirm.

Yes,i did cut the S14 rear spring to lower the height as i use pillowball mount too. The spring hv slightly bigger coils n it fit juz nice but still need to wired it. But i think the shock's oil were still stiff enough(not too stiff).
I will try to use KYB gas shock later n c how does it works.

As for tyre pressure,i found out lately std 1200 were oni approx 25psi. Usually i pumped around 32psi frt n 36psi rear.
But i decrease it now to 30psi frt n 33psi rear as b110 r quite light. Wat tyre pressure u reco?