Scotty Boy

Wacky.Banana - thanks for the insite. Think i will take this area more seriously now and do a bit of learning about tyres, geometry etc ... Scotty "soon to have NON wavey tyres"

easyrider

Only an idea--but could it be the centre diff winding up a bit due to different circumference tyres between the front and rear-on the gearing side of things,with your setup the rears are allways playing "catchup"(which COULD cause the squirmy feeling)-the centre LSD does "catchup" eventually-therefore the CLUNK.
Personally i would shell out for some new fronts also,so you get your tyre wear/circumferences correct-therfore less stress on the centre diff.
It seems to be due to the new rears being put on-so i would do the easy things first(may not be cheap but at least you know youve got new rubber all round)

Hope this helps.

Im going to start a new thread in drivetrain to clarify this+another relaited question on it.

easy

Fat Boy

New on rear and old on front make no difference to the AWD as opposed to say a cavalier 4X4 where the system will destroy itself if there is tyre size mismatch.

This whole thing is, I am 99% certain, the new tyre effect. The releasing compound that allows the tyre companies to get the tyres out of the moulds after manufacture is very waxy and as said above can take between 500 to 1000 miles to really disappear.

You changed the tyres on the back, it's been pi55ing down so you haven't been able to really push it and scrub the tyres (thankfully), an dthey are sliding around at the back. Obvious really. It's fine in a straigt line but watch tehbends until you have really scrubbed them in - will probably need some prolonged dry weather for this so about August should see you sorted

Fat Boy

New on rear and old on front make no difference to the AWD as opposed to say a cavalier 4X4 where the system will destroy itself if there is tyre size mismatch.

This whole thing is, I am 99% certain, the new tyre effect. The releasing compound that allows the tyre companies to get the tyres out of the moulds after manufacture is very waxy and as said above can take between 500 to 1000 miles to really disappear.

You changed the tyres on the back, it's been pi55ing down so you haven't been able to really push it and scrub the tyres (thankfully), and they are sliding around at the back. Obvious really. It's fine in a straight line, but watch the bends until you have really scrubbed them in - will probably need some prolonged dry weather for this so about August should see you sorted

easyrider

LOL-August--probably right though-good ol English weather

Scotty Boy

easyrider - thanks for the reply. i am a little scared now !!! Is it really that important that all 4 tyres are changed together. I will follow your new drivetrain thread and hopefully we shall have this clarified

fatboy - thanks for the reply. that explaination really does explain the importance of wearing tyres in. Is this effect more noticeable with modified suspension compared to standard suspension? - i ask because i never really noticed it when having standard suspension. But then maybe it was not raining so hard every time my tyres were changed. roll on sunny August 2004

Scotty

[Edited by Scotty Boy - 1/2/2004 2:38:19 PM]

easyrider

Scotty-I wouldnt be too worried yet-its just a theory that i had a while ago and im glad you brought this up as it reminded me to find out a bit more about it, and it may be explained to be an absolute pants idea.
Another way it could be described is-on a rear wheel drive car if you drive away quickly,the rear end squats down because the wheels are trying to go quicker than the car is(will also do it due to weight distribution when accellerating)-now if you apply this to our 4wd cars, the front wheels(with less tread/circumference) will spin faster than the rears-this difference in rotation is usually taken up by the centre diff,and on our cars it usually copes very well with it-BUT an LSD being what it is, can only take so much differential in speed on either side before it will lock and transfer the power-therefore trying to make the rear wheel speed catch up with the front wheel speed(making the rear end squat).When the centre LSD cant take any more of this differential, it locks as said before, but because it cant bring the speeds equal the diff "jumps" causing a knock,and starts the catchup process all over again.
Cavilier 4WD units were famous for blowing for the same reason i believe,because they were never man enough for the job.

If you do end up trying new tyres on the front, and it does/doesnt cure it,i would very much appreciate you posting your results-or even mail the results.

Thanks

easy

Scotty Boy

easyrider - thanks for the more detailed response. I understand what is going on now Before i do any front tyre replacing, i really want to see the results of your drivetrain thread. I am not using the car all next week, so hopefully this will be enough time to get some good replies to your thread and allow me to investigate all avenues however, i will keep posting my results.

Fat Boy

Once again, the centre diff on an impreza will not be harmed by new and old tyres across the front and rear axles.

If there was a mechanical LSD in the centre diff then that could be the case, as with teh crap system in teh vauxhall 4X4. indeed when the dccd is locked you do get windup on low speed manoeuvring, but you won't on a uk box. Even the dccd windup sorts itself out and doesn't damage the box. it just sounds horrible (lots of clanking).

Modified versus standard suspension should make no difference to your situation unless the modded suspension is much harder or has been lowered too far.

E mail john felstead and ask him

John P

Scotty
I would suggest that the issue could be tyre related. I have recently replaced both front tyres as a pair, and am convinced that any corner taken at speed will see the front totally understeer with seemingly no grip at all. I have tried pressures when cold and letting them warm up and checking again, seeing a 4-5 psi increase when warm so have let some air out. This seems not to be so bad as when I first had them replaced. I have also put it down to the change in weather conditions i.e slightly wetter and maybe greasier.
Hope things settle for you soon
Cheers

Bubba po

zhastaph

(Bubba, wrong forum mate )

Hi Scotty Boy, just reading through all the posts on this thread, nobody seems to have pointed out the blindingly obvious, why don't you fit the rears on the front and vicky verky and see how she feels then?

And to agree with most of the other posts on here, new tyres can be very "slippy sliddy", but also don't neglect tyre pressures, I run 2psi less on the rear than the front, I find any closer to the front then the rear becomes very 'dancy' when charging into corners.

John P

and of course the more obvious that the ortation direction is correct

Scotty Boy

Fatboy - Thanks. I am glad you are confirming the tyre issue. I understand there are certain costs to scooby ownership, but i would rather avoid having to replace the front tyres if not necessary. In regards to lowering, the car has the prodrive suspension, so is far from being too low.

John P - Thanks. All these posts do seems to point quite simply at the change in tyres, and due to the weather conditions i have not driven in a manner suitable to scrub them in. I will also keep a careful watch on the tyre pressures.

Bubba Po -

zhastaph - thanks and a very valid point !!!! Can i just swap the wheels over myself - or does balancing need to be carried out again? Again, i will check the tyre pressure but will also try a slight difference in pressure between the front and rear.

John P - just checked, the tyre rotation is correct. Can that really make a difference?

Thank you so much people for your comments and patience with such a mechanical beginner

zhastaph

Nope, there is no problem with changin the backs for the fronts, unless you've got a really bad uneven tyre wear pattern in which case the car will feel very odd to drive indeed whilst they wear themselves back in.

It's not that bad an idea anyway as the fronts wear out quicker than the rears, so swapping halfway through their service life means that all four go at the same time. Harder on the pocket, but better on the car (driver feeling, not doing it wont hurt the car itself) as you have all four changed at once instead of a pair.

To answer your question targetted at John P. It really does depend on the tyre, not all tyres are directional. But yes it does make a difference, most noticable in wet performance. The tyre tread pattern will be designed to displace as much water as possible. If this tread pattern is reversed (tyre on wrong side of the car) then this is not going to happen very well. In fact you'll find some tyres with an arrow shaped wet tread pattern such as the Toyo Proxies trapping water underneath them

Scotty Boy

zhastaph - thanks again for the information. WOW i really am getting educated with tyres now. I am sure these bridgestones are correctly on the car because there is a big arrow with direction written on it and they all point forward. Makes it easy for peeps like me !!!!
However, i am interested in the idea of swapping them around anyway to allow the tyres to wear out together. I presume the fronts wear out quicker because of steering then?

zhastaph

Mostly. When you boot it outa corners and round roundabouts and stuff, weight transfers to the back of the car but away from the front, giving the front tyres less grip and so the car will tend to understeer. In this situation the fronts will be scrubbing but the rears as happy as larry. Also under heavy braking the fronts will take a lot more of the load than the rears.

The difference isn't as huge on a AWD scoob as it is on a front wheel drive car, I used to do about 4 sets of fronts to every set of rears on FWD vehicles , but it is nonetheless still there.

Scotty Boy

zhastaph - WOW you must have been some serious driving in that FWD car of yours OK, makes sense really - the weight shifts i feel when driving will of course impact the appropriate area of tyres too !!! Think i will still move the tyres around to test that theory too. Just holding out for a nice dry day which could take quite a while. Thanks again for the info.

Steve Whitehorn

iTrader: (13)

Agree with zhastaph and many others on here.

Tyres make such a massive difference. Pressures,wear,make etc.
To exagerate to make the point... Forget BHP etc the key thing that will make a car quicker and safer from AtoB than another is how it is set up to cope with bends and the foundation stone of that is the tyres.

As zhastaph pointed out to make quick but safe progress in a scoob on the road you want it to progresively understeer near the limit. Therefore the fronts allways wear at twice the rate of the rears.
I have also always found that putting the half worn rears on the front and the two new tyres on the back. Gives the back far more grip (once scrubbed in of course). I to also always run lower pressure on the back and higher pressure on the front to give the back more grip. I always use eagle F1s as they are a great tyre and if you stick with the same tyre you get used to it.

I find that by sticking to the above the handling becomes totally predicatable on the limit which therefore means the car is very quick.

Just my findings after lots of messing about. I have never had a problem with diffs through running different tread depths on fronts and rears. But can fully understand the reason for concern.

Best wishes and hope you get it sorted
Steve

Scotty Boy

Steve - thanks for your comments. Again, it makes sense the importance of tyres and their setup. I am definatly going to try the pressure difference between the front and rears.

The only thing i am slightly confused about is what end to rotate the new tyres too. I understand that zhastaph pointed out swapping the new tyres to the front and the part worns to the rear as a test. However, after the testing, seeing as the fronts wear at twice the rate of the rears - should i always get new tyres put on the rear and keep rotating the part worn set to the front?

Scotty

Scotty Boy

Just a quick update;

I adjusted the tyre pressures to make sure the rears were 2psi less than the fronts. The feeling is still there but that was kind of expected considering the tyres are not scrubbed in. Guess i will have to keep my fingers crossed for some dry weather

Scotty

Steve Whitehorn

iTrader: (13)

Keep us posted scotty as to what happens
Steve

Scotty Boy

steve - The only thing i am slightly confused about is what end to rotate the new tyres too. I understand that zhastaph pointed out swapping the new tyres to the front and the part worns to the rear as a test. However, after the testing, seeing as the fronts wear at twice the rate of the rears - should i always get new tyres put on the rear and keep rotating the part worn set to the front?

thanks, scotty

Scotty Boy

OK peeps, thank you so much for the comments and advice.
i would like to conclude this thread with my final findings;
* still a little wavey in the wet
* in the dry, grips like a beauty
* tyres still feel waxey and still only done 400 miles on the new rubber

* as such i now understand the importance of scrubbing new tyres in

take care and drive safely in the wet on new tyres

scotty

Fat Boy

Well you're still right side up and just about 100 miles to go. Not bad

DemonDave

iTrader: (13)