Ok. I live in PA and it has been snowy here for the past week.

Right before the snow I had a flat tire so I got a new tire put on my factory rims. Same as the factory supplied tires. Potenza 92R.

Well then it snowed. Everyhting seemed fine. I had a lot of antilock break feeddback on the icy roads. But that is normal. Then the next day I noticed a problem. The roads were fine no ice or anything and I felt my breaks acting strange.

When I am doign like 30-40MPH or more I apply my brakes and they feel very stiff. They are stiffer than normal. Then as I slow down to about 20 they let or or get soft and travle down some. Then I get a little ABS feeback in the pedal and it hits another poitn where it gets stiff again.

The car stops but this concearns me and I have no idea what it could be.

Anybody have any ideas or suggestions????

I would take it to the dealer as soon as you can, let them feel it, its hard to say what it could be without actually driving it.

Could be air in the brake system.

Jay McDade
Lincoln/Mercury/Jaguar Tech

How the heck would have air gotten into my break lines.

Could be. Feels like it might be but how and why?

I have cross drilled slotted rotors. YOu think the dealer will try to tell me I voided my warrenty?

Depending on what Impreza you have, I'm pretty sure that you have 4 chanel ABS (reads each tire seperately)
The one new tire may be causing the ABS to be over sensitive...
If you think the ABS is being problemmatic you can "pull" the ABS fuse & do some driving...
As far as air... hmmm

? how many miles are on the other 3 tires ?

If the new tire is too new you are SOL...
The max circumferance diffence between the bigest & smallest is around an 1/8" or 1/4" (I can't rember off the top of my head)

The rotors have little if nothing to do with the braking system lines & ABS controller...
If the system has changed "overnight" at the same time the tire was put on I would have to think that might be the cause.

I guess.

I thought that too. But the other tires are not a whole lot different. I would be suprised if that was the case but it could be. It did happen after the change. But I feel nothing while driving.

What gets me is nto the ABS but the fact that my brake pedal is very stiff to start out and then when I get down to about 30-35MPH the pedal moves down (loses stiffness) and it moves an inch or more then stiffens up again and I get brakign again.

To me that os more than a tire.

So what is the different. I will look at my manual tonight.

If I have one new tire that is bigger than the rest what are my options???

Does that mean I have to get 4 totally new tires? Or can I get the new tire shaved or worn in to the same level as the existing tires?

I don't want this to end up costing me an arm and a leg???

What are my options here?

DO you really think that a tire size different would cause such a noticeable change in the brake feel and pressure and loss of pressure? I could see it affection the ABS but the brake feel itself????




If the sizes were off wouldn't I feel a difference in performance and ride when doing 50MPH and not applying the brakes?

ABS info:

http://www.endwrench.com/pdf/brakes/FtSubaruABSS99.pdf

and the size diff should be <1/4"

Look here:

http://www.endwrench.com/pdf/drivetrain/MeasuringDeviceInfoS000.pdf

Peaty

PS have you checked your tire pressures? I've found the dealer likes to put more air than is proper in the tire. Maybe the new one is higher. A stretch but easy to check.

Good call on the preasures...
Depending on the tire & ballance of the car it can make a diffrence.

Personally I like to run 4 psi less in the rear...
Usually 38front/34rear...

If the new tire is pretty close you could try 1-1.5psi less in the new tire & do some testing... I wouldn't go too crazy on changing left & right mixxing (you don't run on a super speedway do you?)

If the old tires are too far gone & dont match up well you may need to change the other 3...

The difference in tread is about an 1/8 of an inch. I used a quarter to measure it. One tread (old tire) came from the bottom of the quarter up to the begining of the words "In God We Trust". The new tire came to the top of the words.

So that is not 1/8 of an inch it is less so the overall diameter is less than 1/4 inch.

I thought the proper pressures for the front tires was 32 and the reard was like 29 or something.

Those pressures are recommended by the factory. You do not have to follow them but are a good basis to start with. Do you mind keeping all of your brake problems in one post?

Originally posted by jasno999
I thought the proper pressures for the front tires was 32 and the reard was like 29 or something.

If you do any "hard" cornering you will soon find that the factory tires have a slightly soft side wall...
Increasing the tire pressure will help this...
If you read the tires side wall they are rated up to 44-45 psi if I rember...

There is a point of diminishing returns... too much pressure & the tires won't stick as well.
Also "harder" tires have less rolling restance for slightly better mileage.

Dealer told me warranty is void cause I have x-drilled/slotted rotors.

I took my car in for service today cause I am havign brake problems. Before he even got in the car he told me I voided my warranty cause I changed one part on the brake system so the entires system was voided when it came to the warranty.

Is this true. Cany they do that. What if my master cylinder is broken. Can they actualyl say it was caused my different rotors on the car and not pay for it under warranty?

I need some infor from you guys. Anybody else had similar problems?

I think that you really need to measure your tire circumfrence
pie*r^2 hint
3.14*16^2=803.8"
3.14*16.1^2=813.9"
If the new tire is a diff brand or even model you may need to get a diff tire



please don't start a thread and then another so simmilar.




If the tire thing does not pan out find another dealer

Originally posted by jasno999
if the sizes were off wouldn't I feel a difference in performance and ride when doing 50MPH and not applying the brakes?


no

>So that is not 1/8 of an inch it is less so the overall diameter is less than 1/4 inch.


The proper way to measure is a tape measure around the outside of the tire or the circumference Wouldnt that 1/8 inch translate into more than 1/4"? Circumferemce = Diameter X pi so if you add 1/8 radius increase + 1/8 for the diameter then you get C=D+.25pi or 0.785" more circumference.

Originally posted by jasno999
Dealer told me warranty is void cause I have x-drilled/slotted rotors.
I need some infor from you guys. Anybody else had similar problems?

The way the laws are written the part that has been upgraded isn't warrantied (not same Mfg.), but the rest of the system is still covered UNLESS the upgraded part IS causing the problem...

Ex:
If your pads are chewed by cheap slotting ( hey too bad )

If your ABS light comes on because of an electronic falure (they have to fix it unless they can definately prove your mod caused the problem)

Rotors are a simple part... there is slight (not likely) chance that the biasing is AFU & the fronts are too grippy...
The main thing is that if the rotors aren't over sized then nothing has realy changed except the heat disapation is better...

I put a coin in my tread. A quarter to be exact. The old tires cam up to the bottom of the words "IN GOD WE TRUST" On the new tire it came to the top of the words "IN GOD WE TRUST"

Now I know that is not the best way to do it but it is all I had at the time. To me that is about a 1/16 inch difference. So multiply that by two and you get 1/8 inch for the total tire. That should be within spec.


What is the proper way to measure the tire sizes?

Originally posted by Peaty
Circumferemce = Diameter X pi so if you add 1/8 radius increase + 1/8 for the diameter then you get C=D+.25pi or 0.785" more circumference.

I think that we're both wrong
radius*pie=cercumference


edit answered wrong the fisrt time

So what is the proper way to measure this and how do I know what is too much.

I am so confused.

sorry abput the confusion I had posted the worng formula (area)
then I read the post correcting my mistake
then read a liner speed formula but forgot that it was in radians
PEATY is right and I am wrong twice in one thread kinda scary

ok pretend I am an idiot and re-explain everythign to me

Look at the two links I posted above that are in PDF format. That is the Subaru way to measure. You need to measure around the tire's outside with a tape measure.

Peaty

PS: I can't take the credit for the correct answer. My wife helped me with the math, she's the Engineer in the family. And for some bizarre reason she thought it was fun math. Go figure. Then I hit her up with figuring out the reduction of the arc of throw with a short shifter and the difference above and below the pivot (fulcrum) point. She really liked that one. Maybe if I whisper the Pothagarem (SP?) theorem in her ear at night I might get more action :)

Re-explain it to me again.

Originally posted by jasno999
Right before the snow I had a flat tire so I got a new tire put on my factory rims. Same as the factory supplied tires. Potenza 92R.

. . . . . . .

When I am doign like 30-40MPH or more I apply my brakes and they feel very stiff. They are stiffer than normal. Then as I slow down to about 20 they let or or get soft and travle down some. Then I get a little ABS feeback in the pedal and it hits another poitn where it gets stiff again.

Hope you get this message in time... I had this same problem with my 02 WRX. My dealer reported to me that there IS a technical service bulletin on this problem with SOA. Sometimes when the spare tire is put on and the car is driven for a while, the ABS controller fails (or blows up or burns out..whatever). This is because the spare 'donut' has a different diameter from the rest of the wheels--it throws off the ABS system. I had my ABS controller replaced under the standard warranty (36k/3 years).

I was exhibiting the exact SAME symptoms you are, jasno999. Maybe try taking the car to another dealer that knows that crossdrilling the brakes won't blow out an ABS controller. ;) I even had to go to two different dealers before they would recognize the problem. I'll try to look on my service receipt and see if the TSB# is on there.. PM me if you need it.

- breed