Technical weird brake problem

[thrash911]

ok here we go, been a while since ive been on. my sons 54 plate sport 8v was due for some rear tyres so i go to the local scrap yard that my mate owns cos i get my tyres for free. he didnt have the 185/55/15s that the car needed but had 185/65/15s by the dozen, he told me to take them and he would keep 2 good 185/55s for me when they came in as he was expecting a punto in a few days later. fitted the tyres and after 10 mins my son rings me to say theres a problem with the brakes on his car. i take it for a spin and the car was making a noise from what sounded like the abs motor , and the brakes where acting like the front abs was working when the brakes werent even being prerssed hard ,( as in normal driving) not braking hard. also there was a weird ticking noise coming from the n/s rear brakes after you released the brakes, but this didnt do it all the time. (maybe 1 in every 3 times you pressed the brake). i was a bit confused and had a good look round the car incase he had bumped the car some where and wasnt tellin me. didnt find anythin and told him i would look at it later in the day if i had the time. anyway cutting a long story short it was 2 weeks before i could look at the car and try and fix it. (he had been using it for work in that time with the same problems). my mate phones to say he has the tyres i need and i nip down and get them fitted, get back fit the wheels take the car for a spin so i can remember what the exact faults were . and the bloody thing has no faults. get my son to drive it and he says that was quick what was it. i aint got a clue but use it for a couple of days and see if its ok. hasnt missed a beat since. its got me really confused. anybody else had this problem as i couldnt see how fitting tyres with a slightly higher prowfile would cause all this hassle.

 

[Ziggy122]

i take it - you kept the original rims when swapping tyres?

All i can think of is that there was some crud in the drums (rust - dirt - water etc etc) Was shook loose when a impact gun was used?

whats making me worry is that since your using higher profile tyres it has todo less revolutions todo 1mile compared to the fronts

The ABS is picking this up when braking - thinking its locking up act now to prevent it happening

and hence noises and stuff appear
With ABS you need to use the same size tyres all around - or at least the same rolling radius as best as you can
If you check the difference with this neat tyre calculator - this is what you get
http://www.miata.net/garage/tirecalc.html

185/65/15 makes the circumference 4inchs larger then 185/55/15

So in a mile
The 185/55/15 do 876 revolutions
the 185/65/15 do 824 revolutions

Thats quiet abit.... hence abs is working due to a quicker speed been recorded on the front.....

Im gonna stop babbling now

ziggy

 

[Brendan W]

:yeahthat:
The ABS thinks either the rears are locking up or the fronts are spinning or a bit of both and is trying to get all the wheels rolling at the same-ish rate.