[hellspawn]

but you are forgetting that by going for rear disc brakes in place of drum brake,you will be changing the brake bias of the car for which the car hasnt been designed.all cars are designed keeping this is mind during the production stage.under heavy braking,whether the car stays neutral or the rear steps out etc. cannot be calculated due to the tuners not having the resources or the tools to judge this and it will be more of a trial and error.its not wise to tamper with the brake bias of the car without any knowledge.Even GM,when shifting from drums to disks would have changed a lot of things which you would not come to know.and if GM is saying NO,there has to be a reason otherwise why would they say no to money(for the disc brakes).when GM would have changed the rear disk they would also have made some modifications to the front brakes.
do not go for an aftermarket job.
best is as suggested by iraghava,try to source better pads for the optra.you will get them in the us etc.

the other best solution is to drive slow

[gdhiraj]

Originally Posted by Boom Shiva

Happens with my dad's car too. Personally I think it's lack of EBD - the front is braking harder than the rear because of front discs v/s drums at the back. Hence sometimes the car tends to slide a bit sideways and needs course corrections. This has happened a couple of times on the Expressway, NH4 etc when someone's suddenly cut from the left and forced me to stomp on the brakes.

Of course I could be wrong about the cause, which is why I'm asking.

GM Service is useless for anything outside the basic parameters that they're trained for. I could give the car to a bunch of monkeys who'd probably find a better and quicker solution.

Shiva - i am with you on this one .. i agree on ur point of the cause as well as the service levels of GM in India .. We should riase this up with GM as them to test drive it .. the ONLY reason why GM introduced Disc on rear wheels in new models could be this problem alone .. are u with me in starting a conversation with Tech Manager of GM ?

[gdhiraj]

Originally Posted by hellspawn

but you are forgetting that by going for rear disc brakes in place of drum brake,you will be changing the brake bias of the car for which the car hasnt been designed.all cars are designed keeping this is mind during the production stage.under heavy braking,whether the car stays neutral or the rear steps out etc. cannot be calculated due to the tuners not having the resources or the tools to judge this and it will be more of a trial and error.its not wise to tamper with the brake bias of the car without any knowledge.Even GM,when shifting from drums to disks would have changed a lot of things which you would not come to know.and if GM is saying NO,there has to be a reason otherwise why would they say no to money(for the disc brakes).when GM would have changed the rear disk they would also have made some modifications to the front brakes.
do not go for an aftermarket job.
best is as suggested by iraghava,try to source better pads for the optra.you will get them in the us etc.

the other best solution is to drive slow

Just wanted to check ... If we improve the brake pads for front disc then my worry is the the rear outward shift will be more as front wheels will stop much faster ... isnt it ?? Whats a Brake bias ? and what are the parameters for brake pads .. i am going to US soon and would like to secure these stuff you guys are talking about .. shall i try to procure super ventilated disc also ? What are the ways to improve Drum brakes ? Again the pads or something more ?

[hellspawn]

Originally Posted by gdhiraj

Just wanted to check ... If we improve the brake pads for front disc then my worry is the the rear outward shift will be more as front wheels will stop much faster ... isnt it ?? Whats a Brake bias ?

[FONT=Arial][SIZE=2]
Brake Bias is just a fancy way to describe how the braking force will be distributed between the front and the rear tires.[/SIZE][/FONT][FONT=Arial][SIZE=2]As your car decelerates, weight is transferred from the rear to the front tires. This weight transfer reduces the amount of braking force the rear tires can produce. Apply too much braking to the rear wheels and they will lock up causing the rear end to lose traction and possibly swing around violently.[/SIZE][/FONT][FONT=Arial][SIZE=2]As a general rule, 60% of your braking capacity should be on the front tires. Whatever the percentage is for the particular car, the front tires should lock up slightly before the rear tires.thats the reason why most of the cars have disc brakes in the front and drums in the rear and not the other way around.
so for gm to put disc brakes in the rear,they would have definitely increased the braking efficiency of the front discs too.

[/SIZE][/FONT]

[gdhiraj]

Originally Posted by hellspawn

[FONT=Arial][SIZE=2][/FONT][/SIZE]
[SIZE=2][FONT=Arial]Brake Bias is just a fancy way to describe how the braking force will be distributed between the front and the rear tires.[/SIZE][/FONT][FONT=Arial][SIZE=2]As your car decelerates, weight is transferred from the rear to the front tires. This weight transfer reduces the amount of braking force the rear tires can produce. Apply too much braking to the rear wheels and they will lock up causing the rear end to lose traction and possibly swing around violently.[/SIZE][/FONT][FONT=Arial][SIZE=2]As a general rule, 60% of your braking capacity should be on the front tires. Whatever the percentage is for the particular car, the front tires should lock up slightly before the rear tires.thats the reason why most of the cars have disc brakes in the front and drums in the rear and not the other way around.[/FONT][/SIZE]
[SIZE=2][FONT=Arial]so for gm to put disc brakes in the rear,they would have definitely increased the braking efficiency of the front discs too.[/FONT][/SIZE]
[SIZE=2][FONT=Arial][/FONT][/SIZE]
[SIZE=2][FONT=Arial][/SIZE][/FONT]

Agree ... just wondering why would GM enhance braking in new model of Optra ??? was there a problem with the old one ? I mean its not a Fancy / cosmetic enhancement .. its a capability of car .. which should / cannot be changed without a solid reason .. thought ?

[gdhiraj]

Today i applied breaks at about 80K/h and vola ... i felt vibration for a second in the steering wheel then it was gone .. again accelerated applied brakes and felt the vibro again for a second ... gosh .. dont know if its due to worn out brake pads or somethings else is gone wrong with the car ?

[gdhiraj]

Can someone suggest me what should i ask the PepBoys or Advance Auto Parts in US if i want to have replacement high performance brake pads for my Optra .. i mean i dont know the parameters of brake pads .

[iraghava]

Originally Posted by gdhiraj

Today i applied breaks at about 80K/h and vola ... i felt vibration for a second in the steering wheel then it was gone .. again accelerated applied brakes and felt the vibro again for a second ... gosh .. dont know if its due to worn out brake pads or somethings else is gone wrong with the car ?

Could be due to two reasons:

1. Worn out brake pads which could have uneven wear & could be causing the vibrations.

2. Also you could be having warped brake discs which usually results in steering vibrations.

Both are minor problems & do occur in regular running of the car depending on the driving style and GM garage's are qualified enough to handle these problems.

Also Dhiraj please stop being paranoid about the brakes of your car. From what I can see you don't push the car around much & the speeds you've described are very moderate. If you really wanna spend money get your car a good set of alloys & wider tyres & that should improve the grip & stability of your car further. All the suggestions that you've made reagrding the Rear Discs, ABS, EBD etc.are not viable after-market solutions in India. Please don't waste your time or money on these things & if you do have lots of spare cash do venture in the ICE forum sometime those guys love spending other people's money

[gdhiraj]

Originally Posted by iraghava

Could be due to two reasons:

1. Worn out brake pads which could have uneven wear & could be causing the vibrations.

2. Also you could be having warped brake discs which usually results in steering vibrations.

Both are minor problems & do occur in regular running of the car depending on the driving style and GM garage's are qualified enough to handle these problems.

Also Dhiraj please stop being paranoid about the brakes of your car. From what I can see you don't push the car around much & the speeds you've described are very moderate. If you really wanna spend money get your car a good set of alloys & wider tyres & that should improve the grip & stability of your car further. All the suggestions that you've made reagrding the Rear Discs, ABS, EBD etc.are not viable after-market solutions in India. Please don't waste your time or money on these things & if you do have lots of spare cash do venture in the ICE forum sometime those guys love spending other people's money

Buddy if i had lot of cash i would have spent in buying a Civic and not trying to improve my existing Optra .. point is i felt uncomfy when those things (outward shift and vibro) happened at those moderate speeds ... i thought i can get some good education here.. .. otherwise i am cool .. i love the car ... I will leave ICE for kids for now ..... no sweat bro .. i will close this thread ..

[iraghava]

Originally Posted by gdhiraj

i will close this thread ..

No you can't

[gdhiraj]

I am here again, got 205/55 R 15 ... on a HiJoin 15 inch wheel .. car braking has improved but stability have become worse .. it rattles, shakes and what not .. some expert is telling me i have wrong offset of my new wheels and also 205 is too wide for my car engine .. i am fedup

[ananthkamath]

Originally Posted by gdhiraj

Can someone suggest me what should i ask the PepBoys or Advance Auto Parts in US if i want to have replacement high performance brake pads for my Optra .. i mean i dont know the parameters of brake pads .

Pepboys? Not happening. if you do want high performance parts for your optra look online and get them shipped. brake pads like these shouldnt be too hard to ship & get thru customs:

eBay Motors: 04 SUZUKI FORENZA FRONT CERAMIC BRAKE PADS (item 8060943058 end time Jul-22-07 11:00:05 PDT)

Cross-drilling wont help unless there is a problem with fade and I dont think you'd drive hard enough to induce fade.

[BUSA]

Originally Posted by gdhiraj

I am here again, got 205/55 R 15 ... on a HiJoin 15 inch wheel .. car braking has improved but stability have become worse .. it rattles, shakes and what not .. some expert is telling me i have wrong offset of my new wheels and also 205 is too wide for my car engine .. i am fedup

Thats quite a wrong size for the Optra. I had 205/55/15 on mine and after around 15000kms the tyres not even reached 30% wear i changed them to 205/50/15 Dunlop SP9000, since 205/50 is the right upsize for the Opra and not 205/55/15

Offset for Optra is 40mm

No 205 is not too wide for your car, Gods grace i am having no issues with 205's nor with standing on the brakes at speeds in excess of 160 but then mine comes with factory fitted discs, ABS, EBD and alloys, so no such issue of wrong offset.

Whats the offset of your wheels?

[iraghava]

I would suspect that both the offset & PCD are wrong on your alloys which is leading to the shakes & also affecting stability. Where have you bought your wheels & tyres from? And has the balancing being done on the new wheels prior to fitting them?

BUSA - 205/55 is also an acceptable upsize on the Optra.

[BUSA]

BUSA - 205/55 is also an acceptable upsize on the Optra

Its acceptable but not the best, the inner wheels foul with the body on full lock and hence i shifted to 50 profiles.