Speed 3 brakes - I'm wondering.....

[tripledigits]

....if Mazda gets their short stopping distance by using more rear brake bias than other manufacturers. The reason I'm wondering is that I did my first hard braking yesterday on the way to work. I was on the freeway, doing 75 in a 55, when I came around a bend and saw a radar trap. I applied the brakes pretty hard, since I saw the man had the gun on me, and I actually had to react pretty quickly with some steering inputs to keep the car going straight. I was going pretty much in a straight line, and was surprised the car was as squirrely as it was. I have experience the feel of too much rear bias, have lost a single rear brake on the track with my race car, and have spun karts that only have rear brakes. So I have a good feel for what too much rear brake is like. Unless the road surface was goofy (there is some dishing in the lanes on this freeway), I'm betting there's a good amount of rear bias on our brakes. I'm going to test this theory by getting the brakes nice and hot some day soon, and take the rotor temps front and rear. I'll post with the results.

 

[daonly1around]

this might be true, i remember a guy spinning from slamming on his brakes, like the rear end came around on him, it was a silver one

 

[silverspd3]

My car has the best brakes of any car I have owned. I think it does have more rear bias but it seems ok on mine. Only wiggles a little in a panic stop without antilock kicking in. I love it.

 

[cosmic_spd3]

Are you guys driving with the DSC/TC on??it shouldnt do that when ur goin straight..

 

[CosmoMS3]

....if Mazda gets their short stopping distance by using more rear brake bias than other manufacturers. The reason I'm wondering is that I did my first hard braking yesterday on the way to work. I was on the freeway, doing 75 in a 55, when I came around a bend and saw a radar trap. I applied the brakes pretty hard, since I saw the man had the gun on me, and I actually had to react pretty quickly with some steering inputs to keep the car going straight. I was going pretty much in a straight line, and was surprised the car was as squirrely as it was. I have experience the feel of too much rear bias, have lost a single rear brake on the track with my race car, and have spun karts that only have rear brakes. So I have a good feel for what too much rear brake is like. Unless the road surface was goofy (there is some dishing in the lanes on this freeway), I'm betting there's a good amount of rear bias on our brakes. I'm going to test this theory by getting the brakes nice and hot some day soon, and take the rotor temps front and rear. I'll post with the results.

I noticed the same thing driving my regular 3 (Mazda 3), before I got the Mazdaspeed3. Also, on the regular 3 I had a LOT of brake dust on the rear rims. About 3 times more then on the front wheels. However, my MS3 seems to be front biased compared to the Mazda 3. That's how I feel the brake and the brake dust seems to confirm it.

 

[ericrapp]

I was surprised by your statement till you said dishing in road. I have braked this car hard in quite a few intriguing angles and have not found an excessive amount of rear brake bias. I worry that something else might be wrong, high rear tire pressure?

 

[tripledigits]

I was surprised by your statement till you said dishing in road. I have braked this car hard in quite a few intriguing angles and have not found an excessive amount of rear brake bias. I worry that something else might be wrong, high rear tire pressure?

I've been experimenting with tire pressures. Running 40f 38r right now. MPG went up a couple points..... Could be a factor.

 

[ericrapp]

I've been experimenting with tire pressures. Running 40f 38r right now. MPG went up a couple points..... Could be a factor.

Sure, that is going to help mileage. Kind of neat how you upped pressure and stayed consistent balance f/.r. The standard I understood was that raising the pressure would deform the tire a bit by expanding the center and creating less rolling resistance. This might well have changed with the high performance summer tire designs. But it sounds true in your case. I still think higher pressure means slippery but also higher pressure might strengthen the sidewall during cornering . I'm sure sure the rules change with the type of tire used

 

[Conso]

ima hav to replace my rear brakes soon but yet the front ones are fine wtf lol but she does stop pretty freakin fast, 25k miles

 

[6262MS3]

MS3 has electronic brake force distribution, so it can automatically adjust braking bias.

 

[tripledigits]

ima hav to replace my rear brakes soon but yet the front ones are fine wtf lol but she does stop pretty freakin fast, 25k miles

May be an indication that there is a fair amount of rear brake bias.

 

[happy and angry]

I largely doubt that there is a rear brake bias on this, or any other front engined car. This is the sort of talk you hear from people who play a bit too much Gran Turismo.

This vehicle is nose heavy, which is something only made worse when you get on the brakes hard. Something around 80% of your braking force is provided by the front end of your car, because that's where all the weight is when you're slowing down hard. No manufacturer in their right mind is going to give something that gets nose heaving under braking a rear brake bias.

This isn't an rear engined gokart with your ass planted close to the rear axle, this is a 3200 pound car with a 60/40 weight distribution slowing down hard from 75 mph. If your ass end is getting squirrely when you get on the brakes, it could be a number of things, but I seriously doubt it's because there is a "rear brake bias" on this car. Suspension settings, tire pressure, road conditions. Brake bias should be the absolute LAST of your suspicions.

 

[Silver Ecstasy]

There is Brake Assist as well, don't forget that. When you push the pedal super hard, it applies extra force.

 

[ptrautne]

I have also noticed that the cars rear brakes lock-up before the front. I have had hit the brakes hard 7-8 times now in the car and everytime the back end breaks loose and wants to walk around.

 

[mordant80]

Hey, atleast we oughta be able to get the car to rotate at the autocross!

 

[~JoJo~]

i changed my front brake with hp+ and it's been almost 600miles, and I am still hearing the sqeaking everytime i brake, is that normal or did I do something wrong? Perhaps I have to replace the rotors? (hope not) The braking seems very solid, just the noice is driving me nut

 

[ericrapp]

Something is odd here

I have also noticed that the cars rear brakes lock-up before the front. I have had hit the brakes hard 7-8 times now in the car and everytime the back end breaks loose and wants to walk around.

Sorry I am kind of amazed this occuring to more than one driver and car. I certainly believe your experiences, but I can not believe that was the design intention. Especially on our unbalanced weight as mentioned and true, my car does not act that way. Is this is straight line or ass end hanging out braking?

 

[ptrautne]

Sorry I am kind of amazed this occuring to more than one driver and car. I certainly believe your experiences, but I can not believe that was the design intention. Especially on our unbalanced weight as mentioned and true, my car does not act that way. Is this is straight line or ass end hanging out braking?

7-8 times were when I was driving straight on a smooth road, you could feel the rear brakes lock up then the ABS kick-in (showing friends how well the car stops). I have hit the brakes hard twice going around a corner and the same affect happens (I am new to cars but I think thats normal). My car over steers (rear tires break loose in corners) but I hear reviews that the car under steers (front tires push). One day I was following my boss home on curvy roads and we both pushed it through a corner (he has a standard 3) and his car the front end pushed on him but my car the front had traction the back end walked around on me. I am new to cars but I am sure the rear end was locking up first because my truck would do the same if I did not have the portioning value set right

 

[ericrapp]

Houston

7-8 times were when I was driving straight on a smooth road, you could feel the rear brakes lock up then the ABS kick-in (showing friends how well the car stops). I have hit the brakes hard twice going around a corner and the same affect happens (I am new to cars but I think thats normal). My car over steers (rear tires break loose in corners) but I hear reviews that the car under steers (front tires push). One day I was following my boss home on curvy roads and we both pushed it through a corner (he has a standard 3) and his car the front end pushed on him but my car the front had traction the back end walked around on me. I am new to cars but I am sure the rear end was locking up first because my truck would do the same if I did not have the portioning value set right

This is wrong, I am not real smart about cars but i am learning. You need to get this fixed. I am thinking fluid valving. You have way too much rear. some folks might think this is fun. But it is really unsafe, so please take it to an expert or Mazda right away. It might be that the fronts actually are faulty.

 

[happy and angry]

You guys have to keep in mind vehicle dynamics. When you brake, most of the weight is thrown forward, which is why most of the braking is done by the front and also why vehicles have bigger brakes up front. The consequence of this is that the rear brakes can and WILL lock up more easily than the front. It's not a "brake bias" thing. The vehicle is not set up to clamp down at the rear harder than the front.

You're also forgetting chasis rigidity. The Mazdaspeed3 is a lot more stiff and resistant towards tortional (twisting) stresses, which tends to make the rear end oversteer. With enough side to side weight transfer, a vehicle's chasis will actually twist a bit, and combined with softer suspension is a contributer to body roll. Our car is stiff front and rear, the suspension doesn't roll a lot, and neither does the body. That's one reason why we can lift-throttle oversteer in a corner, and it's also a big reason why under braking the rear end gets a bit loose. It's a bit of a simplified explanation, but, I'm lazy tonight I guess.

With your nannies on, ABS, brake booster, etc, this tendency should not ever get out of hand. When the rear starts to lock up or slip, the nannies or ABS or brake booster kick in. High speed and sudden brake inputs can upset the most carefully controlled car, however, and you need to be smooth (not sudden) with your application of the brakes. If you're cruising on a highway and say "Hey check this out!" and then just hammer on the brakes in an emergency stop, I'm not surprised your ass is walkin' around on you a bit. This is true under any circumstance in any vehicle.

If you're having this problem consistently you need to look at all the variables involved. Have you modified your tires or suspension? Your brakes? Your toe, your camber? How's your tire pressure? All normal? Okay, road conditions, they okay? Flat, no camber at all? Cool. Check your suspension components. Ask yourself important driver questions: are you braking hard or suddenly in a corner when you're pushing the limits of traction? (Note: DO NOT DO THIS, YOU WILL SPIN YOUR CAR, IT'S NOT THE CAR'S FAULT AND IT'S NOT BROKEN. In your story you say you pushed into a corner and tried to recover - if you hit the brakes too hot in a corner, no wonder your ass got out of shape. Next time slow down before the turn, and take a driver course to learn some vehicle dynamics).