Shitty Brakes

[rparker]

Hi guys,
This isn't necessarily about my LS400 but actually my hilux surf which is really giving me the scares. I posted it here coz I know you guys know what you're talking about and this is a security thing so I don't want to be messing around.

Anyway its to deal with my ability to STOP with my hilux surf...it just doesn't. The wierd thing is that the tyres just lock-up all the time (I don't have ABS) but I know how to modulate the peddle.
I currently have 265 tyres on 15 inch rims which by the width should be pretty hard stoppers no? I do note that the cars got stupid drum brakes at the read and small little discs in front.

Now my question is this, does the size of your brakes determine the lock-up point or is it purely a function of the tyres? I got 265 up front for heavens sake and my stopping is so much worst than my LS400 on 205s!!!

If I change the brakes to supra brakes will it stop my tyres from locking up so much? Or is there something wrong with my tyres (all 4 are brand new with proper pressure btw) but are semi off-road tyres.

My mind is cast back to a BBC Top Gear moment where Clarkson test the Mclaren SLR and almost got his face ripped off when he tried to brake from 200mph. I'd like that feeling and security, not some train of a surf that I'm driving now. How do I get it??? the brakes?? can't be the tyres....265!!! New!!

Anyway, any feedback would be great.

Ryan

 

[mycarhasposessedme]

I would suggest that your problem lies with your vehicles ability to transfer weight to the front wheels under braking.
Just as a vehicle needs weight transfer to the rear wheels to gain adequite traction under hard acceleration the same needs to happen to the fronts under braking.
Think of it this way, the harder you push the tyre to the road the harder it is to break its grip.
Cars like the Mclaren are designed with front suspension & geometry to maximise braking effort.
I would be looking firstly at your suspension being too stiff.
Missmatched springs and shocks?
Has it been lifted?
If its all standard, I'd probably look at changing to more of a road tyre as they will perform better under braking than a semi.
Cheers

 

[rparker]

I never actually thought about the suspension before! Now come to think about it, that might be the problem!! The thing is that I've got standard suspension (read overly soft). Do you think overly soft springs could be responsible for the problem?

 

[Anaema]

i doubt springs is really the problem, since they only hold the chassis off the wheels. shocks are really the major piece, they control the movement of the wheels as you go over bumps and the weight transfer from front to back. push on each corner of the vehicle. if is gives very easily, then a shock is bad.

 

[mycarhasposessedme]

Yeah, shocks would be definately the next place to look.
Do you have a suspension and brake specialist anywhere near you?
It really is a matter of working through the most likely causes and noting improvements. This is where a specialist can sometimes save you time and money, so you don't needlessly replace the wrong bits.
Personally I'd fix the suspension then look at the tyres.
Also, as I'm sure you're aware, your Surf will never brake as well as your LS but it sounds like there's plenty of room for improvement.
Cheers

 

[UCF3]

Lowering the truck would also help. I've raced a couple of modified tundra and Tacomas, and they're lowered to almost the street level.

do you have any brake-fade?

Now I've upgraded the Stock brakes on my 94 LS with Stoptecs and it definitely helped lower the distance traveled, but this is a passenger vehicle /w ABS we're talking about.

 

[rms]

Do the rear wheels lock before the fronts?
Does it lock all 4 wheels?
Is there a proportioning valve linked to the rear axle?
Is the braking system mechanicaly sound?

Front wheels need to lock just before rears.

If the system and front to rear bias is OK then it will boil down to tyre grip.

Weight transfer, shocks, ride heights etc do have an influence, but I believe your problem is more basic.

 

[rms]

A couple of things about braking/acceleration weight transfer and traction.

While it is true that a rear wheel drive car will benefit from weight transfer to the rear under acceleration, it only has the rear tyres to put power to the road. A dragster with the front wheels off the ground will have all the weight on the TWO rear tyres.

Under braking however it is a different story, you have four tyres to apply the braking force.
A transfer of weight to the front will have a decrease of weight on the rear. The increase in traction at the front is not as great as the decrease in traction at the rear and the TOTAL traction will be less.

Take this to extremes, if the car had the rear tyres off the ground you would only have TWO tyres doing the braking not FOUR.

The McLaren has front anti-dive, and rear anti-lift/squat geometry to minimise weight transfer under brakes, and under acceleration lift the rear of the car - therefore pushing down on the tyre.

 

[rparker]

Hi guys,
Thanks for the replies.

Speaking about these anti-dive geometries, is there anyway that it can actually be incorporated into a 4x4? The rears don't lock up at all but the fronts lock up very easily.

 

[rms]

Seems like your rear brakes are not working at all.
Most road vehicles these days have some degree of anti-dive.

 

[UCF3]

I don't think it exists for the Rx/hilux but coilovers might help since they have settings to reduce ride-heightand stiffness of the shocks. It sounds like you might need a brake-job or at least have the rears looks at.

I know about the anti-dive, but since the truck doesn't have an ABS I doubt it's going to help reduce the stopping distance.

I wonder how the German Chayenne's are setup. I've heard they're not ABS Stocked.