Brake Pedal Fail When Cornering - Australia

[Tinerfeño]

Soft sidewalls would allow the effective rolling diameter to change during hard cornering.

There are steel belts below the tread. How the lenght of these will change?
Sidewall flex changes will not affect the forward movement per tyre rotation.

 

[Skydance]

If I recall rightly, the automotive press reviewers of the new shape Jimny reported a similar issue when taking fast corners. Can't remember if Suzuki adjusted anything or it was just a case of it being that type of vehicle that needed early intervention?

Yes the Jimny does it with its soft rolly polly suspension on fast bends, going up or down hill with barriers in front. It applies the stability control/ABS and it’s quite scary when you don’t know.

Jimny during the testing phase disconnected the auto brake instead opted for the stability control instead.

The fix is to upgrade suspension (with less roll) and fit stronger sidewall AT tyres.

Another thing to mention here is (ADAS vehicles only). People who lift their vehicles, taller tyres, new windows fitted, winch fitted should ideally get their camera on the ADAS re calibrated (within a certain threshold). This is why sometimes it gives false alarms like this.

These are things I learned with the Jimny.

 

[255/85]

There are steel belts below the tread. How the lenght of these will change?
Sidewall flex changes will not affect the forward movement per tyre rotation.

I am under the assumption that, when a tire is under inflated, the steel belt will become slightly concave - bend upward toward the rim - and mirror the normal convex curvature of the tire to retain the length of the tread. The belt (circumference) has to go somewhere when the radius is reduced. We don't see the tread from the side. We see the bulging sidewall and think the tread is straight. I could be misinformed though or my logic flawed. It wouldn't be the first time.

 

[Tinerfeño]

This may happen if:

• The tyre pressure is very low.
• Tyre sidewalls are stiff (bias-ply tyre, radial tyres have softer sidewalls).
• The surface is soft and will allow side areas push into the surface.

With radial tyres on a flat hard surface I really don't believe this will happen. And remember that the weight on the tyre is still supported by the deflatet tyre, in case of en empty Grenadier it is ~675 kg/tyre (~1500 lbs/tyre) and this needs to go to the surface.

 

[NQ94]

This bloke put a Gopro in a car and SUV tyre to see what happens.

View: https://youtu.be/rILyBg7ZjeI?si=TZMbwkD4NotHe0Yc

View: https://youtu.be/UZQXPLfOPXc?si=yc_RuPMPDB68rOA9

 

[Tinerfeño]

Nothing strange on those. But good to see how the balance powder will spread inside a tyre.
And the pulsing of the tyre which we see s actually a bulge constantly rotating as car goes on.
Sidewall flexing is already significant. Much more when tyre is deflated.

And you really can't deflate the first tyre

 

[Pat]

It did happen to me several times but just in one hair needle turn going downwards (steering on the left side) - while braking the outer right front might slip and ABS is intervening - very soft brake pedal for 1 second. In the winter I can replicate it always in that specific turn below 5 degrees Celsius with the standard AT Bridgestone Dueler tires (in the first 10 km) - it does not happen with Michelin winter tyres wich are softer. So guessing a mix of tyre temperature, rubber component of AT tyres and and sensitive ABS intervention.

 

[255/85]

The two videos showing the inside of the tyre look to my eye to bulge inward at low speed. Once things speed up and centrifugal force is stiffening everything up (centripetal force on the beads) then there is much less deforming.

The video below shows how pressure between the tread and surface can be reduced when tyres are deflated. The traction is better when the tyre is at normal inflation pressures. Go to 19:15 in this video...

View: https://www.youtube.com/watch?v=TOweeVYkyps

Does this prove my point? Probably not as there are too many unknown factors. Again, I'm not convinced I am correct. I will say that, if I was asked to illustrate a tyre tread becoming concave at the contact patch when deflated, I would show exactly this. Even the host (ASPW) seems confused by the behavior and says "This made it worse. Not sure why.".

 

[Tinerfeño]

Good basic stuff.

But I strongly disagree with the effect of tire pressure. Here are two examples:

1. I have arranged several offf-road traning sessions. This was for teachers of car mechanics. I had road pressures (2,5 bar) on tires. My Discovery started to bog down on uphill sand. I stopped, reduced tire pressures to 1,2 bar and without moving the car started again and continued.

2. On a two-day off-road safari this Discovery 2 used road pressures on the first day. It had lots of wheel spin and needed reversing, more speed and occasional winching on places we have been driving for years. Conditions were good, dry and relatively warm. No other car had problems. For the second day we lowered pressures and all good!

 

[Tazzieman]

Simply speking , lowering pressures turns your car into a tank/bulldozer. Sort of!

 

[Chops]

Hey All, just thought I'd ask if anyone else has issue with their brake pedals when turning? So I was driving along in the road and decided that I wanted to turn right into a small street, hard brake and turned wheels to right and brake pedal gave way for a split second and then recovered. Each time this has happened since it makes a clicking sound when it happens, just recently it happened travelling slowly when I made a quick right turn on a roundabout. This fail has been frequent and scare the crap out of me every time. It has never happened without wheels being turned. Can anyone help?

I have experienced a “hard” brake pedal a few times but I drive a lot of C roads and I think it is related to lifting a wheel / momentarily losing traction and seems to be part of the ESC response. Only for a split second as you say. The noise I have had is more a vibration than a clicking sound - like ABS feels when it activates, but with a hard pedal and only very briefly. Scared me the first time and not since. 67,000km diesel TM