4x4 brakes
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Thread: 4x4 brakes

  1. #1
    2000+ Brad's Avatar
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    4x4 brakes

    Just a short one...why do most, if not all 4x4's have large diameter brakes at the rear?

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    B to the R to the A from the D
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  2. #2
    Gone Fishin' Ray Bell's Avatar
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    They have a fair bit of weight on the rear wheels, generally... and they would be single leading shoe brakes.

    Are they also fairly narrow?

  3. #3
    2000+ Brad's Avatar
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    Yeah, from what I have noticed they are. Especially RAV4's.
    B to the R to the A from the D
    1994 MX5 Clubman...are you sure it's not French?

  4. #4
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    To look better through the fine spoked 20" alloys they all seem to have these days
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  5. #5
    1000+ Posts cruiserman's Avatar
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    Mine has the same size as the front, slightly smaller swept area due to the stupid handbrake setup in the disk. Fair sized pads and single pot calipers. Dont forget that when reversing down steep, rutted hills the rear brakes do the work. Fronts are of little use when the track is shaly and steep and wet and you are going backwards.
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  6. #6
    2000+ Brad's Avatar
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    As a matter if interest, the new BMW M cars have larger rear brakes than fronts. Apparently it's due to the traction control system, which activates the rear brakes when traction is lost, can overpower lesser setup's.
    B to the R to the A from the D
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  7. #7
    Sense Pug307's Avatar
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    406 does as well.

    IIRC, 283mm at the front (same size as the 206 GTi180, 306 GTi-6, 307) 290mm at the rear.

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  8. #8
    1000+ Posts CHRI'S16's Avatar
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    I noticed this too, but one thing that is considerably smaller on the rears is the contact surface area...
    i think its got to do with the towing abilities of the cars/4wd. The inertia in a 4wd is huge and moving itself and a trailer would require big rear axles to transfer the power to those huge wheels. bigger axles would need to be cleared by bigger diameter disks?? hows this theory sound guys?... just a thougt. - chris
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  9. #9
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    It is simply a matter of cost.

    It is cheaper to manufacture rear discs using an internal drum handbrake setup (I dont know why). The drum on a 4wd would have to be of a reasonable size to actually hold the 2.5 tonnes that alot of 4x4's weigh. The bigger the internal handbrake drum, the bigger the disk diameter...

  10. #10
    1000+ Posts cruiserman's Avatar
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    It is simply a matter of cost.
    It is cheaper to manufacture rear discs using an internal drum handbrake setup (I dont know why). The drum on a 4wd would have to be of a reasonable size to actually hold the 2.5 tonnes that alot of 4x4's weigh. The bigger the internal handbrake drum, the bigger the disk diameter...
    Bollocks internal drum handbrakes are a pandering to the toorak tractor set who cant use a proper drive shaft mounted transmission brake. The inner drum handbrake on the 80 series landcruiser must be kept in perfect adjustment to be of any use whatso ever.
    Neil
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  11. #11
    Real cars have hydraulics DoubleChevron's Avatar
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    Hi Guys,

    just look at what a Cruiser can tow, about 3+ tons (Cruiserman??). Man if I had to tow something heavy they'd be at the top of my shopping list (right next to a light/mediam rigid truck --well they are the same thing).

    Has anyone here actualy looked at the specs for the new HDi turbo deisel cruisers eek! eek! Man the torque those thing create is downright stunning !! With that sort of power and towing capability I'd be downright shocked if they didn't have mamoth sized brakes under 'em wink

    Yes I know the middle aged women will never use the capabilities... but still... If I had something really heavy to move, maybe some mother with 2 kids will allow me to borrow her barge for a couple of hours ...

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  12. #12
    Gone Fishin' Ray Bell's Avatar
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    Originally posted by CHRI'S16
    <strong>I..... think its got to do with the towing abilities of the cars/4wd. The inertia in a 4wd is huge and moving itself and a trailer would require big rear axles to transfer the power to those huge wheels. bigger axles would need to be cleared by bigger diameter disks?? hows this theory sound guys?... just a thought. - chris
    Even on large trucks, the axles don't get to be that big...

    Not a valid suggestion, really.

  13. #13
    Fellow Frogger! seesully's Avatar
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    Hi,

    A larger rear disc, in simple terms, equals greater stopping power.

    You will also find that alot of newer 4x4's and cars have EBD (Electronic Brakeforce Distribution) or the equivalent. Theses systems allow there to be an even amount of braking force applied to the front and rear wheels regardless of whether it is empty or fully loaded. In the instances of when the vehicle is fully loaded, a larger rear disc or drum is required to allow for appropriate stopping power.
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  14. #14
    Member Freddie's Avatar
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    Looking at most front brakes these days on larger cars there appears to be limited space to increase their size by much so its logical for greater braking power to look elsewhere - hence rear disks

  15. #15
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    mistareno:
    It is cheaper to manufacture rear discs using an internal drum handbrake setup (I dont know why). ...
    Internal drum cable operated handbrakes work better than caliper cable operated handbrakes. Anyone who has done any mechanical engineering studies will know that it's just a matter of mechanical advantage. It's very hard to make a cable handbrake work well with a caliper and still get acceptable handbrake lever travel and reliability of adjustment. Percentage-wise there's alot more caliper handbrakes out there which are out of wack and not working properly anymore than there is amongst the drum type.

    Dave

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  16. #16
    Fellow Frogger! BigH's Avatar
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    Have you checked out the torque figures on the new VW Taureg 4X4 V10 twin turbo diesel? 750 Nm. They reckon you can use it to tow cities.
    Hank.

  17. #17
    Gone Fishin' Ray Bell's Avatar
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    Originally posted by Freddie
    <strong>Looking at most front brakes these days on larger cars there appears to be limited space to increase their size by much so its logical for greater braking power to look elsewhere - hence rear disks
    Not really...

    You can only apply so much braking to the rear before you lock the wheels and make it very hard to retain control.

    Brake balance is still required...

  18. #18
    Sense Pug307's Avatar
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    Ray Bell:
    Originally posted by Freddie
    <strong>Looking at most front brakes these days on larger cars there appears to be limited space to increase their size by much so its logical for greater braking power to look elsewhere - hence rear disks
    Not really...

    You can only apply so much braking to the rear before you lock the wheels and make it very hard to retain control.

    Brake balance is still required...
    That's why there's EBD - brake force distribution as used in the PSA cars apportions the maximum safely possible braking effort to the rear wheels, and between the left & right rear wheel.

    Anyone noticed how wheels are getting bigger these days - brake discs are a key reason - that's why the 307 is equipped with 15" wheels as a minimum (& all cars, whether it be a tiddler 1.4 or a 2.0 HDi have 283mm front discs).

    As cars become heavier, they need more powerful brakes. Cars really are heavier these days.

    Anyone noticed how powerful small cars are becoming. Base engine in the Mazda 3 has 104kW, heck the larger 406 doesn't even have that! Again, it's related to weight - power gains have largely erased any progress in fuel consumption.

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  19. #19
    Budding Architect ???? pugrambo's Avatar
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    the rears maybe larger in diameter but the pad surface area is still fairly small compared to the fronts
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  20. #20
    1000+ Posts tekkie's Avatar
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    I think,
    larger rotors dissipate (spelling?) heat better.

    As someone already pointed out 2tons+ of the wagon + 1.5tons of a trailer equals a lot of heat down the Victoria Pass or any number of steep hills.

    Making the rotors large (even when the pads are small) it saves the need to cross drill or ventilate the rear brakes as the safety needs are met to some or other Australian standard.

    my 2_cents worth
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