Why does the handbrake only engage the rear brakes on a car? Why not engage brakes on all the cars wheels, this wouldn’t allow handbrake turns, but that is an activity that probably shouldn’t be encouraged in regular vehicles anyway.
In ‘emergency’ usage, locking up the front wheels would make the car very difficult to control.
Also, two wheels seem to be sufficient. Why add extra weight and complexity?
Good question.
Actually there are some cars where the handbrake acts on the front wheels but I’ve never seen one acting on all four wheels.
I believe it is generaly more preferable to have the car lock the front wheels and understeer rather than lock the rear wheels and oversteer. It is far easier to recover from understeer.
Well the emergency brakes are also used for parking brakes which would benifit from being stronger perhapse. Also braking at the front wheels is more efficient than at the rear because as the car slows its weight moves towards the front giving better traction to the front rather than the rear wheels.
That said, if control is the issue that would make sense.
Just musing that when parked on certain San Francisco streets it would be more reassuring if all the cars brakes were locked.
Ummm…‘emergency brakes’? Isn’t the handbrake a parking brake, in which case it’s an unnecessary complication for it to be on all four wheels?
It’s much easier to have a parking brake, which has a cable linkage instead of hydraulic, on a drum brake. So when cars were front-disks-and-rear-drums, it was easiest to connect the parking brake to the rear wheels. (I’ve seen drums taken apart; the hydraulic slave cylinder pushes the tops of the shoes apart, the linkage from the hand brake pushes the bottoms apart. It’s pretty simple. I don’t know how they do it with disks.)
Well it is both, that is the reason it opperates on as different system as possible from the main brakes, so that failure of the main brakes (by loss of brake fluid for example) doesn’t stop the parking/emergency brakes from operating. But for general use it is just used for parking.
My thought was that having the emergency/parking brakes work on all four wheels would be safer. That said the risk of all wheels locking is obviously bad, though maybe anti-lock emergency/parking brakes is possible?
I have always know it as a emergency brake or E-Brake. FWIM and IIRC one car I had in the repair manual something along the lines that it was a emergency brake for a automatic trans and a parking brake for a manual.
In reality it is a combo of the 2. It does work if you have main brake failure, I have had to use it for this, and it makes parking a bit safer also.
S/he can correct me if I’m wrong, but I think that what awldune was getting at was that if the primary braking system experienced a failure, then for the backup system to act on and possibly lock up the rear wheels results in a more controllable car.
And in any case, the e-brake/parking-brake/call-it-what-you-will-brake is a backup - you are not expecting full emergency braking performance from the backup system, but something to get you to a stop in a reasonable time when the primary system fails, and also to use as a parking backup when the car is left in gear (manual) or with the transmission in park (automatic).
This is the second time I have seen someone post regarding handbrakes acting on the front wheels, could you name a model of car that does this ?
Either historical or one of the newer makes or exotic cars. I think the only time I have seen the park brake operate on the front wheels of a vehicle is on a forklift.
Declan
My automatic Nissan has a handbrake, according to the owner’s manual.
Maybe it’s partly to do with how drivers are taught - we’re definitely expected to use it as a parking brake. Example
True so far as it goes, but recovering from understeer requires unlocking the front wheels, whereas if you can control oversteer at all, you can do so even when the rear wheels are locked.
As far as I know, every Saab for the last 20+ years, and many Subaru models in the early 90’s.
oh, since I have a Saabaru, maybe my hand brake does brake the front wheels currently… quickly goes to check detailed sites…
Not that it changes my question original questioning…
This is probably a better reason for putting the emergency brakes in back.
On my car, which has rear disc brakes, there is a small drum on the rotor for the e-brake.
This is at least not entirely accurate. My 9-3 has rear E-brakes only.
Can someone provide a cite (like a car owners manual) that says the brake is an “emergency brake”. I don’t recall any of my owner manuals calling it anything but a parking brake. In fact, I recall one saying something like “…this brake is for parking use only, and should not be used during driving”.
It wouldn’t make much sense safety wise to have a brake that locks up during driving until one pulls a lever or pushes in a button, does it?
Good point. Trouble is, for those of us who believe the idea of a simple mechanical handbrake being intended for emergency use, this is attempting to prove a negative. The closest I can come, without excessive googling, is an example from the California DMV which has this regulation about the necessity of parking brakes, and this about emergency stopping systems for vehicles with air brakes.
“…for those of us who believe the idea of a simple mechanical handbrake being intended for emergency use is wrong…”
There is also a practical reason for parking/emergency brakes to be fitted to the rear wheels of a car (and to the front wheels of a forklift) - the greater articulation of the steered wheels would complicate the cable actuation mechanism. Obviously this can be gotten around, but if you don’t need to introduce the additional complexity, why bother …