3

Facts - Cars have one brake pedal. Bikes have two brake levers.

So a cyclist can brake fully with the front or the rear, or some combination of both, or alternate between the brakes.

If a car had two separate brake inputs for front and rear, would a skilled race driver benefit or would it make the car more dangerous to drive?

What effect would this have on the handling of a four-wheeled car?


Originally inspired by this question about "sure stop" which claims to use one brake control to balance the front and rear wheel brakes on a pushbike.

https://bicycles.stackexchange.com/questions/46241/how-does-the-surestop-braking-system-work

  • I know some 4WD vehicles have fiddle brakes, which are intended to lock up one wheel and create a pivot point for turning around the whole vehicle in small spaces. That's not quite what I meant. – Criggie Apr 17 '17 at 20:34
  • This is also different to independent braking circuits. There's still only one pedal input. – Criggie Apr 17 '17 at 20:36
  • If you are talking about motor sports, you need to see how they do it with drifting ... pretty wild brake setup. – Pᴀᴜʟsᴛᴇʀ2 Apr 17 '17 at 22:01
  • My 90's mazda has a handbrake that operates on the rear wheels only, so that's kind-of a separate brake system for the rear. Though it tends to have no modulation, its very much on or off. – Criggie Apr 18 '17 at 1:55
5

So, this all gets down to physics - inertia primarily.

following assumes braking to a wheel-lock

When you brake heavily, front only, the rear will try to lift, this will reduce traction of course on the rear, but the broken traction on the front (in a non-ABS scenario) also results in reduced or zero ability to steer or control the front as well.

Conversely, rear-only braking causes the weight to roll forward again. This will result in aggressive changes in your steering and suspension dynamics, but ultimately you'll still be able to steer. Now again, in a non-ABS scenario, the total loss of traction on the rear will cause the backend of the car to swing much more wildly when front end steering adjustments are made.


would a skilled race driver benefit or would it make the car more dangerous to drive?##

Both. A very skilled driver could benefit slightly, but the hazards far outweighs these possible benefits. This is why (even in the manufacturer prototype racing circuits) they use computer controlled or static set systems - and mostly static from my understanding. You don't really need to be actively changing the braking dynamics, just set them correctly and use them right and you're good.

Moreover, I doubt even the best drivers can make the instantaneous braking adjustments needed to take advantage of independent braking systems.

3

It would surely handle differently, and that's why this is also done, but automatically. There's a brake pressure distributor in your car that distributes pressure depending on different factors, eg. how your car is loaded.

For cornering in a four wheeler, it's much more interesting to control the left/right side rather than front/rear. The problem is, it would take a lot of skill and practice to master and use safely, and even then it would still take a lot of focus which you'd rather use to check your surroundings etc. Obviously a no-no to offer as option in the grocery-getter that you mother drives.

So that's why this is also done for you automatically,(but only in higher end cars) it's called torque-vectoring. It's much like ESP, but torque vectoring actively works while driving. In older versions, it applies the brakes selectively left/right and front/rear to create net force in the direction that you want to go. So for example, the wheels on the outer side of the corner get more torque to steer the car into the corner.

1

Many racing cars have the ability to adjust the front/rear brake bias from the cockpit, usually via a rotary dial. Indeed if you watch in-car footage of an F1 car you can see drivers adjusting the brake balance with their left hand very frequently.

In this case a dial is used to adjust the proportion of braking force which is applied to the front and rear brakes respectively and is more convenient and consistent than having separate brake pedals, bearing in mind also that a driver may want the ability to apply brake and accelerator pressure at the same time.

Also many more sophisticated road cars have the ability to automatically apply brakes individually as part of traction/stability control systems.

There are also fiddle brakes, most commonly used on off road vehicles as a manual traction control system these are hand or foot operated leavers which allow braking to be applied to individual wheels or sets of wheels depending on how the system is set up.

Also the 1997 McLaren F1 car had an extra brake pedal which allowed either the left or right side brakes to be applied, the idea being that it helped turn-in and reduced under-steer. This exploited a loophole in the regulations which outlawed automatic stability control via the brakes but (in McLaren's interpretation) permitted a manual system.

Rally drivers routinely use the handbrake (which operates on the rear wheels only) to deliberately induce overseer which improves turn-in on low speed tight corners, especially on loose surfaces.

  • Agricultural tractors have the ability to split the brakes left 7 right but that is usually only the rear wheels - helps sometimes when one is stuck or for turning - not to be used when you have the diff-lock applied ... – Solar Mike Apr 20 '17 at 15:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.