The other day, a rider asked me about changing the brakes. He wanted to change the front brakes of his car (Unxella) to a "big four-piston" caliper (piston area of 45.3cm), and then remove the original front wheel calipers and install them on the rear wheels. Because the original car calipers on the rear wheel also have a pull cord handbrake function, they cannot be removed.
In this way, there are 2 sets of calipers on the brake disc of the rear wheel (the calipers that come with the rear wheel of the original car are only used as pull-wire handbrakes, and do not participate in normal braking). The plates of the front and rear wheels were all changed to 330mm diameter large plates... His biggest worry was that because he did not know the area of the piston of the original car front wheel caliper sub-pump, he was afraid that the total pump belt would not move.
According to the component supplier's reply: Onxella, Artez, CX5 front wheel caliper assembly universal. It happened that an Unxella owner told me the corresponding data. He dismantled the front wheel pump and measured the piston diameter with a ruler: 53mm, so I calculated that the area was 22cm – far smaller than the 45.3cm of the "big four pistons" (almost 1 times smaller).
The braking force of the original car > the grip of the tires
In fact, the original design has a margin
So the change he envisioned could be problematic: the brake pedal travel would become very long! If the piston area of the sub-pump is increased by 1 times, the brake pedal travel needs to be extended by 1 times! Therefore, I don't recommend him to take the risk, the risk is too great! But that's not what I want to say the most! In fact, what I really want to scream is: he really shouldn't think about changing the brakes!
Because you are counting on the friends who expect to optimize the braking performance and increase the braking force by modifying the brakes, here may be to pour cold water on your head: ordinary civilian vehicles can achieve significantly enhanced braking performance by changing the brakes. Because the design of any car will ensure "a certain amount of brake safety margin", that is to say, the braking force is actually far beyond the limit value required by the vehicle itself.
If you don't believe it, try it yourself: on high-adhesion roads (such as very flat, clean, uninhabited dry asphalt roads), we are driving at high speed, and suddenly one foot on the brakes is stepped on the end, as long as we can "step out of ABS", we can prove this. This is because the force of the brakes far exceeds the friction between the tire and the ground, so the tire is directly locked, which causes the ABS to start.
Continental regulations do not allow changes to wheel sizes
Changing the brakes without changing the tires = spending money in vain
The braking system of the original car, the result of one foot down is the wheel locking, and then stepping out of abs; no matter how you change, the result is also a foot down to step out of abs. That is to say, if you do not change the rim (commonly known as the "hub") and the size of the tire, then you simply throw money on the brake system, basically you can responsibly say that the money is adrift.
And you know, the current regulations of the mainland do not allow car owners to change the original rim and tire size specifications without permission. Otherwise, after the car is 6 years old, it needs to be "restored to the factory state" before each annual review, and then changed back after the annual review, afraid that you do not have this energy (such as Shanghai, the annual review will take pictures of the tire archive). ——Since the rim and tire specifications are not allowed to change, what do we change the brakes? Is it difficult to change a lonely?
Ordinary cars really don't need to change the brakes
Violent motorists also only need to improve the heat dissipation
It's very simple: for ordinary civilian cars, if you don't usually involve violent driving every day, then changing the brakes is really a waste of money! If you're used to sexually violent driving, there's only one thing the brake system really needs to improve – heat dissipation speed! That is, to improve the anti-thermal exhaustion ability of the brake system, it is convenient for you to continuously rebrand at high speed.
At this time, you need a set of perforated ventilation discs, and a set of high temperature resistant pure ceramic fiber brake pads, with high boiling point DOT5.1 brake oil. If you are very concerned about the sensitive foot feel of the brakes, change up to 4 brake hoses to "steel throat".
Of course, maybe you will refute me: the braking performance of my original car is really not good enough, and now you big tiger you say that the "braking force" thing has been changed and thrown money in vain, then I can only endure the performance of the original car that is not good enough? - Of course not! Remember what you said above, the force of the original car brake system is always greater than the friction between the tire and the ground?
Changing tires = changing the braking effect N times
Spend less money + good effect + does not affect the annual review
So the easiest way to improve the braking performance is to increase the friction between the tire and the ground! We may often look at some tire performance reviews. One of the tests is "unavoidable": the emergency braking test. But I don't know if everyone found that the same car changes different tires, and the braking distance performance can be very different?
This shows that the friction coefficient between different tires and the ground is also different. In general, tires with soft rubber surface and larger grounding area have a relatively better grip.
You know, whether it is a cement pavement or an asphalt pavement, the essence is a small particle of stone (cement, asphalt is nothing more than a binder). So the pavement is not flat, but there are countless "microscopic potholes"). The softer the rubber surface, the easier it is to embed itself in the "microscopic potholes" of the road surface, greatly enhancing the coefficient of friction, and the braking performance is of course good!
If the same car is replaced by different tires, there may be a 10-meter gap in the results of the brake test! And we desperately changed the brakes (without changing the tires), and in the end, we only increased the distance by up to 1 meter... Which idea would you say is more cost-effective? Is this not the truth that the top veterans who really play with cars chant "whether the brakes are good or not, the tires are decided" do not say this?
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