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Comment by dreamcompiler | Hacker News Reader

Related question: Why must brakes be inside the wheels rather than inboard on the axle? Why not weld disks onto the axle inboard of the wheels and put the brakes there? That would make more room inside the wheels.

Of course on undriven front wheels it wouldn't work because there is no axle, but in front-wheel-drive cars there is one. The brakes could be inboard of the CV joint, no?

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See the inboard brakes on 60's Jaguars - Sure, the unsprung weight and improved handling is nice but they are much harder to maintain because 1. you have to lift the car to see if they are worn and 2. if you have to repair a caliper it is almost easier to drop the entire rear suspension than to try to dig the caliper out while everything is on the car.

As others said, accessibility and cooling. But inboard brakes are still popular in some niche areas, like sandrails:

https://www.dieselworldmag.com/wp-content/uploads/2017/03/DW...

This particular example doesn't even have front brakes.

Two reasons.

1. Brakes generate massive amount of heat and need cooling. There is a ton of airflow down at the wheels, some wheels are even designed to direct more airflow to the brakes.

2. Because changing brakes down at the wheels takes 20 minutes with the proper tools. If you move them inboard and affix the rotor to the axle you would significantly increase labor time and cost in replacing the brakes.

Both good reasons but I'd argue #2 is not considered by the engineering in practical reality. Have you seen the lengths some manufacturers require people to go through for things like a simple battery replacement? headlight bulb change? Or even in some cases the hoops to jump through for an oil change? There's some extreme examples out there of each, I heard horror stories from my friend who used to do automotive mechanical work (alternators only reachable by dropping the engine) and there's countless stories over at reddit's /r/Justrolledintotheshop

Yes, I was previously a mechanic. Truth is even the worst battery replacements (behind the bumper), headlight bulb changes (remove the bumper), still take less than ~45 minutes to complete. Alternators are not generally considered a wear item so they can be difficult to replace if the engineers where not friendly to the mechanics.

Brakes are a wear item, they eat themselves by design and need to be replaceable. Moving them inboard from the wheel does not have any significant benefits, but many downsides.

With regenerative braking on EV's it could possibly make more sense to move the brakes inboard, but there is already all the space in the wheels for brakes to fit, so I don't really see the benefit of moving them.

Because then you'd get a huge amount of torque between the brakes and the wheel, esp through the CV joint it'd be unnecessarily brutal. On the back wheels it could be possible, on the front (where most of the braking is) unlikely.

If the CV joint can handle peeling out it can handle brake torque. The link between tire and ground is basically always the weak point.

I’m not sure about that. Most cars can stop way faster than they can accelerate. The differences in force would be even more extreme for front wheel drive cars where the weight transfer allows for more grip on the front wheels during braking compared to accelerating or peeling out.

Cars have about 700hp of braking. Drop a 700hp motor in a car and have fun using the factory CV/half shafts.

You won't break anything without some big sticky tires to transmit that power to the ground and that (but for braking) is exactly my point.

If the wheel is sliding the torque on the wheel will be lower than if the tires were grippier. I guess the comparison is if braking is high (de)-acceleration than the engine. I'm thinking your idea has a lot of the same stresses as engine braking.

Some cars have had inboard brakes to reduce unsprung mass. Alfa Romeo did it a lot in the 70s and 80s.

There are a lot of downsides, like maintenance is a bit of a nightmare.

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