air suspension

[DL_AU]

I have a RWD with air suspension. The brakes work remarkably well, albeit with a quirk.

Old-school thinking suggests that most braking is done on the front wheels. These days, that does not appear to be the case. I don’t have in-depth knowledge of this, so my understanding may be incomplete: These days, front/rear braking ratio is dynamic. Weighting the rear brakes will achieve greater stability, but under heavy braking the rear wheels will lose traction - so the front brakes take on more of the work if more rapid deceleration is demanded. In the RWD Taycan, I imagine that the car is programmed to use the rear brakes - or more accurately regen coupled to the rear wheels - right up to the limit of traction. I think this setup is quite remarkable!

However, it does lead to a quirk: I’ve noticed that when braking on a downward slope, if the rear wheels encounter a slight bump in the road - the sort of bump that might come close to the rear losing traction - then the system probably needs to react very quickly to transfer braking load to the front wheels. When this occurs, the brake pedal immediately sinks by several mm and there is a barely perceptible momentary reduction in deceleration. It is a little disconcerting at first - until you realise that it is not a problem and the brakes are capable of pulling the car up very quickly if more braking is applied.

Does anyone have a better explanation of how this works?

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[badboy02]

is the steel suspension harsh without the air suspension also would the 21 inch tires make it harsher?

 

[RBGtaycan]

is the steel suspension harsh without the air suspension also would the 21 inch tires make it harsher?

I have the "no air" suspension (19 " wheels) and it is NOT harsh at all (my Taycan replaces an M2 and that WAS the definition of "harsh"!)...Low profile tires will, in my experience, increase harshness...but look good!

 

[badboy02]

so if i get the air suspension with the 21 inch tires the ride would be smooth is that right?

 

[f1eng]

I have a RWD with air suspension. The brakes work remarkably well, albeit with a quirk.

Old-school thinking suggests that most braking is done on the front wheels. These days, that does not appear to be the case. I don’t have in-depth knowledge of this, so my understanding may be incomplete: These days, front/rear braking ratio is dynamic. Weighting the rear brakes will achieve greater stability, but under heavy braking the rear wheels will lose traction - so the front brakes take on more of the work if more rapid deceleration is demanded. In the RWD Taycan, I imagine that the car is programmed to use the rear brakes - or more accurately regen coupled to the rear wheels - right up to the limit of traction. I think this setup is quite remarkable!

However, it does lead to a quirk: I’ve noticed that when braking on a downward slope, if the rear wheels encounter a slight bump in the road - the sort of bump that might come close to the rear losing traction - then the system probably needs to react very quickly to transfer braking load to the front wheels. When this occurs, the brake pedal immediately sinks by several mm and there is a barely perceptible momentary reduction in deceleration. It is a little disconcerting at first - until you realise that it is not a problem and the brakes are capable of pulling the car up very quickly if more braking is applied.

Does anyone have a better explanation of how this works?

The correct brake balance for on the limit braking is probably not optimised on road cars with ABS because it is too difficult to know how many passengers and what weight is in the boot - both needed to get the optimum balance between front and rear disc/caliper/master cylinder.

Obviously this is critical in racing for every braking event but only on a road car with emergency stop which is dealt with by ABS.

The only reason rear wheel braking is used in RWD EVs is efficiency. It isn't a correct balance or in any way optimum but is OK up to the limit of rear adhesion, as you write. Nothing about it is fundamentally better (in fact it is fundamentally worse - front wheels have more braking grip as is obvious).

There is no way a car which isn't using regenerative braking would brake principly either on the rear or front axle - it is technically wrong - but fine when nowhere near the grip limit.

The cleverest pre-electronics road car braking system I have come across was the Citroen power system.
The front brakes were powered via the proportional valve from the main hydraulic high pressure line which also supplies the suspension.
The rear brake proportional valve is supplied by the pressure in the rear suspension hydraulics so more load in back = proportionally more rear braking.

One of the biggest nightmares the engineers face in modern Formula 1 is the fact that they want to get maximum energy recovery from the rear regen system but the front is the most important for car performance so modulating the system to maximise regen without under-rotating the rear tyres is a critical and difficult control problem.

 

[DL_AU]

The correct brake balance for on the limit braking is probably not optimised on road cars with ABS because it is too difficult to know how many passengers and what weight is in the boot - both needed to get the optimum balance between front and rear disc/caliper/master cylinder.

Obviously this is critical in racing for every braking event but only on a road car with emergency stop which is dealt with by ABS.

The only reason rear wheel braking is used in RWD EVs is efficiency. It isn't a correct balance or in any way optimum but is OK up to the limit of rear adhesion, as you write. Nothing about it is fundamentally better (in fact it is fundamentally worse - front wheels have more braking grip as is obvious).

There is no way a car which isn't using regenerative braking would brake principly either on the rear or front axle - it is technically wrong - but fine when nowhere near the grip limit.

The cleverest pre-electronics road car braking system I have come across was the Citroen power system.
The front brakes were powered via the proportional valve from the main hydraulic high pressure line which also supplies the suspension.
The rear brake proportional valve is supplied by the pressure in the rear suspension hydraulics so more load in back = proportionally more rear braking.

One of the biggest nightmares the engineers face in modern Formula 1 is the fact that they want to get maximum energy recovery from the rear regen system but the front is the most important for car performance so modulating the system to maximise regen without under-rotating the rear tyres is a critical and difficult control problem.

Thank Frank @f1eng for the insights. Citroen made some clever cars! At the Vegas F1 race, drivers appeared to be regenerating on the straights. I couldn’t quite get my head around that one! Back to the RWD Taycan: There have been articles published about the basics of how Porsche achieves brake blending to achieve a more-or-less seamless experience (i.e. The brakes just work without the driver needing to know anything about the mix of hydraulic v regenerative braking). I wonder just how sophisticated the systems in our Taycans are. If, for example, they have a nine-axis inertial sensor and load sensors in each suspension then a sophisticated algorithm (including a machine learning approach) could be implemented, addressing dynamically some of the issues you mention.

 

[f1eng]

Thank Frank @f1eng for the insights. Citroen made some clever cars! At the Vegas F1 race, drivers appeared to be regenerating on the straights. I couldn’t quite get my head around that one! Back to the RWD Taycan: There have been articles published about the basics of how Porsche achieves brake blending to achieve a more-or-less seamless experience (i.e. The brakes just work without the driver needing to know anything about the mix of hydraulic v regenerative braking). I wonder just how sophisticated the systems in our Taycans are. If, for example, they have a nine-axis inertial sensor and load sensors in each suspension then a sophisticated algorithm (including a machine learning approach) could be implemented, addressing dynamically some of the issues you mention.

The regeneration in the straights uses a different generator the MGU-H which is the cleverest bit of the engine IMO but totally uneconomic for road cars so the big car manufacturers lobbied for it to be removed from the 2026 engine regulations - yet another dumbing down of F1, we have had so many over the years.
What it is is a motor/generator on the turbo shaft. What it does is to replace the wastegate on the turbo so once set boost is reached rather than opening a wastegate and throwing away any extra energy the MGU-H starts generating electricity and charging the battery, so the boost is controlled by it and little energy is wasted. It also allows a lot of charging over a longer period of time. Brake regen on F1 is over such a short time despite there being a lot of energy to absorb it is too high a rate for too short a time for much to end up in the battery.
Its secondary benefit is largely getting rid of lag because off throttle and at first opening of the throttle the device is used as a motor to spin the turbo up much more quickly than the exhaust itself.
It is brilliant BUT the electrical part has to operate up tp 150,000 rpm in high temperatures - even the air side of the turbo is over 250C and the exhaust side around 1000C (these numbers may be a bit out of date but you get the picture) leading to a very difficult to engineer and expensive component and, in some installations the turbo looks absolutely nothing like any turbo you will have seen.

The 2026 engine will be interesting, I am not sure how they will get it as good as now for efficiency and response.

The Taycan brake blending was developed from the system on the 919 Le Mans car and IMO works well. The 4wd system will inevitably and obviously be better than is possible on a 2wd system - in fact my main reason for buying my first 4wd car, with a simple IC engined car the gain of 4wd doesn't compensate the weight of 4wd for almost all use.

There is no way a road car will get a complex braking algorithm unless sensors get super cheap - and they are orders of magnitude cheaper than 35 years ago - because there is no gain in making them better driven on the limit all the time when almost no owners are capable of that even on a track day. Emergency braking is taken care of by ABS (another thing banned in F1 in 1993 iirc) which is superb nowadays so as good as you will get.

I am impressed by my Taycan's brake blending and based on what many owners have written about 1-pedal driving many people don't even know that their Taycan mainly "brakes" by regen.

 

[CroquetMan]

You can configure the Individual drive mode and set recuperation to On. I use this mode for my daily driving with recup on Auto and I'm adapting to how it functions; almost like adaptive cruise control in my previous ICE.

Think I'm right in saying "yes, you can select Recuperation in 'Individual' mode, but not if you only have access to 'Normal' & 'Sport' ". So my minor peeve stands.

 

[ShiftyWolf]

Think I'm right in saying "yes, you can select Recuperation in 'Individual' mode, but not if you only have access to 'Normal' & 'Sport' ". So my minor peeve stands.

Yes, I think you are also correct. Coming from my last car, an Individual configurable drive setting was a requirement for me.

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