RWD Power/Weight vs Accel Anomoly

[Fish Fingers]

Good thread this.....
Lots of interesting stuff from members.

I do love this forum. A completely different breed to any other car forums I have been on.

Makes me think the Taycan really appeals to this demographic.
Intelligent / analytical.

Sponsored

 

[f1eng]

In fact sometimes I look at it while braking to keep the power level low and spread over time to recupurate the maximum amount of energy.

I always do this in my plug in hybrid, though nowhere near as much back torque as a Taycan so max deceleration before friction brakes are used isn’t huge.
Nevertheless on the way down to Bangor from Snowdonia I gain 9 miles of range from recuperation.

 

[Avantgarde]

The real world driving difference is notable. I have just looked at the stats which show the 80-120kmh figures as follows:

RWD = 3.0s
RWD PB+ = 2.7s
4S (either battery) = 2.3s

If correct this would make 'overtaking' for the RWD PB in between the RWD and 4S.

That said, the RWD will be the lightest and may corner and handle better and be the purists choice.

Ideally someone would do a track test on two similarly specced RWD with each battery.

This is something I put together with data I got from german website. In case it helps. I could not see all this on the same table previously.

 

[Avantgarde]

It sounds like a problem in theory. But in practice it does not seem a problem to only do regen on the rear wheels.
When I brake with my RWD in normal traffic, I do not feel it brakes with the rear wheels. It brakes like any other car.
The screen displays the recuperation energy. You can see when it passed the maximum level of recuperation. After that point it needs to do friction braking.
In normal traffic, you almost never pass the maximum. +90% of the braking is pure recuperation. In fact sometimes I look at it while braking to keep the power level low and spread over time to recupurate the maximum amount of energy.

So It looks like that in practice, in most cases, braking with the rear wheels works fine.

From driving dynamics/brake feel perspective they've done an impressive job with RWD regen blending, I've been paying attention and really can't seem to feel anything off despite the massive structural change a single axle braking would imply on braking dynamics. However i strongly believe that it is not possible to achieve this brake feel without throwing some front brake pad support into the mix even during ~medium power braking. So even when my regen green bar is up I think the vehicle is applying some brake force to the front pads in all but very mild braking, to balance things out. This would mean slight efficiency loss for RWD and data also supports that theory. If you play with the range calculator on UK/German websites you see an interesting relationship between RWD and 4S. If you change the lever to 100% highway, RWD becomes more efficient than 4S (less frictional loss due to single axle motor pays off on constant speed, which makes sense). If you slide it back to primary City driving, 4s becomes more efficient than RWD, despite the weight disadvantage of the former. I would think most range calc. cycles would not involve heavy breaking in City driving. Which makes "RWD front pads engaging in milder braking" a possible explanation for RWD's slightly shorter city driving range.

 

[Jhenson29]

However i strongly believe that it is not possible to achieve this brake feel without throwing some front brake pad support into the mix even during ~medium power braking.

I’ve said before that I think it’ll be interesting to see front pad wear on a RWD vs AWD after some miles.

 

[whitex]

I’ve said before that I think it’ll be interesting to see front pad wear on a RWD vs AWD after some miles.

Actually, the more interesting data point would be the front pad vs. rear pad ratio on RWD vs. AWD. Just comparing front pads would be hard due to different drivers with different driving styles.

 

[Jhenson29]

Actually, the more interesting data point would be the front pad vs. rear pad ratio on RWD vs. AWD. Just comparing front pads would be hard due to different drivers with different driving styles.

Depends on how much rear pad wear there is. I’m expecting very little rear pad wear in both cars. In which case a comparison of ratios is equivalent to a comparison of front only.

 

[Oink]

This is something I put together with data I got from german website. In case it helps. I could not see all this on the same table previously.

Underpromising, overdelivering. German car manfucaturers. You might get 0-100 in 4 seconds without launch, but with launch you'll be in the 3.6s figures. Might have to resort to third-party numbers for all of those stats to get proper results.

 

[whitex]

Depends on how much rear pad wear there is. I’m expecting very little rear pad wear in both cars. In which case a comparison of ratios is equivalent to a comparison of front only.

What you're saying it that you make an assumption that all cars will wear exactly the same (presumably per mile) on the rear, therefore fixing the rear_wear denominator of front_wear : rear_wear ratio. However, if your assumption were true, that means you have no way to account for more braking history of the car, which would make the comparison very inaccurate - even with identical mileage, the car which brakes harder would wear the front more, RWD or AWD. I posit that comparing to the rear will normalize the wear data points, account for braking history.

 

[Jhenson29]

What you're saying it that you make an assumption that all cars will wear exactly the same (presumably per mile) on the rear, therefore fixing the rear_wear denominator of front_wear : rear_wear ratio.

I’m thinking more in averages than any two specific cars, but okay.

 

[Ambroos]

The RWD Taycan definitely has some sneaky logic to make braking safe with regen only on the rear axle.

Stopping in a straight flat line for example it'll use tons of regen. But if you brake before going into a turn and keep the braking going in the turn (eg a highway exit that after a strong turn gets you traffic lights almost right away) or if you brake on a steep down grade, it becomes quite clear that front friction brakes are being blended in. Similarly I've felt the car behave quite interestingly in the rain / on slippery surfaces. All the systems react with blazing speed so it's hard to notice what exactly happens, but losing regen / power (in acceleration) for a split second is quite common.

Completely fine in my opinion, the range on the RWD car is already great, and these are relatively less common situations where safety is paramount. You don't want to lose traction on your rear wheels when slowing down in a turn or when going down a strong hill.

Brake pedal feel is a good way to tell. The Taycan's pedal is very interesting.

My previous EV was an e-tron (SUV / "fat e-tron"). It is the first (and I think still only) production consumer car with 100% brake by wire. The pedal feel is all fake, there's a little motor providing back pressure and a computer translating your input into a mix of regen and friction brakes with no impact on the pedal feel. It's 100% consistent no matter how the braking happens.

The Taycan's pedal on the other hand is wild in how much of a mind of it's own it has. I suspect there's a front buffer area that's used with an electronic system for regen braking. It feels more spongy, and you depress it and do quite a bit of movement to decelerate. The friction braking sits after it, and is a lot more firm. You increase pressure but the pedal doesn't really move that much when you do it. When your brakes are nice and spongy, you're in regen zone. Sometimes you can feel them hardening up suddenly, and that's the car reducing regen availability and forcing you to use friction brakes.

When using auto regen / adaptive cruise control you can actually see the pedal move on its own as it adapts to the driving conditions and needs of the moment. It's very cool to see.

Overall I think the e-tron SUV's brake by wire is the future for EVs, it's incredibly good and consistent. The Taycan on the other hand feels like it trusts you more as a driver, communicates more and lets you get closer to the limits of the car.

 

[whitex]

I’m thinking more in averages than any two specific cars, but okay.

IMO average might be even more misleading considering some people will track their cars, which can very significantly raise averages (you can go though entire set to brakes in a few days of track use).

 

[whitex]

As a side note, Taycans often recalibrate their brakes when charging. This means the onboard computers know exactly the wear on each brake pad. Porsche could collect this data, if they had over the air telemetry. I don't know whether or not they do have this capability though.

Sponsored