the long way downunder
Well-Known Member
I've gotten used to Snow mode and have regen on high now – high is not more difficult to drive than low, they're the same at the threshold of what's called throttle "tip in" but high will go into harder braking effort as the accelerator pedal is further released. That "sweet spot" in the accelerator pedal position between power-on and brake-on could be a tad wider – a touchscreen control to adjust the width of the sweet spot, to widen the on-balance range of the accelerator pedal position would help.
I'm not purporting to be some rally ace Finnish driver dancing the vehicle in a perfect four wheel drift, steering with the throttle and taking rally notes form my co-driver as the tree trunks flash by inches from the tire marks … : ) … but here's my observations from a few months of snow driving in a variety of extreme conditions. I started with the factory Pirelli 20s and then Nokian LT3 full snow tire, no studs.
The software appears to make a front-rear bias adjustment in real time. Maybe it's my imagination or an inherent dynamic consequence of vehicle dynamics that feels more like software than physics. [I deleted a paragraph on torque bias steering, which the quad motor Rivian could be using, but I don't feel anything happening. I imagine there's some torque bias in on-road modes at higher speeds, it would be great to have driver control over torque bias, front and rear.]
The apparent rearward bias shift during a turn with lift-off understeer is "behind" the vehicle dynamics and it's slow and underweighted, meaning it's letting the vehicle plow into understeer before it reduces front end braking effort and then it's not adding enough rear brake emphasis (it feels like it's not adding any more rear braking, just reducing brake effort at the front.) I can feel the fronts losing steering, I can feel the vehicle rotation, so the software has that information through gyros, accelerometers, wheel position and suspension position, steering angle and pedal position sensors. For some reason, the current "tune" of the software intervention is perhaps expecting the traction profile of the factory tires instead of the much higher grip levels of the Nokians, but I don't think that's an excuse for incipient understeer continuing beyond steering control, requiring the driver to counter-intuitively increase accelerator pedal position (to reducing braking effort) without tipping through the balance point and adding power (which will also tend to induce understeer because there's no rear bias control for brake or power.)
My exploration and playing with the R1T was to try each mode on asphalt, including Snow and even Off Road Rock Crawl, low speeds, higher speeds, wide ranges of brake and accelerator input at various steering angles and rates of turn (speed through a turn) to get a feel for the weight transfer.
Pickups and SUVs are "instructional" compared to sports cars – movements are oversized, weight transfer is accentuated and the effect of driver inputs is delayed through the tire sidewall flex and the compliant suspension shifting load. So playing around away from traffic in some wide open space, no obstacles, and controlled speeds, can build familiarity. And it's silent fun (though you can get so much heat in the tires, the smell will let you know you're making them work.)
The required technique is "balanced throttle" (accelerator pedal) – not lifting the foot off the pedal, but finding that neutral balance to modulate between feeding in just enough power to keep the front wheels turning for steering control or "authority" to borrow an aviation term, and feeling the threshold of braking and understeer.
Part of the challenge is the sheer weight of the vehicle for different road conditions … a little downhill and speed needs to be slowed more than might be anticipated, a little uphill and speed can be increased significantly more than might be anticipated.
For the 911 comparison, the more insidious handling characteristic of the R1T (and I assume the R1S) is the amidships center of rotation and high polar moment – the R1T does not want to change direction and all four wheels have equal work. The 911 changes direction instantly and most of the mass is over the rear wheel, the center of rotation is rearward, so the front wheels are on a "lever" to attached to the rear engine and the rear wheels are the fulcrum.
Adding power to the 911 will reduce rear traction and widen the arc of the turn (increase the radius.) Adding power to the R1T will have the same effect but with much less force feedback to the driver (through the steering wheel and through the seat.)
My technique for adding or reducing power is to think about the big toe of my right foot, not moving my foot, just pressing and releasing pressure with my big toe … that will move the pedal amply.
On asphalt, it's easy to practice and requires larger inputs to pedal and steering with the delays of tire and suspension. On snow and ice, it's a muscle memory "feedback loop" carried over from the asphalt practice. Everything happening at lower speeds, smaller inputs.
Well, this post grew into a tl;dr, but maybe someone will read. It was interesting for me to assemble my thoughts, and with another 40+ inches of fluff landing outside in the next 48 hours, plenty of fun driving ahead. : )
I'm not purporting to be some rally ace Finnish driver dancing the vehicle in a perfect four wheel drift, steering with the throttle and taking rally notes form my co-driver as the tree trunks flash by inches from the tire marks … : ) … but here's my observations from a few months of snow driving in a variety of extreme conditions. I started with the factory Pirelli 20s and then Nokian LT3 full snow tire, no studs.
The software appears to make a front-rear bias adjustment in real time. Maybe it's my imagination or an inherent dynamic consequence of vehicle dynamics that feels more like software than physics. [I deleted a paragraph on torque bias steering, which the quad motor Rivian could be using, but I don't feel anything happening. I imagine there's some torque bias in on-road modes at higher speeds, it would be great to have driver control over torque bias, front and rear.]
The apparent rearward bias shift during a turn with lift-off understeer is "behind" the vehicle dynamics and it's slow and underweighted, meaning it's letting the vehicle plow into understeer before it reduces front end braking effort and then it's not adding enough rear brake emphasis (it feels like it's not adding any more rear braking, just reducing brake effort at the front.) I can feel the fronts losing steering, I can feel the vehicle rotation, so the software has that information through gyros, accelerometers, wheel position and suspension position, steering angle and pedal position sensors. For some reason, the current "tune" of the software intervention is perhaps expecting the traction profile of the factory tires instead of the much higher grip levels of the Nokians, but I don't think that's an excuse for incipient understeer continuing beyond steering control, requiring the driver to counter-intuitively increase accelerator pedal position (to reducing braking effort) without tipping through the balance point and adding power (which will also tend to induce understeer because there's no rear bias control for brake or power.)
My exploration and playing with the R1T was to try each mode on asphalt, including Snow and even Off Road Rock Crawl, low speeds, higher speeds, wide ranges of brake and accelerator input at various steering angles and rates of turn (speed through a turn) to get a feel for the weight transfer.
Pickups and SUVs are "instructional" compared to sports cars – movements are oversized, weight transfer is accentuated and the effect of driver inputs is delayed through the tire sidewall flex and the compliant suspension shifting load. So playing around away from traffic in some wide open space, no obstacles, and controlled speeds, can build familiarity. And it's silent fun (though you can get so much heat in the tires, the smell will let you know you're making them work.)
The required technique is "balanced throttle" (accelerator pedal) – not lifting the foot off the pedal, but finding that neutral balance to modulate between feeding in just enough power to keep the front wheels turning for steering control or "authority" to borrow an aviation term, and feeling the threshold of braking and understeer.
Part of the challenge is the sheer weight of the vehicle for different road conditions … a little downhill and speed needs to be slowed more than might be anticipated, a little uphill and speed can be increased significantly more than might be anticipated.
For the 911 comparison, the more insidious handling characteristic of the R1T (and I assume the R1S) is the amidships center of rotation and high polar moment – the R1T does not want to change direction and all four wheels have equal work. The 911 changes direction instantly and most of the mass is over the rear wheel, the center of rotation is rearward, so the front wheels are on a "lever" to attached to the rear engine and the rear wheels are the fulcrum.
Adding power to the 911 will reduce rear traction and widen the arc of the turn (increase the radius.) Adding power to the R1T will have the same effect but with much less force feedback to the driver (through the steering wheel and through the seat.)
My technique for adding or reducing power is to think about the big toe of my right foot, not moving my foot, just pressing and releasing pressure with my big toe … that will move the pedal amply.
On asphalt, it's easy to practice and requires larger inputs to pedal and steering with the delays of tire and suspension. On snow and ice, it's a muscle memory "feedback loop" carried over from the asphalt practice. Everything happening at lower speeds, smaller inputs.
Well, this post grew into a tl;dr, but maybe someone will read. It was interesting for me to assemble my thoughts, and with another 40+ inches of fluff landing outside in the next 48 hours, plenty of fun driving ahead. : )
footnote: Rivian really needs a brake bias and power bias control. These two controls would give the driver control to shift the center of rotation of the vehicle rearward (improving steering control under brakes and under power.) I think this is the "one size fits all" of Drift mode. I haven't spent much time on dirt in drift mode. It looks to be a conventional slip angle control and presumably a modest rearward power bias. It works well on snow, but not for use on public streets, let alone in traffic.
The idea of bias is a control for the driver to be able to slide brake bias rearward, so the fronts are not over-braking in low traction conditions. Shifting power bias rearward will also reduce the tendency for power-on understeer. It's a dull vehicle to drive with both lift-off understeer and power-on understeer with only a "sweet spot" in the accelerator pedal position … hard to find that sweet spot when you're sliding off the road or into oncoming traffic … very easy for the software to widen that sweet spot (and allow the driver to choose the width of the sweet spot to make it easier to hold the vehicle on a balanced throttle.)
I'd suggest using the left-right buttons on the left side of the steering wheel. A touchscreen setting could assign the role of those buttons. The current assignment of those buttons is 99% useless (they should be a simple ok/back/up-down menu navigation interface, not fixed to shifting entertainment, volume and delay-push to see the efficiency/tire/nav … which is so absurdly tedious, it's incomprehensible how anyone came up with this idea, let alone a dev team chose to build such an inept interface.)
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