GMC HUMMER EV Forum | HummerChat.com banner
1 - 16 of 16 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter · #1 ·
I’m supposed to receive my Hummer EV this fall and I’ve just read that it is speed limited at 170kph.

Does anyone know if it will be possible to get it unlocked? For ICE cars it isn’t uncommon for tunes to have this functionality, but since you can’t really tune electric engines I’m afraid to be stuck with a 170kph max speed vehicle.
 

·
Registered
Joined
·
373 Posts
I’m supposed to receive my Hummer EV this fall and I’ve just read that it is speed limited at 170kph.

Does anyone know if it will be possible to get it unlocked? For ICE cars it isn’t uncommon for tunes to have this functionality, but since you can’t really tune electric engines I’m afraid to be stuck with a 170kph max speed vehicle.
I doubt it. If you need to go over 106mph a lot, then Hummer EV isn't right for ya. I can't see GMC ever unlocking these.

Perhaps in future with a special model they sell th a t comes with different wheels/tires more road worthy and rated. I wouldn't expect current builds to allow an unlock though via official software.
 

·
Registered
Joined
·
80 Posts
No, there probably will be no speed unlock, at least not a significant one. The HEV drive units appear to close to "maxed out" both mechanically and electronically.

From what I've been able to reverse-engineer, the Ultium motors appear to "redline" at 14,000- 16,000 RPM. The Hummer's front drive unit, based on tire size and drive unit gear ratio (13.3:1), hits 14K RPM at about 106 mph. (The Lyriq's motors at its max rated speed appear to be closer to 16K rpm.).

Yes, EV drive units, similar to ICE engines, have "redlines".

The redlines are based on a combination of the following:
  1. structural issues beyond a certain motor RPM, (centrifugal forces on the rotor and magnets, bearing speed issues, and/or dynamic rotational balance issues). Tesla's Plaid, which can crank out almost full HP at over 20K RPM, has a carbon-fiber-wrapped rotor (conventional rotors use steel), which both helps to reduce balance issues, contain the magnets from the centrifugal forces, and reduces high-frequency electromagnetic losses (see #2 below).
  2. high-speed power sag issues: Once a motor passes its peak power/torque point (usually around 50-60 mph), the power curve slowly drops. Once it drops below the shaft-horsepower required to continue to be able to accelerate the EV, you are at max speed. This sag is due to a) electromagnetic inefficiencies within the rotor/stator building from the increasing AC frequencies required to push the motor to ever-higher RPM's and b) increased switching losses at the inverter. The Gen 1 Ultium drive units are using conventional silicon MOSFETS, which have a steep decreasing efficiency curve as the switching speed goes up. (Note that GM is coordinating with Wolfspeed to probably use silicon-carbide (SiC) MOSFETS for their power transistors in Gen 2. These allow 800 VDC power systems, reduce inverter losses by 30% or more, and allow higher switching speeds that could drive motors to higher RPM with less power sag. Tesla, Hyundai, and Lucid are using SiC in their drive units, which allows them to have slightly more-efficient drives and run their motors at higher RPM's. Also, SiC is required for any 800 VDC EV power architectures)
  3. Shifting to the braking-at-106 mph situation, remember that a vehicle's embodied kinetic energy increases with the square of the speed. The EV has 75% more kinetic energy at 106 mph than at 80 mph. There is a speed and energy level where conventional brakes will prematurely fail from the massive dissipated heat rate before they will stop a vehicle in an emergency situation. It is very possible GM found that kinetic energy limit for a 9,500 lb truck was somewhere near 106 mph.
 

·
Registered
Joined
·
50 Posts
No, there probably will be no speed unlock, at least not a significant one. The HEV drive units appear to close to "maxed out" both mechanically and electronically.

From what I've been able to reverse-engineer, the Ultium motors appear to "redline" at 14,000- 16,000 RPM. The Hummer's front drive unit, based on tire size and drive unit gear ratio (13.3:1), hits 14K RPM at about 106 mph. (The Lyriq's motors at its max rated speed appear to be closer to 16K rpm.).

Yes, EV drive units, similar to ICE engines, have "redlines".

The redlines are based on a combination of the following:
  1. structural issues beyond a certain motor RPM, (centrifugal forces on the rotor and magnets, bearing speed issues, and/or dynamic rotational balance issues). Tesla's Plaid, which can crank out almost full HP at over 20K RPM, has a carbon-fiber-wrapped rotor (conventional rotors use steel), which both helps to reduce balance issues, contain the magnets from the centrifugal forces, and reduces high-frequency electromagnetic losses (see #2 below).
  2. high-speed power sag issues: Once a motor passes its peak power/torque point (usually around 50-60 mph), the power curve slowly drops. Once it drops below the shaft-horsepower required to continue to be able to accelerate the EV, you are at max speed. This sag is due to a) electromagnetic inefficiencies within the rotor/stator building from the increasing AC frequencies required to push the motor to ever-higher RPM's and b) increased switching losses at the inverter. The Gen 1 Ultium drive units are using conventional silicon MOSFETS, which have a steep decreasing efficiency curve as the switching speed goes up. (Note that GM is coordinating with Wolfspeed to probably use silicon-carbide (SiC) MOSFETS for their power transistors in Gen 2. These allow 800 VDC power systems, reduce inverter losses by 30% or more, and allow higher switching speeds that could drive motors to higher RPM with less power sag. Tesla, Hyundai, and Lucid are using SiC in their drive units, which allows them to have slightly more-efficient drives and run their motors at higher RPM's. Also, SiC is required for any 800 VDC EV power architectures)
  3. Shifting to the braking-at-106 mph situation, remember that a vehicle's embodied kinetic energy increases with the square of the speed. The EV has 75% more kinetic energy at 106 mph than at 80 mph. There is a speed and energy level where conventional brakes will prematurely fail from the massive dissipated heat rate before they will stop a vehicle in an emergency situation. It is very possible GM found that kinetic energy limit for a 9,500 lb truck was somewhere near 106 mph.
Your point on braking reminded me about something I've always wondered: does the regenerative braking system take some of the stress off the brake pads and rotors? My Silverado Trail Boss already has warped rotors after a few trips on I-70 in Colorado. Step on the brakes and the steering wheel shakes now. Same thing used to happen to my Mom's jeep Cherokee in the 2000s (in Houston). I'm curious if the Hummer EV could have the same issues given its weight. and no, my driving style isn't that aggressive.
 

·
Registered
Joined
·
133 Posts
Your point on braking reminded me about something I've always wondered: does the regenerative braking system take some of the stress off the brake pads and rotors? My Silverado Trail Boss already has warped rotors after a few trips on I-70 in Colorado. Step on the brakes and the steering wheel shakes now. Same thing used to happen to my Mom's jeep Cherokee in the 2000s (in Houston). I'm curious if the Hummer EV could have the same issues given its weight. and no, my driving style isn't that aggressive.
Yes, regen takes A LOT of wear and tear off the brakes.
 

·
Registered
Volt, Polestar 2, R1T, Livewire One
Joined
·
898 Posts
Your point on braking reminded me about something I've always wondered: does the regenerative braking system take some of the stress off the brake pads and rotors? My Silverado Trail Boss already has warped rotors after a few trips on I-70 in Colorado. Step on the brakes and the steering wheel shakes now. Same thing used to happen to my Mom's jeep Cherokee in the 2000s (in Houston). I'm curious if the Hummer EV could have the same issues given its weight. and no, my driving style isn't that aggressive.
I drove through the Appalachians. Regen was sufficient to bring the truck to a pretty fast stop going down some of the steeper parts where traffic picked up, without touching the brakes at all.
 

·
Registered
Joined
·
373 Posts
Your point on braking reminded me about something I've always wondered: does the regenerative braking system take some of the stress off the brake pads and rotors? My Silverado Trail Boss already has warped rotors after a few trips on I-70 in Colorado. Step on the brakes and the steering wheel shakes now. Same thing used to happen to my Mom's jeep Cherokee in the 2000s (in Houston). I'm curious if the Hummer EV could have the same issues given its weight. and no, my driving style isn't that aggressive.
As ya learn to use regen driving you'll love it, and probably won't ever have to worry about brake pads this next decade.
 

·
Registered
GMC Sierra, Bolt, Sky, Mach E
Joined
·
686 Posts
I've heard that a common ware item on Telsa vehicles is lubricating the brake pads/system because the brakes are used so rarely, lol. I love it!
I just passed 114K miles on my Bolt, and the rotors and pads look like new, I have never serviced them at all. The Bolt does not have one pedal in reverse, so they do get used very lightly any time you back up.
 
1 - 16 of 16 Posts
Top