Lexus GS450h RPM vs MPH Speedometer
- Gregski
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Lexus GS450h RPM vs MPH Speedometer
Since my 1971 Chevy truck aka GMC used a mechanical speedometer which I am ditching I plan on using MG2_Speed to calculate my miles per hour MPH
so I punched some numbers into the good ol' Lotus 1-2-3 (pronounced: Excel) ha ha to correlate RPMs to Miles Per Hour based on my 3.73 rear end and 215/65R-17 wheels
I relied on the good ol' folks at x-engineer.org to provide the complicated formulas, (and our daughter to recite pi to the 57th digit):
How to calculate wheel and vehicle speed from engine speed
How to calculate wheel radius
so I punched some numbers into the good ol' Lotus 1-2-3 (pronounced: Excel) ha ha to correlate RPMs to Miles Per Hour based on my 3.73 rear end and 215/65R-17 wheels
I relied on the good ol' folks at x-engineer.org to provide the complicated formulas, (and our daughter to recite pi to the 57th digit):
How to calculate wheel and vehicle speed from engine speed
How to calculate wheel radius
"I don't need to understand how it works, I just need to understand how to make it work!" ~ EV Greg
- Gregski
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Re: Lexus GS450h RPM vs MPH Speedometer
this made me consider Taller / higher differential gears like the 2.73 for my GM 12 bolt to drop the RPMs by approximately 2 grand, I'm pretty sure (97.1%) that electric motors don't have a traditional Power Band, so did the "Royal We" determine at what RPMs this Unicorn is most happy happy?
"I don't need to understand how it works, I just need to understand how to make it work!" ~ EV Greg
- Gregski
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Re: Lexus GS450h RPM vs MPH Speedometer
and let's not forget how simply changing our tire aka wheel size can impact RPMing and MPHing
below I use the exact same tire profile on three different size rims 16", 17", and 18"
below I use the exact same tire profile on three different size rims 16", 17", and 18"
"I don't need to understand how it works, I just need to understand how to make it work!" ~ EV Greg
- PatrcioEV-ATX
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Re: Lexus GS450h RPM vs MPH Speedometer
Don't forget to account for the gear reduction from MG2 speed.
1998 Ford ZX2 - DC EV conversion(sold) http://evalbum.com/2093
2012 Nissan Leaf (sold)
2016 Mercedes B250e (sold)
2023 Volvo C40
Current: 1964 Rambler Classic 660 w/ GS450h set up. 36kwh Tesla batteries from B250e.
https://www.instagram.com/rambler_660e/
2012 Nissan Leaf (sold)
2016 Mercedes B250e (sold)
2023 Volvo C40
Current: 1964 Rambler Classic 660 w/ GS450h set up. 36kwh Tesla batteries from B250e.
https://www.instagram.com/rambler_660e/
- Gregski
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Re: Lexus GS450h RPM vs MPH Speedometer
is it 1.900 ?PatrcioEV-ATX wrote: ↑Wed Dec 08, 2021 6:22 pmDon't forget to account for the gear reduction from MG2 speed.
"I don't need to understand how it works, I just need to understand how to make it work!" ~ EV Greg
- PatrcioEV-ATX
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Re: Lexus GS450h RPM vs MPH Speedometer
Yes, these are the pieces of my mph calc, though others have done it slightly differently:
float speedCalc;
int tireRpm=737; //revolutions per mile for tire size
int MPH;
float diff=3.31; //your diff ratio
void Calc_MPH()
{
speedCalc=((abs(mg2_speed/1.9))/diff);
MPH=((speedCalc*60)/tireRpm);
}
float speedCalc;
int tireRpm=737; //revolutions per mile for tire size
int MPH;
float diff=3.31; //your diff ratio
void Calc_MPH()
{
speedCalc=((abs(mg2_speed/1.9))/diff);
MPH=((speedCalc*60)/tireRpm);
}
1998 Ford ZX2 - DC EV conversion(sold) http://evalbum.com/2093
2012 Nissan Leaf (sold)
2016 Mercedes B250e (sold)
2023 Volvo C40
Current: 1964 Rambler Classic 660 w/ GS450h set up. 36kwh Tesla batteries from B250e.
https://www.instagram.com/rambler_660e/
2012 Nissan Leaf (sold)
2016 Mercedes B250e (sold)
2023 Volvo C40
Current: 1964 Rambler Classic 660 w/ GS450h set up. 36kwh Tesla batteries from B250e.
https://www.instagram.com/rambler_660e/
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Re: Lexus GS450h RPM vs MPH Speedometer
I covered this a while back in another thread: viewtopic.php?f=14&t=396&p=32431#p32431
Here it is again to save you clicking:
-----------------------------------------
I saw someone mention speed calculation from MG2 rpm, here's how I did it:
I have this at the top
Then these lines after mg2_speed = mth_data[31] | mth_data[32] << 8;
Change your tyre specs (printed on the tyre) and the differential ratio to suit your application.
For MPH you can just divide the speed by 1.60934. I run the car in kph and just do the conversion in the gauge cluster if needed.
If you never want to use kph then just do the /1.60934 on the lines above.
This code isn't for Damiens VCU so adapt it to suit your needs.
The advantage of this code is that it makes it easy to enter your tyre size and differential ratio. The #define's are calculated by the compiler at compile-time and therefore those calculations do not use any processor or memory.
Here it is again to save you clicking:
-----------------------------------------
I saw someone mention speed calculation from MG2 rpm, here's how I did it:
I have this at the top
Code: Select all
//for 255/40/R17 tyre
#define TYRE_WIDTH 255
#define TYRE_RATIO 40
#define TYRE_SIZE 17 //inches
#define DIFF_RATIO 4.1 //x:1
#define TYRE_CIRCUMFERENCE (TYRE_SIZE*25.4+TYRE_WIDTH*TYRE_RATIO/50)*3.14159265359/1000 //m travels in one wheel revolution
#define DIST_PER_MG2_REV TYRE_CIRCUMFERENCE/1.9/DIFF_RATIO/1000 //km car travels in 1x MG2 revolution
#define LOWGEAR_RATIO 2.05263157895 //how much lower the low gear is compared to high
Code: Select all
veh_speed_kph = mg2_speed * 60 * DIST_PER_MG2_REV;
if (veh_speed_kph < 0)veh_speed_kph *= -1; //for reverse
//if (put your "low gear" check in here)veh_speed_kph /= LOWGEAR_RATIO; //low gear
veh_speed_mph = veh_speed_kph/1.60934;
For MPH you can just divide the speed by 1.60934. I run the car in kph and just do the conversion in the gauge cluster if needed.
If you never want to use kph then just do the /1.60934 on the lines above.
This code isn't for Damiens VCU so adapt it to suit your needs.
The advantage of this code is that it makes it easy to enter your tyre size and differential ratio. The #define's are calculated by the compiler at compile-time and therefore those calculations do not use any processor or memory.
- PatrcioEV-ATX
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Re: Lexus GS450h RPM vs MPH Speedometer
I even added tire RPM and rear diff (since I’m not entirely sure what mine is) to the serial menu for easy updating.xp677 wrote: ↑Sat Dec 11, 2021 12:49 pm I covered this a while back in another thread: viewtopic.php?f=14&t=396&p=32431#p32431
Here it is again to save you clicking:
-----------------------------------------
I saw someone mention speed calculation from MG2 rpm, here's how I did it:
I have this at the topThen these lines after mg2_speed = mth_data[31] | mth_data[32] << 8;Code: Select all
//for 255/40/R17 tyre #define TYRE_WIDTH 255 #define TYRE_RATIO 40 #define TYRE_SIZE 17 //inches #define DIFF_RATIO 4.1 //x:1 #define TYRE_CIRCUMFERENCE (TYRE_SIZE*25.4+TYRE_WIDTH*TYRE_RATIO/50)*3.14159265359/1000 //m travels in one wheel revolution #define DIST_PER_MG2_REV TYRE_CIRCUMFERENCE/1.9/DIFF_RATIO/1000 //km car travels in 1x MG2 revolution #define LOWGEAR_RATIO 2.05263157895 //how much lower the low gear is compared to high
Change your tyre specs (printed on the tyre) and the differential ratio to suit your application.Code: Select all
veh_speed_kph = mg2_speed * 60 * DIST_PER_MG2_REV; if (veh_speed_kph < 0)veh_speed_kph *= -1; //for reverse //if (put your "low gear" check in here)veh_speed_kph /= LOWGEAR_RATIO; //low gear veh_speed_mph = veh_speed_kph/1.60934;
For MPH you can just divide the speed by 1.60934. I run the car in kph and just do the conversion in the gauge cluster if needed.
If you never want to use kph then just do the /1.60934 on the lines above.
This code isn't for Damiens VCU so adapt it to suit your needs.
The advantage of this code is that it makes it easy to enter your tyre size and differential ratio. The #define's are calculated by the compiler at compile-time and therefore those calculations do not use any processor or memory.
1998 Ford ZX2 - DC EV conversion(sold) http://evalbum.com/2093
2012 Nissan Leaf (sold)
2016 Mercedes B250e (sold)
2023 Volvo C40
Current: 1964 Rambler Classic 660 w/ GS450h set up. 36kwh Tesla batteries from B250e.
https://www.instagram.com/rambler_660e/
2012 Nissan Leaf (sold)
2016 Mercedes B250e (sold)
2023 Volvo C40
Current: 1964 Rambler Classic 660 w/ GS450h set up. 36kwh Tesla batteries from B250e.
https://www.instagram.com/rambler_660e/
Re: Lexus GS450h RPM vs MPH Speedometer
I'm not sure this is the right place to ask, but does anyone have a way for a simpleton to work out my expected top speed etc?
(ie a formula rather than code please?)
The rear diff on my Reliant Scimitar is 3.58.1 and I'm wondering if I'll need to change that to use the GS450H transmission.
(ie a formula rather than code please?)
The rear diff on my Reliant Scimitar is 3.58.1 and I'm wondering if I'll need to change that to use the GS450H transmission.
Re: Lexus GS450h RPM vs MPH Speedometer
It's actually fairly simple...
(Motor RPM*60)/[trans ratio/final ratio tire revs/(mi or km)]
The word version: Motor turns per hour divided by the total gear ratio over tire revolutions per unit measure (miles or km) = Distance Per Hour
(Motor RPM*60)/[trans ratio/final ratio tire revs/(mi or km)]
The word version: Motor turns per hour divided by the total gear ratio over tire revolutions per unit measure (miles or km) = Distance Per Hour
Huebner VCU controlling a Gen2 Prius Inverter powering an MGR
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"Talent is equally distributed but opportunity is not." - Leila Janah
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Re: Lexus GS450h RPM vs MPH Speedometer
MG2 max speed is 10000rpm, divide by 1.9 which is the high gear internal ratio gives 5263rpm out the back of the transmission.
Divide by 3.58 gives 1470rpm at the wheels at top speed.
The Scimitar came with various tyre options, a common one was the 185 HR 14 tyre which has a diameter of 650mm, therefore a circumference of 2.04m.
Therefore, the distance travelled at full speed in one minute is 2.04m * 1470rev. Which is 3000.18 metres per minute, or 180 kilometres per hour.
180kph is 112mph.
Divide by 3.58 gives 1470rpm at the wheels at top speed.
The Scimitar came with various tyre options, a common one was the 185 HR 14 tyre which has a diameter of 650mm, therefore a circumference of 2.04m.
Therefore, the distance travelled at full speed in one minute is 2.04m * 1470rev. Which is 3000.18 metres per minute, or 180 kilometres per hour.
180kph is 112mph.
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Re: Lexus GS450h RPM vs MPH Speedometer
xp677, is this the transmission output speed (5263rpm) with the locked input shaft yes?
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Re: Lexus GS450h RPM vs MPH Speedometer
That suits my project much better, I had been working off the info guoted from another thread up to now which was giving a low top speed with the locked input shaft option, but is it true this pushes the MG1 bearing limits?Re: Connecting a GS450H to an existing Transfer Case?
Post by sfk » Tue Jan 05, 2021 9:13 pm
Worth pointing out that MG1 and MG2 could be operating at different RPM depending if you use the Lock Input Shaft method or Lock Planetary Gearset method.
Locking the planetary gearset will cause them to spin at same speed and direction with a max RPM around 11,000ish due to the limits of the bearings. In High gear 1.9 reduction this will result in about 5,250rpm coming out the back of the transmission.
Locking the input shaft will cause MG1 to spin 2.2x in the opposite direction to MG2. Thereby MG1 will reach the bearing speed limits much earlier than MG2 and limit the total output RPM. This will result in a max RPM of about 2,600.
Divide that by your 3.36 axle ratio and you have your rear wheel RPM and it's just a final step to factor in your tyre circumference to find your max road speed.