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Gregski wrote: ↑Wed Dec 08, 2021 5:44 pm 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"

Wheel Size.jpg

PatrcioEV-ATX wrote: ↑Wed Dec 08, 2021 6:22 pm

Gregski wrote: ↑Wed Dec 08, 2021 5:44 pm 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"

Wheel Size.jpg

Don't forget to account for the gear reduction from MG2 speed.

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:

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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

Then these lines after mg2_speed = mth_data[31] | mth_data[32] << 8;

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;

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.

xp677 wrote: ↑Sat Jan 08, 2022 3:10 pm MG2 max speed is 10000rpm, divide by 1.9 which is the high gear internal ratio gives 5263rpm out the back of the transmission.

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.