M1010 gearing
I have a well-used spreadsheet looking at all the options for making an M1010 capable of comfortable highway cruising. Bigger tires, re-gearing the differentials, Gear Vendor overdrive, 700R4, etc. A roof fairing is also an essential component.
Re-gearing the differentials is expensive, and it hurts off-road performance. I looked at it closely, and decided to leave the axles alone.
From what I can tell, the 700R4 and 33" tires is the best solution. (33" being the tallest tire we can run without trimming fenders &/or lifting.) The 700R4 gives a lower first gear than the TH400, which helps compensate for the slightly taller tires on the low end. The 6.2L torque peaks at about 1800-2200 RPM, so I figure that's where I want to cruise for fuel efficiency. The table below shows RPM vs speed with this configuration. I don't plan to drive an M1010 at 99MPH. That is the max speed rating of my tires, so I was curious to see the corresponding RPM.
| 1800 | 55.9 |
| 2000 | 62.1 |
| 2100 | 65.2 |
| 2255 | 70.0 |
| 2415 | 75.0 |
| 3200 | 99.4 |
Gear Vendor with the stock TH400 and 33" tires gives this:
| 1800 | 49.7 |
| 2100 | 58.0 |
| 2350 | 64.9 |
| 2720 | 75.1 |
| 3600 | 99.4 |
The 700R4 OD is .70, where the GV top is .78, which is why the 700R4 gives lower RPMs.
The 700R4 keeps my RPMs lower for a given speed, it's $1000 cheaper, and I don't add a vulnerable gear box behind the transfer case. The Gear Vendor would give me 6 gears compared to the 700R4's 4, which might be an advantage for some. The GV unit only works in 2WD, which is probably OK. For me, bottom line, adding another gearbox adds complexity, is more expensive, and doesn't reduce my RPMs as much. So I'm leaning toward the 700R4 and no GV.
One part of the vision is a roof rack over the cab, with a fairing mounted to that to streamline the front of the ambulance box. It would be easily removed for parades etc where you want the stock configuration. For road use, it would make a big difference in wind resistance and MPG.
Below are the stock RPM vs MPH numbers. The stock truck is clearly geared to cruise efficiently at 45 MPH. Speeds over that start to burn lots more fuel per mile.
| 2200 | 45.2 |
| 2700 | 55.5 |
| 3000 | 61.7 |
| 3160 | 65.0 |
| 3300 | 67.8 |
| 3600 | 74.0 |
To build your own spreadsheet, you need:
- the final gear ratio
- Tire radius in inches (don't worry about the flat spot where the tire hits the road)
- engine RPM
You calculate speed as (RPM*tire_radius)/(168*final_gear_ratio). Here's why:
- tire_circumference is 2*PI*R. R is in inches, so this is in inches.
- engine_RPM/final_gear_ratio gives you tire_rotations_per_minute.
- 60 minutes in an hour, so 60*tire_rotations_per_minute gives you tire_rotations_per_hour.
- tire_rotations_per_hour*tire_circumference gives you inches per hour
- 12 inches in a foot, 5280 feet in a mile, so you divide by 5280*12 to get MPH.
(2*PI*tire_radius * RPM * 60minutes_per_hour) / ( 12inches_per_foot * 5280feet_per_mile * final_gear_ratio)
simplifies to
(tire_radius * RPM)/(168*final_gear_ratio) where radius is in inches
The result is MPH
Fair warning: I was an art major. Check the math yourself before you trust it. It seems to work for me.
![[thumbzup]](https://www.steelsoldiers.com/images/smilies/icon_smile_thumzup.gif "Thumbs Up [thumbzup]"){kind=icon}
