# Thread: New gear ratio with LST diffs???

1. ## New gear ratio with LST diffs???

I know that this has been discussed in some very long threads but i really dont have the time to go through them. So what i want to know is about the gear ratio. What gear ratio do i have to use on my ERBE now that i have installed the lst diffs so that the acceleration and speed are the same with stock which is 18t/65t.
Thank you and sorry for bring something up that its already there.

2. A temp gun is kind of a must have.....

Hot motor + cool esc = under geared.
Cool motor + hot esc = over geared
Everything warm just right..

Motor ~ 180/190*F (82/88*C) maximum, ideally 140/160*F (60/71*C), temps can be 10*F higher inside the motor
ESC ~ pretty much same temps / Fan comes on @ 150*F (65*C)
Lipo's ~ 140*F (60*C) max, ideally 100/120*F (38/49*C).........

Diff ratio LST2

4s = 40 mph
5s = 50 mph
6s = 60 mph

change the motor Kv, cell count, spur & pinion count, & tire size.

BrianG speed chart:

http://www.scriptasylum.com/rc_speed/top_speed.html

Import this:

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1.8333333333333333
Other Ratio: 1
Spur Tooth Count: 68
Pinion Tooth Count: 24
Total Voltage: 22.2
Motor KV: 1800
Tire Diameter (inches): 5.9
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0.006
Spur/Pinion Ratio: 2.83 : 1
Total Ratio: 17.18162 : 1
Tire Circumference (inches): 18.54 inches (470.8 mm)
Rollout: 1.08:1
Total Motor Speed: 39960 RPM
Vehicle Speed: 40.82 mph (65.57 km/h)
Effective KV Value: 1800
KT constant: 0.75 oz-in/A

3. Thanks man thats some great info there. I will just give it a go with my setup and see what i get. I am going to run the calculator with the stock erbe gear ratio (18/65) and diffs first and then change to lst diffs just to see the difference.

4. the LST2 is a little lower diff ratio, worth a couple of teeth on the pinion.........

traxxas
Differential Ratio: 2.8461538461538463

losi
Differential Ratio: 3.3076923076923075

5. RESULTS FOR A STOCK ERBE ON 4S

Differential Ratio: 2.8461538461538463
Transmission Ratio: 1.8333333333333333
Other Ratio: 1
Spur Tooth Count: 65
Pinion Tooth Count: 18
Total Voltage: 14.80
Motor KV: 2200
Tire Diameter (inches): 5.9
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0.006

Spur/Pinion Ratio: 3.61 : 1
Total Ratio: 18.84259 : 1
Tire Circumference (inches): 18.54 inches (470.8 mm)
Rollout: 0.98:1
Total Motor Speed: 32560 RPM
Vehicle Speed: 30.33 mph (48.72 km/h)
Effective KV Value: 2200
KT constant: 0.61 oz-in/A

RESULTS OF ERBE on 4S WITH LST DIFFS
(all input values are same as above except Front/Rear Differential Gear Ratio)

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1.8333333333333333
Other Ratio: 1
Spur Tooth Count: 65
Pinion Tooth Count: 18
Total Voltage: 14.80
Motor KV: 2200
Tire Diameter (inches): 5.9
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0.006

Spur/Pinion Ratio: 3.61 : 1
Total Ratio: 21.89815 : 1
Tire Circumference (inches): 18.54 inches (470.8 mm)
Rollout: 0.85:1
Total Motor Speed: 32560 RPM
Vehicle Speed: 26.1 mph (41.92 km/h)
Effective KV Value: 2200
KT constant: 0.61 oz-in/A

As you can see from the above results the speed reduces by 4.23mph (6.8km/h) when the LST diffs are installed on a stock ERBE. This actually means that the truck will have more acceleration right?

I will play some more with gear ratios and post the results here and i will use it for future reference

6. RESULTS OF ERBE on 4S WITH LST DIFFS and (24T/68T)

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1.8333333333333333
Other Ratio: 1
Spur Tooth Count: 65
Pinion Tooth Count: 24
Total Voltage: 14.80
Motor KV: 2200
Tire Diameter (inches): 5.9
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0.006

Spur/Pinion Ratio: 2.71 : 1
Total Ratio: 16.42361 : 1
Tire Circumference (inches): 18.54 inches (470.8 mm)
Rollout: 1.13:1
Total Motor Speed: 32560 RPM
Vehicle Speed: 34.8 mph (55.9 km/h)
Effective KV Value: 2200
KT constant: 0.61 oz-in/A

Now by changing the pinion gear from 18t to 24t the speed has increased to 34.8 mph (55.9 km/h). The speed looks good but i will have to check it in real life and see hoe the temps are.

7. EDIT lol we were both working it out......funny....
EDIT..edit yes you will have more low end torque with a lower gearing, but watch the temp even with low gearing...

2/2s....... 18/65

losi
26.1 mph
Reduction Ratio 3.61:1

traxxas
30.33 mph
Reduction Ratio 3.61 : 1

================================================== ===========

2/2s.........18/54

losi
31.41 mph
Reduction Ratio 3: 1

traxxas
36.51 mph
Reduction Ratio 3: 1

gear it up start at 18/54 prob go to 21/54
gl2u
Peace........

8. RESULTS OF ERBE on 4S WITH LST DIFFS and (19T/68T)
Vehicle Speed: 27.55 mph (44.25 km/h)

RESULTS OF ERBE on 4S WITH LST DIFFS and (20T/68T)
Vehicle Speed: 29 mph (46.58 km/h)

RESULTS OF ERBE on 4S WITH LST DIFFS and (21T/68T)
30.45 mph (48.91 km/h)

RESULTS OF ERBE on 4S WITH LST DIFFS and (22T/68T)
31.9 mph (51.24 km/h)

RESULTS OF ERBE on 4S WITH LST DIFFS and (23T/68T)
33.35 mph (53.57 km/h)

Well it seams that the closest you can get to the stock erbe speed with lst diffs its to change the pinion from 18t to 21t which gives you 30.45mph and its really close to the speed of a stock erbe calculated at 30.33mph. I will buy a couple of pinions just to check them out and make sure i can find the sweet spot on it.

I would probable buy 20t, 21t, 23t and 24t if they do exist.

9. LOL i am still working on it.....hehehe

Well up to now i have been driving my erbe with everything stock and 18t/65t, i havent tried out that 54t spurgear and i was planning to start from 20t/65t then 21t/65t then 22t/65t then 23t/65t and finnally 24t/65t. Do you suggest using the 54t spur gear?

10. I run LST diffs as well on 4S.

My gearing is 25/54 on 3.8 badlands and all is well with temps. I wish i had more top end though. Im a speed freak.

The batteries do struggle as i am drawing so many amps. On my next battery purchase i plan to jump back to 6s and drop my gearing back down so the voltage gives me the speed instead of high gearing. Its such a balancing act with the truck. Lol

11. Since the 54T spurgear has been brought up i will also post some of the results using that one.

RESULTS OF A STOCK ERBE on 4S (18T/54T)
Vehicle Speed: 36.51 mph (58.65 km/h)

RESULTS OF ERBE on 4S WITH LST DIFFS (18T/54T)
Vehicle Speed: 31.41 mph (50.46 km/h)

RESULTS OF ERBE on 4S WITH LST DIFFS (19T/54T)
Vehicle Speed: 33.16 mph (53.27 km/h)

RESULTS OF ERBE on 4S WITH LST DIFFS (20T/54T)
Vehicle Speed: 34.91 mph (56.07 km/h)

RESULTS OF ERBE on 4S WITH LST DIFFS (21T/54T)
Vehicle Speed: 36.65 mph (58.87 km/h)

So with 18t/54t or 21t/65t gear ratios (on erbe with lst diffs) i can reach similar speeds of the stock erbe as with. Which one would you suggest?

12. Originally Posted by anr2442
I run LST diffs as well on 4S.

My gearing is 25/54 on 3.8 badlands and all is well with temps. I wish i had more top end though. Im a speed freak.

The batteries do struggle as i am drawing so many amps. On my next battery purchase i plan to jump back to 6s and drop my gearing back down so the voltage gives me the speed instead of high gearing. Its such a balancing act with the truck. Lol
WOW you got too much speed there man, i just calculated it and its about 70km/h, and you still want more???? Hahahaha

Well i will also go with the 54t spur gear

13. so now who sells these pinion gears that fit the MMM which has 5mm shaft and 32pitch? I only found the 17t, 18t and 20t from traxxas that fit. Does traxxas make the 19t and 21t or are there any other manufacturers that make them?

does this fit the 5mm MMM shaft???

TRX 3949 Gear, 19-T pinion (32-p) (mach. steel)

14. just change the last two numbers for the tooth count
http://www.stormerhobbies.com/cgi-bi...=ns&pn=RRP8721
jmo put on the 54 spur & work from there with what pinion you might want

15. Originally Posted by 87 GN
just change the last two numbers for the tooth count
http://www.stormerhobbies.com/cgi-bi...=ns&pn=RRP8721
jmo put on the 54 spur & work from there with what pinion you might want
I was hopping to find these pinions from a UK shop or from ebay which offer cheap shipping therfore it would be really helpfull if you know if this part fits the 5mm shaft of the MMM TRX 3949 Gear, 19-T pinion (32-p) (mach. steel)

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