Gearing an ERBE for racing on 4s

Hey guys, I'm trying to finish getting my ERBE ready for next season, Only real drivetrain mods I've made are a Tekin 2250 kV motor and AKA city block truggy tires. I'm trying to decide gearing, but the calculator I've seen say that I'd need to run like a 20/54 or 22/54 to get up near 40mph. This just sounds WAY too high! I was curious what the people on here that are racing on 4S run on their ERBEs.

[suicideneil]

Whats the diameter of those tires?

Educated guess:

Differential Ratio: 2.8461538461538462
Transmission Ratio: 1.8333333333333332
Other Ratio: 1
Spur Tooth Count: 68
Pinion Tooth Count: 24
Total Voltage: 14.8
Motor KV: 2250
Tire Diameter (inches): 5.8
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 2.83 : 1
Total Ratio: 14.78419 : 1
Tire Circumference (inches): 18.22 inches (462.82 mm)
Rollout: 1.23:1
Total Motor Speed: 33300 RPM
Vehicle Speed: 38.87 mph (62.43 km/h)
Effective KV Value: 2250
KT constant: 0.6 oz-in/A

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

68/24 should be good for just shy of 40mph, perfect for racing. Just make sure you have good lipos really.

I plan to use TP 5000mAh 40C lipos, so lipo quality should be fine. That's the calculator I used, but was struggling a bit with. Tires are 5.6 I believe.

[Finnster]

I always found you need to inflate the size of the tires a bit to get an accurate (vs radar) speed reading. I'd aim for an FDR of ~13:1

[suicideneil]

Cool, no lipo worries then. With 5.6" tires that gearing is still good for ~37mph, and thats without factoring in any ballooning, so I'd say either run with 24/68, or maybe 24/65 to bring it back upto ~40mph.

Yeah, I need to play with it a bit tonight, I want to runn smaller spurs to help move the motor down, etc. So if I run the same ratio that works on a 68 or 65 tooth spur on a 54T spur I should end up around where I want to be. Compared to the first set you sent me, a 19t pinion and 54t spur should yield the same numbers. I'll have to play with it more. I was kind of looking for the "easy answer" with someone who ran an ERBE in racing consistently, but I'm starting to think most are using 5s or 6s and lower kV ratings.

[E-Revonut]

There is a lot more to gearing for racing than just gear for 40MPH!!! When I started racing this spring I found that out in a hurry! I started out geared for 39MPH but when I chewed up my pinion I had to gear down a bit because it's all I had available. I wound up running faster laps with it geared between 34-35MPH. I couldn't blow away the nitros on the straight anymore but the power was much more useable and was still faster than any nitro on the straight. Your gearing will depend alot on your track. Also remeber that lower gearing will pull less amps under acceleration and give you a little extra juice for the longer mains. Gearing up and turning your end point down will lower your speed but pull higher amps on acceleration.

[suicideneil]

I see 40mph as the safe upper limit for racing; what I should be typing is " gear for 30-40mph depending on how tight and technical your track is. An open or larger track can use the higher gearing/speed more to blow past the other trucks on the straights, where as a smaller or tighter track can use the lower gearing/ speed to make the most of the added acceleration out of bends and along the shorter straights". Ofcourse, thats the long winded version of "gear it for ~40mph"...

E-Revonut, I know there's more to it than that. I just wanted to get an idea of where I needed to be pinion wise since I plan to order 3-4 pinions to get the truck going and give myself some options. I just didn't want to order, say a 16-17-18-19 setup and then realize I need a 20-21-22-23 set of pinions to be in the ballpark, those suckers aren't cheap.

[SV6000]

Is anyone running 6s in there ERBE and if so what gearing are you running and what temps are you getting???

[suicideneil]

Originally Posted by SV6000

Is anyone running 6s in there ERBE and if so what gearing are you running and what temps are you getting???

Click here for answers to questions like that....

[SV6000]

Not cool dude, Not cool

[suicideneil]

There are a few people running the MMM system on 6 in the erevo for sure, cant remember their setups but check in the BL and revo sub-forums- more of a speed run setup bearing in mind the kv vs voltage..

[shaunjohnson]

Originally Posted by SV6000

Is anyone running 6s in there ERBE and if so what gearing are you running and what temps are you getting???

i started a craze at our club...everyone who is on their first car equipted with a MMM runs 6s
everything from E-revo's, rEvo converts, RC8T truggies and various buggies!!

we are ALL geared for 40mph and no one has temp issues, the ones that drive hard may have the fan flick on for a really short while.
eagle tree data under 6s load and 40mph gearing only shows amp spikes of 70A

my temps never go above 120 on the motor during racing.
my setup is:
rEvo 2.5 convert
E-maxx 3905 tranny, geared for 40mph with LST center diff.
turnigy 6s 30C 5000mah lipo
MMM 2200 combo
17t pinion, 65t spur (never ever stripped a spur since it was converted!!)
ESC fan only comes on when doing speed runs on grass (at 40mph)

something else i'd like to add...
when i gear for 40mph...i set the lipo cell voltages to 4.2v per cell...but as i understand...most people set them to 3.7v nominal voltage.
6s kicks nuts, i can crack 30 min mains, mate with similar setup might push 40 mins, cool temps, loads of power avaliable when you need it (screw up a jump, mash throttle to level out)

recomend it to any racer to run 6s...but i havent taken any consideration to weight though

Originally Posted by suicideneil

more of a speed run setup bearing in mind the kv vs voltage..

speed run setup....pah

[SV6000]

Thanks shaun that gives me something to compare to. I will run my eagletree as soon as i get home from work on Friday