40/15 or 48/15 = 72mph?

72 mph with a 3/1 diff ratio, 40T spur, 15T pinion, 10S @ 3.9V, 750 motor KV, 6.84 tire diameter, 100 amp draw, and .008 motor resistance.

Am I missing something?

i think that 40t spur is gonna be perfect actually. i ordered the 36t and i think that is gonna be too small but i will try and see. i just dont want my esc overheating cuz its geared to high. and with a 36/18 it is just insane speed. i actually have a 16t, 17t, and 18t pinion gear so i can play around a bit with those but i think like a 40/16 is gonna be the ideal setup on 10s. it will be fast. probably in the 50mph range when its actually on the street. i am heading to the machine shop in like an hour and gonna get the gear cut. i am milling out the center are 6mm so that the gear will sit like the stock gear and shed some weight. i am just gonna save the CAD files so then when i get that 40t spur it will be a quick fix. the 48t is way too big. in fact, i bought a 48t gear already remember? that 48t FG gear. i thought it would work but it was WAAAAY too big. go with that 40t and it will be perfect. or if you want Kaz, i will order 2 of them right now, get them machined and hardened, and you can just pay me the actually cost of everything. the gear is $20 if i recall and i will know today how much to CNC will cost and hardening i will have to find out. i dont think it would be more than $50 for everything though. of course, i have already paid for the machinists time for drawing and stuff so you would only actually be paying for machining time. let me know

also SuicideNeil,
what do you think is gonna be the best gear ratio on these things? you seem to know alot about that stuff. keep in mind the largest spur gear is 40t. 10s, 750kv Neu. what do you think as far as pinion?

if the motor is torquey enough it might not even matter what gearing we run...within reason of course. i was just hoping that with the 36t my temps would be ok still cuz i figured this motor has enough torque that it would be fine. i am gonna order that 40t spur just to be safe though.

btw, i just ran the rc-calc. and with a 40/16 gearing on 10s, 750kv and 7" tire it comes out at 53mph. with 36/16 gearing it is 59mph. 36/18 = 67mph. i was gonna run this gearing if temps are ok. 36/18. 2 to 1 ratio. could be crazy.

Yeah, LMK how much it will be and I will decide.

What am I getting such higher speed on the calc then ? Were you using 3 for a diff ratio? What battery voltage?

i was using standard truggy diff ratio of 43/10 or 4.3. i thought that it was the rampage runs, isnt it? if i put in buggy ratio of 43/13 or 3.3 it jumps way up in speed. 36/18 goes from 67mph to 87mph. do you know exactly how many teeth the front and rear diffs/pinions have?

Yep, both diffs are 33/11

oh $#!t!! this thing is gonna be insane fast then. i didnt realize.

Thats why I was looking for a smaller pinion. Even with a 12T it is still in the mid 50's. RC Monster doesn't have pinion smaller than 15T. The company that we are getting the spur from sells pinions. They call them a spur with hub & set screw though.

Are these Mod1? If so, Mike has down to 9T pinions... or are these Mod1.5 pinions?

Mod 1.5 I emailed him earlier today and 15T is the smallest he has.

Cripes, 1/5 scale is beyond the realms of my 'expertease' Im affraid. I know one thing though, 70mph gearing is way too much as a starting point, I cant see the electorincs liking that much, or the tires. If you cant lower the gearing with a larger spur/ smaller pinion, IO would cdoncider dropping the voltage, just for inital testing.

And hit up the other 1/5 scale builds, tons of info in those regarding gearing and whatnot (a 1/5 scale tranny may be needed to drop the gearing perhaps, rather than a straightforward center diff)...

I found some smaller pinions...12T brings the speed down to 58

I think Mod 1 gears is the way to go...there are a lot more gearing options.

The bore on the 60T mod 1 spur is 10mm though...shouldn't be that hard to drill it out to 12mm.

Mod 1 60/15 brings the speed down to 48.33 mph.

qtcgears.com also has some good choices.

I'm afraid but I also think you should switch to mod one gearing. it's easier to get the right spur gear, and further the difference between eg. a 12 and 13t pinion is less then with mod 1.5.

there is a certain calculation to find out the number of teeth of a spur gear, with a specific diameter. but dunno that calc. just measure the maiximum diameter that would fit.

there is an app. to find gear diameter in BrianG's speed calculator.