Gearing question

bicketybam

Drives like a barbarian with a bended brain!
Premium Member
Excellence Award
Build Thread Contributor
Messages
10,418
Reaction score
16,817
Location
New Milford, CT
Arrma RC's
BigRock 4x4, Granite, Infraction, Kraton 8S, Kraton 6s, Kraton 4s, Mojave, Notorious, Talion, Typhon 6s
Other than fitment issues, is there any advantage to decreasing the size of the spur vs. increasing the size of the pinion? For example, I'm running 44T pinion with the stock internal 47T spur on my K8S. I could theoretically run a 39t spur and a 36/37t pinion for the same gearing. What is the benefit of doing this (if any) from a performance standpoint? Thanks!
 

jondilly1974

Speed running rookie, 3D printing fool
Premium Member
Excellence Award
Build Thread Contributor
Messages
8,796
Reaction score
10,407
Location
Toledo, OH
Arrma RC's
Granite, Kraton 4s, Typhon 6s, Typhon 3s
I would say space is a limiting factor. There may be a weight factor too, but I think you’re knit picking at that point.
 

bicketybam

Drives like a barbarian with a bended brain!
Premium Member
Excellence Award
Build Thread Contributor
Messages
10,418
Reaction score
16,817
Location
New Milford, CT
Arrma RC's
BigRock 4x4, Granite, Infraction, Kraton 8S, Kraton 6s, Kraton 4s, Mojave, Notorious, Talion, Typhon 6s
I would say space is a limiting factor. There may be a weight factor too, but I think you’re knit picking at that point.
That was my thought as well but was wondering if I was missing something.
 

Mastaa

Premium Member!
Premium Member
Build Thread Contributor
Messages
167
Reaction score
251
Arrma RC's
Kraton 8S, Kraton 6s, Typhon 6s
I'm no expert on this topic, but I was thinking the same thing when the other thread about possible spur gear options popped up. If the gearing ratio is essentially the same, it comes down to other factors, as you and @jondilly1974 already discussed above. I've read stuff about higher rotational mass with the bigger pinion / spur combos, thus being heavier but giving better mesh... Then again, the closer the number of teeth on pinion and spur are, the more efficient should it be..

Knit picking really seems to be the right expression here :)
 

olds97_lss

Bash Break Repeat!
Premium Member
Excellence Award
Build Thread Contributor
Messages
4,275
Reaction score
4,125
Location
Dekalb, IL
Guessing the smaller the pinion the less deflection/side load there is on the motor bearings... but I can't imagine a few teeth making that much difference in that regard. Would be different if you were going from an 11T pinion to a 30T pinion. Then again, it may not matter because the load is kind of hitting at 90 degrees regardless where the pinion makes contact. Well... I guess the torque transfer would be further out from center on the motor with a larger pinion, so it would be like a larger lever in that regard.
 

Warby

"Hurry up and wait"
Premium Member
Build Thread Contributor
Messages
637
Reaction score
1,145
Location
Australia, WA.
Arrma RC's
4x4-Mega, BigRock 4x4, Kraton 6s
What about he centrifugal effect of a larger gear compared to smaller diameter gear? Like a flywheel, more momentum the heavier or larger it is. or would it not make a difference as the other gear (spur or pinion) would be smaller?
 

soSincerious

Well-Known Member
Messages
35
Reaction score
44
Location
Rhode Island
Arrma RC's
Talion
rotational mass really should only be scrutinized when racing. we shouldn't really be racing with Arrma's, .... should we ?!
 

jonUF02

Well-Known Member
Messages
520
Reaction score
294
Location
Orlando, FL
Arrma RC's
Kraton 6s, Nero, Outcast 6s, Outcast 4s
I think smaller spur and larger pinion works the motor harder?

Small pinion with huge spur would spin the motor very fast, they do have a max RPM rating.
 

MaddogMikeD

Well-Known Member
Messages
118
Reaction score
163
Location
The Big MItten folks!
Arrma RC's
Granite, Kraton 6s
I think smaller spur and larger pinion works the motor harder?

Small pinion with huge spur would spin the motor very fast, they do have a max RPM rating.
Its opposite... for example the Kraton... out of the book has a 50T spur to 12T pinion... but give you a 15T swap for speed... As I saw on line the closer you get to a 1 to 1 ratio the higher the speed, but you burn up in grass or rough terrain the farther you go to that.
 

jonUF02

Well-Known Member
Messages
520
Reaction score
294
Location
Orlando, FL
Arrma RC's
Kraton 6s, Nero, Outcast 6s, Outcast 4s
You're assuming the same spur, but the question was in regards to absolute ratio, changing both gears to achieve the same.
 

MaddogMikeD

Well-Known Member
Messages
118
Reaction score
163
Location
The Big MItten folks!
Arrma RC's
Granite, Kraton 6s
No I'm not... like I said... you change spur and pinion that creates another ratio for that tooth count... So for example a 34T spur and a 29at pinion should have me in high 80's... In his example he wasn't changing the ratio mutch, but the 37 would be faster than the 36...
 
Top