Changing differential gear ration by using different pinion.

[Gee]

Could the beveled pinion used in say 1/8th scale diffs be changed to create a different gear ratio? Giving it is the same pitch.

I have some STRR diffs that are spiral cut and use a 13t spiral pinion and spiral cut ring gear. I picked up some 10t spiral cut GS Racing (Clearance) diff pinions. They didn't have the tooth count listed for the pinons, but $3 bucks a peice vs $15 a piece was chance I took. They seem to mesh fine with the strr ring gear. I think the # of teeth on the GS Racing ring and STRR are the same. Granted that the front and rear diffs would need the same gearing ratio.

Are there any issues I might be over looking?

Is it the ring gear that determines the pitch for the diffs?

Thinking silently but typing it in:

If the pinion came from another rc or manufacture the had the same amount of teeth on the ring gear:
Ofna
43/11
43/13
43/14

HPI
43/13

LST
43/13

H.B.
43/10

Pinions would be compatable as far as meshing goes,

but would the pinion from the:

HPI Hellfire
42/10

or

OFNA Ultra GTP
44/14

would those mesh okay with a 43t ring gear?

[George16]

You can change the ratio by changing the pinion and/or ring gear.

Issues, only if the spiral cut ones were not cut at the same angle.

Both ring gear and pinion determines the pitch.

Either pinion or ring gear gear setermines the gear ratio.

For example:
43/10 = 4.3:1
42/10 = 4.2:1
43/11 = 3.9:1
43/13 = 3.3:1

Anytime you change the number of teeth on either pinion or ring gear, the ratio changes correspondingly.

[magman]

So in reading your above post...what are the pros-cons to say changing from a 43/10 set up to say a 43/13 set up?

[George16]

It depends on what you want to accomplish. With 43/13 (mostly buggy diffs), you can use bigger pinion and/or smaller spur to achieve higher speeds.

[magman]

Originally Posted by George16

It depends on what you want to accomplish. With 43/13 (mostly buggy diffs), you can use bigger pinion and/or smaller spur to achieve higher speeds.

I see now, makes sense..thanks!

[Gee]

Thanks for the help Lito.

[jayjay283]

[QUOTE=George16;337744].[/QUOTE
are you back on land home skillit ?

[Patrick]

A 10t pinion of the same pitch as a 13t will have a smaller diameter, and might not be big enough to reach the ring gear enough to mesh properly inside the diff case. I haven't looked closely before, but I would say ring gears are off set differently to suit 10t or 13t pinions.
If you have a lot of room if the diff housing you may be able to shim the gears close enough, worth trying anyway.

Have you counted the teeth on the st rr pinion? I'm pretty sure the truggy has a 10t pinion anyway, or did they get swapped for buggy diffs?

[George16]

The ST RR has a 10T pinion and a 43T ring gear. I just replaced the diff fluids in my ST RR.

Jay, I'm finally back on land. We returned from our deployment 3 days prior to Thanksgiving. At least I'll be on land until our deployment cycle starts again in May next year.

[Gee]

Welcome back Lito. I was looking for your help a while back. Finallly got around to picking some of the final small pieces to finish the str to strr conversion. Got to this front part and got a bit stumped. I thought you posted something about connecting the upper front arm pins in when you out your strr together but couldn't find it though. I got them in there and nothing has fell apart yet. Not sure if I ended up doing if correctly though. It that last post in this thread:

http://www.rc-monster.com/forum/show...t=14885&page=2

Originally Posted by Patrick

A 10t pinion of the same pitch as a 13t will have a smaller diameter, and might not be big enough to reach the ring gear enough to mesh properly inside the diff case. I haven't looked closely before, but I would say ring gears are off set differently to suit 10t or 13t pinions.
If you have a lot of room if the diff housing you may be able to shim the gears close enough, worth trying anyway.

Have you counted the teeth on the st rr pinion? I'm pretty sure the truggy has a 10t pinion anyway, or did they get swapped for buggy diffs?

Yeah, you guys have it right. I put them down backwards in the op. The GS Racing pinions are the buggy 13t

That's a good point you brought up about the mesh. I don't have the gs ring gear. I thought about ordering two of them. At the clearance price a-main has them listed at it's tempting. They have the GS racing cvd and universial shaft for a great price but I can't get any specs out of them.

It's hard to tell how much different the hang over would be in the ring gear from the pictues.

GS RACING


KYOSHO


I don't know a lot about the metals but if the origanal price is any indication the GS ring gear is made from a better material vs the Kyosho ring gear.

I did measure the widest part on both of the pinon and this is what they are

Kyosho Pinoin
11.6mm

GS Racing
13.1mm

So there probably would be a mesh issue unless the right ring gear was used.


Ironically it wasn't even the STRR or the GS gear that got me thinking about this. When I put the LST diffs into the G3R is took away some snap that I thought I use to have. But I also ran a mm 4s 1515 1y 56/25 on it then went to a 6s MMM and CC/Neu 2200kv setup, changed the diffs out, put 7" terapins on to play with. Put the MMM and CC/neu in the Savage XL and put the 1515 back in the G3R. I am now running a 6s MMM on a 1515 1y on 72/19 and it seems better now. With those tires and gearing it is pretty close to 1:1 rollout. It seems the cc/new 2200kv motor has more torque then my old 1515 1y 2200kv does. I was going to pull the 1515 1y from the maxx and try it out. It hasn't been run very much at all compared to the one that was in the G3R.

[lutach]

Mugen's truggy diff has a 4.6:1 ratio if you want to go higher.

[George16]

Gee, I'm on duty in the ship right now so I can't see any pictures link to photobucket using this government computer. I'll let you know tomorrow when I get home and will also snap some pics of my ST RR.

With regards to using the GS diffs, I say go for it. Just make sure you buy the ring gear and pinion together so they match. Even though gears are Mod 1, there are still small differences in the machining that might interfere in getting a good mesh. I also happen to have some GS ring gear and pinion and you're absolutely right about the better quality compared to the Kyosho parts. I'm just waiting for my Kyosho diffs to grenade so I can install either the GS or Ofna gears.

Ever wonder why they sell ring gears and pinions as a set on 1:1 cars and trucks (same brands) .