Help me pick my JRX2 racer gears?

[RCveteran]

Ready to run my Jrx2 LRM transmission racer this Thursday for some practice. I will be running a a 13.5T (3300kv) brushless.

I have available for my JRX2 slipper spurs in 84, 87, 88, and 90.

I think I want a final drive ratio of between 7.0 and 7.5 if I am not mistaken??

The LRM has an internal ratio of 2.18.

So using the formula, spur gear teeth/pinion gear teeth X 2.18, I am thinking the 88 spur and 26 tooth pinion are a good starting point for a final drive ratio of 7.4.

I will test with a temp gun at track as well but am new to this brushless thing so all thoughts about why I should adjust which gear set etc. are welcome.

Thanks.

[RCveteran]

Not to rush anyone, but I have 24 hours to finish this car. Perhaps a better question would be, if you had to pick a starting point final drive ratio what would it be for a 13.5T brushless LRM tranny. Then I can back into it with any size spur.

Novak site says final drive ratio of 7 is a good place to start for 2wd buggy with 13.5T motor.

[sgirouard]

What rear tires are you running? If you're running original JRX2 rims and no foam, I'd say go closer to 7. If you're running B4 rims with foam, go closer to the 7.5.

Now that being said, I'm a big fan of finding the sweet spot through running. You're definitely in the right area with 7-7.5 but get the car out there and run it through the full range.

[JK Racing]

I have only run a 13.5, but I was geared 30/76 in a XX4 (2.3 internal). Car was fantastic, but my FDR was closer to 6.0. In my Short Course, I was geared 24/88 (Blitz 2.6 internal) 9.5 FDR, but I was also running a Mamba Max Pro with CHEAT enabled (30 degrees of timing @ 9000 rpm).

I would personally start with the smallest spur you have, it moves the motor closer to the rear wheels helping reduce the pendulum effect swinging the rear end around. (I see 84 is the smallest you have ). Try finding/picking up a 78 and starting with a 24. Still starts you @ 7.

[RCveteran]

See I would have never thought about moving the motor forward as I was hung up on the number. I will work on getting a smaller spur for the slipper set up and start with the 84 I have for now. I doubt the LHS will have a spur for a 20 yr. old set up Thanks a lot.

[bearrickster]

here is a 75 and a 78

http://cgi.ebay.com/Losi-JRX-2-T-jrx2-78-tooth-48-pitch-spur-gear-/140496827261?pt=Radio_Control_Parts_Accessories&hash=item20b643737d

http://cgi.ebay.com/Losi-JRX-2-T-jrx2-75-tooth-48-pitch-spur-gear-/150542902882?pt=Radio_Control_Parts_Accessories&hash=item230d0e6662

[RCveteran]

I'm running the losi slipper and don't think those will work. I actually have the robonson adapter on the way and was waiting to see how it paired up to the slipper shaft if at all?

Looking at the Losi parts list I think 84 may be the smallest.

A-3904 84T Hydra-Drive / Slipper Gear
A-3906 86T Hydra-Drive / Slipper Gear
A-3908 88T Hydra-Drive / Slipper Gear
A-3910 90T Hydra-Drive / Slipper Gear

[JK Racing]

Personally, I would just pick up the outer slipper & convert over to the double slipper set up from the XXX, spurs will be no issue then.

[RCveteran]

That's a good idea, will that fit the same shaft and what part numbers will I need?

[JK Racing]

Yes, same shaft, part #s I will have to look up a XXX manual to see, I know it would be slipper pads, spur gear, outer plate & spring w/hardware...off the top of my head.

I do plan on doing a similar build to your car, I keep going back to look at it, fantastic job.

[RCveteran]

Thanks, I put the brushless motor and ESC in this morning. With all my parts cars and shelf queens I have not heard a LRM in a long time, it sounds so smooth with the brushless power. Will be hitting the track tomorrow for open practice and report back on set up and such.

[RCveteran]

A little fun in excel and maybe a handy reference.

[RCveteran]

Yes, same shaft, part #s I will have to look up a XXX manual to see, I know it would be slipper pads, spur gear, outer plate & spring w/hardware...off the top of my head.

I do plan on doing a similar build to your car, I keep going back to look at it, fantastic job.

Looks like the XXcr came with a double slipper set up as well, and the outer spring hardware looks the same, just need to verify if existing shaft would work.

[RCveteran]

Now that I think about it, I have a dual disc slipper conversion NIP for a double XX. I will have to play around with parts.

[Brandon G]

I agree with JK. Aim for a 7 FDR.