Timbulb

iTrader: (2)

He needs to know the internal drive ratio so he can figure out the final drive ratio.


Your 3.3 is not factoring in the internal drive ratio which is usually around 2 or 2.5.

Overall drive ratio : spur diveded by pinion times internal ratio will give you the FDR.

WildBillMassey

iTrader: (5)

Very nice, I'll be adding this to the site.

Please, if I am missing items on my site, let me know and I will get it on there ASAP.

rcwck

iTrader: (2)

Micro-E was asking for the internal(diff ratio) and that is a fixed 3.3 and not 2-2.5. The spur/pinion is the primary ratio and that is a variable.

Micro-E

iTrader: (4)

Thanks rcwck, I think that was the piece I was missing. Soooo, if I have the math correct:

43/13 = 3.30 -- diff ring gear/ diff pinion
51/14 = 3.64 -- spur / pinion
FDR = 3.30 * 3.64 -- 12.01

Wow, interesting, much shorter than 1/10th touring cars. Everyone is always talking about FDR and has an instant guage on how appropriately geared a car is given the motor wind. I don't see FDR discussed much with these cars.

The reason I was curious is that the 14t pinion was wayyy too slow for my last race with a 190' straight. Looks like I'll need to go to a 16t or 17t for my 2050kv motor on a straight like that. FDR of 10.5 or 9.9 respectively.

Just for further curiosity, what are FDRs, motor kv, and track length are folks running with this car??

rcwck

iTrader: (2)

Micro-E,

You'll have to go much BIGGER for mph on the straight. Our straight is ~200' and I am around a 22/47 for ~55mph for that KV and a good 4S. Basically gear TALL and check motor/ESC temps. Track temp is a large factor. I'm testing some turbine(EDF) fans that are variable speed TX controlled for super cooling for those hot days. Play with this, it's pretty accurate:
http://www.scriptasylum.com/rc_speed/top_speed.html

Capt'N_Slow

iTrader: (10)

Run my car on an open 200ft x 300ft ashfalt parking lot at a mass transit depot.

Motor: 1930KV Tekin T8
Tekin Setup : 30deg boost 9000start - 25500end

4S Bashing Setup : (52-55mph)
23/47 = 2.04 -- spur / pinion
FDR = 3.30 * 1.88 = 6.743

4S Track Setup : (43-48mph)
19/47 = 2.47 -- spur / pinion
FDR = 3.30 * 2.47 = 8.151

Motor: 1930KV Tekin T8
Tekin Setup : 10deg boost 10000start - 32000end

6S Bashing Setup : (58-63 mph)
19/47 = 2.47 -- spur / pinion
FDR = 3.30 * 2.76 = 8.151

Just got my 6S batteries 2 weeks ago and they are stupid fast for my small parking lot. (not enough room to brake)

Micro-E

iTrader: (4)

Thanks guys! That was some good info.

I was playing around with that speed site and it seems to me that a 19t pinion is good and safe to start with. If I need more umph, I could add in some boost. One of the GTPs I was comparing mine to - I believe - has a 2650kv and a 15t pinion, so a 19-20t puts me at the same theoretical numbers.

This is great to have some decision factors for $10+ pinions other than guessing... (damn, these pinions are expensive!)

mtrsprt

I assume my LX-2E has the same transmission ratio as the GTP2E. What are the differences in these two chassis? Both are made by Hong Nor I assume? I love my LX-2E to death, but I love on-road speed runs when I get bored of off-road. Bone stock, my LX-2E has hit 75.5mph with only a 19T pinion (51T spur), (2) Venom 30C 3200mah packs and a T8 2250 on 6S. Going for 80mph this week with a 21T pinion. The stock tires I assume are going to come apart anytime now lol. Trying to decide on a set of speed run tires between the OFNA Belted treads, or the Sweep 55's.

What would it take to fit a GTP2E shell on my LX-2E?

First post here folks, and I have been into R/C for over 25 years.

mtrsprt

That setup should hit 85-90mph without an issue with a 19T pinion. Which motor do you run? My RX8/T8 combo is insane.

Micro-E

iTrader: (4)

I have the Tekin RX8/T8 2050kv combo w/4S lipo. The stock 14T pinion wound out 1/3rd of the way down the straight... I borrowed a 15T and still not enough top speed, I was still passed like I was standing still.

mtrsprt

Right. 14.8V X 2050 = 30,340rpm. I can eat rice with chopsticks and still drive my buggy at the same time on 4S. That's with a 2250 motor.

Sounds like you need something along the lines of a 16-18T. Figure @ 30,00rpm, each tooth will net about 3-4mph on AVG.

SNR Graphite

iTrader: (19)

I have a couple of really good 3s 5000 50c packs I am going to try next at Charlie race.

I am going to gear it 19t with Tekin 2650 see how it goes.

mtrsprt

Just ordered a GTP2-E. Going to swap the electrics from my LX2-E over to it, and go for 100mph.

My LX2-E just went 83.8mph yesterday after the swap to a 21T pinion, and removal of rear wing.

Going to be locking the center differential with hot glue like I did with the LX2-E. Worked like a charm. Much more traction.

rcwck

iTrader: (2)

Gotta remember Micro's road racin with a 4S. Mid 50mph is more like it.

rpompeu

iTrader: (1)

You won't need this, it doesn't come with a center diff, it has a spool;