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I have a Worlds Car that i've re-built & have fitted a 6.5 brushless set-up into it (LRP Sphere & Hacker 6.5 motor) I've tested it out in the street & seems pretty rapid!

I intend to race it at the local track which run 5min qualifying & finals, the surface is pretty high grip grass, can anyone indicate what kind of gearing I should be running as a good starting point?

I've currently got it geared with an 84 tooth spur on a 20t pinion (gearbox internals are standard stealth with B4 slipper) Although v.quick it does 'feel' a bit undergeared? I understand the gearbox internals are the same (Ratio-wise) up to the B4 so i'm guessing theres got to be guys out there in the know?

Thanks in advance

Dan

DerbyDan wrote: I understand the gearbox internals are the same (Ratio-wise) up to the B4

the internal trans ratio are NOT the same from the original stealth up to the b4:

2.25 - rc10/10t/ds
2.40 - b2/b3/t3
2.60 - t2/gt/b4/t4/sc

sorry..... can't help you on gearing though. haven't made the brushless to fully understand it yet.

Thats great info Scr8p - at least knowing the ratios of the later buggies, I can make a comparison.

According to Hacker's site, the final drive ratio for that motor in a 2wd buggy should be 9.5. Since you are using a stealth with a ratio of 2.25, you should consider 20/85. That gets you pretty close (9.56). Otherwise you are a little over geared with what you have now. If you drop to a 19t pinion you will be slightly under geared.

Now for my .02.......

I run a 6.5 in a 4wd buggy. There's no way I'd even consider it in a 2wd buggy. For most tracks I don't go below an 8.5 in my B4. If you've seen the 2wd modified race I posted in the Florida racing thread, my son is running a 9.5 in his buggy. He beat Jason Ruona, Ryan Eckert, Jeremy and several others. My point is that too much motor is a bad thing.

Hey Dan
Have a look at BrianG's top speed calculator
http://scriptasylum.com/rc_speed/_top_speed.html


RC10 with Traxxas 3500kv

Differential Ratio: 1
Transmission Ratio: 2.25
Other Ratio: 1
Spur Tooth Count: 81
Pinion Tooth Count: 21
Total Voltage: 7.4
Motor KV: 3500
Tire Diameter (inches): 3.3
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 3.86 : 1
Total Ratio: 8.67857 : 1
Tire Circumference (inches): 10.37 inches (263.33 mm)
Rollout: 1.19:1
Total Motor Speed: 25900 RPM
Vehicle Speed: 29.3 mph (47.06 km/h)
Effective KV Value: 3500
KT constant: 0.39 oz-in/A

JHarris wrote:According to Hacker's site, the final drive ratio for that motor in a 2wd buggy should be 9.5. Since you are using a stealth with a ratio of 2.25, you should consider 20/85. That gets you pretty close (9.56).

This is the sort of info I'm on the hunt for at the moment... got a link to that site handy?

JHarris wrote:

Now for my .02.......

I run a 6.5 in a 4wd buggy. There's no way I'd even consider it in a 2wd buggy. For most tracks I don't go below an 8.5 in my B4. If you've seen the 2wd modified race I posted in the Florida racing thread, my son is running a 9.5 in his buggy. He beat Jason Ruona, Ryan Eckert, Jeremy and several others. My point is that too much motor is a bad thing.

I completely agree JHarris.... given the choice I probably would go for an 8.5.... however I was kindly given/leant the 6.5 motor & can't afford to buy another at the moment (after breaking the bank buying a Black Diamond speedo for my touring car)

My saving grace I suppose is that our tracks over here tend to be laid on high grip (and draggy) grass or astroturf - I guess also theres some backward logic in that, if I try the 6.5 & its definately too fast - I can buy an 8.5 or 7.5 (see what the other guys are running) which is better than buying a slower motor and finding out that in order to keep up I need something faster??

As I said, so far i've only driven the car on the street (not the best test) and although theres definately more mid-range torque... the speed & initial launch feels similar to a good 10 or 11 turn brushed motors we ran back in the day... i've been racing continuously for nearly 25 years now - so even if the 6.5 is rather too lairy, i'm hoping theres some skill left behind the sticks to keep it between the track markings LOL!

Thanks for the info on the gearing too - seems like I nearly got it spot-on, lucky guesstimate!