final drive ratio

Fatty · Postby **Fatty** » Tue Oct 02, 2007 7:12 pm

i'm selecting between 2 ratios, i need to know the one that will give me the higher speed . this is for my tamiya eunos roadster

6.82:1 vs. 6.10:1

which of these gives me the higher top speed ? ? i think i know the answer but need to check with you guys as i have too many beers and the brain is playing tricks on me

RobbieRat · Postby **RobbieRat** » Tue Oct 02, 2007 7:15 pm

i'm selecting between 2 ratios, i need to know the one that will give me the higher speed . this is for my tamiya eunos roadster

6.82:1 vs. 6.10:1

The 6.10:1 would have the higher top speed.

Cheers Rob

Fatty · Postby **Fatty** » Tue Oct 02, 2007 7:17 pm

i knew that, thanks for confirming it. the reason i was asking is that the 6.82:1 is an mod option... it threw me coz i can't think of any reason you would want to make the car SLOWER

..

thanks!

zoomzoom · Postby **zoomzoom** » Tue Oct 02, 2007 7:22 pm

For better acceleration

Fatty · Postby **Fatty** » Tue Oct 02, 2007 7:25 pm

yes true. this sports tuned motor should take care of that tho!

StanTheMan · Postby **StanTheMan** » Tue Oct 02, 2007 7:46 pm

excuse the ignorance......Final Drive is that refering to the Diff ratio or 5th gear in the the gearbox?

AJ · Postby AJ » Tue Oct 02, 2007 7:47 pm

they're talking remote control cars stan

StanTheMan · Postby **StanTheMan** » Tue Oct 02, 2007 7:48 pm

ROFLMHO........i was going to say.....6.8 diff ratio is farking tiny.
ROFLMHO

Fatty · Postby **Fatty** » Tue Oct 02, 2007 7:48 pm

AJ wrote:they're talking remote control cars stan

yeah but it's still the same terminology :lol:

i believe final drive ratio refers to the ratios between 1 engine revolution and 1 wheel revolution.... errr...i think ?

AJ · Postby AJ » Tue Oct 02, 2007 8:03 pm

fattima · Postby **fattima** » Tue Oct 02, 2007 9:05 pm

Just remember higher numerically will give acceleration lower numerically will give top speed

Casey · Postby **Casey** » Tue Oct 02, 2007 10:13 pm

Fatty wrote:yes true. this sports tuned motor should take care of that tho!

But if you fit a high kv (rpms per volt) motor you may need a lower final drive to allow it to work efficiently. I fly RC planes and have recently got into electrics - lordy lordy things have come a long way since powered gliders with 1200 mA 7.2v NiCd packs and 540 brushed motors would struggle around for 2 mins of power runs.

With the planes I've got a couple of low kv brushless motors to allow direct drive props (high kv require a gearbox to spin a reasonable sized prop at an effective speed), coupled with lipo batteries I easily get 2 x 10 minute flights between charges flying hot little aerobatic or warbird craft.

ben wilson · Postby **ben wilson** » Tue Oct 02, 2007 11:41 pm

Putting it simply, higher gearing = more speed = less battery life = more heat.

Benny · Postby **Benny** » Wed Oct 03, 2007 3:57 pm

If you have a hot motor, a numerically lower gear may actually mean that the car goes slower, and not faster!
It has to do with the torque of an electric motor .
Generally, the hotter the motor, and the more it revs, the lower its torque is, so it may not be able to comfortably pull the lower gearing.
The lower gearing will also mean a shorter run time, as the motor needs to draw more current (which causes more heat) to pull the taller gearing.
Having a taller gear will also hurt your acceleration.

If you want to go fast, get a brushless motor for it, which will probably blow the diff, but it will certainly go, especially if you run it on Li-Po batteries.
I believe that the world record for a brushless R/C car is over 250km/h and even a standard brushless motor can get most R/C cars to go over 160km/h!

I used to have a petrol powered on-road R/C car ( an Italian made Serpent with a hot Nova Rossi engine) that could pull 130km/h in top gear (2-speed auto box on that one), and that was very difficult to control at those speeds, but it would out accelerate my friends hot HSV up to about 300M.