XRAY - Model racing cars

Hello everybody,

I would like to ask a couple of questions about the gearing of my Xray T4 2017 to get the optimal performance possible. According to the instruction manual of my LRP x22 4.5t motor, the recommended gear ratio for this motor is 9.5 for "short tracks" and 8.5 for "long tracks". Those are values for a timing of 0 degrees.

I have some basic knowledge on gearing and timing. According to my research, if the same motor is kept in the car, having higher gear ratio would be better on tracks that have a large number of corners and very short straights because the full torque of the motor would be easily applied in a short period of time and therefore the acceleration of the car will be huge. In this track configuration a lot of top speed is not required because there are no long straights. If there are long straights the gear ratio should be lower to achieve higher top speed.

Timing of a modified motor has a similar role to the gearing process. A timing of 0 degrees gives better acceleration, a timing of 30 degrees gives better top speed.

Now for my questions. I found setup sheets of champions such as Bruno Coelho, Alexander Hagberg (Xray drivers). Those are drivers who use 4.5t modified motors all the time. It seems that they almost always use a gear ratio of 7.4 up to 8.0 maximum (110t spur and 25t-28t pinion). Furthermore, they use timing close to 30 degrees. This is a configuration for tracks with a high amount of long straights. However, I saw them racing on tracks such as the Reedy circuit – track with a lot of corners and not a very long straight. Their cars have amazing top speed and acceleration. So I am wondering why is there this big difference between the recommended values and the values the champions use. Is the ESC timing involved in the equation? Could you please give me an advice on this matter because I feel the data that I found is somewhat inconclusive and incoherent for me?

Any feedback would be very appreciated.

Kind regards,

Boris

The manufacturer doesn't want you to blow your motor and ESC up, then go back to them and say "you told me to run these settings, please give me a new motor". So they quote very conservative settings that will create little heat.

You need to be an incredible driver to run the settings that the top factory guys run, as it creates a huge amount of power. You also need a lot of grip, which they have at the big meetings.

So start on the tame LRP recommended settings, and if you feel you need more power, and the motor isn't getting hot, you can gear up and add timing. I'd also set the ESC punch settings as soft as possible to start with.

Thanks for the reply Dale. I actually never thought of this pure marketing aspect. I'll take your advice and probably go with a ratio of 8 and 0 timing just to be on the safe side. However, there is one thing that I can't agree with and that is your statement about changing gears. Changing gears does not increase nor decrease power. The change just modifies the application of the motor's power to the wheels/tires though belts, drivetrain etc. The thing that I find very interesting and mysterious is that pro drivers somehow get both amazing top speed and acceleration at the same time. I believe that the ESC is somehow the decisive factor. I read somewhere that people use the boost function. Maybe this boost function allows better acceleration with lower gear ratio? So much I don't know, so much to learn...

Actually, you'll tend to find that gearing even higher (around the 7.5ish mark) actually will make the car easier to drive, as the high gearing helps to reduce the torque from the motors, making the power band smoother. On my local track track, which is short and low-med grip, I'm geared at 7.5FDR, with 30° of end bell timing, and the ESC in blinky mode (HW G2 4.5t and XR10 Pro). I also have a 12.1mm rotor fitted to further smooth the power band.

You are right that ESC can make a big difference, running stock settings of max punch is not advisable for sure, but gearing does also play a big part. IMO, start around 7.8 for a 4.5t, run the ESC in blinky mode with punch settings down low, then gear it up and down, and feel the effects. The LRP motors are also quite renowned for being a bit more punchy than most with their delivery too...

Thanks for your reply and reccomendations TryHard! I actually thought about this and I am happy that you confirm my reasoning. The only thing I worry about is motor temperature. How does your motor preform with smaller gearing ratio? Doest it heat up a lot? I don't want to use a fan on my motor...