Xrt Speed Runner

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Nutts4RC

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What would be a good mod 1.5 gearing to start out speed running with on the xrt?
TIA all
 
Does that have the same setup as the X-Maxx? Not familiar with that kit, but www.wforccustoms.com has 1.5 gearsets for the X-Maxx. You might check there.
 
Get the smallest spur and biggest pinion you can get and then tune down from there if it overheats the rig to quickly.
 
By tune down you mean make the spur bigger in tooth size?
 
By tune down you mean make the spur bigger in tooth size?
or smaller pinion, either way. could do both if you needed to but if top speed is what your after Id start with the tallest gearing possible.
 
or smaller pinion, either way. could do both if you needed to but if top speed is what your after Id start with the tallest gearing possible.
Idk what you mean by tallest gearing Grey. This is my first speed build. Not trying to chase or break anyones pb just set my own in the high 80s to low 90s
 
The smallest spur and the biggest pinion possible would be the tallest gearing possible. If you're not going for maximum possible speed then maybe start with 1:2 gearing and tune from there. Lemme know if you have anymore questions. It can be alot to take in initially :)
 
The smallest spur and the biggest pinion possible would be the tallest gearing possible. If you're not going for maximum possible speed then maybe start with 1:2 gearing and tune from there. Lemme know if you have anymore questions. It can be alot to take in initially :)
Thank you grey. Yes its alot to take in but i like going fast so i wanna learn i just dont want to set my truck and or esc on fire? What causes fires like the ones people post on youtube I've asked but no one has ever really answered the question directly
 
Thank you grey. Yes its alot to take in but i like going fast so i wanna learn i just dont want to set my truck and or esc on fire? What causes fires like the ones people post on youtube I've asked but no one has ever really answered the question directly
Drawing more amperage than the ESC and/or battery can handle for too long. Gotta keep an eye on those temps :)
 
Drawing more amperage than the ESC and/or battery can handle for too long. Gotta keep an eye on those temps :)
I'm putting in a max 4 and probably a castle 1650kv motor so hopefully that combo will be minimal on the amps. I'm gonna use better batteries than the hoovo i got like gensacearespammers or cnhl
 
I'm putting in a max 4 and probably a castle 1650kv motor so hopefully that combo will be minimal on the amps. I'm gonna use better batteries than the hoovo i got like gensacearespammers or cnhl
Max4 should be good but the 1650kV is a 1717 series motor which are designed for 1:8 and 1:7 scale rigs. You need to look in to something for 1/5 scale.

My first choice would be a TP Power 5680 1440kV motor on 8S
Second choice would be a Castle 2028 series 1100kV motor on 10S.

Id look at CNHL or Liperior Pro lipos myself. Gens arent as good and more expensive.

This is the TP Power motor.
20210624_172507.jpg
 
Max4 should be good but the 1650kV is a 1717 series motor which are designed for 1:8 and 1:7 scale rigs. You need to look in to something for 1/5 scale.

My first choice would be a TP Power 5680 1440kV motor on 8S
Second choice would be a Castle 2028 series 1100kV motor on 10S.

Id look at CNHL or Liperior Pro lipos myself. Gens arent as good and more expensive.

This is the TP Power motor.
View attachment 159024
Wouldn't a 1440kv motor be slower than the 1650kv motor and also have more torque? Where would a person even look for a tp motor? And couldnt you run a castle 2028 series on 8s? Whys it just have to be 10s?
 
Wouldn't a 1440kv motor be slower than the 1650kv motor and also have more torque?
The 1650kV as mentioned earlier is a 8th/7th scale motor with a 46mm diameter can size.
The 1440kV is a 5th scale motor with a 56mm diameter can size.

They are both 8S capable motors but the lower kV rating and bigger can size of the 1440kV makes it much more efficient at producing torque while still being able to produce close to the same max RPMs. What does this mean for doing speed runs? It means the electronics will be under a lot less strain, will take longer to heat up, and will last longer overall. It also means that you can run taller gearing to make up for the small loss in kV.

All that aside, the XRT is a 5th scale rig and should have a proper 5th scale motor.

Where would a person even look for a tp motor?
www.TPPowerUSA.com
LINK to the 5680 1440kV specifically

And couldnt you run a castle 2028 series on 8s? Whys it just have to be 10s?
You absolutely could run the 2028 on 8S but will be slower than the 1440. Even if you ran the 2028 on 10S it still produces about 2000 less max RPM than the 1440kV. On 8S the 1100kV will have about 10,000 RPM less than the 1440kV on 8S.

That being said, I know you said you werent out for absolute max speed and thats how I'm approaching this topic. Its hard for me to talk about "speed runs" without talking about it from the all out perspective lol. If you never plan on going over 8S and you're never go for flat out max speed runs, You could go with MAX5 ESC instead of the MAX4. The MAX5 is a 5th scale ESC and is about half the price of the MAX4. Not that you couldnt do max 8S speed runs with the MAX5 it just has less headroom than a MAX4 meaning the MAX4 will be more efficient for that task and therefore less likely to have issues down the road. Again though, as long as you're watching those motor/ESc/LiPo temps, you'll be fine, generally speaking.
 
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Hey Nutts. Sounds like fun. XRT is fast out of the box. 50+mph according to the TRX XRT site. What speeds have you gotten out of it so far? What are you using to record speed?

Reading the specs, XRT comes with 20/50 pinion/spur gearing for a ratio of 2.5:1. Option gearing for 60+mph TRX lists as 23/46 for a "higher, taller" ratio of 2:1. Also of note is that the TRX skill level recommendation goes from a Level 5 to a Level 6 when using the 2:1 ratio. That seems to indicate there will be some chassis tuning coming into play at the increased speed.

Knowing that, were it my truck, that is the two baseline ratios I would begin with. Find a good, safe wide spot without obstructions for some runs. Get used to the feel of the truck in speed runs. Then begin the process of incremental changes. Speed comes slowly and in plateaus to do it safely and make it easy on the wallet.

Hope this helps. Good luck. XRT is a massive package. 'AC'
 
Grey you are absolutely awesome my friend. Thank you so much for explaining it the way you did it really helped me understand it. And i greatly appreciate that. I do plan on going beyond 8s just not right out of the gate. And now that you explained it to me i am def gonna be getting the tp 1440kv along with the max 4. I prefer the max 4 simply because I like to future proof things for as long as possible if that makes sense. Also someone told me something last night that i did not know and it didnt make sense to me at all but it came from one of the top speed guys i know on Facebook and youtube. He said the motor gearing isnt the only gearing that needs changed, that the differential gears need changed too or something to that effect. I was under the impression that the only gears i needed to adjust were the spur and pinion of the motor gears? I also dont even know what tooth to start out on either as no one has ever given me a straight concise answer. I was told that it depends on the diameter of the wheels i will be using for runs which ill be using gone bananas racing skins and they are between 6.5 and 7 inches in diameter. Thank you for all your help my friend. I'm definitely learning a lot from you
Hey Nutts. Sounds like fun. XRT is fast out of the box. 50+mph according to the TRX XRT site. What speeds have you gotten out of it so far? What are you using to record speed?

Reading the specs, XRT comes with 20/50 pinion/spur gearing for a ratio of 2.5:1. Option gearing for 60+mph TRX lists as 23/46 for a "higher, taller" ratio of 2:1. Also of note is that the TRX skill level recommendation goes from a Level 5 to a Level 6 when using the 2:1 ratio. That seems to indicate there will be some chassis tuning coming into play at the increased speed.

Knowing that, were it my truck, that is the two baseline ratios I would begin with. Find a good, safe wide spot without obstructions for some runs. Get used to the feel of the truck in speed runs. Then begin the process of incremental changes. Speed comes slowly and in plateaus to do it safely and make it easy on the wallet.

Hope this helps. Good luck. XRT is a massive package. 'AC'
Hey buddy thank you for the tips i really appreciate you my friend. I havent even ran the xrt on stock yet its been too wet and cold where I'm at and i dont want to risk breaking anything yet. I've just been doing small slow upgrades (wing mount, battery trays so i can remove the battery hold downs, replacing the front and rear bulkheads, upgrading the drive train to m2c, and taking notes from people here and on Facebook about what to get so i can outfit the xrt right and hopefully not worry about starting any esc or lipo fires (I'm still not sure why some people on youtube even video their rigs going up in smoke to begin with, and i still dont fully understand what causes a lipo fire but I've heard its from mostly castle escs which I'm not using although speed guys think those are the ultimate go to. As far as gps i have a sky rc gsm 020. And i totally get you on when you said speed comes in small numbers.
Grey also do i want the 1440kv vented or sealed? Or does it make a difference?
 
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GSM020 is a good choice. It is on my wish list for future purchase. Watched a YouTube vid on it out of U.K. and the acceleration and speed graphs are top notch.

Currently using the reliable and rugged GSM-015. I like the instant read feature on its face. That and having the run pattern layout in download quickly shows if it was a straight run or there was a pattern or pull in one direction or the other. A good driving and tuning aid. I see it is listed as sold out at Amain. Perhaps SkyRC is transitioning to the 020 entirely?

BTW, TRX website lists additional spur gear choices for the XRT so mix-and-match pinion/spur is an option. For now, my recommendation would be not to worry too much about diff gear changes. Save that as useful info when it gets down to wanting that extra mph or two. I took a look at the XRT manual on line. Looks like there is a wealth of info there to get you started in your quest for speed. Good luck. Luck forward to seeing the speeds you get.

I didn't see a set-up sheet in the manual. May have missed it. You'll need one to keep track of baseline and changes and how they work or don't work.

Oh, RCCA (Radio Control Car Action) magazine, February 2023 issue, has an eight-page spread on the XRT. Might want to pick up a copy at your LHS or bookstore. May even be available for review on the RCCA website? I subscribe to both the print and digital issue so have access there.

Cheers. 'AC'
 
Grey you are absolutely awesome my friend. Thank you so much for explaining it the way you did it really helped me understand it. And i greatly appreciate that. I do plan on going beyond 8s just not right out of the gate. And now that you explained it to me i am def gonna be getting the tp 1440kv along with the max 4. I prefer the max 4 simply because I like to future proof things for as long as possible if that makes sense. Also someone told me something last night that i did not know and it didnt make sense to me at all but it came from one of the top speed guys i know on Facebook and youtube. He said the motor gearing isnt the only gearing that needs changed, that the differential gears need changed too or something to that effect. I was under the impression that the only gears i needed to adjust were the spur and pinion of the motor gears? I also dont even know what tooth to start out on either as no one has ever given me a straight concise answer. I was told that it depends on the diameter of the wheels i will be using for runs which ill be using gone bananas racing skins and they are between 6.5 and 7 inches in diameter. Thank you for all your help my friend. I'm definitely learning a lot from you
Glad I'm able to help. If you get to the point where you want to go beyond 8S, TPPower is a good place to look for a motor that will be good for it. (They even make custom motors) The 1440kV is limited to 8S although it will produce higher RPMs than the Castle 1100kV on 10S or the Castle 800kV on 12S. If you're not already familiar, you can calculate the max RPM by multiplying the battery voltage by the kV rating. At least with no load on the motor anyway. Lower RPMs doesn't necessarily mean slower though, gearing can make up for some of that and there are theoretical speed calculators online that you can plug in all of your gearing info etc to find out what is theoretically faster. A lower kV motor will be able to handle taller gearing (closer to 1:1) better than a higher kV motor.

Speaking of gearing, When you go really deep down the speed run rabbit hole you'll start encountering terms like "Final Drive Ratio" (FDR) and "rollout" etc. Your FDR takes in to account all the gearing in your drive line not just the pinion and spur. Thats why those hardcore guys were talking about diff gearing. Rollout has to do with the diameter of your tires and how much they move compared to the rotation of the pinion. Using larger diameter tires produces the same affect as using a bigger pinion. Higher top speed at the cost of acceleration/torque. I wont overload you with details as you have to get really deep in the rabbit hole for these things to start becoming of importance and you're not to that point yet but Ill post a couple of links that give some brief explanations in a little more detail if you're curious. The bottom line is your pinion, spur, diff gears, and tire diameter all play a part in the overall top speed and/or acceleration of your RC.

Final Drive Ratio
Rollout
 

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