End Points, Dual Rate and Expo: Which One You Actually Need
End point is where the wall is, dual rate is how close you can get, expo is the shape of the ramp. A symptom table telling you which of the three to reach for, why sub-trim is not a fix for a bent linkage, and the order to set them in.
Updated Jul 22, 2026 · RC Crash Crew
Dual rate, expo and end points all change how your car responds to the same stick or wheel movement. They are constantly confused with each other, and using the wrong one means fixing a symptom while leaving the cause.
The distinction is genuinely simple once you see it:
| Setting | What it changes | Analogy |
|---|---|---|
| End point (EPA) | The mechanical limit of servo travel | Where the wall is |
| Dual rate | How much of that travel you can reach | How close to the wall you're allowed |
| Expo | The shape of the response getting there | How steep the ramp is |
Set them in that order — end points first, then dual rate, then expo — because each one operates inside the one before it.
End points (EPA / ATV): the mechanical limits
What it does: sets the absolute furthest the servo will travel in each direction, independently.
What it is for: protecting hardware. It stops the servo driving the steering linkage into a mechanical stop, and it stops the throttle servo on a nitro car forcing the carburettor past its range.
How to set steering end points:
- Wheels off the ground.
- Turn the wheel fully one way. Watch and listen to the servo.
- If the servo is straining, buzzing, or the linkage has visibly hit a stop, reduce that end point until it stops just before the mechanical limit.
- Repeat for the other direction, separately. They are almost never the same number, because linkages are rarely perfectly symmetric.
Why it matters: a servo held against a stop is drawing high current, generating heat, and stressing its gears — every time you reach full lock. It is a slow way to destroy a servo, and it also loads the BEC, which can cause brown-outs under hard steering.
Signs your end points are wrong: a buzzing or humming servo at full lock, a servo that gets hot with no crash to explain it, or steering that visibly reaches further one way than the other.
⚠️ Set these before anything else. Dual rate and expo both work inside the range end points define, so changing end points afterwards invalidates everything you tuned on top.
Dual rate: how much steering you can actually use
What it does: reduces the maximum travel you can reach at full stick, as a percentage of the end point.
What it is for: when the car has more steering lock than it can usefully apply.
That happens more than people expect. On a high-grip surface, full lock often just scrubs the front tires sideways — the car turns *less* than it would with less steering input, because a scrubbing tire has lost its grip. Winding dual rate down means full stick gives you the amount of steering the car can actually use.
How to set it:
- Start at 100% and drive.
- If you find yourself never using full lock, or the car washes out when you do, reduce in steps of about 10%.
- Keep reducing until full stick produces the sharpest turn the car can actually make.
- Raise it back up for tight, technical, low-speed sections where you genuinely need the lock.
Common practice: many drivers set a switch on the transmitter to flip between a low rate for fast flowing sections and a high rate for tight ones.
Dual rate on throttle exists too, and is genuinely useful — limiting maximum throttle is one of the best ways to make a very fast car learnable, and to hand a model to a beginner without terrifying them.
Expo: the shape, not the limit
What it does: softens the response around the center of the stick or wheel while leaving full travel at the ends completely unchanged.
This is the key point people miss. Expo costs you nothing at full lock. You still get every degree of steering; it just takes more stick movement to reach the first part of it.
What it is for: a car that is twitchy, darty, or hard to hold in a straight line — where the first few degrees of input produce far more reaction than you wanted.
How to set steering expo:
- Start at zero.
- Add expo in steps of about 10%.
- Drive a straight and a sweeping corner between changes.
- Stop when the car holds a line without constant small corrections, but still turns in willingly when you ask properly.
Too much expo feels vague and disconnected — you move the wheel and nothing happens for a moment, then it all arrives at once.
Throttle expo does the same job for power delivery. On a car with far more power than traction, throttle expo makes the bottom of the trigger usable and is often more effective than reducing punch on the ESC.
⚠️ Some radios use negative numbers for softening and positive for sharpening; others are the reverse. Do not copy an expo value from someone else's setup without knowing which convention their radio uses — you can easily apply the exact opposite of what you intended. Test it on the bench: add expo, and small stick movements should produce *smaller* servo movements than before.
Which one do I actually need?
The question that resolves it: is the problem how much, or how fast?
| Symptom | Setting | Why |
|---|---|---|
| Car darts / twitchy on straights | Expo | Softens response around center without losing lock |
| Car washes out at full lock on high grip | Dual rate | You have more lock than the tires can use |
| Servo buzzes or strains at full lock | End point | It is hitting a mechanical stop |
| Steering reaches further one way than the other | End point (each side separately) | Asymmetric linkage |
| Too much power off the line, spins up | Throttle expo, or ESC punch | Softens delivery without capping top end |
| Car is simply too fast to learn on | Throttle dual rate | Caps maximum power |
| Steering feels vague and delayed | Too much expo — reduce it | Over-softened |
Sub-trim, and why it is not the answer
Sub-trim shifts the servo's center point in software. It exists to correct the last small amount of misalignment when the servo horn's splines will not let you get it perfectly centered mechanically.
It is not a fix for a misaligned linkage. If you have used a lot of sub-trim or trim to make the wheels point straight, you have now made the available travel unequal in each direction — the car genuinely turns better one way than the other, and people spend seasons blaming the diff for that.
The right order: adjust the steering turnbuckles so the wheels sit straight with trim and sub-trim at zero, *then* use a small amount of sub-trim for the last fraction.
Model memory: set it up once per car
Every one of these settings is per-model. A transmitter with model memory stores a separate set for each vehicle, which is the main reason to own one good transmitter rather than a cheap one per car.
Two habits worth having:
- Name each memory clearly and consistently, so you can find the right one quickly.
- Turn on model match if your system has it — it ties a receiver to a specific model memory so the car simply will not run under the wrong settings. That removes the mistake entirely instead of relying on you noticing.
The setup sequence
- Mechanically center the steering with turnbuckles, trim and sub-trim at zero.
- Set end points, each direction separately, just short of the mechanical stop.
- Add a small amount of sub-trim if needed for the last fraction.
- Drive. Then set dual rate based on how much lock the car can actually use.
- Then add expo until it stops being twitchy.
- Save it to that model's memory, and write down what you did.
What we could not confirm
We are not publishing recommended dual rate or expo percentages. They are personal — they depend on your car, your surface, your radio's response curve and how you drive, and expo values do not transfer between radio brands because the curve shapes and sign conventions differ.
Two experienced drivers on identical cars will run noticeably different numbers and both be right. Start from your radio manual's defaults and adjust in 10% steps, testing the same section between changes.