Suspension & Gearing Guide
The Basic Setup-Understanding Suspension
Suspension. Ok, there is a TON of information on suspension out there because in RC (and in real racing) suspension pretty much makes or breaks a good setup. There’s a lot that happens to your shocks and springs when you drift. Again, I don’t want to make this really techincal, and again, it depends on your chassis. A lot of the times, setups are very subjective. What works for one person doesn’t always works for another.
Shocks aka “Dampers”
For drifting, you typically want your rear suspension “softer” than your front.
- get soft springs. Springs come in different spring rates. The lower the spring rate, the less weight is needed to compress that spring. In other words, springs with lower rates are softer. Many companies color code, so pay attention to what you are buying.
- use lighter shock oil in the rear. Shock oil is measured by “weight”. The higher the number, the heavier the oil. Meaning that a heavier oil will make the shock piston compress slower. Note that some companies (like yokomo) label their shock oil 100, 200, 300, etc. It’s the same concept.
- soft springs all the way around (usually HPI titanium orange or something similar in rate)
- 35 to 40 wt in the front
- 15 to 25 wt in the rear.
A typical shock setup looks like this:
Some guys like to use the same shock oil all the way around, and change the springs in the front to a stiffer spring, or even use a stiff spring AND heavy oil in the front. Since suspension tuning has so many dynamics to this, I won’t confuse you guys by explaining every little bit of tech about shocks (it would take up the entire post). But you should understand that shocks and springs work opposite of each other. When a shock compresses, the spring is resisting the compression and wants to rebound. The damper controls how fast your suspension will compress, while the spring determines how fast your suspension will rebound when weight is transfered. This sentence sums how suspensions works really well: “Springs may dictate HOW MUCH weight is transferred, dampers dictate HOW and WHEN that weight is transferred.”
I get a lot of people asking if they HAVE to buy HPI titaniums or the Yok titaniums to drift. The answer is no. As long as they are soft, it doesn’t matter what brand or type you have. Titaniums are nice, I’ll admit. But I’ve used generic, HPI, Tamiya, and springs from japan. Springs all work the same. They compress and rebound and give similar results. Don’t feel the spring to test the softness..look at the spring rate.
Shock Positions. You usually want the shock more upright in the rear, and more “laid out” or angled towards the center of the chassis in the front. Simple as that. Won’t go into suspension geometry…lol
Ride Height vs. Droop. Guys get this mixed up all the time. First, they are not the same, but they are related. Ride height is exactly what it sounds like. It’s how high the bottom of your chassis is from the ground standing still. Low ride height means lowered center of gravity, and it usually means better handling and and less body roll. To adjust your ride height, simply lower the collars on your adjustables or add fatter clips on the shocks for non-adjustables. You can also change shock positions, but doing so affects how your shocks work.
Droop is something different, although it looks like you’re adjusting the height. Droop is adjusted using droop screws that are in the lower suspension arms of your chassis (both front and rear). It is the amount of upward or downward travel of your suspension above or below your ride height. In other words far up the chassis will “raise” after you’ve pressed down on it. The purpose of droop is to help with the weight transfer from front to rear when on throttle or braking. Say that your car is under steering when you let off on the throttle in a turn. What the chassis is doing at this moment is shifting the weight from the rear of the car to the front (imagine coming to a dead stop after going 60mph at a stop sign). When this happens, the rear end lifts a little. By adding more droop to the rear (letting your suspension have more upward travel), more weight is transfered to the front tires, giving it more steering and grip, and lessening the load on the rear.
The wrong gear ratio is one of the leading causes to overheating issues in the motor and the ESC. First, understand that FINAL drive ratio is different from PRIMARY gear ratio.
Pinion gear: small gear that goes on the motor shaft
Spur gear: large gear that is on the chassis
To calculate your primary gear ratio:
Spur Gear # teeth / Pinion Gear # teeth = primary gear ratio
So…if we have a 61T spur and a 19T pinion you would get:
61/19 = 3.21
So your primary gear ratio is 3.21.
Now, to calculate your FINAL drive ratio (which is what we use when figuring gearing out) you need to know your internal gear ratio, meaning the gear ratio of your transmission only:
Spur / pinion x internal ration = Final Drive Ratio (FDR)..remember, divide first and then multiply…;)
So in the case of a TT-01 which has an internal ratio of 2.6, it would look like this:
(61/19) x 2.6 = 8.34 FDR
If you don’t feel like doing math, go here to our tools page and input your numbers. You can also find out what your internal ratio is on that site.
So what does it all mean? This means that the pinion needs to make 8.34 revolutions to get the wheels to turn 1 revolution. For primary ratio, it takes 3.21 revolutions of the pinion to get the spur to turn 1 revolution. The higher the FDR, the more low-end torque you get. A lower FDR gives your more high end RPMS (some guys relate this to more horsepower and top speed). For drifting, usually a setting between 7.25 and 8.5 is good since you want that torque to pull you out of a turn. But it’s always good to look at your motor and ESC specs to find out what your electronics can handle, and it gear ratios will differ depending on chassis setup. There isn’t really any “magic number” for gear ratios. A lot of it is trial and error.