ECX Boost suspension tuning (?)

i_r_beej

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I thought I'd break this discussion off into it's own thread. I had been going back-and-forth with @rob5059 regarding the use of RPM's 2-stage shock pistons in the aluminum ECX "upgrade" shocks.

There are a few issues that are preventing a "bolt-on" upgrade:

The first difficulty is that the design of the RPM piston requires 2.5mm between the E-clips on the shock shaft and the ECX shaft only has 2mm.

The second problem is that I measured the diameter of the stock ECX pistons at 9.9mm and the RPM pistons at 10.02 mm. That's just enough of a difference to cause some problems. The stock plastic bodies appear to have some taper that causes the RPM piston to bind about halfway through a stroke. The aluminum shock bodies are more consistent, but the RPM pistons *just* barely fit and there is some drag the full length of the stroke.

Finally, I have not yet found a compatible shaft for the front ECX shocks. Traxxas produces a 51mm long shaft (part number 2765) that is a direct replacement for the ECX rear shock shaft.

So it seems that the only really "serious" performance upgrade in terms of spring and damping adjustment is system from another manufacturer such as Losi, TLR, Traxxas, or associated.

For the time being I will continue to experiment with different springs and shock oils in the ECX aluminum shocks.

If you have any experience swapping out the shocks on your Boost (or other ECX car) please share your experience here (with part numbers!).

Dimensions of stock ECX Boost shocks:
REAR: Total length - 95mm center-to-center; shaft - 3mm diameter, 51mm long

FRONT: Total length - 85mm center-to-center; shaft- 3mm diameter, 42.25mm long

Piston diameter: 9.9mm; 2mm thick

SPRINGS:
REAR: 14mm ID, 74mm (2.9") long
FRONT: 14mm ID, 58mm (2.28") long
Stock spring rate: not provided by ECX (based on my experiments with Associated springs, I guess around 2ft/in rate for the stock springs)​
 
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I don't have a boost, and ECX's page sadly doesn't list specs. Could you post up some measurements for what you are looking for? Length and diameter of the shaft, body, springs and total shock length would all be useful. As well as anything else you can think of. That way myself as well as other can help look.
 
Assuming that your front shafts are indeed 42mm (not 42.25mm, and even if it is it wouldn't matter much), then there appear to be many direct replacements. Brands like HPI and Kyosho have some. Sadly I have not found any yet that would be an "upgrade". Are you ultimately looking to piece together an upgraded shock? Or replace altogether with an upgraded shock?
 
I used a digital vernier caliper and it showed 42.25. I measured three times. ;)

Part of the problem with locating a suitable replacement is the lack of published dimensional information. I can't look up on line and the hang-tags at the LHS don't show anything. So it would require a lot of legwork on the part of the sales clerk for a US$3.00 sale. Why do you think the HPI and Kyosho shafts would not be an "upgrade?" Provided they have clearance between the E-clips I can fit the RPM pistons and that would be all the "upgrade" i need.

And yes, that is the ultimate goal: an upgraded ECX shock. It's a hassle but that's where the fun is. However, I'm also thinking about just swapping out the ECX shock for a different brand. I've read about Traxxas "big bore" shocks being used but that's just not any help without a part number. The RPM pistons will also fit the Traxxas big bore shocks so... there's that.
 
By upgrade I mean the benefit of a better material (like titanium), or a larger diameter shaft....things like that. .25mm is nothing to worry about with the shock shaft, all you lose is a small amount of travel.

If you feel like trying something different, these come off an HPI Savage XS (as well as other vehicles).

upload_2016-3-1_14-18-16.png

There are two part numbers there. One for fronts, one for backs. They should fit your application. Annoyingly though they are fairly expensive.
 
Those look interesting. I note the assembly of the piston and shaft utilizes threads and locknut instead of E-clips. (I just looked it up online.) They ARE a bit pricey, so that's a bummer.
 
I just upgraded my shocks to the ECX aluminum shocks on my amp, and put 37.5 weight shock oil in them, and screwed everything down as far as it will go, and they are still too soft. I read on one of the forums that losing springs will work, bust, I don't know which ones I will like.
 
First, please understand that I'm not trying to be a jerk. I have years of experience working with moto and MTB suspension plus a rather intensive year tuning the suspension on my Boost, AMP, and TLR 22 3.0 (and a significant collection of springs from various manufacturers).

Unless you've added a brick to your AMP, its suspension is not "too soft." The AMP (and the Boost and Circuit) all have front ends that are too light and thus do not sag properly. If anything, the springs on the front are too stiff (too high a spring rate). The rear end will sag a proper amount and you can adjust the rear ride height by adjusting the spring pre-load with the threaded collars.

To function properly, the suspension system (spring and hydraulic damper unit) must sag or settle a little under the weight of the car. This sag allows the wheels to drop into depressions in ground/track/road and maintain traction without unsettling the car too much. In a turn, the car can roll (to varying degrees) to the outside, compressing the suspension on that side, while the inside unloads (extends) but the tire maintains contact with the ground. These are desirable handling traits that can be tuned to improve handling in various running situations (race, bashing, dirt, road, whatever).

When you add pre-load to the springs on a shock, the compression rate remains constant and what you are doing is adjusting the ride height. Increase the pre-load and you raise the car off the ground. Decrease the pre-load and you lower the car closer to the ground.

Oil viscosity alters the responsiveness of the shock (damps the effect of bumps, or shocks to the car), it has nothing to do with the "stiffness" of the shock. For example, a thin oil will allow the shock to respond quickly to small bumps but will allow the car to bottom out on landing from a jump. A thick oil will will respond slowly to small bumps (causing the car to bounce around) but will better absorb the force of landing a jump.

For general driving of your AMP I'd recommend no spring pre-load on the front and maybe half an inch pre-load on the rear. Keep the 37.7 weight oil in the rear (because of the weight in the rear of the car) and go with a 32.5 weight in the front. Lowering the front ride height: increases steering traction (car may over steer), decreases rear-end traction (the rear end is more likely to slide out in a turn). Lowering the rear ride height: decreases steering traction (car may under steer), increases rear-end traction.

Finally, if you DO want to try different springs, i recommend giving these Associated springs a try: Truck front #1580 and truck/buggy rear #1582. The will be a hair narrow and you may have to gently twist them onto the spring cups and pre-load collars on the ECX shocks. They're US$13 for a set of four different springs so you can experiment with the different rates to see how they affect your car's handling.

Have fun!
 
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Thank you for the tip, I will look into it. As it stands, my truck is flipping over when it hits a jump, and there are scrapes on the front skid plate. I am thinking that it was bottoming out on the front
 
First, please understand that I'm not trying to be a jerk. I have years of experience working with moto and MTB suspension plus a rather intensive year tuning the suspension on my Boost, AMP, and TLR 22 3.0 (and a significant collection of springs from various manufacturers).

Unless you've added a brick to your AMP, its suspension is not "too soft." The AMP (and the Boost and Circuit) all have front ends that are too light and thus do not sag properly. If anything, the springs on the front are too stiff (too high a spring rate). The rear end will sag a proper amount and you can adjust the rear ride height by adjusting the spring pre-load with the threaded collars.

To function properly, the suspension system (spring and hydraulic damper unit) must sag or settle a little under the weight of the car. This sag allows the wheels to drop into depressions in ground/track/road and maintain traction without unsettling the car too much. In a turn, the car can roll (to varying degrees) to the outside, compressing the suspension on that side, while the inside unloads (extends) but the tire maintains contact with the ground. These are desirable handling traits that can be tuned to improve handling in various running situations (race, bashing, dirt, road, whatever).

When you add pre-load to the springs on a shock, the compression rate remains constant and what you are doing is adjusting the ride height. Increase the pre-load and you raise the car off the ground. Decrease the pre-load and you lower the car closer to the ground.

Oil viscosity alters the responsiveness of the shock (damps the effect of bumps, or shocks to the car), it has nothing to do with the "stiffness" of the shock. For example, a thin oil will allow the shock to respond quickly to small bumps but will allow the car to bottom out on landing from a jump. A thick oil will will respond slowly to small bumps (causing the car to bounce around) but will better absorb the force of landing a jump.

For general driving of your AMP I'd recommend no spring pre-load on the front and maybe half an inch pre-load on the rear. Keep the 37.7 weight oil in the rear (because of the weight in the rear of the car) and go with a 32.5 weight in the front. Lowering the front ride height: increases steering traction (car may over steer), decreases rear-end traction (the rear end is more likely to slide out in a turn). Lowering the rear ride height: decreases steering traction (car may under steer), increases rear-end traction.

Finally, if you DO want to try different springs, i recommend giving these Associated springs a try: Truck front #1580 and truck/buggy rear #1582. The will be a hair narrow and you may have to gently twist them onto the spring cups and pre-load collars on the ECX shocks. They're US$13 for a set of four different springs so you can experiment with the different rates to see how they affect your car's handling.

Have fun!
I was thinking about what you posted here, and had a few questions. First, I am not running the stock motor, I have the tazer combo ESC/motor, the 3000kv, and it is quite a bit heavier than the 20t motor that came with the kit, would you still recommend the 37.7 shock oil? Second, ride height would correct my problem of my truck doing front flips, correct?
 
Try this: put the battery in your car so it's at "driving weight." Pick the car up about 8 inches off the floor (or table/worksurface) and drop it. What happens?

If the rear bottoms out, repeat the test but from a height of about 6 inches. Does the rear sill bottom out? Consider giving 40wt (approx 500cSt) oil a try.

About you flips: how exactly is the car flipping? It's the rear flipping over the front? Am I understanding that correctly? If this is the case add some pre-load to the front springs. What's happening is that the front is absorbing the impact of the ramp and the rear comes along and bottoms out immediately and the force kicks the rear end up and causes the car to endo.

No matter what you do, make only one change at a time.

My suggestion: do the drop test I mentioned. Make not of how the car behaves. THEN add some pre-load to the front and test drive. Maybe add some more preload.

In racing we typically run heavier oil in the front (and a lowered ride height) as the heavier oil slows the response of the shocks and helps keep the front of the car up and flying more or less level.

Let me know how it goes.
 
Thank you for giving me the advice. I went to my lhs, and the owner helped me with getting the ride height up in the rear, and I was planning on using lighter weight oil in the front. I am going to test the adjustments in the rear of the vehicle first, to see how I like it.
 
My front end is still too high. I can't turn at high speeds very well.
 
Yeah, my AMP didn't turn very well under power either. Just to confirm, you have NO pre-load on the front springs, correct?

As for turning, different tires can help improve that. In addition to suspension, tires play an important role in your car's handling. The primary issue is the rubber compound in the stock tires: it's hard and long wearing. But for improved steering you'll want a set of new tires (and wheels) with a softer, grippier rubber compound. Look for tires from Pro-Line or JConcepts. There are a couple of other brands that I forget. Stop by your LHS and see what they have. It would be a good idea to take your AMP with you.
 
@Bgrunst1 I never did address your question about using Losi springs.

Losi springs will not fit the ECX shocks: their inner diameter is too big to fit securely. They will pop off the lower spring cups under load. However, they WILL fit Traxxas Big bore shocks (and quite possible other brands). I run the Traxxas Big Bores on my Boost (#2660, #2661) and on my AMP/Circuit (#2661, #2662 also #5862 set with springs) and they are a good fit.

Here's the list of Losi springs:
FRONT BUGGY SPRINGS
Losi Part #
5128 2" Spring 2.5 Rate (Red)
5129 2" Spring 2.9 Rate (Orange)
5130 2" Spring 3.2 Rate (Silver)
5132 2" Spring 3.5 Rate (Green)
5134 2" Spring 3.8 Rate (Blue)

REAR BUGGY & TRUCK (front and rear) SPRINGS
Losi Part #
5144 2.75" Spring 1.4 rate (Gold)
5146 2.75" Spring 1.6 Rate (gray)
5147 2.75" Spring 1.8 Rate (White)
5148 2.75" Spring 2.0 Rate (Yellow)
5150 2.5" Spring 2.3 Rate (Pink)
5152 2.5" Spring 2.6 Rate (Red)
5154 2.5" Spring 2.9 Rate (Orange)
5156 2.5" Spring 3.4 Rate (Silver)
5158 2.5" Spring 3.7 Rate (Green)
5160 2.5" Spring 4.1 Rate (Blue)

Unfortunately these are out of production so you may have difficulty finding them at your LHS. Check around. Then maybe hit Ebay.
 
Thank you. Also, you are correct, I have no pre load on my front shocks. I did pick up some 32.5wt oil for the front shocks, and I will see how that goes.
 

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