Internal Shock Springs?

[Ckrobin]

I am trying to get my cars to a lower ride height and still have droop. I would rather not cut my springs. I am thinking of using a spring like out of a pen instead of a solid limiter.

Has anyone tried this and what springs did you use? I can get an assortment of pen springs with different lengths and spring weights for $15. Not only would that be cheaper than buying an assortment of external springs it would take up way less storage space to carry with me to the track or bash park.

What other options do I have to lower the ride height and still have droop?

 

[Arise0185]

Softer spring rate would achieve a lower ride height, but maintain full range of motion.

 

[Dan B.]

Why not use a $0.07 internal limiter? Keep the spring rates however you want them.

 

[SrC]

A Solid Internal limiter is the best way to get more precise Shock "droop". Remember that MORE shock "droop" means the chassis is lowered "more".. The Internal Spring thing is usually done on Crawler models. And for different reasons.

 

[Arise0185]

I think OP needs to clarify what they mean by "still have droop."

In my mind, droop is defined as the amount of downward travel that is available, relative to where the shocks sit at ride height.

 

[Ckrobin]

I think OP needs to clarify what they mean by "still have droop."

In my mind, droop is defined as the amount of downward travel that is available, relative to where the shocks sit at ride height.

Correct, which is why lowering with solid internal limiters sounds like a terrible idea. That would leave you with zero droop and terribly unbalance the car if you hit a pothole or other dip in the road. I understand its what the pros do, that doesn't mean its right. Can someone explain from a physics standpoint as to why having zero droop would be a good thing? Ideally I want my starting ride height to be 50% of my total suspension travel while having a flat lower control arm and adjust from there if needed at the track. I know I wont be able to achieve exactly that but I want to try and get close.

This is from So Dialed's website about Droop

"Droop measures how far down the car’s suspension arms are able to travel, or specifically the difference between the car’s natural ride height and its maximum ride height when the wheels just lose contact with the ground.

There are, however, a variety of ways that people actually measure droop. Common methods are (all taken with the car's wheels off the ground):

• Distance between the bottom of the chassis and the bottom of the wheel nut (shown in the diagram above)
• Distance between the bottom of the chassis and the bottom of the hub (shown in diagram below)
• Distance between the center of the shock’s two mounting screws (this is more accurately described as "shock length", but in some types of racing it is called droop and is a good substitute for the other measures.

Droop is sometimes changed via internal shock limiters (which control stroke) or on some cars via specific downstop adjustments that limit how far down the arms can travel..

Droop allows (or limits) weight transfer from one side of the car to the other, or the front to the back.

Please note, changes to the car’s ride height will also change its droop if no other adjustments are made.

Downstop is a setting that controls how far down the suspension arms can travel. It is not the same thing as droop, although many racers use the two terms interchangeably."

I feel like the car could use stiffer springs already so a softer spring would not give me the effect I want. Plus Like I said if I could do this with "pen Springs" they would travel better for tuning.

 

[Arise0185]

Sounds like you've thought about this a great deal.

I would think that the "perfect" way to adjust ride height without adjusting stroke length, spring rate, etc. would be to change where the shocks mount to the car. Specifically, if you have different mounting points for the shock upper eye on your shock towers. If you move to a shock mounting position that is 3mm higher, doesn't that reduce your ride height by 3mm, but maintain the same stroke, sag (how much the shocks are compressed at ride height), and available droop?

I'm not familiar with suspension setup on cars, but am fairly competent with motorcycle and mountain bike suspension. In those worlds, people rarely talk about "ride height," and instead use "sag" as a tuning parameter. Basically, how much does the shock compress when the vehicle + rider is at rest. If you can't achieve the correct sag, then you change the spring rate (either by adding/removing air from an air shock, or physically swapping out the coil).

I could see why actual ride height (distance from bottom of chassis to the ground) would be more important in cars from a CG and aerodynamics perspective.

 

[Ckrobin]

Sounds like you've thought about this a great deal.

I would think that the "perfect" way to adjust ride height without adjusting stroke length, spring rate, etc. would be to change where the shocks mount to the car. Specifically, if you have different mounting points for the shock upper eye on your shock towers. If you move to a shock mounting position that is 3mm higher, doesn't that reduce your ride height by 3mm, but maintain the same stroke, sag (how much the shocks are compressed at ride height), and available droop?

I'm not familiar with suspension setup on cars, but am fairly competent with motorcycle and mountain bike suspension. In those worlds, people rarely talk about "ride height," and instead use "sag" as a tuning parameter. Basically, how much does the shock compress when the vehicle + rider is at rest. If you can't achieve the correct sag, then you change the spring rate (either by adding/removing air from an air shock, or physically swapping out the coil).

I could see why actual ride height (distance from bottom of chassis to the ground) would be more important in cars from a CG and aerodynamics perspective.

That is one option however I have several cars and some run in classes that that wouldn't be allowed. my spring idea may not be allowed.

 

[Dan B.]

That is one option however I have several cars and some run in classes that that wouldn't be allowed. my spring idea may not be allowed.

So the car will be used in multiple ways? If class racing, then you may be correct in thinking it isn’t allowed. But who is going to open up your shocks to ever look for internal springs?
Solid internal limiters are not a terrible idea at all if your suspension is properly set up. It isn’t like you said, where if you hit a pothole or something it upsets the chassis. That wouldn’t really happen unless your spring rates were ridiculously soft. Bear in mind that internal limiters are used to limit extension. External limiters are used to limit compression. If you get too aggressive with those then yes, it could upset the chassis if your spring rates were too soft. That’s why I use more pliable external limiters like these:

They’re much better than the old method of using fuel tubing and they don’t split.
Using springs internally would not work well at all for my intended goal, the need to limit extension. Period. Mic drop. I would not want a spring compressing before coming into play to limit extension precisely. If they did, then they would do so when coil bound (completely compressed) so it would kind of defeat the very purpose of using internal springs to limit shock shaft extension. Internal springs have a purpose in certain applications, but it’s not to limit extension. It’s to stiffen compression like any other external spring.
In my cars that I use internal limiters with, they are used with really firm setups and are primarily intended to take a huge amount of force off the droop screws so they can be used just over the range of a couple of mm’s to balance the ride height and not be used for complete height adjustment fighting all of the compression forces of some super stiff titanium springs for 20-30mm or more of lowering. That’s a ton of force that the lower a-arms, droop screws, and chassis tabs no longer have to contend with to lower the car.
If you finish the experiment I’d really like to hear your thoughts and observations. It’s an interesting approach.

 

[Ckrobin]

I agree 100% with using soft external limiters for the same reason. searching the house for two matching pens is turning out to be a real challenge however...

 

[SrC]

Sounds like you've thought about this a great deal.

I would think that the "perfect" way to adjust ride height without adjusting stroke length, spring rate, etc. would be to change where the shocks mount to the car. Specifically, if you have different mounting points for the shock upper eye on your shock towers. If you move to a shock mounting position that is 3mm higher, doesn't that reduce your ride height by 3mm, but maintain the same stroke, sag (how much the shocks are compressed at ride height), and available droop?

I'm not familiar with suspension setup on cars, but am fairly competent with motorcycle and mountain bike suspension. In those worlds, people rarely talk about "ride height," and instead use "sag" as a tuning parameter. Basically, how much does the shock compress when the vehicle + rider is at rest. If you can't achieve the correct sag, then you change the spring rate (either by adding/removing air from an air shock, or physically swapping out the coil).

I could see why actual ride height (distance from bottom of chassis to the ground) would be more important in cars from a CG and aerodynamics perspective.

Absolutely.
"Shock" Droop limits the amount of the Compression stroke. Overall chassis height is a different measurement when all said and done It's inter-related to some extent. Shock "Preload" gets set after the Shock's laydown position and droop is set. Always measure shock droop from the shocks eyelet's with a digital caliper. Best most accurate way. How Race kit builds are done and written on the setup sheets. Basher platforms should always follow the same.
Shock droop and Laying down the shocks is something I almost always do as my first tweaks out the box, or after a few runs. Then evaluate from there.
My droop setting usually ends up with the Arms at level or well below level. (more sag)

 

[Ckrobin]

I have done some testing. I started with the front of my Traxxas 2wd Slash. I took this photo with just one shock built with no oil but with the internal spring.

Even in the phot you should see the chassis trying to twist because the shock with the internal spring is trying to sit lower. I was tempted to continue and use a 65ish shock oil because I am really trying to control body roll. We are not allowed to run sway bars so shock oil is one of the few things I can do, and lower cog.

I decided instead to stick as close to stock as I had which was TLR35. Now when I take it back to the track I only have one change made to get a good comparison of how it drives. Keep in mind this is a small, tight offroad carpet track. With the exception of the jumps it is a fairly smooth track with great grip. Traction roll is a serious issue.

I found every pen we had in the house and was unable to find a matching pair so off to the dollar store for some ink pens. I spent the next several hours with a set of scales testing compression rates and cutting, heating, stretching and testing more till I found what I thought I was looking for. I installed the rebuilt shocks and found I had a 10mm lower ride height.

I did the same thing in the back and installed external shock limiters on the both sets to prevent the chassis from grabbing and scrubbing off speed when I land. This lowered the back by 9mm but raised the front back up 1mm.

The best part is now not only do I have a full 18mm of droop in the front and 14mm in the back. It also feel like it is going to have way less body roll. I might even end up going with a lighter shock oil. Hope to head to the track one day this week and will do some more testing there. Its dark and cold here so going out for a test drive isn't going to happen till tomorrow. It will just be a short run in the yard as one of the reasons I like a carpet track is less cleaning.

These next two photos I should have panned back far enough to get the front bumper. What you miss in these photos is the first one is sitting at rest with me not touching it. In the second one I am lifting the middle of the front bumper with my finger till the tires try to lift off the table.

Anyway, that's what I learned today. Will let you know later in the week how it drives.

 

[Arise0185]

Are you running spec slash?

 

[Ckrobin]

Well I'm not good enough to really "run" any class but yes those are the rules I am trying to follow as I practice my driving and tuning skills.

 

[Dan B.]

Well I'm not good enough to really "run" any class but yes those are the rules I am trying to follow as I practice my driving and tuning skills.

Well one thing that immediately leapt out at me when I saw your pictures was…your stock shocks. Spec Slash allows the use of factory Traxxas shocks if they appeared on a Slash model from the factory. Do yourself a HUGE favor and buy a set of Traxxas GTR shocks. If you want a total transformation (in a positive way) of how your truck handles on a track then this simple swap will blow your mind. They are so much better that the plastic ones, or even the “Big Bore” shocks. They are a must to be competitive in that class, IMO.

 

[Arise0185]

Well I'm not good enough to really "run" any class but yes those are the rules I am trying to follow as I practice my driving and tuning skills.

Nonsense! Get out there and start racing! Well, maybe your local scene is different than mine, but our Spec Slash class is as entry-level as it gets. That's where people learn to drive/race, and the races are often chaotic with people crossing lanes, crashing into each other, etc.

If you're interested, I started a Spec Slash racing thread in the hopes of sparking discussion about this great racing class!

https://www.arrmaforum.com/threads/spec-slash-racing.66194/

*Edit* - I looooove how little you have to clean your cars after running on carpet. My Spec Slash is a dedicated carpet car - I never run it outside or bash with it. Simpler/easier just to have dedicated cars for each purpose.

Well one thing that immediately leapt out at me when I saw your pictures was…your stock shocks. Spec Slash allows the use of factory Traxxas shocks if they appeared on a Slash model from the factory. Do yourself a HUGE favor and buy a set of Traxxas GTR shocks. If you want a total transformation (in a positive way) of how your truck handles on a track then this simple swap will blow your mind. They are so much better that the plastic ones, or even the “Big Bore” shocks. They are a must to be competitive in that class, IMO.

I'm sure every track is different, but the two tracks closest to me do not allow anything but the plastic shocks that come stock on the 2wd brushed version. You can change springs, spacers, and shock oil, but can't even upgrade the caps to aluminum to prevent them from popping off.

 

[Ckrobin]

Here's my problem with running a track. I live in Central Arkansas and we don't have anything to race on here. The closest track is a dirt oval and is over an hour drive each way. That's not too far but its still just a dirt oval. Not my preferred form of racing. And its outdoors. I have thought about going there to race some and if I do they do allow aluminum caps. Haven't had this thing long enough to witness any caps popping off yet so was going to skip that upgrade for weight. I will reconsider that if it is allowed where I end up racing.

There is another track about two hours away in Jonesboro called FORC that I haven't been to but it looks like a great indoor dirt track. They have a stock slash class there but I cant find their rules. I am thinking of going there one day this week to check them out so I can get the rules then.

Finally we have the track that I have been going to but its over 2 hours away in Ft Smith at GS Hobby. This is barely a 10th scale track. Its small and very tight. its a great track for mini B and other small scale racing. And IMO makes a great track for me to practice due to its tightness. Its also carpet so what I am doing to set up for it isn't going to come close to FORC. But I feel like I need to return there at least one more time to get a comparison with the adjustment I just did. It doesn't have a spec slash class racing right now so I am just doing practice sessions.

My final and most challenging issue is I drive for music and other theatrical shows and tour season is from mid Feb to sometime Mid Nov or Dec. This means when its tour season I might get home for a day or two here or there but usually not long enough to go play with RC cars and spend time with my family. I usually take a few cars with me in the truck and on days off I can check out some tracks across the country. Something that is a challenge by itself because not every shopping center wants an 18 wheeler on their parking lot. Then during winter break I can work on all my cars and get them ready for next year. I have been to some pretty killer tracks like Thornhill just outside of Austin, TX. My Typhon buggy is still broke from that trip.

This year I plan to take the slash and a drag car and I cant decide if I want to take one of my nitro cars or one of my Typhons.