Back end slides out when turning, even when not on throttle

[Hector_Fisher]

Help me understand what my RC is trying to tell me. This isn't for an Arrma, but i think the principles should apply regardless of the make. Edit: this is for a street basher.

The back end wants to slide out when i turn, even when coasting (not braking, not on throttle). It might be awesome if this were a drift car, but it's not. It's the point where anything over 20-30mph can get super sketchy since, if I have to make a quick correction or avoid something (like a parked car...), the back can suddenly shift it's weight and the rear end will go sliding out -- then it's bye bye control.

I don't have a racing background in RC or anything, so i don't have an extensive experience with how suspension changes affect handling. It's a SWB car, so is it just part of the game? Should i start by replacing parts to get rid of some of the slop in the suspension (it's an older truck)? One thing I think I need to do is rebuild/refill the front shocks. I was having "death wobble issues" at speed until I rebuilt and refilled the rear shocks -- no more death wobbles. I'm thinking the fronts might need a rebuild/refill too? Just spit balling ideas here.

 

[Garcbomber]

More rear weight bias and/or grip may be required, oversteer can be much worse than understeer.

You probably need more spring rate too if the front end is diving down coasting/deceleration into the turns and lifting inside tires and the rear end. All depends on the surface and center of gravity.

Got a picture of the setup, corner weight scales are reasonably priced investments for even begginer racers

Document any setup change and start with only one revision to a component at a time until you become familiar with tuning. There are probably a lot of great visual tuning videos from pro buggy racers on YouTube

 

[Hector_Fisher]

More rear weight bias and/or grip may be required, oversteer can be much worse than understeer.

You probably need more spring rate too if the front end is diving down coasting/deceleration into the turns and lifting inside tires and the rear end. All depends on the surface and center of gravity.

Got a picture of the setup, corner weight scales are reasonably priced investments for even begginer racers

Document any setup change and start with only one revision to a component at a time until you become familiar with tuning. There are probably a lot of great visual tuning videos from pro buggy racers on YouTube

Just to clarify, this is for a street basher, I modified the thread description to reflect. I was meaning to say that I think some principles of tuning for racing could definitely help here. Most of my experience is just bashing, so however the truck came setup from the factory was good enough for me. Never needed to change settings so far.

To your points: are you saying essentially that a softer setup would contribute to more "looseness"? For example, if the front shocks have lost some fluid over time and aren't working as well (and maybe the springs have lost some of their sprung), could that be contributing to throwing the weight around rather than cornering flat?

 

[KnowAir]

4 or 2wd? You could try moving some weight to the rear if feasible. Stiffening the front, softening the rear. Also, ride height. Raise the front and or lower the rear.. one thing at a time though, so you know what did or didn't work and what effect each change makes..

 

[joshludden]

Which tires are you using? A grippier compound could be a cheap easy fix

 

[Garcbomber]

Just to clarify, this is for a street basher, I modified the thread description to reflect. I was meaning to say that I think some principles of tuning for racing could definitely help here. Most of my experience is just bashing, so however the truck came setup from the factory was good enough for me. Never needed to change settings so far.

To your points: are you saying essentially that a softer setup would contribute to more "looseness"? For example, if the front shocks have lost some fluid over time and aren't working as well (and maybe the springs have lost some of their sprung), could that be contributing to throwing the weight around rather than cornering flat?

It doesn’t matter what the application is, but as a baseline you will absolutely need to confirm diff and shock fluids are filled properly and functioning as intended. Those are all preventative maintenance expectations before advanced tuning from original equipment.

 

[KnowAir]

As an uneducated guess..sounds like the front is diving, thereby allowing the rear to unload and loose traction..too much weight transfer.

 

[3x9rtse]

A bad bearing in one of the rear hubs would cause this , if sticky , when you go to turn , it is like pulling the e brake in a car and the back will spin out .

 

[jkflow]

If this occurs without power input, you can eliminate the diffs from that equation, not saying that they are wrong but would only come into play under power.
No power butt breaking out can only be traction, weight distribution or suspension.

Are you sure there is no power or using some gyro, and you are just not aware?

 

[SrC]

Help me understand what my RC is trying to tell me. This isn't for an Arrma, but i think the principles should apply regardless of the make. Edit: this is for a street basher.

The back end wants to slide out when i turn, even when coasting (not braking, not on throttle). It might be awesome if this were a drift car, but it's not. It's the point where anything over 20-30mph can get super sketchy since, if I have to make a quick correction or avoid something (like a parked car...), the back can suddenly shift it's weight and the rear end will go sliding out -- then it's bye bye control.

I don't have a racing background in RC or anything, so i don't have an extensive experience with how suspension changes affect handling. It's a SWB car, so is it just part of the game? Should i start by replacing parts to get rid of some of the slop in the suspension (it's an older truck)? One thing I think I need to do is rebuild/refill the front shocks. I was having "death wobble issues" at speed until I rebuilt and refilled the rear shocks -- no more death wobbles. I'm thinking the fronts might need a rebuild/refill too? Just spit balling ideas here.

Your issue is dependent on many factors. I would start with making sure ride height is lower. The front and rear shocks should be the same "Pack wise".
A loose font/rear end /slop is not the main issue. But yeah its a given to reduce as much slop as possible.
The diff's truly matters the most. I can get into more detail, but as you admitted, there is a learning curve yet to gain. Baby steps.
Roll Center and tire scrub angles matter. The chassis may not be balanced well enough. A simple thing like Tires matter also. I would soften the Rear end shocks, i.e. softer springs and/ or thinner shock oil, to gain traction at the rear, as a start. Add some negative camber at the rear maybe
Always rebuild the 4 shocks, so they are all matched first. So you have a baseline. Then dial in the front or rear shocks as necessary. Driving style matters also. But if she wants to spin out all day long at the rear, yeah there is the suspension to dial in. Is the rig in question over powered? Dropping the Punch down really helps.
I could go on and on. Start out with the easy and obvious adjustments first. Alignment must be spot on to begin with.
Good luck.

 

[Senton_Prime]

What's your rear tires look like and how soft are the front shocks, how much preload is on the fronts I should say!? Also what size fluid is in the rear diff, might not matter since it's under braking!?

 

[Hector_Fisher]

4 or 2wd? You could try moving some weight to the rear if feasible. Stiffening the front, softening the rear. Also, ride height. Raise the front and or lower the rear.. one thing at a time though, so you know what did or didn't work and what effect each change makes..

4wd. I don't think it has to do with drivetrain wise though. Even just just coasting, the car just seems unstable if you give it any steering. The back ends just wants to kick out way too easily.

As an uneducated guess..sounds like the front is diving, thereby allowing the rear to unload and loose traction..too much weight transfer.

Agreed, improper weight transfer is sounding like the culprit here. But from what i understand there are several ways for that to happen.

It doesn’t matter what the application is, but as a baseline you will absolutely need to confirm diff and shock fluids are filled properly and functioning as intended. Those are all preventative maintenance expectations before advanced tuning from original equipment.

Thanks, I think you're right. My first thing now will be to rebuild front shocks. I know rears are good, and all diff were serviced not long ago. I'd love to have the depth of experience that some of you do to be able to see a symptom, know the underlying cause, and understand how it affects the vehicle during driving. From a conceptual standpoint, such as the purpose of sway bars, I understand it all. But I don't have enough driving experience to have a "feel" for how an installed sway bar (or thicker/thinner one) would really affect driving experience.

A bad bearing in one of the rear hubs would cause this , if sticky , when you go to turn , it is like pulling the e brake in a car and the back will spin out .

The car rolls very smoothly (and for a long time too). Otherwise, agreed I might be suspecting a bad bearing as well.

If this occurs without power input, you can eliminate the diffs from that equation, not saying that they are wrong but would only come into play under power.
No power butt breaking out can only be traction, weight distribution or suspension.

Are you sure there is no power or using some gyro, and you are just not aware?

Unsure about the gyro. If there ever is a gyro I'm aware of, i turn it off. I prefer the "bare" experience. It's a flysky GT5 with fs-bs6 rx. Don't seem to have these same issues with the other RC's i have tied to the GT5, and aside from EPA, i've never messed with default settings on any of them. I'll peruse through the setting just to be sure.

I'm leaning towards suspension issues and perhaps and unbalanced setup. I think the suspension might be too soft for street bashing, and i'm just throwing the car's weight around too much. But that's just a hunch.

 

[KnowAir]

Trial and error beats studying IMO. That's how my brain works anyway Make sure everything is up to snuff and start tunin'
Off road designed rigs need alot of stiffening for street duties..

 

[3x9rtse]

Rear toe adjustment ? Locked diff / thick rear diff fluid ? To much steering / oversteer ?

 

[SrC]

4wd. I don't think it has to do with drivetrain wise though. Even just just coasting, the car just seems unstable if you give it any steering. The back ends just wants to kick out way too easily.

Agreed, improper weight transfer is sounding like the culprit here. But from what i understand there are several ways for that to happen.

Thanks, I think you're right. My first thing now will be to rebuild front shocks. I know rears are good, and all diff were serviced not long ago. I'd love to have the depth of experience that some of you do to be able to see a symptom, know the underlying cause, and understand how it affects the vehicle during driving. From a conceptual standpoint, such as the purpose of sway bars, I understand it all. But I don't have enough driving experience to have a "feel" for how an installed sway bar (or thicker/thinner one) would really affect driving experience.

The car rolls very smoothly (and for a long time too). Otherwise, agreed I might be suspecting a bad bearing as well.

Unsure about the gyro. If there ever is a gyro I'm aware of, i turn it off. I prefer the "bare" experience. It's a flysky GT5 with fs-bs6 rx. Don't seem to have these same issues with the other RC's i have tied to the GT5, and aside from EPA, i've never messed with default settings on any of them. I'll peruse through the setting just to be sure.

I'm leaning towards suspension issues and perhaps and unbalanced setup. I think the suspension might be too soft for street bashing, and i'm just throwing the car's weight around too much. But that's just a hunch.

Forget about using a gyro for now. A rig should be setup without one first IMHO. Or it just becomes a crutch, and will mask other issues. Complicating an easier fix short term.
Also, A tight rear diff will still let the rear slide out even OFF throttle while steering.. Especially if the shocks are not right. Focus on the frint when the rar is too loose even though traction seems ok with the rear tires.
Some ideas.

Does your rig have P-balls or a C-Hub up front.
Are you a baller???

 

[Hector_Fisher]

I'm starting to realize maybe I should have titled this thread "I don't know as much as I thought I knew about suspension"

Some things about the car off the bat based on the questions asked above:
-C-hubs up front
-unsure about actual thickness since I rebuilt a little bit ago (need to write this stuff down!), but front diff is thicker than rear (guestimating maybe 20k front 10k rear?)
-this truck has very minimal adjustability (no rear toe adjustment, no F/R caster adjustment, only a few shock spring inserts to adjust preload).
-Default shock setup is same spring all around with some preload in the front and slightly more in the rear.
-Tires are still relatively new, even wear throughout. Gold Hoons 85mm.

I'm starting to learn more about suspension tuning, thanks to you folks. This is what i've learned so far.
Overarching principles for suspension tuning:
-suspension tuning is a process of trial and error, time behind the wheels is needed to feel for changes you make
-make changes incrementally, taking note of difference and how they react on the truck

Consider the following when making changes:
-validate that everything suspension-wise is in working order and repair as necessary (filled shocks, tightened fasteners, etc).
-validate front diff is slightly thicker than rear, center diff at least as thick as front if not more.
-check weight balance of car Front to Rear and side to side. A neutrally balanced car will handle more neutrally. Consider ballasting if overly unbalanced.
-experiment with shock preload (how to adjust ride height without adjusting preload?). Change front to have more pre-load than rear.
-uniform shock oils? Soften up the rear end with thinner oils than the front?
-expecting the problem to be at the rear end since it's causing the slide out. Focus on making additional adjustments in the rear end first.
-validate that there's no conflicting steering input from a gyro (if present).

Thanks again, everyone for the input. This is really a great forum!

I've got a good list to start tweaking/trying things, let me know if I've missed anything.

 

[SrC]

^^^Its all trial and error ultimately. Each rig is different. Do Only one change at a time, evaluate and see if you are getting closer or further from your objective. If its a no go , undue that last change and start over with a different change. Different and Softer springs at the rear may utimately help. Thinner fluid, the same.
You said you have more preload in the rear. Try removing preload there or conversely add more preload at the front shocks to offset the rears. Then evaluate what happens. If removing preload at the rear shows a slight improvement, then you may need softer springs at some point to make her hook up even better.

 

[Surchaufeur]

Generally means more traction in the front. You have to tune the car to lose front traction and make the rear gain traction. You achieve that bybmessing with spring rates, shock oil and pistons, diff fluid, camber and caster, and roll point(the turnbuckle holes on the shock tower)

 

[PrerunninF150]

Pictures of the car might make it a lot easier for us to get an idea of your setup and give better suggestions.