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Understeer oversteer

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Understeer oversteer

Old 04-12-2020, 08:57 PM
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Default Understeer oversteer

Is there a priority or an order to tune understeer/oversteer? I think my priorities are off and Im missing something.

1-I think I missed this (the arcs that toe creates from front to rear)
2-ARB stiffness
3-mass distribution
4-dif fluid
5-roll center
6-transient mass control through springs and dampers
7-camber and camber gain
8-end points
9-caster

Ive been really focused on everything but the independent arcs created from front and rear toe and I think this is why each of the lesser priorities havent had as dramatic of an effect as I thought they should.

I believe the arcs need to be correct first and then you can go faster and refine the lesser priorities. By the way its a mmx amx. 1 degree total toe out in the front and 3 degrees of toe in per wheel on the rear. i left dynamic toe at stock thinking i would worry about it later. Its a medium traction asphalt and always oversteers.
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Old 04-12-2020, 10:32 PM
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You should probably have a 6a. Steady state mass control through springs & ARBs. When I make one end of the car stiffer than the other, that stiff end transfers more weight to the outside tire. And the other outside tire doesn't get as much weight transfer. The stiffer end with the most weight transfer doesn't stick as well as the soft end. That's because the amount of increased traction due to more weight is not linear, thus the increase in traction on the outside tire does not increase as much as the traction you lose on the inside tire. Think of it as the law of diminishing returns.

So if I make the rear of the car stiffer than the front (stiffer springs and or ARB's), the rear of the car will lose traction and the front of the car will gain traction. In my opinion this is the first thing I change in order to balance a car. Everything else is secondary or tertiary.

As a side note, when you increase chassis flex, it makes this tuning tool less effective. That's why I like a stiff chassis, it allows me to control the weight transfer using springs and ARB's. And as a side note, the weight transfer is a function of the weight of the car, the center of gravity, the cornering speed and the radius of the corner. I can't control how much weight is transferred, it's just physics. But I can control how much of that total weight transfer is shared between the front and rear of the car.
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Old 04-13-2020, 05:25 AM
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There's no fixed order. It depends on:
  • Where is the understeer or oversteer
  • What's the overall grip level
  • What's the balance like in the other sections
  • Where you are already on settings
it comes with experience I'm afraid

There are some good videos on YouTube from Tonisport, really worth watching as they help break it down https://www.youtube.com/channel/UCZt...nWs_YLGysfDDuQ
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Old 04-13-2020, 08:46 PM
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Thank Glenn. That’s good info. i used rc crew chief and it does a good job of visualizing the diminishing return.

Truth be told Im correcting oversteer for the entire entry, mid, and exit on throttle for every corner radius. I can soften it with all of the stuff I listed but as traction comes up I have to hunt for more softness just so I can keep up with the corrections.

and thank you dale. Yea, its a process and but if my head leads then my tail should follow. Ill check out the videos.

I can calculate slip angle from wheel base and so on. Has anyone worked out some on track logic to tuning front and rear toe? Maybe even the toe gain on the rear for active toe.

I think I found a method to start tuning front toe other than just setting static toe to what someone else has used. You want toe out gain as steering angle increases and the shims on the servo help you add more.

does the rear need toe out gain in a left turn on the right rear or is it the opposite?
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Old 04-13-2020, 10:12 PM
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Whenever I lose rear traction, I put in softer springs in the rear, if that's not enough, I disconnect the ARB, and still not enough, I stiffen the heck out of the front. But one other trick is to treat the rear tires with traction compound and not the front.
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Old 04-14-2020, 08:44 PM
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Ive gone full soft on the rear spring and damping. No arb in the rear and went up one arb in the front. I ran the front stiffness up to 125gf/mm and still have oversteer. I certainly show changes in straight line stability and could soften the oversteer to some extent.

I have another chassis that is fairly similar and its sitting firmly in the middle of the tuning curve. I dont have to make anymore changes.

By process of elimination and being able to feel a good setup versus bad I’m going to test some toe settings. I’ll report back.

Interestingly enough. This chassis of mine that works well (aluminum chassis). I built an identical car in 17.5 on carbon. It over steered. I tuned everything but toe and it got close to the aluminum but it seemed like it was more susceptible to changes in traction and needed a little tuning as each race day progressed to keep up with traction. Nothing big but I had to predict the mild changes from heat to heat. I removed the carbon chassis and put the aluminum on and it locked in like the good chassis. If i played with the setup a little it didnt make allot of difference. It seems like for the club track I run an aluminum chassis creates a very large tuning window.
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Old 11-15-2020, 03:22 AM
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Originally Posted by glennhl View Post
Whenever I lose rear traction, I put in softer springs in the rear, if that's not enough, I disconnect the ARB, and still not enough, I stiffen the heck out of the front. But one other trick is to treat the rear tires with traction compound and not the front.
You want harder springs for more rear grip. You are forcing the tyre to work harder and increasing rear grip.

Using a softer spring works in high traction conditions by freeing the car up.
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Old 11-15-2020, 10:01 AM
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From the Hudy onroad Setup Book:
Stiffer rear springs
Car will have less rear grip.
More steering, especially on power.

EDIT: And to explain why, the more you load the outside rear tire then the less you load the inside rear tire. Overall rear traction is based on both rear tires. Due to the characteristics of the tires, you lose more traction on the inside tire than you actually gain on the outside tire so as a pair of tires you lose overall traction.

From Nasaspeed: "Traction increases as the vertical load on the tire increases, but it is important to understand that the relationship between vertical load and traction is not linear. Being nonlinear means that if the load on the tire is increased, the traction also increases, but it does not increase as much as the load.
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Last edited by glennhl; 11-15-2020 at 10:52 AM.
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Old 11-15-2020, 12:08 PM
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Yeh I donít think that hudy advice is great really. Get the Ryan Maker book or watch the tonisport videos. Or the T4 group on Facebook Hagberg recommends trying harder rear springs amongst other changes.
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Old 11-15-2020, 12:37 PM
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Originally Posted by glennhl View Post
From the Hudy onroad Setup Book:
Stiffer rear springs
Car will have less rear grip.
More steering, especially on power.
I've found the exact opposite to be true. The hudy book is a bit lacking. Try the RCMaker one.
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Old 11-15-2020, 12:58 PM
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Originally Posted by ShaunMac View Post
I've found the exact opposite to be true. The hudy book is a bit lacking. Try the RCMaker one.
I'd be very surprised if the Ryan Maker book doesn't say the say thing.

EDIT: Sorry I can't find any excerpts from Ryan's book, I really need to buy it! From other sources on the net comes the following:
Springs – probably the quickest way to get a big change in handling. Stiffer springs give less feeling of grip but more responsiveness.
And from RCMart, there the common table that shows stiffer rear springs creates more oversteer: https://blog.rcmart.com/rc-basic-rc-...ngs-explained/

Also, I have found that an RC car will respond the same way as a full size car. Here's a typical chart for a full size car to correct understeer and oversteer. Note it says to soften the springs on the end that is not gripping and stiffen the end that is gripping too much. http://www.morpca.org/drivers-educat...eer-oversteer/

However, if it works for you, that's what you need to keep doing. I've always done the opposite. If I have a loose car (like my VTA car) I stiffen the front springs and soften the rear. If I still need more rear grip I disconnect the rear bar. I've been doing this for years and it always works. Of course, the springs are my second tuning option, at first I'll increase the camber on the end that needs more traction. Good luck and thanks for your input.

Last edited by glennhl; 11-15-2020 at 01:13 PM.
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Old 11-15-2020, 02:13 PM
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Ryan Maker book says ďharder springs are generally used more in low traction conditions, to generate grip from the tyres and provide aggression a car often lacks in low tractionĒ

100 percent what Iíve experienced.

to the original poster grab the RC Maker book itís great to refer to when you have an issue.
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Old 11-15-2020, 02:18 PM
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Stiffer springs will increase traction on that end of the car as a static measurement. However, stiffer springs also hinder weight transfer, this will reduce traction in the corner, unless you compensate by lowering the roll centers.

As a quick adjustment, make the opposite end of the car stiffer for more traction. If my car is over steering in the corner, I make the front end stiffer, thus limiting weight transfer to the front under breaking going into the corner and getting the weight back to the rear in the corner to allow the weight to roll the car.

The problem sometimes something is off. Letís say your droop isnít enough and a soft spring allows the inside tire to lift. Then a stiffer spring will yield more traction in the corner.

Anyway, that has been my experience.
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Old 11-15-2020, 03:27 PM
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Originally Posted by BKUK View Post
Ryan Maker book says ďharder springs are generally used more in low traction conditions, to generate grip from the tyres and provide aggression a car often lacks in low tractionĒ

100 percent what Iíve experienced.

to the original poster grab the RC Maker book itís great to refer to when you have an issue.
Is there a table on what to do if your car pushes or is loose?
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Old 11-15-2020, 08:44 PM
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iíve found something that i can remember and always seems to work.

softer rear=understeer (more traction)
I start by getting as much rear traction as I can get.
stiffer rear oversteer (the car rotates and has less rear traction)

I donít adjust the front I just adjust the rear (for now) but I think the following works too
softer front=oversteer (more front traction)
Harder front=understeer (less front traction)


but I had to wrap my head around under/over steer. I think of it as rear rotation. too much rotation and you lose rear traction and spin but you do want to free the rear up to just before that point.


I start with some online setup that is close to conditions and only sauce the rear. I adjust droop and ride height until I start to get understeer. it seems like the stuff I find online from the top guys they like a ton of steering so i work that out. usually flattening the car gets me to that first point of understeer. then i sauce half of the front tires and it gets a little twitchy at full epa. I then take epa down to 75-85%. then as traction changes I can sauce the fronts more or take some epa out.

I need to start working on overall grip. I think I have a problem with overall grip (I can handle allot of high speed in corners) because I see allot of tire scrub under the body after each race that other guys donít get. I go through a set of sorex 36 on asphalt every 6 qualifiers and 2 races.


I donít think in terms of loose yet. it seems to me some people say loose and it means a very responsive front while others say it and it means a rear that rotates quickly so I stick with understeer/oversteer because it works when i think of it as the rear rotation.

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