Go Back  R/C Tech Forums > General Forums > Electric On-Road
Understeer oversteer >

Understeer oversteer

Like Tree2Likes
  • 1 Post By glennhl
  • 1 Post By daleburr

Understeer oversteer

Old 04-12-2020, 08:57 PM
  #1  
Tech Addict
Thread Starter
 
Join Date: Jul 2018
Location: Florida
Posts: 716
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.
Bry195 is offline  
Old 04-12-2020, 10:32 PM
  #2  
Tech Master
iTrader: (14)
 
Join Date: Sep 2013
Location: Arizona
Posts: 1,374
Trader Rating: 14 (100%+)
Default

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.
Bry195 likes this.
glennhl is offline  
Old 04-13-2020, 05:25 AM
  #3  
Tech Fanatic
 
daleburr's Avatar
 
Join Date: May 2010
Location: Oxfordshire, UK
Posts: 993
Default

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
Bry195 likes this.
daleburr is offline  
Old 04-13-2020, 08:46 PM
  #4  
Tech Addict
Thread Starter
 
Join Date: Jul 2018
Location: Florida
Posts: 716
Default

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?
Bry195 is offline  
Old 04-13-2020, 10:12 PM
  #5  
Tech Master
iTrader: (14)
 
Join Date: Sep 2013
Location: Arizona
Posts: 1,374
Trader Rating: 14 (100%+)
Default

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.
glennhl is offline  
Old 04-14-2020, 08:44 PM
  #6  
Tech Addict
Thread Starter
 
Join Date: Jul 2018
Location: Florida
Posts: 716
Default

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.
Bry195 is offline  

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.