Anothing question

[bbcc]

How tall of tire are you going to run? Try and set up your rc to be an inch or two under the axle center line. Your roll understeer looks a little high, but I have no practical experience to say if it's to much. And I think that the 70% AS is a good number to start out with for handling on the street. And with the power you plan to put down, the ability to bump it up to 100% on the track will really help.

Cheers, Ryer

[GMracer]

29" tire it says that top left, so that put's it 1.5" lower that Axle Center Line, understeer high as in to be more in the negatives? Or high number as in it should be -3 -2 -1 ?

[bbcc]

Try and get numericly lower with that program. So that would be -3,-2,-1.

[The WidowMaker]

a positive roll understeer in that program is acutally roll oversteer. it will convert once you go positive and show you that you are now at a roll oversteer.

remember that a roll over/understeer is not the same as over/understeer. although its been argued, it is just the amount of input at the steering wheel required to make the car turn and will not affect the handling until it is at the extremes. roll over/understeer is just the rear axle contributing to the steering through the turn. it does provide for a weird feeling in the turns though.

hopefully someone with more suspension knowledge will chime in regarding where you want your roll over/understeer.

[GMracer]

ahh, see at first I was trying to get it to zero but then I read that you want more understeer than oversteer so I figured -3 would be ok. But clearly I'm lost right now where I want to be, luckily being that I'm doing a satchell it's very tuneable.

[Rhino]

ahh, see at first I was trying to get it to zero but then I read that you want more understeer than oversteer so I figured -3 would be ok. But clearly I'm lost right now where I want to be, luckily being that I'm doing a satchell it's very tuneable.

I'll try to explain roll under/over steer in a different way...
When entering a corner, Your vehicle will roll due to weight transfer toward the outside of a corner. The difference in alignment between static over/under steer (car at rest) vs your "rolled" position (in a corner) is what is considered your roll steer.

Here are two situations of a vehicle entering a corner:
Roll under steer: When your vehicle rolls toward the outside of the corner, the axle will steer toward the inside of the turn corner. This action is easily counteracted by the driver adding more steering input.

Roll over steer: As the vehicle rolls, the axle steers toward the outside into the corner. This requires the driver to pull a little bit of steering to maintain the same radius.

If you have any roll steer at all, it's usually said to be better to have roll under steer. The correction for under steer seems rather natural to a driver. In addition to this, having to correct for oversteer has the potential to shift the weight distribution throughout the turn, possibly causing instability.
Does this clear things up any?

[GMracer]

Yes, it sure does and thank you... so I guess how much so I head for? My spread sheet reads anywhere 3-4* Roll US right now with some of the possibly layouts I'm working on.

[Rhino]

The closer to zero the better, but just as with everything else, it's a balancing act. 3* doesn't seem bad in my opinion, but I'm far from an expert.

I would say as long as you're under steering, and it's close to zero, roll steer wouldn't be one of my primary concerns. I would focus on roll centers, RS migration, AS, and lateral axle control. I'm quickly finding that designing a suspension can drive you crazy with numbers.

[The WidowMaker]

thats a good explanation of roll steer as i understand it.

ive also read that the perfect setup would have slight roll oversteer while entering a corner and through the middle which helps turn in, coupled with roll understeer on exit when youre getting back into the throttle. any roll oversteer with sudden throttle input on exit would be a little scary in my opinion.

Tim

[bbcc]

Great explination guys. Couldn't say it any better. From all that I've read, a slight roll understeer or a completely neutral setup is a great starting point. And like you say GMracer, the satchel is very adjustable. I'm going to try and aim for as close to neutral with mine and tune from there.

[GMracer]

So I finally came up with a good setup I believe, and all I have to do is lower the top bar 1" and 100% AS with 2* Understeer for the strip.

hows it look to you guys?



if I make it 18 5/8" on the frame end it bring it to roll understeer and still 0* just figured I'd mention that, while putting the AS at 80%

[bbcc]

The only thing I would check is to make sure your svsa isn't going to become to small. Issues with brake hop start to arrise when the svsa is around the 60 in. or less. Other than that, looks like a solid set up.

Cheers, Ryer.

[Norm Peterson]

Are those Performance Trends roll steer figures percentages or are they something else? I've never been able to get any PT software to work onmy computer either, so I work with the conventions in the various literature (%, in this case).

2% - 3% in the vehicle understeer direction is a pretty good place for a PT car to be, at static ride height. 5% is high, and at 7% the car is starting to really dislike slalom maneuvers.



You should do the math at least at a couple of positions other than static. Roll steer and anti-squat both vary with suspension position, and the geometry is involved with how rapidly this occurs. It is possible to design in a slight amount of roll oversteer on deceleration (corner entry, rear rising slightly) that transitions to slight roll understeer as you add power on corner exit (rear squatting a little), though I don't know what would be required to make a Satchell work that way (haven't tried any Satchell simulations on a spreadsheet solution for the general triangulated 4-link arrangement yet).


Norm

[Bruning Auto Design]

Are those Performance Trends roll steer figures percentages or are they something else? I've never been able to get any PT software to work onmy computer either, so I work with the conventions in the various literature (%, in this case).

Norm

Looks like "Triaged" 4 link calculator from Pirate4x4.com .

In case others are interested

http://www.powerblocktv.com/sites/xt...arLinkV3.0.zip

edit - post by triaged on pirate with all of the different versions

http://www.pirate4x4.com/forum/showp...99&postcount=7

[Norm Peterson]

Just took a peek at the downloaded xls file, and . . .

YIKES!!! (20.91% understeer)


Anyway, the coordinate math is probably similar, but he goes off more into designing the links where mine plots anti-squat and roll steer as a function of ride height.


Norm

[GMracer]

I was trying to figure out how I could go about seeing the AS and Roll at different heights but couldn't figure out how to do so.

[Norm Peterson]

You need to write the equations for the chassis-side Z-coordinates (and CG height) in such a way as to include ±suspension movement as a separate variable. If the rest of the formulas are written in terms of pivot coordinates as variables it all sorts itself out. Then you can copy a line of formulas to create a table, and generate whatever plots from that. The X coordinates of either the chassis- or axle-side pivots also vary slightly (a (1-cos) thing) and you might want to consider that as well if your situation has very short links (or if you're just being picky).

This still does not consider pitch, however. Maybe some day.


Norm

[The WidowMaker]

there is a page which allows for suspension movement, but it doesnt work on my computer.

i suck with formulas, but using some trig i manually found mine at .5" increments.

[GMracer]

I read your post, but I'm completely lost haha, not sure I could figure that out. I get the gist of what you're saying, but no way understanding how to do it.