johnyIROC

What are the benefit of adjustable A-arms?

Is it primarily for making small camber/toe adjustments at the track?

Could adjustable A-arms be used to pull the overall track width in (strut mounts would have to move as well)?

johnyIROC

Is there anything that can be done to narrow the track width, and correct the scrub radius after installing a brake kit?

Only things I can think of are:
1. Order custom offset wheels
2. Shorter A-Arms and relocated strut mounts

Base91

iTrader: (1)

Why would you want to narrow the track width? The usual aim is to go wider.???

sofakingdom

iTrader: (1)

A brake kit changes the scrub radius by about ¼". How much are you looking to spend, to correct that little bit of nothing, that's probably actually less than the production-line tolerances on the car? (I.e. the car can vary randomly off the prod line by as much OR MORE THAN what the brakes cause)

"Measure with micrometer, mark with chalk, cut with axe".

What makes you think there's something wrong with it, as is?

Andrew91GT

The adjustable A arms that I've seen, such as these:

http://www.racecraft.com/index.php?m...roducts_id=285

Allow finer control of alignment as well as allow you to introduce stagger into the front wheels, which gives you more rollout.

//<86TA>\\

iTrader: (14)

my question with the a-arms, is that they are mounted to the car at a rearward angle, so lengthening the arms would move the wheels back too. Unless you can fudge one side of the arm longer, the other shorter, to keep it straight? I dont see how this works, maybe somebody can enlighten me further on that.

As for correcting the scrub, ultimately, custom wheels would probably be the best bet.

or, put "rear" wheel on the front with a small spacer of the appropriate size, if you are running wheels with fronts and backs

hellz_wings

iTrader: (2)

My track width is wider in the front by around 1.5" total. So 0.75" on each side. The rear is 1.5" narrower. How this affects handling I don't know, but I do know that having equal track width on all 4 wheels is optimal for handling.

Guest

you can NOT correct scrub radius via a control arm length. Scrub radius is the pivot of the ball joint and the offset of the tire footprint when it turns about that radius

johnyIROC

That makes perfect sense now that I think about it. I guess the only way to really run big brakes and stock scrub radius is with custom offset wheels. Definitely not worth it right now.

Guest

Adjustable arms can be used for a few different things. Caution needs to be focused on spring can alignment so as not to make adjustments too far where it causes the spring to rub against the side of the can.

With the above said and respected, you can utlilize the adjustments to lengthen the rear ear leg, and shorten the front ear leg so as to move the lower ball joint forward. What happens to alingment? you gain positive caster. Same goes for slightly moving both longer going lateral and widening the front track- you gain negative camber range. Toe settings have plenty of adjustment to be reset to a wider track keeping most cars at about 3/32" toe in normal settings.

The ball joint placement compared to the strut mount is what determines your alignment range of settings- just like it would static with a upper and lower ball joint car. Dynamic range differs- but thats irrelevant here for any comparison. (static- stagnant ride height, dynamic- range of motion when forces are applied to moving suspension parts in articulation)

What other benefits? When moving the balljoint forward via control arem adjustments, you are also moving the weight of the chassis over the nose slightly backwards and slightly weighting the rear tires more- Yes, you are slightly changing the chassis weight bias more in the direction towards 50/50. You are extending the wheel base which is good for high speed stability, but bad for low speed agility (low speed direction changes- shorter wheel bases turn easier, but not a stable. A general rule of thumb: car easier to turn is also easier to spin out, and visa versa). So now you want to keep the factory wheel base? shorten the rear LCA's and slightly move the rear tires forward also. You have again moved chassis bias rearward making the car better towards 50/50. Watch driveshaft length and spring misalignment in the rear also. You can go a tad, but not too much Varies between cars but most can do 3/4" move forward of the rear axle safely.

Adding track width- pros and cons.
1)Wider track width give corner stability but takes away agility. It makes the car harder to transition. Wider track is generally good for higher speed corners where a car is set into steady state longer distances.
2) Longer A-arms is MORE unsprung weight. The longer the arms the more stable the chassis from changes in geometry, BUT the more effort it takes to control the wheel over bumpos and dips. The wheel now has more leverage against the chassis to unsettle it- spring rates need slight increase, as well as shock values to compensate for the increased or decreased leverage of lengthening or shortening the overall pivot distance of the tire footprint from the chassis mounts. This all delves into "Polar Motion". I did a post on polar motion a few years back- basically is like a figure skater trying to rotate with arms extended outward as opposed to picking up speed closing the arms closer to the body with centrifical force- once you rewxtend the weight of the arms further from the "pole" or spinning axis the motion slows with leverage. Its harder to stop with the arms outward because of enertia of the outward weight as compared to the same weighted object spinning with the weight more centered towards the pole. Stopping the motion and moving it back in the opposite direction is easier the shorter the polar weight is. A longer A-arm is more polar weight- so are wider wheels and tires generally unless you go to something extreme like Pablo with those wide but lightweight CCW's and R6's Suspension articulation lightness is EVERYTHING in movement to absorb the road and maintain the tire footprint on the road without the assembly throusting upward to unsettle the chassis.

Sound confusing? well it is. So now what do we do? This is why chassis setups will vary depending on the racing curcuit driven on. Is it a high speed curcuit? is it smooth and fast, or bumpy and slow, is there compression on the suspension from high banked turns or is the cornering flat or off camber....etc. All these factors will greatly vary what a chassis will do resting on the suspension assemblies. What do you use your car for? most use it for daily driving and spirited performance excurtions- somethings like autox and light road course use. The chassis is for the most part engineered for normal driving use and is plenty agile on its own without these adjustments being needed. If you do use adjustments like this, you really need to know the pros and cons as to whether it is helping or hurting what your efforts are. It all takes a marraige of componants and setting to make things better- ignorance of settings generally make people headaches, not rewards.

Dean

Guest

To go further on this subject of chassis setup using A-arm length- I will give an example of how I use this adjustment in NASCAR and how critical it is towards getting each driver I have worked with to his most advantage in basline setting regading RULES.
We are allowed a 70" front track width and a 69" rear track width. We are allowed a 55.0% left side weight MAX and a 50.0% max rear weight.
The MINIMUM overall weight of the truck and driver is 2700lbs.

So where do I start? drivers weigh different. Mason was 137 lbs (wet I might add- skinny young kid), Derek is 210 lbs, and Bob is 174 lbs
You start by weighing each driver and car and anything under this weight you start adding lead to the left rear of the chassis frame rails in 10 lb increments til you get above 2700 with driver (both hands on steering wheel), full tank of fuel, and complete chassis weight racing trim and safety gear in place. Lighter drivers have an advantage with the placement of weight being artificially added to the lower left rear of the chassis- just a mute point I wanted to add.

So now I put the entire package on scales and see where it all weighs in left of right weights. Remember, I can have a maximum advantage of 55.0% left side weight when we go through the tech scales prior to the race. Each car is different based on who built it- these are individually built and things like the simple placement of the battery or the fresh air breather box can vary the weight distribution as well as the lighter drivers have more weight added to the left of tthem in the seated position via lead in the frame rail than the heavier driver.

I now have to use A-arm lengths on both left and right sdie of the car to shift the chassis weeight back and forth to get my maximum left side weight advantage as well as I use the panhard to shift the rear axle left and right to blance the right side track of the wheels in line. Yes the rights stay in direct wheel track front to rear, but the left front is 1" wider than the left rear ustilizing the max track width of 70" in front. That left front being outward helps levearge the steering and makes the car turn better.

Wheel base is 108" max. Here again shifting A-arm leg lengths I set the right side wheel base at 108" max, but I decrease the left side wheel base with a LF setback of about 1/2 to 3/4" based on the chasiss tolerances manufacturing differences and what I can safely work with while still having adjustment ranges needed. SO the left side is about 107 1/4 to 107 1/2" wheel base based on the chassis. Why this? SO I leverage the diagonal x-weight of the chassis from LR to RF tire wheight on its widests footprint in comparison to the opposing diagonal. THis is like a tetter tottor combined with a wide stance on a skateboard- we are getting a little too advanced for this discussion (I would need a bigger novel to explain further) Just showing how A-arm lengths are used to setup a NASCAR chassis in circle track and what effects they have on the chassis in leverage. Basicaly the wider x-weight stance keeps the LR weight down from rolling over onto the RF in a banked corner. The LR tire is the hardest to get heat/grip into compared to the others dynamically when tuning into a left corner under braking on a car that only sees left corners.

Dean

Stroke

So what are the pros and cons in shortening the rear LCAs besides having a closer to 50/50 weight. I understand that in it self is very useful but to be more clear i guess what are the the cons in doing this. Im going for high speed stableness here.

Thanks One more question i have been trying to figure out what exactly Rear Roll Steer is. In other words does more Rear Roll Steer make you lose or does it tighten you up?

Guest

Shorter wheelbase will turn quicker than a longer wheel base. Longer is more stable at high speeds. 3/4" is really not much noticible but I always use every advantage I can get. You keep adding things that will give you 1/10th a second off a lap time and next you know they add up to a half second or more.

Roll steer will do either lose or tight depending on how you set the rear geometry.Outer lca being parallel to the ground at 3* body roll and the inner lca down towards the rear (outer and inner meaning in reference to which way the car is turning)will induce roll oversteer and make a car loose- and vica versa. The shorter the LCA's the more sensitve this effect can be due to the articulation arch of the LCA's being tigher and moving off vertival parallel length at a greater rate

Stroke

If you did this wouldn't this put strain on the rod ends?

How far forward could you move the lower ball joint by doing this?

Would it be a better idea to order custom A-arms that moved the ball joint forwards X amount of inches?

If you wanted to widen the front track width witch method would be better in performance type view? To widen the A-arms or to get offset wheels? Or is this a adjustment better based off of track conditions?

Guest

Some things I do not like to share when it comes to top secret designs I have and plan to build. The bast I will answer that question is:

Better to move extend the a-arm for a wider track than to use a wider offset wheel because the wider offset wheel increases scrub radius or better put- you drag the tire more. This is really a complicated question to answer. SO many hidden details to which way is correct. It takes a whole lot more than what you list in each choice to do each choice correctly.
Lets just anwer that easily and say you mess up the entire factory geometry. Geometry is all about tire footprint and contact patch. To mess this geometry up is to mess up the tire contact patch. Witht his statement you will understand why I ran 8" wheels on my car but still acheived 1.07g'ds in a skidpad test (Not a spiked G-tech recording, actual timed skidpad run)

Guest

People need o realize that one little change like this where someone things they are gaining track width so theuy are gaining grip is so wrong. THe sus[pension could be balanced and one little change like this changes geometry and leverage and can potentially cause the entire suspension to be readjusted and rates changed to make something go from good to soso to better. It does not just always go from good to better.

Start messing with this stuff and you had better know what you are doing otherwise 99% of the time you are hurting and not helping.

Let me give an example of something in recent topics here on TGO.
Alot of talk has been on aftermarket Kmembers and their usefullness. Are they worth it? and main talk is are they strong enough. Thats only half of it. the weight savings which everybody thinks is great is actually terrible.

Why? How can loosing weight be terrible?

Well, you are loosing weight in the wrong place unless you car nothing about cornering (THUS WHY I SAY AFTERMARKET KMEMBERS ARE GREAT FOR DRAG CARS ONLY)

Why is it the wrong place? afterall it looses weight off the heavier front half of the car making a better 50/50.....YES this is true, but the evil outweighs the benefit.

You are loosing lower lateral weight. You are better off loosing upper lateral weight in the hood, aluminum heads, battery box relocation, windsheild glass, aluminum bumpers, plastic headlights, lexan hatch glass....all mid level to upper level roll weight.

Here is the explination so you get the big picture. Cars have a 'center of gravity' or 'cg' as we will refer. They have a fore and aft cg, they have a vertical cg, they have a lateral cg. You need to think of the chassis as for what it is...3 dimensional. So now we look at what is body roll and how does weight affect it? Well body roll is about the imaginary 'roll axis'. The lateral cg is what influences roll based on its verticval osition to the roll axis. The higher off the ground the roll weight is (measured off the ground since the ground ultimately is where the grip is from the tire contact patches) the more the leverage or polar motion of the weight. these contact patches connect through the suspension and gewometrically determine where the imaginary roll axis is that the weight moves laterally over or under. Weight and leverage over this imaginay line causes roll of the body, weight under this imaginay line causes ANTiroll of the body. Roll is positive, anti roll is negative.

Now, a typical thirdgen has a very positive roll weight- hence why we need preety big sway bars like the 36mm up front to control that positive roll weight. Older cars like 70 chevelles need even larger bars because they have even heavier positive roll weight that needs to be controlled.

Starting to understand what swaybars do and how size is determined? yep I hope.

So back to that kmember we just replaced with an aftermarker tubular unit that is something like 50lbs lighter. That Kmember is low. Laterally most if not all of that lateral weight is negative that counter acts the heavier positive roll weight. For every pound you have lets say up near the hood which is about lets say 20" higher than the roll axis, you need about 20lbs of negative anti roll weight to counter act it if the negative is only 1" lower than the roll axis. See how the money would be much better spent on a fiberglss hood?.... so now you know.

Guest

So now that you all have read my last post, lets get back into wider tires that also end up making wider track. THis is just making more lateral grip 'hopefully" if lets say you are in fact getting you setup correct and getting all of that tire contact patch width planted for extra help...then what? well as a result you are now producing more body roll since the force of positive roll weight is even greater. You are lifing weight of the inside tires and just simply replacing it on the outside tire.

Why not leave the smaller 8" wide tire and reduce the roll weight which leaves less eight on the outside tire and more weight on the inside tire in hard corners compared to the example I just listed with wider tires.

Now think how transition cornering will improve. Yes it will be much quicker to change directions if the roll is less nad chassis weight is changed direction faster and lighter in roll. footprints will stay better planted.

Now you see why my little V6 car was so deadly to race against in cornering when I had merely little factory 8" wheels on it. Lighter car with less positive roll weight and the tires more evenly distrubuted weight upon all 4 in hard corners- I did not need the wide tires to bear alot of you V8 guys with large meats and lots of power.

Most inportant in part purchase is how you adjust things. Life is all about leverage. A small enough man can lift the weight of the world if he had a long enough lever and the understand to make it work.

Stroke

How does this increase positive body roll?

I thought wide wheels and tires or longer A-arms are unsprung weight.

Is this scenario with a after market k member or with a stock one?

What would you have to do to gain more lateral grip with out raising Positive roll weight?

Well i some what understand what you are saying so let me tell you what i learned and would please correct me if Im wrong.

Ok more weight that sits higher in the chassis (higher of the ground) well increase roll and have a Higher center of gravity (Positive roll weight)

Weight that sits lower in the chassis (lower to the ground) decreases roll and will have a lower center of gravity (Negative roll weight)

Sway bars help reduce roll.

More positive roll weight the bigger the sway bar.

This all retains to wider A-arms right? Nothing to do with my Ball joint relocation
Question right?

Guest

More tire grip combine with the exact same roll weight equals more lateral force which equals more body roll. Simple really.

They add to unsprung weight yes. Don't know how that refers to what I wrote but yes. I think you are just loosing translation in reading what I wrote, Nothing wrong with tht, its hard to grasp. THis is just refering to spending money on lightweight sprung parts rather than what most spend on shiny new unsprung parts that more often then not hurt rather than help when setup wrong.

With both in comparison. I really do not understand why you ask this qustion. I think if you re-read what I wrote you will see I talk about saving weight down low with a new aftermarket kmember compared to leaving it alone and saving weight up top spending your money instead on a lighter weight fiberglass hood and such.

You are not understanding the paragraph. I am not raising positive roll weight, I am reducing it and keeping the anti roll weight higher retaining the factory kmember down lower than the roll axis.

Please take no offense, but you have it wrong in general. Nothing to be ashamed of though, no of us were born with this knowledge and its really hard to grasp imaginay points of roll, especially reading someone elses type.
off the ground yes. to a smalll point. Higher off the roll axis is the big yes. THe weight rotates on the roll axis, not the ground. if the inside tires lift then the weight rolls around the ground where the outside tires are touching somewhat as it is also roll about the roll axis also. THis gets very complex in imaginary though and hard to protray in any graph or photo without lots of multiple drawings overlayed showing roll dynamics.
.
You need to understand vertically you have ONE center of gravity . The center of gravity IN RELATION to the roll axis (cg to RA distance) is what influences positive roll or negative roll. Most vehicles have positver roll weight were the cg is higher than the ra. Think in lateral or sideways thoughts as weight is being exerted. If you do not understand this then you need to back way up in suspension knowledge and pick up some basic chassis dynamic books so you can better understand the terms and points in space before you try and grasp dynamic movement through and around those mostly imaginary points.

yes. They balance out the remainder of lateral roll resistance that the springs do not support. Often if the spings were raised high enough in rate to support lateral roll, they would be far to stiff for longitudinal mechanical grip (forward motion grip or road impact)

yes to a certain extent. Too large locks up the suspension from artculating over straight line mechanical grip. Better to reduce roll weight towards netral then to keep putting on bigger and bigger bars.

I actually did not try and answer your ball joint question. I just re looked at it so here goes. (And no, it really had nothing to do with anmswering that question but yes balljoint position laterally and heightwise will influence roll centers and roll axis- this gets back to me asking you to buy a book on suspension geometry or try and learn a little bit what I showed on roll centers from my "ultimate suspension posts above in the sticky column.

The balljoint moving forward will help positive caster. It will nopt affect swivel a-arm mounts joints or bushings like Spohn's delsphere joints or UMI's Rotojoint. Both somewhat copies of Currie Enterprizes Johnny Joint (Famous Currie 9" Rearends- they make offroad joints for jeep competitions for many many years, they are the innovators of this type of joint). Moving the ball joint outward in track width will help negative camber. It will afect so many ither things like said track width, bump steer, ackerman, x-weights, leftside weight, roll centers, unsprung weight, spring rates, shock rates, antidive properties... the list goes on.

Stroke

Whats a good Chassis Book?

Stroke

Is there a school you can go to and learn more?

hellz_wings

iTrader: (2)

What about Lexan t-tops? From what I understand from what you wrote Vetruck, the higher the weight from the CG, the more effect it will have on handling when removed?

Also, this is different than polar weight though, so how would relocating the battery to the rear (polar weight relocation) affect the car's handling, compared to removing weight above the cg?

And what effect would relocating the battery to the rear have on handling? (understeer, oversteer, etc.)

Thanks in advance!
-Marc

Guest

Your local race tracks. Find a few drew guys walking around and ask them if they know of any team looking for volunteer work on a race crew. You'll do alot of wiping and puching the car around, but keeping your eyes open and ask questions afterwards (not in the heat of decissions) and you will pick up things alot faster than in a classroom.

@Hellzwings- Polar weight has alot of different definition points based on the vehicle dynamics. As said earlier there are lots of different points of cg on a car pertaining to weight transfer. The further the weight is the more leverage it will have when trying to resist its movement. In a day where the average new dealership performance car is ranging 40k, this can easily build a 3rd gen supercar wribaling the 100k exotics if one is handy with knowledge and fabricating skills.

Moving things low and to the center of the car are best. Less polar fore and aft in the chassis can also lead to high speed instabilty because the car will want to change direction 'quicker'.

You have to think of vehicle dynamics alot like airplane dynamics (roll, pitch and yaw) but overlayed in a few different ways since there is grip resistence and steering imput as well as the typical areo. Its basically way fast cars are low and lightweight exotic carbon fiber like Formula1, Ferrari, Koenigsegg, Riley, etc. You never see a car like that with heavy rear hatch glass. My next third gen will have lexan rear hatch definately. I will do alot of the same features someday keeping the low unsprung weught to balance the low sprung weight to keep a very good ride ratio. Then its about controlling what weight you are left with in balance around the roll axis cg straightline cg, and the lateral cg (roll pitch and yaw). The other polar movements in the 'overlaay I speak of is things like the CF driveshaft, drilled axles, aluminum hubs, chrome moly rear housing, lightweight pinion gears etc etc etc. all reducing their individual plane or arch of movement.

Hor rodding is all about re engineering stuff to male it better than factory production line results without going completely crazy in the pocketbook.