4 bar rearend trail

[racer22]

How much is too much trail either shortening the rr or lenthening the lr, i am new to the mod deal and have been pretty sucessful so far, i have won 2 features already this season but i have been kinda fumbling my way threw it. I was told that the right side being shorter will help the car from trying to step out off the corner. I have the rr 1/2 shorter than the left, could i go more than that.

[stock car driver]

Usually trail or lead is referenced as the rr..

so you would be running 1/2 lead

Ive never heard of a person being able to run lead with a 4 bar modified or even a 3 link for that matter, with a 4 bar you can get infinite traction by changing the lr bars etc. Therefore rr trail is needed so the car goes around the corner vs shove the nose.

If your cars working for you like it is make small changes after noting every detail of your set up now and calling that your BASE.

[pig tracker]

Makes me think that maybe where he measures could be misaligned and not giving correct numbers. Just doesn't seem right. JMO

[racer22]

I measured the links in the back, both sides were the same top and bottom, i shortened the right side bars 1/2 inch each side. If both the links are the same the rearened is square,

[racer22]

Stock car driver, can you pm me, i have a few other questions if ya have time

[pig tracker]

Oh. On my car there is designated spot that if both sides measure the same, the rear end is square. Of course, I never have ran the identical length bars on both left and rear. Sorry, sometimes I need to keep my thoughts to myself. LOL

[stock car driver]

The rear end isnt square based on bar lengths... that is not accurate since they are NOT in the same holes side to side.

You need to measure from the motor plate back to the rear end. I measured from my motor plate back on all my mods and squared the rear end at ride height.....

Then took a 12 piece of tape measure cut off a old tape and put it on the front of the axle housing facing forward and scribe a line on the inside of my 4 bar bracket... so anytime on scale stands while rolling around under there on a creeper I could stick that 12 tape section up in there and see my exact lead or trail...... I had it so it took about a minute to measure every single ride height angle lead trail etc.

I used angle finders, 12inch tape and cut a piece of metal to fit between axle tube and frame for rr ride height. I drilled holes in my frame above the front a arms so 3 was my base setting for ride on both sides.

[25jrjr]

I would first call the mfr. They usually put some kind of mark or tab on the framerails to square the rearend.

I always liked to include the frontend settings with my wheelbase measurements. I establish a true chassis centerline off of the lower balljoints all the way back to the rearend. Then drop a plumb bob equi-distant from the centerline on each side. Then, measure from the balljoint to the rearend on each side, and you will have the wheelbase for both.

[JustAddDirt]

I would first call the mfr. They usually put some kind of mark or tab on the framerails to square the rearend.

I always liked to include the frontend settings with my wheelbase measurements. I establish a true chassis centerline off of the lower balljoints all the way back to the rearend. Then drop a plumb bob equi-distant from the centerline on each side. Then, measure from the balljoint to the rearend on each side, and you will have the wheelbase for both.


how do you compensate for a clip that is turned with that process?
Also depending on amount of castor being ran that will roll the RF wheel back the more castor that is being used, which will skew the length?
lower balljoint or zerk fitting is not a true 0 line. it is pretty close, but not exact.

[25jrjr]

how do you compensate for a clip that is turned with that process?
Also depending on amount of castor being ran that will roll the RF wheel back the more castor that is being used, which will skew the length?
lower balljoint or zerk fitting is not a true 0 line. it is pretty close, but not exact.

I only use it for reference. That way I always know what each side measures.

You sure about the caster. Positive caster increases the wheelbase.

I had a good friend who crewed on a truck team and their engineer used this method. This method is pretty complicated when you first try it, but it gets easier the more you do it.

[JustAddDirt]

***depending on clip design***

IF you have a strut style car, (late model) or a rear steer ford clip car...
then you would lengthen RF wheelbase, because you adjust the front lower a-arm strut rod's length shorter, which increases castor, and wheelbase

On 99% of modified's, or equivalent, with a fixed lower a arm, you must adjust the top ball joint towards the rear of the car which shortens wheelbase to get more castor.

Guess it depends on which front suspension being used as to the method. (and since this is a Modified Tech Forum that is why I said it shortens.)

[stock car driver]

I only use it for reference. That way I always know what each side measures.

You sure about the caster. Positive caster increases the wheelbase.

I had a good friend who crewed on a truck team and their engineer used this method. This method is pretty complicated when you first try it, but it gets easier the more you do it.

haha, positive caster makes the wheel base shorter.

your way of checking each side is a complete waste of time, all your measuring is the wheel base you can do that wheel to wheel with a tape measure, that side to side measurement has nothing to do with a rearend and lead or trail.

[25jrjr]

haha, positive caster makes the wheel base shorter.

your way of checking each side is a complete waste of time, all your measuring is the wheel base you can do that wheel to wheel with a tape measure, that side to side measurement has nothing to do with a rearend and lead or trail.

Way more to it than that, but I knew you wouldn't understand!

You must own the only square racecar ever built!

[stock car driver]

Way more to it than that, but I knew you wouldn't understand!

You must own the only square racecar ever built!

baha why the new user name?

if the front stub is turned and you do all your stupid measuring and your wheel base is equal side to side your rearend is not square

[25jrjr]

baha why the new user name?

if the front stub is turned and you do all your stupid measuring and your wheel base is equal side to side your rearend is not square

Duhhhhh....In school, did you fail reading comprehension? See post 10 above!

[stock car driver]

Duhhhhh....In school, did you fail reading comprehension? See post 10 above!

post 10 says nothing except that positive caster increases the wheelbase which is incorrect...

Ill block your dum as new user name your not even a racer you should stick to the tailgate where you can be around like minded dumbies instead of actual racers who know something.

[JustAddDirt]

Whomever that engineer was I am sure he is not employed in racing now, or someone finally told him he is doing it all backwards.
Not trying to start a pissing contest here, but I have been setting and trying stuff on dirt cars for 25 years, and have a pretty good track record at it.
Plus asphalt stuff, I would bet would not want much of any castor in the RF on backstreer, because how much do they backsteer, and need the jacking effect it provides?

[25jrjr]

Whomever that engineer was I am sure he is not employed in racing now, or someone finally told him he is doing it all backwards.
Not trying to start a pissing contest here, but I have been setting and trying stuff on dirt cars for 25 years, and have a pretty good track record at it.
Plus asphalt stuff, I would bet would not want much of any castor in the RF on backstreer, because how much do they backsteer, and need the jacking effect it provides?

His name was Ray Stonkus. In his latter years, he crew chiefed for Rick Crawford. Before that, he won a ton of races in asphalt late models. Pretty sure, he knows his stuff.

http://racing-reference.info/crewchiefs/Ray_Stonkus

[25jrjr]

post 10 says nothing except that positive caster increases the wheelbase which is incorrect...

Ill block your dum as new user name your not even a racer you should stick to the tailgate where you can be around like minded dumbies instead of actual racers who know something.

Please do.....as the only positive thing you add to a discussion is......NOTHING!

Why haven't you ever been banned? 4m minds want to know!

[junebug]

Hey racer22 if u can just call the chassis builder or anyone else u know with same type of chassis as u...they should have refence points for checking trail...when the cars on the jig is the easiest time to have everything square and they usually have a place to measure it from set up when ever they build it....i kniw u said ur new to modifieds and some of these other ways described are pretty complicated for a new racer

[25jrjr]

Refer to the caster section at the bottom of the page. I would like to hear an explanation how positive caster doesn't lengthen wheelbase.


http://www.car-engineer.com/suspension-design-definitions-and-effects-on-vehicle-behavior/

[rsawyers9]

On a dirt modified, you cannot adjust the lower control arm. So to increase positive caster, you have to adjust the upper balljoint toward the rear of the car, effectively shortening the wheelbase by a small amount.

[25jrjr]

On a dirt modified, you cannot adjust the lower control arm. So to increase positive caster, you have to adjust the upper balljoint toward the rear of the car, effectively shortening the wheelbase by a small amount.

Since the upper and lower balljoints are connected by the spindle, if you tip the top back how can the bottom not move forward a slight amount.

What about Ford style lowers?

[JustAddDirt]

25jrjr
that link you posted, in the diagram, you need to look at which way forward is ( it is listed in black to the left of the illustration). I think you are confused.

also read what you posted above., and think about it. the spindle is 2-3" above the centerline of ball joint, so if you move the upper ball joint rearward the spindle snout goes back as well (shortening wheelbase). If the lower a arm never moves, how can anything tip forward?



I work with SAI (Steering Axis Inclination) angles daily, and build the computer software that calculates it if you vehicle has been in a collision.
I know what I am talking about here.

[RDBracer]

positive caster moves spindle back this is true but the contact patch of the tire moves forward since the piviting point is the lower ball joint.

[25jrjr]

positive caster moves spindle back this is true but the contact patch of the tire moves forward since the piviting point is the lower ball joint.

yep, always been my thinking too!

[dave41]

haha, positive caster makes the wheel base shorter.

your way of checking each side is a complete waste of time, all your measuring is the wheel base you can do that wheel to wheel with a tape measure, that side to side measurement has nothing to do with a rearend and lead or trail.

if you are on here I don't see your post

[JustAddDirt]

no, the tire contact patch is directly under spindle pin, but the steering axis moves forward of tire contact patch, as positive castor is increased.

[25jrjr]

no, the tire contact patch is directly under spindle pin, but the steering axis moves forward of tire contact patch, as positive castor is increased.

Can you post a diagram? Im from Missouri! :)

[billetbirdcage]

Can you post a diagram? Im from Missouri! :)


http://i.imgur.com/RsNIMDR.png

[JustAddDirt]

thanks billet, I tried to post, but got blocked by work security police.

[25jrjr]

[QUOTE=JustAddDirt;2110978 If the lower a arm never moves, how can anything tip forward?

So if it doesn't move forward or backward, why does the wheelbase change?

[JustAddDirt]

That was stated that way because the lower a arm has no length adjustment.once bolted in it cannot be adjusted.
When more castor is needed the upper ball joint / a-arm is used for the adjustment and it is adjusted rearward for the increase in castor, thus shortens wheelbase.
Look at diagram and were it says + castor. Picture that going rearward, and the spindle pin has to go rearward. As well. The more castor. The more it will shorten wheelbase.

[25jrjr]

I've always considered the steering axis as the contact patch.Its pretty negligible with lower pin heights isn't it?

Its true....you can teach an old dog new tricks! Thank you sir!

[Lizardracing]

According to the diagram above. If you were to move the upper BJ back on the horizontal plane (or less than the BJ to pin radius) the pin will move back but if you could move the BJ along the radius of the pin it stays put. So the real answer is the wheel base may or may not change as it depends on where the BJ is moved to.