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Author Topic:   trailing the RR / leading the RR
bachshute
Dirt Maniac

Total posts: 118
posted January 08, 2005 05:46 AM  
Ok - lets see what everyone thinks , i figure i will get some different opinions on this because i tested with this a little last year and found opposite of what i thought.

When i trailed the RR the car got tight on entry , I always heard the opposite ???

If you lead the RR what will happen ?

Thanks for any info , I am confused about this one - lol .

Xtreme12x
Dirt Forum Champ
Total posts: 874
posted January 08, 2005 11:40 AM  
We ran around 2" of Trail in the RR
Plus take in to account the left rear coming foreward too. The more trail you can run the better. You'll know when you've got too much when it pushes in the center. It also takes a driver that is ready for the major drive towards the wall coming off to tackle that much Trail.

A2KY2K88
Dirt Maniac

Total posts: 141
posted January 08, 2005 11:43 AM  
If you trail your RR, this means moving it towards the rear of the car which will LOOSEN you through the turns. If you lead the RR, this will tighten you through the turns and could potentially make you push in the middle. Some people trail RR for dryslick, Some people do the opposite, its more of a driver preference than anything.

fastdad12
Dirt Full Roller

Total posts: 33
posted January 08, 2005 03:29 PM  
I am still confused. I always felt that if I didn't lead the RR a little that the car would be too loose, but this may be my Oldtimer Leaf Spring mentality. I would like to hear more detail on this. Do you have to increase the roll out when you run the rr trailed?

------------------
Jesus is life everything else is just racing!!

bachshute
Dirt Maniac

Total posts: 118
posted January 08, 2005 04:02 PM  
maybe it depends on what suspension we have - leaf - 4-bar - etc. not sure .

i always thought that trailing the RR would loosen the car or free it up , but when i had my car handling very well i tried trailing the RR 1/2" and it TIGHTEN entry , this was on a swing arm suspension???

all help on this appreciated .

showtime13
Dirt Full Roller

Total posts: 60
posted January 08, 2005 04:16 PM  
I think I would just leave everything straight up/equal and find another way of tighting my car up and leave it as driver friendly as I could. JMO

bachshute
Dirt Maniac

Total posts: 118
posted January 08, 2005 06:38 PM  
yea, your right showtime13 , i"m just one of those guys that will test different things and just got a different result on this than i thought i would , trial and error - lol - you never know when you will luck on to something .

[This message has been edited by bachshute (edited January 08, 2005).]

boas51
Dirt Maniac

Total posts: 190
posted January 10, 2005 10:42 AM  
if you listened to all the people who have said dont do this, dont do that, this is a crutch, leave the car square, you would have jack bolts to work with, and some people dont think you should touch them. not much fun, or consistantly fast. we should all be running bombers if we dont want adjustable cars.

yes trailing the rr will tighten entry, i have tried to explain why many times and some one always says no it wont, because you are "steering" the diff to the wall, which will loosen the car.
but i will try again.
to start with are you lifting off the throttle? if you are, the deacceleration is causing wheel braking. which means the rear tires are pulling on the car. pulling!? "if" and i said "if" the diff was actually turned in relation to the center line of the car, with the rr trailed, it would be "pulling" the diff to the left.

what everyone seems to mistake is that the car does not run with the diff on any angle other than 90 degrees to the centerline of the car (90 degrees to the direction of travel), (unless you have lost traction and are spinning sideways). so, by trailing the rr you have added yaw to the car. the diff is still travelling the same direction as the front, 90 degrees to the centerline of the chassis, but is now "dog tracking". you have moved the centerline of the diff to the right of the centerline of the chassis.
almost the same effect as putting a 2" bs wheel on the right, and a 4" bs wheel on the left, or simply adjusting your track bar to move the diff to the right.
moving the diff to the right tightens entry, loosens exit, of coarse this depends on the amount of rear weight, but most mods have lots.
you have also altered the rear steer characteristics slightly due to the different lengths of the trailing arms.


dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 10, 2005 11:05 AM  
I understand what you are saying about trailing the RR is like moving that wheel out because as the cars tracks down straight ahead the RR will move out as compared to havieng the rearend squared up. But in my experience anytime we have moved the RR out it has loosened the car not tightend it. Therefore whether the actual trailing loosens the car or the effect of trail on backspacing loosens the car the effect should be the same, a looser car. But thats just been my experience.

Xtreme12x
Dirt Forum Champ
Total posts: 874
posted January 10, 2005 11:49 AM  
Like i said... the more trail the better!! It's made a decent car better for sure. It's not un common to run a good inch to start... Trail will loosen the car to a point, but the main goal is to get it through the center of the corner quicker

NJantz
Dirt Forum Champ
Total posts: 755
posted January 10, 2005 12:55 PM  
Boas51-
I've sat here for 20 minutes drawing my self free body vector diagrams trying to understand this. I've always just believed what the majority has told me, didn't get real critical about understanding what they were telling me until now.

The key concept that you touched on is the fact that the differential will always be perpendicular to the direction of the vehicles travel. That differential is the driving force pointing the entire mass of the car towards the wall, not just the rear end.

Works just like "centripetal force" back in highschool Physics.

Thanks for helping me see the light!!!

[This message has been edited by NJantz (edited January 10, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 10, 2005 01:33 PM  

[This message has been edited by dirtbuster (edited January 10, 2005).]

bachshute
Dirt Maniac

Total posts: 118
posted January 10, 2005 04:43 PM  
boas51 -- I think i understand it a little better now , after reading your reply i can understand why the car got tighter on entry , never too old to learn . nothing ventured nothing gained , thanks for all the replys

fastdad12
Dirt Full Roller

Total posts: 33
posted January 10, 2005 09:56 PM  
Thanks for all the input on this post, it has been helpful.

WPP
Dirt Freak

Total posts: 451
posted January 11, 2005 05:49 AM  
Am i seeing things right here if you trail the right rear you can not enter the corner sideways you have to enter the corner almost straight or the car could be loose if sideways and when you trail the rr the car would be loose off the corner so you could run more lr bite if you trail the rr to tighten off am isee ing things right here thanks

juliaferrell
Dirt Freak

Total posts: 370
posted January 11, 2005 12:00 PM  
Sounds like we need a remote control car here for an experiment........give the thing about an inch of RR lead......stomp the peddle to the metal.........which way does it go? speed it up and let off........which way does it go......get your remote control cars out and learn from them.........my grandpa taught me with a vega and 80 pound bags of mortar mix....and platforms sticking out from each fenderwell..........He was so tired of arguing with me jumbling this up and believing what this guy said and that guy that he shut me up real quick.....it was funny..........

Question: Same as I argued with grandpa.

If I air the right side tires how will this effect corner entry...........my answer *loosen* the right answer ??? boas51, xtreme12x, A2hy288, and others?

I'm talking a neutral balanced same static weight on each corner before airing right sides with same spring rates ect. ect. ect.

racnfool
Dirt Forum Racer

Total posts: 89
posted January 18, 2005 02:30 PM  
BOAS,
So would rear steer have the same effect?

[This message has been edited by racnfool (edited January 18, 2005).]

Kromulous
Dirt Forum Champ
Total posts: 796
posted January 18, 2005 03:22 PM  
IF your "dog tracking" a car because you got 2" of trail in the rear end, then the said rear end is not at 90* to the CL of the chassis.

The CL of the chassis, is static, permanent and does not move. Unless you move some physical characteristics of it around.

Trailing the RR in essence gives you a parrellagram, Shift the front over to the left and the rear over to the right, would thoeriticlly do the same thing, while going straight.



boas51
Dirt Maniac

Total posts: 190
posted January 18, 2005 07:23 PM  
sorry i did not mean centerline of the chassis, i meant, as i also said, 90 degrees to the direction of travel. i think most understood what i was saying.
by rear steer, i assume you mean the travel of the diff due to the trailing arms swinging in arcs during body roll? roll steer? yes roll steer has a very similiar effect as statically setting the diff unsquare. except!!!! roll steer will react to braking and acceleration, as well as roll. roll steer will nor effect entry as much as statically trailing the rr, but as the car rolls and the lr moves forward it is moving the diff to the right, as compared to the direction of travel.
theoretically you are adding bite with steeper thrust angles on your trailing arms, and roll steer is a product of the steeper angles.
trailing the rr to loosen the car when on the gas, and then adding bite to help tighten off is not the way i would go. are you having a specifc problem wpp? and trailing the rr will tighten any rear heavy car on entry if you are lifting off the gas.
the tire pressure question has me confused, you are adding the same amount of air to both right side tires? to a car that is neutral, and handling well? why?
my baseline, with the g-60, on the right side started out at 12lbs. as recomended. went to 16, then 18, then 18 rf, 20-22 rr. my car gained speed everytime i went up. most of the cars i race against have half the american racer wore off the side wall, i just cant see that being good traction.
air in the right side tires will loosen the car all the way around, because you have added stagger with a bias ply tire, you have also added rf and rr spring rate.

Kromulous
Dirt Forum Champ
Total posts: 796
posted January 19, 2005 08:30 AM  
Another interesting view point.

Trailing the RR or leading the LR, in essence wouldnt that be doing the same thing, correct?

Sounds like to me, unless you need it tighter on entry, leave the rear end square in the car.

I dont run any, never have, but i have often heard of people doing this and it has been suggested to us. Although i always kinda thought of it as a patch or crutch to other issues.

Although, looks like i dont need to. I like the car to be serously loose going in.

boas51
Dirt Maniac

Total posts: 190
posted January 19, 2005 05:36 PM  
my opinion is, there is no such thing as a crutch. running with the rr trailed/lr forward, will also loosen exit.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted January 20, 2005 05:50 AM  
I have been putting a lot of thought into this lately after reading this several times. And applyng it to our car which a is a 4/z car just for4 reference. WE were trailing the RR to free the car up in the middle and off. Driver always complained about it not wanting to turn in on entry he had to turn the car. Our old 2 link car would kind of pull itslf into the corner. I can see now where trailing the RR will prob give the driver a tight or pushy feeling at the time he gets off the gas and on the brakes. because the rearend (especially on a 4 link car) is steered to the wall anyway and the driver is back steered to the right to keep the car straight. As he gets off the gas and the car settles down he still has the wheel turned to the right for an instant so the car feels tight and he feels he is having to turn the car into the corner when actually he is just catching up to the car settling and straightening the wheels to catch up. Plus while all of this is going on the rearend trail in the RR will make the rear track to the right furthur which will then try to pull the car to the right, prob more so on the brakes and depending on how much it is trailed. So up to this point I can see where it could 'tighten' the car up or at least give that feeling. Now once the car settles down and the car is through entry and rolling to the middle it would free the car up because again the rear is steered more to the wall making the rearend turn out while the driver is turning in. This would continue as the car exits the turn, just like putting a little more roll steer in with bar angles will tend to free the car up to a point due to the extra steering.

So in general I can see now why trailing the RR could tighten the car on initial entry but after that it should loosen the car through the rest of the turn.

Kromulous
Dirt Forum Champ
Total posts: 796
posted January 20, 2005 07:26 AM  
I'll agree, its not a crutch or a patch. THe adjustment is there so use it you need to, we may have to from time to time, who knows.

duece
Dirt Full Roller

Total posts: 28
posted January 22, 2005 07:25 AM  
Always run bout 1/2" trail on my dirt works,4-z or straight 4 bar.still run the trail. Won many races with this setup. Free's the car up in the center, kind of like the effect of adding stagger. But everyone is different and likes to feel differnt things with their car. Used to actually run lead and while it tightened exit (sometimes) it was very tight in the center,to the point that you would have to scrub the car to get it to turn,once added trail it was much more driveable.

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