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Author Topic:   Cross weight %
racer13
Member
posted April 05, 2002 06:23 PM
I have heard both sides! So which is right?
If I rise cross weight above 50% does that tighten or loosen the car. So if I ws at 53% would that be looser or tighter than if I was at 48%. Thanks!


BK19
Member
posted April 05, 2002 07:41 PM
i would think that you would be tighter at 53 %


sdhnc29
Member
posted April 05, 2002 10:08 PM
The higher you run your cross weight , the looser the car will be on entry into the corner due to the LR still being loaded , and the tighter it will be coming off . The less cross weight you run , you will see the opposite reaction .

------------------
Hendren Racing Engines
Rutherfordton , NC
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BK19
Member
posted April 06, 2002 03:55 AM
you are correct that is the exact thing that was going on with my car last year it was going in nice but about hitting the wall with the front of the car going out


SLEEPY GOMEZ
Member
posted April 06, 2002 11:46 PM
First the front end should be properly set up. I like 4-5 degrees caster stagger with 7-9 degrees in the right front. Maybe no more than 2 1/2 degrees camber in the right front.
Your springs must be right for your car and track and I'm not sure what you have.

Now set the cross weight to make the corner entry correct. Set whatever it takes, but use only as much cross weight as necessary.

Only when corner entry is correct can you begin to work on corner exit. Use rear tire stagger and wheel offset then to work on corner exit. More stagger will loosen the car up and keep it off the wall on exit while having little effect on entry. Extending the right rear out with wheel offset will have a similar effect but stagger is more effective. Yes, stagger wil have a small effect on cross weight. Remember, everything is a compromise on a race car. Hope this helps, SLEEPY.



racer13
Member
posted April 07, 2002 05:46 PM
Thanks for the help you guys. It is nice to fine out the right answer. Thanks


c21
Member
posted April 09, 2002 03:31 PM
Hi c21, cross weight is not affected by the strength of the springs until after the suspension begins to move. This means roll couple distribution is not affected by STATIC cross weight settings. The heaviest corner will have the most traction. Remember cross weight is a STATIC setting. As the suspension begins to move, a stiffer spring will not allow as much weight to transfer to the right front as a softer one. Thus,the cross weight could be correct allowing the car to begin its turn. But with too strong of a rt front spring, not allowing enough weight to continue transferring, there might be a push in the middle of the turn. The necessary amount of cross weight can be different for each car. Several factors of car design affect it. Left weight seems to have the biggest effect. Hope I've not confused you too much, SLEEPY


c21
Member
posted April 10, 2002 10:33 AM
I think you hit it c21 . The stiffer the spring , the faster it loads and unloads . If your RF is too stiff , regardless of cross weight % , the immediate weight transfer during the initial corner entry will be taken , and deflected . Also I think a problem with the "hobby stock push condition" ,that is often overlooked and difficult to deal with , is the below ground front roll center involved with having to use stock mount's and components .


SLEEPY GOMEZ
Member
posted April 10, 2002 10:56 PM
Hi again c21, The first paragraph you have right. Let's leave the second paragraph for a book sometime. However, in the last paragraph about the right front spring there is a problem. A heavier right front spring will NOT allow as much weight to transfer to that corner as a softer one, period. Please don't let me confuse you. SLEEPY


c21
Member
posted April 11, 2002 10:13 AM
doesn't happen


jammin
Administrator
posted April 11, 2002 11:10 AM
C21, the spring is going to compress so far to reach a certain rate that the chassis is looking for when in the turns. The centrifigal force on the car in the turns is going to require this spring rate dynamically. If your car is reaching a 900 lb spring roll resistance in the turns and your have a 700 lb spring, the car will compress that spring approx 2 or 3 inches to get to the 900 lbs. If you put a 900 lb spring on the rf, its gonna compress 1 inch to acheive that 900 lb resistance. Still getting the same weight on that spring, just different movement and roll in the car. The weight transfers yes, but your spring tension is only going to determine the amount that it rolls. The only way you can increase the weight to that specific corner is to put a taller spring in it or to decrease put a shorter spring it it. The spring rate has absolutely nothing to do with weight distribution providing they are the same height spring.

Hope this helps.

jammin


c21
Member
posted April 11, 2002 11:38 AM
Yes, it will loosen the car, but you have to remember, at the same time the front spring is compressing, the rear spring is also extending. It is more of a weight transition. The weight might transfer to the front, but the same crossweight applies. Doesn't actually change the wedge. It changes front to rear. That is unless you have something in the car that dynamically changes the crossweight, then you are in another ballgame. This situation I am speaking of is a generic setup with springs on top of the rearend. But, on entry, your still in static mode because your suspension returns to static state because your off throttle. On exit is another story.

Jammin


c21
Member
posted April 11, 2002 01:00 PM
The exact same scenario would be to change the spring rate on the right front....put your car on the scales, change the spring on the right front(same height spring) and tell me what you see.

jammin


jammin
Administrator
posted April 11, 2002 02:11 PM
The reason that this doesnt happen is simple. The numbers do change, but the actual relationship of the weights stays the same in the car, mathematically, it will always work out the same because each of the wheels changes. Upon entry, both front wheels take on more load. This is true. But in a crossweight situation, upon entry, the car gains weight on the right front because of the heavier spring, true and the left front also takes on more weight, but usually people are running a little bit lighter spring on the left front. The reason for this is that they want to keep the left rear of the car down. When weight transfers to the right front, it lightens the left rear, but your wedge is the same(more weight on right front, less weight on left rear, they equalize), will not change. Same with the numbers of the left front to right rear. These settings are what makes these cars work. Thats why you add wedge to the car to make it tighter off of the turns generally, because your putting more of the total car weight on the left rear and the right front. Either or but they both make wedge, not just the left rear.

jammin

c21
Member
posted April 11, 2002 04:08 PM
Play with the scales more and do things to your car while on the scales it will show you a few things. Such as, just jack the front weight jacks all the way up in the front, see if it makes a difference in your rear percentage. Or let them down, see if it changes, some of these are characteristics of exactly what you are talking about.


jammin


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