Whats more important - Weight Balance or Exit Angle?

[MNC]

...After much reasearch when I did mine I found the general concensus for COG was top bell housing bolt height from ground.

Interesting, im guessing this is approx 40" (my truck still at my brother in laws) which would give me 105% Anti-squat. Not too bad...

[niblik]

Suspension Geometry:
Upper Links x y z
Frame End 20.00 17.70 28.00 in
Axle End -1.00 2.40 26.80 in
Lower Links x y z
Frame End 40.00 18.60 20.50 in
Axle End 1.00 21.20 15.00 in

sorry about figures, my print screen's playin up..



Static Anti-Squat 71 %


i made some adjustments to what ya had guy.. lowered the chassis end of your bottom arms by a bit and lifted the bottom axle end by a touch, plus bought it in fornt of your axle line slightly.. top arm i bought it into the chassis rail more and in a tad, shortened it slightly.. anti squat of 71% now..

play round with these figures, adjust certain heights of links to adjust anti squat.. unfortunately a few changes might have to happen dude, but overall, ya not far from it guy..

[MNC]

...i made some adjustments to what ya had guy.. lowered the chassis end of your bottom arms by a bit and lifted the bottom axle end by a touch, plus bought it in fornt of your axle line slightly.. top arm i bought it into the chassis rail more and in a tad, shortened it slightly.. anti squat of 71% now..

play round with these figures, adjust certain heights of links to adjust anti squat.. unfortunately a few changes might have to happen dude, but overall, ya not far from it guy..

OK, so 71% would be better than 100%?

Looks like the main impact is from flattening out that bottom arm. Its not a bad idea really as it will also get that bush up currently under the diff up higher improving clearance also...

[darinz]

The biggest thing I think is your upper arms are too short! You should be aiming for 70% minimum of the lower links. The greater the travel the closer the lengths need to be.
The problem will be the pinion abgle change that may cause driveshaft problems. (depending on travel)
I'd cylce the calculator and see what sort of pinion change you get before you weld too much.

[MNC]

The biggest thing I think is your upper arms are too short! You should be aiming for 70% minimum of the lower links. The greater the travel the closer the lengths need to be.
The problem will be the pinion abgle change that may cause driveshaft problems. (depending on travel)
I'd cylce the calculator and see what sort of pinion change you get before you weld too much.

Thanks for the comments...

My top arms are 720mm long vs bottom arms are 1000mm - thats 72%. Do you mean they don't extent far enough down the chassis?

Articles I read stated top arms should be between 70-75% of the bottom arm lengths so at 72% I'm at the mid point.

Have checked my setup and it gives 'Pinion Change' at 0.00 degrees (listed in yellow box at top right hand side). Is this the best place to confirm this?

I'm not really following what you mean by the above comments ( not surprising really as only two days ago I had no idea how to use the calculator) - do you have any suggested changes? .

From the first lot of calculations listed I intend to:
1. Drop the diff mounts for the upper links approx 30mm. Makes top links flat.
2. Raise and move the lower link diff mounts to the front face of the housing (raises back of lower arms approx 60mm).
3. Drop the chassis mounts of the lower links 30mm.

These changes reduce Anti-squat to 79% - which should be better from what I'm being told.

Hopefully might get a bit more out of those adjustments but I expect AS to be between 70 - 79% once done. From what I can see I shouldn't have any major issues with that level of AS - correct?

Cheers,

[suzolla]

Hi,
I think what Darin is getting at about the length of the top arms is that even though thay are 72% of the bottom arms in length, because they appear to be on about a 45 deg angle (in plan view) their effective longitudinal length is only about 50% of the bottom arms.
I don't know much about the calculator (will do soon as will be going through the same exersize when I put some 80 series axles under my Surf) but the pinion angle change is dependent on the ratio of the top and bottom arm lonitudinal lengths.

Hope that makes sense.

Cheers
Tim

[darinz]

What Tim says basically.


If you look at the 'pinion change' field then look below that there is the ability to move the axle up and down and see what that does to the AS, pinion angle etc. There are 2 buttons, bump and droop that control this.

All I'm saying is use these control and check to see what the pinion change is. 'If' it is too much then you'll need to increase the length of the top arms.

Also the length of the arms we are talking about is measured from the mounting point on the diff to the mounting point on the chassis and parallel to the chassis rail. (like above)

So I'm, not saying what you have done is wrong, I'm saying the tools are there to check it BEFORE you weld it up.

[MNC]

...Also the length of the arms we are talking about is measured from the mounting point on the diff to the mounting point on the chassis and parallel to the chassis rail. (like above)...

Ahhhh, I missed this 70% distance in a straight line from the diff thing completely - FARK!

What is an acceptable degree of angle change for the pinion?

A quick play is showing:
With a 6" Bump I get 6.78 degrees pinion change,
With a 8" Droop I get 3.32 degrees pinion change,

[darinz]

Tough one to answer.
Again there aren't many hard and fast rule as there are so many variables.
With pinion angle change there are a few things to consider. In an ideal world you want the flanges on the diff and the T-case to be parallel. Pinion angle change means at different points in the cycle they will be. The reason for this is about the change in speed as a uj is moves at an angle. In a straight line the is no movement and so no change in speed. When the angle is big then the change is speed is huge so causes vibration. Having the flanges parallel means they 2 uj cancell each other out and reduce the vibes.
Now some pinion change caused by shorter upper arms is good as it points the pinion towards the t-case on droop and compression and so reduces the some of the extreme angle and delays UJ bind. BUT too much and then there will be vibes as the angles will be too different being the 2 uj's.
So that is a whole lot of theory that in most cases is a load of crap. (Sorry).

All the stuff I've read points towards less than 6* 'should' be ok. I'm designing less than 6* into mine and that is with far far more travel than you have. I think you should try for less angle if you can but that does mean a huge amount of work so you have a choice. The risk is at bump you will have vibes. Droop looks OK. At ride it should be sweet as assuming flages are parrellel.

Like has been said a few times in this thread. There is a whole lot of science and whole lot of black art in this at not many rules that are 100%.
I'd suggest you make sure you are in the 70 to 75* range adn it should be OK.

To show how hard this is, to get less than 6* on mine I have upper arms at 90* of the lowers but I am talking almost double the travel you have and lower arms that are 1300mm long.

PS I'd also be looking at close 100% AS BUT that is a personal thing. The adjustments in mine will allow from about 85* to 100* variation.