Roll height front vs rear (1 Viewer)

[ltoy]

Hi All,

I am building a new buggy (first one with 4 links front and rear) Been doing a ton of reading all over the Internet. I think I understand what I should be looking for for Anti-Squat Number. and I think I want a high Roll Center and a Flat Roll Axis. That Said

I don't know if I can package the Anti-Squat High Roll center in the front. How Important is it to have the Roll centers the same height Front to rear?

And How much is too much when it comes to Roll Axis Angle? and is one direction better than another?

 

[Eskimo]

Being very broad and general, it matters more (safety-wise) the faster you're gonna go. (Roll center height and roll axis angle)

How far apart are your RC heights going to be in your current proposed config? We talking 27 vs 25, or 27 vs 17?

Roll understeer would be "safer" than roll oversteer..

 

[ltoy]

Here is a screen shot of the front and rear 4 link numbers at ride height.

30 in the front vs 35 in the rear. And the Front would slope towards the rear end and the rear is flat.

I am looking for Good stability while climbing under power and good manners in off camber situations. I plan on Upper Frame link mount adjustability for Anti-Squat (proably 2 inches up and 2 inches down on both ends)



Front

Rear

 

[atl zj]

Good topic- subscribed.

When the roll axis on my rig sloped downhill toward the front of the rig, it did not want to climb vertical ledges when pointed straight on. I would always end up having to climb with one tire first, and then the other. Otherwise it felt like I was trying to overcome 2-3 times the force of gravity and would buck a little as it tried to climb any 70-80 degree face. Antisquat was in the 75% range.

30" is already what I would call a high roll center with 42s, and 35" is very high... but out of curiosity, what's in the way in the front, chassis or motor? Assuming it's a front engine design, does your front axle tuck in front of your crank pulley at full bump?

 

[ltoy]

The Rockwell chuck wants to hit the Crank pulley. I could push the front forward more but I am shooting for a 118 wheel base. and I need the rear to stay where it is so the tires will not hit the body when in full turn at full stuff.

On your rig did you change anyting but the slope of the roll axis to make it climb better?

Just for added info The Tires are 44" Boggers but at trail psi measure 42 and the Rear links mount to the top of the chunk giving me the high roll center in the back. I also may bring the Upper Link Y dimension from 25 to 20 Inches for better tire clearance in the front at full turn / full stuff. I will test that tonight or tommarow

 

[Eskimo]

On my rocks, my RC heights are 33 rear and 29 front and it's OK... but I also haven't tried running any sway bars yet, either. I get a moderate amount of body roll on off-camber sections, but the rig doesn't roll under throttle much, I'm pretty happy with that aspect.

If you're running Boggers on rockwells, I'm gonna guess and say you're a throttle-happy driver - lower AS numbers might work even better for you. FWIW, I'm at 29% front and 50% rear and love it. but, those AS numbers don't change more than 8% on the front and 5% on the rear throughout 5" up or down of travel, which is important when you're bouncing up a hill under throttle.

Here's an idea.. on the rear axle, drop the axle end uppers down to 32" from the current 35", and see how that models.. I think you'll find it stays consistent through travel, and matches the front.. and, it gets your instant center further out (I'm a big fan of that)

 

[ltoy]

I was shooting for an As of 80% at ride height at both ends. I have adjusted the lenght of the uppers to keep the AS throughout the range of travel stable. I think ranges from 86 to 89 throughout the 14 inches of rear travel. Do you think I would benifit from even lower as number ( I was planning on being able to adjust down to like 60 and up to like 100?

My front is some what locked in as far as Roll height. and the Roll axis angle is 0 with a few tweeks. I guess the biggest question is should I set the rear to a 30 inch roll center or just leave it at 35?

I am also very intrested in AS numbers that others have run high Hp and and heavy foot.

Just so we are all taking the Same AS. 0% AS = On level ground the buggy's rear body will get lower to the ground when accellerating. the only thing that will keep the suspension from total bottoming out is the resistance of the coilovers / springs.

100% AS = The rear of the buggy will remain perfectly stable when accellerating on level ground due to the fact the that torque generated as a result of the axle wanting to twist will be transfer through the links and counter act the effect of the weight transfer.

over 100% AS = The rear of the buggy will rise on accll on flat ground because the torque generated from the axle wanting to twist is overpowering the force from weight transfer causing the rear to rise.

Is my thinking correct on those points or is there an error in there some where?

 

[Eskimo]

To answer your question, I think you would like a lower AS number, as the "effective" A/S seems to rise when you point the nose uphill and hammer down.

I am using the same method of using AS numbers you are by the way.

 

[ltoy]

what effect does roll oversteer or understeer have? And how much is to much. I am playing with the number and I am having trouble keeping that axis level with my setup (I got 1 degree of oversteer in the back with the new numbers and 4 degrees in the front)