DTSFab.com (Desert, Trail and Sand)
UTV's Off Road ( RZR, YXZ, Mini Buggy, Carts,etc.) => UTV Chassis and Suspension => Topic started by: Engineer on January 14, 2009, 08:54:34 PM
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Ok, someone school me on how the anti-dive principle works.
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Ok, someone school me on how the anti-dive principle works.
It is simple, shake your head back and forth abruptly, then smack it on the wall a few times, by then you should have forgoten about it all together, go back to designing a buggy...Hope that helps... ;D
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Personally I swim against the stream on this so I'll stay out while others tell you why you don't want it. I'll chime in later.
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Swim all you want, i wont tell you you wont want it, I'm only telling you your wasting your time... ;D I personally see no way at all your gonna anti dive 20"+ of plush travel in the sand and no front brakes...
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*clears throat. adjusts monocle with pinky extended*
As "rake" introduces more dive under brakes one can angle parallel arms so they have negative rake and get the opposite effect. BUT (yes fab) and it's a big but (bug sit back down) it prevents weight transfer to the front which is quite undesirable.
Now to use this principle in practice we only want to add a "little bit" of anti-dive so we can keep our suspension softer for better grip and not hit the bump stops when braking heavily. We only want a little so we still get weight transfer and the grip it provides.
To my understanding to do this you start with a previously tested amount of rake and then, when looking from the side, angle the top arm back towards parallel, how much you angle it must be tested and the difficulty of having a fully adjustable front end to test is where I think bug is quite rightly coming from.
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"Sand" is not a religion....
Prior to this I was willing to forgive your condescending uptight bs attitude, but this! This is over the top!
Wanker.
(Oh, alright, if you promise never to speak such foul words again, I might still like you.... :-*)
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Hmmmm assuming 20" of travel won't this bring about quite a bit of caster change? And how is it different than just reducing rake?
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Hmmmm assuming 20" of travel won't this bring about quite a bit of caster change? And how is it different than just reducing rake?
Basic principle is simple, when you grab the front brake, the caliper locks onto the disc and tries to rotate the spindle forward, pulling the front end down. By putting less rake in the upper a-arm only, the top of the spindle is rotated back as it cycles, canceling out the diving effect. The more upper a-arm rake you have, the less dive you get.....
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would not some dive be good to transfer weight for better stopping?
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would not some dive be good to transfer weight for better stopping?
I prefer dive for that reason.
Antidive was designed for street cars with heavy motors in the front to keep the front end from slamming to the ground under braking, I don't see any use for it in sandrails.........
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Yep you get castor change for free ;D not that it's a good thing. and it will mess with bumpsteer... everything's a compromise :police:
The idea is that you get all the benefits of rake without so much dive.
In the blessed Sand with no front brakes I would guess there would only be room for relatively little anti-dive and the amount I'm suggesting for a racing buggy would be relatively small in the first place.
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Thanks Yoshi.
Without front brakes, it will do nothing but make you caster change through the travel.
With front brakes, The brakes try to force the caster change which in turn trys to lift the front of the car, counteracting the brake dive.
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In the blessed Sand with no front brakes I would guess there would only be room for relatively little anti-dive and the amount I'm suggesting for a racing buggy would be relatively small in the first place.
With no front brakes, there would not be anti dive no matter how you set it up. The torque on the spindles that the brake creates is what makes it work.
5:
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I have fronts.
How can it be a sand rail with front brakes? No matter how much you polish them, they're unclean!
I sure hope the engine is mounted so far back it wheelies at idle or you'll surely be excommunicated!!
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I am collecting aluminum cans to have them. The retro fit kit comes with a free exorcism, so it's all good.
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Thanks Yoshi.
Without front brakes, it will do nothing but make you caster change through the travel.
With front brakes, The brakes try to force the caster change which in turn trys to lift the front of the car, counteracting the brake dive.
correct. If you don't plan on running front brakes, antidive design will do nothing, as dive is only prompted by front brakes, and requires front brakes to counter the effect...
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could not dive be also prompted by weight transfer? would not momentum transfer the force forward with rear breaks only?
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With no front brakes, there would not be anti dive no matter how you set it up. The torque on the spindles that the brake creates is what makes it work.
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so a buggy wont dive at all with only rear brakes? mine does :-[
or if you like, rear only brakes cause no weight transfer?
Weight transfer causes (is the bigger component of) dive. the mentioned spindle torque causes more weight transfer.... I think ;D
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I would say that the rear brake could induce some dive, just like acceleration lifts the front end. But not nearly to the extent that front brakes would.
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but the dive from rear breaks only cannot be counter-acted with a corresponding mechanical force on the spindals as the anti-dive requires front breaks? - Correct?
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I would say that the rear brake could induce some dive, just like acceleration lifts the front end. But not nearly to the extent that front brakes would.
Correct :police:
it also reduces the lift aka anti-lift ;D
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Yes, rear brakes will induce dive on the front end due to the torque the caliper exerts on the frame. Adding anti dive to the front will not help without front brakes because there is no caliper to put torque into the front control arms, which would essentially keep the front end level.
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so a buggy wont dive at all with only rear brakes? mine does :-[
or if you like, rear only brakes cause no weight transfer?
Weight transfer causes (is the bigger component of) dive. the mentioned spindle torque causes more weight transfer.... I think ;D
Listen up boy! I said with no front brakes you would not have ANTI-DIVE. The anti-dive is created from the torque of the brake acting on the spindle, and the spindle working on the A-arm's.
What I am saying is you can angle the upper arm however you like, but with no front brakes, it will not affect dive.
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but the dive from rear breaks only cannot be counter-acted with a corresponding mechanical force on the spindals as the anti-dive requires front breaks? - Correct?
not in my opinion.
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Listen up boy! I said with no front brakes you would not have ANTI-DIVE.
you did, my mistake :-*
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not in my opinion.
Which I just changed after I thought about better what Yoshi/Eng said ;)
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but the dive from rear breaks only cannot be counter-acted with a corresponding mechanical force on the spindals as the anti-dive requires front breaks? - Correct?
Correct......
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It's been fun.... One less thing to worry about designing into my rail with no front brakes. ;D ;D
Ok Fabr let's have your $.02.
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What kind of sand rails are you running that you are worried about anti-dive? Its sand and it does not work like a street car. You can always make a car ride better but I think some people put too much into trying to get as technical as they can on a sand rail.
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*clears throat. adjusts monocle with pinky extended*
As "rake" introduces more dive under brakes one can angle parallel arms so they have negative rake and get the opposite effect. BUT (yes fab) and it's a big but (bug sit back down) it prevents weight transfer to the front which is quite undesirable.
Now to use this principle in practice we only want to add a "little bit" of anti-dive so we can keep our suspension softer for better grip and not hit the bump stops when braking heavily. We only want a little so we still get weight transfer and the grip it provides.
To my understanding to do this you start with a previously tested amount of rake and then, when looking from the side, angle the top arm back towards parallel, how much you angle it must be tested and the difficulty of having a fully adjustable front end to test is where I think bug is quite rightly coming from.
You gotta explain that to me.I've seen it many times and do not agree.If it is applying a force that resists dive then the stiffening of the front on braking will result in a more firm planting of the front tire upon application of the brakes.If what you are saying is that no dive allows the nose to drop and transfer weight that way I'll agree but do not see that as desirable.Therefore I maintain antidive ,at least to some balanced degree,IS needed.
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could not dive be also prompted by weight transfer? would not momentum transfer the force forward with rear breaks only?
Yes but that has nothing to do with anti-dive as it relates to front geometry WITH front brakes.
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What kind of sand rails are you running that you are worried about anti-dive? Its sand and it does not work like a street car. You can always make a car ride better but I think some people put too much into trying to get as technical as they can on a sand rail.
Wanna explain that? The principles ARE the same and those principles don't give a rats ass about whether there's sand beneath the tires. It's just as easy to design with or without antidive as it is to "skip" because "it's the sand and it doesn't matter". Bottom line is no brakes =no antidive. Front brakes = anti-dive is good. The car I'm doing now has none designed in. First time without.I'll likely hate it.
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So, as i dozed off to sleep, the discussion on torque on spindles got me to thinking.
If the mechanical forces of braking can be applied to stop dive under breaking, can the same forces - torque - be applied under acceleration to create weight transfer?
Now, if the answer to that is yes can it be accomplished with a rear trailing arm design or does it require rear A arms or five link to allow for the multiple pivot points / radius movement?
Finally, if all this is occurring, it would seem that the suspension, especially one with 15 - 20" of travel would be working hard against the force of the anti dive and or transfer? In effect negating some of the benefit in an off road application vs street car application as the travel / suspension design is more? That is, with five inches of travel, you would "notice" 1 inch of dive (20% of stroke) much more than with 20" (5% of stroke.)
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Fabber, did you design anti dive into the BBQ car?
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So, as i dozed off to sleep, the discussion on torque on spindles got me to thinking.
If the mechanical forces of braking can be applied to stop dive under breaking, can the same forces - torque - be applied under acceleration to create weight transfer?
Now, if the answer to that is yes can it be accomplished with a rear trailing arm design or does it require rear A arms or five link to allow for the multiple pivot points / radius movement?
Finally, if all this is occurring, it would seem that the suspension, especially one with 15 - 20" of travel would be working hard against the force of the anti dive and or transfer? In effect negating some of the benefit in an off road application vs street car application as the travel / suspension design is more? That is, with five inches of travel, you would "notice" 1 inch of dive (20% of stroke) much more than with 20" (5% of stroke.)
It requires a solid rear axle to get the torque reaction through the suspension links.That is exactly how a 4 link rear suspension works and depending on the links length and relative mounting points you can vary the reaction from nearly none to severe. On my drag car I would set it to carry the front wheels about 2" off the ground for 60-100' on launch smooth as glass BUT if I was just wanting to screw around and have wheelie fun I could make a quick one hole adjustment to the top link and pull the front so high you could literally walk under the front wheels.
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Yes I did.
Note to self: Fabber has personal experience, Dont doubt his knowledge on anti Dive... :)
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If the mechanical forces of braking can be applied to stop dive under breaking, can the same forces - torque - be applied under acceleration to create weight transfer?
Yes. And they are. I like to look at it as the pinion gear climing the ring gear. The tires are resisting movement, and that resistance causes a twisting motion on the rear end (car) / Tranny housing (IFS). This is why when you hit the gas the front end lifts, and when you hit the brakes the front end falls.
Now, if the answer to that is yes can it be accomplished with a rear trailing arm design or does it require rear A arms or five link to allow for the multiple pivot points / radius movement?
This is where it gets trickier. With a IRS design, the acceleration has no (read very little) affect on the suspension, because there is no torque applied to the hub (5-link) or trailing arm. On a IRS the ring and pinion is in a case connected solidly to the frame. When acceleration or deceleration is applied, it puts that torque directly into the frame. (Lift or dive).
Now when it comes to braking there can be more consequences. If the brakes are inboard, they work directly on the frame just like the ring and pinion on an IRS. If the brakes are outboard, now it depends if your a 5-link or trailing arm. On a trailing arm with outboard brakes, braking action will try to push the front of the trailing arm down. It will try to compress the suspension. It can be argued whether this is good or bad, but the point is some of the torque will compress the suspension, and that in turn will cause some dive.
If you have a 5-link with inboard brakes, then braking force is not induced into the rear suspension. If you have outboard brakes, then it is and can cause multiple affects depending on the 5-link geometry. If the 5-link is "parallel" then the affect will be similar to having the brakes inboard, except that when applied the forces on the 5-link will cause it to "tighten" because of the forces induced and friction. That being said, depending if the 5-link arms are above or below horizontal, when braking force is applied , it will try to bring them to horizontal. Think about pulling on a rope, it straightens. When the tire is trying to hold the car back, it is going to try to straighten the link mounting points.
If the 5-link is not parrallel with outboard brakes, depending on the geometry, it could cause the rear to squat under braking or it could cause it to lift. It will occur from the torque on the rear carrier and its motion relative to the frame. Similar to how the anti-dive works.
Finally, if all this is occurring, it would seem that the suspension, especially one with 15 - 20" of travel would be working hard against the force of the anti dive and or transfer? In effect negating some of the benefit in an off road application vs street car application as the travel / suspension design is more? That is, with five inches of travel, you would "notice" 1 inch of dive (20% of stroke) much more than with 20" (5% of stroke.)
First, the problem with all these ideas with reference to a suspension that travels 15-20" is that we want anti-dive to work, we want camber to work, etc. But they are really needed in a smaller part of the travel. However if you build it in for that part of the travel it will have affects throughout the whole travel. If you build in anti-dive, it means that you will lose caster the further the suspension travels. This in turn makes it difficult to control bumpsteer. Camber change is good, but where is it needed? Probably a few inches from ride heigth, but we have to limit how much is put in at a few inches from ride heigth, or it will get plum crazy at full bump and full droop.
I believe you are somewhat correct with you analogy to the street car, however their spring rate is much more sever, with only 5" of travel. We want our buggy's to ride nice over the chop, so the spring rate is much softer in comparison to the weight, and that allows things like acceleration and brake dive to have a bigger affect.
Hope it helps...... Tell me what to clarify.
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Good in depth explanation.
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I think antidive is fine for vehicles heavy in the nose with very little travel, light front ends with long travel just have too many disadvantages in changes as the suspension cycles,...IMO
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Hope it helps...... Tell me what to clarify.
Wow, thanks for all that. I think I get it.
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Antidive is one of those things that can be a little ,none or a lot designed in.It's how you balance the pro and cons that matters for the particular car.
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Engineer, are you ready to wrap your head around the next set of geometry puzzles?
Tilting the upper arm mounts more than the lower introduces anti-dive which is bascially caster gain on compression. That also means caster loss on droop. Coming in nose down at an angle with zero caster will suck.
Another way to introduce anti dive is to mount the front of the upper A-arms closer together than the rear. From the side of the buggy, the upper and lower arms are at at the same angle. When viewed from above, they are not. When that upper arm moves from straight out upward, the ball joint moves back due to the rake and due to the angle viewed from above. When moved from straight out down, the angle when viewed from above would also cause the ball joint to be moved back. It will be offset by the rake angle though. With a large angle when viewed from above, you would have caster gain on compression and caster gain on droop. So you get your anti brake dive without having zero caster at full droop. You would want the cross over point to be at ride height. It complicates bump steer further. I still got mine down to .1 degree and .3 degrees on 2 setups I did though.
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Anti-squat was brought up a bit. There is another way to introduce some anti-squat in IRS. If you have ever driven a front wheel drive with bad torque steer, you have felt the effect. A bent CV will resist changing it's shape with torque being applied to it. If the shafts angle forward, they will induce a downward force as the shaft is rotating. If they angle back like on a lot of VW rails with extended arms, they will pull up on the arms. It has to do with rotation, not torque twisting on the suspension. So acceleration and braking have the same effect. That is with inboard brakes.
A front wheel drive car with two different length axles will apply more downward force to one tire than the other causing torque steer.
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Engineer, are you ready to wrap your head around the next set of geometry puzzles?
Tilting the upper arm mounts more than the lower introduces anti-dive which is bascially caster gain on compression. That also means caster loss on droop. Coming in nose down at an angle with zero caster will suck.
Another way to introduce anti dive is to mount the front of the upper A-arms closer together than the rear. From the side of the buggy, the upper and lower arms are at at the same angle. When viewed from above, they are not. When that upper arm moves from straight out upward, the ball joint moves back due to the rake and due to the angle viewed from above. When moved from straight out down, the angle when viewed from above would also cause the ball joint to be moved back. It will be offset by the rake angle though. With a large angle when viewed from above, you would have caster gain on compression and caster gain on droop. So you get your anti brake dive without having zero caster at full droop. You would want the cross over point to be at ride height. It complicates bump steer further. I still got mine down to .1 degree and .3 degrees on 2 setups I did though.
I think I know where you are headed here. We are gonna have to start drawing pictures to be sure. ;D I don't know if you are suggesting angling one arm a little bit to get the affect, or are you talking about a suspension that has both arms at an angle as viewed from the top? Someone was going to coin a term for that when the rear A-arm mounts are wider than the front.
I have seen many cars built with the arms angled front to rear with two basic senario's.
The first is when the front mounts are a few inches apart, and the rear mounts are back on the sides of the car, allowing the driver's and passenger's feet to be in between the A-arms, and making for a more compact design. It became real popular when they started building 4-seaters while trying to keep the wheelbase down.
The second is when the frame is tapered from front to rear, and the A-arms are mounted to the outside of the frame rails, causing them to be angled front to rear. In this case the angle is usually less. This design allows for feet in the middle, but makes for short arms.
WARNING, an opion is about to follow:
I don't have a problem with anyone building a car how they want, but with the first scenario above, most designs like this are knock off's of what someone else has done. If you keep the arms almost parallel, mabey build in some caster at the spindle, you can get away with a lot, and still have a good working car. But if you start figuring what the suspension is doing, going in and out of rake, etc. It gets very complex very fast. Caster and Camber change become interrelated.
Sorry I have gotten off topic.
LiveWire, I see what you are saying, and I see how it could be better than tilting the arm....... I have to think about it some more........ Specially when I decide to run front brakes. ;D ;D
Still waiting for someone to coin that term!
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. I don't know if you are suggesting angling one arm a little bit to get the affect, or are you talking about a suspension that has both arms at an angle as viewed from the top?
just angeling the top, the bottom would stay parallel to the chassis.....
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Engineer, are you ready to wrap your head around the next set of geometry puzzles?
Tilting the upper arm mounts more than the lower introduces anti-dive which is bascially caster gain on compression. That also means caster loss on droop. Coming in nose down at an angle with zero caster will suck.
Another way to introduce anti dive is to mount the front of the upper A-arms closer together than the rear. From the side of the buggy, the upper and lower arms are at at the same angle. When viewed from above, they are not. When that upper arm moves from straight out upward, the ball joint moves back due to the rake and due to the angle viewed from above. When moved from straight out down, the angle when viewed from above would also cause the ball joint to be moved back. It will be offset by the rake angle though. With a large angle when viewed from above, you would have caster gain on compression and caster gain on droop. So you get your anti brake dive without having zero caster at full droop. You would want the cross over point to be at ride height. It complicates bump steer further. I still got mine down to .1 degree and .3 degrees on 2 setups I did though.
I guess the problem that I see is you get additional positive caster, above and below when the arm is sticking straight out from the frame. The braking force is going to try to force the spindle to the smallest caster location. That location is where the arms are sticking straight out from the frame. On all of my designs the arm is sticking straight out when you are about 4"-6" from full compression. So in that case, the braking force would want to cause dive, becaue the location it is seeking is 8" below ride heigth.
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just angeling the top, the bottom would stay parallel to the chassis.....
Right.
The cars with both upper and lower arms angled greatly, the wheels move back as the arms drop. That means when landing nose down on one wheel, the wheel has to go forward and up when being shoved back and up. So I believe it will tend to bind. It is a very copied design.
I guess the problem that I see is you get additional positive caster, above and below when the arm is sticking straight out from the frame. The braking force is going to try to force the spindle to the smallest caster location. That location is where the arms are sticking straight out from the frame. On all of my designs the arm is sticking straight out when you are about 4"-6" from full compression. So in that case, the braking force would want to cause dive, becaue the location it is seeking is 8" below ride heigth.
If the arm is also higher in the front, then it shifts the cross over point lower in the travel. It won't really be when they are straight out, but somewhere lower than that.
As for the terms, here are some thoughts: Trailing arm is pivot point lateral across frame. Leading arms would be lateral also with the arm facing forward. Semi trailing-pivot has a slight angle. A-arms are longitudinal pivots. So semi-longitudinal or partial-leading?
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How about just something simple like----screwy?
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As for the terms, here are some thoughts: Trailing arm is pivot point lateral across frame. Leading arms would be lateral also with the arm facing forward. Semi trailing-pivot has a slight angle. A-arms are longitudinal pivots. So semi-longitudinal or partial-leading?
How about just something simple like----screwy?
Screwy I can remember......