It sounds like drivers of other SXSs have no prayer of keeping them on 4 wheels. So if a Speed UTV ends up flipping was it merely because the driver messed up?
Not merely driver, but mostly driver.
Roll center is gonna be super similar on the X3 since it's parallel too:
LOL. There's a total change in track width of 15%, which corresponds to change in roll center relative to ride height. That's hardly "all over the place" and at no time does it get remotely close to the CoG of the vehicle, so not really going to see a bunch of jacking forces that will cause it to geometrically roll over like grandpa's Corvair...
I am saying the roll center moves A LOT more with radius rods than with trailing arms...Roll center is gonna be super similar on the X3 since it's parallel too:
Wildcat XX uses trailing arms. Would need to see the offset on the pivots from above to determine roll center, but assume it's close to what Robby says (2").
YXZ1000 appears close to RZR, with maybe a slightly lower RC since there's a marginal offset on the links:
LOL. There's a total change in track width of 15%, which corresponds to change in roll center relative to ride height. That's hardly "all over the place" and at no time does it get remotely close to the CoG of the vehicle, so not really going to see a bunch of jacking forces that will cause it to geometrically roll over like grandpa's Corvair...
Keep in mind that we're nearly measuring suspension travel in feet at this point. Roll centers will move. Considering the ride height of the vehicle changes by 22" during cycling, the roll center getting increased by 3" at full droop isn't chit.
Like I said: if it's so bad, why does he use that exact same geometry up front? Shouldn't he have used his "patented shocks" to control the suspension and get the geometry right instead of chasing travel numbers to lower roll centers?
That's the case for any side by side or vehicle for that matter.
15%, ish by my guesstimates. Maybe it's 30%.
I’m pretty sure I agree with what your saying. A bit over my head but sounds right to me.The video jumped around a little on the explanation. Radius rods don't cause vehicles to flip, their geometry does. Saying "our chit doesn't have geometry" (trailing arm) isn't a good explanation on why vehicles roll.
Roll centers determine how much body roll your vehicle will have, and is determined by drawing a bunch of imaginary lines. All those lines break down like this: having a higher roll center means the sprung mass has less leverage over the suspension, meaning less body roll. Like all suspension geometry, there's a tradeoff. He's correct that if the roll center is too high, you end up with jacking because the suspension geometrically binds and instead of body roll, you get the whole vehicle rolling.
But, how bad is it? For the PoPo, my MS Paint skills sorta failed me because the geometry hilariously puts the instant centers somewhere in China, and NFW I'm taking the time to model it in SW or whatever... Either way, at ride height, here's my rough guesstimate on roll center:
View attachment 41022
And here's one at full droop:
View attachment 41023
Looking at the above, I think Robby's statement on jacking isn't 100% accurate. It doesn't "go all over the place" like said in the video, but it does increase because the arms on a RZR are mostly parallel to each other. This means the roll center will increase at about the same rate the track decreases. Since the thoughts are 10" of track reduction at full droop, that's about a 15% rise in roll center beyond the normal amount of increase in ride height. This will cause the jacking forces to increase as the suspension droops, but I don't think the roll center is so egregious that there's some terminal point of jacking and you get geometrically thrown over. I think the rollover tendency has more to do with the fact that it's a tall ass car with only 64" of total width than suspension geometry.
In any case, if the roll center geometry was such a problem, why'd he use it up front?
It's the same parallel geometry that puts the instant centers in China, so he's going to have the same jacking forces and changes in roll center. Is he saying the Speed UTV will cartwheel around the front tire instead of just rolling over on its side? :biggrin:
That aside, with the 2" roll center in the rear, this means he'll have a downward sloping roll axis that increases non-linearly the more the car squats. Driving style wise, I think the Speed might be more "drifty" as a result. The RZRs and Can Ams, as we already know, understeer more and REALLY don't want to drift.
In the end, trailing arms aren't really superior for suspension, just different. No suspension geometry is perfect, since you have a gazillion competing priorities that will change the characteristics of the vehicle. Parallel links/control arms allow you to dial out bumpsteer, and give consistent CV angles so you don't need plunge. Non parallel will give you the ability to dial out jacking forces and increase grip through camber gain (like a Funco's front suspension), but you won't be able to dial out bumpsteer and driven axles will require plunge. It's all in the compromise you want and to say something is "wrong" like that it just dismissing the design goals.
Check out this clip from RG explaining roll center and geometry. Start at the 39 minute mark. I’m very interested in what your thoughts are. He explains geometry much better here. I also believe Kawasaki doesn’t have as much track width change even though it has radius rods. Speed uses trailing arms and dual plunging CVS to help. Front suspension geometry has VERY DIFFERENT REQUIREMENTS than rear suspension geometry...
I did see that video.. makes sense.. The Black One was on it's lid for 30 minutes and it cooked the motor.. weak internals for sure... Fortunately warranty covered it.. no scratches.. forgot to mention the 'slow roll'... :rofl:
Yep. But for the phenomenon of jacking, it's the same physics whether it's the front of the car or the rear since we're talking about body roll.
I've been driving The Black One and The Orange One (I know they are NOT Pro R's) both bought with less than 1 mile on them.. they run great in a straight line and can eat ANYTHING, but the body roll is significant. I had to 'save' The Orange One a few times when I ran it solo at my Mom's in Rialto.The video jumped around a little on the explanation. Radius rods don't cause vehicles to flip, their geometry does. Saying "our chit doesn't have geometry" (trailing arm) isn't a good explanation on why vehicles roll.
Roll centers determine how much body roll your vehicle will have, and is determined by drawing a bunch of imaginary lines. All those lines break down like this: having a higher roll center means the sprung mass has less leverage over the suspension, meaning less body roll. Like all suspension geometry, there's a tradeoff. He's correct that if the roll center is too high, you end up with jacking because the suspension geometrically binds and instead of body roll, you get the whole vehicle rolling.
But, how bad is it? For the PoPo, my MS Paint skills sorta failed me because the geometry hilariously puts the instant centers somewhere in China, and NFW I'm taking the time to model it in SW or whatever... Either way, at ride height, here's my rough guesstimate on roll center:
View attachment 41022
And here's one at full droop:
View attachment 41023
Looking at the above, I think Robby's statement on jacking isn't 100% accurate. It doesn't "go all over the place" like said in the video, but it does increase because the arms on a RZR are mostly parallel to each other. This means the roll center will increase at about the same rate the track decreases. Since the thoughts are 10" of track reduction at full droop, that's about a 15% rise in roll center beyond the normal amount of increase in ride height. This will cause the jacking forces to increase as the suspension droops, but I don't think the roll center is so egregious that there's some terminal point of jacking and you get geometrically thrown over. I think the rollover tendency has more to do with the fact that it's a tall ass car with only 64" of total width than suspension geometry.
In any case, if the roll center geometry was such a problem, why'd he use it up front?
It's the same parallel geometry that puts the instant centers in China, so he's going to have the same jacking forces and changes in roll center. Is he saying the Speed UTV will cartwheel around the front tire instead of just rolling over on its side? :biggrin:
That aside, with the 2" roll center in the rear, this means he'll have a downward sloping roll axis that increases non-linearly the more the car squats. Driving style wise, I think the Speed might be more "drifty" as a result. The RZRs and Can Ams, as we already know, understeer more and REALLY don't want to drift.
In the end, trailing arms aren't really superior for suspension, just different. No suspension geometry is perfect, since you have a gazillion competing priorities that will change the characteristics of the vehicle. Parallel links/control arms allow you to dial out bumpsteer, and give consistent CV angles so you don't need plunge. Non parallel will give you the ability to dial out jacking forces and increase grip through camber gain (like a Funco's front suspension), but you won't be able to dial out bumpsteer and driven axles will require plunge. It's all in the compromise you want and to say something is "wrong" like that it just dismissing the design goals.
CoG on a RZR is pretty high, and the track is narrow. Not the best to fight body roll. X3 has the same geometry, but CoG is lower (plus you sit way lower, so it "feels" better), and body roll is considerably reduced (at least to me). I've driven the 64" X3 and RZR back to back, so it's not the 72" RS model's track advantage. X3, however, has to put the gas tank in an odd spot to allow the seats to be so low...
The Canned Ham (buddy has one) is much MUCH lower COG.. trade off, he can't take the 4 seater anywhere like I can with mine.. forget rock crawling altogether, but I have to 'turn out' in G when he doesn't occasionally.
I hear you. Like all things, it depends though. :biggrin:
