(for purposes of this post, IRS=Independent Rear Suspension, specifically the double A arm type, and SRA=Solid Rear Axle)

On a recent ride with some friends, a casual conversation came up about rear ends. No, not of the female type, but of the atv type. One fella who hasn't been riding for very long, nor had very many types of machines, was shocked when I said I actually preferred an SRA machine. Seems he had bought into the "IRS is better" idea just because most utility type atv's have gone that way in recent years. Well, I didn't want to come off too strong in a casual conversation, so I just told him that I preferred SRA's mainly because of their stability and simplicity. But, in truth, I could have gone a lot farther. This is probably a better place to do that.

So if you're contemplating buying a new or used atv, you may want to consider this point....to put it bluntly, IRS machines (and specifically the double A arm type) only have two advantages over an SRA. Yep, that's right, two. The entire utility atv market is being swayed by two positives. Sounds funny, but it's sadly true.

And what are those two points you ask? Ground clearance and slow speed riding comfort. (Ok, I suppose you could argue a third being greater suspension travel, but a lot of that benefit is negated by other downsides of the design, so I don't really think it has a lot of real world value. On paper, it looks more impressive when an atv has 9" of travel, but the reality is that an atv with 6" or 7" of travel will work just as good in 99% of situations one may encounter).

The irony is that their positives actually disappear or oppose themselves when you put them to use! By design, when you load up a an IRS equipped machine with weight (rider, fuel, cargo, trailer, fluids, etc.), the advantage shrinks. And in most instances, it shrinks enough to be equal or less than the unchanging and always constant ground clearance associated with an SRA equipped atv. As for riding comfort, the faster you go (which is where impacts become harshest) the less the IRS will help. It really is only going to work best at slow speeds, and can actually hinder handling at faster speeds.

Well, so much for looking at the upsides. Now let's look at the downsides of the IRS.

Inherently, the IRS rear end is more complicated. It has more parts, and requires more maintenance. It also raises the center of gravity of the machine, and increases rollover leverage. It also adds more weight due to the more numerous parts. Well, those are the more obvious downsides. But there are some less obvious downsides that most folks don't know.
One of them is scrub. That is the sideways wear the tire feels as the suspension moves up and down in it's arc. It is unavoidable in a double A arm IRS suspension design. It wears rear tires a bit faster than an SRA design does, and it angles the contact patch of where the tire meets the ground. This is a big problem with bias ply tires, but can be negated to some noticeable degree with the addition of radial tires.
Second of the lesser known negatives is the loading of the front end of the machine on an IRS design. The geometry of an essentially "loose" rear end IRS design simply transfers more weight to the front--especially on down hill deceleration. This is why IRS machines feel very unstable in this situation. The back end gets light and squirrelly and the front gets heavier and tends to dive. This also tends to wear out front tires faster than an equivalently weighted SRA machines would.
Starting to sound like IRS may be over rated? Read on.

Let's talk about the positives of SRA. They are basically the opposites of all the negative IRS points. Simple, lightweight, low maintenance, lower roll center, less tip leverage, no scrub, no loading of front suspension, more stable at all angles front to back and side to side, constant and consistent ground clearance no matter what the load, tires last longer, and constant and centered contact patch of tires.
The downsides? A little less ground clearance (when the IRS is loaded light), and a little rougher ride over the bumpy stuff at slow speeds.

Hmmm....tough choice. But I think I'll take all the advantages of the SRA and simply stand up on the bumpy stuff if I have to! Ok, maybe I'll get stuck in deep snow a bit quicker too, but only by an inch or two. Around my neck of the woods, the snow gets deeper as you get higher in elevation, and two inches is good for about 500' extra elevation. So that means that the IRS equipped machines will just get stuck higher up on the hill about a quarter mile ahead of me and have a farther walk to the truck!

But choice is getting less and less every year I'm afraid. I'm actually quite disappointed that the atv manufacturers have basically tried to erase SRA's from their line-ups. Or, if they haven't, they only put them in their lower-end entry machines thereby implying that the design is less sophisticated and not as good as IRS. But once one does his homework, he can plainly see that SRA isn't as bad as some marketing department would have him believe! In reality, it might just be a better design for you! It certainly is for me!

 

Well, I've been on dozens of examples of both types of machines. I think it really comes down to a) What you can afford. b) What kind of terrain you're going to encounter c) What are your needs?

I messed up my back so, given the observed comfort advantage of IRS I'll keep to them. IRS just does not beat up my back like SRA's do.

I agree that the IRS is more complicated. Straight axle wins if cost and simplicity are your main concerns.

I live in New England. Not much soft sand riding, lots of rocks, roots, deep water, deep mud, deep snow, and hard pack. Not too much terrain where you can just open it up. Advantage, IRS. I don't get hung up on rocks, roots, and ruts or as stuck in mud and snow as I did with the SRA quads.

I didn't, personally, find any more compression of the front end going down hills with one axle over the other.

A lot of it also depends on which IRS quad you get. I had a Polaris Sportsman X2 with a true 400 lb. rear rating. It didn't squat much even fully loaded and with my 340 lbs. on it. In fact, it towed things with more ground clearance than the lighter SRA's. Now, if you get a normal IRS quad like a King Quad 500 you will get more squat than an SRA. Let's throw a weird one into the mix. Can-Am Outlander XT-P with air suspension. I can dial that in to be as soft as a Polaris Sportsman 500 or as stiff as the Sportsman X2. So, I can dial it in for a soft ride or a stiff ride for a passenger or heavily loaded racks. All I'm saying here is that there is a quad for everyone out there, pretty much. Some IRS quads have other suspension features that make them better for work type situations than the SRA's I've been on. Some are softer and aren't quite as good as an SRA.

On scrub.... Yes, IRS does scrub some. Not the Can-Am system where there are trailing arms that are essentially always parallel to the chassis. But, even with the normal A-arms I've been on for a couple thousand miles I didn't find it significant. These are my own observations and things I've noticed.

On the suspension travel, why do high speed desert machines have IRS? It's for that very reason. Longer suspension travel soaks up bumps better at high speed than a straight axle. I personally saw the differences firsthand when comparing my son's Polaris ATP 500 to my Sportsman X2. His was a straight axle rated for 400 lbs. Mine was an IRS rated for 400 lbs. On smooth trails they behaved about the same. He had a slight edge in power slides. I could go faster in the rough going at slow speeds and in high speed situations like whoops in soft sand. We took both machines over a whooped out section of a sand pit and did speeds from 15 to 40 mph or so. Once that straight axle got going to fast it pogoed straight up and down and became uncontrollable. I could squeeze a few more mph's out of the X2 before it behaved the same way. The only difference that mattered between the two machines is one had IRS, one had an SRA. In slow speed rock crawling, or in ruts IRS with greater suspension travel shines. It's just better to keep 4 tires planted on the ground and clawing for traction than to have one up in the air.

I'm really not disagreeing with you for the most part. It's just that my (personal and, like yours, opinionated ) observations don't see the disadvantages of IRS or advantages of SRA as sticking out like a sore thumb quite as much I guess.

It comes down to this for me: Whatever you can afford, works best for you, you are most comfortable with, and meets your needs, is what you should by. Not by my opinion or anyone else's for that matter.

 

You bring up three points that I've listed above that I would like to comment on.

Suspension travel of a desert race machine vs travel of an atv is like comparing apples and oranges. On race machines designed for jumps and high speed, they use long arm suspension with angles and anchor points that are totally different in application and geometry than what can be used on an atv. An atv is much too short and narrow to utilize that type of design, and therefore, will never attain the travel numbers that a true desert race machine will. If you want a better apples to apples example, look at sport atv's designs. ALL of them use an SRA. Why? Because of reasons I've previously listed.

Second point:
This one is so false it's amusing. I hear this one all the time too. Every time I ride at the world's ultimate rock crawling area, Moab, of which I live less than three hours away, there is always somebody touting this same old line. After watching thousands of different types of machines on the rocks there and riding them myself, I can easily tell you the best built machines that make it up the most stuff have solid rear axles. And many of them also have solid front axles! The IRS design does feel softer over the bumps, but unless you detach the sway bar on an IRS machine, it doesn't articulate any better than an SRA! Then once you take your sway bar off, have fun trying to keep up with an SRA over any kind of terrain at speed! That usually ends in an ambulance ride.
Furthermore, when you're on that off camber, steep rock, an IRS machine doesn't feel near as stable. That's because it's not. It has a higher center of gravity, and more of a tippy feeling. Also, the seat height on IRS machines is usually higher than comparable SRA machines, and that adds to the tippy feeling and higher rollover leverage.
I've been up stuff on IRS machines that made me very nervous, then walked down and got an SRA and went up and didn't even feel like it was any big deal. The IRS design easily felt twice as tippy.

Third:
Some of my post was opinion. I'll grant you that. But most of it was pure mechanical fact. To what degree you notice the effect is debatable, but the facts remain. I learned this stuff in my first mechanical engineering class I ever took. Sometimes our physical limitations and personal biases cloud the facts, but nevertheless, they remain. An elephant can still be in the room even when you turn the lights off.

Me, I have no physical limitations. I am athletic and in great shape and health. I can buy and ride anything I want. If I were riding rutted out mud pits, or riding in deep snow all the time, I'd get an IRS. If my back was bad, or if I just liked to put-put around, I'd get an IRS. If I rode with a passenger a lot, I would get a two-up IRS.

For everything else, I'd buy an SRA and never look back.

 

Found some videos that anyone considering buying an atv should watch:





This guy knows his stuff. He's built a few dune buggies and other toys too..

 

Yep, before knee injuries and a back injury I was pretty athletic also. I had fun on solid axle machines that would cause me to end up in an emergency room now.

The main usage up here is wooded trails with deep mud and water holes with tons of rocks and roots added for fun. And snow riding on groomed snowmobile trails. The main issue we had with SRA machines is they just get hung up more than the IRS machines. The machines we need to winch most often are Honda (before this model year without full lockers) and solid axle machines like Suzuki Vinsons and others. We got to the point where we got tired of constantly winching that 95% of the riders went to IRS machines. It's just what works best here. After riding both the Polaris ATP and the Polaris Sportsman X2, I can tell you without a doubt that the IRS X2 kept the wheels on the ground better than the ATP with the solid axle. Both machines had a 500, CVT, front A-arm, same tires, and same rear load rating. With the IRS X2 one tire in the rear could go down a bit before the front end would lift up. With a straight axle the left tire effected the right front end when in the ruts and rocks more than the X2. Just my own observations. You can call them false if you'd like but I'm not known to be a liar. It wasn't a huge difference. Maybe 3-4 inches or so. But, going up those rocky, rutted trails the IRS kept the tires on the ground better than the solid axle machine. I guess too each his own. As far as feeling stable, for me, the jury is out. I never felt the solid axle Xplorer I had felt any better than the Sportman 500's I've been on. Same thing with the ATP and X2. Never felt much stability difference personally. The biggest difference I've felt is riding the longer wheelbase machines like the Sportsman X2, ATP, and Can-Am Outlander Max. Nothing beats wheelbase for climbing up and down steep hills.

In the rocky places like Moab a solid rear axle machine is going to do fine. But, what you seem to be describing is Jeep sized rigs with more suspension travel built into them than a common, OEM standard equipment Jeep. I'm just going by observations on what works the best in our terrain. Rules for smooth rocky surfaces like Lions Back don't apply to a 30 degree slope littered with 1-2 foot sized rocks that are likely to get hung up, especially on a sport quad that has only a few inches of clearance.

Yep, all sport machines are now SRA. But, the Honda 700XX had an IRS rear that had as much clearance as a utility machine and oddly enough, won several desert races over the few years Honda sold them. Not sure if they still sell them or not but it was a nice bridge the gap machine that worked fairly well here with aggressive mud tires.

I honestly agree with most of your points. But, they just don't work out that way here. If I was constantly in soft sand, on mostly smooth rock, on open fire roads, and that type of terrain I'd honestly go with a SRA if my back wasn't so screwed up. They are more stable in turns, especially. But, here the machine that works best is an IRS.

To me the biggest factor is rider ability. I could throw out everything that I've said if my only observation was Jgar from here on the forums. He got his Honda 400ex into, over, and through some places I never thought I'd see a 2wd go based on all the other sport riders I've seen around Maine and New Hampshire. But, he is truly the exception. Instead of my athletic 6'3" 240 pounds I'm now quite gravitationally challenged. I can throw around a big utility machine pretty well. I wouldn't want someone who weighs 150 to try some of the things others can do on utility machines. Big, IRS machines are more dangerous in that respect. All I'm saying here is rider ability and experience go a long way towards what works best.

Random thoughts.

 

can I ask what type of ATV(s) you own Kickstart? I'm surprised TLC hasnt commented yet lol

 

Moose,

You seem to be applying what you've seen with one brand of atv to a universal attribute of all IRS/SRA atv's. But that isn't really fair to either type of rear suspension. Look at the different anchor points and geometry of the different IRS machines on the market. Also, look at the different swing arm designs of many SRA machines. Obviously, some are going to work better than others. And some will work better in only certain situations. Comparing two Polaris designs only shows a sliver of a sliver of the slice of pie. And for me, (warning-opinion ahead) Polaris isn't exactly what I'd choose to compare anything to unless I was showing how NOT to do something.

Also, I think you have the wrong idea about what you encounter at Moab. It ain't all just smooth slickrock like what is found on Lion's Back (which incidentally has been closed off for many years now). Most of Moab slickrock is bumps, steps, off-camber ramps, and other various nasties with many boulders and rocks thrown in for good measure. It is truly the acid test for any type of machine. And I've seen them all in action there, and IRS atv's are far and away the most disadvantaged machine for those situations--unless the sway bar is removed. But as I said, once you remove it, you're basically screwed for the rest of the trail if it involves any type of speed or cornering after the technical spots. The SRA machine can just keep on going.

Also, Moab just happens to sit smack dab in the middle of a little geographical phenomenon we call the Rocky Mountains. They didn't get their name for being smooth and sandy. I have thousands of miles of trails out my back door that are nothing but rock. Tires don't touch soil for hours. IRS machines do take some of that tediousness out of it, but, I still prefer an SRA for when those trails get steep and off-camber. And as I said, I can simply stand up over the worst sections, and put that shock into my knees rather than my back. I find 99% of ATV riders never unglue their butts from the seat regardless of what type of suspension they have. Then they complain about back pain and fatigue......?

As to the "hung up" comment, when I go from an IRS machine to an SRA, I don't find I get "hung up" more. The ground clearance becomes nearly the same on a trail machine once you load up the IRS. The SRA still has a axle hanging out back there that can get caught, but at least I can get used to the clearance I have because it never changes. Once I learn what rocks or logs I can clear, it's always the same. The IRS changes minute by minute as the tank empties! And any good rider can simply change his technique when he gets on an SRA machine to try to hit the large rocks with his tires instead of gapping over them. It's really not that hard to do.

In a rutted out mud pit where you can't steer and can't see what's coming, obviously an IRS will do better there. But as with mud and snow, once it's too deep, it won't matter what type of rear end you've got. And the fine line there between the two designs is maybe a couple inches. I got stuck in a snow bank just last night that no IRS machine on the planet would have worked any better than the SRA machine would. When it's too deep, it's simply too deep!

As I said earlier, the advantages of IRS are just not as big or as numerous as some believe. And it's just sad that most utility type atv's are going that way. If you truly NEED an IRS, great. But don't just buy one out of ignorance because you've heard they're better. Research it, ride a few different types, and maybe, just maybe, you might pick something different. I just hope that the choice to pick something different won't be phased out by the next great marketing dept someone hires.

 

I've had both types. But it shouldn't surprise you that my main trail riding machines these days are three SRA's. They just fit my riding style better, which is fast and technical. Frankly, comfort is way down on my list at this point in my life. Even if my back was in bad shape, a LazyBoy on wheels doesn't do me a lot of good if it's rolled end over end to the bottom of the hill!
And I certainly don't miss the maintenance of grease zirks and bushings up the **** end!

 

I was just using Polaris because that's the fairest comparison I could find. Two machines were basically identical in every way except for the rear suspension. The ATP with it's solid axle lifted tires more in the rocks than the X2. It also tended to pogo more in the whoops (rare find here to have enough sand to have whoops). The IRS tended to sway a bit more side to side, while the straight axle tended to launch the quad straight up and down. We had very good service out of our Polaris and I only traded mine in for more speed. To throw another quad in the mix, the Can-Ams have trailing arms that are independent of one another. It's kind of an odd mix of the IRS with a bit more straight up and down pogoing then other IRS quads. I noticed Doug Meyers made a quick mention of the Honda Rincon in his video. I rode one for a day. That's all my back and knees could take. I've never been on a more bricklike ride in the dozens of different machines I've been on. Just a mention.

I want to get to Moab because I do love rock crawling. I did over generalize. I've seen enough videos to know it's not tame by any standard. Hope to get out there. Still, I've climbed with just about every quad out there. But, I've only got the sometimes dry, sometimes wet, sometimes wet and slimy rocks here. Probably not on the scale of Moab from what I've seen but equally challenging. You guys have ruts between rocks. Ours are mostly eroded wet clay. All fun!

If it was just my back I'd do a lot more standing to soak up the rough bumps but my knees are messed up too. I can't do it all day anymore. Still searching for solutions after 10 years... On smooth roads I can hang off one side of the quad, pushing my weight to the front, and goosing the throttle to rip around corners in a powerslide. Just not for too long anymore.

I'm not saying EVERY SRA gets hung up on EVERY rock more than an IRS, just scrapes more often than I like and we had to stop more often to rethink a line or lift a machine over an obstacle. Big, huge difference? Nope. But more stopping than we liked. I like having the clearance to clear the minor obstacles without having to have a tire up on them to increase usable ground clearance. Then, when the trail gets worse I still have the option of using the rocks' height to get through.

From what we're saying here I think we're both mature (semi in my case ) buyers who have a good grip on what we need and what works in our areas. It's too bad that SRA's are going away. If Honda is the only maker with a 4wd SRA it's kind of bad in my mind. They just don't have the power that some of the other maker's are putting out. As I said earlier, I went from the Polaris Sportsman X2 to the Outlander. Both are two rider machines that I can have a passenger and a big cargo box for the long excursions where my wife likes to tag along. I really, really, really liked the X2. With the dump box that changed to a passenger seat it was the most versatile machine out there. But, with the 500 I was being left behind, especially on snow rides where the snow robs so much of the power. When I had the cash to upgrade I just could not find an X2 with anything bigger than a 550. With the Outlander Max 650 I have no trouble keeping up with anybody.

 

I do plenty of fast and plenty of technical riding. If I didn't have the quad I couldn't really get way out into the outdoors like I used to hunting and hiking. So, I'm happy with my fast LazyBoy on wheels. And, get this, the only time I rolled any quad was going on a trail we discovered later was a motocross trail that the signs were gone. (It was my Trail of Death day). My son and I got to a steep downhill off camber spot where the right track was almost a foot and a half higher than the left track. We had gone through miles of rough trail and decided to keep going rather than go back the way we came. I stood with both feet in the right footwell holding on to the X2's dumpbox and the right hand grip. Was almost through when a rock sticking up a couple inches was enough to get the whole package to go over. I got thrown downhill, almost into a swamp and turned around thinking I'd see the quad following me down the hill. By the grace of God the dump box got caught on a pine tree, so it didn't follow me down. Took some interesting winching to get my machine upright and we both stood on the right side and got through the section. We did the same with his solid axle ATP. Even with both of us in the footwell it was close to going over. Scary day. Right after that a lightening bolt hit the trail about 500 feet away.... Other than that we've never had a flip over. Come close a few times though.