I have a question about IRS suspension

"BATC42" (BATC42) 11/20/2014 at 08:42 • Filed to: None

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Why do you guys make such a big deal out of it ? I'm ignorant about the American car market so that may be why. And AFAIK, quite the majority of the cars sold in Europe feature an IRS.

(I figured a new Mustang was an appropriate picture).

DipodomysDeserti > BATC42 11/20/2014 at 08:48

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The vast majority of cars sold in the US also feature an IRS. The regular Mustangs did not up until this year. That's why people made a big deal about it.

Mattbob > BATC42 11/20/2014 at 08:48

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it works better than a solid rear end for car applications. What exactly do you mean "make a big deal" of? In the mustang, I think most of the controversy was the whole "tradition" of the mustang having a solid rear axle. Like a corvette having to have round tail lights. It was dumb.

But IRS tends to cost more, and people say you can't put as much power down, but I think that latter point is kind of bullshit at this point.

mazda616 > BATC42 11/20/2014 at 08:48

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I'm not sure if IRS itself is such a big deal or the fact that the Mustang was one of the few passenger cars remaining that didn't feature it.

KirkyV > BATC42 11/20/2014 at 08:49

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It's all about the torsion bar, bro.

TwinCharged - Is Now UK Opponaut > BATC42 11/20/2014 at 08:49

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I think it's because the Mustang never got IRS until now. Throughout its entire life until recently, it had a live rear axle. Which can get pretty lively...

itschrome > BATC42 11/20/2014 at 08:53

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People believe you can;t push as much power or get as much traction. IE they don't think it's good for drag racing, which is apparently all people here care about..

Nibbles > BATC42 11/20/2014 at 08:55

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Well an IRS suspension would probably cause some issues with social security payments, which is a big deal to the olds

BATC42 > Mattbob 11/20/2014 at 08:57

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I knew about all big deal it was for the Mustang, but I didn't understand why someone was making a big deal of a car gaving an IRS on the Scion iM article.

Party-vi > Mattbob 11/20/2014 at 08:59

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From a ALMS and Rolex driver, a live axle is apparently more predictable at the track and easier to service.

SidewaysOnDirt still misses Bowie > BATC42 11/20/2014 at 09:00

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Apart from trucks, IRS should be standard and with a few exceptions, it is and has been for probably about 20-25 years. The Mustang has been the most glaring exception, and for no reason other than Ford being cheap. It's especially bad because Ford insists on pretending that it's a sports car and has managed to convince most of the American public of this.

EL_ULY > BATC42 11/20/2014 at 09:01

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the early 2000's SVT Cobra has IRS but many people went back to solid because racecar!!! Well, mostly drag racing. For 900-1500 HP budget speed machines, a classic solid rear end just made more sense. The Boss 302 Mustang held it's own with the likes of the e90 M3. It's not as bad as 13 year old Youtube commentors make it seem lol :]

It's like the whole Corvette leaf spring hubbub. It beats supercars around the track and at the same time, the technology was found in Triumps, Volvo, and other non american vehicles.

All childish judgement aside, when it's about performance, it's about the numbers. Those system had the number since forever.

OPPOsaurus WRX > BATC42 11/20/2014 at 09:05

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I think solid rear axles were favored at the drag strip for being stronger and giving better straight line performance but I dont think thats really what people look at any more. Its all about the 'ring now but the old timers got sand in their mullets and cried.

njp1589 > BATC42 11/20/2014 at 09:06

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A lot of compact cars use a torsion beam system for the rear suspension, which could be viewed as not "true" IRS. I guess they figure it's a big deal if a thrifty automaker like Toyota went with a true IRS.

I may be completely wrong on this though.

Mattbob > Party-vi 11/20/2014 at 09:06

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I could see that, as a track doesnt have pot holes. Definitely more serviceable too. For the road though, I would want a IRS.

crowmolly > itschrome 11/20/2014 at 09:06

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Huh? I'll bet there's one drag racing post on here for every 25 rally posts and 50 F1 posts. Even then the comments are probably half filled with hate on the NHRA or whatever.

These days modern IRS setups can hold a formidable amount of power. I do not know if I would really trust one in an 8 second drag car though.

itschrome > crowmolly 11/20/2014 at 09:10

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Oh sorry, I meant here to mean america not the amazing micro culture of OPPO! :)

Viggen > BATC42 11/20/2014 at 09:15

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We didn't. Jeremy Clarkson did, and then fanboys started screaming so the world knew.

DoYouEvenShift > BATC42 11/20/2014 at 09:21

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Main reason its a big deal, is that its relatively new for alot of our cars. Camaro got it 2010, Mustang this year, although there were a few Cobras that had it in limited production in the the early 2000s. Corvette got it 63, so no biggie there.

Not as many cars as you would think have IRS either. Especially FWD cars. Alot of them, even new cars use torsion beam rear suspension.

Distraxi's idea of perfection is a Jagroen > BATC42 11/20/2014 at 09:23

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Live axles have more unsprung weight than IRS, so they give worse wheel control and ride on bumpy surfaces. Also, there's no ability to vary camber (either statically or dynamically), so often cornering grip isn't so good. Plus they don't package very well - you need to allow space for the diff to bounce up and down.

Against that, they always keep the wheels parallel with each other, so you maintain a good contact patch under squat and dive. And they're cheaper than most IRS setups, although that's a less valid argument once you move away from cart springs and add in all the linkages you need to properly control a live axle.

What this means in practice is IRS is better for real world driving, has pros and cons on the track (arguably better grip but less linear behaviour), and is worse on the drag strip.

In Europe IRS is so dead nobody even bothers mentioning it, largely because of windier roads, smaller lighter cars (so live axle has more impact on ride and space), and no tradition of drag racing. Also there are no cheap RWD cars in Europe to speak of, so the cost argument doesn't matter. I don't even think you've been able to buy a new live axle car in Europe for years, with the exception of US imports and oddballs like Morgan and Caterham.

In the US, the move to IRS has been slower, because big cars, RWD, and drag racing are more popular. So it's still fresh enough in the memory that car makers feel the need to point out to the less onto-it among their customers that they have the "new" technology. Just like they kept talking about fuel injection long after it was standard, and still feel the need to stick "i' on model names.

spanfucker retire bitch > BATC42 11/20/2014 at 09:28

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Most cars sold in the U.S. come with IRS as well. Usually it's the cheapest sub-compacts that tend to go thrifty and not use IRS on the rear suspension. Some models still use drum brakes in the rear for the same reason.

BATC42 > Distraxi's idea of perfection is a Jagroen 11/20/2014 at 09:29

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Thanks for the lesson :)

Andy Sheehan, StreetsideStig > Nibbles 11/20/2014 at 09:30

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I want that machine that goes to the ATM for me.

ly2v8-Brian > BATC42 11/20/2014 at 09:31

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First letter is the key. Independent, each side has free articulation.

BiTurbo228 - Dr Frankenstein of Spitfires > BATC42 11/20/2014 at 09:35

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There are a couple of practical differences between an IRS setup and a live axle. In an IRS setup, each wheel can react to changes in the road independently of the other. What that means is that over rough ground, each wheel can react to changes in the surface more efficiently and maintain a higher peak grip.

In a live axle setup, each wheel is rigidly fixed to the other. That means that on a bumpy road, if one wheel hits a bump not only does that wheel lose grip slightly but the other one does as well (as it's lifted off the road slightly). However, each wheel is held perpendicular to the road throughout the whole suspension travel which means that as the suspension squats under power you don't get any camber change (changing the angle of the wheel so it's not flat against the road surface). That makes them good for drag cars as you can maintain peak grip through the vast majority of the suspension travel.

The other big practical difference is in unsprung weight. Although IRS systems usually weigh more total than live axles, a far lower percentage of that weight is unsprung (weight carried below the springs). High unsprung weight is bad as it slows the wheel's reaction time to irregularities in the road.

So, what you end up with is two systems that are close enough to be indistinguishable on the track where surfaces are nice and smooth (at most levels of motorsport anyway), but with IRS more capable on real-world roads where there are plenty of bumps and cracks and potholes and live rear axles more suited to off-the-line grip (useful for drag racing).

 V8 Rustler > BATC42 11/20/2014 at 10:13

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LONG LIVE THE LIVE AXLE

crowmolly > OPPOsaurus WRX 11/20/2014 at 10:13

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Well, old IRS setups were not the greatest, so there's that too.

crowmolly > DoYouEvenShift 11/20/2014 at 10:14

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Corvette's IRS wasn't really that great until maybe 1984.

DoYouEvenShift > crowmolly 11/20/2014 at 10:31

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True, but at least it was out there.

nermal > BATC42 11/20/2014 at 11:04

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Short version:

Live axle is better for drag racing, trucks, and low-speed off roading.

IRS is better for ride quality, handling in turns, and dealing with bumps.

Party-vi > Mattbob 11/20/2014 at 12:53

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Agreed.

Mattbob > Party-vi 11/20/2014 at 12:58

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We both know how bad the live axle in an xj takes pot holes. This is where most of my experience with them comes from.

Party-vi > Mattbob 11/20/2014 at 13:26

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This is why I agreed with you - fucking hated potholes in my Jeep.

1337HPMustang > BiTurbo228 - Dr Frankenstein of Spitfires 11/20/2014 at 15:42

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as a mustang driver, thank you for that last paragraph...

Also wheel hop with a tight suspension is fucking terrifying, it should be noted.

ranwhenparked > BATC42 11/20/2014 at 20:13

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We don't. The vast majority of cars sold here have had it for many years. IRS is only a big deal on the Mustang because it was such a hold out for so long. Its an iconic car and was the last one on the market to finally give up the solid rear axle quite a long time after everyone else already did.

Axial > TwinCharged - Is Now UK Opponaut 11/20/2014 at 20:52

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Not counting the SVT Cobra, I guess...

TwinCharged - Is Now UK Opponaut > Axial 11/20/2014 at 20:58

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/hush