Be all end all IRS > SRA thread

[SpatiallyAware]

Have you driven or owned either of these cars? ... I've owned both.
For every type of driving, be it ride quality while commuting, spirited cornering, or strong acceleration the Mustang's current SRA is superior to the GTO's IRS.

As someone who actually does race, I can tell you that I don't go looking for bumpy roads to have my fun on. Racing on a poor surface sounds like turning something already dangerous into something stupidly dangerous.

If people are actively searching out roads in disrepair to push their vehicle's limits on, I guess that explains why so many people end up wrapped around telephone poles.

No doubt that a current mustang 5/6 link is better than the early GTO IRS. The mustang SRA is also probably better than IRS from the 70's, it doesn't automatically mean SRA is flat out superior like you're trying to make out.


We aren't talking about racing here... On a racetrack the SRA issues are hidden because it's so smooth. It's on the street (canyon carving, up in the mountains) where SRA issues are extremely noticeable. And no, you don't have to be at 'race speeds' or 'hooning around' for the limitations to show up..

 

[jlee]

No doubt that a current mustang 5/6 link is better than the early GTO IRS. The mustang SRA is also probably better than IRS from the 70's, it doesn't automatically mean SRA is flat out superior like you're trying to make out.


We aren't talking about racing here... On a racetrack the SRA issues are hidden because it's so smooth. It's on the street (canyon carving, up in the mountains) where SRA issues are extremely noticeable. And no, you don't have to be at 'race speeds' or 'hooning around' for the limitations to show up..

Can you bold where he said that?

I can't find it.

 

[heymrdj]

Rofl more personal "I'm offended" drama...

I (and the other IRS supporters) have clearly stated from the get-go that IRS is not ideal for literally every situation (drag racing/strength and cost), so stop trying to twist words around like this.

Your ranger analogy shows how little you truly know about the SRA vs IRS debate. I also have a ranger, and it shows SRA problems much worse and much earlier than any other SRA I've driven. You not noticing this speaks volumes to your driving experience. As is typical with your arguments, apples to oranges...

Really? You own one and you have SRA issues. So you know in a high speed pot hole it'll jump right? And you can therefore correct it right? So you understand how it works and control it since you're still alive. If you have issues though bring your ranger on to Fort Wayne and I'll show you how to actually drive it if you have issues. Rangers are alot of fun to sling around when you know how. :thumbsup:

 

[Throckmorton]

I'm not sure you understand what logic is.

You said that an econobox is just as good on the street... Justifying the Mustang's SRA because supposedly on the street IRS vs SRA doesn't matter. So why wouldn't the Mustang be an econobox? Imagine how much Ford could save if they didn't have to spend $10 on a long driveshaft and $50 on that big 9" rear diff!

 

[Howard]

Cuz it's a great topic for debate, and we have many threads derailed by this exact argument.

So you care because you can't live with yourself unless you can convince everybody else to believe that SRA no longer has any purpose on street cars?

You don't even have to answer that question, actually.

 

[Howard]

Following that logic, the Mustang should be a FWD econobox. After all, a "properly set up" FWD car handles "very well" and can handle "better" than a bad RWD car.

Sure. Just look at the Cobalt SS.

 

[SpatiallyAware]

So you care because you can't live with yourself unless you can convince everybody else to believe that SRA no longer has any purpose on street cars?

You don't even have to answer that question, actually.

How dare someone make a thread to discuss a topic which is clearly a good debate!

 

[Howard]

How dare someone make a thread to discuss a topic which is clearly a good debate!

How could it be a good debate when clearly "IRS > SRA"?

 

[JCH13]

A few thoughts:

Skimming some mustang forums I learned that a SRA seems to be 125lbs - 150lbs lighter than an IRS setup (from the Cobras).

I think it's nearly common knowledge that Mustangs have low damping (i.e. soft shocks) from the factory and can benefit greatly from better shock control. Even a Miata, when it has shitty shocks, will hop and skitter over bumps.

Further debate:

There are great benefits to be had by dropping 125-150lbs of sprung and semi-sprung weight, when does the mass trade-off start to become not worth it?

Some or most of the Mustang SRA skitter could come from poor shock control. How much?

Does the fixed toe/camber of a SRA setup mitigate its other short-comings? It won't suffer from bump steer or camber loss in roll.

 

[exdeath]

Um, ok.

Other than drag racing or for cost savings, give me an example of when a (properly setup) SRA is preferred over a (properly setup) IRS setup.

A Griggs GR40 equipped solid axle 1982 Foxbody Mustang will destroy any factory IRS equipped car on the street and the track?

Its not always about what's theoretically perfect in textbooks.

 

[JCH13]

Um, ok.

Other than drag racing or for cost savings, give me an example of when a (properly setup) SRA is preferred over a (properly setup) IRS setup.

Locost 7 or Lotus 7. Simpler, lighter, more robust, lower rotational inertia of the vehicle, and better packaging.

 

[SpatiallyAware]

Locost 7 or Lotus 7. Simpler, lighter, more robust, lower rotational inertia of the vehicle, and better packaging.

.......and cheaper

 

[Throckmorton]

I think I've posted this link before. http://7faq.com/owbase/ow.asp?deDionOrIRS

They chose to go with a De Dion axle for the Lotus 7 because it worked best for the chassis. IRS would have needed additional structure and weight.

That doesn't mean the solid axle itself is superior for handling

 

[melchoir]

I think I've posted this link before. http://7faq.com/owbase/ow.asp?deDionOrIRS

They chose to go with a De Dion axle for the Lotus 7 because it worked best for the chassis. IRS would have needed additional structure and weight.

That doesn't mean the solid axle itself is superior for handling

Ah, so what you're saying is that Lotus was able to save costs, weight, and add strength all while engineering a vehicle that handles exceptionally well with a SRA?

Who'd have thought??? Intradesting. /chinrub

This is not advancing your argument that proper setup IRS obliterates a proper setup SRA.
What I'm getting out of this is that many chassis may work best with an SRA and the compromises you folks describe may be near non-existent in many circumstances.

 

[OCGuy]

Who cares...very few of us go to the track every weekend.

 

[JCH13]

.......and cheaper

Lol, I thought that was implied!

I think I've posted this link before. http://7faq.com/owbase/ow.asp?deDionOrIRS

They chose to go with a De Dion axle for the Lotus 7 because it worked best for the chassis. IRS would have needed additional structure and weight.

That doesn't mean the solid axle itself is superior for handling

Exactly. Each design decision must be made in the context of the vehicle as a whole. This is why SRA designs can be used so effectively.

Talking just about the weight concern for a moment: in a vehicle that is truly a blank slate every pound of un-sprung and semi-sprung weight that is eliminated reduces 3-5 pounds of additional mass from the vehicle to maintain performance (lighter wheel -> softer suspension spring and softer shock -> lighter spring mount and suspension links -> lighter chassis bracing, smaller suspension bushings -> smaller engine needed for same pwr/weight ratio -> smaller brakes for same stopping ability... etc). So the weight savings from a SRA are multiplied and could offset in part, or entirely, any sacrifices in suspension performance. Particularly if the lighter car can use softer springs to be more tolerant of said bumps.

 

[Throckmorton]

Ah, so what you're saying is that Lotus was able to save costs, weight, and add strength all while engineering a vehicle that handles exceptionally well with a SRA?

Who'd have thought??? Intradesting. /chinrub

This is not advancing your argument that proper setup IRS obliterates a proper setup SRA.
What I'm getting out of this is that many chassis may work best with an SRA and the compromises you folks describe may be near non-existent in many circumstances.

I've been saying, since we first started arguing on this forum, that solid axles are better for some vehicles. For example, I bought a Jeep specifically because it has two solid axles.

The Lotus has the same drawbacks that every solid axle vehicle has, but the designers considered the tradeoffs to be worth saving weight. Just like a Mustang, a Jeep, a Unimog, and a dumptrunk, when one tire goes over a bump the camber of the other wheel is changed. You can't change that fact with any amount of engineering. It doesn't go away just because a particular vehicle uses a SRA or DeDion to save weight

But that's exactly what certain people on this forum used to argue about the Mustang's SRA.... that it's so well engineered by geniuses at Ford that it doesn't have the drawbacks inherent to the solid axle. And no one who is not an automotive engineer was allowed to question that.

 

[exdeath]

You are aware that tires deform right?

In the case of that Lotus running some huge soft hot fat meats and probably 15 psi, I seriously doubt the camber or contact patch on either end of the axle is going to be affected when one tire runs over a pebble...

 

[Howard]

some huge soft hot fat meats

:wub:

 

[Throckmorton]

You are aware that tires deform right?

In the case of that Lotus running some huge soft hot fat meats and probably 15 psi, I seriously doubt the camber or contact patch on either end of the axle is going to be affected when one tire runs over a pebble...

Well the softer and fatter the better but what about the Mustang and its low profile tires?

 

[heymrdj]

Well the softer and fatter the better but what about the Mustang and its low profile tires?

They actually deform quite well..there's a video of it somewhere on youtube.. :hmm:

 

[melchoir]

Well the softer and fatter the better but what about the Mustang and its low profile tires?

From what I read the locust 7 runs anywhere from 185-205, 50-60, r14-15.
This gives it a sidewall profile of 92.5mm to 123mm.

My stock Mustang runs 245/45R19 tires, a sidewall height of 110.25mm. Right in between what the Locust seems to use.

From the article you linked from the Seven's creators,

Technical:
I can't agree with your statement that:
IRS improves the dynamics of a vehicle in every aspect.
Then or now, a GOOD IRS may be better than a good solid axle, in some, repeat some, circumstances. If it's good, it may give better wheel control on bumpy corners, and may offer better traction in difficult conditions. Even a good IRS, though, is unlikely to give better outright dry road grip than a dD, because the IRS can't maintain the wheel upright in a corner without sacrifices in the geometry that will give up performance elsewhere.

I suppose it comes down to whether a manufacturer wants to use IRS as a genuine technical benefit or a cynical marketing ploy - I doubt that anyone would cite the Triumph Spitfire as an argument for adoption of IRS. Or for that matter, the miserable semi-trailing system that BMW persists in using on its low-end models..

In contrast, the term live axle usually conjures images of Cortinas and cart springs, although the Seven system is actually very effective: giving good location, good geometry and low mass - it's a difficult act to follow ! To get back to the point, we felt that we had a very good live axle suspension, and weren't prepared to give up that level of performance just to have a new acronym on the car. Which leads to the next point...

SRA has proven to perform, and perform well when designed correctly. All while having reduced costs, weight, and increasing strength over IRS solutions.
There's no clear cut "best".

 

[JCH13]

There's no clear cut "best".

Yahtzee!

 

[SpatiallyAware]

<snip>

SRA has proven to perform, and perform well when designed correctly. All while having reduced costs, weight, and increasing strength over IRS solutions.
There's no clear cut "best".

From a consumer sports car perspective, there is absolutely a 'best'.

Yes, there are special situations where you want SRA.. as throck mentioned, a HD truck, or a 'built from scratch' 800lb car where every 1lb matters...

But for a consumer driven supposed sports car, IRS is absolutely the clear cut "best" solution. It might not be the cheapest, therefore sometimes doesn't make sense (such as in the mustang, where saving $100 per car is apparently worth it), but they did this due to cost, not performance.

The mustang engineers wanted IRS, but it was canned due to cost. SRA performs acceptably in some situations, but it is very rarely the ideal setup.

 

[jlee]

From a consumer sports car perspective, there is absolutely a 'best'.

Yes, there are special situations where you want SRA.. as throck mentioned, a HD truck, or a 'built from scratch' 800lb car where every 1lb matters...

But for a consumer driven supposed sports car, IRS is absolutely the clear cut "best" solution. It might not be the cheapest, therefore sometimes doesn't make sense (such as in the mustang, where saving $100 per car is apparently worth it), but they did this due to cost, not performance.

The mustang engineers wanted IRS, but it was canned due to cost. SRA performs acceptably in some situations, but it is very rarely the ideal setup.

Well, at least you've made progress from your stance in the OP.

SRA has its place... In budget drag cars. There is no other reason to specifically want a SRA setup, and drag racing is the only positive aspect of SRA.