Solid Axle or IRS, which is better?

[hrosenthal]

Are there any benefits of using a solid axle vs Independent Rear Suspension?
I assume IRS is a more comfortable ride, but what is the advantage of a solid axle?
Thanks

[David Hodgkins]

There are 3 basic variations of solid axels in FFRs. 3, 4 and 5 link. Since you are asking about what the best solution is, let leave the 4 link out of the equation.

A 3 link solid axel is stronger overall, so if you are planning a lot of track time then a solid axel is your better bet. The challenge series cars run 3 link, and there is a group of coupes being built for the track and they are using 3 link as well, for reasons related to strength and reliability.

The 5 link is a weld-in after-market solid-axle option that you can investigate. It has it's fans and few - if any - detractors. Basically you'd purchase the 3 link option from FFR and then install the 5-link bracketry.

The IRS is the best option for the street, where there is greater potential for uneven roads. You will hear lots of variations of this theme but those are the basic rules.

[hrosenthal]

I really plan to use this as a fun weekend car. No plans for track. I think I'll stick with IRS.

[CraigS]

In my opinion IRS is the best for everything except drag racing on slicks where 4 or 5 link solid axle is strongest. There is a reason that lower end street cars used to use solid axle (not so much anymore w/ front wheel drive in 90% of the cars) while any car manufacturer who wanted a good rep put IRS in his cars.

[marlin]

How hard would it be to replace a 3 link axle to a IRS after a build is done? FFR IRS package in the catalog seem like it can be bolted in. Unless I don't understand something? This would be on a MKIII

[edwardb]

How hard would it be to replace a 3 link axle to a IRS after a build is done? FFR IRS package in the catalog seem like it can be bolted in. Unless I don't understand something? This would be on a MKIII

The change from 3 link (e.g. solid axle) to IRS is far from a bolt-in. Guys have made this change, but requires cutting, fixturing, welding, etc. Pretty much need to make the solid axle vs. IRS decision up front when the chassis is ordered.

[Avalanche325]

Are there any benefits of using a solid axle vs Independent Rear Suspension?

Higher performance, lower cost, fewer problems, easier installation, easier set up.

[CraigS]

It's been a while since I read a howto on irs upgrade after the fact but I remember that it is bolted in to get it located but then needs to be welded.See here and scroll down a little for an irs retrofit writeup.
http://thevenom.net/cobra/index.html

[trublue]

I have a Mark3 and use it strictly for pleasure cruising. I opted for the rear 3-link and the donor rear axle from a 2000 Mustang GT. I have 5,000 miles on the finished car and have enjoyed a comfortable, stable ride every mile of the way. It was very easy to install too. I like the fact that the car can be used for track events by a future owner. This might also add to resale value.
Art

[cwrandolph]

I would make sure that FFR is doing something about all the axles failing before I signed up for IRS. Every week it seems that somebody has an axle fall out. It would be great if someone from FFR addressed the situation on this forum.

[Itzdapig]

There are 3 basic variations of solid axels in FFRs. 3, 4 and 5 link. Since you are asking about what the best solution is, let leave the 4 link out of the equation.

A 3 link solid axel is stronger overall, so if you are planning a lot of track time then a solid axel is your better bet. The challenge series cars run 3 link, and there is a group of coupes being built for the track and they are using 3 link as well, for reasons related to strength and reliability.

The 5 link is a weld-in after-market solid-axle option that you can investigate. It has it's fans and few - if any - detractors. Basically you'd purchase the 3 link option from FFR and then install the 5-link bracketry.

The IRS is the best option for the street, where there is greater potential for uneven roads. You will hear lots of variations of this theme but those are the basic rules.

David, I believe if you going 5 link you would order a 4 link set up from F5. None of the 3 link will work.

[aesthetect]

im extremely interested in IRS to build a FF33 track (road race) car. can anyone comment who has maybe driven on both aggressively around some corners? ... coming from a solid IRS background im curious as to how cumbersome the solid axle would be, i imagine very.

[DoogieT]

im extremely interested in IRS to build a FF33 track (road race) car. can anyone comment who has maybe driven on both aggressively around some corners? ... coming from a solid IRS background im curious as to how cumbersome the solid axle would be, i imagine very.

Solid Axle Only - 4,000+ miles, 15 Road Tracks (some dups) MkIV, 331 Stroker 324WHP, 12" Yokohama rear 200TW
Rear slips, learning maintain acceleration (counter intuitive, hard to relearn) steering to control. Nothing feels better than slip... acceleration and steering... when it works!

I thought I wanted IRS but now probably not:
- I don't need a big bill and fabrication expense
- Will IRS save me 10ths traded for a fragile setup?
- I need to drop seconds with an unbreakable suspension

HP won't help on the turns, save seconds on long tracks: Homestead, PBI, Sebring, Rd Atlanta, VIR, NCM, MidOH, Rd America, Gingerman

I have no engineering or mechanical skill so I'm open to being advised on what my options are for suspension.

Thanks,
Doug Tally

[BradCraig]

I would make sure that FFR is doing something about all the axles failing before I signed up for IRS. Every week it seems that somebody has an axle fall out. It would be great if someone from FFR addressed the situation on this forum.

I planned for two years and it's been over 2 years since I got my kit and I've never heard of IRS axles failing on this forum or the FB group. Mine is rock solid...maybe the older IRS setups?

[JohnK]

Given that this thread is from 2012, all the discussion is about the old IRS. I'm also not aware of any reliability concerns with the current IRS.

[BradCraig]

Given that this thread is from 2012, all the discussion is about the old IRS. I'm also not aware of any reliability concerns with the current IRS.

LOL! Yeah, I just noticed this was an ancient post, disregard!

[Chainsaw]

Higher performance, lower cost, fewer problems, easier installation, easier set up.

By “higher performance”, do you mean the capability to handle higher horsepower?

[FF33rod]

Wow, holy resurrection Batman!

[NAZ]

A decade has past since the OP asked the question and it's still relevant today. The choice of rear suspension is still one of the decisions car builders struggle with today. Which is best depends on several things, not the least of which is the intended use of the vehicle. The different style rear suspension systems all have pros and cons that will work better or worse than the other depending on what you're doing with them.

The good news is that for a garden variety street cruiser, most builders would be happy with either of the FFR offerings. However, I'd suggest you limit your choice to IRS or three-link. That Mustang triangulated four-link has handling issues you'd be wise to steer clear of. But do your own research beyond this forum as it can be expensive to change from one style to another after the car is built.

[edwardb]

Through multiple builds, I've had 4-link (all aftermarket so not plagued with some of the donor part issues), 3-link, Levy 5-link, and now two 2015+ IRS. All were driven extensively, although admittedly I'm 99% street cruiser. I had the solid axle builds before IRS, and like many on here, thought they rode just fine when I had them. But once I had the newer style IRS (new for 7 years now...), a Roadster and a Coupe, I was sold. It's a much nicer ride and for my driving rock solid. My wife even noticed the difference, and that's somewhat unusual for her. So I always recommend IRS as the best choice for ride quality and street manners. The newer style has proven to be very durable, and according to testing by Factory Five, is also the highest performance, e.g. best track times. There have been at least a couple dedicated Coupe track builds. Used IRS. Having said that, of course may be situations where solid axle may be the better choice. Primarily, as I understand, for hard core straight ahead performance with really sticky tires or racing slicks. Like drag racing. But for most of us, that's a low time if ever use. Also, perhaps for extremely high HP applications, again especially with sticky tires. But the Mustang guys are doing this with much heavier cars. A lot of time using more robust CV axles. But the rest of the parts seem to hold up OK. I haven't found the IRS is necessarily any more difficult to put together. Just different. The instructions are pretty good. Does require a rear alignment (camber and toe) but the newer design makes it relatively easy. IRS is a bit more expensive, but options there too.

[tonywy]

Let me throw this out there. Has anybody ever tried running a solid axle 4 link with a panhard bar set up. This would stop the problematic lateral movement of the rear end housing.

[Chainsaw]

By “higher performance”, do you mean the capability to handle higher horsepower?

Hahaha. I gotta start looking closer at the posting dates.

[PG_Cobra]

Let me throw this out there. Has anybody ever tried running a solid axle 4 link with a panhard bar set up. This would stop the problematic lateral movement of the rear end housing.

I installed a Maximum Motorsports (MM) Panhard bar on my Mk1 last year, finishing in the fall, so not many miles on it yet. So far, so good. All the twitchy quirks of the 4 link are gone. More extensive driving this year will show me if there are any other issues.

It was a lot of work. I had to fabricate a mini-sub frame mounted to the frame to set up the mounting points for the MM fixed bracket. Also the Panhard bar axle mounting removed the FF squat brackets so I added LCA lowering brackets from StreetRays. Lots of other details.

If I didn't have a muffler behind the axle for my under car exhaust I would have probably installed an FF 3 link.

[J R Jones]

I don't have a dog in this fight, but I have road raced live axle muscle cars with good results, using watts links or panhard bar for lateral control. The traditional four bar design gets a bad rap on this forum.
The problematic suspension critiqued here is a production Ford design trading cost for high performance functionality. You get what you pay for in this instance.
Traditional four bar live axle designs have four parallel longitudinal links. On leaf springs lateral control is not required, but advisable for hard cornering. With coil springs, lateral control is mandatory.
As mentioned previously a (traditional) four bar linkage is the most robust design.
jim

[Ted G]

The IRS is so pretty.... even though you are the only one who really knows how pretty!

[Mike.Bray]

Personally I love IRS. They ride better, handle better, and look neat. When I was building street rods I used to build my own, partly for looks and partly to get the ride height I wanted (low).







For my MKIV I'm about to build I debated long and hard to go with IRS or 3 link. I've always been an IRS guy and the added expense didn't bother me. But in the end I went with a 3 link solid axle. For what I'm planning, street cruising, the improved ride would be a benefit but then who are we kidding it's a 90" wheelbase car that's never going to ride like a Cadillac. The real deciding factor for me going with the 3 link was simplicity and reliability. Not that the Mustang IRS isn't reliable, but fewer parts always means less chance for failure.

[rich grsc]

So back in March, I was at the 12 hrs of Sebring. That track is demanding and rough, very hard on the cars and suspensions. Not one of those cars ran a solid axle.
just saying

[NAZ]

And every weekend you can see NASCAR running super speedways, short tracks, or road courses and they all use solid rear axles. But wait, there's more. Every weekend you can see the dirt track boys running WFO with their alcohol sipping wild open wheel cars and you won't find an IRS under them.

I have two race cars -- one with a solid axle and one with both an IRS and IFS (FWD). They both handle great and both throw you back in the seat when you mat the loud pedal. Pick the one that works best for you. But please don't make a blank statement that one is "better" than the other without stating in what context because each is better than the other at something but neither is better at everything. I've owned and driven a bunch of IRS and solid rear axle vehicles, I currently own five IRS equipped vehicles and four solid axle vehicles. I think I've seen a well rounded mix of each -- enough to know how well they perform over a wide array of uses. Neither one is superior in all areas. And both can be made to perform exceptionally.

[Namrups]

For this year Nascar has come out with a new car for the CUP series. It now has IRS!

[NAZ]

For this year Nascar has come out with a new car for the CUP series. It now has IRS!

Thanks. Next they'll be running on batteries.

[rich grsc]

I think in 2 yrs

[Namrups]

That's when I stop watching ......

[edwardb]

What's not to like?



Reminds me of the slot cars I used to run at tracks when I was a kid. Just a lot bigger (and more expensive...) Even sound similar.

[Namrups]

I have to be honest ... it's the sound .. or lack of it. Same reason I went with a push rod V8. I'm old school. Grew up with the sound of muscle cars. Side pipes. Cut outs. Straight pipes. I'm 69. That sound is music to my ears.

[NAZ]

I hear you brother -- it's just hard to get excited about electrons whirling through conductors. That video above really does remind guys like us of slot cars we used to play with. Maybe if I grew up playing video games like kids do now I might relate to electric cars. I grew up around gasoline and alcohol burning IC engine powered toys that made lots of noise and smelled. My childhood heroes piloted gasoline powered cars and motorcycles that were loud, dirty and in your face. That was exciting.

Electric motors are for powering washing machines not cars.

[JohnK]

Sorry to continue the thread jack...

I felt exactly the same way about electric cars until recently. Then I went and test drove one of these. Go try one and come back and tell me it's not exciting.

[J R Jones]

John, It is my observation that Porsche is not only a apex predator in performance cars, they know how to market them.
jim

[JohnK]

Jim, this is very true. Moreso, they know how to make cars "feel" like performance cars, regardless of whether they are performance cars, SUV's, electric cars, or whatever. Every other electric car I've driven feels like the physical embodiment of an internet browser. The Taycan feels like a Porsche.

[J R Jones]

John, Yeah, skilled design and implementation. It took a second viewing for me to realize it is 4800 lb battery cart with four doors. "It hurts my kidneys".
jim

[Mike.Bray]

Electric cars. Toyota and Volkswagen are neck and neck for worlds largest car company. Volkswagen did it by purchasing other companies and currently owns 12 brands while Toyota built up on their own and currently owns four brands. It's safe to say Toyota know a thing or two about cars. Toyota was among the first to introduce gas-electric hybrid cars into the market, with the Prius twenty years ago. It hasn’t been afraid to change the car game. All of this is to point out that Toyota understands both the car market and the infrastructure that supports it perhaps better than any other manufacturer on the planet.

When Toyota offers an opinion on the car market, it’s probably worth listening to. Last week, Toyota reiterated an opinion it has offered before. That opinion is straightforward: The world is not yet ready to support a fully electric auto fleet.

Toyota’s head of energy and environmental research Robert Wimmer testified before the Senate and said: “If we are to make dramatic progress in electrification, it will require overcoming tremendous challenges, including refueling infrastructure, battery availability, consumer acceptance, and affordability.” Those necessities are far from being available today. Wimmer noted that while manufactures have announced ambitious goals, just 2% of the world’s cars are electric at this point. For price, range, infrastructure, affordability, and other reasons, buyers continue to choose ICE over electric, and that’s even when electric engines are often subsidized with tax breaks to bring price tags down.

Toyota warns that the grid and infrastructure simply aren’t there to support the electrification of the private car fleet. A 2017 U.S. government study found that we would need about 8,500 strategically-placed charge stations to support a fleet of just 7 million electric cars. That’s about six times the current number of electric cars but no one is talking about supporting just 7 million cars. Simply put, we’re gonna need a LOT bigger energy boat to deal with connecting all those cars to the power grids.

We will need much more generation capacity to power about 300 million cars if we’re all going to be forced to drive electric cars. Whether we’re charging them at home or charging them on the road, we will be charging them frequently. Every gas station you see on the roadside today will have to be wired to charge electric cars, and charge speeds will have to be greatly increased. That power, like all electricity in the United States, comes from generators using natural gas, petroleum, coal, nuclear, wind, solar, or hydroelectric power according to the U.S. Energy Information Administration.

Electrifying the auto fleet will require a massive overhaul of the power grid and an enormous increase in power generation. Elon Musk recently said we might need to double the amount of power we’re currently generating if we go electric. He’s not saying this from a position of opposing electric cars. His Tesla dominates that market and he presumably wants to sell even more of them.

Toyota has publicly warned about this twice, while its smaller rival GM is pushing to go electric. GM may be virtue signaling to win favor with those in power in California and Washington and in the media. Toyota’s addressing reality and its record is evidence that it deserves to be heard.

YOU CAN IGNORE REALITY, BUT YOU CANNOT IGNORE THE CONSEQUENCES OF IGNORING REALITY!

I think we're safe from all of us driving electric cars for the foreseeable future.