Question: 3-link or IRS? Which is best for all out cornering performance?

[FFR65Coupe]

I just ordered my 65 coupe complete kit a couple days ago. I'm wondering if I made the right choice ordering it set up for the 3-link rear suspension. I want the all out best handling and cornering performance for the street. I don't plan on tracking the car but I do want track performance. I drive VERY spirited and want to be sure that the car will perform for my driving style. You know, "like a cat on carpet". The one thing that I fear is that I'll be able to "feel" the 3-link solid axle moving side to side under the car during hard cornering. If I could get some input on the 2 different setups from those of you that have experienced both in spirited street driving situations that would be great. Maybe some pros and cons of each that you have experienced would be great to.

Thanks,
Albert

[edwardb]

When Factory Five introduced the now current IRS setup based on the 2015+ Mustang center section and spindles, they did extensive track testing. Result was they beat the previous times of the 3-link setup. Up to that time, 3-link was described as the best performance setup. IRS the best comfort setup. Since then, IRS is described (and apparently proven) as the best of both. There are some situations where a solid axle may be the best choice for straight-ahead performance. But for what you're describing, IRS would be the way to go IMO. I've had both, also only for street driving, and strongly prefer IRS.

The main con against IRS is usually cost. If you compare all new to all new (e.g. new Ford Performance IRS parts plus chassis mod to new Moser solid axle) the price difference isn't huge compared to the overall cost of the build. Similar results if you compare used, e.g. salvage. I've seen some comparisons where new IRS was compared to resurrecting an 8.8 solid axle, and that will always be much more expensive. There are deals to be had with low mileage and perfectly useable IRS and brake components that can help control costs.

[Logan]

No question, IRS is best for performance driving. A few points off the top of my head, which is by no means comprehensive:

1. If you drive over racetrack curbing, or potholes on the street, or bumps mid-corner, it only affects one side of the car instead of both

2. Usually less unsprung mass for the suspension to manage

3. Driveshaft and pinion angles are fixed, so changes to ride height and suspension travel do not affect them

4. Fully adjustable camber and toe, critical for performance setups

5. Camber gain under compression

6. Bonus: more comfortable ride while also performing better

[Erik W. Treves]

one aspect of your question I think you may not be considering - while we claim that we like to drive things in a "spirited" manner - I would submit that if you are not building a track only car - that only about 10% of your total time will be in the spirited zone..... this is also where the IRS shines as well... the roads are not perfect... the overall comfort in the all the transitions in the road that come with street driving is far superior in my mind... I have owned 4-link, 3-link and IRS versions of the design... I think that the IRS setup has many advantages beyond just the corning aspect of the design... not dismissing the comments above - but I would highlight Logan's point 6. I even drag race the IRS and I honestly haven't had any negative thoughts about the choice on IRS... even at my HP level. As far as cost - by the time you go through everything you need to do to get a solid axle "close" to the IRS feel - you will be at the IRS cost or within the margin of error. Anyway - if you get an opportunity to ride or drive in both I would and make your own decision since you will have to live with it :)

[svassh]

I just ordered my 65 coupe complete kit a couple days ago. I'm wondering if I made the right choice ordering it set up for the 3-link rear suspension. I want the all out best handling and cornering performance for the street. I don't plan on tracking the car but I do want track performance. I drive VERY spirited and want to be sure that the car will perform for my driving style. You know, "like a cat on carpet". The one thing that I fear is that I'll be able to "feel" the 3-link solid axle moving side to side under the car during hard cornering. If I could get some input on the 2 different setups from those of you that have experienced both in spirited street driving situations that would be great. Maybe some pros and cons of each that you have experienced would be great to.

Thanks,
Albert

I just converted my MK2 from worn out 4 link Mustang setup to 3 Link. You won't feel the axle moving side to side its held in place firmly. That said if I was building a new kit I would go IRS for all the items mentioned already.

[Tom Veale]

"The one thing that I fear is that I'll be able to "feel" the 3-link solid axle moving side to side under the car during hard cornering."

The 3rd Link is the Panhard Rod. It connects laterally the Axle to the Frame. Because of that there isn't any side to side movement of the axle under the chassis. Hence no "rear steer."

I think I agree with the commentary here: Independent Suspension at the rear will be more satisfactory for your application of mostly Street driving. I can't say this from personal experience with FFR cars as both of mine have been 8.8" solid axle cars with the 3-Link. My Challenge Series roadster was initially built with 4-Link and one race was all it took for me to realize I had to upgrade to the 3-Link. It was much better and safer to drive as a race car afterward and no worse for ride comfort. The cars I've owned with rear independent suspension generally rode well and performed well.

Best of luck with your build.
Tom

[Ltngdrvr]

"The one thing that I fear is that I'll be able to "feel" the 3-link solid axle moving side to side under the car during hard cornering."

The 3rd Link is the Panhard Rod. It connects laterally the Axle to the Frame. Because of that there isn't any side to side movement of the axle under the chassis. Hence no "rear steer."

Actually, the panhard bar is the 4th link, the 3-links they refer to are the trailing arms, 2 lower ones, same as the FFR 4-link, and a single custom upper link, this allows for better ability to move through the 3 axis it needs to travel through.

But, no matter, definitely the IRS is the better setup all around.

[GoDadGo]

Here is the official IRS Suspension Video from Factory Five Racing:

https://youtu.be/Few8Ppf0_GY

I personally like the 3-Link over the IRS; however, it is only because I like the is the strength and simplicity of that set up...In addition, the 3-Link gave me the option to shorten the wheelbase of my MK-4 so I was able to center the rear wheels within the wheel arches.

https://youtu.be/9WEe6-wdNtA

Wheelbase was shortened to:..89.25"

[tonywy]

I'm running a 4 link with a panhard bar that I just built. The car feels much more planted in a turn. In my opinion this gives me the strength of the 4 link an lowers the the roll center significantly. 166946166947

[jamminj]

There is a reason all the race cars are going to independent rear suspension even Nascar
Not to mention the ride quality especially on bumpy corners your car will stay more planted

[FracAG1980]

I just ordered my 65 coupe complete kit a couple days ago. I'm wondering if I made the right choice ordering it set up for the 3-link rear suspension. I want the all out best handling and cornering performance for the street. I don't plan on tracking the car but I do want track performance. I drive VERY spirited and want to be sure that the car will perform for my driving style. You know, "like a cat on carpet". The one thing that I fear is that I'll be able to "feel" the 3-link solid axle moving side to side under the car during hard cornering. If I could get some input on the 2 different setups from those of you that have experienced both in spirited street driving situations that would be great. Maybe some pros and cons of each that you have experienced would be great to.

Thanks,
Albert

You only have to watch the movie "My Cousin Vinny" and listen to Marrisa Tomei's Academy Award Winning description of the difference between a solid rear axle and independent rear suspension to realize that IRS keeps the opposite wheel flat on the ground (keeping traction maximized) when the opposing wheel is lifted. (One of the most fun movie scenes I have ever seen - IMO)

However, I opted for the 3-link myself.

Steve (FracAG1980)

[FFR65Coupe]

Thanks everyone for all the great comments, suggestions and advice. I really appreciate it. I contacted FFR and changed the 3-link to the IRS. I do believe this will be the best option for me. My kit completion date it set for the middle of January 2023. Now I get to hurry up and wait, LOL.

[racingandfishing]

Anyone know what the weight difference is between the IRS and the Mosier setups?

Also, the IRS diff (especially the Torsen) has overheating issues in the Mustangs when run hard unless you add a diff cooler which is standard on GT350 track pack and R. I had a 2015 that didn't have a sensor, but from 2016 on they put one in and it puts the car in limp mode if it gets too hot. However the Mustang has a more restricted space, is likely passing less air under the car by design and the exhaust runs right by it.

All that said, not sure if you would know unless you had a diff temp gauge hooked up or if you cooked the oil - But anyone run into over heating issues with the IRS diff on either Torsen or the standard limited slip?

[Chopper]

Also, the IRS diff (especially the Torsen) has overheating issues in the Mustangs when run hard unless you add a diff cooler which is standard on GT350 track pack and R. I had a 2015 that didn't have a sensor, but from 2016 on they put one in and it puts the car in limp mode if it gets too hot. However the Mustang has a more restricted space, is likely passing less air under the car by design and the exhaust runs right by it.


I'm curious about this as well. I did want to point out that a Type 65 weighs a lot less than a Mustang, so that probably contributes to some degree as well. There certainly is room for an external cooler if needed.

[racingandfishing]

The base weight of a Mustang is around 3600 lbs and could no doubt contribute. Also, the manuals use a cast iron housing vs. the aluminum on the automatics (and we all know that cast iron doesn't shed heat very well).

As far as the Mustang, even some of the more dedicated track cars that get down around 3200 lbs still have the issue. Folks have tried different fluids, wrapping the pipes, adding fins to the diff cover, etc. but a diff cooler seems to be the only solution. Auto cross doesn't seem be an issue due to the short runs, but HDPE and even long spirited runs is where the issue arises.

On top of that, I am in Texas and heat is a little bit of a problem here. So if I go IRS, I will likely add the diff cooler, but would like to have feedback if possible from current owners. Thanks!

[marshallmosty]

I raced an American Iron '89 FOX Mustang with 330RWHP and 350RQTQ with a Traction-Lok Diff (stock other than the tried and true alternating clutch/steel arrangement) with 3.55 gears for about 12 seasons before the diff finally "let go". Most of our races were between 15-35 minutes but that's 100% the entire time. I'd wager that unless you are doing endurance races over an hour at a time (even with fuel stops), a diff cooler isn't really worth the effort.

Worst case you can monitor the diff temp between sessions using a non-contact pyrometer and if you see temps you think are too high (wouldn't even know what that would really be), then consider the cost/effort/weight/complexity of a diff cooler then.

Just my $0.02


I too have a Jan-2023 build date for my Coupe. This is going to be FUN!!

[Tom Veale]

.....The one thing that I fear is that I'll be able to "feel" the 3-link solid axle moving side to side under the car during hard cornering.......

The Panhard Rod that is part of the 3-Link option pretty much removes this fear completely. It works to locate the axle "side to side" and remove 99.9% of rear steer activity.


......Best Handling and Cornering Performance.......

Please remember to "Invest In Yourself" as well as in equipment. The best money I ever spent on Handling and Performance was the 4 day High Performance Driving class I took at Bondurant School in 1988. I not only left there with a competition license but more track time than I could have gotten in a year's worth of club days and with excellent instruction. Look into one of the pro driving schools and do at least a 3 day school. Skid pad training, Accident Avoidance, Threshold Braking are hard things to practice safely on public roads. Vehicle dynamics, maintaining optimum tire contact and real time laps will change your driving world forever.

After 20+ years of competition driving it is still the best money I ever spent on my "hobby." Ask around for who's the current "best" school(s) available. Better yet, take schools at various race tracks that offer their own schools. That way you check off a lot of "Bucket List" drives while learning!

Best wishes,
Tom

[J R Jones]

The Panhard Rod that is part of the 3-Link option pretty much removes this fear completely. It works to locate the axle "side to side" and remove 99.9% of rear steer activity.



Please remember to "Invest In Yourself" as well as in equipment. The best money I ever spent on Handling and Performance was the 4 day High Performance Driving class I took at Bondurant School in 1988. I not only left there with a competition license but more track time than I could have gotten in a year's worth of club days and with excellent instruction. Look into one of the pro driving schools and do at least a 3 day school. Skid pad training, Accident Avoidance, Threshold Braking are hard things to practice safely on public roads. Vehicle dynamics, maintaining optimum tire contact and real time laps will change your driving world forever.

After 20+ years of competition driving it is still the best money I ever spent on my "hobby." Ask around for who's the current "best" school(s) available. Better yet, take schools at various race tracks that offer their own schools. That way you check off a lot of "Bucket List" drives while learning!

Best wishes,
Tom

In a world of supplicant miracles like Prevagen and Viagra, the idea of IRS improving your driving skill is intoxicating.
I remember the season my engine did not blow-up, and the resulting track time contributed more than increased power.
jim

[Tom Veale]

.......the resulting track time contributed more than increased power.


This is great! Seat time counts! There's a guy named Burt Levy who is hailed as the world's most unabashed "Ride Mooch." He's driven more different cars than almost any racer anywhere. Because he's an author, people are more willing to turn over their precious race cars to him with the hope of ending up the subject in one of his articles.

What's interesting is that it's very rare that he doesn't "best" the car owner/driver's best lap times.
There have been exceptions, but this tells me a lot about the subject of Driver's Training/Education vs Driver's Equipment Expenditures.

Best wishes,
Tom Veale
PS: Burt's web site for books and articles: http://www.lastopenroad.com/

[J R Jones]

This is great! Seat time counts! There's a guy named Burt Levy who is hailed as the world's most unabashed "Ride Mooch." He's driven more different cars than almost any racer anywhere. Because he's an author, people are more willing to turn over their precious race cars to him with the hope of ending up the subject in one of his articles.

What's interesting is that it's very rare that he doesn't "best" the car owner/driver's best lap times.
There have been exceptions, but this tells me a lot about the subject of Driver's Training/Education vs Driver's Equipment Expenditures.

Best wishes,
Tom Veale
PS: Burt's web site for books and articles: http://www.lastopenroad.com/

Yes I know of Burt, and Brock Yates before him. Driving fast is one thing, competition is another. Yates wrote in Sunday Driver about competing in the Trans Am, driving professional equipment.
Flat out at Elkhart Lake Brock was overtaken at high speed by another car. Mark Donohue recognized the editor's car, slammed the brakes, and door to door, gave Yates a grin while wiggling fingers in his general direction.
Randy Probst (65yrs) has been a popular (professional) guest driver and evaluator that understands equipment quickly and gets the best from it. Randy writes pretty good too.
In my experience driving someone else's equipment has an influence on attitude. I pride myself with getting performance out of a car without consuming it, however, risk taking and pushing the envelope is different with non-owned equipment. I spent a season sorting a banker's Sunbeam Tiger setting lap records and wins that still amaze me.
jim