IRS VS Truck Arms

[Problem2420]

Still trying to decide on a rear suspension set up for my 90 c1500 truck. I can get a really good deal on a irs from a c4 corvette, or can go with a trailing arm set up from elevated concepts. I know the irs will definitely have the cool factor and also maybe a little more work to install. Any input would be appreciated.



BTW the truck is a single cab stepside with a supercharged 350. I mainly run good guys autocross and drag race once in a while.

[andrewb70]

I've never been a fan of the C4 IRS. I don't like that it uses ujoints and that the axles are a structural member of the suspension.

Andrew

[cornfedbill]

I would go with the truck arm suspension over he C4 IRS.

[Randy67]

I agree. If you were using an IRS from a C5-up Corvette, or even a Gen5/6 Camaro, then I would say IRS.

[Sbeck09]

I have to say, I agree with those before me. And this is exactly what I'm working on myself right now on my truck build. I'm using the Mark VIII IRS due to cost, availability, and design/components. The C4 stuff is too basic and doesn't offer any real geometry or travel improvement. Especially considering the amount of work to get it done.

My 2 cents...if you want a better street ride and autox performance to be the priortiy, get a more modern IRS. Make no mistake...it's not cheaper or easier. It is worth it though.

[79 Camaro]

Go over to Corvette Forums on how much HP a C4 IRS can stand. I bet it's not much. I redid a C3 Corvette. Double of number u-joints. Special skills to really set up the center section. Special skills and tools to set up the trailing arms. I don't know if you can get a 1350 u-joint for the pinion. Plus the added margin cost for "Corvette" parts.

I would suggest speaking with Rob at No Limit or the folks at Ride Tech in regards to their pro-tour type suspensions.

[dhutton]

Some good C5/C6 IRS ideas here. I’m using the front and rear adaptors to put a full C5 drivetrain in my 56 Cameo.

http://rick486.wixsite.com/dobbertinperformance

Don

[ProTouring442]

I'm using the Mark VIII IRS due to cost, availability, and design/components.

I'm also installing the IRS from a Mark VIII, though I'm putting mine in a '72 Olds Cutlass/442. It's a decent design, with a good number of parts available from the aftermarket.

[rustomatic]

Apparently, nobody who has posted to this thread thus far has actually looked at or understood a C4 rear suspension before. First, there is absolutely no comparison to a truck arm setup, which was only used in NASCAR-type stuff because of rules, not because anybody liked or wanted it. The C4 setup can take tons of power (two different differentials available), can be adjusted infinitely, weighs very little, is cheap, and applies traction awesomely. No, the axles are not part of the suspension. Research decades of road racing and autocross success with the C4--there are many reasons why it was around for so long. Yes, I have C4 suspension in my car . . .

You will get a much easier setup with the truck arm suspension, but adjustment will be very limited (no camber/toe), and weight will be like a truckload more. You will probably also pay more for all of that dead weight, unless you use your existing stick axle.

[FlyDoc]

I would do IRS, the C4 has descent Geometry, you can get the 1350 for the pinon, the axles are not structural member of the suspension, on the C3's they are. the Dana 44 will hold about 600, but in a pickup you will have traction issues before you should break a 44. I would not waste your time with a D36.
a C5/6 has the capability to be better but when you consider the cost to upgrade the C5/6 is costly. there will be considerably more work in setting up the C5/6 then the C4. With transplanting the C4 gives you the ability to set your geometry. and no special tools for the C4 ring/pinon setup.
in my opinion i would do the C4 1st if it is a D44,if not find a D44. a distant 2nd a C4 D36, the center section is the only difference which you can replace later in just a few hrs, then the truck arm, but if you have a big budget and a suspension program, then go with a C5/6 setup.
I put a C4 in one of my cars, so much better than a solid axle, traction, handling, and ride are superior.

[andrewb70]

I'll bite....Please show me what link in the C4 rear suspension keeps the wheel from going full negative camber in case an axle breaks...



https://tech.corvettecentral.com/201...sion-overview/

From the above link (third paragraph):

"From a performance standpoint, there are a couple of interesting facts to be aware of. If an axle shaft breaks from extreme torque loading, you can expect maximum negative camber immediately resulting, with the tire rubbing on the inner fender well."

Sounds to me like the axles are a structural member of the suspension.

The lower link supports the bottom of the spindle. The two links going forward support the spindle fore and aft. The rear link controls toe....and the axle keeps it all stable by serving as the upper support of the spindle.

I am not saying it is bad...or better or worse than a truck arm, but the axles are definitely structural.

Andrew

[Typhoon1015]

With the current prices of C5 front and rear suspensions. Why would anyone consider a c4 setup at all unless it was free? C5 stuff can be had for 500-1k and has tons more aftermarket support and lots of uneducated vette owners to get cheap 2nd hand parts off of.

[FlyDoc]

Andrew
thanks for the pic. I not sure what I was thinking!
I don't know which IRS rear I was thinking of. but I did screw that one up.

[andrewb70]

Andrew
thanks for the pic. I not sure what I was thinking!
I don't know which IRS rear I was thinking of. but I did screw that one up.

No worries!

Andrew

[David Pozzi]

C4 IRS isn't bad performing but I wouldn't put one behind a supercharged engine.

[Peter Mc Mahon]

So the axle acts like a limit strap in extension and compression?

[ProTouring442]

So the axle acts like a limit strap in extension and compression?

The axle on 2n-4th generation corvettes is actually one of the control arms (like an old Jaguar IRS). Basically, it takes the place of an upper arm.

[Mark@lateral-dynamics]

Wondering why your options are limited to the two systems you noted? As was stated above, the only real reason that Truck Arms are in pretty much any performance suspension conversation is because of NASCAR (the same folks who only introduced fuel injection a few years ago, WAY behind the technology curve). There are WAY better options out there other than the two choices you noted. If you have the knowledge and tools to pull off an IRS conversion, you probably have what it takes to do an alternative setup which may perform as good or better, with far less complexity.

Sounds like a fun project!
Mark

[bret]

We are in the final stages of a new wishbone rear suspension for the 88-98 C1500. Here is a link to the same suspension we do for the 99-06 1500...the 88-98 system will be very similar in construction and price. https://www.ridetech.com/application...006-silverado/

Should be shipping in time for Christmas.

This system is super easy to install and has correct anti-squat, roll center, and instant center geometry. I used a form of this suspension design on my 33 Ford a few years ago that I raced in the optima and Goodguys series. That car was reasonably fast and handled well.

[Sbeck09]

I just had a thought. I've seen in done one here without spending a ton too. What about fabbing up a Watt's Link for your existing axle? It would work well for the different ways you use the truck, has much better geometry than stock, and is simple as hell for what it is.

Had to throw it out there.

Here's an example I stole for reference. Would probably be a fun project if you're handy with a welder.