Heidts IRS and wheel sizes.

[Betelgeuse]

Sorry if this question has been answered before but I tried the search and lurked through various threads and didn't find an answer. I even tried calling Heidts tech support and they wouldn't give a definitive answer due to liability issues. They did say they redesigned the IRS to an outboard brake system on the second gen camaros due wheel clearance concerns.



Before I blow 13k on an IRS, does anyone know what width wheel you can stuff under a mini-tubbed 78 Camaro with the Heidts IRS? I'm looking to run something like a 18x11 wrapped in a 315 or a 18x12 with 345s. I'd hate to waste time and money just to find out a control arm rubs on wheels with deep backspacing.

[SomethingClever]

Either of those sizes should fit just fine. Our ‘80 TransAm runs 19x12’s out back with 315’s (will go to 335’s next time around) and 18x10’s up front. I’ve attached some pics that will hopefully help give you an idea of what it looks like and the room it has back there.

Pay more attention to the fronts. The Heidts front subframe has a pretty tight turning radius. We didn’t do a good job measuring our backspacing and we can’t turn full lock in either direction without the inside of the wheel lips rubbing the control arms. Added some 1/4” spacers and that mostly fixed it, but we really need about 1/2” more offset to totally cure it.

Overall the IRS is great. We got creative with the exhaust routing, but I’d recommend using Spintech’s oval exhaust tubing to route it through the rear control arms. I saw a guy on HRPT last year that had done that and it worked great.

Hope this helps.

[Betelgeuse]

Thanks! I did end up going with the Heidts IRS but I have the newer gen 2. The IRS is currently dry assembled on a pallet waiting for me to get my car off the rotisserie. As for front end I went with a Speedway Unser edition front subframe that should be shipping in a couple weeks. I should probably start a build threads. Haha

[SomethingClever]

You definitely should! And holy crap I just noticed your post was from July. Sorry for raising the dead. I had no idea Heidts got away from the inboard brakes. That’s one thing I love about it. Going to the strip? Slap on some 15’s with slicks. I just checked their website and they have zero pictures of the updated design. Hell, I couldn’t even find the second Gen IRS on there. Id love to see what they updated and what you do with your exhaust. Post a link in here when you start a build thread so I can subscribe and follow your progress!

[Betelgeuse]

You definitely should! And holy crap I just noticed your post was from July. Sorry for raising the dead. I had no idea Heidts got away from the inboard brakes. That’s one thing I love about it. Going to the strip? Slap on some 15’s with slicks. I just checked their website and they have zero pictures of the updated design. Hell, I couldn’t even find the second Gen IRS on there. Id love to see what they updated and what you do with your exhaust. Post a link in here when you start a build thread so I can subscribe and follow your progress!

Sorry for the Necropost but I totally forgot I made this thread. I managed to stuff 335's in the rear wheel welsl with room to spare. I'm a bit disappointed that Speedway says 275's are the widest that you can run for front tires on their Unser Edition subframes. I went with their suggest max of 275s on 18x10s and there's so much room. Toyo says 10" minimum wheel for a 305 so I'll eventually pick up a set of front tires



As for the exhaust routing theres no room. I'm just going to do an axle dump. Here is some pics of the IRS fully installed. (except for the driver coilover which I need to flip because the adjustment knobs nearly kiss the lower A-arms and for some reason I didn't mark that side when I torqued everything down.)

I have a build thread over on NastyZ28 - https://nastyz28.com/threads/1978-z-...malgam.344828/
Maybe I'll copypasta all my posts over there to over here one day.

[Betelgeuse]

Heidts isn't exactly great at providing instructions or pictures. The assembly instructions used old pictures and I had to sort of trial and error assemble the rear.

[Blackarrow222]

My god that's an expensive item. You could get a C5 Corvette IRS with the Corvette still attached for that much money. OEM designed, government tested, and proven by countless miles on the road! Versus Heidts mushmouthing around in fear of lawsuits over a basic question?

[lees02ws6]

My god that's an expensive item. You could get a C5 Corvette IRS with the Corvette still attached for that much money. OEM designed, government tested, and proven by countless miles on the road! Versus Heidts mushmouthing around in fear of lawsuits over a basic question?

This argument never made any sense to me. Let's play a substitution game:

"My god that's an expensive LS3 swap! You could get a newer car that doesn't have leaf springs, and a flexi-unibody. The C6 will have the LS3 already and attached and be much better all around. Why spend all that money?"

You could sweep away the entire aftermarket car enthusiast world with that line of thinking. Lateral-g, pro-touring, ls1tech, thirdgen.org, Heidts, Holley, BMR, AME, DSE, UMI and all the rest could fold up shop.

[Blackarrow222]

To clarify, I meant you could buy a whole Corvette and take the IRS out of it to use in the swap, yielding the remainder of the Corvette to do with as you please. Really though, I was only using the rest of the Corvette to illustrate the price disparity.

[lees02ws6]

Just curious as to why you went with Heidts instead of AME?

[Betelgeuse]

I went with Heidts because I dont have to butcher my car to run an IRS.

[dhutton]

I went under the center with the exhaust on my Art Morrison IRS. Worked well. Dumps are a hard pass for me. Dusty, smelly and noisy….

[Betelgeuse]

The car sits pretty low, I maybe have 4.5" below the IRS cradle. I wish I diy'ed my subframe braces because I would have tucked them up into the floorboard like Detroit Speed braces. Then I could run side pipes.