315/30R18 Square on 1968 Camaro w/ Stock subframe

[Sleeper68]

Hi Everyone,

I have a 1968 Camaro RS that I autocross regularly in SCCA Solo, CAMT class. I currently am running 245/45R17 squared on 17x8 wheels. In this class tire size is unlimited, Thus I would like to fit more tire. The car weighs 3200 lbs w/o driver and 245s are not enough. I would really like to run square 275/35R18's square soon and I believe I can do it w/o major mods.

I am interested to know if anyone fit 315/30R18 on the FRONT w/ stock subframe and what mods are required to do so. Also suggestions for required mods to fit 275/35r18 on the front are also welcome.

Current pertinent mods include:

~400HP/425 lb-ft gen 1 SBC
open diff
4spd Muncie
SPC adjustable upper a arms w/ Tall howe ball joint
SPC tubular lower a arms w/ ride height adjustment shims
DSE 2" lowering coils springs
DSE 2" lowering leaf springs
Unisteer power rack&pinion 2.5 turns lock to lock, 2.25 turns before rub on frame
17x8 Amer. Racing +11mm offset on front wheels
Hellwig ARBs

Thanks to all in advance for help with this issue.

Regards,

Ryan

[72_Nova]

you should be able to fit 275 no problem with a 9.5'' wheel. 315 on an 11'' will work as well with the right offset up front and a little rolling of ur fender. For either 275 or 315 you will need to mini tub the rear. I have 315 on front of my nova which has the same subframe as the 1st gen Camaro but it does rub on the subframe once I go past a certain point. For autocross and road racing it is not an issue unless you run a good guys course...

[the owl]

I would be curious to know what mods people are doing to fit a 315 up front. I am running a 265 up front and hit the stock subframe and don't have too much room between the edge and fender.

[Sleeper68]

you should be able to fit 275 no problem with a 9.5'' wheel. 315 on an 11'' will work as well with the right offset up front and a little rolling of ur fender. For either 275 or 315 you will need to mini tub the rear. I have 315 on front of my nova which has the same subframe as the 1st gen Camaro but it does rub on the subframe once I go past a certain point. For autocross and road racing it is not an issue unless you run a good guys course...

I know I can fit 275/35r18's on the rear no issue, because I have physically bolted some on; 18x9.5 wheel with +14 mm offset I believe. I think 68-72 Novas may be a little more narrow in the rear compared to 67-69 camaros. 275's on the front of my car seems to be a bit more of a challenge, mostly with the rear side of the inner fender. The tire hits the inner fender before the inner lip can contact the frame. I imagine a more positive offset wheel is needed. I have yet to experiment with different wheel widths and offsets. I plan to make or purchase a wheel "test fitter" which would have adjustable width, diameter, and offset and a hub drilled for common 5 lug bolt patterns so fine tune the positioning if the tire.

315s on the front w/ stock frame is a great goal and you seem to have achieved it. What suspension do you use? I am thoroughly impressed if you have use of your inner fenders.

Thank you for the reply, I apologize for the late response.

[Sleeper68]

To help those who may be interested in this topic, I have successfully fitted 275/35R18 tires on a 9.5" wide wheel on my car. Stock subframe, sotck inner fenders, no mini tub, with leafsprings.

If you want more info, reply to this thread.

[btmatt]

I am interested; my front suspension is very similar to your original post. Thanks, Matt

[Chad-1stGen]

To help those who may be interested in this topic, I have successfully fitted 275/35R18 tires on a 9.5" wide wheel on my car. Stock subframe, sotck inner fenders, no mini tub, with leafsprings.

If you want more info, reply to this thread.

Carl Casanova (CarlC), a longtime forum member and moderator has successfully done the same thing on his car. In fact, I think he now has 285's on all four corners. His old site documented is original effort to fit 275's on a 17" wheel. Still viewable on the wayback machine https://web.archive.org/web/20091026...s.com/casanoc/

It would be great to get an updated guide for folks running 18" wheels. I'm also aware of a 68 Camaro running local autocrosses with 305's on a 19" wheel but he notched his stock subframe.

[lbsurfer11]

To help those who may be interested in this topic, I have successfully fitted 275/35R18 tires on a 9.5" wide wheel on my car. Stock subframe, sotck inner fenders, no mini tub, with leafsprings.

If you want more info, reply to this thread.

I would be stoked on more info. 275’s all around without a mini tub and leaf springs is what I am shooting for. Thanks in advance.

[Sleeper68]

The wheels I purchased are from a company called Kansei. Newer company run by a wheel design engineer. The wheels are made by his partner company Raceline. They have been making offroad racing wheels for years.
They did a "custom" bolt pattern for me 5x4.75" (5x120.65) and added 60° steel wheel nut seats at no cost which is awesome. No need to drill you wheels yourself in a mill or otherwise.

The wheels at 18x9.5 +22. In the rear I used a 0.5" (13mm) spacer and added a hub centering ring that I made, although it's probably not necessary. The front of my car is probably alot different than most though because of the interesting stuff I did. The hubs I'm using are original 1st gen Camaro Drum hubs. Knocked out the 7/16" studs, drilled and tapped them for 12/2-20 studs, and installed the 3" ARP screw in wheel studs. I am using a C4 J55 rotor (13") and a 2 piston D52 caliper. 52 is the 7.0625" pattern floating caliper that was used on F bodies, A bodies, X bodies, etc from 1965-1976 I believe. To make these work together I made my own caliper bracket.

This somewhat unique front hub assembly is what allows me to use the +22 offset on the Kansei's. Using Wilwood, Baer, or Corvette hubs would likely change what offset you'd need.

I also had to modify my SPC upper control arms. The inboard curved male threaded link was inverted to help clear the wheel barrel. I also had to notch it slightly to clear the upper control arm mounting hron. It has worked great so far. the Tire do rub the frame but I still get about 30° of steering angle. Pictures attached.

Ryan

[CliffsBlueCamaro]

I've got 275/35/18 on 18x10 wheels on all four corners of my 67 Camaro. Backspace is 5.75"

I did roll the fenders and I have tubular front control arms - but honestly they fit without much hassle.