315's on a Mark I

[FFR1545]

So it has only taken me 11 years to decide to put 315's on FFR 1545. Any old timers here who remember what all is involved in making the change. I am going with 315x35x17 on 10.5 cobra R wheels with like a 27 mm backspace. I have a three link with VPM swaybars. I know I am going to have to do some cutting and re-arranging of some trunk sheet metal. Any old posts or build sites that show the modification. I have had no luck finding any real details. I am only doing this to put wider race rubber on the car, I hope it is worth the trouble, I already bought the tires, so I am committed.
Thanks, Aron

[Roadster]

Pic's here.

http://www.norcal-cobras.com/projects/FFR_1046-mods/tire-clearancing/

It involves cutting back the shock tower a bit and cutting back the 2x3 square tubing. You will also have to modify the sheet metal near the rollbars. Easier to just cut out the 3/4 bar and make some aluminum panels.

David bordon did it YEARS ago and the pics still work... take a look and ask questions.

EASIER TO DO WITH BODY OFF. But it can be accomplished with body on.

Heres a newer version... Scroll daown to 315 mods.

http://legacygarage.com/prod02.htm


Rgds

Rob

[Mike N]

Here's what I did to mine to get 315's on

For those that are not familiar the MkI / MkII chassis have a slightly different structure at the back of the car that makes running 315 section tires questionable due to tight clearances to the 2X3 steel behind the seats and the trunk side aluminum.

http://www.ffcars.com/photopost/data/550/tire-clearance.JPG

The right hand photo shows the passenger side after surgery and the left hand photo shows the drivers side before. Here is the clearance to the tires, the tight clearance area is at the back of the cockpit by the 2 X 3 steel behind the seats.

http://www.ffcars.com/photopost/data/550/chassis-mods.JPG

Here is a before and after photo showing the inside 3/4" tube relocation. All I did was cut it out and re-weld it with the diagonal going in the opposite direction. I then put a slight bend in the aluminum along the lower edge of the 3/4" tube and trimmed and relocated the front (cockpit) edge of the aluminum to the inside of the vertical 3/4" tube that comes off the end of the 2X3.

http://www.ffcars.com/photopost/data/550/shocks.JPG

This photo shows how I moved the top shock mount down and inboard slightly. This allows me to eliminate the shock 'tower' intrusion into the trunk space, if you look at the above photo again you can see the new shock tower is now below the trunk floor. I also made a double shear bracket and welded it to the FFR lower control arm bracket to relocate the inner shock mount inboard and directly in line with the upper. This allows me to run the Konis body down and gives plenty of clearance to the rear Cobra brakes which I still have mounted behind the axle.

http://www.ffcars.com/photopost/data/550/off-cuts.JPG

The last photo shows what was removed from the 2 X 3 and the old Mustang spring mount which was cut out to save weight and make room for a rear sway bar. I will box in the open end of the 2 X 3 and top of the shock mount before painting.



My intent was to make it a very subtle mod which wouldn't be apparent to the untrained eye. I'm pretty happy.

I am also replacing the straight trunk 3/4" tube with a curve piece, welding in extra roll bar 'stubs' to accept a full width roll bar and I intend to weld in door bars. I'll start another thread with those when I get that far.

[Mike N]

Here's an after photos with FR500 10.5 x 17 replicas and Sumitomo 315 tires.

http://www.ffcars.com/photopost/data/550/DSC_0150-crop.JPG

http://www.ffcars.com/photopost/data/550/315crop.JPG

And here's a photo with 315 Kumho V710's

http://farm6.static.flickr.com/5175/5425911596_2d5d905776_o.jpg

[FFR1545]

Thanks Guys, That should get me started, as soon as the tires and wheels show up I will tackle the project. I am going to try and race more this summer and hope I can shave a little time with some wider rear tires.

[Ophitoxaemia]

I did mine 315 mod with the body on. Key point is you have to cut out, make a new longer piece, and reweld the horizontal 3/4" square tub directly in front of the tire. The 2x3 needs to be cut inside the attachment points. I cut and bent the tubes inwards, but used the same aluminum, just bent inwards and re-riveted.

Don't omit the diagonal on the side of the trunk. It's what holds up the gas tank.

Note you end up may cutting off your welded chassis number (I did)

(I had also previous retrofitted IRS to my car, so it might be a little different for a straight axle)

Great mod! I've got 11 inch wide rear wheels now.

[patpur]

I guess I'm lucky, the MKI I just bought came with 315's and ET spoke wheels. No rubbing, nice smooth ride. Eventually I plan on switching the wheels out.

[CraigS]

I have been able to get away w/ leaving the 3/4x3/4 that runs out to the door latch in place.Mine looks much like the first pic of MikeN's.The finished one. I still get just a little rub on that 3/4x3/4 right where it connects to the 2x3 but it's been that way for three yrs w/o hurting the tires.So make that as smooth as possible. It depends on your combination of ride height and spring rate.

[Mike N]

I only get very slight rub on the aluminum at the front of the tire there is at least 2" or clearance to the 3/4" tube. The early chassis seem to have more variability than the later ones so best to evaluate your own situation carefully before you commit. By the way it makes the change a lot simpler by not moving that short piece of 3/4" tubing. If you move that the aluminum requires a lot more massaging to make it work. I don't have carpet in mine and the aluminum stills looks very nice of course if you needed to patch the aluminum it would be covered with carpet in most instances.