My $2.01 insurance policy....

[2ndgen]

Dodgestang has a great fitment chart for tire/wheel combos, but lets face it - the tolerances on these cars are +/- 1/4 inch...

Cull 1x6 lumber from home depot: $0.72
1/2 inch dowel from home depot: $1.29

Piece of mind: priceless!

It looks like for my car the optimal backspace for a 9.5 inch rim is 5.75 inches, and yes there was variance from side to side.

Hope this idea helps someone else!

-Rory

 

[blue65coupe]

nice thinking

 

[AzPete]

Does that backspacing take into consideration the tire bulge also? Not a bad idea.

My first thought was an ins. policy using a 1x6 to secure the car??????????

 

[buening]

Damn, and here I thought I'd find a way to save on insurance. So easy a caveman can do it :lol :lol

Slick thinking, I'll have to remember that when I measure for my rims. There is a tool that does this, but it costs much more than $2

 

[2ndgen]

Does that backspacing take into consideration the tire bulge also? Not a bad idea.

Yes, it does take tire bulge into consideration. What it does not take into consideration is the shoulder of the tire (e.g. the curvature between the tread width and the max tire width, so the model is conservative in nature. For example the tire being modeled is a 275/40/17 which has a tread width of 9.6 inches and an overall width of 10.8 inches. The outer dowel is showing the 10.8 inch width at the edge of the tire (e.g. at 25.7 inch diameter)

-Rory

 

[KBMWRS]

Ya know that's gonna break on the first rotation....ask me how I know. Made a bunch of noise too. :vic :lol :lol

 

[tarafied1]

I've got 275/40/17's on 9.5" rims with 5.75 BS on mine. I like your gage! I used a straight edge and my calipers. I have about a 1/4" difference side-to-side

 

[stangg]

That is super simple.... I like it. To go 1 step further with it ... you could drill holes every 1/2" or so and you could set one dowel up at the treads radius and then another at the tires sidewall and maybe even another at the rim radius. To get a feel for the bulge. Cut one dowels the width of the rim, the second the width of the bulge ( is that considered the tire's section width ), and the last on the tread width.

Edit... I read too fast, you already have two dowels... just add one for the tread width as that seems to be where the majority of interference is is on the inboard side of the tire against the front of the inner wheelhouse.

 

[2ndgen]

That is super simple.... I like it. To go 1 step further with it ... you could drill holes every 1/2" or so and you could set one dowel up at the treads radius and then another at the tires sidewall and maybe even another at the rim radius. To get a feel for the bulge. Cut one dowels the width of the rim, the second the width of the bulge ( is that considered the tire's section width ), and the last on the tread width.

It may not be obvious...

The inner dowel is at the rim radius, and is cut to the width of the rim (taking into account the rim thickness - so on these 9.5 inch rims the inner dowel is about 10 inches wide. I thought about a dowel at the middle of the sidewall, but in the end I decided that since I could not determine the shoulder radius or model the full suspension travel, the next best thing was to put the tire's widest point all the way out at the edge.

Overall I am quite happy with this since I was considering a 6 inch backspace and it was just too close on my car - although I am sure it could be made to work with a BFH.

-Rory

 

[SELLERSRODSHOP]

great minds think alike! :craz here's a similar tool i made out of scrap in the shop. it extends out to measure up to 20"x 11" wheels. i bolt it up, set the diameter then test width & backspacings. i cut & attach a cardboard template of the tire cross section based on specs given at tire rack. maybe i'll beadblast & paint it someday....

 

[daveSanborn]

It looks like for my car the optimal backspace for a 9.5 inch rim is 5.75 inches, and yes there was variance from side to side.

Your gauge is pretty neat for getting an idea of what will fit, but I'm fairly certain that using a 275/40/17 tire on a 9.5 with 5.75" BS will cause you an interference problem at the front inside lower corner of the inner fenderwell.

My son's '68.... and if I recall correctly Rick's '68 (fast68back) both use this size tire on a 5.5" BS wheel and both of ours hit the inner fenderwell under slight suspension compression/articulation. Many others have reported the same results. Using a 5.75" BS wheel would only pull the tire closer to the inner fender than ours did.

Good luck!

 

[2ndgen]

The area you describe is the exact reason I cannot run a 6 inch backspace... some minor adjustment of the pinch weld and it looks like it will now clear the 5.75 backspace with a margin for safety. My car is a 69 though...

-Rory

 

[daveSanborn]

My car is a 69 though...

Ah, this changes things then.... I tried searching through some of your posts to determine the year of your car, but got side-tracked. A '69 should give you a little bit more room.