School me in the art of backspacing

[blykins]

I'm trying to get this perfect in my mind before I order a set of wheels.

Tell me if I'm seeing this correctly......Consider this scenario:

You have two wheels. One wheel is a 15x10 with a 4.5" backspacing. The other is a 15x9.5 with a 4" backspacing.

Now if I've been reading the material right, a 10" wheel is actually 11" wide from lip to lip because wheels are generally measured from tire bead to tire bead. (Taken from Team III website.)

So in our cases above, we have in all actuality a 11" wheel and a 10.5" wheel.

Backspacing and front space make up this distance.

So if our 15x10 wheel is actually 11" wide and has a 4.5" backspace, then there is 6.5" of front space....or pretty much wheel dish.

Likewise, if our 15x9.5" wheel is actually 10.5" wide, but has a 4" backspace, then there is again 6.5" of front dish.

So in both cases, we have the same dish, but the 9.5" wheel is gonna be an inch narrower and therefore sit back in the wheel well further.......

Is all this correct reasoning?

[vettestr]

This site has many of the answers you are asking and from the pros on top of that. Just bounce around till you are an expert like me, well I did read 1/2 so guess im half an expert. Also good prices
http://www.tirerack.com/wheels/tech/offset.htm

[strictlypersonl]

Just to muddy the waters up a bit more...

Remember that increasing the "front spacing" while keeping the same tire moves the tread only half the distance out. The tire always stays centered on the rim. (Duh...)

[trularin]

Take an edge off the lip of the fender and measure the distance from that edge to the face of the rotor ( where the studs are ). Then subtract 1/2".

I hope I got that right, it's been a while.

Goofy as this sounds, you can make a model of your tire setup with a sheet of cardboard and bolt/tape it to the rotor. Then you can see if there are clearance problems. Once you are done, you can just measure what you have.

Just my $ 0.02

[blykins]

Guys.....I did a little AutoCAD'ing at work today (don't tell anyone) and made a diagram of some wheel widths and backspacing. I was wrong in my first post on how I explained it....and drawing it out made me realize it. I'll post the pic below. It shows the relationships between 15x10's and 15x9.5's with various backspacing measurements. The wheel is represented by a square of course....the vertical line in the middle represents the inside mounting face of the wheel flange. By lining these different drawings up in line with each other, you can see how the backspacing and widths change the positioning of the wheel.

[blykins]

What gets me, however, is the differences between the actual wheels or wheel manufacturers themselves.

If you look at the blue Shell Valley car below (courtesy of Luc and Club Cobra gallery), this car uses 15x10 Team III's with a 4.5" backspacing. Note how shallow the rear wheel looks. It doesn't look deep at all.

Now if you look at the picture below that (courtesy of www.ffcobra.com wheel gallery), this FFR uses a PS Engineering 15x9.5 with a 4.25" backspacing.

If you glance back up at my wheel comparison drawing, you'll see that there really isn't that much difference between the two. The 9.5" wheel is of course smaller, but if anything the "dish" in the wheel should be more shallow.....but if you look at the FFR, the wheel looks twice as deep as the Shell Valley car.

This leads me to believe there are differences in wheel manufacturers and how thick their mounting flanges (or wheel centers) are......I guess if you have a thinner flange, it would leave more room for a deeper dish.

If anyone else has any insight, I'd love to hear it.

[blykins]

Other pic...

[Dominik]

I would go with Trularin's advise, because backspacing kept buggering me around as well.

just consider that your 235 adds just above 1/2" to the rim and the 275 about 3/4".

1 degree of camber though let's the tire tilt inwards by 3/8".

I posted measurements of the TRIGO here:
http://www.clubcobra.com/forums/t509...-&pagenumber=2


"Cobra wheels have 3.1/2'' backspace I am told.?"

I took some measurements from the TRIGO set. I never really got used to "backspacing" or "offset":

25.4 mm = 1" (sorry for metric values)

front nominal width 7.5"
total width: 214 mm
wheel mounting face towards brakes: 92 mm
center section thickness: 67 mm
take wing nut off and measure to outside: 55 mm
wheel mounting face to outside (towards fender): 122 mm

rear nominal width 9.5"
total width: 264 mm
wheel mounting face towards brakes: 92 mm
center section thickness: 67 mm
take wing nut off and measure to outside: 105 mm
wheel mounting face to outside (towards fender): 172 mm

Dom

[trularin]

Blykins!!! Is that your car?

Looks very nice.

You did a great job.

Details???? Why the Blue with the Dark blue stripe? Looks excellent.

[BMK]

Blykins

Just had a look also. Great combo. with the blues. Looks really sweet.

We have a similiar blue to the body colour over here on the early Ford Falcons (Comets). Viking Blue if I'm right?? (Photo 2)

Anyway looks great if the second photo is your car??



I'm going to turn my tyres/tires around after seeing the B. F. Goodrich TA on the outside. Cannot recall why but I placed the writing/letters inside.



Bernie

[blykins]

Guys....before everyone else congratulates me on a nice paint job....neither of the cars are mine.....hehehe.....

I mentioned earlier in the post who they belonged to.....they are sharp looking rides though..

Thanks to all for their input.....