Rim And Tire Expert Chime In Because I Am Still Totally Lost

[kingcolbert83]

http://www.rims-n-tires.com/rt_specs.js ... t1=&text2=


I want to do the 18's in front and 19's in rear like the corvette with the same tire sizes. Rims are 18 by 8.5 in front and 19 by 9.5 rear. Tires are 245/40/18 front and 285/35/19 rear. Overall diameter is 25.7 on front and 26.9 on rear. These rims are really for a bmw with 5 by 120. I think our cars are 5 by 120.65 but they will fit. I will have to run some spacers probably because they have +15 offset.

I put all these numbers in the calculator but I still have no clue if the rear tires will clear without any problems and finding out what size spacers I will need. I am not worryed about the tires height in rear because I have adjustable air shocks. More concerned about them rubbing the frame on the inside. I had 255.70.15 on the rear before and they rubbed the inside frame rail on dips and some tight corners. I think these were taller than the 19" tires.

 

[billyjack]

4 inch backspace is just about right to keep the tires away from the frame. 4 1/4 may work, but it will be real tight, and it won't leave you much sideways play when the bushings flex under cornering load.

Bill

 

[khan0165]

4 inch backspace is just about right to keep the tires away from the frame. 4 1/4 may work, but it will be real tight, and it won't leave you much sideways play when the bushings flex under cornering load.

Bill

billyjack is right...
specially if you have an 8.5 rear end, I would not recomend more than 4" backspacing.
Forget that fancy calculator, it'll give you nothing but headaches. Go out and place the rim+tire at the hub, and measure how much spacing you need. Then buy the next size up spacer.

 

[kingcolbert83]

viewtopic.php?f=25&t=14287

This guy backspacing is 4.75. Thanks for the help. Still want a definite answer or better understanding of the calculator. I just dont want to go get new tires and they dont fit or I have to do so much modifying that its more headache than its worth. I want to go in there and get my tires and leave. I've done the I think it will work thing too many times and had to modify something to work and wasted money trying stuff to get it to work. LOL. Rather not do that with rims and tires. Think I will try getting it right the first time.

I think I wont run into any problems with rubbing the frame that much though. I know I still may need spacers because of the offset. I used to have 255/70/15 on the rear and it rubbed the frame rails in slow tight corners and inclines but I just checked tirerack on overall diameter and the 15" tires I had have an larger overall diameter than the 19" tire. Considering that I may just buy them, put on hub and then get the required spacers. 😀 Knowing what spacer size I need in advance would be nice though so I can have everything at once instead of having to order them and wait. And we all know how it feels waiting for something to come in the mail.

 

[FE3X CLONE]

You need to measure, measure, measure!

Take a wheel off and place a straight edge against the brake drum/wheel mounting surface. Then take a tape measure and measure back to your frame. Record that length.
Next, tape a plumb bob to your inside fender lip and then measure from the wheel mounting surface out to the string. You can also measure your overall width from the frame out to the string as well.

The measurement from the wheel mounting surface to the frame will tell you how much backspacing you can run.

In the case of that calculator, your rear wheels have a 5.8" back spacing. So to get them to clear the frame, you would need a 1.8" thick spacer. Of course that now means you have moved the entire wheel 1.8" out towards the fender lip.

Do you have any sort of AutoCAD program? When I was measuring for my wheels/tires, I took all of my measurements of my wheel wheels and then drew a section in AutoCAD of the wheel well, wheel/tire combo and frame rail. Then I moved the BS around until I could visually see what would fit properly.

 

[khan0165]

I've tried to do this on several cars now, and the outcome always ends up WAY too expensive.

For example, I once thought I got a heck of deal when I bought 17x9.5" ZR1 Vette wheels, polished Alloy for $400. But, the tires for these (275s all round) would run me into $700 if I went for a good brand like Goodyear or BFG. And 2.5" spacers (billet alloy type) for 4wheels would add another $300 to that cost.

The end result would be $400wheels + $700tires + $300spacers = $1400 for a so-called amazing deal on upgrading to 17" wheels on my car.

... in the end, you need to look at how badly you want to do this, and if that outways the costs... To me, $1400 was not worth it...