The official Tire and rim Thread!

[NixVegaGT]

Excerpt from "MegaVega" project journal:

the backspacing is listed, its in the section where the car with wheels on it at ride height is. 4 inchs of backspacing, the tire size is a 235/45/17 on a 8 inch rim. You could go larger with rear tire size if you dont want the car as low as I have mine set up, its just in what kind of look your trying to achieve and your own personal taste/like.
I will be using a 17 x7 front rim with 4 inch backspacing and a 215/45/17 tire. The 235's will clear as far as the width up front, there is plenty of clearance even at full wheel lock to the frame and the tie rod ends BUT they do interfere with the fenders front lower edge when turning, so you either have to section the bottom front lip edge( this is the part of the front fender down by the little brace that runs to frame rail) or just run a slightly smaller tire as I chose to do.

This seems to support Scott's setup concept of 215 or 225/40 r17 up front. Fat. I think I'm doing this.

[NixVegaGT]

I found a good source for wheel information:

https://www.rsracing.com/tech-wheel.html

Good stuff. I'm going to need to measure for tires/wheels. I'll post what I discover. Here's the table from that website. Good stuff:

[spyder_xlch]

Nice find Nic.

[NixVegaGT]

It was suggested I post a portion of my latest part of my project journal that deals with tire/wheel choice. I wanted to get some actual measurements of my car to be certain of my rim and tire choice. I was burned by the FAQ on the 8.5" rim w/3.75" backspace fits the wheelwell post. That might work on a Monza but definitely not an early Vega. So I decided to build a test rig to get some measurements of the sweep of some tire/wheel choices I wanted:

***************************************************************************

I decided to build a rig to measure how big I could go for tire size. This should also help others for tire size. I've removed the inner gusset that would technically interfere with the widest tire. Here's another pix of that:



As you can see I've flattened that gusset out. Here's a pic of my rig. For the sake of outlining the factors I've got 28-spline S10 axles in a Monza housing. I'm retrofitting '04 Malibu Maxx rear discs. They are 0.3" thick at the flange. I pushed the rear axle way up into the well. I figured out I could use as large as 245/45 R17. The specs on that tire are: 9.6" sect. width, 8.7" tread width, and 25.7" dia. That would come really close to the full extent of the well. 245/40 R17 worked out as well: 9.8" sect. width, 8.7" tread width, and 24.7" dia. With these tires the width is right at the extreme with 1/2" to spare at the rear and about 1/4" from my rolled wheel well rim. I may go with 235/40 R17 just to be safe: 9.5" sect. width, 8.4" tread width, 24.4" dia. The more I think about it the first one is the best choice though. It's got good section width, clearance to spare, and extra tread width. The only thing is the overall dia. It's an extra inch, raising the ride height 1/2". Hmm. Anyway here's my pix. In order to fit these tires in here with even clearance I worked out that I would need 4.2" backspace. Looks like if I get the Torqlite 8x17 0-offset that should work out to needing a 0.3" spacer. I figured I could get an extra couple rear rotors and have the flange cut off then use it as a spacer!





Hopefully this will help others make the right choice for them. I think it's pretty important to get the right measurements for your actual car. I think we are dealing with some inconsistencies based on what axles we are using or modifications we've made. Good luck everybody.

[NixVegaGT]

I ran into some inconsistencies about using 4.5" backspace with an 8" rim. After thinking it over for a while I went back and measured based on offset only. That was WAY easier! I suggest doing that if you can. It turns out many times backspacing can vary up to 1/2" or more. Using offset is not only more accurate but a lot easier.

When I went back to adjust my a rig I discovered that I was off by about 1/4" so that means my idea of using a 300 thou spacer is probably not necessary. It put the tire in almost the same location as I had with the backspace measurement + 300 thou spacer. Interesting!

[AusRs]

i like that test rig
i think our cars are all different
i have 7 inch rims with zero offset ,on the passenger side i have approx 5/8 inch space between the frame and the tire
on the drivers side i have around 1/4 inch clearance on the gusset you removed clearance (i will clearance a little more with a BFH
i have read many posts and FAQ on what will fit .none of which appear to relate to my car
BTW are you comfortable removing that gusset ? i was not as it appears to me that it would take a lot of the forces when cornering as it is a brace for the panhard assembly ,just be carefull that you put something back to replace what you are taking out even if you transfer some form of gusset to the inside

My car is stock Monza axle width rims are 14x7 zero offset (3.5 in 3.5 out ) Tires are Maxxis 205/60x14

Personally i would like to have a slightly different offset i would like 3 inch in and 4 inch out as it would fill the wheel wells better However i have never seen rims with that offset/backspace

[Astre-mutt]

This is where I think people can make a mistake when mathematical figuring backspacing. The problem is that a 8" wheel for example is not 8" wide. This is a pic from the site NixVegaGT posted. The wheel width is inside the beads, but backspacing is figured from outside the bead. So for example a 8" steel wheel will be narrower overall then a 8" cast wheel. On my car the 9" wheel is actually over 10" wide.

These measurements will not be as important on a wheel, and tire combination where the tires are wider then the wheels.

[megavega]

I guess I will have to agree to disagree with your statement Scott, "ALL" rims are measured the same way. Its always been done as the rims width is measured at the bead seats. Buy any 8 inch rim from either of any aftermaket company or any stock automobile company and it will measure 8 inchs between the bead seats. Its this measurement which is crucial for the tire fitment, this determines the sidewall bulge,tread width and various other measurements provided by the tire manufacture. As if it was not held true your tires would not fit correctly, you cant simply put say a 245/45/17 on a 6 inch wide rim, nor a 12 inch wide rim. Tire manufactures all reccomend a rim width for tires, thats why the std is the rim width to be measured between the beads. It has always been checked this way since rims were built, both factory and aftermarket.

The biggest confusion comes from the offset vs backspace measuring methods, the offset method takes in consideration the overall width of the rim inluding the bead stiffner edge, while maybe on some applications this would be crucial but most any tire you put on covers that up. I beleive its a personal choice as to which method you use. Both work and get the job done.

[Astre-mutt]

Just for the record, I did say that rim width is measured from inside of the beads. So all 8" rims will measure 8" from bead to bead no mater what they are made from. The point I was making is that the backspacing isn't measured from the inside of the bead, but from the outside of the rim. So if you have a 8" rim with 4" backspacing, doesn't mean you will have a 0 offset. You have to take into consideration bead width.

[NixVegaGT]

BTW are you comfortable removing that gusset ? i was not as it appears to me that it would take a lot of the forces when cornering as it is a brace for the panhard assembly

Thanks for asking, Man. I did consider the gusset strength as relates to the panard bar mount. I actually ended up welding a bar across the rear of the axle hump. Here's a link to the page that talks about the mount I made:

viewtopic.php?f=20&t=19422&st=0&sk=t&sd=a&start=45

[AusRs]

BTW are you comfortable removing that gusset ? i was not as it appears to me that it would take a lot of the forces when cornering as it is a brace for the panhard assembly

Thanks for asking, Man. I did consider the gusset strength as relates to the panard bar mount. I actually ended up welding a bar across the rear of the axle hump. Here's a link to the page that talks about the mount I made:

viewtopic.php?f=20&t=19422&st=0&sk=t&sd=a&start=45

I should have taken more notice of your project journal shouldnt I !!!!!!!

[NixVegaGT]

Your point remains though that we should consider the gusset strength as relates to the panard bar when removing it. Maybe we need to then build a gusset that welds to the inside of the axle hump. Like a triangular gusset that welds up inside. Make sense? Anybody else?

[spyder_xlch]

When GM put that gusset there they didn't intend on stuffing fat 15" tires in the wheel well. I think you made a nice improvement Nic.

[AusRs]

Your point remains though that we should consider the gusset strength as relates to the panard bar when removing it. Maybe we need to then build a gusset that welds to the inside of the axle hump. Like a triangular gusset that welds up inside. Make sense? Anybody else?

It is kind of a tough one ,makes you wonder why GM did not make the support an inni instead of an outy .......could have something to do with leverage on corners ,i agree that it looks way nicer(and more practical ) without it though ,main thing is you have taken it in to consideration when removing it from the inner fender

[gt350fme]

This was our answer for strengthening that fender well clearencing, 1/4" bar stock tucked in real tight as to clear the coil spring.