Wheels-Tires-BackSpacing-Offset-HELP!!!

[Ludigdrums]

Ok, I've been doing a lot of research about all this stuff and have some questions:

1. What is the effect of having different size rims between the front and the back? Example: 17" Front 18" Back. As long as the tires make up for the difference in total tire height, is that ok...does it affect speedo/rearend ratio?

2. What were the stock specifications for an '81 Vette in regards to offset/backspacing/tire height/etc. I think I know some of this but would like clarification. Also, as far as offset goes...what are the effects +/-

3. I think different tire manufactures have different measurements for the same tire sizes...this can cause confusion because a tire that's 255/60/15 from Goodyear will measure differently than the same size BFGoodrich. Am I correct with this?

Any reccomendations regarding all this is greatly appreciated. My Vette has Duntov Turbo body panels, which makes the fenders come out much farther than a regular Vette. I already have custom rims from the previous owner, and it uses spacers, which I want to get rid of consider my rear wheel almost fell off a couple months ago...which lead to a disguised messed up spindle/bearings that cause me annoying brake problems. Anyhow, I'm replacing the whole trailing arm assembly with offset ones and would like to pair everything up with a nice new set of rims and tires.

Thanks as always for reading and offering whatever advice you can!

- Jeremy

 

[70 LS1]

Different size rims and tires front to rear is no big deal. That all depends on the look you want. I personally like the front wheels to be 1" smaller in diameter than the rear which is why I run a 17/18 combo. Changing overall tire height will affect your speedo slightly as well. Stock tire height is right around 27" so you want to keep it close to that. My 275/40/18's are 26.7" wich is close to the ideal 27".

Stock rims are 15x8 with 4" backspacing. You can run more backspacing to move the wheel inwards and less to move it outwards. I have no idea how much wider you fenders are from stock, but you will be able to run some pretty wide wheels and tires under there. When I was choosing mine, I checked with the various tire company websites to get measurements such as tire height and width.

What size rims and tires are you currently running? What size spacers? What size rims and tires are you considering?

hope this helps.

 

[Ludigdrums]

Thanks for replying Jeff. I currently have 255/60/15 in front and 275/60/15 in rear with 7/16" spacers. From what I could gather with the tires still on the rims, I think they are 15x10...it's hard to tell.

I was considering 17 or 18 in rims...like you said, I was thinking maybe 17 in front 18 in rear. I currently have regular trailing arms, but will be getting offset ones from VanSteel...I guess I'd like to go as big as I can without getting too close to anything.

I was also wondering the advantages and disadvantages to real large tires, other than rubbing.

I've attached some pics of what it currently is.

Thanks again!

- Jeremy

 

[70 LS1]

Jeremy
Do you know the backspacing of your current wheels?

If not, lay them on the ground, face down and measure from the outside of the wheel to the mounting surface. This will be your backspacing.

Do you like where the edge of the tires are now in relation to the fender?

Do you have spacers on the front and rear?

 

[Ludigdrums]

Hey Jeff,
Yes, it's 4" currently, and I have 6" from the front of the rim to the top of the mounting surface.

Yes, I also like where the tires are in relation to the fender...they are almost perfectly in line, if not, just a bit inside the fender.

Yes, the spacers are in the front and the rear.

Thanks again...keep 'em coming!

- Jeremy

 

[ChrisH]

If you like where your wheels come out to now and I underatand how this all works? I think offset trailing arms give you an additional 1.5" of backspacing so, can't that plus your backspacing on your wheels now and your spacer be added all together to come up with the disired new wheel backspacing. Which would be 1/16" shy of 6'' for your new backspacing. That 6" plus present 6" to the front would equal a 12" total wheel width. Any way thats what I come up with, I hope this is of some help. My '68 has ZL-1 type flares and I went through this when I was looking for new wheels about two years ago and posted a question like yours here. Also you are correct in that tire manufactures have measurements different for the same size. I studied up and am pleased with my wheel and tire choice. Good luck!

Chris

 

[70 LS1]

I would go with 10.5" wheels up front and 12" in back. 4" backspacing up front and 5.5 in the rear.
As for tires I would look for something near 275/40/17 up front and if you can find them something near 315/35/18 out back. I don't know if these sizes are even available, but off the top of my head they seem about right.

 

[70 LS1]

Or if you want something a little more affordable, try stock Z06 size tires.

Front - 17x9.5 with 3.5" backspace and 265/40/17

Rear - 18x10.5 with 4" backspace and 295/35/18

 

[ChrisH]

Sorry I only figured the back wheel. I would say 10.5" for the front wheel width and 12" in back.Chris

 

[ChrisH]

I went the wrong way with the spacer measurement, 70 LS1 is right in the 5.5" backspacing for the rear wheels with a 12'' width and 4'' backspacing 10.5'' width up front.

 

[Ludigdrums]

Thanks a lot for you responses guys!

What sizes do you guys run?
Any bad things to know about as far as running such large tires?

I just am hopeful that my measurements are correct, and it comes out the way I want to.

Thanks again!

- Jeremy

 

[70 LS1]

I am running stock C5 sizes on my 1970.

front - 17x8 with 245/45/17 Kumho Ecsta MX
rear - 18x9.5 with 275/40/18 Kumho Ecsta MX

I can post some pics if you want.

 

[Ludigdrums]

Sure, I'd love to see some pics! Thanks...

 

[70 LS1]

I tried to attach some pictures, but the files were too big. Here are the links.

http://temp.corvetteforum.net/c3/70lt1//rearwheel.jpg

http://temp.corvetteforum.net/c3/70lt1//frontwheel.jpg

http://temp.corvetteforum.net/c3/70lt1//garage.jpg

 

[Ludigdrums]

Nice car and wheels! I think I really like the rim to tire size. Not too small of a sidewall.

Hey, what kind of brakes are those?

- Jeremy

 

[70 LS1]

The rotors and calipers came from a 2001 Z06. I had to make the brackets for them to fit.
http://temp.corvetteforum.net/c3/70lt1/brakes.shtml