Tyre Combo for 18x8 ( Front and Rear )

[69CVET]

Hi All,

Looking at a upgrade from the Standard 15x8 Wheels to 18x8 on a 73 & 77

Is anyone running 245s on the Front without any modifications ?
What is the max size on the rear with Standard Trailing Arms & Calipers
A lot of reading on USA forums and still no clearer .....

All feedback is welcomed

[rosco]

18x8 with zero offset 4 " back space, 245 x 45 on front and 275 x 40 on the rear no problems with anything.
Stu is running this set up but his rears are 255 x 45.
I think Warren is running the above combo.
Rosco

[bfit]

18x8 with zero offset 4 " back space, 245 x 45 on front and 275 x 40 on the rear no problems with anything.
Stu is running this set up but his rears are 255 x 45.
I think Warren is running the above combo.
Rosco

Im running 18x8 front -6 offset 245x40
bfit

[69CVET]

Thanks guys.

Rims will be 18x8 ( 4.5" back space with Zero Offset now confirmed )

Now will do the homework on the tyres to ensure no issues with clearance etc....

[craigh]

Thanks guys.

Rims will be 18x8 ( 4.5" back space with Zero Offset now confirmed )

Now will do the homework on the tyres to ensure no issues with clearance etc....

How can the rims be 8" wide 4.5" backspace and zero offset.

Sounds like something is not correct,

To be zero offset on an 8" rim it needs to be 4" backspace..

As for size I run 245/45/18 with no rubbing and lowered susp3nsion.

[69CVET]

Thanks Craig.
Maybe they are actually 8.5"... Will confirm tomorrow

Cheers

[bfit]

How can the rims be 8" wide 4.5" backspace and zero offset.

Sounds like something is not correct,

To be zero offset on an 8" rim it needs to be 4" backspace..

As for size I run 245/45/18 with no rubbing and lowered susp3nsion.

An 8'' rim is measured inside the lip the rim will measure 9'' wide over all
That's how you get 4.5 BS  with an 8'' rim zero offset
Bfit

[craigh]

An 8'' rim is measured inside the lip the rim will measure 9'' wide over all
That's how you get 4.5 BS  with an 8'' rim zero offset
Bfit

That may be correct but the industry norm is to uses the inside measurement when it  describes wheel widths so somewhat confusing.

Just want to ensure 69cvet gets the best options with his rims, choosing  larger offsets on same width rims will just move the rim inwards.

[bfit]

That may be correct but the industry norm is to uses the inside measurement when it  describes wheel widths so somewhat confusing.

Just want to ensure 69cvet gets the best options with his rims, choosing  larger offsets on same width rims will just move the rim inwards.

Move wheel inwards .
That would depend on if the offset is positive or negative .
Something to note when working on a 40 odd year old Chev, do not assume that everything  is symmetrical.
A BS Of 5.3/4'' may work on one side but not the other.
The thing to keep an eye on is clearance on full lock,  tyre to chassis clearance to the frame
Bfit

[Jethro]

To be zero offset on an 8" rim it needs to be 4" backspace..

As for size I run 245/45/18 with no rubbing and lowered susp3nsion.

I'm with Craig and thats what I'm running too :)

[craigh]

Move wheel inwards .
That would depend on if the offset is positive or negative .
Something to note when working on a 40 odd year old Chev, do not assume that everything  is symmetrical.
A BS Of 5.3/4'' may work on one side but not the other.
The thing to keep an eye on is clearance on full lock,  tyre to chassis clearance to the frame
Bfit

Not being symmetric is so true Bfit.

You can do you mind in if you start trying to compare body measurements side to side.

Manufacturing tolerances at the time these cars were built were fairly loose :-)

[69CVET]

Thanks Gents.

Also Bob thanks for passing on the details for contacts at Vansteel , hopefully they will look after me for the suspension upgrade parts required.

Cheers

Chris

[bfit]

Thanks Gents.

Also Bob thanks for passing on the details for contacts at Vansteel , hopefully they will look after me for the suspension upgrade parts required.

Cheers

Chris

I'll email Danny to let him know you got his info from me
Bob

[craigh]

I'll email Danny to let him know you got his info from me
Bob

I dealt with Danny after Bfit passed on details, very helpful and i have a set of new arms sitting here ready to go on soon.

[Vettech]

Confusing topic, I thought 73-76 used 15x8" offset: -1mm backspace 4.5", Std OEM tyre 225/70R15.
So? if you go up to 18" dia - do the other diamentions  stay the same esp if the width remains at 8" ?????????

[craigh]

Confusing topic, I thought 73-76 used 15x8" offset: -1mm backspace 4.5", Std OEM tyre 225/70R15.
So? if you go up to 18" dia - do the other diamentions  stay the same esp if the width remains at 8" ?????????

Normally if you +size a wheel you aim to keep the new rim offset the same as the original.

So if its 15" x 8" 4" backspace today you would go to 18" x 8" 4" backspace.

If you went with a wider rim  you would modify the backspace to have the rim so the increase in width is evenly distributed in and out.

This is not always possibly but it allows the suspension geometry etc to work as intended.

Go to this site to play around and it will show you visually what the changes are and explains how offset and backspace are related.

http://www.rimsntires.com/specspro.jsp

As for 8" C3 rims I thought they were all 4" backspace

[bfit]

From what I have seen earlier c3 have 15x8 4.5'' BS
Later c3 I think with the alloy wheels are 15x8 4'' BS
LIMITED observation I only have only worked on one later c3 A 79 model
The rims on that are 8'' with 4'' BS  stock vette rims
Bfit

[craigh]

I had a look at 2 sets I have here, 71 & 76 both 15 x 8" 4" backspace.

From NCRS c3 guide on steel rims.
The back space on a 15 x 8 Rally wheel for a Corvette should be 4 inches. The back space on a 1968 15 X 7 Corvette rally wheel is 3 3/4 inches.

So 68"s were narrower at 7" wide then it went up to 8" for 69.

Just to confuse it more In GM cars of the era corvette was the only one using 4" backspace with 8" rim, the camaro etc with 8" uses 4.5" backspace.

So in 40 years I imagine a lot of things get swapped around between cars etc etc.