Treasure Trove of info for 70 Z/28

**MBD** · 10-15-2005

For those who missed it, Horsepower TV just ran a piece on stuffing the widest possible wheels and tires on cars. They used what appears to this Ford man to be a 70 1/2 Z/28.

Here's what they discovered through careful measurements and turning the wheels from lock to lock.

The rear wheelwells can accomodate 12.5 inches of overall tire width. They used an 11.0 inch rim with 6.5 inches of BS.

The fronts can accomodate 11 inches of overall tire width. They used a 9.5 inch wheel also with 6.5 inches of BS.

They did not mention if they rolled the lips so I'm assuming they didn't.

They chose Yokahoma AVS Sport Tires in a 315/35/17 and 275/40/17 with American Racing Hopsters.

That's a lot of meat.

MBD

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**formula** · 10-15-2005

that seems huge relative to what most people say.....if it's true though, that's awesome!

**essenge** · 10-15-2005

Didnt popular hot rodding do 275/40's in the front? Ive always heard over a 295 in the back requires a minitub...

**MikeDVC** · 10-15-2005

The Hotchkis F-71 Camaro has 17 x 9.5 on the front and 17 x 11's on the rear, not tubbed. But, I can't remember what size tires they were using.

**yody** · 10-15-2005

6.50" of backspacing on the back is next to impossilbe on a second gen if your actually going to drive it, and I am not even sure if it will clear the leafsprings, when trying to fit 11's on the back the extra width has to go outwards. The front sounds about right though, but also a bit much backspacing.

**zbugger** · 10-15-2005

The Hotchkis Camaro was running 17x9.5 w/ 275/40's up front and 17x11 w/ 315/35's in the rear. The backspacing was 5.5" in front and 5.75" rear. They did have rubbing issues as the car was lowered. I highly doubt that the 6.5" backspace would work. I think on the show they said 6" backspace, actually. The 315's fit without minitubbing the 2nd gen. It's just an extremely tight fit. The lips HAVE to be rolled for that as well.

**MBD** · 10-16-2005

I'm just the messenger, so take it for what it's worth. I recorded the show on TIVO and just went back and watched that portion.

They did an excellent job of presenting the material. They showed the audience how to use the Wheel Works Mount Mate to figure out the largest possible tire and wheel set up. I wish I had access to one.

The guy even showed the camera a close up of the back wheel size measurements and it was 11 with 6.5 BS.

They definitely said 6.5 BS in the front as well. The car's exterior appearance was factory stock.

MBD

**MBD** · 10-16-2005

Two other items. I got a good view of the rear wheelwells and they looked stock to me.

They used a plumb bob and tape measure to get their initial measurements and order the tires based on overall width.

Then they used the Mount Mate to figure out the wheel size and backspacing.

MBD

**qwik1320** · 10-16-2005

I saw that episode yesterday too. I think they're nuts. They measured from the OUTSIDE of the rear qp to the inside of the wheelhouse and got something like 12 inches of space. And I think that was straight in, not to the front spring perch mount (I think that's the narrowest spot). I had my tires out to the outside edge of the qp when I had airshocks on the car back in the 80's (yes I'm old). Maybe they were working on a "hardtail" Camaro. I think it was option HT under the BS group...

Plus 275's in the front, how?? I have 245's on the front of my 73 and they just "kiss" the sway bar at full lock. I have the stock steel 15" Z wheels on and I think the backspacing is about 5"

**MBD** · 10-16-2005

Originally Posted by qwik1320

I saw that episode yesterday too. I think they're nuts. They measured from the OUTSIDE of the rear qp to the inside of the wheelhouse and got something like 12 inches of space.

You're right, the measurement was to the outside of the lip, but they said they subtracted "about an inch" to take this into account.

**yody** · 10-16-2005

The back is a joke, under a hard bump the tires will hit the edge of the QP rolled or not. You can do 275's on the front, you just have to limit the steering radius, a third gen steering box does that

**qwik1320** · 10-16-2005

You're right, they did say they subtracted an inch. It still looked like the tires came out past the lip though. I guess they'll have to drive it and

**zbugger** · 10-16-2005

275's in front, 315's in back, on the wheel sizes and measurements I listed. It's as close as you can get. It does rub on the front sway bar at full lock. Hotchkis springs in front, landrum in back, I think with a 1" drop.

**jimmybpei** · 10-16-2005

funny i've been researching tires tonite on the internet and found what i think i'm gonna run on my '73 firebird: i have 17x8 with 4.75"bs tt2's in the front and thinking of 275 40 17 nitto nt555rii the dim are 26"dia 10.83 wdth and 110mm of sidewall

on the back i'm thinking of 18x10 with 6"bs because im switching to 92-97 camaro disc brakes and so i've researched they protrude an extra 1/4"
Tires will be 305 35 18 Dim: 26" dia 12.01 wdth and 107mm of sidwall this tire choice should give the appearance of both front and rear tire bulg the same

gonna drop the car about 2". i want this wheel/tire combo to be stuffed inboard of the rear quarers.

any comments would be appreciated

thanks
JimmyB.

**Ralph LoGrasso** · 10-16-2005

Jimmy,

What 305/35/18's are you going to be running? The Nitto Drag Radials? If you do run those on an 18x10, I would greatly appreciate if you could take a few measurements. Mostly, overall diameter and section width on the 18x10. Most nittos run small, and I'm wondering what the actual real world tread width of the 305s are. If they're bigger than my 295/35/18 Kumhos, I may swap to them.

**essenge** · 10-16-2005

Originally Posted by jimmybpei

funny i've been researching tires tonite on the internet and found what i think i'm gonna run on my '73 firebird: i have 17x8 with 4.75"bs tt2's in the front and thinking of 275 40 17 nitto nt555rii the dim are 26"dia 10.83 wdth and 110mm of sidewall

on the back i'm thinking of 18x10 with 6"bs because im switching to 92-97 camaro disc brakes and so i've researched they protrude an extra 1/4"
Tires will be 305 35 18 Dim: 26" dia 12.01 wdth and 107mm of sidwall this tire choice should give the appearance of both front and rear tire bulg the same

gonna drop the car about 2". i want this wheel/tire combo to be stuffed inboard of the rear quarers.

any comments would be appreciated

thanks
JimmyB.

Not to hijack the thread...where did you find the info on the backspacing of the LT1 style disc brakes? I am going to do the same swap but havent been able to find that.

**Ralph LoGrasso** · 10-16-2005

Essenge,

Not to speak for Jimmy, but by saying the brakes will protrude an extra 1/4", I believe he is referring to the discs sticking out a 1/4" farther than drums would (normally when swapping from drums to discs, the discs will stick out 1/4" farther). I'd assume he currently has drums on his car now.

**jimmybpei** · 10-17-2005

exactly about the brakes, as i am currently running drums. as for the tires i just used a tire calulator on line and plugged the nubers to get the measurements, some one had mentioned before that different tire companies measurements vary. this is very true as i found out today at a local tire company when comparing tires. Would like to know what kinda Kumhos you are running.

**Ralph LoGrasso** · 10-17-2005

Jimmy,

I'm running Kumho Ecsta MX 275/35/18 up front and 295/35/18 in the rear. This is on my '01 SS. Nittos tend to run noticeably smaller than other brands, so I'm curious as to the actual size of the 305s, I have a feeling they're smaller than my 295s. The Kumhos are pretty wide. Probably 12.0-12.2" tread width on my 18x10s.

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Treasure Trove of info for 70 Z/28