Been searching for a while now, and im looking at some 1 pc torq thrust IIs in pvd. They come in 8, 9, and 10" widths. With BS of 4.5 for 8", 5 for 9", and 5.75 for 10". I haven't found any definitive answers but from searching I gather these are close for fitment. I don't want to use spacers or have the wheels stick out.

My question is what's my best option here? I like the look of a staggered setup. My bumpstops are cutout and some minor BFH. I'm leaning to 10" rear and 9" front. But I'm not sure if that BS will work up front.

Then my other question is what tires to run? I'd like to run as wide as possible in the back and slightly taller. I'd like to stay at least 245 in front or slightly wider if it won't rub. My stock irocs rubbed so I can't see going wider than them.


Here's a pic of my iroc. Its in dire need of an update. With the new paint the wheels throw it off. 15x5 up front, 15x10 in back weld draglites, 275/60 stuffed in the back. Had to put cc635 springs in there so it wouldn't rub (and grind calipers), I went from 3.23 to 3.73 geaes so the tire negates any gain there. I've had the car since I was 18 so its time to undo all the dumb things and get this car handling again!!! (Drag shocks/struts have to go!!!)

 

Oh and I have tubular lca's, adj. Panhard and lcarbs. I heard that might help with wider tires/rims. Eibach pro kit might be installed in the future as well

 

If it were me, I would go 10" all the way around with either a 275 or 285 width tire.

Other may trash me, but having a really wide "square" wheel and tire setup is so smart and modern it makes me smile.

 

If you can wait till the weekend I'll show you a set of 18x10.5 wheels with 285/35/18 all the way around.
They will for sure rub the plastic liners slightly and will hit the frame/swaybar at full lock until I lengthen the stops.

 

10" in the front seems so wide to me, they barely fit in the back!! If I were to go "square" what would you think of 275/35 in front and 275/40 in back? Or would that look stupid? I'm really tempted to get 18x9.5 z06 rims but I'm trying to stay away from spacers!

 

As long as you get wheels with the right backspacing (or spacers), you can fit up to a 10.5" up front and an 11" out back. I know of a few people on this board who have 18" x 10.5" all around with 295-35-18 tires.

Personally (and what I would recommend) is to go 10" all the way around with either a 275-35-18 or 285-35-18 tire on all 4 corners. You will get better handling balance and be able to rotate tires.

 

Thanks. The front and back have different offsets though right? So if I was to put 18x10 on all 4 with 5.75" BS would that work?

 

Factory 16" wheels did, but that was one hell of a stupid thing GM did.

My company's wheels (CTW Motorsports) are 17" x 9.5" with 5.25" of BS - and just clear the tie rods on the inside. Move up to 18" and the tie rods are no longer a concern - so another 0.5" of width and BS will work and sit flush with the wheel wells.

So yes - it should work.

 

Thanks paul. 9.5" width with 5.25" BS would be the same as 10" with 5.75" BS then right? I've searched all over the board I can't find anyone running 18x10 tt2's. Despite the complaint that they're a "common" wheel. Doesn't seem to be much wheel selection anymore for our cars in 17 or 18s

 

Can't wait to see that >>!!!!

 

In terms of both wheels sitting flush with the outside fenders - yes.

5.75" BS would be the proper measurement to get a 10" wheel flush.

I think you are confusing "common wheel" for "common bolt pattern". The 4th gen and C5 and later wheels use similar offsets and can fit most of those vehicles. The 3rd gens require a lot less back space (around 2" less) to fit the same width wheels. Too many people on this board have fallen into the "4th gen rear swap is easy" and then have to get new wheels and/or spacers. Until the 5th gen, F-bodies all used the GM 5 x 4.75" bolt pattern (120.65mm) - that is the common thing...

 

Guaranteed to look goofy on my car. I need more backspace than that to not stick out.

A 285/40-18 will give you that extra inch of height you're looking for in the back. 18x10 with 6" backspacing is the norm and will put the tire flush with the edge of the fender. About 1/4" more backspace if you want it a bit tucked. Remember, a little movement looks like a lot in this case. Suggest you buy the tire and mock it up to figure out where you like it relative to the fender lip, and then buy the wheel.

 

Paul and/or QuikTrip,
Can you educate me on the "proper" way of discussing/measuring backspacing and offset? Please confirm or correct the following:
1) a wheel's quoted width is from bead surface to bead surface, where the tire sits. Inside-to-inside measurement.
2) meanwhile a wheel's overall width includes the 1/4" bead on the inside and outside, making the wheel 1/2" wider than stated. Outside-to-outside measurement.
3) offset from the centerline needs to include that 1/4" bead to figure the inner distance (back space) and the outer distance (front space).

Examples:
a) A wheel called 8" will have a total width of 8.5". For a 0" offset, the backspace is 4.25" and the "front space" is also 4.25"
b) A 10" wheel total width is 10.5".
b1) 0" offset = 5.25"/5.25",
b2) +1/2" offset BS=5.75", FS=4.75" and moves the entire wheel inboard 1/2".
b3) +1" offset BS=6", FS=4.5" and moves the wheel inboard 1" vs the 10"/+0 wheel, and keeps the outer face the same as stock. (But, is that stock front or stock rear with 16x8 IROC wheels?)

Example (b2) matches what you are saying, and (b3) matches QuikTrip's post... right?

 

My spacers were wheel and hub centric so I had to get a new pair for the front. Small delay but they tuck under the fenders better than the 17x9.5 ZR1's I had in there before. Not worrying about tierod clearance is a huge bonus of the 18" wheels as they can swallow about 1.25" on the inside comfortably.
The ZR1's were effectively 0 offset 5.3" backspacing
The Z06's are effectively 7 offset 6" backspacing

 

You are correct on #1.

#2 - Typically overall outside wheel width is stated width plus 1". So a 9.5" wheel is in reality 10.5" wide.

#3 - offset is indeed the distance (positive or negative) from the wheel centerline. So a 9.5" wheel (10.5" overall width) has a centerline that equals 5.25" - or in offset specs: 0mm

a) 8" wheel would be 9" total and have a centerline of 4.5" at 0mm offset


I'm going to answer all the additional questions in a different manner:

3rd gen "front space" from wheel mounting surface to fender lip is 5.25" when using a 3rd gen rear (front is always 5.25" with OEM style suspension).

You can fit up to 5.25" BS on the front of a 3rd gen with 17" wheels - any more and the wheel barrel hits the tie rods. Once you get to 18" and larger, the front is not as much of an issue as the tie rods tuck into the wheels - you can run 10.5" wheels up front if you don't have coilovers.

The rear of course has more inside clearance - many have fit 11" wheels out back with the right spacers (and sometimes some hammering work). The "front space will still be 5.25 with a 3rd gen rear", but you can get in the ballpark of 6.75" BS on the rear axle.

So think about it this way - there is always going to be 5.25" of "front space" to deal with, and up to 6.25" BS up front/6.75" BS in the rear to accommodate wheels and tires. The math becomes much easier when you look at the width (with the 1" additional for lips), the BS/offset, and the fact that there is 5.25" of "front space".

As an example if you have a 9" wheel (10" overall width) with 5" BS it would sit into the wheelwell about 0.25" from flush. The same wheel with 5.25" backspace would sit 0.50" in from flush (4.75" FS).

 

No, just a coincidence. I try to account for where the tire is, not the edge of the wheel. Tire can buldge out beyond the wheel.

 

Oh, now that's interesting. I measured my car and came out at 5" with a Strange 12 bolt. I nearly always want 1/4" to 1/2" more backspace than other people and now I am understanding why! Thanks for the info.

I guess that just proves a point to the OP to always measure out your own car. I know what fits my car but didn't realize it was a bit abnormal.

 

Absolutely correct!

But in most cases, the tire is not too much wider than the wheel to cause additional problems - unless of course you want to run a 315 tire on a 9" wheel or something like that.

 

18x10.5 with 285/35/18 front and back. I would have gone with 295's but tirerack had 2011 Pirelli pzero nero's for $71 each and I'm cheap. Tires rub the swaybar and frame just like the 275/40/17's did. No worse. Yes I know I need moar low.

 

Personally (and what I would recommend) is to go 10" all the way around with either a 275-35-18 or 285-35-18 tire on all 4 corners. You will get better handling balance and be able to rotate tires.

Paul, what wheels are these guys running? I really want a set of 18's on the car to get the extra width but can't find a good quality rim in that size. Since your production quite a while off and I figure I will need tires in September to get the car to pass safety inspection, I have to come up with a wheel option by then.

 

Looks good, but where's the pic's from the rear..??
3 feet off the ground 10 feet back.. ya

 

I'll get one in the mornin

 

Ramit those look good, but Id agree you need more low. I feel like with 18s its got to be lowered where 17s I feel its not as critical. I hate driving lowered cars and scraping everywhere tho! You got any pics with the 17s? Im debating which to get 17 or 18s

 

Which Morin...???? LOL !
Ya I think you should drop it 1 to 1 1/2 inch all around

 

Slowly workin on the drop. We have speed humps around here so I have to cut 1/4 coil at a time. Coils have been off 3 times already. What a biatch that is on the front. Still needs more low.

 

I think another half off the back oughta do it

 

The coils are wound tight at the top where I cut them. I realized that if I take a full turn off the rears I only get 1/2" drop.
At least they are easy to r and r. 20 minutes to remove cut and reinstall.

The 18" tires are the same OD as the 17's

 

Try the heater hose trick?

 

Guys I have another question for you, if I was to put 245s up front and 275s in back with 18s, what width rims should I get? 8 or 9 will work up front but so will 9 or 10 in rear.

 

[QUOTE=RamIt;6012193]Slowly workin on the drop. We have speed humps around here so I have to cut 1/4 coil at a time. Coils have been off 3 times already. What a biatch that is on the front. Still needs more low.


That's what i'am talking about
U Gotta love a meaty rear...... even on cars...LOL !
Keep working on the drop, it's gonna look sick when your done.

 

And finished cutting. 26 3/8 to 26 5/8 all the way around.