ROLEXrifleman

I've been asked to put this together now for over a year, so here we go.
When I did the conversion there was no real thread that explained a lot of the things i needed to know in regards to what needed to be done. It was a lot of trial and error on my part so learn from my experience! The information below is based on the rim and tire choices I made. The information being presented can be used to make sure what you are considering will work.

Lets start with some numbers which are extremely important, and these aren't up for debate!

1st, my OEM wheels and tires.

16" rim
8" wide
235/55 R16 rubber
5x120.65mm (5x4.75") bolt pattern
55mm offset
70.64mm(2.781") hub diameter
26.18" overall diameter

These rims and tires were the ones that were on the car since the day it was purchased! 1998 Firebird


2nd, the wheels and tires I ended up buying

19" rim
8" wide
245/50 R19
5x120mm (5x4.724")
38mm offset
67.44mm(2.655") hub diameter
28.65" overall diameter


I'm gonna let you guys sit on these numbers for a while. If i had this alone presented to me it would have made me really think about what I was doing.

ROLEXrifleman

now lets start looking at these numbers, what they mean and comparing them

1) Rim size (diameter): pretty self explanatory. It is the diameter of the rim, with no tire. i am going from a 16" to a 19". It is possible to get a rim to large that it wont fit. For example a 30" will not even fit in the wheel well.. I don't know what the max size is but would think a 20" with a rubber band for a tire might be the max.

2) rim width: how wide the rim is. My oem rim is 8" wide, so is the 5th gen rim. The width of the rim determines what size tire you can get on. an 8" rim will not fit a 275 or larger tire properly! it's just not right. Will it fit, yes, but it is not correct and will bulge. So be aware of your rim width if your looking at running wide tires. Know what the tire manufacturers recommend as this may force you into a wider rim. I have used up to a 9.5" wide rim on the front with nu rubbing during turns, that is with the right offset.

3) Tire size: critical for several reasons! if the overall diameter of the tire is to large then it will not fit in the wheel well! Game over! For example. My 5th gen rims came with rubber that had 25K+ miles left on it. But the 245/50 tires would not fit in the wheel well. Know your limits! this is where the overall diameter comes into play, more on that later.
See what I mean about the 5th gen 245/50R19 not fitting



4) Bolt Pattern: Here's one of the big one's! The bolt pattern is the diameter of an imaginary circle formed by the centers of the wheel lugs.



this is a critical point as our rims are LUGCENTRIC and not HUBCENTRIC. Meaning, our rims center themselves on our wheel hubs via the lug nuts and not the wheel hub like other vehicles. Because the bolt pattern on a 5th gen in .65mm, yes than minimal a number makes a huge difference, larger than a 4th gen the wheel studs are bent outward in order for the lug nuts to seat. Now, will 5th gen wheels fit a 4th gen, YES. Are 5th gen rims designed for 4th gen cars, NO. Can there be complications due to bolt pattern difference, POSSIBLY. Broken wheel studs are the most noted. I have not had an issue with this but it needs to be mentioned.

5) Wheel offset: is the distance from the hub mounting surface to the center line of the wheel. What this means for this application is that the 5th gen rim will sit 17mm deeper into the wheel well when compared to the OEM 16" rim. 16" rim = 55mm offset, 5th gen rim = 38mm offset. 55-38= 17. And this is a positive offset. i wanna say you can go as low as 32mm b4 you see an rub but don't quote me on that. My 38mm offset has no issues with rubbing during turns.

6) Hub Diameter: This is the single biggest physical hurdle you must overcome. our 4th Gen wheel hubs are 70.64mm (2.781") in diameter while a 5th gen hubs are 67.4mm(2.653"). Since the 5th gen rims are cut for the smaller hub you must open them up to fit our larger hubs. 3.24mm (.127") must be taken off the 5th gen wheel evenly. Looks like nothing on paper, till you gotta do it in real life!





Overall (outside)Diameter: This is pretty much the same as tire size. You can only go so big b4 it wont fit. the reason i named this point overall diameter is so we can talk about speedometer accuracy. Your cars PCM was calibrated at the factory for the size of the tire it left with. In my case a 235/55R16 tire which has a outside diameter of 26.18. My cars speedometer will read true with any tire that has this measurement diameter. If you pick a tire with SMALLER DIAMETER your car will be running FASTER than the speedo reads. If you pick a tire with a LARGER DIAMETER, and it fits, your car will be running SLOWER than your speedo reads.



Now that we have the real deal info out of the way, on to the tutorial!

ROLEXrifleman

Well, with this info now you don't have to pull your tires off to get measurements! Unlike when I did it it was all from the hip.

first take off a tire, or tires. I started in the rear! lol
took the tires off and lined them up so you can see what your working with



As we've learned from the post above, our 5th gen wheels wont allow the larger 4th gen hub to fit in them. We need to open them up. The 4th gen hub is 2.781.



i didn't want to keep using my calipers so I found something exactly 2.75" in diameter to use to check my progress.



as you can see fit perfectly in the OEM 16" rim:







lets check it against the 5th gen rim, REJECTED:





basically what the conversion consists of is removing these 5 nubs. It's as if GM created the nubs and changed the hub diameter just to F' with us 4th gen guys:



Again, as stated earlier, your removing about .127" of material. i thought it was gonna be easy and all i had was this:



don't waste your time! After about 15 minutes on the 1st rim i hadn't even made a dent. Luckily I have a cool *** neighbor, he came over and handed me this!!!!



less than 5 minutes later:





remove the nubs till they are flush with the center and you did it! your rim will now fit snug on the hub. Don't go crazy and mess up the rim, just get rid of the 5 nubs.
Clean your rim of any metal shavings and move on to the next. That's all it takes to make the rim fit! This is the 1st half of the conversion. the 2nd half is getting proper tires on.

I ended up with Pirelli P-Zero Nero GT's 235/40ZR19



What this did for me was give me an overall diameter of 26.4" which was as close to the PCM calibration of 26.18", Which means my Speedo is on! one less thing to have to get done.

And here is the end result with the comparison:

Majestic9C1

iTrader: (19)

when I picked up my camaro it had 5th gen heritage wheels on it.. gave them to my coworker lol

chrysler kid

iTrader: (14)

I couldn't even get a set of heritage rims to fit on my car, the hub is not shavable

JDEP162

I was skeptical from the first pics, but actually look good. Any with all 4 on from diff angles?

blackandgold

iTrader: (2)

They look better than the 20" ss wheels on a 4th gen. I'd be interested in pics of them all around.

HotWhipT/A

iTrader: (31)

Look very similar to my OEM C6 wheels. All are 19X10 with a 79mm offset. I have 1.25" spacers on all 4. The bolt pattern is the 120.65mm just like the 4th gens.

Majestic9C1

iTrader: (19)

ugly heritage wheels when I first got the car

Rise of the Phoenix

iTrader: (27)

I'm just not digging it, but to each their own.

SparkyJJO

iTrader: (11)

Just wanted to point out this is backwards.

A tire with a larger diameter than stock will make you go faster than your speedometer reads (speedo will read slow), smaller diameter will make you go slower than the speedo reads (speedo reads fast).

Reason is every revolution of the wheel on a larger tire will cover more distance than a smaller tire.

I have 10% taller tires on my Trailblazer, so my speedometer reads 10% lower than actual speed, for example.

Robert Bayless

I'm so glad I wasn't the only person to catch that.

capelajc

OMG those are FUGLY!! But pretty much how all black wheels look so I can understand why they didn't care what it looked like.

Mr.z/28

iTrader: (8)

Pretty much what 6LE told me was to shave the hub. He did so on his recent 4th gen that he had.

98MNBZ28

iTrader: (21)

^What hood is that?

98MNBZ28

iTrader: (21)

what hood is this??

badchev

Great thread....! Any pictures of all 4 rims on the car?...................... Im going to do the same .... will post up picks,... 2000 camaro Z28 convertable.

badchev

So I tried using the carbide bits but the aluminum gums it up so I went to lowe's and bought a pack of 1 1/2" barrel sanders, $8.... the 80grit works like a hot knife through butter,...5 min a rim and done... 235/40/19.