Wrong Tires On My Truck?

[1969_CM2590D]

I've had a bit of a surprise tonight. Let me go in steps first:

1. Truck is a 1969 GMC C2500

2. SPID says it came with 3R67BA 7.50x16x6 front
and 3R67AL 7.50x16x6 rear. Transposing from the 1969 Chevy Truck Fact Book I have stored in the PC here, option code "R67" is for a 7.50x16 6PR tube tire with a 6" rim width.

3. Measuring from bead seat to bead seat by the moonlight and flashlight right now, I get 16". The rims look to be the original 8-lug argent face with a fair amount of surface rust

4. Truck now has 8.00x16.5 front and 9.50x16.5 rear bias belted tubeless tries. The spare is an old dry rotted Uniroyal 8.00x16.5. These tires were on it when I got the truck. Tires hold air fine

So do I have the wrong tires on there? Can you mount 16.5" on a 16" rim and have have it hold pressure? Am I measuring the bead seat wrong?

Thanks

[Stocker]

Your truck came with 7.50-16 tires so the wheels were most likely split rims (actually, locking ring wheels). Are your wheels one-piece or locking ring wheels?

Your hand-measure is probably off just a bit. It's doubtful that you have 16.5 tires on 16" wheels, even more doubtful they would hold air, or that they could be balanced. Certainly no tire shop would ever mount them. Also, 16.5" wheels have a differently shaped bead area than any other wheel.

Many wheels have their size stamped into the rim, usually on the back side of the rim.

[CCCC]

Likely that a PO installed 16.5 wheels as replacements for the 16s, especially if the originals were locking ring type. On 16.5 wheels I have seen, the final outer aspect is slightly angled outward toward the wheel edge when com[ared to the 16 and, as Stocker noted, wheel diameter is most likely stamped on an inside center surface (and sometimes on outside) of the wheel. Seems like 16.5 tires have become more spendy, with not much selection available. 16.5 tires on 16 wheels = dangerous.

[davepl]

Just a quick data point - I need a fifth 16.5" tire as a spare, and I asked the shop to grab me a used one. Assuming it would be cheap I didn't even ask, which I should have, because it was $150. And it took a week or two to find one. So the 16.5" tires are not easy to find nor cheap when you do. If you do find them cheap, take advantage I guess, but they're getting harder and harder.

[jocko]

Originally Posted by 1969_CM2590D

Can you mount 16.5" on a 16" rim and have have it hold pressure? Am I measuring the bead seat wrong? Thanks

No, never, ever.
Can you read the tire size on the tires on your 16.5 rims?
If you need 16.5 tires, recommend Firestone TransForce HT or AT. Specialty Tire of America also makes 16.5 mud lugs - more for K trucks.

As mentioned above - someone likely swapped to all 16.5s, the MOST common 8 lugger in the early 70s, to get away from split rims.

If you want to convert to 16s, I'd forego trying to find a shop that will install on a split rim - they are few and far between - and get a GM 16" 8 lug wheel. Backup plan would be accuride Fords. They look identical, are just lug centric rather than hub centric - they don't fall off, so it doesn't matter. Look at member Sicklajoie's wheels for ref - they look perfect and you have a modern, correct looking 8 lug wheel that holds your hub caps on.

I doubt you currently have the wrong tires on there if they're old, they'd have fallen off by now if it were truly a 16 and 16.5 mismatch. Easiest way to tell if you have a 16 vs 16.5 is to look at the shape of the rim at the other edge - it is distinctly different (16.5 very "curvy" curvy and protrudes beyond the tire a bit more - 16 is very angular, almost a 90° angle just inside the lip rim. Green truck = 16.5, white truck = 16.

[1969_CM2590D]

Well we all know a picture is worth a thousand words, so...

The spare wheel is black but looks to be identical to all but the driver rear. The driver rear was the spare rim when I got the truck, I switched them (mistakenly), it's way too wide compared to the rest. Might want to swap it out for a stock one. I tried cleaning up the spare to get a size, but the ancient GA/AL mud and the surface rust won't make it a quick proposition. The spare and the 3 "stockers" angle in to the rim center from the bead seat and have a weld(?) seam (not a crack) from rim lip beyond the wheel center- so no split rims and likely 16.5"

I'm thinking the 8.75 x 16.5 Transforce would be the best as I have manual steering, and a smaller contact patch would be good.

In order 1) Spare 2) Driver front 3) Pass. front 4) Pass rear 5) Driver rear

[Sicklajoie]

Thanks jocko for referencing my truck. Again.
16 x 7 F#rd rims on 265/75/16 tires