OEM Wheel Question

[Tkrysl]

This is my 72 C15 Base

I'm pretty certain that these wheels are not factory. I found this in a barn with no back story whatsoever.

A friend said I needed some bigger wheels and tires to get better speeds on the highways.

Does that make sense? How big of wheels came on this rig? What would my OEM wheels have looked like?

Why do I see alot of threads where trucks have two different size tires on the rear from the front? Sorry for questions that are most likely elementary. I'm a Noob at this!

As always, you guys are appreciated!

[jessemthompson]

Those are truck rally wheels and you’re correct. They are not factory for the 67-72 model. They are fine for your truck though. Better freeway speeds? Lol. If you want new wheels and tires, that’s fine, but what you have are fine as well. Idk what size you have on there, but they appear close to factory. As far as people running different size tires in the front and back, that’s personal preference. For looks, traction, handling. The one disadvantage is not being able to rotate your tires.

[special-K]

Looks like your slightly newer than the truck GM Truck rallyes are 7" on front and 8" on back. Stock wheels were 6" so you already have wider than stock wheels. There are people who need to sound like they know what they are talking about even when they have no idea, such as your friend... or so it appears on this question. I have no idea where he got that false impression or if he made that up, but wheel diameter has nothing to do with wheel speed. I had to chuckle, too. Most of your cars at the drag strip have traditionally run 15" wheels/tires. For instance, Farm Truck runs 15" rims.

Wider wheels/tires on rear are done for various reasons, but it comes down to a look. Wider tires get better traction off the line, help stabilize rear for hauling or cornering, 7" wheels are often used on front with drop spindles to help clear steering parts when 8" wheels are used on rear because 8" don't clear well. It gives a cooler stance, but scratches out any ideas of rotating tires for proper tire wear.

The truck looks good with the rallyes, and even painted white. These are timeless classic wheel for these trucks and will always be in favor. The new group of enthusiasts over the past 10-15 years got easily jaded on them in favor of new looks in wheels. But as always happens, the eyes are turning back to them and they have gone from couldn't get much out of selling to being worth what they once were and even more. Might be because hubcaps for the factory wheels have gotten so expensive. It's a great look and they will spin as fast as any truck can go

[Tkrysl]

Awesome info. Sucking up all the knowledge I can. Next question would be how big of tires are guys fitting on their 15" rims? I'd like to fill up those wheel wells if possible.

[Mike C]

I have a 71 GMC longbed that I put Rally wheels on. I am running 225 70 15 in the front and 255 70 15 on the rear.

[Tkrysl]

Originally Posted by Mike C

I have a 71 GMC longbed that I put Rally wheels on. I am running 225 70 15 in the front and 255 70 15 on the rear.

Does that fill up the wheel wells good?

[old51sedan]

You can always opt to lower it some to help fill up that space, giving it a lower stance also.

[3757chevy]

My daughters '72 long bed has 15x7 with 235-70-15 front and 15x8 with 235-60-15 rear and my '67 step side has 15x8 with 245-60 front and 255-70 rear . Original wheels would be 15x6 with 225-75(H78-15) like my '72 blazer in these pictures. I just like the look of big and littles on a 2 wheel drive.

[jocko]

You will fill up the wheelwell better without getting too wide by using a higher numerical aspect ratio tire - ie a 70 or even 75 series tire rather than a 60 series. 255-70 are a great stock look that will fill the wheelwell better than the original factory size tire. I’d put them all the way around. If you want wider in the back, recommend 275-60 with 235-70 in front for a balanced similar height with the fat rears, slight rake maybe too. Note that if you only alter the series, front to back (like a 70-235 in front and a 60-235 in back), the rear tires will actually be shorter than the fronts by a small amount. Do you indeed have wider rear rallies as Tim mentioned? I’ve had white rallies, preferred the stock argent silver - if you do too, then when swapping tires is the time to paint or powder coat them. Note, as far as what your friend said about highway driving, a taller tire will very slightly reduce rpm for a given speed, but it’s not a substitute for an overdrive trans or higher rear gear (lower ratio) - those are the only real options, or something like a gear vendors overdrive unit, to noticeably reduce highway rpm. Can’t really do it with tires alone. So, choose tires for looks and performance, not highway rpm.