Wheel Lug Base Circle, 5 on 5 Only?
 

My wife recently inherited a solid 74 GMC stepside, which we are going to keep in the family and go through (completely). I'll post some shots once we get moving on it, but I was looking at it over the weekend and was puzzled by something. The truck currently has aftermarket wheels, which we are going to replace with something a little "cooler," and I confirmed that the base circle on them is 5 on 4 3/4", NOT 5 on 5" which is what I thought all 1500's came with? This is actually good news as I have a set from a different project that will fit, but begs the question is the truck had been previously modified. I haven't pulled the wheels off to check into it more, thought I'd post the question for the experts here.

Did the light duty GMC's indeed come with the 5 on 4 3/4" base circle, or is there more to the story on this truck?

Thanks!!!
Mark

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

It should be 5 on 5. All 1/2 tons were, AFAIK.

Slonaker

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

never seen a 5 lug truck that wasn't 5x5

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Gm 5 lug truck is 5 on 5. There was never another pattern used. 5 on 4.75 is car pattern. Theres no way it came from the factory with anything but 5 on 5. It could have been converted at some point but thats not something normally done on an otherwise stock vehicle. Are you sure your measuring properly? https://www.rsracing.com/tech-wheel.html

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

i dont remember exactly where, but i read the rotors off of a early 70's van fit these trucks, and they were indeed 5x4.75, and some changed them out for different wheels, not sure about it, but remember reading it somehwere.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Nope the vans are the same as the truck. They have been since they went to 5 lug in 71.Even astro vans are 5 on 5. The wheels all interchange between trucks,vans and astro vans.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

So just curious what other vehicle has the same bolt pattern as ours?

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Caprice, Impala SS.

Slonaker

EDIT: There was some discussion here recently where it was mentioned that some Jeeps used 5X5 pattern.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Thanks guys, that is essentially what I thought as well. I'll have to pull the wheels off and see if someone redrilled, etc. I measured using a tape measure, so not horribly accurate but did verify with a 5 on 4.75 wheel that I had, same result. I also took one of the axles from my Camaro project (also 5 on 4.75...) and stuck it in the lug openings on one of the wheels on the truck, it seemed to line up perfectly well, but there is a possibility that the cold beer that was accompanying me yesterday affected my accuracy!!

In the end, my plan is to use the CPP modular drop spindles, initially with the stock brakes and then move into a set of 13" Wilwoods for this package. When I was looking at the Wilwood site, they too showed 5 on 5 for the hubs that come with their kits. So, if someone did some monkey business on the fronts, then my concern is that I won't be able to use the CPP drops with what is currently on there. The Wilwood brake hats are a dual bolt pattern, but the hubs with their kit doesn't show that it is or could be drilled for the smaller base circle, I am guessing it probably can though (most of their hubs are dual or even triple drilled).

Funny, I was looking at the truck and commenting on how simple a project it was going to be, haven't made to step one without a funky issue though!!!!

I'll report the findings back, but I am 99% certain that the wheels are 5 on 4.75. Yippee, sleuth work!

Mark

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Unless you took the wheel directly off of a car and put it onto the truck, no measuring involved.....I am willing to bet on mis-measuring. It is very common with 5 lug wheels.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

ALSO MID 70 LINCOLN MXIIIIs. I'VE GOT A 9" THAT I HAD A POSSI CENTER SECTION & NEW RING & PINION W/A 350-1 RATIO PUT INTO IT. THEY HAVE REAR DISCS ALSO. IT'S GOING INTO MY NEVER ENDING MONEY PIT SHORT FLEET 72 PROJECT. ;) :chevy: JOHN

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Caprice, Impala and all other GM b-body cars were 5x5 from 71-76 then again in 91-96. They were 5x4.75 from 58-70 and 77-90.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Also Im pretty sure the caprice wagons and 9C1s in the 77-90 time period were 5x5 also.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

.:dohh:My mistake, wagons, electras, caddies( not sure of model) were 5x5 those years. Still never seen a 5x4.75 truck tho.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

actually my mom used to drive a swb chevy van, think it was either a 74 or 75, and it was 5x4.75 lug pattern from the factory. i had a old camaro project at the time and put the original rims from it on the van since they had good tires. i was really puzzled too, i thought they were all the same as the truck, but i was wrong. ill have to do some part number searchin on this one, because im interested in at least knowing what it takes to swap to this pattern on our trucks. but i do remember doing the front brakes and having to buy one rotor and yes it was 5x4.75 too.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

oh yeah, and also, ive had a 78 cadillac seville. they are 5x5 pattern, and 76-79 were RWD with disc brakes. they are based on a Nova platform so they are a little bit narrower, but thats good if your tryna tuck in some 10's out back, and m pretty sure most all of them were 3.73. i figured ths was some pretty good info for someone else to lock in.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

If you measure center to center its 4.75.. but thats not the correct way to measure the bolt pattern on a 5x5 pattern. why, dont know. the correct way to measure it is top of the wheel stud to the center of the other... kinda dumb but some genius though of it .... the 6 lug folks measure center to center... normal people... haha. When I redrilled my rear rotors, I should have measured 2x and drilled once.. lol

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

It's because you're measuring the diameter of the circle created by the center of all the lugs. You measure the ones opposite each other on an axle with an even number of lugs, because they are directly across from each other. You can't do this on a 5 lug axle because none of the lugs are directly opposite each other. Luckily, if you put a tape measure on the end of one lug and measure to the center of the one that is two lugs away, you will get the correct measurement.

see here for visual reference:

https://www.rsracing.com/tech-wheel.html

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

ok just verified, the van was a 73 van and even autozone and orielly websites list them as being 4.75 pattern. for $33 a piece id try them if i was going that route for some wheels i had already or somethn. would be so much easier and safer than adapters and even cheaper than redrilling them... as far as the back i guess the b-body 77-90 rear would work for ease of things. just a bit of weldng the perches on. i bet itll work....and dangit got me really thinking now. I can get ahold of plenty more wheel sets with the car pattern.

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Knew I was somewhat right, I knew I reAd somewhere it was only two years or something, iirc 73-74

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Re: Wheel Lug Base Circle, 5 on 5 Only?
 

Team, thanks again for the input here. I looked at it again, and I'll tell you, I am still not sure but believe that it probably is a 5x5 and that I measured incorrectly. Quarter inch diameter really is a small amount, so I need to pull a wheel and try it that way.

Just wanted to reiterate thanks for the input!
Mark