1970 GMC C2500 rear axle hub diameter? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tow rig · Yesterday, 10:01 PM

I have a 1970 GMC C2500 (2WD) that I have bought aftermarket wheels and tires for. The wheels are 8 X 6.5 bolt pattern. The center hole in the wheel is just under 131mm. If I bolt a wheel onto the hub of the Dana 60 full-floating rear axle, the wheel has a significant gap between the center hole of the wheel and the hub of the axle. The axle hub is difficult for me to measure despite having a digital caliper and 4-5" micrometer. The studs get in the way of my making an accurate measurement. Does anyone know the diameter of the hub at the wheel mounting surface? (I will need to order some rings to fill the gap between the hub and the inside of the rims center hole if I want my rims to be hub-centric.)

**jerry moss** · Yesterday, 10:11 PM

your tapered lug nuts center the wheel to the mounting flange of the hub. you must be thinking of a Ford truck that uses hub centric wheels.

tow rig · Today, 12:57 AM

Nearly all factory installed wheels are hub-centric. The 1970 GMC had steel wheels that mated tightly to the hub. I know that many aftermarket wheels are designed to be more universal, and center off of the lugs, in order to have a single wheel casting be useable with several applications. My opinion is that lug centering wheels may be less than ideal, especially for a HD truck that will be carrying heavy loads, driven in rough terrain, abused with dragstrip launches, and/or towing a trailer. Anyway, it looks like my question is turning into something that I haven't asked. Are hub-centric rings needed for aftermarket wheels?(This is a simple google search that I have already done. The jury seems to be about evenly divided on the subject.) Thank you for sharing your experience.

**Stocker** · Today, 08:29 AM

FWIW, I have owned my K20 for 47 years and during that time it has had four different sets of wheels.

1) The stock 16" lock-ring wheels.
2) Aftermarket 15x8" white wagon spokes.
3) Aftermarket 16.5x9.75" chrome wagon spokes.
4) Ford (Accuride?) 16x7" steelies.

I couldn't say if the stock wheels were hub-centric, but none of the others were. The truck has been heavily loaded more times than I can count (up to a verified 3 tons in the bed), with no wheel-related problems ever.
I agree with Jerry Moss, hub-centric rings are absolutely not needed in your configuration.

tow rig · Today, 01:03 PM

Thank you for weighing in, Mike. You and Jerry supplied just the kind of advice/reassurance that I was needing. I will install the wheels without hub-centric rings and feel confident that there won't be any wheel related issues. I came to the right place.

Thanks Again

Brad

**PbFut** · Today, 06:59 PM

Just one thing to consider when not using the hub to center a wheel. It will be all the more important to sneak up on tightening those lug nuts allowing the wheel to slip some as the nuts center the wheel before too tight for movement. Rotating the wheel when doing so may also be advisable, in a way centering the weight during the tightening process. This might be overkill, but I've had wheels bind up at the track while mounting. You think everything is fine till that 165MPH section of track comes up. It about blinds you.

**mr48chev** · Today, 09:37 PM

Quote:

Originally Posted by PbFut

Just one thing to consider when not using the hub to center a wheel. It will be all the more important to sneak up on tightening those lug nuts allowing the wheel to slip some as the nuts center the wheel before too tight for movement. Rotating the wheel when doing so may also be advisable, in a way centering the weight during the tightening process. This might be overkill, but I've had wheels bind up at the track while mounting. You think everything is fine till that 165MPH section of track comes up. It about blinds you.

Good point there. It's better to cinch them down a little at a time and spin the wheel a bit when you do it to get it centered. My 71 GMC 3/4 ton has Ultra 50 8 lug wheels that are not hub centric and I have to do that. In truth you should do it on all wheels even rusty stock steel wheels as they can get cocked a bit if you run one lug all the way down before working the wheel into the mounting surface.

**Sheepdip** · Today, 11:14 PM

In this era GM rear hubs are 4.56"+/- Ford rear hubs are 4.77"+/-

Yesterday, 10:01 PM	#1
tow rig Registered User Join Date: Jul 2018 Location: Ripon, WI Posts: 12	1970 GMC C2500 rear axle hub diameter? I have a 1970 GMC C2500 (2WD) that I have bought aftermarket wheels and tires for. The wheels are 8 X 6.5 bolt pattern. The center hole in the wheel is just under 131mm. If I bolt a wheel onto the hub of the Dana 60 full-floating rear axle, the wheel has a significant gap between the center hole of the wheel and the hub of the axle. The axle hub is difficult for me to measure despite having a digital caliper and 4-5" micrometer. The studs get in the way of my making an accurate measurement. Does anyone know the diameter of the hub at the wheel mounting surface? (I will need to order some rings to fill the gap between the hub and the inside of the rims center hole if I want my rims to be hub-centric.)

Yesterday, 10:11 PM	#2
jerry moss Born Psycho Join Date: Feb 2001 Location: brentwood,cal,usa Posts: 4,888	Re: 1970 GMC C2500 rear axle hub diameter? your tapered lug nuts center the wheel to the mounting flange of the hub. you must be thinking of a Ford truck that uses hub centric wheels. __________________ jerry moss 72 cheyenne super K20- tilt,tach,vacuum,speedwarning,buckets,shoulder belts,am/fm,tow hooks,bumper guards,toolbox,aux. fuel tank,posi front and rear,plus other goodies!!! SOLD 69 suburban K20-tilt,tach,vacuum,speedwarning,buckets,shoulder belts,am/fm,4 inch all spring lift,4 speed, 14 bolt full floater, dana 44 HD,warn winch,posi front and rear,tow hooks,plus other goodies. 73/80 chevy/gmc K20 SB400,turbo 400,205,tilt,a-c,gas hog. 77 K/5 cheyenne blazer-daily driver/beater. SON HAS IT NOW BRENTWOOD,CALIFORNIA

Today, 12:57 AM	#3
tow rig Registered User Join Date: Jul 2018 Location: Ripon, WI Posts: 12	Re: 1970 GMC C2500 rear axle hub diameter? Nearly all factory installed wheels are hub-centric. The 1970 GMC had steel wheels that mated tightly to the hub. I know that many aftermarket wheels are designed to be more universal, and center off of the lugs, in order to have a single wheel casting be useable with several applications. My opinion is that lug centering wheels may be less than ideal, especially for a HD truck that will be carrying heavy loads, driven in rough terrain, abused with dragstrip launches, and/or towing a trailer. Anyway, it looks like my question is turning into something that I haven't asked. Are hub-centric rings needed for aftermarket wheels?(This is a simple google search that I have already done. The jury seems to be about evenly divided on the subject.) Thank you for sharing your experience.

Today, 08:29 AM	#4
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,650	Re: 1970 GMC C2500 rear axle hub diameter? FWIW, I have owned my K20 for 47 years and during that time it has had four different sets of wheels. 1) The stock 16" lock-ring wheels. 2) Aftermarket 15x8" white wagon spokes. 3) Aftermarket 16.5x9.75" chrome wagon spokes. 4) Ford (Accuride?) 16x7" steelies. I couldn't say if the stock wheels were hub-centric, but none of the others were. The truck has been heavily loaded more times than I can count (up to a verified 3 tons in the bed), with no wheel-related problems ever. I agree with Jerry Moss, hub-centric rings are absolutely not needed in your configuration. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

Today, 01:03 PM	#5
tow rig Registered User Join Date: Jul 2018 Location: Ripon, WI Posts: 12	Re: 1970 GMC C2500 rear axle hub diameter? Thank you for weighing in, Mike. You and Jerry supplied just the kind of advice/reassurance that I was needing. I will install the wheels without hub-centric rings and feel confident that there won't be any wheel related issues. I came to the right place. Thanks Again Brad

Today, 06:59 PM	#6
PbFut Senior Member Join Date: Feb 2022 Location: Ca Posts: 518	Re: 1970 GMC C2500 rear axle hub diameter? Just one thing to consider when not using the hub to center a wheel. It will be all the more important to sneak up on tightening those lug nuts allowing the wheel to slip some as the nuts center the wheel before too tight for movement. Rotating the wheel when doing so may also be advisable, in a way centering the weight during the tightening process. This might be overkill, but I've had wheels bind up at the track while mounting. You think everything is fine till that 165MPH section of track comes up. It about blinds you.

Today, 11:14 PM	#8
Sheepdip Senior Member Join Date: Nov 2018 Location: Waterford California Posts: 2,539	Re: 1970 GMC C2500 rear axle hub diameter? In this era GM rear hubs are 4.56"+/- Ford rear hubs are 4.77"+/-



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