Taller tire

[lutronjim]

The more I read about wheels and tires, the confusier I get. Most of the threads I have looked at here seem to have dropped or raised trucks.

I have a 70 C10 stepper that is stock height. It has 373 gear driven by LS drive train. I have to get new tires and hope to get a taller tire to help with highway mileage.

It looks like from what I have read here that I would like to go with a 18" riim and tire. I currently am running P235/75R15's. They come close to the edge of the finderwell - see pics.

Could some one recoment a 18 wheel size (backspace and width) and tire that would be taller and not hit. I would prefer to run same size on front and rear.

Many thanks

[ga-stepside]

https://tiresize.com/calculator/

Use this to calculate tire size.

[1972RedNeck]

Do you want to go to 18" wheels specifically or do you just want a taller tire? A 235/85R16 is going to be right around 32" tall and the same width as what you have now - should fit fine without rubbing. A set of wheels off of a '90's Chevy should fit perfect fr your truck.

[lutronjim]

Thanks for comebacks. I didn't mention truck has 15" 6 lug wheels that came off a 4x4.

I thought 90's wheels needed spacers to keep them from being too near frame.

[Mike C]

I will start by saying you need to convert to 5 lug and disc brakes. It’s not mandatory to go 5 lug, but the wheel choice is so much better. And lowering the truck at least a little will make it handle so much better and you will get so many ridiculous compliment about how awesome your truck is you will wonder why you didn’t do it sooner.

But the safety factor of discs is HUGE, especially if you have a modern driveline in the truck. You say modern driveline so I am assuming 5.3/4l65? I would think that would be an awesome combo and not really need an rpm reduction. But the taller tires really improve truck appearance IMO.

You can run same size front and rear, but again, the look is much better IMO if you stagger. Either way, these trucks do best with a zero offset rim. You should be able to run 255 50 18 on 17x8 zero offset rim. But that is me extrapolating a little.

I went to 17’s on my truck and would do that or 18’s again. 275 55 17 on a 17x9 rear 5” backspace wheel. Front is 235 55 17 on 17x8 4” backspace wheel. If you are keeping score, they are zero offset rims. BUT that is pretty much max size rear tire with the 7” drop on the back of my truck and that is also using the wider 71-72 rear axle to make that work.

My truck has 2 1/2” ECE conversion spindles and 2” springs in the front with a DJM flip in the rear for a 4.5/7” drop.

My truck in 6th post. IPad won’t let me post directly.

http://67-72chevytrucks.com/vboard/s...d.php?t=723516

[CC69Rat]

For what it's worth -- if it were my truck:

There were two different rear end housings in these trucks. The earlier model years axle (6 luggers) were 1.5" narrower than the later housings. 67-69, then in 70 it was sort of the 'conversion' year. The 71 models were coming out, and the factory had some 71-72 model housings laying around.. so basically they just used up whatever they had left. What this means to you, is depending on when your truck was built (maybe a late 70 year model build?) it would have a longer axle in it. Most of the longer ones were 5 lug starting in 71-72 but I have seen a handful of 70 6 luggers with the longer axle in them.

How do you tell?

The easiest way I know to tell is to lay down underneath the back of your truck. Hold a tape measure against the inside edge of the brake backing plate on one side.. then have your wife / buddy pull the tape across to the other side in this same spot. The earlier axles are 55.5" long at this measurement using this method. You may hear it mentioned as 'Plate -to-plate" Just meaning from one backing plate to the other. The later housing is 57" in this same spot.

Why does it matter ?

If youre thinking about changing your wheels, (you asked for backspacing recommendations) If your truck has the early axle in it, vs. the later axle it can throw your measurements off bu .75" on either side. This can mean the tires just wont fit, it means they rub, etc.

.. I'll watch the post and yes I can make some backspacing suggestions but we need to know what rear axle housing you have first.

Later ..

[lutronjim]

I measured the width between the rear backing plates at 571/4". This was at the 'flats' trying to avoid the bumps.

FYI I have disk in front. The engine tranny are LC9 with 65E. Original except for 69 cab = pine tree needles got in the old cab cavity and ate it up. Pedal ebrake was kept. I bought truck new so there is no previous owner.

The truck is ddwt. It goes to the farm so I don't want it lowered.

Thanks

[Mike C]

Fair enough. Before I switched to the 5 lug setup and my truck was at stock height, I had 265 75 15 on the 7" wheels that were originally on my '72 Jimmy. They fit find and had no issues rubbing. That would be a 31" tall tire. If you had an 8" rim with same backspace as stock wheel that would provide a little more clearance to the inner bedside.

[CC69Rat]

Yes, it has the longer 71-72 housing. I'd say it is a late build 1970 model truck. Since you bought it new I'm betting it was later in the year and / or a leftover model in early 71. Unless it's been changed at some point..

But anywho, if you're not going lower your backspacing really won't make that much of a difference unless you're doing 10-12" wide wheel.

8-9" wide, 4-5" backspacing you'll be fine.

[lutronjim]

Thanks