Question on tire size for an '85 K20...

[7900_Blazer]

Purchased an '85 K20... my daughter wants it to be her daily... all original.. needs some work of course.

Two questions:

1. Do these trucks benefit from a leaf-spring upgrade in the front to level the stance?

The 'natural' stance of these trucks seems to be 'high' in the rear - I'm assuming so that when you hook up a trailer it will be a bit more leveled out??? Also, the fronts do seem to have the slightest 'reverse' arch which makes it sit a bit lower... not sure if that is normal or just worn out sprints after 37 years.

2. What tire size can I go with without having to upgrade the springs all the way around?

I'm looking at either a 285/70 R16 (33" tire) or a 265/70 R16 (31" tire)...

Thoughts on either of these tires? Will they fit without a spring upgrade?

I'd like it to 'stand' a bit taller than it does now.

You must be registered for see images attach

 

[FireTruck1984]

Yes the reverse arch is normal for front leafs on the K20.
I hope you’d consider keeping the steel wheels and caps, that’s a very popular look these days. A taller side wall is also the way to go. Here’s an 85 r16

You must be registered for see images attach

 

[Dutch Rutter]

@7900_Blazer

My 83 k20 has 305/70 r16s and is on a 2" lift. The front springs are either aftermarket or have been re-arched by one of the previous owners. I also have ORD's HD shackles up front which give it 3/4 inch more up front. I have not yet had any rubbing even offroad. But I'm sure its pretty close at some points when twisted up good.

I wouldn't try a 33 with complete stock suspension and any offroad use in its future, strictly street use might be fine. If it were mine, and I wasent going to change any suspension, I'd go with the 31 or even a 32 OD tire.

Edit: to answer your questions.

New front leaf springs will always be an improvement over clapped out/sagged out factory springs.

It is possible that you could change out only the front springs to level it out more, and add more tire. That way you wouldn't have to change the rear springs, add blocks, or a flip kit to match.

 

[SquareRoot]

@7900_Blazer

My 83 k20 has 305/70 r16s and is on a 2" lift. The front springs are either aftermarket or have been re-arched by one of the previous owners. I also have ORD's HD shackles up front which give it 3/4 inch more up front. I have not yet had any rubbing even offroad. But I'm sure its pretty close at some points when twisted up good.

I wouldn't try a 33 with complete stock suspension and any offroad use in its future, strictly street use might be fine. If it were mine, and I wasent going to change any suspension, I'd go with the 31 or even a 32 OD tire.

Edit: to answer your questions.

New front leaf springs will always be an improvement over clapped out/sagged out factory springs.

It is possible that you could change out only the front springs to level it out more, and add more tire. That way you wouldn't have to change the rear springs, add blocks, or a flip kit to match.

That's a good looking rig DR!

 

[Catbox]

While I am not a 4wd truck, we run around on a set of 265/75/16's with no issues of rubbing at all at stock 3/4 ton ride height.
These are 31.5" tires.
Just so you have an idea.

You must be registered for see images attach

You must be registered for see images attach

 

[Dutch Rutter]

That's a good looking rig DR!

Thank you sir! Of course it was just washed in that picture.

Almost sold it a few months back TBH. Glad I didn't.
But now the trans is making some awful noise (I've been expecting it to) so that's going to need addressed this month or next.

 

[68post]

Your rim width, if wider than stock, will have an effect on what rubs. 33's on a ten inch rim will hit the back of the front fender on a K30, I can hear mine touch with new springs, 1" zero rates, and ORD HD shackles (extra 1/2"). My rims are 10" tho' and 305 tire size, 285's fit better - especially on a narrower rim. 265's fit on a 10" rim, but it's too much rim width.

 

[7900_Blazer]

@7900_Blazer

My 83 k20 has 305/70 r16s and is on a 2" lift. The front springs are either aftermarket or have been re-arched by one of the previous owners. I also have ORD's HD shackles up front which give it 3/4 inch more up front. I have not yet had any rubbing even offroad. But I'm sure its pretty close at some points when twisted up good.

I wouldn't try a 33 with complete stock suspension and any offroad use in its future, strictly street use might be fine. If it were mine, and I wasent going to change any suspension, I'd go with the 31 or even a 32 OD tire.

Edit: to answer your questions.

New front leaf springs will always be an improvement over clapped out/sagged out factory springs.

It is possible that you could change out only the front springs to level it out more, and add more tire. That way you wouldn't have to change the rear springs, add blocks, or a flip kit to match.

Love your truck!... I think 307/70's are ... 35's right?

 

[Dutch Rutter]

Love your truck!... I think 307/70's are ... 35's right?

Thanks. They measure out to be 32.8 overall so a 33 just wider then a 285/75r16. When I bought these, I was trying to get the narrower 285s but the tire shop had these on hand and the 285s would have been a 4-8 week wait.

Side note: these Falken Wildpeak ATW3 have been a fantastic tire.

 

[Grit dog]

Love your truck!... I think 307/70's are ... 35's right?

315-75-16s are a "nominal" 35" tire

 

[Frankenchevy]

315-75-16s are a "nominal" 35" tire

Yep a metric 35. By the math it calculates to a 34.6, but it could be more or less.

I learned from a tire guy that most tires are labeled based on OD including tread now. Whereas in the past, a 35” tire was based on the carcass dimension. Just like gatorades, they keep on shrinking. Keep the price the same, but shrink the product. Sly way of raising the price.

 

[Grit dog]

Yep a metric 35. By the math it calculates to a 34.6, but it could be more or less.

I learned from a tire guy that most tires are labeled based on OD including tread now. Whereas in the past, a 35” tire was based on the carcass dimension. Just like gatorades, they keep on shrinking. Keep the price the same, but shrink the product. Sly way of raising the price.

Interesting. I didn’t know sizes used to be before the tread thickness.

 

[Frankenchevy]

Interesting. I didn’t know sizes used to be before the tread thickness.

Neither did I, but I don’t know a whole lot about tires either. I’m still learning. I just ordered a set of Nitto Ridge grapplers in 35x12.50-18 F2 load range. The guy at America’s Tire told me at the time about the measurement of a tire’s OD. He mentioned there are a few companies that still measure the old way such as Maxxis and TSL.