Wheel and tire size help!!

[ajwic1]

Hi there, new to the forum. I just purchased an 81 GMc c2500 long bed and am looking to lower it.
Firstly how low can i go without doing a c-notch?
And secondly, if im doing a 3/4 drop. If i stick with a 16/17inch rim, What size wheels and tires can i fit under there without rubbing? Does offset matter?

 

[RanchWelder]

https://67-72chevytrucks.com/vboard/showthread.php?t=795641
https://www.streettrucksmag.com/c10-suspension-buyers-guide/
http://forum.73-87chevytrucks.com/smforum/index.php?topic=22497.0
https://www.speedwaymotors.com/the-toolbox/how-to-c-notch-a-c10-truck-frame/32497

Top four searches: 0:00.3495 seconds. Duck Duck Gone

It depends on the actual tires/rims width.
Nobody can tell you that without exact specs on tires, wheels and drop vs actual tire diameter.
Only you can call that shot, after you engineer the stomp.


What's wrong with stock OEM ride height?
Lots cheaper, less frame damage/tire wear.
Less chance of hitting a frost heave in Canada and ruining your truck?

Do you live on a flat race track or normal defective roads with abnormal manhole cover's and speed bumps seeking to destroy your transmission pan?


Welcome!

Edited: Because I guess asking a guy to reconsider dropping his rig makes people upset.

My OPINION is now in green writing, so you can see my opinion more easily.

 

[ajwic1]

I appreciate the reply but i feel like my questions were pretty clear. You sent me links for c10s not c2500s (different leafs and suspension), and then asked me to question why i want to do it… im just looking for people with experience who’ve done what i want to do and tell me what wheels they fit under theirs.
Thanks for taking the time tho!

 

[ChuckN]

Paging @bluex - not sure if he’s worked with the C20/25 lowering or not.

It’s my understanding that the limiting factor for lowering our trucks in general is the size of the inner fender well, and I’ve never been told that there is a difference fender well between the C10s and C20s.

My lowered ‘81 C10 on a 4.5” drop on front (yes, I realize that you’re only going for 3”) has 255/60/15 which calculates to 27” high and 10” wide per my quick search. And it rubs at full lock when hitting a bump (not all the time). You can buy the 73-79 inner fenders and that will provide a little more room.

It’s my best guess. I do remember @OldBlueDually lowered his so maybe he can shed some more light on the subject. Best of luck and welcome!

 

[bluex]

Hi there, new to the forum. I just purchased an 81 GMc c2500 long bed and am looking to lower it.
Firstly how low can i go without doing a c-notch?
And secondly, if im doing a 3/4 drop. If i stick with a 16/17inch rim, What size wheels and tires can i fit under there without rubbing? Does offset matter?

1. Depends on how you want to use the truck. A flip can be done without a notch, but if you plan use it to it capacity it will bottom out on the axle sooner.

2. On a 3/4 drop you can pretty much stick with the same overall height tire as stock.

 

[bluex]

Everything mentioned in this thread will also apply to a C20/C30.

Thread 'Wanna slam that 63-98 C10/C1500? Lets talk about it!' https://www.gmsquarebody.com/threads/wanna-slam-that-63-98-c10-c1500-lets-talk-about-it.38131/

 

[bluex]

It’s my understanding that the limiting factor for lowering our trucks in general is the size of the inner fender well, and I’ve never been told that there is a difference fender well between the C10s and C20s.

No difference on inners between 10/20/30. Only difference is 73-80 and 81+. 73-80 inners will give a little more room on an 81+.

 

[bluex]

https://67-72chevytrucks.com/vboard/showthread.php?t=795641
https://www.streettrucksmag.com/c10-suspension-buyers-guide/
http://forum.73-87chevytrucks.com/smforum/index.php?topic=22497.0
https://www.speedwaymotors.com/the-toolbox/how-to-c-notch-a-c10-truck-frame/32497

Top four searches: 0:00.3495 seconds. Duck Duck Gone

It depends on the actual tires/rims width.
Nobody can tell you that without exact specs on tires, wheels and drop vs actual tire diameter.
Only you can call that shot.


Dropping is not often discussed on this forum.
Take your time and research before you spend your Hot Rod money or end up dragging your fenders into your tires.
Most drops require serious spring ratio calculations and body lift, in order to mod the proper way.
It can be big money to lift the chassis and drop the frame and drive line safely.

What's wrong with stock OEM ride height?
Lots cheaper, less frame damage/tire wear.
Less chance of hitting a frost heave in Canada and ruining your truck?

Do you live on a flat race track or normal defective roads with abnormal manhole cover's and speed bumps seeking to destroy your transmission pan?


Welcome!

SMH, This is all nonsense, OP please ignore it...

Well the links are helpful but the rest isnt...

 

[Elliot W]

@bluex a while back I did the axle flip kit as you recommended (and while we are on the topic of lowering), currently procrastinating grinding off the stock bump stops to install low profile ones. The stock stops are resting on the axle...is there any damage that could happen to the axle for basic onroad driving?

 

[Grit dog]

Hi there, new to the forum. I just purchased an 81 GMc c2500 long bed and am looking to lower it.
Firstly how low can i go without doing a c-notch?
And secondly, if im doing a 3/4 drop. If i stick with a 16/17inch rim, What size wheels and tires can i fit under there without rubbing? Does offset matter?

Answer, depends on offset. But a 3/4 drop on a 3/4 ton will fit some meaty tires. Especially in the rear.
I’d drop it first then do some measurin.

 

[Grit dog]

Not sure why @RanchWelder is all butthurt about your question. But a C20 is a great vehicle to lower.
Quite arguably better bang for the buck as well. 3/4 tons are comparably cheaper than 1/2 tons to purchase. Have bigger brakes and much stouter rear axle.
Aside from counting lug nuts, you can make a 3/4 ton look identical to a half ton and have better/heavier duty components for less than free.

Ifn I was gettin a 2wd square to drop or even slam, I’d consider it an advantage and a bonus to start with a c20 vs a c10.

 

[RanchWelder]

Flip your axle and buy some magnesium skid bars for your rear bumper.
Bump stops are un-nessesary, when you are lowering the truck.
Slamming on the ground and bending your frame is cool.

Adjustable Air shocks control that frame slam, not bump stops.

My bad for suggesting the links. (Even though you liked them).

Pardon me for questioning slammed trucks, without proper engineering of the frame and suspension, so a guy doesn't wreck hids truck..

Tell me one good reason to be mad at anything I posted?
Seriously?

My but don't hurt at all.
Ya'll are acting stoopid and ganging up on nothing but common sense.
Grow up. Making up drama where ther isn't any?

 

[ChuckN]

@bluex a while back I did the axle flip kit as you recommended (and while we are on the topic of lowering), currently procrastinating grinding off the stock bump stops to install low profile ones. The stock stops are resting on the axle...is there any damage that could happen to the axle for basic onroad driving?

I think there might be a term for it- I think it’s “infinite spring rate”? Not sure- anyway, what it means is that there’s no travel so it basically bottoms and you lose traction when it bounces- forgive me, I’m just parroting what I read.

Send me a PM @Elliot W! An angle grinder to take off the rivet heads and then drill into the center of it to release the pressure- then punch ‘em out. You got this!

Sorry to go off topic

 

[OldBlueDually]

Hi there, new to the forum. I just purchased an 81 GMc c2500 long bed and am looking to lower it.
Firstly how low can i go without doing a c-notch?
And secondly, if im doing a 3/4 drop. If i stick with a 16/17inch rim, What size wheels and tires can i fit under there without rubbing? Does offset matter?

Welcome! Cool truck you have, I am bias to the 73-78's but hey, I like them all @ChuckN mentioned me in the post, otherwise I did not see this.

To answer your question, with a 2/4, or a 3/4 drop, you do NOT need a C-notch and you can run your stock size tire no problem at all, as others have also stated.

I have a 6/8 drop on my dually, and it is suggested to run a 28" or smaller tire, but since I liked the "filled in" look and I don't like following directions ( ) I went larger. My rims are updated to 16" (were 16.5"), and I picked the 29.3" diameter tire, which are 10 ply, 225/75/16.

@RanchWelder be nice & help support the new guys/gals coming onto this site.

For a drop kit for you, I HIGHLY suggest these guys, Switch Suspension. They are very helpful, and a great wealth of knowledge for lowering if you have any questions for them.

Chevrolet C-20/C-30 1973-1991 Deluxe 3/4 Drop Kit

Deluxe 3/4 Drop Kit for Chevrolet C-20 and C-30 1973-1991 has front 3 inches drop spindles, rear 4 inches shackle and hanger that fits 8 lugs 2wd only.

switchsuspension.com

Here is my build thread if you'd like to see what I started with, and how I got to where it is. It was fun.

https://www.gmsquarebody.com/threads/76-gmc-crew-long-box-dually-gotta-get-it-on-the-road-again.29806/

You must be registered for see images attach

 

[ajwic1]

Welcome! Cool truck you have, I am bias to the 73-78's but hey, I like them all @ChuckN mentioned me in the post, otherwise I did not see this.

To answer your question, with a 2/4, or a 3/4 drop, you do NOT need a C-notch and you can run your stock size tire no problem at all, as others have also stated.

I have a 6/8 drop on my dually, and it is suggested to run a 28" or smaller tire, but since I liked the "filled in" look and I don't like following directions ( ) I went larger. My rims are updated to 16" (were 16.5"), and I picked the 29.3" diameter tire, which are 10 ply, 225/75/16.

@RanchWelder be nice & help support the new guys/gals coming onto this site.

For a drop kit for you, I HIGHLY suggest these guys, Switch Suspension. They are very helpful, and a great wealth of knowledge for lowering if you have any questions for them.

Chevrolet C-20/C-30 1973-1991 Deluxe 3/4 Drop Kit

Deluxe 3/4 Drop Kit for Chevrolet C-20 and C-30 1973-1991 has front 3 inches drop spindles, rear 4 inches shackle and hanger that fits 8 lugs 2wd only.

switchsuspension.com

Here is my build thread if you'd like to see what I started with, and how I got to where it is. It was fun.

https://www.gmsquarebody.com/threads/76-gmc-crew-long-box-dually-gotta-get-it-on-the-road-again.29806/

You must be registered for see images attach

thanks for the help! what did you do to combat the rubbing for your larger tire?

The truck im buying does not have stock tires/rims on it, it has 31s which i doubt will fit. this puts me in a bit of a predicament when buying new tires/wheels (will need to be done before i drop it).
i have that exact kit in my shopping cart! I'm looking to start with a 3/4 and maybe go lower to 4/5 if im feeling comfortable. maybe add a lowering coil in front and remove some overload springs in rear (i will not be hauling or towing).

SO i guess my questions now are if i buy a 16x8 for front and 16x10 for rear, if i stick around 27/28" tall tire does offset or backspacing matter? and how wide could i go without rubbing?