Need help with wheel offset selection - The 1947 - Present Chevrolet & GMC Truck Message Board Network

JWG · 10-27-2015, 01:14 PM

I'm installing a CPP 4 wheel disk brake kit on my '65 stepside. Of course, now I need new wheels and am about to place an order, but concerned with which offset I need.

I'm going to run a 20" x 8.5" front wheel with an offset of .3"
(20 X8.5 5-127.00 7 DGMCML)

The rear wheel is a 20" x 9.5" with an offset of .6"
(20 X9.5 5-127.00 15 DGMCML)

Front tires will be 255/40R20
Rear tires will be 285/40R2

Do these offsets sound right?

Thanks for any help!

**The Rocknrod** · 10-27-2015, 01:31 PM

Until you get the wheels installed it would be difficult to know exactly. However when you do you can use this chart to determine various dimensions:
http://www.thewheelsmith.net/WheelGeometry.html

forestb · 10-27-2015, 04:57 PM

That doesn't sound right to me. I have 8 inch wheels front and back and they have the standard offsets (I think 4") and they fit grate. I am running a 275 tire front and back. But I am no expert.

JWG · 10-27-2015, 05:05 PM

I'm being told that back spacing on the front should be 5.25" and 6.5" on the tears with a 10" wide wheel. Does this sound correct?

geezer#99 · 10-27-2015, 07:02 PM

Best to measure it yourself.
Like this.
http://www.hotrod.com/how-to/wheels-...heels-fitment/

You can buy a tool if you want to make it easier.
Like this.
http://www.summitracing.com/int/part...1201/overview/

The Percy's tool lets you simulate tire sizes too.

wilbur46 · 11-02-2015, 06:54 PM

I sure agree with Geezer.
Measuring, even if you have to make up a tool is a LOT cheaper than buying rims that don't work.
My current el cheapo tool is made from 2 wooden yardsticks.
they both have slots routed in them .
I hold the vertical one against the wheel mounting flange and adjust the horizontal up to wheel/with tire diameter and then out to fender well clearance and WHAM. Don't forget to count the 1/2" of the vertical yardstick in your backspace decision.
W

JWG · 11-03-2015, 10:02 AM

Great advice guys, thank you!
I will take measurements once the brakes kit is on the truck and then will order my wheels.

JWG · 11-13-2015, 09:50 AM

Well, I have it done! I went with the following wheels and tires with the CPP big brake kit

The wheels are 20" Rev Classic

20 x 8" front wheel with a 4.5" backspace
20 x 9.5" rear wheel with a 5.84" backspace

Front tires are Nitto NT420S 255 /40 R20
Rear tires are Nitto NT420S 285 /40 R20

dwcardfan · 11-13-2015, 11:25 AM

Looks like you made a good decision. Very nice.

creep · 11-13-2015, 12:53 PM

Nice!

J1MMY · 11-13-2015, 02:05 PM

Lovely looking truck.

How much clearance is there from the outside of the rim/tyre and the inside lip of the fender?

Also, how have you converted to 5 lug?

10-27-2015, 01:14 PM	#1
JWG Registered User Join Date: Aug 2014 Location: Berwick, LA Posts: 33	Need help with wheel offset selection I'm installing a CPP 4 wheel disk brake kit on my '65 stepside. Of course, now I need new wheels and am about to place an order, but concerned with which offset I need. I'm going to run a 20" x 8.5" front wheel with an offset of .3" (20 X8.5 5-127.00 7 DGMCML) The rear wheel is a 20" x 9.5" with an offset of .6" (20 X9.5 5-127.00 15 DGMCML) Front tires will be 255/40R20 Rear tires will be 285/40R2 Do these offsets sound right? Thanks for any help!

10-27-2015, 01:31 PM	#2
The Rocknrod Moderator Join Date: Aug 2011 Location: China Spring, TX Posts: 7,280	Re: Need help with wheel offset selection Until you get the wheels installed it would be difficult to know exactly. However when you do you can use this chart to determine various dimensions: http://www.thewheelsmith.net/WheelGeometry.html __________________ Master Chief, US Navy, Retired 1964 C10 Step-side Short Bed - In Progress 2009 2500HD Duramax LTZ 1948 GMC Panel 1956 Big Window Stepside 1953 5 Window Chevy Stepside 1932 Coupe New Seat Foam for Bench Seats?

10-27-2015, 04:57 PM	#3
forestb Registered User Join Date: Jan 2009 Location: Burbank, CA Posts: 3,611	Re: Need help with wheel offset selection That doesn't sound right to me. I have 8 inch wheels front and back and they have the standard offsets (I think 4") and they fit grate. I am running a 275 tire front and back. But I am no expert.

10-27-2015, 05:05 PM	#4
JWG Registered User Join Date: Aug 2014 Location: Berwick, LA Posts: 33	Re: Need help with wheel offset selection I'm being told that back spacing on the front should be 5.25" and 6.5" on the tears with a 10" wide wheel. Does this sound correct?

10-27-2015, 07:02 PM	#5
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,626	Re: Need help with wheel offset selection Best to measure it yourself. Like this. http://www.hotrod.com/how-to/wheels-...heels-fitment/ You can buy a tool if you want to make it easier. Like this. http://www.summitracing.com/int/part...1201/overview/ The Percy's tool lets you simulate tire sizes too.

11-02-2015, 06:54 PM	#6
wilbur46 Registered User Join Date: Mar 2015 Location: Sebastopol, Ca. Posts: 46	Re: Need help with wheel offset selection I sure agree with Geezer. Measuring, even if you have to make up a tool is a LOT cheaper than buying rims that don't work. My current el cheapo tool is made from 2 wooden yardsticks. they both have slots routed in them . I hold the vertical one against the wheel mounting flange and adjust the horizontal up to wheel/with tire diameter and then out to fender well clearance and WHAM. Don't forget to count the 1/2" of the vertical yardstick in your backspace decision. W

11-03-2015, 10:02 AM	#7
JWG Registered User Join Date: Aug 2014 Location: Berwick, LA Posts: 33	Re: Need help with wheel offset selection Great advice guys, thank you! I will take measurements once the brakes kit is on the truck and then will order my wheels.

11-13-2015, 09:50 AM	#8
JWG Registered User Join Date: Aug 2014 Location: Berwick, LA Posts: 33	Re: Need help with wheel offset selection Well, I have it done! I went with the following wheels and tires with the CPP big brake kit The wheels are 20" Rev Classic 20 x 8" front wheel with a 4.5" backspace 20 x 9.5" rear wheel with a 5.84" backspace Front tires are Nitto NT420S 255 /40 R20 Rear tires are Nitto NT420S 285 /40 R20 Attached Images

11-13-2015, 11:25 AM	#9
dwcardfan Registered User Join Date: Sep 2013 Location: Strawberry Arkansas Posts: 1,137	Re: Need help with wheel offset selection Looks like you made a good decision. Very nice. __________________ http://67-72chevytrucks.com/vboard/s...d.php?t=605217

11-13-2015, 12:53 PM	#10
creep Registered Loser Join Date: Jun 2009 Location: Elyria, OH Posts: 1,523	Re: Need help with wheel offset selection Nice! __________________ ((..)) ((0)) '63 GMC lwb, 383, th350, lays frame, genuine patina. The Build Thread - http://67-72chevytrucks.com/vboard/s...d.php?t=374267 '88 Astro cargo bagged, shaved, phantom grille. SOLD '50 Chevy 2 door sedan awaiting attention. 2014 Silverado Ext cab, 5.3, daily driver.

11-13-2015, 02:05 PM	#11
J1MMY Registered User Join Date: Aug 2009 Location: Wiltshire, UK Posts: 157	Re: Need help with wheel offset selection Lovely looking truck. How much clearance is there from the outside of the rim/tyre and the inside lip of the fender? Also, how have you converted to 5 lug? __________________ '63 C10 Longbox fleetside '94 C1500 Sierra ex-USAF beater



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