Wheel Fitment Question for IFS k2500

[Pookster]

my 92 k2500 has stock 16" wheels. While nothing wrong with them, the supply of tires are kinda expensive to say the least.

I would LOVE to run 15" tires. I dont mind using steel wheels, but would simple caliper grinding be enough?

 

[LongIslander26]

caliper grinding

I don't think you'd be able to fit a 15" wheel on this truck, with the size brakes it has, and "Caliper grinding" doesn't sound like something I'd even want to think about. You may want to consider moving UP to 17", since most of the new trucks nowadays come with that size stock, so tire supplies are plentiful.

 

[nemesis_pyros]

A buddy of mine runs 15's on his 92 1500 now I don't know how much different the brakes are between the 1500 and the 2500 but you might want to get a 15 inch rim and check to see if it fits.

 

[Pookster]

people here grind d60's to fit 15" rims. I just dont know if I can do the same for my truck...

 

[sweetk30]

o.k. now lets play nice. now you need to give use more info. the 88-up is totaly diffrent. 2500 is both 6 lug and 8 lug. and if you go aftermarket rims on 6 lug 15" will fit. do it all the time at work. and no grinding. as to 16" tires to price. keep looking thay are getting more and more styles all with better prices.

 

[Pookster]

My apologies if anyone was offended.

I thought caliper grinding was pretty much a "known" method for fitting the 8 lug SFA front axles with 15" wheels.

I have the 2500 8 lug- By your statement, the 6 lug 15" wheels should fit- Do you know if it would fit the 8 lug model?

I have several sets of 15" tires, and all my other trucks use 15" tires, so keeping it all at 15 would be a definate plus.

 

[Pookster]

Digging for more info...

On an avalanche review page, I got this (2002-2004)
Rotor diameter x thickness
(in / mm): front: 12 x 1.14 / 305 x 29;
rear: 13 x 1.18 / 330 x 30

2004 silverado 1500: front: 12.01 x 1.14 / 305 x 29; rear: 13 x 1.18 / 330 x 30
silverado 2500/1500HD: front: 12.8 x 1.5 / 325 x 38; rear: 1300 x 1.14 / 330 x 29

The 2003 Suburban shares the same brakes as the Silverado of equal 1/2 or 3/4 ton series.

The best info I could find on the net was this:
D44, 8 lug: (74-91)
Overall Diameter: 317.5mm (12.5")
Minimum Thickness: 30.861mm
Overall Height: 71.040625mm

71-91 6 Lugs (blazer, burb, etc)
Type: Ventilated Disc
Overall Diameter: 301.228125mm (11.859375 inch)
Minimum Thickness: 30.861mm
Overall Height: 58.340625mm

Avalanche (all models)
Type: Ventilated Disc
Overall Diameter: 304.7mm (11.996063 inch)
Minimum Thickness: 27.2mm
Overall Height: 58.2mm

2000 GMC SUBURBAN 1/2 TON (4WD) K10, 15, 1500 8 Lug
1998 - 1999 GMC SUBURBAN 1/2 TON (4WD) K10, 15, 1500 8 Lug
1989 GMC 3/4 TON K25, 2500 SERIES PICK-UP (4WD) w/ 13" Rear Drum; 6.375" Tall
1990 - 1999 GMC 3/4 TON K25, 2500 SERIES PICK-UP (4WD) w/ 13" Rear Drum; 5.25" Tall
1990 - 1999 GMC 3/4 TON K25, 2500 SERIES PICK-UP (4WD) w/ 13" Rear Drum; 6.375" Tall
1992 - 1996 GMC 1 TON K35 SERIES PICK-UP (4WD) w/ SRW; w/ 13 x 2.5" Rear Shoe
Type: Ventilated Disc
Overall Diameter: 317.5mm (12.5")
Minimum Thickness: 30.86mm
Overall Height: 70.2mm

------

Judging by these numbers, it would *seem* that to fit 8 lug 15" wheels, the same amount of grinding would be had on both the IFS, as well as the SFA.

 

[Pookster]

Other Odd Variations

According to Brembo, the 88-89 k30's in SRW use a 317.5mm (12.5") diameter front brake, when used with the 6 3/8th tall rear drum and uses the same exact part number for the DRW application.

However, they state that from 90-91, the the SRW uses the same size again for the front, but uses (using a 5.25" rear drum). THe DRW then gets a new front rotor size, 327.00 (12.8740157 inch)

From 92-96, they go back to the same part number, with the same 317.5mm diameter front rotor. (12.5 inch)

the biggest brake rotor sizing was avaliable on the DRW, and on the SRW with 9000-9200GVW (maybe the 2500 HD?) only avaliable on the 1 ton, 90-91 years. (361.6mm) (14.2362205 inch)

At least according to brembo, certain years, starting from 1990, have DRW's that had rear disc applications- these would then get the significantly larger 351.8mm rotors. (13.8503937 inch)

http://www.brembo.com/NR/rdonlyres/6779C1CA-6120-4B3C-AF18-004FF88A2375/0/AMCatalog101104.pdf

 

[Pookster]

Fitment and Backspacing

According to some sites, the stock backspacing on a IFS chevy is 1.5"

Tirerack claims a +3mm (16x8) 8-165 bolt pattern, for a k2500 in the 88+ body years.
Wheel Offset: +20mm (16x8) Bolt Pattern: 6-139 for a k1500 in the 88+ body years

Tirerack also claims a 0mm offset, for a k1500 of the 71-91 years of the k5's.
They claim the same 3mm offset for a k2500 in the 71-91 years.

As i understand it, backspacing is the overall width of the wheel (lets say 8") divided by 2,=4". So when someone says, "I have 4" of backspacing on a 8" wheel" it really = 0 offset!

From a positive standpoint, the same backspacing used for the old SFA 8 lugs, should fit without problems to the new IFS 8 lugs.

 

[HarryH3]

According to some sites, the stock backspacing on a IFS chevy is 1.5"

Tirerack claims a +3mm (16x8) 8-165 bolt pattern, for a k2500 in the 88+ body years.
Wheel Offset: +20mm (16x8) Bolt Pattern: 6-139 for a k1500 in the 88+ body years

Tirerack also claims a 0mm offset, for a k1500 of the 71-91 years of the k5's.
They claim the same 3mm offset for a k2500 in the 71-91 years.

As i understand it, backspacing is the overall width of the wheel (lets say 8") divided by 2,=4". So when someone says, "I have 4" of backspacing on a 8" wheel" it really = 0 offset!

From a positive standpoint, the same backspacing used for the old SFA 8 lugs, should fit without problems to the new IFS 8 lugs.

Backspacing is the distance from the inner edge of the wheel to the mounting flange. You could theoretically have a 15 inch wide wheel with zero backspacing, by having the mounting flange flush with the inner edge of the wheel.

The stock backspacing on GM IFS trucks is around SIX inches. The FRONTspacing is in the 1.5 inch range. (Measuring from the outer edge to the wheel face). Look at your wheels and you'll see that the center section of the wheel is mounted way out near the edge of the wheel on an IFS wheel. The backspacing on a stock SFA wheel is considerably less than on an IFS wheel.

While the bolt pattern for SFA 8-lug wheels is the same as for IFS 8-lug wheels, you'll find that the backspacing difference will make the tires stick way out of the fenderwells if you try to use SFA wheels on an IFS truck. You'll also find that the very expensive unit bearings do not like having that kind of offset load placed on them. The cost of replacing wheel bearings would soon offset any saving in tire costs.

 

[Pookster]

Right. I have seen what you are talking about- But doesnt that only apply to the half ton IFS units, and not the 3/4 ton?

I redid the math for the IFS- the offset is .787", which (I think and I could be doing this wrong) on a 8" rim, would be (8/2)+.787=4.787 backspacing.
On a stock 6" rim, it would be 6/2 +.787=3.787 backspacing.

It did seem a bit on the odd side, but tirerack says the offset (which is more universal than backspacing, since backspacing depends on overall rim width, where as offset can be any rim width) on both the SFA and IFS 3/4 tons are the same.
On an 8 inch, it would be 8/2 + 0.1181102= 4.118 backspacing.

 

[Pookster]

Just an off topic thought but... Couldnt I run Humvee (h1) beadlock wheels then without any mods to the wheel?