Is anyone running 285's on a 98 Suburban K2500. I would like to go up one more size. 245's are the standard and I have 265 now. The truck is stock for the most part.

I ran 285's on my 96 2500 silverado for 3 years. I then dropped back to the 265's. the only probelm I had with the 285s is that they rubbed the fenders on tight turns. I will have 285's again as soon as I need tires. 265's just don't get it.

my next move will be 285/75's or 305/70's

Newbie here-

I run 305's on most of my trucks with minimal rub. The rub occurs mostly with the snowplows on, and at full lock. I'll try to attach a pic of the 96 diesel with 305 Bridgestone Dueler A/Ts.

When I had my suburban, I had the 285s on it. A little rub but not enough to bother me. It was only if I cut the wheel to the right all the way to the limit.

iv got 265's also, how much did they change the truck height

You can use this link to help figure out tire sizes

www.miata.net/garage/tirecalc.html

Do you guys know what offset you were running? I have aluminum wheels with a non-stock offset (dunno what it is, they were on the truck when I bought it) and the 265s rub pretty good when I turn the wheel (and when they're new...) I would like to run 285s, but I had tried them on with these wheels, and they were rubbing on the fender also... Sooo, now that these wheels are in need of some TLC, I thought maybe I'd get some MT Classic IIs, but I don't know what's an appropriate offset.

-Chris

Thanks for the reply's. I'm going to be putting Bilstiens on soon before the tires.(Anyone Cheaper then Kennedy?) My current 265 don't rub unless I'm doing a tight turn at some speed. Might just be that the shocks are worn out and stock. I might also get the leafs re-arced and maybe add some to them. Have a friend that does that type of work.

I was thinking of getting the following tires.

265/75/16 maybe 285 but they are load D
</FONT>Bridgestone Dueler A/T Revo
Load E

Does anyone have them? What do you think of them? Worth the cost.

I just bought 285 Revos a couple of months ago and have put about 1500 miles on them. 1000 of those miles were on one ice fishing trip a couple weeks ago to Northern Minnesota. I hauled an enclosed 16'~20' trailer full of a 4-wheeler, several portable ice fishing houses, and gear for 6 guys. And all 6 guys rode in the burb (3rd row seating).

The tires rubbed frequently when turning into a driveway/approach with a slight bump (such as convenience stores, gas stations, grocery stores, etc...) till I trimmed the little pieces of plastic in front of the tires near the bumper ends. They've only rubbed once since, and I hit a bump quite hard while turning, so I wasn't suprised.

This pic is before I trimmed that plastic piece that sits just under the front of the fender flare...
http://image28.webshots.com/29/6/14/24/247461424HyRuic_ph.jpg

Here's a full view of the burb sitting on the new tires..
http://image32.webshots.com/32/6/6/93/247460693lHqUBf_ph.jpg

Are the Revos worth the extra $ ?

I haven't made up my mind yet. Only time will tell. I did noticed that my icey road traction is IMMENSELY improved over the Firestone Steeltex's that I replaced, but they were worthless worn-out tires and I may have noticed the same improvement with a less expensive new set of tires. The snow traction seems to be pretty good too, as I did a lot of driving off the beaten paths on the lakes when I was ice fishing, but again, maybe I could have gotten that same traction improvement with a cheaper tire. I don't know.

One drawback of the Revos is that they don't offer a load range E in the 285 size.

I liked the 285's much more than the 265's. I think the Buckshot mudder is the better tire. But I should have bought it in a 285 like the Wild Country TXR. The Maxxis tire has great snow, wet road, sand and mud traction but I miss the width and clearance of the 285.

First off nice truck. Thanks for the pics. They look like it's a very close fit not leaving much room. How close is the tire to the front or back fender?


The bigger tires look nice on the burb.

When I upsized my tires, I went from the stock 245/75 to a 235/85 because the stock rims are so narrow. My concern with using 265, 285, etc. sized tires is the section width on the skinny rims causing uneven tread wear. Has anyone noticed this with the larger wide tires, or am I just worried about a non-issue?

My experience is with running a set of 31x10.5R15 tires on stock 15x7 Jeep rims and wearing out the tread unevenly, so I didn't want to repeat that mistake on the Sub'.

My factory 265's came stock on 7" wide GM 16" 6 bolt rims, I uprated for MT rim for more weight carry capacity which is 8" wide no unusual wear to report on 265s there, I also had no odd wear on the stock rims prior to swapping to HD rims.

pretty good discussion here http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=13;t=000323 on tires & rims, I think you have to guest register to view it.

I did have more wear in the center of the tire than on the shoulder. When I ran the 285 on stock 8 bolt GM rims. It was not enough for concearn.

I was thinking of getting the following tires.

265/75/16 maybe 285 but they are load D
</FONT>Bridgestone Dueler A/T Revo
Load E

Does anyone have them? What do you think of them? Worth the cost.
I have 265/75/R16 load range E Revo's and they seem to be a good tire. I can't really say how they'd do on snow and ice since Uncle has had me in SC with them mostly.

I can rub my 265's on my K3500 CC SRW I'd think that 285's would rub badly....

Does anyone know if we can do speedometer correction for larger tires through the PCM? I know that most other GM OBD2 PCM's can be programmed for tire/gear ratio, but Bill Heath seems to think that the 6.5 PCM cannot. I know that early TBI gas trucks had a DRAC(which can be modified for speed correction), and I don't think that my 97 does.

PCM doesn't do it there is a device called a VSSB (vehicle speed sense buffer???) that can be modded to give correct ratio that talks to the PCM I don't have the procedure handy but maybe someone can pop in that knows zactly. AHEM GMCTD you are up on deck again.

Yep - be rite witcha, folks..............

I actually think I have answered my own question. I already know about modifying the DRAC/VSSB, but I wasn't sure that our 6.5 trucks had them as the gas engine trucks stopped using them in 96, and speedometer calibration was through the PCM. Looks like I have located the VSSB under the ECM behind the glove box.

Yep - DRAC is VSSB samo samo no sweat GI.

This will require soldering and desoldering skills to remove wires and replace components on a printed circuit board.

This will require one - or two - 7-bit DIP SWITCH(es) with 14pins for 7 switches - depending on your module.

Remove VSSB module from somewhere behind glove box, open the plastic box, remove the VSSB circuit board.

Two versions of the VSSB pcb exist, one early version with two 7-position wire jumper sets, and a later version with one 7-position wire jumper set.
You'll need a 7-position dip switch for each position .

You'll see several integrated circuits soldered to the pcb, and one area which has several wire jumpers soldered between opposing pin pads.

The jumpers 'decode' the digital ratio required for final gearing and tire diameter in a binary 7-bit code..

Make careful note of each jumpered pad pair, as this will be your oem stock code.

On the 14-position pcb, you'll notice each 7-position block book matches the other - 1's equal wired, or closed, 0 equals not wired, or open - 1-1-0-1-0-0-0--1-1-1-0-1-0-0.
The positions are numbered ---------7-6-5-4-3-2-1--1-2-3-4-5-6-7
This was required to satisfy the logic of the particular ic's used.

On the 7-position pcb is simply 1-1-1-0-1-0-0
Improved design equals--------1-2-3-4-5-6-7

The equation is (tire rev per mile) x (axle ratio) x (40 speed sensor teeth) / (4000 pulses per mile)
tire revs per mile = inches per mile/ tire circumference in inches
1mile = 63360"

Trying to figger out how to post the decoded ratios, available from GM

Thanks for the information. My biggest obstacle was just to find out if my 97 used a DRAC/VSSB and find the location. Now I know the answer to both.:cool:

I have a few links that have a little more information:

This site has a great link to a calculator to find your input ratio based on tire and gear information:

http://614streets.com/drac.html

This is information from a guy off of a couple of offroad boards (I wanted to link, but his site is down, so I copied from a post over at FullSizeChevy.com), same information, different presentation:


i. Introduction

This Tech article shows you how to correct your speedometer, cruise control, and ABS systems by modifying the DRAC or VSSB unit on 1990-1995 General Motors vehicles with the electronic vehicle speed sensor.

Vehicle Speed Sensor (VSS) is the electronic sensor found on the tailshaft of the transmission on 2 wheel drives, or the transfercase on 4 wheel drives. This pulses several times for each revolution of the tailshaft. Most GM vehicle speed sensors pulse 40 times per revolution of the tailshaft. The output signal of the VSS is an AC signal.

Digital Ration Adapter Controller (DRAC) and Vehicle Speed Sensor Buffer (VSSB) are both electronic devices that simply convert the input AC signal (from the VSS) to a calibrated digital DC signal. The DRAC sends 2,000 digital pulses per mile to the ECM (Electronic Control Module), 4,000 digital pulses per mile to the cruise control module, and 128,000 digital pulses per mile to the ABS (Anti-Lock Brake) computer. The DRAC and VSSB units are pre-calibrated from the factory according to the vehicle's stock gear ratio, and tire size. But, it can be re-calibrated by simply moving jumpers around. 1990-1991 vehicles should have the DRAC, and 1992-1995 vehicles should have the VSSB unit. The main difference between the DRAC unit and the VSSB unit (from what I can tell) is that the VSSB unit has an extra "bank" of 7 jumpers in addition to the same bank of 7 jumpers that the DRAC unit has. I would assume this extra bank of jumpers is for the electronically controlled transmission that GM started using in 1992.

If you change your tire size and/or gear ratio, your speedometer, cruise control, and ABS systems will not function correctly because they are receiving an incorrect signal from the DRAC or VSSB. Your options to correct this problem are to fork out $300+ for an add-in calibrator, buy a new DRAC/VSSB from the dealer for $$$, send off your DRAC/VSSB to a gear shop for $$$, or spend $2 and some change on a Radio Shack part, and do it yourself. hmmmmm... that's a tough one.....

ii. Tools & Materials

Calculator

Tape Measure

Soldering Iron

Solder

Small Pliers

Sharp straight pin or paperclip

DIP switch (pick one - or search google for online dip switch retailers)

7 position 14 pin DIP Switch (recommended for '90-'91 DRAC)

*8 position DIP Switch Radio Shack part# 275-1301 (retro-fit for '90-'91 DRAC)

2- 6 position DIP switches (required for '92-'95 VSSB)

*only get the 8 position switch if you don't want to order online, and just want to drop by your neighborhood Radio Shack. The 7 position switch will fit better (for the 90-91 DRAC).

I. Determine your vehicle's gear ratio

If you're positive that your vehicle still retains it's factory gear ratio, use the RPO code list here to match a code with a code in your glove box.

If you are unsure of your gear ratio, pop the diff cover and see if you can find markings on the ring gear that tell you what ratio they are, or count ring gear and pinion teeth and match the numbers with a ratio here.

Note that your final calculations will be more accurate if you do not round your measurements. Divide your pinion gear tooth count into your ring gear tooth count to get a more accurate value for your gear ratio. (4.56 has 9 and 41.... which comes to 4.55555555)

II. Determine your tire's rolling circumference

First, remove a rear tire/wheel from the vehicle, mark a line on the sidewall with a piece of chalk, and mark a line on the ground. Align the mark on the tire to the mark on the ground, then roll the tire straight one complete revolution, then mark a line on the ground where the mark on the tire is. Measure the distance between the 2 marks on the ground to get your tire's rolling circumference.

You can also look on your tire manufacturer's website to find your specific tire's revolutions per mile at a certain speed. Divide that number into 63,360 (number of inches per mile). The result should be the tire's rolling circumference.

Compare both results. They may vary depending on rim width, tread wear, and the fact that the circumference increases at higher speeds. But, the results should be close. Again, do not round yet. Keep as many digits as possible.

III. Locate & Remove DRAC/VSSB unit

It should be located behind/under the dashboard somewhere, usually near the ECU. It is in a white plastic box with 2 wiring harnesses connected to it. Simply, remove the wiring harnesses, and pull the white box out. Open the white box, and remove the DRAC/VSSB unit.

IMPORTANT - you are dealing with a very sensitive piece of electronic circuitry! It is VERY sensitive to static electricity, and other forms of electronic shock. You can destroy the board if it comes in contact with some type of electronic shock, grease, oil, or other liquids. If you do not feel comfortable dealing with this, please bring the board to an experienced electronic engineer, or computer technician to do the soldering on the board. I am not responsible for any damaged equipment.

IV. Determine your new Input Ratio

Use your results from Steps I & II in the equation below to calculate the correct input ratio

Retain as many digits as possible to achieve a greater accuracy


Input Ratio = [63360 x Gear Ratio x pulses per revolution of speed sensor {40}] / [tire rolling circumference in inches x 128000]


63360 = inches per mile
*most GM speed sensors produce 40 pulses per revolution
128000 = pulses per mile

Once you have done the calculations, compare your result to the input ratios in the "Jumper Settings" chart below. Find the closest value to your answer.

Go across the chart and look at the correct jumper settings. a 1 means there should be a jumper across the terminals, and a 0 means there should not be a jumper. Compare that to your DRAC/VSSB's current Jumper setup. The jumpers are not numbered on the board itself, but, the way my chart is written, if the black wiring harness plug is at the top, the jumpers are numbered 1-7 from Left to Right. (see pictures below)

V. Remove Jumpers

Note - If you do not feel comfortable working with sensitive electronic equipment, this is where you need to take your board to an experienced electronic engineer, or computer technician.

Use a soldering iron to heat up the ends of the jumpers that are currently on the board. They are soldered on both sides of the board. Once you heat up one end, pull it out of the board using some pliers. After the jumpers are out, heat up each hole one by one and use a sharp, narrow straight pin or small paperclip to poke through the holes to clean all the left-over solder out. The holes need to be open to fit the DIP switch on. DO NOT remove the #1 jumper if you are installing 2- 6 position DIP switches on the 92-95 VSSB board. Leave both #1 spots alone, as they do not change.

Be very careful not to spread the solder around too much. it can cause the board to short out, or produce incorrect signals. Also, be careful not to damage the board when pulling the jumpers out.

VI. Install DIP switch

1990-1991 DRAC:

If you bought the Radio Shack 8 pin DIP switch, you'll need to bend the leads on switch 8 out of the way, or cut them off. Be sure they do not lay across leads when it's on the board. You will also have to slightly move the blue resistor out of the way, but do not damage it. If you bought a 7 pin DIP switch, it should fit very nicely.

Carefully, push the DIP switch into the holes. If your using the 8 pin switch, you may need to trim a small amount of plastic by switch 8.

1992 -1995 VSSB:

The left bank of jumpers should be an exact mirror of the right bank. For example: if the jumpers of the left bank were numbered as 7654321, and the jumpers in the right bank were numbered as 1234567, each jumper on the left bank should be the opposite of the jumper with corresponding number in the right bank. (see picture below for reference) Jumper space #1 does not change ever. the left bank #1 should stay open, and the right bank #1 should stay closed (with a jumper).

Carefully, Install the two 6 position dip switches on spots 2 through 7 by pushing the leads through the holes on the board. Leave both #1 spots as they are. (see pictures below for reference)

Flip the board over, and carefully solder each switch terminal to the back side of the board. Be careful not to use too much solder as it may short across other leads.

Use the input ratio you found in Step IV to find the closest value in the "Jumper Settings" chart. Set the DIP switches according to the 1's and 0's in the chart next to your input ratio. On the VSSB, remember we left both #1 jumpers as they were, so the first switch on the DIP box will be starting with jumper setting #2. Be sure to set the 6 switches on the left dip switch opposite of the jumpers on the right dip switch in a 'mirror' fashion. (see picture below for reference)

VII. Re-install DRAC/VSSB and Test

Install the DRAC/VSSB board back into it's white plastic case. The DIP switch should have just enough clearance to fit into the case. Make sure the case lid isn't hitting the switches.

Install the case into the vehicle and plug both wiring harnesses back in.

Check the accuracy of the speedometer with a GPS unit, or by pacing another vehicle.


1 = Jumper connected or switch ON
0 = Jumper NOT connected or switch OFF
1-7 = Jumper/switch #

Jumper Settings
Input Ratio 1 2 3 4 5 6 7
0.500000 1 1 1 1 1 1 0
0.505958 1 1 1 1 1 0 1
0.511230 1 1 1 1 1 0 0
0.517090 1 1 1 1 0 1 1
0.522949 1 1 1 1 0 1 0
0.528809 1 1 1 1 0 0 1
0.534668 1 1 1 1 0 0 0
0.540527 1 1 1 0 1 1 1
0.546875 1 1 1 0 1 1 0
0.552734 1 1 1 0 1 0 1
0.559082 1 1 1 0 1 0 0
0.565430 1 1 1 0 0 1 1
0.571777 1 1 1 0 0 1 0
0.578125 1 1 1 0 0 0 1
0.584473 1 1 1 0 0 0 0
0.591309 1 1 0 1 1 1 1
0.598145 1 1 0 1 1 1 0
0.604492 1 1 0 1 1 0 1
0.611328 1 1 0 1 1 0 0
0.618164 1 1 0 1 0 1 1
0.625448 1 1 0 1 0 1 0
0.632324 1 1 0 1 0 0 1
0.639648 1 1 0 1 0 0 0
0.646484 1 1 0 0 1 1 1
0.653809 1 1 0 0 1 1 0
0.661133 1 1 0 0 1 0 1
0.668457 1 1 0 0 1 0 0
0.676270 1 1 0 0 0 1 1
0.683594 1 1 0 0 0 1 0
0.691406 1 1 0 0 0 0 1
0.699219 1 1 0 0 0 0 0
0.707031 1 0 1 1 1 1 1
0.714844 1 0 1 1 1 1 0
0.723145 1 0 1 1 1 0 1
0.731446 1 0 1 1 1 0 0
0.739258 1 0 1 1 0 1 1
0.747559 1 0 1 1 0 1 0
0.756348 1 0 1 1 0 0 1
0.764548 1 0 1 1 0 0 0
0.773438 1 0 1 0 1 1 1
0.781738 1 0 1 0 1 1 0
0.790527 1 0 1 0 1 0 1
0.799805 1 0 1 0 1 0 0
0.808594 1 0 1 0 0 1 1
0.817671 1 0 1 0 0 1 0
0.827148 1 0 1 0 0 0 1
0.836426 1 0 1 0 0 0 0
0.845703 1 0 0 1 1 1 1
0.854980 1 0 0 1 1 1 0
0.864746 1 0 0 1 1 0 1
0.874512 1 0 0 1 1 0 0
0.877441 1 1 1 1 1 1 1
0.884277 1 0 0 1 0 1 1
0.894043 1 0 0 1 0 1 0
0.904297 1 0 0 1 0 0 1
0.914551 1 0 0 1 0 0 0
0.924805 1 0 0 0 1 1 1
0.935059 1 0 0 0 1 1 0
0.945801 1 0 0 0 1 0 1
0.956055 1 0 0 0 1 0 0
0.966797 1 0 0 0 0 1 1
0.978027 1 0 0 0 0 1 0
0.988770 1 0 0 0 0 0 1
1 0 0 0 0 0 0

Excellent - just requires some caution in posting info verbatim from another website, tho, wouldn't you think?

Is anyone running 285's on a 98 Suburban K2500. I would like to go up one more size. 245's are the standard and I have 265 now. The truck is stock for the most part.

I have been running 285 for almost a year now and have never yet had them rub, even when off road. It comes close to rubbing the sway bar on the inside tire but that is it. It looks great though to go up I went from 245's and it rides better as well now with the 285's :cool2: :cool2:

Well the Bilstein have been ordered. Once I get them in and on the truck I'll be going for the new tires.

I'm still iffy on the 285's.


Some one said to me that I should watch size because it could put extra wear on the trans? Also told that the larger tires will drop gas MPG?

Any truth to this?

Yes, larger tires create more wear on suspension and drivetrain components. However, this is more prevalent in going from stock sized tires to 35" diameter and larger. The amount of additional wear in going from 265's to 285's would be pretty insignificant.

And as far as mileage goes, I don't think you'll notice any drop in MPG in going from 265's to 285's. Yes, the larger tire will weigh a little more and turn a little harder than the 265's, but RPM's are lowered by the larger tire and it seems to me that these two factors cancel each other out in this particular tire size change.

if you see a lot of highway drivin, you might see an increase in mileage if your speedometer and odometer is corrected for the new tires. say you run 2100 rpms at 70 with 245's, with 285's you might only run 1800 rpms at 70.

I never kept track of mileage on my 95 except when i went on holidays once pulling my 8K 32' travel trailer through the mountains from Alberta to BC, IIRC i was getting from 14 MPG to 17 Canadian MPG with the 35" rubber, if anything i think if you have the power and torque you mileage should increase. Never checked it without the trailer

Canadian gallon = 4.546 liters Canadian Mile = 1
American gallon = 3.7854 liters American Mile = 1 :lol:

My mileage didn't change at all other than bringing the rpm's down from 2800 (at 75) to 2300 (at 75). If I had better gearing 3.72 rather than 4.11 it might increase my mileage some but I still get 15-16. But going from 245 to 285 means I need to compensate for the incorrect speedo which is about 10% off now.

Also when I went from the 245 to 285 I bought 01 chrome steel rims to install them on. Not any wider just better looking.

a couple companies sell devices to correct speedo and odometer. summit sells a couple of them. i just don't know if the price is worth it. i just wish they made a superchip for a 6.5 and then we could do it with that.

I've noticed that my speedometer seems more accurate based on the roadside radar displays with the upsized 235/85 tires versus the stock 245/75 size, so I haven't considered recalibrating the speedo. However, my ABS has become much more sensitive... if I twitch the steering wheel when coming to a stop, it sets off the ABS. I assume this is because the larger diameter tire creates a bigger difference in the readings between the left and right wheel speed sensors than the system was designed to see with the stock tires. Any options for recalibrating the ABS without affecting the speedometer?

Not sure about your ABS, but I noticed that my truck with 245's, the speedometer was fast, and now with the 265's, it is dead on accurate clocked by the milemarkers on the interstate (within 4/10's in 100 miles).