Is Changing Tire Size A Big Deal?

Silver Wraith · November 21, 2009

Hi All;

I'm shopping for winter tires; I'm going to put them on my stock rims (08 Silverado crew cab 2wd) and then buy either takeoff rims or aftermarket rims in the spring.

The truck came with 245/70/17 on aluminum rims, and I've always disliked the 'too small' look of the tire. I've noted other Silverados on the dealership lot almost always have the 265 17s so I don't know why I got the sucky smaller tire.

So, I plan on going with an 18 or 20 inch wheel in the summer, but I want to do this right. If I put larger rubber on now, do I have to get the computer flashed? And then, what size can I use on my stock 17 inch rim that I can swap seasonally with something bigger and not have to re-flash the computer every time? Since I'm shopping for the winter tires now I want to try to plan ahead and do this right.

I'm thinking either Michelin X Ice or Goodyear Nordic winter tires.

Nytemare · November 22, 2009

you can pop 265/70/17 on a 2wd truck...I have 265/75/16 on mine.

You don't have to do a re-flash on the computer...but you have to keep in mind that your speedo will be off by about 7%...maybe a little less.

You will be traveling 7% faster than the speedo reads...IOW, 60mph on the speedo means you are actually going 64.2mph

This will also translate into 7% less milage on the odometer.

Heres a site so you can see how different sizes affect your speed.

http://www.miata.net/garage/tirecalc.html

You can however buy a recalibration tool for yourself...they're not really expensive.

Like this one

They're about 200 bones.

Just play with the tire calculator and try and find a wheel/tire combo that will match up winter and summer so you only have to re-flash once.

Silver Wraith · November 22, 2009

Interesting.

Thanks for the tire calculation tip.

I just found out that if my truck DID come with 265/70/17, I could swap up with 275/55/20s and they are within 1% of each other. Pardon me for those who already knew this...I'm just catching on.

So, if I purchased 265/70/17 and had the computer flashed, and decided to buy a set of 20s for the summer, I'd be right there.

Which leads me to the inevitable question...why the heck would they sell me a truck with this oddball size.

Stevens03 · November 22, 2009

Which leads me to the inevitable question...why the heck would they sell me a truck with this oddball size.

It's cheaper, thats why.

Nytemare · November 22, 2009

Different packages have different options.

Tire size, engine size, gear ratios..etc. You probably have a truck that came with higher gearing ratio (smaller numbered gears) and therefore got the smaller tires...thats all.

Silver Wraith · November 22, 2009

I did get the locking differential and towing package, don't know if that makes any difference. I'm presuming if I get the dealer to flash the computer to correct the tire size I shouldn't have any issues.

Nytemare · November 23, 2009

Nope....I don't even have mine flashed.

I know I am 7% under...I can do math. When I get HPtuners I'll do it than while I'm screwing around with the ECM.

If you get it programmed for 275/55/20 than the 265/70/17 would be fine. Like you said...1%...and that's perfectly acceptable.

lawheelsdirect · November 23, 2009

You can use our Tire Size Calculator to compare tire sizes. Hope it helps.

Silver Wraith · November 23, 2009

Well, it's been an interesting day. I called the dealer to ask, if I buy a larger size tire, how much will it cost me to 'reprogram' my truck? I was told 92 bucks (ouch), as long as I didn't go over 2 sizes it could be done

Instead of winter tires, I bought a set of Michelin LTX AT2 LT265/70R17 (An 'E' rated tire, sweet). For the first time, the truck looks as it should.

Then I get to the dealer. Service guy says, 'ah, I don't think we can do that'. I say talk to the Service Manager. 20 minutes later they come out and tell me it can't be done. Printout they give me says, 'Attempted to recalibrate tire size, Tech 2 does not have this function.' I talk to the service manager and ask, WTF? I'm told that they never know for sure until they see what the 'vehicle computer allows for'.

Based on the fact that he also told me that my speedo/odo wouldn't be affected because of 'where the sensors are' in the wheel, I'm guessing that I need to find a dealership that knows their arse from a hole in the ground?

Silver Wraith · November 24, 2009

Just found this; looks like they need to make a phone call!

A VCI number is what dealers use when they need a calibration that isn’t readily available as a download from Techline’s TIS 2 Web. Dealers call GM Techline’s helpdesk and give them the VIN along with their dealer code. Their help desk then puts together a special calibration to either fix an unusual service problem or in this case change the math done by the PCM as it buffers the speed sensor signal. In my experience this phone call typically results in waiting on hold a while and / or finally leaving your phone number for a call back. Dealers are charged $50 for VCI numbers that are required for tire size / axle ratio changes. Only tire size / axle ratio combinations that are available as either factory or factory upgrade are available so those huge monster truck tires just aren’t going to work if you want accurate speedo / odo / TCC lock up, radio volume comp, and ABS operation. I know independent shops do sometimes purchase a year’s subscription to Techline’s TIS 2 Web for calibrations (starting at $1000) but I don’t believe they get a free tire size change VCI number with the purchase of a subscription. One tidbit of info involving this $50 VCI programming number is that it stays with that vehicle’s VIN from that day on so in case there is a later update, you still have the corrected tire / axle ratio calibration. Also, they give you a number to put in the calibration menu to return the vehicle to the original tire size / axle ratio calibration should the owner decide to return to stock tires and rims. If the wheel / tire upgrade is done with Mr. Goodwrench factory accessory tires / wheels, the VCI number fee is waived.

Nytemare · November 24, 2009

Sounds like someone was on break when you went in.

Just buy yourself that super chips one, use it to re-cal and sell it again man. Or keep it...it reads trouble codes also.

Speed sensors in the wheels....will that's a first...are you driving a bicycle? That's the only time I have seen speed sensors in the wheels.

Those AT-2 tires are nice hey...I was looking at them too...but I got the straight LTX as I don't go off road with my 2WD...and I see about 3 days of snow in Victoria a year....maybe.

The LTX are super quiet on the highway, and absorb bumps so much better then the no-name cheapies that came on the truck.

Silver Wraith · November 25, 2009

Those AT-2 tires are nice hey...I was looking at them too...but I got the straight LTX as I don't go off road with my 2WD...and I see about 3 days of snow in Victoria a year....maybe.

The LTX are super quiet on the highway, and absorb bumps so much better then the no-name cheapies that came on the truck.

Yeah, they're sweet tires...for the first time, the truck looks proportioned and adequately 'beefy' :-0 Good to know I'll be a little safer when the snow flies too. I don't even see the need to get aftermarket wheels any more...the problem was never really the wheels in the first place, just the wimpy tires.

deerchooper · November 26, 2009

not to high jack your thread but i would like to do the same thing but with larger rims. my 07 nnbs came with r16 and ballon tires, its 2wd as well. i would like to jump to a larger rim and found with the above calcuators if i got a 245/55 r20 i would be .5% off or if i went with 235/45 r22 i would be .5% off. one was slow and the other was fast but it would be real close, just under 1mph eather way.

would i need anything from a superchip or dealer if i went this way?

adding a larger rim would i loose any mpg, wouldnt the rim be lighter than all that rubber.

i could also go 245/65 r18 and be .2% off

i would like a little wider width maybe an 1" or 2 but dont know what back spacing to run

crenca · November 26, 2009

I don't know about the back spacing, but at only .5% calculated diameter difference I would not bother to get reflashed. I think 3 % difference is the rule of thumb as to when you need to start thinking about a recalibration for ABS and the like.

Shoot, .5% is probably within normal tire pressure/sidewall construction difference of even same sized tires...

Nytemare · November 27, 2009

not to high jack your thread but i would like to do the same thing but with larger rims. my 07 nnbs came with r16 and ballon tires, its 2wd as well. i would like to jump to a larger rim and found with the above calcuators if i got a 245/55 r20 i would be .5% off or if i went with 235/45 r22 i would be .5% off. one was slow and the other was fast but it would be real close, just under 1mph eather way.

would i need anything from a superchip or dealer if i went this way?

adding a larger rim would i loose any mpg, wouldnt the rim be lighter than all that rubber.

i could also go 245/65 r18 and be .2% off

i would like a little wider width maybe an 1" or 2 but dont know what back spacing to run

LOL...20's and 22's are heavy man...like in the 70 pound and up range with rubber... your 16 is about 40 lbs... so yeah you will be adding about 100+ lbs to your ride...and also requiring more power to make them turn...and they will be harder on your brakes to stop too...so you will go through brake pads a touch faster.

I have 265/75/16 on my truck...original tire was a 235/75/16...I have no issues with rubbing and they're 1.2" wider.

And yes...like crenca said...0.5% is nothing...tires will fluxuate by 0.5% through the seasons.