• If you currently own, previously owned or want to own an Avalanche, we welcome you to become a member today. Membership is FREE, register now!

Mileage Difference With 20" Tires

Blader

Blader

Full Member
Joined
Jan 2, 2006
Messages
99
Location
ST.George Ontario Canada
Hi all was wondering about how much difference the mileage would vary on my Av if I went to 20" tires. She already hurts for mileage the best I ever got was 20.5 mpg that must have been the wind pushing me.On average I get about 18.5 MAx so Im wondering how much worse would the AV be on fuel? I love the look but if the mileage drops like crazy then it wouldn't be worth it for me. Thanks for all input.
 
I don't notice any difference when swapping from the stock 17's to the 20's. I stay consistently at 14.5-15 mpg in my back-and-forth to work drive. Highway-only averages 16-17.
 
It's not really a matter of the wheel size (although weight is a MINOR component), it matters when you alter the overall height (diameter) of the tire.  If your 20" tire is effectively the same height as the 17" setup, you won't notice any real difference.
 
Ok kewl so you dont have to reprogram onboard comp to compensate? Was wondering too if tire is taller then it would take more to turn it at first, but when running it would turn less? I was wondering too if the new rims are lighter than factory rims/tires considering all this before sinking a pile of dough into this thanks again
 
The reprogram is for the speedo, IF the height is different.
 
DougD said:
It's not really a matter of the wheel size (although weight is a MINOR component), it matters when you alter the overall height (diameter) of the tire.? If your 20" tire is effectively the same height as the 17" setup, you won't notice any real difference.
Click to expand...

And Doug nails another one out of the park...If you change to overall tire height then you will have to reprogram your speeo for the difference
 
Blader said:
I was wondering too if the new rims are lighter than factory rims/tires considering all this before sinking a pile of dough into this thanks again
Click to expand...

20's are way heavier than stock.
 
The calibration is not for the speedo..... it is for the VSS sensor in the tranny which counts revs in the output shaft of the tranny... the VSS output is then used for many, many functions.... one of which is speedo.... I would argue the ABS and traction control system are equally dependent on the calibrated VSS output.....

But hey, what do I know......... :D
 
sssMOkinAV said:
and of course you dont HAVE to reprogram anything... only if you really want to know how fast youre going :p
Click to expand...

......only if you want to start ignoring SES lights going off for the ABS and tracking system...... :wave:
 
FlaBouy said:
The calibration is not for the speedo..... it is for the VSS sensor in the tranny which counts revs in the output shaft of the tranny... the VSS output is then used for many, many functions.... one of which is speedo.... I would argue the ABS and traction control system are equally dependent on the calibrated VSS output.....

But hey, what do I know......... :D
Click to expand...

I was simlifying, Rick :)
 
FlaBouy said:
simlifying? Can you simplify that for us simpleton's?...... :laugh:
Click to expand...

Uurrrrrrrrr.....[drool].....ummmm......[spit]
 
FlaBouy said:
......only if you want to start ignoring SES lights going off for the ABS and tracking system...... :wave:
Click to expand...

really? I went from stock size tires (17s) to 305/50/20's and had a JB tune which took into account the new tire size but after my tranny probs I put the stock PCM back in and havent had a light come on. Of course I assume my speedo is off, right? It is a Denali speedo.. so hmmmmm... i dunno....
 
sssMOkinAV said:
really? I went from stock size tires (17s) to 305/50/20's and had a JB tune which took into account the new tire size but after my tranny probs I put the stock PCM back in and havent had a light come on. Of course I assume my speedo is off, right? It is a Denali speedo.. so hmmmmm... i dunno....
Click to expand...

It is 50/50 on whether you set lights for all systems.... depends on the factory calibration and where it was set in relation to the ABS system threshold...

the 305/50/20 is only 1" taller and about an inch and a half wider.... so that may fall within the threshold the ABS and Traction system was calibrated too...wait..you have a 04...don't think you have traction control do ya...
 
one more dumb blonde question... and please answer in simple terms (rick :p )... does the PCM set the speedo or is the speedo calibrated some other way? (mine is nto a stock AV speedo and I cant remember if when I got it he asked me what size tires I had...I know I gave him the mileage... but cant remember if there were any other things he asked me for)
 
sssMOkinAV said:
one more dumb blonde question... and please answer in simple terms (rick :p )... does the PCM set the speedo or is the speedo calibrated some other way? (mine is nto a stock AV speedo and I cant remember if when I got it he asked me what size tires I had...I know I gave him the mileage... but cant remember if there were any other things he asked me for)
Click to expand...

My simpleton answer.... the speedo (and most dash gauges) get their input over the class 2 databus... so no it is not a standard voltage signal as many think...

The VSS sensor reads revolution of the output shaft of the tranny... this is used in a formula that also uses what gear you are currently in and rear gear ratio....this calculation is then sent to the PCM which distributes it to the other computer units....via the class 2 databus...

The tire manufacturers usually provide the VSS value with the specifications so it is a simple matter to plug in that value, gear ratio of the rear housing, and overall tire diameter.. Takes about thirty seconds with HP Tuners....
 
so just to clarify :p since I put my stock PCM back in... the one that thinks I still have 17in wheels and 265/70's... then it is most likely that my speedo is off a little bit, right?
 
about 1.5 mph........ :wave: Hold a sec and I will get you specifics.....

While you wait....Here ya go.....
 

Attachments

  • VSS.GIF
    VSS.GIF
    25.2 KB · Views: 83
Best I could do on short notice..... :D

 

Attachments

  • TireSize.GIF
    TireSize.GIF
    20.8 KB · Views: 84
wow, for such a dramatic difference in looks they really are close in height size ... weird how they LOOK so much bigger...THANKS Rick :wave:
 
sssMOkinAV said:
wow, for such a dramatic difference in looks they really are close in height size ... weird how they LOOK so much bigger...THANKS Rick :wave:
Click to expand...

Optical illusion... tire width coupled with the larger rim size makes it look bigger.... Wish I could put that trick to use in other areas of my life..... >:D
 
You must log in or register to reply here.
Back
Top