I recently went up in size on my tires after installing a Leveling kit. Today for the first time since I had to take a long trip and was checking my speed against what the GPS was stating.. there is about a 8mph difference.

So if the truck says 65, the GPS was saying 73/74, and the faster I went the bigger the difference got.. so if the truck said 70, I was going closer to 79/80

I know that there needs to be some adjustments made so it read correctly again, just wondering if there is also some adjustments that can be made to get the RPM's down at crusing speeds also..

In the past when I would do around 70 or 75, the RPM's would be around 1500 to 1700, now im staying steady at 2000.

What am I looking at to get back to somewhat normal again?

 

Waiting on the dealership to call me back with a price to have them do it, but been looking around at programmers, if I decide to go with a programmer instead of a one time change from the dealer.. any brands better than others..

I found a hypertech brand "Max Energy Power Programmer" which will do the speedo and shift points and has more flexibility.. and alos just a speedo calibrator from them also..

 

Either ...Or ...BTW ... This will also resolve your transmission's shift points.

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Goth 150
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Did you check original tires with GPS,something doesn't sound right as you should be turning less rpm with taller tires with GPS. Quick and easy measure heights of tires multiply by pi and find % of height change and add to your speedo that % amount.

 

Go here:

Tire Size Calculator - Tire & Wheel Plus Sizing

Your GPS is giving you the proper speed. At this point, ignore how many rpms your turning as the taller tires have slowed down the number of revolutions per mile.

 

how about a pic with that level and new tires

 

Is that all the possible options? the tires I put on are 295/70/18 which looks like suppose to be 589 Revs...

So is it 2 things I need to have done? resting the revs and recalibrating the speedo? or is that one in the same?

 

Ill see when I can get a good pic, the only thing that sucks is that I forgot to take before pics.. which is something I do with all projects.. im restoring a 74 Camaro and I am always taking pics before, during, in between and after.. and for whatever reason I forgot on the truck..

but I can post some as soon as I can.
After the kit now I want just a tad bit more lift.. and looking to make more mods to the truck..
Like adding some super bright lights to the back under the bumper to help with reversing, adding the backup sensors and swapping out the headlight housings with the tinted ones.

 

before the change, yea I would notice that GPS and speedo would match. Now the speedo is about 8mph slower than the GPS.. so until I fix, just need to remember the difference.

 

Is there any chance that going with the bigger tires, I would need to change the gears also? or just the recalibrating and revs would help and not damage the truck in the long run.

 

IMHO if you're not towing often, and you can live with the slight decrease in performance with the more appealing aesthetics, you should be ok. My rpms are down not up as previously stated with the same size tires. I got an SCT from 5 Star and it corrected all the issues, I'd recommend Mike to anyone. My speedo is off some but I just make sure I'm not going faster than the others on the highway. Its closer at lower speeds on my truck. Theres a sticky for the brighter reverse lights, I did Rigid Industries SR-M diffused under my back bumper and tied them into the reverse wire for the trailer plug. Works great

 

I went up to 18 inch from the 17 stock wheels. I lost about 4or 5 mpg. The dealer charged me $100 to recal my computer for the larger tires and wheels.

 

Yes ... If you have the the dealership flash the PCM those are the valid IDS parameters which correspond to the OEM stock|optional wheel sizes.

The speedometer's vehicle speed sensor uses the same table(s), there is only 1(one) flash necessary to adjust the wheels RPM (Revolutions Per Mile).

BTW ... There is speedometer gear.

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Goth 150
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thanks for the info guys, im leaning toward the SCT with some custom tunes, since im looking into modding the truck some more..

 

Ok here is a pic after the lift before the tires(they hadn't arrived yet)


Here is a pic of the tires installed on the stock rims


Here is the truck lifted and new tires, but from different angle


Ill have to see if remember to park the truck in the same place and take the after pic and wash it also