Speedo out after 305/70/R16 HELP

Please help me guys!!!!!!!!!
On my 2000 Chevy Silverado Z71 I changed the stock tires from the 265 to 305's. Now my speedo is off and it does not shift right. How can I fix this?? I was told I can recalibrate the computer, what kind of instrument will I need, does anyone know?????

Thanks in advance,
Tom Martin:banghead:

the dealer can recalibrate your computer for you.....you need a scanning tool......but the best thing you can do is get yourself a custom tune.......so you'll get the performance upgrade along with the recalibrated wheels).....nelson performance charges about $400.00, and wester's is about the same......I have a jesse tune, where I got my whoop ass tune for 150.00 plus 7.50 shipping....or you can send your computer, and he'll do it for $75.00......good luck.....

The dealership can only reprogram to a size offered as a stock option, so the only way to resolve is with a custom tune...

Thank you Gentlemen,,
I forgot to mention my gas mileage went down the drain by about 3 MPG...
I didn't think a couple of tire sizes whould make that much differance...:shakehead
But it sure made the truck LOOK better..

Well I am sure that jumping up to 305's meant you also had to adjust your torsion bars, unless you had a lift done. If you messed with the bars an alignment is absolutely necessary. Also realize that by going to that large of a tire from a stock tire the gear in your rear end is still the same. that large of tires means much less off the line and low speed torque and that will affect the shifting of the truck..Invest in a hypertech or similar programmer. You can recalibarte your speedo, and change your shift points with the programmer as well as increase your top speed and gain up to 20 hp and some serious foot lbs of torque. programmer is about 350-400 bucks.

I would agree with RyAmber. A handheld programmer is the way to go. Not only can they adjust the speedometer to recognize a different size, they can also do extra performance stuff.

I would agree with RyAmber. A handheld programmer is the way to go. Not only can they adjust the speedometer to recognize a different size, they can also do extra performance stuff.

yeah they can, but nowhere the performance gains of a custom tune. The only thing god about a handheld is the fact that you can change it when yo want. if you want power, get a Nelson tune. He can adjust anythng you need adjusted also.