Bigger tires, shifts into OD later

[eej711]

I moved up from 31" tires to 33" tires and my truck shifted at 41mph into overdrive but then when i go the bigger tires it shifts at 46mph now. I changed the tire size to 2654mm if i'm remembering correctly to put in what the new tire size is. Is it normal for it to shift later?

[Jackpine]

Originally Posted by eej711

I moved up from 31" tires to 33" tires and my truck shifted at 41mph into overdrive but then when i go the bigger tires it shifts at 46mph now. I changed the tire size to 2654mm if i'm remembering correctly to put in what the new tire size is. Is it normal for it to shift later?

Yes. By installing larger tires, you've essentially reduced the rear axle ratio (Gear Ratio). The engine load is higher, so the shift up has to occur at a higher speed.

- Jack

[eej711]

Originally Posted by JackandJanet

Yes. By installing larger tires, you've essentially reduced the rear axle ratio (Gear Ratio). The engine load is higher, so the shift up has to occur at a higher speed.

- Jack

Ok thanks, should i change my gear ratio on the tuner or leave it since i have 3.55 gears on the truck? sorry if thats a stupid question.

[Jackpine]

Originally Posted by eej711

Ok thanks, should i change my gear ratio on the tuner or leave it since i have 3.55 gears on the truck? sorry if thats a stupid question.

No, it's not stupid at all. You should make sure the programmer has your actual 3.55 GR set in. The only thing you should change is the Tire Size to match what you have mounted now. You'd like to get the speedometer and odometer reading correctly.

Larger tires MAY hurt your gas mileage, since your engine actually has to work harder just to maintain a set speed. And, your acceleration will suffer too, since the larger tires reduce the effective gearing. But, you gain ground clearance and you probably like the look better, so that's what really matters.

- Jack

[eej711]

Originally Posted by JackandJanet

No, it's not stupid at all. You should make sure the programmer has your actual 3.55 GR set in. The only thing you should change is the Tire Size to match what you have mounted now. You'd like to get the speedometer and odometer reading correctly.

Larger tires MAY hurt your gas mileage, since your engine actually has to work harder just to maintain a set speed. And, your acceleration will suffer too, since the larger tires reduce the effective gearing. But, you gain ground clearance and you probably like the look better, so that's what really matters.

- Jack

Thanks, just one more question and i should be good. I did change the tire size on the programmer so does that fix the odometer and speedometer on the truck itself so they aren't off? And ya i expected the mpgs to go down a little but i love the look way much better, I feel like a kid on christmas everytime i look at them

[ticopowell]

as long as you have the right tire size and gear ratio your speedometer on the gryphon will read accurate, the mechanical dash speedo will almost always be slightly high but the odometer will be correct.

[Jackpine]

^^^ What he said! ^^^. You're good to go.

- Jack

[eej711]

Thanks for the help