Bigger Tires - Acceleration Impact?

[Silver dude]

I have a Xterra with the same 3.3 engine manual transmission and 4.6 gears. I went from the stock 29's to 32x11.50x15's. There was a noticeable difference but by no means overwhelming. The truck used to move smartly around and power up long hills without having to downshift. Now it just requires a little more go pedal. Braking, and handling weight of the tires was much more notable. I have zero regrets on tire size choice. Really made the truck look as it should. Offroad performance improved dramatically. On the highway the engine sinks into a deeper overdrive which is nice as with the manual the engine used to be rather buzzy at 65. I noted a 1-2 mpg loss. It backs up rather quick in reverse and low range isn't quite as low as it could be but I'll never go back to a smaller size.

 

[IggyB]

You will lose some power and braking. It's tolerable

I have a 2000 Frontier with same engine and gear ratio. Currently running 235/85-16, but I had 30/9.50-15, 31/10.50-15 and 32/11.50-15 on it

 

[Incusus]

ya ya ya i know my truck is EXCESSIVLY over powered lol...

heh hee he, na its fine... I just thought it was funny

who really needs 350hp at the wheels?

Dare I say EVERYBODY??? too bad the fact is my lil' 3.5 will never make that

 

[michaelgroves]

Larger diameter tyres don't have any significant effect on power. They do require more torque to accelerate any given load. That's what transmissions are for.

However, most gearboxes and drivetrains are optimised for the standard engine and standard tyres. So you may find that with bigger diameter tyres, first gear is a bit too high, and you'll be changing into each subsequent gear at a higher road-speed than you were previously. Top gear will be very fast - perhaps either too fast to be useful, or your engine simply won't't have the power to drive the truck at that higher speed.

Two solutions, assuming you have increased wheel diameter by 10%, are: regear the diffs (or gearbox) by 10% to compensate for the increased tyre diameter. This will make everything back to the way it was. Or, modify the engine to increase torque by ~10% across the entire rev range. This will enable the engine to accelerate the vehicle at least as fast as before, in any gear. In fact, in most gears, it will improve your acceleration. In top gear, your top speed will also be higher (but not by 10%, of course, as wind resistance is the issue, not gearing).

I'd have thought the 3.3 engine would have some potential for this route, rather than spending the money on regearing. Just a thought!

Regarding braking, whatever you do, you will need to apply more braking pressure - probably just push the pedal harder! You won't have any additional brake overheating problems, though (other thing being equal), as the brake disks/drums will be turning more slowly than before.