help with tire upgrade

[joemamaugly]

i have just put thornbirds on my truck they are 31's and now when i accelerate it feels like i'm losing power....like i have a miss. please give me an idea of what i need to do to fix this. thank you for your anticipated help.

 

[Redrig]

if its a larger tire than before it will lose some power. but if the engine is actually missing than its something else.

 

[james t]

a 31 thornbird is about twice as heavy as a stock size 30" passenger tire. unsprung weight is what killed your acceleration.

 

[X~FACTOR]

I never understood the science behind heavy wheel/tire = lost of power. Like how much would a difference be if you ran a 10 lbs heavier wheel/tire? 20 lbs?

Also, on a slightly different subject:
I know tires weigh more than aluminum wheels. For example a wheel set up of 15x7 with 255/70 would weigh more than 18x7 with 255/55. Is this about right?

 

[bndrulez]

Should weigh less because there is less.

 

[Alec]

Rotating mass usually increases with plus sizing.

Weight affects performance greatly because of the rotating mass concept. Essentially multiply the extra weight times 4 and it's like you're towing that extra weight behind you all the time. You know how it feels when you have 4 friends in your truck vs just you?

Also larger tires affect your overall final gear ratio, essentially raising your gearing and lowering your RPMs at any given speed.

Don't forget that braking also suffers with more mass, as does handling and ride due to more unsprung weight (weight is under shocks, not above).

 

[Byrd91]

Another thing to consider with larger tires is the weight being out further from the wheel. This increases the moment of inertia of the wheel, causing it to be harder to accelerate. Combined with the fact that it is also more weight it will slow your acceleration. To understand this concept more find a piece of threaded rod (the bigger the better) and put a bunch of nuts in the middle and twist it back and forth. Next move the nuts to the two ends and do the same thing. You'll notice it is much harder to change directions (accelerate). Pretty cool stuff.