leedogg

So how do these 2 correlate? Will the stress on your transmission always increase given a larger rim diameter (or overall diameter of the rim + tire)? or is weight the primary factor?

i.e. if my 19's are lighter than, but overall a little wider than my oem 17's, does this place a greater stress load on my transmission?

mishar

With larger and heavier wheels transmission is stressed more just like you have some junk in your trunk, so you can forget about it. But your suspension is more stressed and for the worst it transfers some of that stress to the body. Add to it additional stress that drop cause and you will hear it for sure in some time.

desper

Even if you have 19's if they are lighter the stress will be much less on the tranny.

Suspension will have some more stress but no big deal...

Even if your rims are heavier you just need to take it easy on the car and not beat the hell out of it and over stress your ride

csmeance

my think says that the heavier the wheel, the more torque needed to spin them. THe more torque, the more damage on the componets.

rodneyc77

iTrader: (1)

My theory:
car was designed to carry 5 adults @ average weight of 160 lbs = 800 lbs PLUS about about another 100lbs +/- in the trunk WHICH gives a total of 900 +/-

If the average owner only drives with three (3) people on average (including the driver) and the trunk weight (100lbs) = that's only 580lbs AND ADDS bigger wheels that weight on average 15lbs more that's only 60lbs of additional weight... 580+60 = 640 lbs...

You'll still be 260 lbs below the design parameters...

PLUS people have to KNOW that when a car company designs a vehicle... they have to have a factor of safety on the design parameters of at least 1.3 to 1.5 ===> so that 900 lbs just jumped to either 1,170 lbs to 1,350 lbs....

So... in conclusion... bigger wheels & additional weight SHOULD not be a factor on the transmission...

PS: Number above are assumptions, since I'm not a automotive engineer...

leedogg

I cant help but think of comparing this to a racing bike vs a mountain bike. Even though the wheels may be lighter than the mountain bike, the fact that they are much bigger creates more torque stress...granted thats quite a difference in wheel size (racing bike vs mb)

/edit I should say more low gear torque stress and less high gear...

6spMike

Tire diameter (within reason, don't put 45 inch tall gumbo mudders on it) doesn't matter much for either transmission load or suspension load.
The engine/trans will have to deliver more torque to a larger wheel in order to have the same acceleration or maintain the same speed, all else being equal. So you are asking the engine/trans to put out more torque with larger tires, but it's a pretty small effect if you don't change the diameters much. The TLs have a lot of margin in this area, since one doesn't usually drive around with it floored all the time.

The weight of the wheel doesn't matter too much, since the trans pulls the whole weight of the car, it doesn't just spin up a free wheel. So if it's 4000 lbs fully loaded, and the wheels add 15 lbs, that's a 0.3% increase, which is really small.
The suspension sees the weight of the vehicle against the road surface. Sprung weight (everything on the wheel side of the suspension) will affect how fast the suspension can respond to road irregularities, but not the load the suspension sees while doing it (not even the .03%).

Tire offset (which you didn't ask about) does affect the load on the wheel bearings. A larger offset (tires further away from the hub) will increase the load on the outer wheel bearing.
I hope this helps.

leedogg

Thanks sandymike, sounds reasonable. So the dealer shouldnt be able to pull any bullshit about the transmission breaking because of larger rims...

6spMike

It'd be a stretch, but they might.
Note it's not rim size that makes the difference, it is the outside diameter of the tire.
diameter = Rim size + 2*(width*profile).
For 235-45/17:
(17*25.4) + (2*235*45%) = 643 mm.
For 235-40/18:
(18*25.4) + (2*235*40%) = 645 mm.
These are the sizes they came stock with, according to tirerack.com for a manual. If the calc for your 19s comes out less that 645, then the dealer can't claim more stress.

If they take a look at your car and it shows that you drive the piss out of it (tires, brakes, engine history, etc), they'll probably claim you abused it, though, and you'll be SOL.