tire aspect ration 255/55/18 to 255/45/18

[bgnmi]

What do you think about going from 55 factory aspect to 45? will it improve handling or detract? Is it adviable either way?

It would lower the center of gravity and improve. right?

[dkl]

Going to a 45 series (without adding width to the tire) will decrease your rolling diameter, which will throw off your speedometer readings; not to mention that your engine will rev higher going the same speed - consuming more fuel. All of which will lead to more wear and tear on your drive train.

[DoubleA]

I'm in the same boat, as I need to remove the winter shoes on my X5 4.4i, the closest size would be 275/50/18 but I dont think the stock BMW 18's wheel could take this size, this is not saying those will be tough to find if any.

How do I know that ? check this out: Tire size calculator

[sprocket1200]

craigslist for tires.
to improve handling just add 2-3 psi to the tires

[JCAPX5]

yea be careful changing the overall diameter of the tires. I've heard of this throwing off DSC errors as well. Do some reading and you'll find the maximum you should aloow this diameter to change. Do the math from the various tire sizes and you'll be good if you are in that range.

[bgnmi]

got it thx. i guss it makes sense to keep the same unless i increase rims

[anerbe]

you may also run into issues with your GPS if it is factory by changing overall rolling diameter.

[motordavid]

It's about a 7%+ reduction in circumference, rolling diameter, & rpms increase at a given cruise speed, and of course the speedo error.

You might noodle around on some tire joint sites and look for a "bigger tire", eg "285/45R" that will come closer to the orig rolling
specs, but with that "wider look/footprint" you seem to be after.

As for the lower aspect ratio "improving the handling", there are pages of opins on Google, some of which go against the
Conventional Wisdom of wider, lower aspect tires equals better handling, fwiw.
GL,mD

Good tire size change checker sites:
Tire size calculator

Tire Size Calculator - tire & wheel plus sizing

Good Wheel Offset and new Tire Size Comparo Site:
Wheel / tire size calculator / comparer - BIGCUSTOMWHEELS

[bgnmi]

thx. I will stick to the factory size