245/50/18 vs 245/45/18

[Ndx]

Hello,

My car calls for winters in 245 50 18 …. But I do have set of tires pretty much new … from another car that are 245 45 18 ?

Beside the speed being off … do I risk any damage to awd (x-drive) system or any other issues ?

Thank you

 

[FowVay]

There will be about 3" difference in rolling circumference (0.97" diameter difference) which is quite a bit. As for it affecting the vehicle's electronic monitoring systems - I don't believe that if all four wheels are the same that the vehicle would know the difference.

 

[bugeye]

X-drive, BMW ?
If all four tires are the same diameter, then no concern with different axel rotational speeds.
Concern is when one tire or one pair of tires is a different diameter causing wear to the drive units

 

[krzyss]

Load index. Smaller tires very likely have smaller load index.
You would need to find load tables for both sizes and adjust pressure (very likely up) to provide the same load capability.

Or drive without load.

Krzyś

 

[bonjo]

Add to the above comments:
If 3" is the difference between circumference, then would the speedo calibration not go out?
The 45, will give a sharper handling & steering responce at the expense of comfort and possible road noise.

 

[krzyss]

OP is aware of "Beside the speed being off". S/he was interested in other stuff.
Improved handling - possible but it will depend more on particular model of the tire.

Performance winter tires would provide better steering than studless tires regardless of size, probably.

Krzyś

 

[Quattro Pete]

Also less ground clearance with shorter tires.

 

[BMWTurboDzl]

Hello,

My car calls for winters in 245 50 18 …. But I do have set of tires pretty much new … from another car that are 245 45 18 ?

Beside the speed being off … do I risk any damage to awd (x-drive) system or any other issues ?

Thank you

Other than a loss of 12mm in ride height no.

 

[jurko]

Running wide tires with small aspect ratio in winter is not a good thing.
Wide tires with short sidewall don't bite into deeper snow as good as narrower tires with higher aspect ratio.

Using tires with short sidewall in winter also leaves you vulnerable to wheel damage if you run over potholes which are not as visible as they are in the summer.

For winter I have a second set of wheel/tire combo with 15" steel wheels and 65 aspect ratio winter tires. Works really good in snow.

 

[DriveHard]

Running wide tires with small aspect ratio in winter is not a good thing.
Wide tires with short sidewall don't bite into deeper snow as good as narrower tires with higher aspect ratio.

Using tires with short sidewall in winter also leaves you vulnerable to wheel damage if you run over potholes which are not as visible as they are in the summer.

For winter I have a second set of wheel/tire combo with 15" steel wheels and 65 aspect ratio winter tires. Works really good in snow.

I would argue that aspect ratio has NOTHING to do with the ability for a tire to bite into snow.

I would agree that narrow tires do bite into snow better, and provide better winter traction, but I don't understand how sidewall height would have anything to do with it...unless you get to the point where you are running lower pressures for more contact patch (which I believe actually decreases snow and wet traction).