19” spare on set of 21” wheels?

[ttran203]

I have a staggered set of 21” twin turbines (245/35R21 front, 265/35R21 rear) currently on my vehicle. Can anyone tell me if I will be able to temporarily use a 19” Cyclone wheel (245/45R19) as a spare for the front wheel without any issues?

 

[PCMc]

I just pulled up an on-line tire size/diameter calculator.

The 245/35R21 comes up with a diameter of 27.8 inches
The 245/45R19 comes up with a diameter of 27.7 inches, or a difference shown as about 0.4% smaller.

That difference is about the same as having roughly 1.5-2/32nd of an inch difference in tread depth on the tire on one side versus the other.

So I think you'll be ok if you're just doing this for a few days until you can get a tire repaired/replaced. Realize you may feel a difference in handling due to different tire stiffness and tread width, but seems like the two sizes are pretty well matched unless the on-line calculator I'm using is lying to me.