This will cause a bad burn.

You must burn at the minimum speed supported by the disc, which will be much higher than 1x.

A 1x burn creates lots of errors and a bad disc.

See for yourself: do a surface scan (Scan Disk) and check Disc Quality in Nero CD-DVD Speed

Once you have made a good disc with low errors (for a CD, I expect <150 errors per CD) then try it in the car!

I bet your disc burnt at 1x produces a very poor surface scan.