You're comparing Android head units with 32GB, 64GB or 128GB of storage. It's tempting to pick the biggest one and be done with it.

If your phone handles navigation and music through CarPlay or Android Auto, I wouldn't pay for extra head-unit storage just to make room for files already on the phone. If you want apps, offline maps and a music collection stored on the head unit itself, extra space has a much clearer purpose.

Start with what you'll save on the head unit. Then choose the capacity.

Using CarPlay or Android Auto? Start with the phone

For navigation and music, CarPlay and Android Auto let you use compatible phone apps through the car's screen. The phone is still doing that part of the job.

Take music downloaded in Spotify on your iPhone. That download uses the phone's storage. Bringing Spotify up in CarPlay doesn't automatically copy that whole offline library into the head unit.

The head unit still needs space for its own software and data. But if you rarely save anything on it, the size of your phone's music library is a poor reason to move up a storage tier.

Want the head unit to keep its own maps and music?

That's a different shopping decision. If you install apps directly on the head unit and download or copy content onto it, those files need room wherever they're saved. Signing into the same account you use on your phone isn't the same as downloading your offline collection again.

Think about what you'd actually keep: maps for the areas you travel through, music you want available offline, and the apps you'll use. Having that content stored locally is useful; the trade-off is space for the files and their updates. A collection you keep adding to gives extra storage a real job to do.

Use the download sizes for your chosen app and areas, rather than someone else's map collection as a guide. Offline availability varies by service and region, and the app needs to support your device. For music services, the subscription also matters. Choose the offline service and collection first, then budget for their storage.

For music, separate the cache from the collection you deliberately download. Spotify, for example, distinguishes cached content used for playback from offline downloads. When planning space for music you want to keep, count the downloads you intend to make.

Recordings: which device saves them?

Adding a camera doesn't automatically put its recordings in the head unit. The Garmin Dash Cam Live, for example, records to a memory card in the camera. Buying more head-unit storage wouldn't increase that card's capacity.

For a recording setup controlled through the head unit, look at its storage destination. The example settings screen here lists USB2 under the recording storage path. For your own space budget, count the files where they actually end up; a saved copy on another device takes space there too.

Chinese-language recording settings on one unit, with USB2 listed as the storage path.

So if recording is part of your plans, work out whether you're buying space in the head unit or in the recording device. Those are different purchases.

So which capacity is worth paying for?

Compare the space available after the system and your usual apps are installed, then allow for the files you want to keep and future updates. The advertised total isn't the amount left for your downloads. More capacity buys room; the capacity number alone tells you little about loading speed.

If you mostly use phone apps through CarPlay or Android Auto and keep little on the head unit, I'd favour the lower-priced option when its available space covers that use and the other features meet your needs. There's no reason to budget for a second copy of your phone's entire library.

If you want a growing collection of maps and music on the head unit, I'd give storage more of the budget. Choose enough available space for that collection with room to add to it, instead of buying a capacity you already expect to fill and repeatedly clear out. Recordings belong in that calculation only when they're saved there.

Pay for the files you want to keep on the head unit, not for the size of the library on your phone.

32GB, 64GB or 128GB: how much storage does your head unit need?