This answer is for the UPPAbaby Cruz (2015–2019), though one maker didn't say which version. Not sure which Cruz you have?
Key specs
Adapter
about $49.99
Weight with carrier
31 lb
Seat rated to
35 lb, 32 in
On planes (FAA)
Yes
Stroller folded
22 W x 14 L x 37 H in (seat attached)
Good to know before you click it on
Vista 2015 and later; adapter folds with the stroller.
About this pair
The Peg Perego Primo Viaggio 4-35 goes on the UPPAbaby Cruz (2015–2019) with the Peg Perego Primo Viaggio adapter for UPPAbaby strollers (model IKCS0027), about $49.99. With the carrier on, you are pushing about 31 lb (21.5 lb stroller, 9.5 lb carrier). The seat itself is rated up to 35 lb and up to 32 in, per Peg Perego.
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32 other infant seats fit the UPPAbaby Cruz (2015–2019); UPPAbaby Aria V2, UPPAbaby Mesa (original), UPPAbaby Mesa Max and 2 more need no adapter at all.
Summary from the makers' published data.
How to set up the Peg Perego Primo Viaggio 4-35 on the UPPAbaby Cruz (2015–2019)
What you need
The UPPAbaby Cruz (2015–2019)
The Peg Perego Primo Viaggio 4-35 carrier (its car base stays in the car)
The Peg Perego Primo Viaggio adapter for UPPAbaby strollers (model IKCS0027)
The adapter maker shows the fitting steps in pictures; see the manuals below.
Before every walk
Check that the carrier is locked on both sides the way your manual describes. How we check our answers
Last check: give the carrier handle a gentle tug. A seat that is fully latched does not lift off.