Immediate difference? BTR 80 and 90 are much better armed, and have firing positions, including forward firing points, for the passengers inside, unlike Stryker. The original first and second generation BTR 60 and BTR70 wheeled personnel carriers have had their twin gasoline engines replaced with a more powerful and safer Diesel type, and many of the faults and failings found in the first generations of machines have now been corrected or at least improved in the later models- side exits for troops, should the vehicle turn on one side or upside-down, for instance, as killed three Stryker crewmen so far.
Stryker's 40mm grenade launcher system was found to be wildly inaccurate during testfirings in the USA, and live weapons shooting with it was ordeerd halted; once in Iraq, some of the first US casualties aboard a Stryker occurred when a 40mm round fired while the crew was mounting a Mark 19 grenade launcher on the remote weapons mount of a Stryker. The Russian equivalent, 30mm AGS-17 Plamya is battle tested in Chechnya and Afghanistan, and is much safer; the 30mm gun fitted aboard BTR 80 and 90, especially on the new Kliver turret with twin Kornet antitank missile launchers, is even better, and longer ranged.
Going to a war like in Iraq? Send me in a BTR90, any day. But better, an MTLV tracked personnel carrier. Wonderful machine.
I think the BTR vehicles captured from Iraqis were BTR- 70s. Good thing for the Strykers that they got there after the combat had ended, I don't think the 14.5mm automatic gun aboard even the older BTR-70 wiould have had trouble penetrating Stryker's half-inch/13mm armor.
Oh, and BTR 70 is amphibious, of course, probably not a big deal in Iraq. And it also can be air transported or airdroppped; Stryker cannot.
So BTR 80 and 90 are not predecessors of Stryker, but alternates whose performance Stryker cannot match. Predecessor vehicles for Stryker were WWII-era M8 and M20 *Greyhound* 6-wheeled armoured cars built by Ford.
