I'm confused. Which stack is less aggressive? 544 mm or 528 mm? How I understand it is that the lower the number the more aggressive it is when it comes to stack. Because it's like the elevation of your entire arms and hands when you're on the bike. Am I wrong? I'm planning to get a new bike. My choices are the Giant TCR and Specialized Tarmac. I want to pick the bike with less aggressive geometry. TCR has a 528 mm stack and the Tarmac has a 544 mm stack. Reach are almost identical with 1 mm difference. Thank you for your replies.

Yes, greater stack height is less aggressive.

Stack height is to the top of the headset though. So out of the box or out of the store, how many spacers are under that stem between both bikes? Though adding or subtracting a lot of those spacers will affect reach some too.

Thank you, Carbonfiberboy. Enjoy riding!

My understanding is that it's out of the box configuration. Spacers won't matter to me because I'm only looking for out of the box specs without adding or subtracting spacers. Thank you for your reply.

In the stores, many of the bikes I recently looked at came with about three almost four CM of spacers under the stem. I don't remember what the TCR had as they didn't have any near my size and didn't get any before I found a bike that rode well and had what I wanted.

What I was trying to convey was just because the bike will allow you to get very agressive in position, it may not be any more aggressive than the other if they ship them with more steerer tube above the headset than another brand.

So if you can try out both bikes. I wouldn't eliminate one based the spec'd geometry when the bars and stem aren't at that position when they build the bike in the shop.

Got it. I would definitely ride them both before pulling the trigger. I would discuss with the mechanic about the spacers and would do measurement in the store. Thank you.