What's the advantage?
What's the advantage/disadvantage of adding or removing spacers from underneath your stem.
Now for the obvious reasons, it depends on riding comfort, style, etc.........
I've been rding pretty hard for 1 year now. When I bought my Reign 2008, it had 3 spacers under the stem - about 7/8 - 1". The Reign also comes with a large headset - maybe 1" tall.
Not knowing the difference, it felt fine and I've been riding it well. Yet, many question the height.
Is there a basic rule of thumb with height and where to start? Most pictures I see of other bikes have maybe 1/2" - 3/4" under their stem. That includes the height of their headset.
Naturally, I experimented and removed spacers, but it feels totally different. But that difference might be what I should be riding.
Someone told me most bike shops add spacers under the stem to add uniformity to their bikes on the showroom.
You can swap the spacers, and run them on top of your stem (thus lowering your stem/bars). You can also remove the spacers entirely, and cut your steer tube down if you're SURE you're happy with that lower height. Once you cut, you can't (easily) go back.
I seem to have something in the back of my mind...
Many magazine articles I've read for giants bikes (Trance in particular) have stated that they ran the stem at minimum height (all spacers above).
Nope the shop didn't add....
those spacers, the manufacturer set them up that way. The reason being is steerer tube length can be adjusted as a fitting tool. It can be used to permanently change bar height and adjust the bike to a given riders preferences or needs. Not every one that rides a medium frame is exactly the same proportions body wise or has the same flexibility. So manufacturers leave what they feel is "a little extra" to accomodate fine tunning of the fit. Everyone is different and wants their bike to fit differently. Rules of thumb are just that and not binding. What YOU should be using is what makes the bike fit and ride the way you want. As you've noted changing the bar height makes things feel completely different. The key is what is comfortable and what works for you!
Don't let anyone tell you where your bar height should be or how long your steerer should be. Only you can determine that. You can experiment further by actually riding the bike with different spacer configurations. Get some smaller ones to replace the larger spacers. I'd recommend geting a stack of 2.5mm spacers and replacing two of the larger spacers that you have now with them. Then experiment by moving them. pull the top cap and stem and remove a spacer, put the stem back on and drop the removed spacer on top of it. Re-install the top cap and tighten everything back up and go ride. Note the difference in the way the bike feels, handles, climbs and descends. Then repeat the process by moving another one and so on. You'll notice the changes. The lower your bar height is the further you have to get back off the saddle when descending, and the less you'll have to lean forward when climbing. It'll be just the reverse for a taller bar height. But do keep in mind that at some point you'll end up leaning too far forward. This can lead to hand numbness on extended rides due to too much weight being supported by your hands, lower back pain due to bad angle etc. The key is to find the compromise between performance and comfort. So experiment away. You'll find the "sweet spot" that works for you.
My personal preference for an XC/Trail bike is to have the bars about 1 1/2 to 2 inches lower than the seat. For more agressive type of bike I prefer the bars even with the seat for a more upright (descent friendly) position.
So experiment for a while, move spacers around, ride it. Once you find that sweet spot for you, then cut the steerer if you want to. But don't let anyone tell you how long or short YOUR steerer tube should be. It's likely based on their preferences and may or may not work for you. Always veiw any statement like "Wow your bars should be lower." or "How do you ride that thing with the bars so high.", with suspision. Bike fit and configuration is a very personal thing. What works for you probably won't work for everybody else.
"I do whatever my Rice Cripsies tell me to!"