Yes, you’re overthinking it. A couple of rides and you’ll never know the difference.


Sent from my iPhone using Tapatalk

 

...the handle bar is now behind the front hub...

This does not matter at all (in the range to which you are referring).

-F

 

One time I put a 50mm stem on a bike that originally came with a 90mm stem, and the results were disastrous. It totally screwed up the reach, I reinstalled the 90mm stem a week later.

 

It'll affect your ability to weight the front end in flat turns and reduce leverage for standing power output. That's why XC riders bias longer stems and tend not to upsize frames. But it'll also sharpen the steering and improve your weight balance on the downhills.

 

That's why XC riders bias longer stems and tend not to upsize frames

With bikes getting longer slacker I will likely size down with the next bike

 

The hub SHOULD appear in front of the bar.
=sParty

 

Did I just wake up in the 90s? I think I still have a 110mm stem around here somewhere (with 25.4 clamp diameter) for a proper XC riding position.

 

Did I just wake up in the 90s? I think I still have a 110mm stem around here somewhere

I bequeathed my 110 mm stem to the Smithsonian.

 

Steering might feel just a little twitchy on climbs but it's not a big deal. You won't feel much of an overall difference going from 70 to 50.

 

I disagree. I went from 50mm to 32mm on 3 different bikes with the same result of wandering/twitchy front on each of them (XC hardtail, fat bike and trail/enduro). Bought the stem to experiment and moved it from bike to bike. Just couldn’t properly weight the front. Bike size and geometry didn’t matter.

 

But in doing so the handle bar is now behind the front hub.

This method of sizing a bike or determining fit became obsolete about the time we stopped having head tube angles in the 70's.
I'm pretty sure I can see not only my hub, but most of my front fork in front of my handle bars on both my bikes.

 

I didn't even know there were mountain bikes with the handle bar in front of the hub. What am I missing here?

 

I didn't even know there were mountain bikes with the handle bar in front of the hub. What am I missing here?

he means line of sight from the rider's perspective.
Way back in the day when mtbs were based on road bikes, a common way of sizing a frame and/or cockpit was that the handlebar should obscure the view of the front hub when seated on the bike.
It's dumb, and probably no more applicable as KOPS (knee over pedal spindle). Even the guy who made it up admits it was at best a generalization and didn't work for many people.

 

It depends really. You can certainly go shorter than stock but at some point a stem can be too short and result in twitchy steering and inability to properly weight the front wheel. I'd say from 70mm to 50 is not unreasonable. If you find you don't have enough traction on the front wheel maybe lower the stem/bars by one 5mm spacer. If not happy, try to borrow a 60mm stem to test.

The super-short <40mm stems seem to not work for most bikes, very few people have tried them and kept them. It might not sound much, but 5-10mm in stem extension can make a difference in handling, and 40 to 35mm is significant.

 

I have a Fuel EX 8 Gen 5 in large. I’m 6’1”. The EX has close to the same geometry as the new Top Fuel. Well the EX is about a cm shorter reach. It came with a 45mm stem. Road it for a bit and switched to a 60mm. Then 70mm 13 degree rise. For me it works better in a the tight stuff and allows me to stretch out. The shorter stems were just too cramped. i also switched to a 750mm bar. Was hitting trees and felt too wide. I could have gotten a Top Fuel but wanted more travel. Have not used it all yet.

 

Just went from a 50mm to a 40mm on my ebike, can definitely feel the difference in handling, it turns quicker now. I ride a 35mm on my other bike but wouldn't want to go any shorter on the ebike I don't think.

 

I have found that what ever stem length I run (with in reason) I make adjustments and after a couple of rides I am unaware of the handling changes in length.