Thomill

Hello all,

I have a hopefully simple question on stem lengths. I am looking to replace the stock Bontrager RaceOS 90/7 stem on my Trek 5200. I was looking on their site (https://bontrager.com/Road/Components/Stems/5831.php) and was going to get the 90/17 via my LBS. But, here is the question: is the length listed simply the end-to-end length of the stem, or the amount of horizontal reach instead? If it is the latter, then the 90/17 would actually leave my bars a bit closer to my trunk and, as such, I would need a slightly longer stem.

Any help would, as always, be appreciated.

Thanks.
T

timmhaan

stem length is measured seperately from rise. however, you're also correct in thinking that a greater rise will effectively make the reach shorter.

DannoXYZ 

I like to calculate the horizontal reach of a stem. Use this formulae:

reach = StemLength * cosine(17 +/- angle)

where angle is degrees above parallel with the ground, assuming a 73-degree headtube. So a 90/7 stem has the following reaches:

90/7 aimed up = 90*cos(17+7) = 82mm
90/7 aimed down = 90*cos(17-7) = 88mm

and a 90/17 stem would be:

90/17 aimed up = 90*cos(17+17) = 75mm
90/17 aimed down = 90*cos(17-17) = 90mm

Notice that the 90/17 stem aimed down is perfectly horizontal, so all of its length is effectively the reach.

bvfrompc

Now that is a disturbiing way to start any post!

Now going from 88mm to 90mm in reach is really dialing in your fit!






BTW, I am statistician so I actually appreciate starting a post with "I like to calculate..."

timmhaan

i wish stems with in between sizing were more common. for example, i could really use a 8.5cm, but almost everywhere you look they increment in 1cm units.

biker7

I have a 105mm ITM road racing stem on my latest road bike...sold in that odd length.
George

biker7

With respect Danno, I think considering a stem only in the horizontal plane is myopic. Reason being that the arms effectively come down to the handlebars at a 45 degree angle, 90 degrees to the torso and the vertical component of reach to the handlebars is just as important. It is the resultant combination of rise and run that determines reduction or increase in handlebar reach.
George

DannoXYZ 

Yes, if anything the change in height makes for an even greater change in reach. The 90/17 stem above actually has a much greater range than the 75/90mm reach as calculated. In the up position it would feel really close and tight, like a 70mm stem. Then with it flipped down, it would feel like a 95mm stem due to the lower drop. Quite a wide range with a single stem.

You also make up for a lot of height differences with the bend in the elbows. That picture of Hincapie's just cruising warming-up. In a race, his elbows would be bent and his back and forearms horizontal. So the reach to the bars is effectively the actual horizontal distance between the saddle and handlebars. Then the bent elbows makes up for differences in height/drop between the saddle & bars. Imagine the motion of your forarms when shaking hands. Moving your hands up and down by pivoting at the elbows doesn't change the reach to the other person that much when they are horizontal.

What happens with a lot of people is that they have their bars too low, then they don't have as much of a bent elbow. Locked arms will lead to a lot of shoulder and back soreness on rides because it transmit a lot of shock through. So when they get higher-rise stem to raise the bars, they have to get a longer one as well to maintain the same reach. I like to set up my bike so that my forearms are horizontal with the ground when I'm in the drops. Handlebars are about 2-3" below the seat. Taller riders can use more drop.

timmhaan

provided, of course, they have the flexibilty.

DannoXYZ 

Yes, I was mainly talking about maintaining the same back-angle because taller riders have longer arms. If a 5'5" rider were to have the same back-angle as Hindcapie above, he'd would only use a 2" drop instead of 4" drop.

Thomill

As always gang, thanks for the info!

T