Fit: Long vs. short stem?

[ty-ro]

I'm looking at a new race bike for this season.

I can fit the frame in size 56.5cm with a 130mm stem OR the size 58.2cm with a 110mm stem. I am leaning towards the 56.5cm with a 130mm stem. Right now I ride a 57.5cm with 120mm stem. The longest stem I have run is a 120mm.

What are the pros/cons of running such a long stem? Any benefit of running the longer top tube with a shorter stem?

Thanks!

[yourdaguy]

Longer stem = more leverage and more precise handling. Your arms move through a longer arc and have to move farther, but don't have to push as hard. Most pro's are using in the 120-130 range. I generally like to be 120-130. You can also do almost the same thing with a shorter stem and wider bars, although that brings other issues. Also, bars with longer reach require a shorter stem so depending on the bars you choose the proper stem could vary by 20 cm or more. You really need to consider the bars and stem together and with the frame sizing. In general, you are probably better off with the shorter of 2 sizes of frame because your seatpost will often be too short on the larger size. Also, the shorter frame will tend to be more comfortable since you will have a longer post sticking out and more impact absorption.

[pharding]

With a smaller frameset you can get lower. The pros are extremely fit and very flexible. They like smaller framesets in general because they can assume a lower, more aero position on the bars.

[yourdaguy]

Yes, lower head tube is another reason to go with a smaller frame. I am 5'10" and I generally ride 54's with no spacers and have sold 56 frames because I could not get the bars low enough without a negative stem. But I am one of very few people that have this problem. I can touch ground with flat palm and knees locked. Most can't get far past touching ground with fingertips. The difference is around 4" and translates fairly straight (not quite linear relationship) to comfortable bar height.

[CTiride]

Keep in mind seat tube angle when making a comparison. Sounds like you are considering a Specialized. If that is the case, the 56 has a steeper seat tube angle the effect of which is that your current bike (assuming it has a 73 degree sta) effectively will be roughly 7 mm shorter than the 58 and 7 mm longer than the 56.

[Mr.Gib]

Yes, lower head tube is another reason to go with a smaller frame. I am 5'10" and I generally ride 54's with no spacers and have sold 56 frames because I could not get the bars low enough without a negative stem. But I am one of very few people that have this problem. I can touch ground with flat palm and knees locked. Most can't get far past touching ground with fingertips. The difference is around 4" and translates fairly straight (not quite linear relationship) to comfortable bar height.

I am very flexible also - no problem putting my palms on the floor with locked knees, but I am more comfortable with a relatively standard drop of 8 cm. There is more to this issue than just flexibility. Worth checking power and heart rate at various levels of drop.

[STARNUT]

Stack and reach is what you should worry about not TT length unless, in the highly unlikely event, both frames have the same STA and HT height and differ only in TT length. Choosing a frame size based on what size stem you "need" to run to make it work is a bit like buying a car based on what tires come on it......... buy the correct size and use the correct size stem.

All things being equal - they never are - you *may* be able to run a 110 stem with no stack/spacers where as with the smaller frame you *may* need to run spacers or a different angle stem. However, running spacers actually shortens the reach via negative reach - see the comment below -.


and


pros are no more flexible than your average athlete, they just happen to have their bikes fit correctly.


Starnut

[ty-ro]

I am not super flexible but comfortably run 12.5cm of drop. Yes, I am looking at a Specialized SL3. I have already considered the ht length and other fit issues. Sounds as though the 56.5 size will work best for me. The wheelbase is about 7mm shorter on the 56.5 SL3 vs. my current bike. My saddle height is ~81.4cm, so I'll have quite a bit of seat post showing, but I'm ok with it. I'm 6'1" with a 36" inseam and the 56.5 size just *seems* small. Thanks for the help guys.

[DaveS]

The 58cm might have a head tube that's just a bit too tall to get the drop you want. It seems like you would need a about a 210-215mm head tube length with the headset to get a 12.5cm drop with a 73 degree stem. The difference in reach is about 15mm, so you're kind of in-between stem sizes. Using a 20mm longer stem on the 56cm will produce more reach than a 110mm on the 58cm.

While the comments about reach and stack are valid, if the maufacturer doesn't list them, there are other ways to closely approximate the same values, by correcting the TT length for any difference in the STA and comparing head tube lengths, with the headset. In this case, the reach difference due to the STA difference is quite small - only 2-3mm.

http://www.specialized.com/us/en/bc/SBC ... temId=9256

[elviento]

Sorry I am going off topic a bit -- who offers a "58.2cm" frame? Haven't seen any company going beyond centimeters.

[ty-ro]

Sorry I am going off topic a bit -- who offers a "58.2cm" frame? Haven't seen any company going beyond centimeters.

You're not off topic. It's called a "58cm" by Specialized, but the actual measurement is 58.2cm. Maybe the virtual seat tube (if it were not compact geometry) would be 58cm? Who really knows how they come up with the sizing label these days. Each company seems to do it their own way.

[merkyworks]

im 5'8" and ride a 53.5TT and have a 130mm stem on my bike and love the way it steers in the crit races i do

[fogman]

In general, you are probably better off with the shorter of 2 sizes of frame because your seatpost will often be too short on the larger size. Also, the shorter frame will tend to be more comfortable since you will have a longer post sticking out and more impact absorption.

In general, how much seatpost should be sticking out on a standard geometry (not compact geometry) bike?

[DaveS]

The amount of post exposed is totally irrelevant. With 350mm seatposts so common, you'll never have a seatpost too short, even with a 6cm slope to the TT. Since you're talking about horizontal TT frames, the old standard was to buy a frame with 2-6cm of standover clearance, in bare feet. The post exposure would be what it would be.

Those who wanted less saddle to bar drop would pick the largest size and those want more would pick something smaller. Riders with short legs and long torso might lean toward the larger sizes, just to get enough reach.

FWIW, with a 73cm saddle height, the largest frame I ever owned was 55cm c-t (frames sizes without a c-t or c-c designation are not complete). The top of the saddle would be about 17cm above the TT. These days, I'd select a 53cm c-t or 51cm c-c. My current LOOK 585 frames are 51cm c-c, but the TT slopes 6cm, so I have a very large standover clearance of about 10cm. Even so, a 350mm post has about 50mm more length than I need.

[1centaur]

As someone once said, 130mm is not a long stem.

I also have a couple of 57.5TT bikes with 120 stems, and I found the transition to 56.5 with 130 stems very easy. Longer stems theoretically put your weight a little more forward in comparison to the mass of the frame than shorter stems with longer TTs. I'm not sure I notice a difference in my riding.

I agree that sometimes those bigger frames have HTs that are kind of tall, and as I noted in my Parlee Z5 thread not all HTs start and stop at the same point even if their height is the same.