I'm after some general guidelines as to finding the optimum stem length on my Trek 520.

I recently bought a used 520. The 520 is the first drop bar bike I've owned. It has an ETT of 555mm. I've currently got a 110mm stem and Nitto Randonneur bars on it, so it has a combined ETT/stem length of 665mm. The tops are pretty much level with the seat.

My other bike is a flat bar road bike with an ETT of 570mm. It also has a 110mm stem and bar-ends. The combined ETT/stem length is 665mm, this being 15mm less than the Trek. I ride on the bar ends a lot. The flat bars are about an inch lower than the seat.

Now here's the thing, the 680mm combined ETT/stem length on the flat bar bike feels about right, but the 520, at 665mmm, feels way too long. Riding on the hoods has me really stretched out.

Riding in the drops feels OK, with about an inch of clearance between my knees and elbows, and is much more comfortable than riding on the hoods, but I prefer to sit more upright.

So, is there any magic formula for arriving at a combined ETT/stem length for drops versus flat bars? Or to put it another way, assuming you were working with the same road bike frame and changing bars, would you normally change the stem length, and if so, by how much?

Should the distance from the seat post to the hoods on the 520 be about the same as the seatpost to the flat bars on the other bike, or is there some other guideline O should use?

I don’t have a supply of stems to try, so I’ll have to buy and try some. I’m just after a ballpark estimate of what length I should be looking at.

Thank you for reading.

I haven't found an adjustable stem that gets a drop bar on a road bike up to where I want it. So I make do with an upswept Nitto Albatross bar and my back feels good.

Bar height also has an effect. With a higher bar -- you will need a shorter stem. I just converted from flat bars to drop bars on my Brodie Ocho. I found that I needed a 30mm shorter stem with a rise vs. 110 mm and no rise. Most bike shops do have take-off stems in a box that you can try.

Thanks, but the main problem isn't so much the height, it's more the length.

Before I run off and buy a stem, or five, I want to narrow down the range of stems I should be looking at.

My presumption is that seeing as the "primary" riding position of a drop bar bike is on the hoods, the total length from the seat post to the hoods for a given rider ought to approximate the total length from the seat post to the handlebars that the same rider would find comfortable on a flat bar bike.

Is this presumption right or wrong?

In my case, the flat bar bike seems about right with a combined ETT/stem length of 680mm.

Does this mean that the optimum ETT/stem/reach length of the 520 should be about the same?

Seeing as the 520 has an ETT of 555mm, and the Nitto bars have have a reach of 105mm, this would mean I would have to look around for a 20 or 30mm stem. Such a stem would clearly be too short, so I guess I would have to sell the bike and get somethig else.

Or am I missing something obvious?

Can't say I agree. Raising the bar should reduce reach, requiring a longer stem.

I think changing bar types may be confusing the issue.

You should be measuring reach to your hand position, not to the top of the bar.

There's a HUGE distance difference between bar top and hoods. There are plenty of online fit calculators that could get you headed in the right direction.

Thanks diesel-dad, that gives me something to work with. By riding the bike around, and putting my hands on "imaginary" hoods and tops. 30-40mm shorter is about the range that feels right. That means I'm looking for a 70 or 80mm stem.

At what point is a stem too short? ie, at what stage to you say the frame is just too big, sell it and buy something smaller?

Thanks. I tried that, and thought I had it right. I guess I didn't.

Most of the online calculators don't specify whether they are assuming drop bars or flat bars, so I assumed they were assuming drop bars, if that assumption makes any sense.