RocThrower

Which measurement is more important when comparing sizes of two different bikes? My current bike has a reach of 381 and TTL of 565. The bike I'm looking at in one size has a reach of 380, but a TTL of 545 which sounds a little short. The next comparable size has a TTL of 565, but a reach of 386 which seems long. So in this scenario, is it better to get the size which is closer in reach (380 vs 381) or TTL (565 vs 565)? Is this even a logical way to size the other bike?

Unfortunately, the bike I'm looking at isn't available locally, so I would have to order it online.

oldbobcat

Reach is the measurement that really counts, but many of us have been fitting ourselves before geometry charts indicated reach (and stack), so we're just in the habit of talking about top tube length, and a lot of catalogs still don't include this measurement. And a 56 cm horizontal from the seat to the head tubes is easier to measure with a tape and remember than a reach of 398 mm.

Considering that within anybody's size range of several makes of functionally similar bikes, seat tube angle usually does not vary a lot more than a degree, so top tube length is helpful though less precise. Just remember that a slacker seat tube will probably warrant less saddle setback, leading to a slightly shorter fit than a similar bike with a steeper seat tube.

fietsbob

divide the cockpit at the plumb line over the BB Axis,, setback is behind that, reach is ahead of that..

AnthonyG

The measurements are telling me that the newer frames you are looking at have steeper seat tube angles than your current bike. To get as close as possible to the same fit that you currently have the smaller frame would be better but you would need a seatpost that moves the saddle 35mm further back than current. This is a hard ask.

As to the larger frame you would still need to move the saddle rearwards in order to get the same saddle/pedal relationship as current which would exacerbate the reach issue.

To be honest I would keep looking.

Anthony

RocThrower

An update with more questions than answers...

I ended up ordering and returning the smaller bike (Ridely X-Trail), which had an ETT of 545, and reach of 380. While the reach to the bars felt very comfortable, I had to use 30 mm of spacers under the stem to get the bars to a comfortable height. The saddle to bar drop was between 3 and 4 inches, which is more than I'm used to. Surprisingly, it didn't feel too bad seated on the hoods, but when I was in the drops I felt a little uncomfortable and my knees and elbows were very close to hitting each other. Out of the saddle, my knees were close to hitting the bars, and the front end felt unstable. I felt like a lot of my weight was over the front of the bike, and this was not a sensation I've felt from other bikes I've owned. I never took it out for longer than a 30 mile ride, and my suspicions were that maybe the bike was too small. I'm between 5'9 and 5'10, and the Trek dealer in my area says I should be on a 56, while the Specialized dealer says a 54.

I have returned the bike, and after looking at other bikes, at least spec-wise, I keep coming back to the X-Trail. The next size up has an ETT of 565 and a reach of 386, but has a 20 mm taller headtube. My thinking is that I would benefit from the taller headtube, but have always read that top tube length is the most important measurement to get correct. Would it be wise to size up, or accept the fact that the X-trail's geometry is not suitable for someone with my dimensions? Would a longer stem help the out-of saddle issues, even if the bars would still be lower than I'm used to? Am I wrong in thinking that this many spacers is an indication that the size might not be correct?

Unfortunately there are not any Ridley dealers in my state, so again, I would not be able to try the bike out. I'm most likely going to settle on something I can get and fit locally, but I'm just curious as to what BF might have to say.

Although a picture of me on the bike would be better, this is all I have to show what the setup looked like:

oldbobcat

The 56.5 cm top tube of the X-Trail is pushing it for your height, and you've got 3cm of spacers on the smaller size.

If you're hunting around for the right size, I recommend looking at brands you can buy locally so you can learn what fits you. F'rinstance, I know that if I order a 56 cm Pinarello Dogma with 175 mm cranks and a 130 mm stem, it will fit me perfectly. If I could afford one. That comes from studying geometry charts and years of road riding experience.

You're overall height puts you on the plus side of medium. By your setup on the Ridley, it looks like you have longish legs. And if your arms are proportional with your legs (longish, too), don't be afraid of a 3-4 inches of drop to the bar. The length of your reach beyond your hips should allow you to handle it. But not with 3 cm of spacers.

The recommendations from the Trek and Specialized dealers aren't off. Treks run generally a half-size smaller per the nominal size. In other words, a 56 cm Trek pretty much fits like a 55 cm Specialized would, if it existed. Scott is another brand that is sized a little larger than Trek.

RocThrower

Thanks for replying again, oldbobcat.

My last two road bikes have both been size 56 Treks, with H2 geometry, and both had ETT of 560. Even with a 100 mm stem, I always felt a little stretched out on them. When going with the Ridley, with the 545 top tube, I thought I'd try going smaller for the reason above, and because I've read Ridley's run large. Again, the reach to the bars felt so good, and I hadn't considered your statement about my longer arms taking some of the drop out of the equation.

When you say the 56.6 TT is pushing it for my size, are you saying it's going to be long for me? I'm starting to feel like I'm on the short end for a 56, and slightly on the tall end for a 54. I was looking at a Roubaix in a 56 at one of the local shops, and both of the employees thought it would be too big and 54 would be a better fit. I'm not sure I want a Specialized or another Trek, but, ultimately I am looking for the bike which fits me best.

oldbobcat

Yeah, for 5'9"+, the top tube of a 56 cm Madone is long.

I had to look up the Ridley X-Trail to see what size you bought. It's a small, and it is rather big for its size, but especially in reach, at least for this class of bike. Judging by your setup, it looks like 380mm might the upper limit of your reach with a moderate stem, but you'd be a lot happier with a couple more centimeters of stack.

But since you're looking at all-road bikes, what's keeping you away from Trek's Domane? There are two disk brake models, the 4.5 with full Shimano hydros and the 4.3 with hybrids (cable-actuated hydro). The 54 has a reach of 374mm, and the 56 is only 3mm longer. And the stack dimensions are 575mm and 591mm, respectively, vs. 558mm for the small Ridley. Either size should give you some wiggle room in both stem length and and rise. On a similar note, a 54 cm Roubaix Disk has a reach of 380mm (same as your Ridley) and stack of 564mm.

Wildwood 

The measurements that I like to compare when measuring bike to bike:
1. Seatpost to rear of handlebar (assuming level top tube or Effective top tube length).
2. Saddle to bar drop (without spacers or hugely uptilted stem) - tells me if there's enough head tube.

If you are buying only frame/fork or for the first time more factors are added for more variability. And the type of saddle is another big factor.

Some people have a large database of commonly acceptable (for decades) measurements published by nearly every manufacturer that will fit them to a diamond frame acceptably. The specific geometry of various frames could be different while the fit remains constant. Determining the measurements to 'fit' is only one aspect of determining if the bicycle will feel good or best serve the purpose you most put it toward - ie winning races, riding centuries, or just fast/fun/fitness (not to mention gravel, commuting, touring, basic recreation, grocery getting).

fietsbob

Buy a shorter extension Stem.