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Bike frame size

Old 10-03-20, 07:35 PM
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ritzkraft79
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Bike frame size

I was at the trek store today and was looking at some bikes. When I asked one of the employees about availability of a certain road bike (Domane SL5 disc) they told me they only had size 50 which would be perfect for me. I am 170cm tall and ride a 54cm Specialized Tarmac so this confused me. I told the employee that I usually ride a 54 frame and they were surprised as well, saying that my bike was way too big for me. So who is right here? Did I ride a too big of a bike for two years with no problems or is the employee wrong? Will I benefit from getting a 50 or 52 frame in the future? The employee kinda seemed like they knew what they were talking about but Iím not sure.
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Old 10-03-20, 07:56 PM
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I am 5í9 with a 31 inch inseam and the Trek employee tried me on a 52cm Emonda. It was way too small.

You border a 52 and 54 I would think.
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Old 10-03-20, 08:01 PM
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Go to both websites and do the bike fit guide. I did that and the Trek would be a 60 and the specialized, I would be a 61 cm
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Old 10-03-20, 08:30 PM
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You can find charts that show it either way... I would agree that a 54 sounds a bit big for someone who is around your height, but not ďway too bigĒ at all. It depends on the bike, geometry, tires, stem, bars...

I have ridden 54, 56, 58 comfortably. So itís possible the 50 would work as they think, but youíll just need to try it and go with your honest observations about how you feel riding it. Key is just donít settle if it doesnít inspire confidence when riding.
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Old 10-03-20, 08:58 PM
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Just looked at the Trek website and Domane SL 5 in 54cm suits a rider height of 168-174cm (inseem 30.7"-32.3") A 50cm fits 158-163cm tall rider. The employee was wrong...Just wanted the sale purhaps...
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Old 10-04-20, 02:36 PM
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Originally Posted by Charliekeet View Post
You can find charts that show it either way... I would agree that a 54 sounds a bit big for someone who is around your height, but not ďway too bigĒ at all. It depends on the bike, geometry, tires, stem, bars...

I have ridden 54, 56, 58 comfortably. So itís possible the 50 would work as they think, but youíll just need to try it and go with your honest observations about how you feel riding it. Key is just donít settle if it doesnít inspire confidence when riding.
Trek says 54cm and big S says 52. I think the employee is kinda shady and I donít think I should buy from there
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Old 10-04-20, 03:02 PM
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Did you tell the bike shop guy your height? Maybe you just look shorter than you actually are. It can be hard to guess. Also, if you are in a shop just random Lookie Lou-ing you shouldn't be surprised if they don't give you the full VIP treatment. I'd say give them another chance when you are in the market. I doubt they have any interest in putting you on a bike that doesn't fit.
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Old 10-04-20, 03:14 PM
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Forget height. What's your inseam. Start there. My inseam is 32.5" and my height is 5'9". A 54-55 frame is perfect for me. But, I can also ride up to a 58 with modification.
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Old 10-04-20, 03:42 PM
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Originally Posted by shelbyfv View Post
Did you tell the bike shop guy your height? Maybe you just look shorter than you actually are. It can be hard to guess. Also, if you are in a shop just random Lookie Lou-ing you shouldn't be surprised if they don't give you the full VIP treatment. I'd say give them another chance when you are in the market. I doubt they have any interest in putting you on a bike that doesn't fit.
I asked a few questions about pricing and I told them I was in the market for a more comfortable bike before them telling me I should get a 50cm. I was as tall as the salesperson but they still said 50cm so maybe they were talking from experience? Maybe they had a good experience with a 50cm bike, but Iím pretty comfortable on my 54cm Tarmac. Strange. Maybe I should try a 52 as a middle ground
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Old 10-04-20, 03:44 PM
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Originally Posted by bruce19 View Post
Forget height. What's your inseam. Start there. My inseam is 32.5" and my height is 5'9". A 54-55 frame is perfect for me. But, I can also ride up to a 58 with modification.
I measured my inseam and itís around 81cm which is 32 inches?
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Old 10-04-20, 03:59 PM
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Don't look at the seat tube length. The stack and length will be far more accurate in demonstrating the fit of a bike.
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Old 10-04-20, 04:16 PM
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Originally Posted by ritzkraft79 View Post
I measured my inseam and itís around 81cm which is 32 inches?
I would think that a 54 would work well for you. Just my opinion after 40 years of cycling.
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Old 10-04-20, 04:20 PM
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Originally Posted by Moisture View Post
Don't look at the seat tube length. The stack and length will be far more accurate in demonstrating the fit of a bike.
I could be wrong about this but I think Stack & Reach are a result of manufacturers going to sloping TTs. Which they did because it was cheaper for them to manufacture bikes, not because it gives better sizing for the buyer. If I am mistaken about this I would welcome an explanation to the contrary.
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Old 10-04-20, 07:07 PM
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Originally Posted by bruce19 View Post
Forget height. What's your inseam. Start there. My inseam is 32.5" and my height is 5'9". A 54-55 frame is perfect for me. But, I can also ride up to a 58 with modification.
You're kidding, right?
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Old 10-04-20, 10:11 PM
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My guess is that the sales guy is just trying to shoe-horn you into the only frame they have on hand. I wouldn't consider buying from a shop like this.

It also could be that the sales guy is more of a racer or younger rider than you. Racier riders tend to like smaller frames so they can get the handlebars lower (shorter head tube). More recreational/relaxed, and maybe older riders tend to wand less drop to the handlebars so they like taller head tubes - which would steer them to larger frames.

All of this is within what is do-able for the rider. Meaning, if a person "could" fit a 50, 52 or 54 in any given frame, the racier rider would opt for the 50 (or 52) where the more relaxed rider would opt for the 52 or the 54.

What you should do is look at these dimensions of your current frame vs. the one he's trying to sell you:
"effective" or "horizontal" top tube length
Seat tube angle
Head tube length
Head tube angle
Maybe standover height

I don't bother looking at the seat tube length because depending on whether it's a slanting top tube or a horizontal top tube, they can be radically different.

They will give you a fairly good comparison between the frames and how you can get them to fit similarily.

How do these compare?
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Old 10-05-20, 05:31 AM
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Originally Posted by cxwrench View Post
You're kidding, right?
Kidding about what?
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Old 10-05-20, 07:26 AM
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Originally Posted by bruce19 View Post
Kidding about what?
He is incredulous that you placed emphasis on inseam/leg length. This is a minor factor, and quite adjustable on most bikes.

The more important measure, and the more difficult/costly to overcome, is the horizontal reach of the bike frame plus stem plus bars. In the sloping top tube world, this is the sum of effective top tube (length), plus stem reach, plus reach measure of the drop bars (and width to a lesser extent). The horizontal measure that these three factors afford is the more critical. That's what he was saying.
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Old 10-05-20, 08:08 AM
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I am the same height 170 cm. My ride is a Cannondale Synapse 4. At 53 cm I'm of the opinion that a 52 or 51 would be better it is the absolute biggest frame for me. I got is used.

My friend has a Trek Allez 54 cm and it seems to be the same size as my Cannondale.
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Old 10-05-20, 09:47 AM
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Originally Posted by Phil_gretz View Post
He is incredulous that you placed emphasis on inseam/leg length. This is a minor factor, and quite adjustable on most bikes.

The more important measure, and the more difficult/costly to overcome, is the horizontal reach of the bike frame plus stem plus bars. In the sloping top tube world, this is the sum of effective top tube (length), plus stem reach, plus reach measure of the drop bars (and width to a lesser extent). The horizontal measure that these three factors afford is the more critical. That's what he was saying.
^Exactly this^
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Old 10-05-20, 11:13 AM
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Originally Posted by Phil_gretz View Post
He is incredulous that you placed emphasis on inseam/leg length. This is a minor factor, and quite adjustable on most bikes.

The more important measure, and the more difficult/costly to overcome, is the horizontal reach of the bike frame plus stem plus bars. In the sloping top tube world, this is the sum of effective top tube (length), plus stem reach, plus reach measure of the drop bars (and width to a lesser extent). The horizontal measure that these three factors afford is the more critical. That's what he was saying.
This makes a lot of sense. I am 165cm tall and rode a 51cm Cannondale Synapse for several years. The bike shop told me it was a perfect size for me, but I ended up swapping the stem for a shorter one (80 mm vs 90) and replacing the handlebar with one that has shorter reach. (I was a pure novice back then.) After that I still felt stretched out, though I got used to it.

Now I just bought a 49cm Specialized Roubaix. OMG the difference was night and day. Everything feels very natural now. I wish I had known better.
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Old 10-05-20, 11:39 AM
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Originally Posted by Phil_gretz View Post
He is incredulous that you placed emphasis on inseam/leg length. This is a minor factor, and quite adjustable on most bikes.

The more important measure, and the more difficult/costly to overcome, is the horizontal reach of the bike frame plus stem plus bars. In the sloping top tube world, this is the sum of effective top tube (length), plus stem reach, plus reach measure of the drop bars (and width to a lesser extent). The horizontal measure that these three factors afford is the more critical. That's what he was saying.
I use the LeMond-Guimard method which starts with inseam. And, I have found that seat tube size and TT size are very often pretty close. I've also found adjusting stem length to accommodate reach is not a difficult task. This has worked for me for 40 years so far.
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Old 10-05-20, 12:08 PM
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Originally Posted by bruce19 View Post
I use the LeMond-Guimard method which starts with inseam. And, I have found that seat tube size and TT size are very often pretty close. I've also found adjusting stem length to accommodate reach is not a difficult task. This has worked for me for 40 years so far.
But with sloping geometry, seat tube size goes out the window, doesn't it? I know it's a critical measurement, along with TT length, when sizing a frame with a level top tube, but we're no longer in the days of "a fistful of seatpost above the clamp".

When I bought a new bike this year, I had to go back to my other 3 bikes and figure the stack and reach, because even as late as 2006 Bianchi didn't include those measurements in their geometry chart. It took me three nights with a tape measure, a beam level, and an Excel spreadsheet for me to determine what size bike I'd have to get to replicate the fit I have on the other three bikes.
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Old 10-05-20, 02:10 PM
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Originally Posted by Mulberry20 View Post
I am 5í9 with a 31 inch inseam and the Trek employee tried me on a 52cm Emonda. It was way too small.

You border a 52 and 54 I would think.
That is my take. I am now 5' 8.5" and now ride a 55cm. I had downsized due to age shrinking as my old bike was a 57cm frame (was 5' 10" when I got it). It fit in college, but was now aa bit tight 43+ years later.

5 years ago, I was looking for a new steel frame bike and my research was pointing my towards a 'cross type of design so I could do canal towpaths, some dirt roads, and paved road. The first LBS tried said I needed a 52-53 During my test ride, I felt like I was hovering too forward over the front wheel, that the seat post was too long, and out of the saddle riding felt very twitchy, plus I was getting toe overlap with the front wheel.

I went to another store and the owner said try a 54, but it was not available in a bike I liked. I was going to leave, but he asked about my then current bike and we got to chatting and he said, I might like a 55, based upon my riding and prior bike sizing. I tried the floor model and really liked it, and was going to buy it and he said I should think about it and he would hold it if I wanted to come back the next day with my old bike and test them back to back on the MUP that ran right next to the shop. I took advantage and did that. He even swapped in my old saddle and post for the test. I was sold. He said when he saw the old bike with the relatively long top tube, and my riding positions that I would probably be happier and do better with a 'traditional' fit, or as some call it, a 'French fit'

He then told me they had received a new shipment. It was the new year, same bike with a better color (black frame) but identical component selection (silver components - yes!) and I could take the new color or the old. I picked it up next day, with a whole package of the individual component manuals, owner manual, and their standard offer of free adjustments for a month as well as an offer of a stem swap if I found the reach needed a tweak as long as the stem was not scratched of altered. He said I would probably not need it as he had measured the old bike dimensions. I did not need a stem swap. My only changes/upgrades have been a Brooks Cambium saddle in Rust, a Nitto 83 seat post, and a second wheel set.

Many shops recommend a far smaller size due to the many current compact frames, although the gravel bike trend is beginning to shift that mantra towards a more open design. You just have to try and test the recommendations. Trying up (or down) a size may be what you like.
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Old 10-05-20, 02:27 PM
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Originally Posted by genejockey View Post
But with sloping geometry, seat tube size goes out the window, doesn't it? I know it's a critical measurement, along with TT length, when sizing a frame with a level top tube, but we're no longer in the days of "a fistful of seatpost above the clamp".
Exactly...add to this that different brands measure to different locations and the seat tube measurement is pretty much meaningless these days. So is actual top tube. Effective top tube was a thing for a few minutes but then everyone decided to include 'reach' and 'stack' so you can now compare bikes from different brands much more easily.
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Old 10-05-20, 02:51 PM
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Originally Posted by genejockey View Post
But with sloping geometry, seat tube size goes out the window, doesn't it? .
Actually it doesn't. Just use a virtual TT intersection with the seat tube to measure actual seat tube.
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