# How do you conclude the type of a road bike from a geometry table—using one specific example?

The boundaries between the different types of road bikes are not firm. If the boundaries are indeed fluid, then one bike builder might label a bike as, say, a racing bike, but it would in fact not be a pure racing bike. I'd like to understand what will reveal the bike type, with the objective of being able to determine where exactly a bike fits on the continuum of bike types.

To reach this understanding, I will provide you with numbers from a geometry table for a road bike, without specifying brand, model, or type of bike.

Although I am asking you to tell me what type of road bike it is, I don't really care about that answer. I extracted the numbers myself and I know the (purported) type. What I do care about is your explanation: How did you reach your conclusion? What in the numbers revealed the road bike type?

• Wheel Size 700C
• A - Seat Angle 73.3°
• B - Top Tube (mm) 570
• C - Head Angle 73.0°
• D - Offset/Fork Rake (mm) 45
• E - Head Tube (mm) 170
• F - BB Drop (mm) 68
• RC - Chainstay Length (mm) 415
• FC- Front Centre (mm) 598
• Stack (mm) 562
• Reach (mm) 396
• WB - Wheelbase (mm) 1004
• G - Seat Tube C-Top (mm) 530

##### Related
• A common measurement is the effective seat tube length. It's a shame that's not given here. That would be found by continuing line G until it intersects the line labelled Reach Commented Dec 6, 2022 at 14:51
• @ChrisH When we're talking (or used to talk) about a frame of size 17", 19", etc, were we really talking about the effective seat tube length of the frame? Commented Dec 6, 2022 at 16:20
• once upon a time it was the real seat tube length. These days theoretically it's the effective length, but the manufacturer has a bit of room for creative labelling. Commented Dec 6, 2022 at 16:28

This is an artificial question, because when buying modern bikes, you will be able to tell from marketing materials, reviews, and other cues what the bike's intended use is. Alternatively, you should roughly know the stack and reach numbers (and possibly other parameters, e.g. seat angle) for the type of position you want to achieve. If the bike grossly mismatches those numbers, then it's wrong for you.

I assume the main distinction we care about is racing vs endurance bike. You are correct that this may be more like a continuum with no clear cut point. In geometry terms, one of the key metrics may be the stack to reach ratio. That ratio tells us how upright the bike is (but note that this is measured to the top of the headset; you can modify this somewhat by changing the final handlebar position).

I normally ride about a size small, so I'm not familiar with geometry norms for other sizes. Judging by the top tube length and other cues, I think this is a large-ish frame (i.e. it may be the nominal size large or medium-large). I would compare the stack and reach numbers to bikes similar in size. I don't know these off the top of my head. I think that this is an endurance bike, as 562 is objectively quite a high stack (although the reach seems long as well; I'd have to compare to norms for the frame size).

There are a lot of other factors not captured by stack to reach ratio, however. I'd expect endurance bikes to have more comfortable ride characteristics (influenced by the layup schedule if carbon, choice of material and tube diameters and thicknesses if metal). If there are fender mounts, it's much more likely to be an endurance bike. Wider tire clearance may also indicate that it's an endurance bike. To some extent, trail and head angle can be indicative of a race or endurance bike, although you have to know the averages for the size of bike you're looking at - which wasn't supplied in the question. On endurance bikes that are medium to large in size, I'd normally expect a less than 73 degree head angle - but I normally ride size small bikes if shopping stock, so I don't know for certain. Wheelbase may also be indicative, with endurance bikes possibly having longer wheelbases.

• @Sam can you explain why do you want an endurance bike, and if you can't select based on frame geometry, why don't you use other criteria?
– ojs
Commented Nov 12, 2022 at 21:24

The differences between road bike categories are more marketing than geometry (for example, years ago Bianchi had "racing" and "C2C" aka coast to coast comfort lines of road bikes that had identical geometry). The most significant number in this example is chainstay length that puts upper limit to tire size and effectively says that this is not a gravel or cyclocross bike.

Some numbers are completely insignificant: With sloped top tube the seat tube length doesn't tell anything useful because you would never put the saddle below top of head tube, and different headset types can add anything from zero to couple of centimeters to effective head tube length (that not really useful without BB drop, and fortunately being replaced by stack).

In the past there used to be a difference between European and US-based brands, so that road bikes from American brands would typically have a couple of centimeters longer top tube for the same size. For most riders this would mean that on American-style bike they would fit a size smaller frame and use some spacers under the handlebar stem, but for someone with short legs it made a difference. As far as I can tell, this difference has mostly disappeared.

If you're looking for the \$10.00 answer, look elsewhere. The present answer is the \$0.02 one.

The tell-tale sign that a road bike is an endurance road bike is that it will have a long head tube.

Likewise, seeing a short head tube on a showroom floor means you're looking at a racing road bike.

This does not help you in the absolute, because a size XL, 61 cm, or similar racing bike will still have a sizeable head tube. But if you look only at medium, or 54 cm, frames, you should clearly see the difference between an endurance and a racing road bike. At some point (medium? small?) the head tube on a true racing bike will be so small it will seem that the top tube and the down tube meet nearly at a point.

Why "should"? Because there are too many bike builders, and there is no formal definition for what constitutes one type or another of bike. You may find in the details "this bike is intended to blur the lines between an endurance and a racing bike", despite that the heading declared as one type or another at the outset. You're then on your own determining whether it's closer to this or that.

The longer head tube will mean that your posture will be more upright. The smaller head tube means your back is arched quite steeply. It may be a more aerodynamic position, but it's not the most comfortable to maintain for a long day.

This answer is work-in-progress. Determining the type of the bike in the question is only possible if we: 1- determine whether it is "medium", and 2- compare its head tube, as one litmus test, with other bikes of the same or similar size. In other words, the conclusion is in general not a Boolean "endurance" or "racing". It lies in general on a continuum.

• For what it's worth, in the case of Origine (French manufacturer), they offer their frames in endurance (GTO) and race versions (GTR). The geometry/molds are the same, both are proposed with different head tubes lengths (for a same size). The difference between the two is only the layout of the carbon, race versions being more stiff. Commented Jan 3 at 11:32
• @Renaud. Sure, I'm a believer. And that makes perfect sense. What I find most perplexing is when I read a claim that a frame (an endurance frame, specifically) remains strong to counter-act arm-muscles injected into the handlebar despite being supple to absorb vibrations. See engineering.stackexchange.com/q/54904/36266 . Notice that I'm not saying that it's false or that it's impossible, only that my engineering sense is unable to grasp the possibility of this near-Utopian construction. Commented Jan 4 at 1:41
• And if the area around the headtube is the same, and vibration absorption is the role of the fork? I don't see why it should be the role of the headtube. Commented Jan 4 at 7:14