Building a carbon gravel bicycle - Shimano 105 7020 vs GRX RX600/800

Question

I've got into cycling around two years ago, mainly going to the office and cycling around the city/when traveling. Around two months ago I started experimenting with long-distance and speed, and realized that my bike is not very well-equipped for it.

After some research, I realized that I would need a gravel bike with enough flexibility to change the road tires for off-road depending on the itinerary (maybe from 25 to 32cc). This type of bike would allow me to achieve good speed, but also to get off-road without compromising the integrity of the bike.

I searched in stores and online for a quality bike that would align with these objectives and my dimensions (180cm height and 90=>85kg), and got a bit confused. There are many brands of bikes and components, but only a few that are really trusted, and I found them relatively expensive for my budget. After some frustration, the idea of building my own custom bicycle came to my mind.

Anyhow, I decided to go on a carbon direction and to choose some good quality components. The total weight of the bike should be below 8kg by the end of the build, and should be capable of giving me enough power and flexibility.

Here is the list of items for the build, with the prices and relative weights: spreadsheet

I couldn't find so much information about this, but some people recommend Shimano GRX600/800 over 150 7020, but I couldn't understand the reasons of this, and I would like to make the right choice as it would be the most expensive component of my bicycle.

What are the main differences between these two, and is there a lot of difference between mechanical and hydraulic? Could I get a less expensive option to start?

Also, if someone with experience could review my list and tell me if there's something off or something that I could improve, and if I really need this high in my budget, or I could build it with less expensive gear?

Answer 1

There is some incorrect information in the other answer.

But hydraulic disc brakes aren't perfect either. All disc brakes suffer from extremely fast pad wear even in non-wet conditions. Also, hydraulic disc brakes don't offer good braking for heavy bike+rider+cargo combinations. Usually with rim brakes, it's at least possible to raise the rear wheel using the front brake. But with hydraulic disc brakes, you may run out of lever travel before that happens.

The first statement about pad wear is wrong. Disc brakes do not necessarily suffer from faster pad wear than rim brakes. The categorical statement about "extremely fast pad wear" is misinformation.

The second statement that disc brakes don't offer good braking for heavy bike systems is wrong. Disc brakes do generate greater braking force than rim brakes. If a disc brake provides insufficient braking for "heavy bike+rider+cargo combinations", that is because the manufacturer under-specced the brake for that bike's intended purpose. For example, a manufacturer might spec larger rotors (160mm is standard on road and most gravel bikes) or even 4-piston brakes (which do tend to be MTB rather than drop bar brakes).

Additionally, the discussion about rim brake systems is potentially misleading, because GRX does not support rim brakes at all. There are versions of the R7000 group that do support rim brakes, but we generally expect a 12s R7100 group to launch soon, and it probably won't support rim brakes.

The other answer advises you to think about what most of your riding is. This is admittedly correct. If you do most riding on-road and you occasionally venture onto tame gravel, then a 32mm slick tire is sufficient, and you could choose road gearing (e.g. 50/34 chainrings, 11-30 or 11-34 cassette). If you are mainly riding on gravel, then chances are that you'll want a 48/31 or 46/30 crank, because larger tires will increase your effective gearing. A 50/34 crank will be a bit steeply geared.

That said, if you take a gravel bike with gravel gearing that normally has 40mm tires and you mount 32mm tires on it for road use, chances are this is fine. It will decrease the stability of the bike a bit (i.e. decrease trail, which makes the handling faster). This will usually be manageable.

Answer 2

The difference between GRX600 and 105 is "variable": some components taken individually might be very similar and there can be overlaps between the ranges (brifters, cassettes, brake calipers,...), but Shimano like to offer their components as part of a system, so GRX offers some combinations that does not exist in 105 (for example 1x, brifters for dropper posts,...), and the same is true for 105 (larger chainrings, mechanical rim brakes,...).

GRX600 can be seen as 105 tweaked to be better at gravel riding (GRX800 as equivalent to Ultegra and GRX400 to Tiagra): clutch derailleur to have more chain stability on rough terrain (nice to have on 2x, critical in 1x). There are some minor variations in shape/angles/textures of the hoods, chainrings are smaller (46/30 vs 50/34 for example) to offer more climbing capabilities,... There are also differences in chainline, which is a benefit to have wider tires.

On mechanical brakes vs hydraulic, a further split needs to be done in practice: you have mechanical rim brakes, mechanical disc, and hydraulic disc brakes. Mechanical disc are often offered in entry level segments and in that case, they are not recommended over hydraulic brakes. In some applications (touring), they make sense, but then you need to find high quality components. Mechanical rim brakes are OK on road bikes, if you are fine with narrow tires, but if you want wider tires, disc brakes are the way to go. On gravel bikes, disc brakes also have another advantage: you can have a pair of 700x38 wheels for light offroad, and a pair of 650x47 for rougher offroad.

About your list, it seems to be a good spec for an endurance road bike rather than a gravel bike (recent endurance road bikes are perfectly capable on light gravel), but it depends ultimately on where you ride, and that is not explained in the question: if you have for example 15% slopes on gravel, a 105 groupset might not be the best option (because of the larger chainring).

The choice of tire is strange to me: 35mm is now fashionable on endurance road bikes, but the tread pattern is off-roadish. That will be a bad compromise on-road because of the treads, and bad off-road because of the width (and the implied higher pressure). The question implies that you want to have have a "road-bias", so better to have something with a smoother rolling band, and some knobs on the side for stability when cornering offroad (for example: Pirelli Cinturato Gravel H, Teravail Washburn, but there are many options, and these may not be available on your market...). If you plan to have something that works well on-road and light off-road, 40mm seems a better compromise to me: you can lower the pressure, which provides additional grip and comfort.

Also, if your budget is limited, two remarks:

• prefer aluminium over carbon for the frame ...but take a carbon seatpost.
• light weight for the bike is overrated, it can make a difference if you are competing, because marginal gains can make a difference, but if you ride alone or on a non-competitive way, the gains are often not worth the expenses. Some lightweight components also wear faster, which means higher maintenance cost. Also, if you want something a bit offroadish, some components are heavier, because they need to be heavier. It may not be a good compromise on weight to choose something less suitable (thinking about the tires here, I'll take the extra 200g without hesitation to have 45mm instead of 35mm).

Answer 3

My gravel bike is just a flat bar fitness bike with a carbon frame, disk brakes, a 105 group set and 38mm gravel tires mounted on alloy hookless rims (25mm internal width). I keep my tire pressure at 55 psi. Half of my riding is on paved bike paths and the other half is on gravel roads, dirt trails and rough pavement and the 105 group set works just fine. You really learn to appreciate gravel tires in wet conditions. You also really learn to appreciate a lighter bike when you get past 60 years old.

Answer 4

After some research, I realized that I would need a gravel bike with enough flexibility to change the road tires for off-road depending on the itinerary (maybe from 25 to 32cc).

My experience has been that you don't want to do this. Changing tires makes only sense if it happens rarely. For example, if you live in an area where ice and snow are common, you want the bike to accommodate summer and winter tires which you change twice per year. It's then up to you to choose between having two wheelsets with possibly full brake discs and cassettes installed, or installing the tires to the same wheelset which takes more time, requires less storage space, but costs less.

I ride on 28mm slick tires, and I have observed them to work extremely well for off-road. 32mm slick tires would be even better off-road without sacrificing on-road capabilities. Choose 32mm slicks and use them always.

It's a major misconception that riding on singletrack would for example require gravel tires, or a gravel bike, or worse, a mountain bike!

is there a lot of difference between mechanical and hydraulic?

Mechanical disc brakes should probably be avoided. They don't offer the same feel for braking that hydraulic disc brakes offer, require very frequent adjustment, and worse, in most models the adjustment needs turning two adjustment screws per brake as opposed to turning only one adjustment screw. (Some TRP Spyre models are an exception.)

Mechanical rim brakes have some benefits and drawbacks:

• The "road" caliper brakes should be avoided. They usually don't allow enough tire clearance.
• Cantilever brakes in my opinion are somewhat troublesome. At least on my Surly Long Haul Trucker, they tend to squeal. Also in the BR-R550 that I have are almost impossible to remove the cable from the brake for wheel removal. I need a separate Shimano SM-CB90 quick release to avoid several minutes of fighting with the cable removal.
• V brakes don't work with Shimano STI levers so you need special V brake drop bar levers. Of course this is not necessarily a bad thing: it encourages you to choose more durable bar-end shifters that you can operate with thick winter gloves. Also, typically V brake drop bar setups don't have enough barrel adjustment screw threads, meaning you may need as many as three barrel adjusters in the cable to allow adjusting for pad wear (adjuster #1: noodle with barrel adjuster, adjuster #2: Jagwire mickey on top of the noodle, adjuster #3: Shimano SM-CB90). This need for many barrel adjusters is caused by V brakes being long pull brakes and most adjusters not having enough screw threads for this long pull.
• All rim brakes have two wheel revolutions of reduced braking when the rim is wet. For experienced riders, this isn't a problem (when you anticipate the possibility to need to stop, you already clear the rims from water by gentle pre-braking). But for inexperienced riders, it may be a dangerous surprise.

But hydraulic disc brakes aren't perfect either. All disc brakes suffer from extremely fast pad wear even in non-wet conditions. Also, hydraulic disc brakes don't offer good braking for heavy bike+rider+cargo combinations. Usually with rim brakes, it's at least possible to raise the rear wheel using the front brake. But with hydraulic disc brakes, you may run out of lever travel before that happens.

Also, if someone with experience could review my list and tell me if there's something off or something that I could improve

Your tires seem to be optimized for off-road conditions. Think about how you actually use the bike. If you ride 10km to a forest trail, then 15km on the forest trail, then 10km back to your home, you are actually riding 20 km on road, and 15 km off-road, meaning your tires should probably be optimized for on-road conditions.

About the only situation where these special "off-road" tires make sense is if you carry your bike with car to an off-road trail, then ride on the off-road trail, then carry your bike with car back to your home. Or maybe if you happen to live very near an off-road trail, then special "off-road" tires might make sense.

I'd say for the vast majority of riders who think of themselves as off-road riders, actually ride more on-road than off-road, because they don't happen to live near the off-road trail.

Besides, I have serious doubts about the viability of your bike for off-road use. It seems you are optimizing everything for weight rather than durability. It's very odd to construct a bike that's only expected to survive smooth pavement, never any off-road paths, never any curbs, and then put off-road tires on it. For off-road, I would put more spokes on the wheels and maybe consider some other frame material than carbon fiber (and same for seatpost, stem, fork, handlebars, cranks, rims, in fact any load-bearing component).