AllRoadsRacing.com’s guide to Shimano DI2 12-speed

 

This guide is intended to be used as a purchasing guide for buying a complete DI2 performance road groupset. We primarily seek to answer these questions:

1. What are the most meaningful differences between Dura-Ace, Ultegra, and 105?
2. Is there a more optimal outcome by mixing groups? 
3. What are the major competitive differences with SRAM AXS?   

This guide is not intended to be technically comprehensive in all details of these group-sets, it is intended to weigh the most meaningful differences in performance, weight, and cost. 

What are the most meaningful differences between Dura-Ace, Ultegra, and 105?

When reviewing the Dura-Ace and Ultegra 12-speed groups the story is fairly simple; performance wise these two groups share all the major technologies: they both have the servo-wave brakes (think more powerful lever feel for the hydraulic disc brakes) like the mtb groups and gravel groups, and they both have the new Hyperglide+ gear, tooth, and chain profiles- (think better faster shifts). So the meaningful differences come down to weight and cost. 

	weight	cost
Dura-Ace	2507g	$4,310.88
Ultegra	2707g	$2,622.87
105-DI2	2992g	$1,664.87

There is a $1688 price jump going from Ultegra to Dura-Ace that gets you an approx 200g weight reduction, less than half a pound. That jump in cost is getting you higher end materials but there is obviously a diminishing return. 

The story gets a little more interesting when you compare Ultegra to 105. The 105 DI2 group has three key performance differences. First, riders do not get the servo-wave braking tech, secondly, they do not get the new shifting tech in the front derailleur, and lastly, they don't get the Hyperglide+ tooth and chain profiles. It is clear the focus of the 105 group was to bring the new wireless shifting down to 105’s price point. 105 DI2 does have the unique feature of having double coin cell batteries in the shifters vs. the single coin cell batteries in each Dura-Ace and Ultegra shifter units. This extends the 105 shifters’ battery life to 3 years approx from 1.5 years. Shifter battery life was prioritized over weight in 105. 

These changes raise the question: “should a performance enthusiast or privateer racer pass on 105 DI2 for one of the higher end groups? 

We don't think so, in terms of performance there are many road riders that still have not switched to disc and may still feel reluctant to switch feeling that discs may be too grabby or too disstabilizing relative to the rim brake they have used exclusively until now. Are the 105 brakes weak because they don’t have the servo-wave leverage? No, but they will require the rider to squeeze harder to achieve the higher levels of stopping power. This lower leverage braking feel will probably feel more natural to rim brake enthusiasts and may make the transitions to disc brakes easier for riders with this type of concern. 

Is 105 DI2 shifting bad? No, it is competitive and on par with 11-speed Dura-Ace in terms of shifting speed. Hyperglide+ and the new derailleur tech in 12-speed Dura Ace and Ultegra is superior by delivering lightning fast shifts and we feel consensus is building that hyperglide+ shifts extremely well under heavy load. Additionally, riders wanting the superior shifting of the newer front derailleur and the Hyperglide+ tech should note there is a relatively inexpensive upgrade that can be done to bring the 105 DI2 group up to the Hyperglide+ level shifting (see more in next section) 

On price, there is a $958 price jump to go from 105 to Ultegra. That price jump gets you the superior servo-wave braking, the new front derailleur, and Hyperglide+ shifting tech and it also saves about 285g or little over half a pound 

So, who should buy or be riding each group?: We feel the best match for Dura-Ace is a professional level athlete that is looking to accumulate marginal gains or an enthusiast working with a generous budget. We think most performance enthusiasts and privateer racers should be on Ultegra, the Ultegra group offers the best balance of all the newer tech, competitive weight, and is meaningfully less expensive than Dura-Ace. We think the ideal match for 105 Di2 will be enthusiasts that prioritize cost savings and delaying cost through upgradability. We think 105 DI2 would also be a strong match for riders that are reluctant first time disc converts that want a more rim-brake like feel.  

Is there a more optimal outcome by mixing groups?

Whenever we look at the different tiers of groupsets we always get the question “is there a more optimal group to be had by mixing parts or groups?”. In general, we think Shimano did a good job of keeping the thesis of each level consistent but we did come up with a few ideas for those looking to performance hack their group. We will take a look at our two best options here, an upgraded Ultegra group and an upgraded 105 group. 

What is the best way to upgrade the Ultegra group? 

Consider this; the Ultegra group is only 200g heavier than Dura-Ace but it’s $1688 less expensive, but what if I told you can drop that weight difference by 92g, from 200g heavier to 108g heavier, for only $248 additional? - Let that sink in, you would be getting almost half at 46% the weight savings for only a 15% of the cost difference. Well you can do this by buying the DuraAce cassette instead of the Ultegra cassette.

Cassette weight in grams 11-34T
	DuraAce	253
	Ultegra	345
	delta	92
Cassette cost in USD$
	DA	$359.99
	Ultegra	$111.99
	delta	$248.00

   

What is the best way to upgrade the 105 group? 

While the Ultegra was easy to upgrade with a single part things are more complicated with 105 but we think we still have some good options. There is no inexpensive way to upgrade the brakes to servo-wave tech, but there is a fairly easy way to upgrade 105 DI2 to the ultra fast shifts of Hyperglide+. This can be done by upgrading the front derailleur to Utegra (that has the new internal hardware) and the Ultegra cassette which has the Hyperglide+ teeth profiles. The front derailleur will run you $107 extra and the cassette is only $46 extra, so for basically $153 additional you get the latest shifting tech (the 105 rear derailleur already has the new internal electronic hardware). These two upgrades will also save you 47g in weight.  

What are the major competitive differences with SRAM AXS?

We wanted to comment briefly on what we see as the benefits of going with a Shimano DI2 group versus the SRAM AXS family of road groups. This is not intended to be a comprehensive comparison, but more briefly commenting on the most meaningful differences.

We think the differences boil down to four major areas:   

1. Battery strategy
2. 10t cogs
3. Shifting speed  
4. Installation difficulty

Battery / Charging Strategy 

Shimano and SRAM are now similar in that both road groupset families now have wireless shifters powered by coin cell batteries. They differ in that SRAM’s derailleurs are fully wireless utilizing a small proprietary cartridge battery that plugs into the derailleurs. Shimano drops the junction boxes and extra connecting wires of 11-speed DI2 for a much simpler system of wiring just the derailleurs to a single seatpost internal battery. There are two cool things about the Shimano system, first you can plug your bike via the rear derailleur directly into the power source via the charging cable. This makes it easy to leave a charger where you store the bike and let it charge. As long as you remember to charge you will have power, while with AXS there are more places for errors to occur. If you forget to bring your batteries, forget to charge them, forget to plug in the charger, or forget to reinstall them after charging you could potentially miss your ride or event. So, while having fully wireless may sound more technically advanced there is little to no benefit in ensuring your bike is always ready to go. 

10t Cogs 

Having the 10t cog is marketed as giving a groupset more range, but consensus is building that cogs this small suck alot of energy or watts. The more the chain has to wrap around the cog the less energy efficient it is going to be. Shimano passes on this with their road groups

Shifting speed      

AXS derailleurs do not shift as fast as 11-speed DI2, 12-speed DI2 at the DuraAce and Ultegra levels shifts noticeably faster than 11-speed. When considering this a narrative starts to build where AXS is really offering the novelty of a full wireless group, where Shimano’s 12-speed DI2 derailleurs combined with their Hyperglide+ teeth and chain profiles offer the very real performance benefit of hyper-fast shifts. These extremely fast shifts translate into a group that shifts extremely well under load in high stress race situations.  

Installation difficulty

Ease of installation is often marketed as the key selling point for AXS. We agree not having to route wires or shifting cables is a benefit, Shimano is not fully wireless but has significantly improved in ease of installation. Shimano DI2 12-speed will require a wire routed from the seatpost battery to the front derailleur and another from the battery to the rear derailleur. This is not difficult to achieve and we feel there are benefits to  allowing the derailleurs to share one power source as well as making charging the whole system super easy through the rear derailleur and charging cable. Additionally we feel it is worth pointing out that once a bike is built there is zero installation benefit while actually riding. 

Final thoughts

So, what we think we have presented here is what the major differences are between the three levels of Shimano 12-speed road groups, a few suggestions for mixed groups, and how the Shimano road family differs from SRAM’s AXS family of road groups. Overall we feel Shimano has delivered a vey compelling platform with three distinct levels. Which one is best for you will likely depend on your budget and your performance needs.  

What about gravel?

The lines between road and gravel continue to blur. Many top manufacturers are now offering road models with tire clearance up to 35-40mm tires. This allows the owner to throw a set of gravel tires in their primary road bike to do gravel events. It is also worth noting the somewhat controversial Gravel Worlds event held in Europe where many top athletes and teams opted to use road bikes with 35mm tires to race the gravel (grassy in many areas) event. This raises the question: “should a rider use 12-speed road groups or 11-speed GRX groups for gravel events?”. We think that is not an easy question to answer for a few reasons. The DuraAce and Ultegra 12-speed groups now have powerful servo-wave brakes (like mtb and gravel groups). The two major differences between the 12-speed road groups and the 11-speed GRX groups is the road groups do not have a clutch system in the rear derailleur, we are guessing the higher gear ratios shift faster without a clutch engaged, and the GRX shifters have some texturing in the hood covers that allow better grip. We are assuming the road hoods have been kept fairly smooth for aerodynamic purposes. Depending on the event these differences might not matter. We do not feel that running a road group would put the gravel racer at a disadvantage given they are using appropriate gear ratios for the given event. The other thing worth considering is there are already rumors of a 12-speed GRX group in the pipe. 

Thank you- Keyth Beck 

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