One of the big talking points about disc brakes recently is the use of mountain bike rotors on road bikes. This first came to light in the 2019 Road World Championships in Yorkshire, where Maciej Bodnar was spotted using an XTR rotor in the rain-soaked race.
Things came to light in the 2020 Tour de France when the pros such as Julian Alaphilippe, Adam Yates, and Marc Hirschi were spotted using XTR mountain bike rotors on their road bikes instead of the Dura-Ace rotors.
In September 2021, Shimano launched the 12-speed Dura-Ace and Ultegra road groupsets with XTR mountain bike rotors. In mid-2022, Shimano finally launched an updated Dura-Ace rotor to pair with the 12-speed road groupsets.
So what are the differences between a Shimano Dura-Ace and XTR rotors?
Naming Convention
Both the Dura-Ace and XTR rotors have 900 at the end, which indicates they’re Shimano’s top-of-the-line models. Pay attention to the letters before the 900.
RT for road bikes and MT for mountain bikes.
- Dura-Ace (12-speed) : RT-CL900
- Dura-Ace (11-speed) : SM-RT900
- XTR : RT-MT900
All three rotors are cross-compatible with each other.
Rotor Design
The rotors use the Shimano ICE and Freeza Technologies for efficient heat dissipation. The main difference lies in their design.
Dura-Ace rotor design
- Both have four arms that curve with the wheel rotation connecting to the braking surface.
- Dura-Ace SM-RT900 rotor has larger cooling fins which makes them look more solid and aero.
- Dura-Ace RT-CL900 rotor has cooling fins only where it’s needed most, with more significant gaps between the fins and arms.
With the smaller fins on the Dura-Ace RT-CL900, cooling and heat dissipation could be slightly compromised, but generally, this is not an issue as the brakes aren’t designed to be continuously dragged down a descent.
XTR rotor design
- Four arms at a 90º angle for 140mm and 160mm, and five arms for 180mm and 203mm rotors to provide additional strength.
- Cooling fins are placed where needed most, with larger gaps between the fins and arms.
Braking performance
With the difference in rotor design, many have claimed that the XTR rotors have a slight edge in braking performance. This is because the pros use them on the long and steep descends in the Tour de France, where the braking performance is tested to its limits.
Besides that, many also assumed that because they’re designed for mountain bikes, they should perform better.
From my point of view, it’s hard to quantify these, but they do hold some truth in them, with the fact being somewhere between those two arguments. To further strengthen this argument, the Dura-Ace RT-CL900 looks similar to the XTR rotor design.
Rotor weight
One of the main reasons cyclists, especially the weight weenies, prefer the XTR rotors is because it’s lighter.
The Dura-Ace RT-CL900 and SM-RT900 have the same overall weight of 210g with a 160mm front and 140mm rear combination.
A road bike with 160mm front and 140mm rear rotor could save up to 20g just by switching to XTR rotors.
| Series | Model no. | Rotor size | Weight |
|---|---|---|---|
| Dura-Ace (12-speed) | RT-CL900 | 140mm | 96g |
| Dura-Ace (12-speed) | RT-CL900 | 140mm | 114g |
| Dura-Ace (11-speed) | SM-RT900 | 140mm | 94g |
| Dura-Ace (11-speed) | SM-RT900 | 160mm | 116g |
| XTR | RT-MT900 | 140mm | 85g |
| XTR | RT-MT900 | 160mm | 106g |
| XTR | RT-MT900 | 180mm | 132g |
| XTR | RT-MT900 | 203mm | 150g |
Rotor sizes
The Dura-Ace is meant for road bikes, they’re only available in;
- 140mm
- 160mm
The XTR, which is Shimano’s mountain bike range is available in;
- 140mm
- 160mm
- 180mm
- 203mm
One important thing to note about the 180mm and 203mm XTR rotors is the design. They have five instead of four arms to provide the additional support needed.
Pricing
Pricing-wise, the Dura-Ace and XTR rotors differ between $5 to $10.
The challenge many cyclists face is the availability of the XTR 140mm rotors, as they’re hard to come by since there are not many mountain bikes that use them these days.
| Model | Model no. | Rotor size | Retail price (USD) |
|---|---|---|---|
| Dura-Ace (12-speed) | RT-CL900 | 140mm | $86 |
| Dura-Ace (12-speed) | RT-CL900 | 140mm | $86 |
| Dura-Ace (11-speed) | SM-RT900 | 140mm | $82 |
| Dura-Ace (11speed) | SM-RT900 | 160mm | $82 |
| XTR | RT-MT900 | 140mm | $80 |
| XTR | RT-MT900 | 160mm | $80 |
| XTR | RT-MT900 | 180mm | $85 |
| XTR | RT-MT900 | 203mm | $85 |
What are the similarities between these rotors?
We’ve discussed the differences, but there are also some similarities between them that you should also know about.
- Shimano’s top-of-the-line rotors. The Dura-Ace is for road bikes, and XTR is for mountain bikes, although they’re cross-compatible.
- ICE Freeza Technologies is Shimano’s latest technology to cool down the rotors for consistent performance, especially during hard braking. The rotors have a three-layer sandwich structure; stainless steel, aluminum, and stainless steel. The Freeza is where the aluminum extends into the cooling fins for better heat dissipation.
- Centerlock (AFS). Both are Centerlock rotors and will fit all of the disc brake wheelsets. Older wheels that use a 6-bolt pattern will need an additional adapter.
- Brake pads. They work with Shimano’s and other third-party road bike brake pads for the R9200, R9170, R8100, and R8070 calipers. Brake pad compatibility is the function of the brake calipers and not the rotors.