The main difference between the two shoes are:
- The ASR4 have a larger toe box - this is a much needed feature for running down steep hills
- The ASR4 have a more durable "water resistant" upper - they do not keep any water out, this is a bad feature as they do not dry out as fast as the road version and your feet remain wet longer while running, but they are more durable
- The ASR4 have a much more aggressive tread pattern
- The ASR4 have a beefier toe guard
- The ASR4 are somewhat stiffer than the road version, but not too stiff as you can used them on the road with no regrets
The main similarities between the two shoes are:
I have wore the ASR4s to train on trails and asphalt. The normal local trails I run require a few miles on the pavement prior to hitting the trail. The shoe has proven itself and I would wear it for easier trail running or even road running. It is a great crossover shoe that can meet all your needs. If you can only have 1 pair of shoes for trail and road these are the shoes.
In addition to training I have wore the ASR4s to run the Holiday Lake 50K ++, the Promise Land 50k, and for the majority of the 70 mile Laurel Highlands Ultra. These shoes did not let me down. These races go from easy fireroad terrain at Holiday Lake to nasty rocky rooty single track at Laurel Highlands. I had no issues with the shoes. In fact at Laurel Highlands I started off the race with Hardrocks and was kicking rocks at least once per mile, upon switching to the ASR4s at mile 19 I stopped kicking rocks (Hardrocks are heavy) and me feet were much happier. I am a backpacker and there is an old saying that a pound on the foot is like 10 pounds on the back. This proved to be true as the lighter ASR4s served me much better than the heavy "bomb proof" Hardrocks.
- Great Crossover Shoe, wear on the road and the trail
- Fairly Light and flexible
- Brooks technology
- Great fit and feel
- Large Toebox
- Good Traction
- Just enough protection
- Water resistant upper does not allow fast "on the run" drying of the foot.
Note: I wore the ASR4s with smart wool socks at Promise Land and developed bad blisters on the balls of both feet after a stream crossing. I switched to Injini socks for Laurel Highlands and had wet feet for the entire run with no blisters on the balls of my feet. Problem solved for now.