DND_Reborn
The High Aldwin
Well, I think the hardest thing is getting a proper balance between accuracy and simplicity.
Following the information on chases, you can dash for 3 rounds + your Constitution modifier. Each round after, you make a DC 10 Constitution check or suffer a level of exhaustion.
Honestly, I think this is too low. First I would increase the number of rounds by your proficiency bonus if you have proficiency in Athletics. Second, I would change it to a DC 10 Constitution (Athletics) check to avoid the level of exhaustion.
Now, on to altering the Dash action:
Dash
When you take the Dash action, you gain extra movement for the current turn. The addition equals your speed, after applying any modifiers, plus 5 times your Strength modifier.
When you take the Dash action, you can use your Bonus action to run.
Running. You make a DC 5 Strength (Athletics) check and the additional movement you gain from dashing is doubled. Each round you spend running or sprinting increases the DC by 1.
When you take the Dash action , and use your bonus action to run, you can use your reaction to sprint.
Sprinting. You make a DC 10 Strength (Athletics) check and the additional movement you gain from dashing is tripled. Each round you spend running or sprinting increases the DC by 1.
Examples:
A character with STR mod +3 would be able to move (30) and either: dash (45), run (90), or sprint (135). Thus, moving and "sprinting" would have a total movement of 165 (30 + 135). This would be a 11.93 second 100-m sprint.
A character with STR mod +5 would be able to move (30) and either: dash (55), run (110), or sprint (165). Thus, moving and "sprinting" would have a total movement of 195 (30 + 135). This would be a 10.09 second 100-m sprint, so falls short of the current world record. But for races like Wood Elf, or using feats like Mobility, or classes like rogue and monk, you could be faster than the WR.
Now, I toyed with the idea of using proficiency bonus instead of STR mod, but with expertise the numbers become ridiculous. I also toyed with the idea of making a check and increasing speed by the result, as @doctorbadwolf did.
Following the information on chases, you can dash for 3 rounds + your Constitution modifier. Each round after, you make a DC 10 Constitution check or suffer a level of exhaustion.
Honestly, I think this is too low. First I would increase the number of rounds by your proficiency bonus if you have proficiency in Athletics. Second, I would change it to a DC 10 Constitution (Athletics) check to avoid the level of exhaustion.
Now, on to altering the Dash action:
Dash
When you take the Dash action, you gain extra movement for the current turn. The addition equals your speed, after applying any modifiers, plus 5 times your Strength modifier.
When you take the Dash action, you can use your Bonus action to run.
Running. You make a DC 5 Strength (Athletics) check and the additional movement you gain from dashing is doubled. Each round you spend running or sprinting increases the DC by 1.
When you take the Dash action , and use your bonus action to run, you can use your reaction to sprint.
Sprinting. You make a DC 10 Strength (Athletics) check and the additional movement you gain from dashing is tripled. Each round you spend running or sprinting increases the DC by 1.
Examples:
A character with STR mod +3 would be able to move (30) and either: dash (45), run (90), or sprint (135). Thus, moving and "sprinting" would have a total movement of 165 (30 + 135). This would be a 11.93 second 100-m sprint.
A character with STR mod +5 would be able to move (30) and either: dash (55), run (110), or sprint (165). Thus, moving and "sprinting" would have a total movement of 195 (30 + 135). This would be a 10.09 second 100-m sprint, so falls short of the current world record. But for races like Wood Elf, or using feats like Mobility, or classes like rogue and monk, you could be faster than the WR.
Now, I toyed with the idea of using proficiency bonus instead of STR mod, but with expertise the numbers become ridiculous. I also toyed with the idea of making a check and increasing speed by the result, as @doctorbadwolf did.