How this instrument works
When a breakaway group rides away from the main field, the gap between them changes at a rate set by the difference between the two groups' speeds — their closing speed. If the chase is faster than the break, the gap shrinks steadily; the closing speed tells you exactly how many kilometres of gap disappear per hour, and dividing the current gap by that rate gives an estimated time until the two groups meet.
This instrument takes the gap distance in metres and both groups' speeds in km/h, converts the gap to kilometres, divides by the speed difference, and scales the result into minutes. It's the same closing-speed estimate cycling broadcasts and team directors use on the road to judge whether a break up front has a realistic chance of surviving to the finish, or is about to be swallowed.
The estimate assumes both speeds hold constant, which real racing rarely does exactly — a peloton often eases off once a gap looks safely manageable, breakaways can lift their pace near the finish, and terrain changes both groups' effective speed differently depending on group size and drafting. Treat the result as a working estimate to check against the actual gap as the race unfolds, not a guaranteed catch time.
- Enter Gap distance (m) — the current time gap converted to a distance, or a distance gap reported directly by race radio.
- Enter Chasing group speed (km/h) — the average speed of the group doing the chasing.
- Enter Breakaway group speed (km/h) — the average speed of the group up the road.
- Read Time to catch (minutes) — the estimated time until the gap reaches zero, assuming both speeds hold steady.
- The chasing group's speed must be greater than the breakaway's, or there is no catch to estimate — the instrument will prompt you if the two are equal or reversed.
Worked example — a 1,000 m gap closing at 5 km/h
Enter 1000 into Gap distance (m), 45 into Chasing group speed (km/h) and 40 into Breakaway group speed (km/h) — a peloton riding 5 km/h faster than a break that's a kilometre up the road. Time to catch reads 12.00 minutes.
That comes from a 1 km gap (1,000 m ÷ 1,000) divided by the 5 km/h closing speed (45 − 40), giving 0.2 hours, then × 60 to convert to minutes, giving 12.00. In other words, at that 5 km/h closing speed the peloton pulls back roughly 83 metres of gap every minute, and the full kilometre disappears in exactly 12 minutes if both groups hold their pace.
Questions
What happens if the two speeds are equal?
The gap never closes — if the chasing group and the breakaway hold identical speeds, the distance between them stays constant forever, and there's no finite catch time to calculate. This instrument requires the chasing speed to be strictly greater than the breakaway's speed before it will return a result.
How accurate is this in a real race?
It's a working estimate, not a guarantee — real closing speeds shift constantly as terrain, wind, group size and tactics change. Team directors and broadcasters use exactly this closing-speed calculation as a live rule-of-thumb, updating it continuously as the actual gap is reported, rather than treating a single calculation as the final answer.
What's a realistic gap for a breakaway to survive to the finish?
It depends heavily on the closing speed a chasing peloton can sustain and how many kilometres remain, so there's no single number — a gap that comfortably survives on a hilly, technical stage can evaporate quickly on a flat run-in favouring a fast, organised chase. This calculator's job is only to translate a specific gap and pair of speeds into an estimated time, which you then weigh against the distance left to race.
Why does group size matter to the closing speed, even at the same rider effort?
A larger group can rotate riders through the front and share the aerodynamic workload, letting it sustain a higher average speed than a small break can manage at a similar per-rider effort, since each small-group rider spends more time exposed to the wind. That's the physical reason a big, organised peloton very often closes down a small breakaway even when the riders up front are working just as hard.
What is 'closing speed' in physics terms?
Closing speed is the relative velocity between two objects moving in the same direction — mathematically, the difference between their two speeds. If a chasing group and a breakaway are both moving forward but one is faster, subtracting the slower speed from the faster one gives the rate the gap between them shrinks, which is exactly the quantity this calculator's denominator represents.