William Dai

Born : 1969 Cat. M55 Ultrarunner since 2012

DUV-index ?Largest integer N such that the runner has at least N credited races of at least N km.

DUV-index+ ?Largest integer N such that the race distances provide at least N complete segments of N km in total. A single long race may therefore contribute several segments. See the DUV-Index tab for the detailed calculation. calculation details

Countries visited ?

United States

21,3%

Rank quotient ?This runner's calculation uses 97 eligible race(s): Σ(rank − 1) = 2 957; Σ finishers = 13 867. 2 957 / 13 867 × 100 = 21.32%. A win adds 0 to the numerator. Lower is better.

Totals

Ultras completed97

Km — ultra races7 574 km

> 100 km14

> 160 km13

> 24h2

Longest race191,2 km

3rd San Francisco Summer Solstice 24h — 20/6/2015

Km per year (ultra races)

341

2022

617

2023

486

2024

598

2025

180

2026

Race types (share of distance)

Road18,9%

Trail81,1%

Wins & podiums (ultra)

🏆 Win2

🏆 Win M2

🏅 Top 36

🏅 Top 3 M6

Longest winning streak1

Current streak0

Records

50 km4h00'47 100 km9h54'54 50 mi8h06'37 100 mi21h37'58 6 h48,81 km 24 h191,24 km

HISTORY

97 race(s)

Date		Race	Perf.	Rk
2026
09.05	100km	43rd Quicksilver 100 km Endurance Run	14:21:03 h	82
14.03	50mi	14th Marin Ultra Challenge 50 Mile Race	9:26:02 h	26
2025
29.11	28.4mi	40th Quad Dipsea Trail Run	5:41:43 h	62
11.10	50mi	39th Ruth Anderson Ultra 50mi	8:06:37 h	4
28.06	100mi	52nd Western States 100 Mile Endurance Run	23:33:00 h	80
06.06	100mi	24th San Diego 100 Mile Endurance Run	28:11:18 h	46
10.05	100km	42nd Quicksilver 100 km Endurance Run	13:34:43 h	30
22.02	50km	14th Montara Mountain 50 km Trail Run	5:30:27 h	9
2024
21.12	50km	12th Woodside Ramble 50K - Winter	5:22:00 h	17
30.11	28mi	39th Quad Dipsea Trail Run	5:38:38 h	65
29.09	50mi	42nd Dick Collins Firetrails 50 Mile	10:08:56 h	13
19.07	100mi	26th Cascade Crest Classic 100 Mile	27:49:47 h	48
04.05	100km	27th Miwok 100k Trail Race	12:49:40 h	56
02.03	50km	3rd North Marin Ridge 50km Run	5:28:30 h	3 🥉
2023
25.11	28mi	38th Quad Dipsea Trail Run	5:52:06 h	97
14.10	50km	37th Ruth Anderson Ultra 50km	4:29:31 h	14
30.09	50mi	41st Dick Collins Firetrails 50 Mile	9:28:54 h	10
03.09	50km	13th Crystal Springs 50 km Summer Trail Run	5:18:00 h	5
15.07	100mi	22th Tahoe Rim Trail 100M Endurance Run	27:46:39 h	24
13.05	100km	40th Quicksilver 100 km Endurance Run	14:46:01 h	38
08.04	50mi	15th Lake Sonoma 50 Mile Race	10:26:42 h	57
18.02	50km	11th FOURmidable 50K	5:33:46 h	53
2022
05.11	100mi	22nd Rio Del Lago 100 Mile Endurance Run	22:09:16 h	22
08.10	50km	36th Ruth Anderson Ultra 50km	4:55:39 h	12
24.09	50mi	40th Dick Collins Firetrails 50 Mile	10:41:45 h	19
07.08	50km	41st Skyline 50k Endurance Run	5:32:59 h	37
2020
14.03	50mi	7th Pioneer Spirit 50M	9:25:22 h	27
07.03	50km	31st Way Too Cool 50K Endurance Run	4:37:56 h	69
15.02	50km	8th FOURmidable 50K	5:22:26 h	35
01.02	50km	42nd Jed Smith Ultra Classic - 50 km Race	4:11:55 h	10
2019
30.11	28mi	35th Quad Dipsea Trail Run	5:51:15 h	62
12.10	100km	33rd Ruth Anderson Ultra 100km	10:31:37 h	1 🏆
05.10	50mi	37th Dick Collins Firetrails 50 Mile	9:39:49 h	12
14.09	100mi	13th Headlands Hundred 100 Mile Endurance Run	26:45:19 h	16
24.08	31.5mi	20th Tamalpa Headlands 50K	5:32:18 h	24
20.07	100mi	18th Tahoe Rim Trail 100M Endurance Run	31:08:54 h	77
19.05	50km	32nd Ohlone 50K Wilderness Run	6:27:44 h	19
11.05	100km	36th Quicksilver 100 km Endurance Run	14:15:06 h	52
04.05	100km	24th Miwok 100k Trail Race	11:29:00 h	31
06.04	50mi	40th American River 50 Mile Endurance Run	8:58:03 h	37
02.03	50km	30th Way Too Cool 50K Endurance Run	4:57:40 h	84
16.02	50km	7th FOURmidable 50K	5:24:28 h	46
02.02	50km	41st Jed Smith Ultra Classic - 50 km Race	4:31:02 h	14
2018
08.12	50km	10th Hunter S. Thompson Fear & Loathing 50 km	6:45:00 h	18
24.11	28mi	34th Quad Dipsea Trail Run	5:53:23 h	52
03.11	100mi	18th Rio Del Lago 100 Mile Endurance Run	23:24:14 h	49
15.09	110km	4th Folsom Lake Ultra Trail	14:39:01 h	10
25.08	31.5mi	19th Tamalpa Headlands 50K	5:48:03 h	24
19.05	50mi	33rd Silver State 50 Mile	11:01:14 h	37
22.04	100km	32nd Ruth Anderson Ultra 100km	10:29:13 h	3 🥉
07.04	50km	2nd Napa Valley 50k Trail Race	7:11:16 h	16
17.02	50km	6th FOURmidable 50K	5:31:26 h	26
03.02	50km	40th Jed Smith Ultra Classic - 50 km Race	4:24:58 h	12
2017
25.11	28mi	33rd Quad Dipsea Trail Run	6:09:14 h	75
04.11	100mi	17th Rio Del Lago 100 Mile Endurance Run	21:37:58 h	37
07.10	100km	35th Dick Collins Firetrails 100 km	13:27:18 h	13
26.08	31.5mi	18th Tamalpa Headlands 50K	6:19:30 h	35
06.08	50km	36th Skyline 50k Endurance Run	5:18:48 h	39
21.05	50km	30th Ohlone 50K Wilderness Run	7:09:15 h	35
13.05	100km	34th Quicksilver 100 km Endurance Run	12:50:23 h	32
06.05	100km	22nd Miwok 100k Trail Race	12:03:11 h	65
23.04	50km	31th Ruth Anderson Ultra 50km	4:15:38 h	5
11.03	50mi	6th Marin Ultra Challenge 50 Mile Race	9:34:05 h	17
18.02	50km	5th FOURmidable 50K	5:48:44 h	52
2016
04.12	50km	8th Hunter S. Thompson Fear & Loathing 50 km	6:14:09 h	13
26.11	28mi	32nd Quad Dipsea Trail Run	6:07:30 h	76
08.10	50km	8th Skyline to the Sea 50km	5:47:59 h	18
16.07	100mi	15th Tahoe Rim Trail 100M Endurance Run	25:20:58 h	18
14.05	100km	33rd Quicksilver 100 km Endurance Run	12:38:55 h	25
07.05	100km	21st Miwok 100k Trail Race	12:36:00 h	98
16.04	50km	30th Ruth Anderson Ultra 50km	4:21:15 h	5
06.02	50km	38th Jed Smith Ultra Classic - 50 km Race	4:00:47 h	13
2015
27.12	50km	14th Woodside Trail Run 50K	5:03:15 h	12
06.12	50km	7th Hunter S. Thompson Fear & Loathing 50 km	4:54:00 h	1 🏆
28.11	28mi	31st Quad Dipsea Trail Run	6:13:13 h	103
10.10	50mi	33rd Dick Collins Firetrails 50 Mile	9:26:57 h	33
12.09	100mi	9th Headlands Hundred 100 Mile Endurance Run	21:54:38 h	2 🥈
29.08	31.5mi	16th Tamalpa Headlands 50K	5:38:04 h	72
08.08	50km	34th Skyline 50k Endurance Run	4:58:14 h	26
20.06	24h	3rd San Francisco Summer Solstice 24h	191.241 km	5
16.05	50mi	30th Silver State 50 Mile	9:23:55 h	18
09.05	100km	32nd Quicksilver 100 km Endurance Run	12:38:44 h	51
18.04	100km	29th Ruth Anderson Ultra 100km	9:54:54 h	4
22.02	50km	2nd West Coast 50K	5:32:28 h	4
31.01	50km	9th Fremont Fat Ass 50k	4:50:00 h	3 🥉
2014
28.12	50km	13th Woodside Trail Run 50K	4:54:32 h	12
23.08	31.5mi	15th Tamalpa Headlands 50K	5:43:39 h	47
21.06	24h	2nd San Francisco Summer Solstice 24h	162.213 km	11
18.05	50km	27th Ohlone 50K Wilderness Run	5:55:18 h	24
10.05	50km	31st Quicksilver 50 km Endurance Run	4:57:54 h	12
19.04	100km	28th Ruth Anderson Ultra 100km	10:15:18 h	5
2013
24.08	31.5mi	14th Tamalpa Headlands 50K	5:54:54 h	57
11.08	50km	32nd Skyline 50k Endurance Run	5:07:44 h	47
14.07	50km	10th Pacifica 50 km Trail Run	6:09:05 h	8
20.04	50km	27th Ruth Anderson Ultra 50km	4:17:20 h	5
24.02	50mi	1st San Bruno Mountain 50 Mile Ultramarathon	10:55:21 h	10
2012
07.07	6h	3rd Dirty Dozen 6h Endurance Run	48.811 km	19

Filter

Runner	Races in common

DUV-index calculation details

#	Date	Race	Credited km	DUV-index+
✓ 1	20/6/2015	3rd San Francisco Summer Solstice 24h	191,24	×3
✓ 2	21/6/2014	2nd San Francisco Summer Solstice 24h	162,21	×2
✓ 3	28/6/2025	52nd Western States 100 Mile Endurance Run	160,93	×2
✓ 4	6/6/2025	24th San Diego 100 Mile Endurance Run	160,93	×2
✓ 5	19/7/2024	26th Cascade Crest Classic 100 Mile	160,93	×2
✓ 6	15/7/2023	22th Tahoe Rim Trail 100M Endurance Run	160,93	×2
✓ 7	5/11/2022	22nd Rio Del Lago 100 Mile Endurance Run	160,93	×2
✓ 8	14/9/2019	13th Headlands Hundred 100 Mile Endurance Run	160,93	×2
✓ 9	20/7/2019	18th Tahoe Rim Trail 100M Endurance Run	160,93	×2
✓ 10	3/11/2018	18th Rio Del Lago 100 Mile Endurance Run	160,93	×2
✓ 11	4/11/2017	17th Rio Del Lago 100 Mile Endurance Run	160,93	×2
✓ 12	16/7/2016	15th Tahoe Rim Trail 100M Endurance Run	160,93	×2
✓ 13	12/9/2015	9th Headlands Hundred 100 Mile Endurance Run	160,93	×2
✓ 14	15/9/2018	4th Folsom Lake Ultra Trail	110,00	×1
✓ 15	9/5/2026	43rd Quicksilver 100 km Endurance Run	100,00	×1
✓ 16	10/5/2025	42nd Quicksilver 100 km Endurance Run	100,00	×1
✓ 17	4/5/2024	27th Miwok 100k Trail Race	100,00	×1
✓ 18	13/5/2023	40th Quicksilver 100 km Endurance Run	100,00	×1
✓ 19	12/10/2019	33rd Ruth Anderson Ultra 100km	100,00	×1
✓ 20	11/5/2019	36th Quicksilver 100 km Endurance Run	100,00	×1
✓ 21	4/5/2019	24th Miwok 100k Trail Race	100,00	×1
✓ 22	22/4/2018	32nd Ruth Anderson Ultra 100km	100,00	×1
✓ 23	7/10/2017	35th Dick Collins Firetrails 100 km	100,00	×1
✓ 24	13/5/2017	34th Quicksilver 100 km Endurance Run	100,00	×1
✓ 25	6/5/2017	22nd Miwok 100k Trail Race	100,00	×1
✓ 26	14/5/2016	33rd Quicksilver 100 km Endurance Run	100,00	×1
✓ 27	7/5/2016	21st Miwok 100k Trail Race	100,00	×1
✓ 28	9/5/2015	32nd Quicksilver 100 km Endurance Run	100,00	×1
✓ 29	18/4/2015	29th Ruth Anderson Ultra 100km	100,00	×1
✓ 30	19/4/2014	28th Ruth Anderson Ultra 100km	100,00	×1
✓ 31	14/3/2026	14th Marin Ultra Challenge 50 Mile Race	80,47	×1
✓ 32	11/10/2025	39th Ruth Anderson Ultra 50mi	80,47	×1
✓ 33	29/9/2024	42nd Dick Collins Firetrails 50 Mile	80,47	×1
✓ 34	30/9/2023	41st Dick Collins Firetrails 50 Mile	80,47	×1
✓ 35	8/4/2023	15th Lake Sonoma 50 Mile Race	80,47	×1
✓ 36	24/9/2022	40th Dick Collins Firetrails 50 Mile	80,47	×1
✓ 37	14/3/2020	7th Pioneer Spirit 50M	80,47	×1
✓ 38	5/10/2019	37th Dick Collins Firetrails 50 Mile	80,47	×1
✓ 39	6/4/2019	40th American River 50 Mile Endurance Run	80,47	×1
✓ 40	19/5/2018	33rd Silver State 50 Mile	80,47	×1
✓ 41	11/3/2017	6th Marin Ultra Challenge 50 Mile Race	80,47	×1
✓ 42	10/10/2015	33rd Dick Collins Firetrails 50 Mile	80,47	×1
✓ 43	16/5/2015	30th Silver State 50 Mile	80,47	×1
✓ 44	24/2/2013	1st San Bruno Mountain 50 Mile Ultramarathon	80,47	×1
✓ 45	24/8/2019	20th Tamalpa Headlands 50K	50,69	—
✓ 46	25/8/2018	19th Tamalpa Headlands 50K	50,69	—
✓ 47	26/8/2017	18th Tamalpa Headlands 50K	50,69	—
✓ 48	29/8/2015	16th Tamalpa Headlands 50K	50,69	—
✓ 49	23/8/2014	15th Tamalpa Headlands 50K	50,69	—
✓ 50	24/8/2013	14th Tamalpa Headlands 50K	50,69	—
51	22/2/2025	14th Montara Mountain 50 km Trail Run	50,00	—
52	21/12/2024	12th Woodside Ramble 50K - Winter	50,00	—
53	2/3/2024	3rd North Marin Ridge 50km Run	50,00	—
54	14/10/2023	37th Ruth Anderson Ultra 50km	50,00	—
55	3/9/2023	13th Crystal Springs 50 km Summer Trail Run	50,00	—
56	18/2/2023	11th FOURmidable 50K	50,00	—
57	8/10/2022	36th Ruth Anderson Ultra 50km	50,00	—
58	7/8/2022	41st Skyline 50k Endurance Run	50,00	—
59	7/3/2020	31st Way Too Cool 50K Endurance Run	50,00	—
60	15/2/2020	8th FOURmidable 50K	50,00	—
61	1/2/2020	42nd Jed Smith Ultra Classic - 50 km Race	50,00	—
62	19/5/2019	32nd Ohlone 50K Wilderness Run	50,00	—
63	2/3/2019	30th Way Too Cool 50K Endurance Run	50,00	—
64	16/2/2019	7th FOURmidable 50K	50,00	—
65	2/2/2019	41st Jed Smith Ultra Classic - 50 km Race	50,00	—
66	8/12/2018	10th Hunter S. Thompson Fear & Loathing 50 km	50,00	—
67	7/4/2018	2nd Napa Valley 50k Trail Race	50,00	—
68	17/2/2018	6th FOURmidable 50K	50,00	—
69	3/2/2018	40th Jed Smith Ultra Classic - 50 km Race	50,00	—
70	6/8/2017	36th Skyline 50k Endurance Run	50,00	—
71	21/5/2017	30th Ohlone 50K Wilderness Run	50,00	—
72	23/4/2017	31th Ruth Anderson Ultra 50km	50,00	—
73	18/2/2017	5th FOURmidable 50K	50,00	—
74	4/12/2016	8th Hunter S. Thompson Fear & Loathing 50 km	50,00	—
75	8/10/2016	8th Skyline to the Sea 50km	50,00	—
76	16/4/2016	30th Ruth Anderson Ultra 50km	50,00	—
77	6/2/2016	38th Jed Smith Ultra Classic - 50 km Race	50,00	—
78	27/12/2015	14th Woodside Trail Run 50K	50,00	—
79	6/12/2015	7th Hunter S. Thompson Fear & Loathing 50 km	50,00	—
80	8/8/2015	34th Skyline 50k Endurance Run	50,00	—
81	22/2/2015	2nd West Coast 50K	50,00	—
82	31/1/2015	9th Fremont Fat Ass 50k	50,00	—
83	28/12/2014	13th Woodside Trail Run 50K	50,00	—
84	18/5/2014	27th Ohlone 50K Wilderness Run	50,00	—
85	10/5/2014	31st Quicksilver 50 km Endurance Run	50,00	—
86	11/8/2013	32nd Skyline 50k Endurance Run	50,00	—
87	14/7/2013	10th Pacifica 50 km Trail Run	50,00	—
88	20/4/2013	27th Ruth Anderson Ultra 50km	50,00	—
89	7/7/2012	3rd Dirty Dozen 6h Endurance Run	48,81	—
90	29/11/2025	40th Quad Dipsea Trail Run	45,71	—
91	30/11/2024	39th Quad Dipsea Trail Run	45,06	—
92	25/11/2023	38th Quad Dipsea Trail Run	45,06	—
93	30/11/2019	35th Quad Dipsea Trail Run	45,06	—
94	24/11/2018	34th Quad Dipsea Trail Run	45,06	—
95	25/11/2017	33rd Quad Dipsea Trail Run	45,06	—
96	26/11/2016	32nd Quad Dipsea Trail Run	45,06	—
97	28/11/2015	31st Quad Dipsea Trail Run	45,06	—