Finding Highest Current Number Only For Increasing Range

RecordNo Speed
-------- -----
1 0
2 0
3 0
4 0
5 23
6 66
7 48
8 0
9 31
10 0
11 34
12 23

The above data shows the speed of vehicle over a time period, given the above data I need to achieve the result below:

RecordNo Speed LastAcceleration
-------- ----- ----------------
1 0 0
2 0 0
3 0 0
4 0 0
5 23 23
6 66 66
7 48 66
8 0 66
9 31 31
10 0 31
11 34 34
12 23 34

The code below is almost there but falls over on Recordno 8:

select
curr.recordno,curr.speed
,CASE WHEN curr.speed >= ISNULL(prev.speed,0) THEN curr.speed
ELSE (
SELECT MAX(speed) FROM speedtest
WHERE recordno between (CASE WHEN curr.speed >= prev.speed then curr.recordindex else prev.recordno end ) and curr.recordno

[code]...