diff --git a/TODO.txt b/TODO.txt
index cf34c0d..80a365b 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -3,10 +3,6 @@
 - car deglitch idea: deglitch only if the middle joint collided this frame?
 - some kinda easteregg in menu or smt
 - make the U-ramp map taller due to new physics
-- replay format should probably record game version
-  - also there should probably be some version system that says version of
-    physics vs version of everything else; replay could only record physics
-    version (maybe just two or three chars?)
 - on 1st map the camera is obscured by the wall at the start, fix it somehow
   (not the best first impression)
 - culling is very slow now, it showed that distance bailout can accelerate it
@@ -62,12 +58,18 @@
 
 =========== BUGS =================
 
+- sometimes getting a SLIGHTLY slower time counts as beating it (prolly
+  conversion fail)
 - immediately after starting the map countdown seems to be lower
 - the pinch collision test seems to sometimes stop the car e.g. after falling
   from bigger height or when running into ramp at high speed (or not?) - FIX
 
 =========== HANDLED ==============
 
+- replay format should probably record game version
+  - also there should probably be some version system that says version of
+    physics vs version of everything else; replay could only record physics
+    version (maybe just two or three chars?)
 - player name (modifiable via resource file) <-- prolly not
 - address the bug with driving on curved ramp diagonally, try DECREASING number
   of reshapes
diff --git a/data b/data
index 6e04051..7a035ce 100644
--- a/data
+++ b/data
@@ -3,6 +3,8 @@
 #Rrep2;testmap;482f70f9 00000843:0173:0081:0029:0111:0039:0071:00a3:0061:0169:0051:00b3:0041:0073:0081:0033:0041:0033:0231:0030:0098:0029:0011:0163:00f1:0053:0081:0033:0051:0023:0031:00f0:0032:0023:0131:00b9:0081:0023:00a1:0119:00e1:00c9:0071:0039:00a1:00d3:0021:01f9:0091:0079:0091:0039:0051:0049:0021:0083:0031:0083:0031:0083:0061:0089:0121:00a0:0058:002c:0048:0061:0013:0150:0052:00c0:00a1:0053:0041:0043:0031:0020:0092:0063:0181:0010:00a2:0013:0071:00e0:0028:00e9:0078:00a9:0043:0032:0123:0042:0080:0038:004c:01a8:0050:0032:0033:0101
 #Btestmap;
 
+#Rrrr;00LCtiny1;8ecff5c0 0000531:0011:03a9:0041:0179:0021:0059:0031:0039:0091:0049:0031:0253:0041:0013:0051:0053:0041:0023:0051:0043:0031:0064:0016:0022:0026:01a4:002c:0040:0042:0013:0081:0053:0102:0050:0021:0049:00e1:0043:0091:0049:01a8:0119:0130:0072:0026:0082:0048:0039:0111:0050:0022:0036:0132:0018:0049:0151:0033:0121:00c3:0041:0059:0041:00d0:0048:0050
+
 #Maaaaa;4321 0
 :*B2vJ
 
diff --git a/racing.h b/racing.h
index 989a758..1531d8e 100644
--- a/racing.h
+++ b/racing.h
@@ -17,9 +17,17 @@
     because the offset is too big (input didn't change for more than 2^12
     frames), there must simply be inserted an extra word that just copies the
     current input state.
-  - Replay text format: first there is the name of the map terminated by ';',
-    then hexadecimal hash of the map follows (exactly 8 characters), then
-    blank character follows, then achieved time as a series of decimal digits
+  - Physics engine version: LCR_RACING_VERSION1 and LCR_RACING_VERSION2 define
+    a two-character version string of this module that determines compatibility
+    of replays. Whenever a change is made to this module that changes the
+    behavior of physics, the version string must be changed because replays
+    will stop being compatible. It's still possible to make other changes to
+    this module (such as optimizations or comments) without having to change
+    physics version.
+  - Replay text format: first there are two characters saying the physics
+    engine version, then immediately the name of the map terminated by ';', then
+    hexadecimal hash of the map follows (exactly 8 characters), then blank
+    character follows, then achieved time as a series of decimal digits
     expressing the physics frame at which the run finished, then the replay
     data, i.e. the series of 16 bit words in hexadecimal, each preceded by ':'.
     The events (but nothing else) may otherwise be preceeded or followed by
@@ -30,6 +38,9 @@
 
 typedef int32_t LCR_GameUnit;  ///< abstract game unit
 
+#define LCR_RACING_VERSION1 '0'      ///< first part of physics eng. version
+#define LCR_RACING_VERSION2 '0'      ///< second part of physics eng. version
+
 #define LCR_GAME_UNIT 2048           ///< length of map square in LCR_GameUnits
 
 #define LCR_RACING_INPUT_FORW        0x01
@@ -174,6 +185,9 @@ void LCR_replayOutputStr(void (*printChar)(char))
 
   const char *s = LCR_currentMap.name;
 
+  printChar(LCR_RACING_VERSION1);
+  printChar(LCR_RACING_VERSION2);
+
   while (*s)
   {
     printChar(*s);
@@ -225,11 +239,23 @@ void LCR_replayOutputStr(void (*printChar)(char))
 int LCR_replayLoadFromStr(char (*nextChar)(void),
   uint32_t *mapHash, uint16_t *nameHash)
 {
-  char c = ' ';
+  char c;
 
   LCR_racing.replay.eventCount = 0;
   LCR_racing.replay.achievedTime = 0;
 
+  // has to be like this to force correct evaluation order:
+  c = nextChar() == LCR_RACING_VERSION1;
+  c |= (nextChar() == LCR_RACING_VERSION2) << 1;
+
+  if (c != 3)
+  {
+    LCR_LOG1("wrong physics version");
+    return 0;
+  }
+
+  c = ' ';
+
   if (nameHash)
     *nameHash = _LCR_simpleStrHash(nextChar,';');
   else
@@ -243,7 +269,10 @@ int LCR_replayLoadFromStr(char (*nextChar)(void),
     c = nextChar();
 
     if (_LCR_hexDigitVal(c) < 0)
+    {
+      LCR_LOG1("wrong hash");
       return 0;
+    }
 
     if (mapHash)
       *mapHash = ((*mapHash) << 4) | _LCR_hexDigitVal(c);
@@ -275,7 +304,10 @@ int LCR_replayLoadFromStr(char (*nextChar)(void),
         break;
       
       if (LCR_racing.replay.eventCount >= LCR_SETTING_REPLAY_MAX_SIZE)
+      {
+        LCR_LOG1("replay too big");
         return 0;
+      }
 
       LCR_racing.replay.events[LCR_racing.replay.eventCount] = e;
       LCR_racing.replay.eventCount++;