This is wheel section ripped from the coupe. The red numbers are the width for the right rear tire, the blue numbers are the width for the left rear tire. The game reads the pairs of numbers backwards; the 80 position changes attributes in small steps, the 3F position changes attributes in larger steps. Unless you want rediculously fat tires, you will probably only need to increase the 80's.

00017940 3F2C 7385 3E00 0000 0057 4C4F 4358 0100 ?,s.>....WLOCX..
00017950 0001 0000 0000 0080 3F00 0000 0097 F869 ........?......i
00017960 3612 FF4B 3800 0080 3FD2 55F6 3505 C1D8 6..K8...?.U.5...
00017970 37CE DE02 B600 0080 3FCE E318 3FFC 1AA6 7.......?...?...
00017980 3EAD 53B0 3F00 0000 0001 0000 0000 0080 >.S.?...........
00017990 3F00 0000 0000 0000 0012 FF4B 3800 0080 ?..........K8...
000179A0 3FD2 55F6 35FB D7DC 37CE DE02 B600 0080 ?.U.5...7.......
000179B0 3FD9 0519 BF04 1BA6 3EAF 53B0 3F00 0000 ?.......>.S.?...
000179C0 007C 2067 0048 2B42 0066 96F7 BF77 42F7 .| g.H+B.f...wB.
000179D0 BFE0 F9FB BF82 96F7 BF77 42F7 BFE0 F9FB .........wB.....
000179E0 BF42 97F7 BF01 0000 0048 2B42 0038 F765 .B.......H+B.8.e
000179F0 00E6 5AF7 BF00 0000 00FE 0000 0048 2B42 ..Z..........H+B
00017A00 0020 0000 0001 01F7 BF9C 825C 8100 0000 . .........\....
00017A10 00A0 4142 0029 9B41 0006 0000 0080 2067 ..AB.).A...... g
00017A20 0000 1000 006C F765 0000 0000 0000 0000 .....l.e........
00017A30 0001 0000 0000 00
80 3F00 0000 0000 0000 ........?.......
00017A40 0012 FF4B 3800 0080 3FD2 55F6 35FB D7DC ...K8...?.U.5...
00017A50 37CE DE02 B600 0080 3F91 E318 3FFC 1AA6 7.......?...?...
00017A60 3EE9 55B0 BF00 0000 0001 0000 0000 00
80 >.U.............
00017A70
3F00 0000 0000 0000 0012 FF4B 3800 0080 ?..........K8...
00017A80 3FD2 55F6 35FB D7DC 37CE DE02 B600 0080 ?.U.5...7.......
00017A90 3FDF 0519 BF04 1BA6 3EAD 36B0 BF00 0000 ?.......>.6.....
00017AA0 0048 4C4F 4358 0000 0046 4331 5F47 5046 .HLOCX...FC1_GPF

courtesy of King's Custom Rods