The tutorials in this game are very good and I recommend completing them to get a good handle for the game(at least up to the stunts).

I am searching for knowledge to improve and compiling some here that I find. If there is other knowledge worth referencing here please let me know; or corrections to something I have assumed!
*anything in [ ] is unconfirmed
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Common Mistakes I have made:

-Not making enough adjustments to my alignment with the track; you can do a lot of both vertical and horizontal adjustments and compared to other games like Wave Race it's always faster to make additional adjustments than settle for a worse line.

-Not aligning properly out of turns before boosting. As a general tip wait longer before boosting after a turn until you can get the line. Boosting while turning builds temperature far faster than boosting facing straight; this is a prominent factor in boost routing

-Make sure you boost when hitting the ground. Route your turbo usage so you always have the temp to make a quick landing. If you have the wrong angle landing + don't boost when landing even once you lose so much time

-Trying to cut jumps too short pushing nose down early generally loses time where it's tempting to turn down early often times the kickers are setup in ways that look more inviting than they actually are

-Sometimes it's crucial you don't hold drift and instead tap it a couple times; holding drift for too long instead of tapping it loses a lot of time and doesn't help you turn much

-when doing handbrake turns make sure to boost after to get back up to speed; a lot in this game depends on getting up to top speed and staying as close to it as possible with minimal braking/drifting

Starting
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During the countdown there are a number of options for movement and turbo to get a faster start.

Standard Fast Start

1) Hold Throttle and Turbo until the Temp dial gets to yellow; release Turbo

2)When the Announcer says Go do a Wheelie(Down + Turbo) while holding Throttle; continue holding down briefly with a longer wheelie on courses without an immediate turn.

It's possible to Wheelie early and adjust your starting angle before the countdown starts; be aware of this as several courses use it to save time at the start

There's a strategy on some course where you start with less than yellow temperature; this can allow you to Turbo more to get up to top speed more quickly to make jumps(useful on levels like phoenix and blizzard blitz)

[It's possible to Crash by holding a Wheelie too long before the race starts. I haven't tested or used this enough to say whether it's good or bad just be aware it's an option. This could be a consistent start strategy for RTA untested though.]
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Cornering
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Before drifting use the joystick to start the turn, you might not need to drift just holding the joystick. Move your stick to diagonal down if you need to make a very sharp turn, drifting only after you have started the turn. If done correctly you should be able to avoid using brake most of the time if not all the time.

Tapping Turbo once after a drift seems to stabilize nicely if you haven't overturned; important for keeping on your bike and pushing your speed into the next corner or jump. If you turbo after drifting without stabilizing your bike you will crash or lose a lot of speed; often best to avoid using it other than when you need it to make a jump until you get more comfortable with cornering.

Try to practice the timing for Turbo out of corners; mastering this seems essential for some routing.

When the angle is too sharp you may need to turn more quickly than is possible with just a drift and the joystick. Use Drift then Brake to turn more quickly

I asked Pancakes about turning; putting it here in case it helps others

My Question:
"For sharp corners there appears to be some decision-making. Do you use brake or is it better to rely on the stick for sharp turns? brake+drift seems like a really fast way to turn and combined with turbo/ stick down-back there are actually a number of different turn options.

Can you give me some advice or guidance on which options to use and when?"

Pancakes' Answer
"No problem, it really depends on the turn you'll have some turns where it is banked like on Long Island, of Las Vegas, where itll be faster to hit that banked turn while holding brake to get a nice turn. For the turns like orlando I tend to do two hand brake turns each trying to go 90 on each turn I make, to me it feels faster, but it might not be." he is referring to turns that turn 180 degrees or more without a bank.

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Airtime
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In the air it's often important to change your angle before you land to move quickly through a course. Adjust your height(Up/Down on joystick) before adjusting your landing angle(Left/Right) if you need to do both in a jump. Once you start turning left/right you are unable to have the same adjustment on height.

Use Drift and hold a direction in the air to adjust your landing angle.

For quicker angle changes use Drift then Brake to turn quickly in the air; very important in several courses

Press Up on the joystick to reduce air time & Down to increase air time. Use these to maximize your time boosting and accelerating; don't be in the air longer than you need to and make sure to press down when needed to reach landings.

Make sure not to hold Accelerator or Boost in the air to conserve heat
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Jumping
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What you do before you leave a ramp has a drastic affect on where you end up in the air and landing. Avoid turning on ramps before jumping from them try to go up them straight on.

If you press down on the joystick before jumping from a ramp your jump height will be increased; If you press up on the joystick before jumping from a ramp your jump height will be decreased. Using turbo at the edge of a ramp will give you a Boost that increases your speed and launch distance.

If you are worried about not getting a Boost at the edge of a ramp you can mash the Turbo button and you will get a Boost without having to time it perfectly.
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Landing
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Landing wrong can kill all your speed or crash you easily so it's important to try to get each landing right. Try to hold any angle adjustments from airtime as long as possible before adjusting the landing angle as the adjustment usually slows you down a bit until you land.

The closer to parallel with the angle of the ground you are when you land the faster the landing. Try to match it exactly before landing; often landing with your nose too high up or too far down kills all your speed and/or wipes you out.

Faster to land without an angle change left/right(facing straight forward) unless the slower landing allows you to setup for a better line(common).

Turbo when landing to get back up to speed; airtime slows your character down. Make sure to hold turbo as you hit the ground
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Turbo/Boosts
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One of the big mistakes I made starting this game was boosting too often trying to go faster. It looks like it's often the case that you should refrain from using turbo except when you know to use it; blindly using turbo into and out of corners can waste a lot of time on collisions and missed turns.

Start off just trying to get around a course using throttle, angle changes, and drifting. Use turbo only on boosts on jumps to start with and on ramps then gradually start adding them in as you get more comfortable with the lines. You may be able to replace height changes with turbo use so look for opportunities to remove angle changes by boosting to get over gaps it's faster to boost over a gap than do extreme up/down height adjustments though both may clear the same gap.

Note: I am finding that it's often fastest in turns to hold the stick all the way to one side and hold turbo to get out of the turn; often the additional acceleration from the turbo allows you to just barely miss collisions with the walls; this appear to be how to get extra speed off of a jump like top players on Kyoto use to glide over extra jumps and save time over most submissions.

Avoid overheating
You will begin to overheat while using turbo when racing. To get your temperature gauge back down, just wreck one of the other racers by clipping their front tire with your back tire. Your gauge will go down to nothing.

On the Uphill Challenge(and places with large hills) it appears as though you can boost multiple times by doing a wheelie repeatedly(Down + Turbo). There may be potential to exploit these physics outside of Uphill but this seems almost essential to boosting without overheating.

[High and quick jumping
Pop a wheelie, then hold "Turbo". Release "Turbo" just before the top of the jump, then tap "Turbo" at the top while still maintaining the wheelie.]

[Ride around after race
Hold [Z] + [A] to pull a wheelie in training mode just before you cross the finish line. Release [Z] to slow down, then fall off the bike. You can now ride around the entire track.]
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Settings
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Using control configuration C personally; imitating Pancakes. Seems like potential for other control schemes as long as you are using control stick for movement.

Turning the Drones Option to Off removes extra riders from the track in Season mode and is generally standard.
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Extras
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[Custom course win
Place a landing ramp in the middle of the track, with no jump in front of it so that the steep slant of the landing ramp functions as a jump. Each time you pass the ramp, at least one of the CPU riders will fall off their bike. Tricks and air turns are unhindered.]

Most updated old FAQ(Needs review for important knowledge): https://www.neoseeker.com/excitebike64/faqs/25977-excitebike-64-b.html

From http://uk.codejunkies.com/search/codes/Excitebike-64_Nintendo-64_6291711-6___.aspx

These gameshark codes possibly could be used to cheat "low temp" is the only one I see that's worth being aware of

Hey Ghillie, most cheats are banned. The only one that is legal is the "Wheeeeeee" cheat, which turns uphill into downhill. Just watch out using that cheat as if you finish a downhill run, the game will save the time as if you did the run uphill. Just to let you know here, I did DM you on discord if you wanted any tips and tricks, but as I'm typing this I realize I can use the comment feature under the run

Thanks Pancakes, sorry if it seems like a bunch of stuff all at once trying to figure out everything.

Will respond on discord just trying to start on a public archive for learning so it's easier; thanks for working on this game and good luck on your runs!

edit: my discord account is lost for now please don't try to contact me there; most responsive to YT comments, or twitter. Will respond to messages here but might be a delay

Some advanced knowledge I'd like to share that can help improve times:

Turbo tapping

Landing sweet spot

"Pop jump"

Wall bounce

Double wheelie start

Wheelie start cooldown

Errant turbo jumps

Wheelie maintenance

Air turning