Power loss at altitude - Colorado.

The 3% rule...you lose about 3% for every 1000ft altitude.

Don't know how high Thunder Valley is though.

6100 ft

So if we had a race in Death Valley, California (282 feet below sea level) you would gain close to 1%, correct? :o)

Theoretically - due to the greater air density and if everything else was equal.

However, the usual high air temps would decrease the density (thereby decreasing potential HP) and the motos would be shortened to 30 seconds plus 2 turns so no one would possibly sweat through their "kits".

I always heard them throw around the 20% number and per formula above and altitude it's close 18--20%

LOL....thanks!

Zach-O said this week that their bikes dynoed at ~30% less HP when they were at these high altitude tracks.

It’s definitely noticeable. I normally ride/race around sea level. I went to a race around 4000ft, and forgot about the altitude until I hit the first deep berm and the bike fell on its face instead of pulling like it should have. I ended up running a gear lower in several areas. 

The other part is the human element. I definitely got winded much more quickly at altitude. 

 

With altitude and say, 90f temps...I believe it. Hell when I raced 125cc back in the 80's and 90's, when the temps at night races got into the 50's with low humidity (compared to 80's and humid) - we would just run 50:1 with some minor jet changes instead of 32:1 and the power increase was substantial.

Even on a 450 with say 60hp, imagine how much slower even a 15% decrease would feel! That's nearly 10hp less for you math challenged types.

Look up a density altitude chart

The whole start in first is BS. 

I live up here at 8500' in New Mexico and when I raced enduros in TX, my 150 and 300 had so much more power that it definitely took a minute to get used to.  And me?  So much oxygen down there, I'd take a breath like every 30 seconds or so. 

Power loss ~ 3% per 1000-ft as stated above. Not sure why anyone would downvote that - it's science. Literally.

So, as stated, 6,100 feet = ~ 18.3% down on power. This is a CRAZY deficit to start with, but oh-so nice for vet riders who full 450 power is a handful for (me!). But also a challenge for bikes that are perfect power at sea level (350) ... and then you lose 20% of your power. Oi!

@HighPlainsSquid mentions something interesting. AI says: "The body produces more red blood cells at high altitude to compensate for the lower oxygen concentration in the air. This is an adaptive response to ensure tissues receive sufficient oxygen." This also means you feel like an Olympian at sea level for a few days until your body adjusts --- it's pretty fun this way and you do catch yourself thinking "when's the last time I took a breath?" I travel a lot for work, so I get to run at lower-elevation destinations and feel like a champ. A fadass champ, but a champ nonetheless.

High elevation is a beast for oxygen consumers - no 2 ways about it.

Ah - there's the downvoter - hi there, cutie! 🥰

I’d be scared of my 450 at sea level 🙂

Why

I think it was your inference that science is truthful.  Just a sign of the times.🙄

fact:  a mid '00s CR125 in Socal is faster than a factory 450 in Colorado

...And everywhere else if Profeshional is riding it. 

I don't understand why they make such a deal about this, they're all on 450cc, or 250cc, so the competition is still the same in the races.

*Elevation

Why would you change your oil ratio?

Make the bike run richer.  More fuel, less oil = richer mixture.  

I did the same thing moving from 8500' to 4000' in Texas. I run 40:1 up here and going to TX, I'd mix more like 45:1 on the 150 and 50:1 on the 300.  More fuel, more power, cooler running. I ran Lectrons on both and so adjusting the gas/oil mixture was just a small tweak but it worked well. 

Is that the pro125 super duper pooper scooper double boost port 125, or production?

but how is seat bouncing a properly sprocket bolt-torqued steed at "elevation" affected, is the question. 

I grew up racing in CO, lived at 8800’, went down to the old Lakewood frequently. Even in the early 80s starting in 2nd was easy, and preferred, on a 2t 250. 

Today, bikes have more power, and for the national the teams are massaging the motors to help make up for power loss from sea level. While an identically prepared engine would produce less at elevation, many of these are not identically prepared. They are producing less, but not what some calculator would suggest based purely on elevation. 

I don’t know If your 80’s butt dyno has more information than a factory team analyzing the data. Not to mention grates and the start straight most likely ripped deeper. Maybe 2nd worked better back then, 1st is definitely better now there. Unless the whole gate is wrong?

There, I did the number punching. About 20% from standard sea level. That lines up with race car data I have from Utah, takes about 17-18% more turbo speed to make the same boost.

I am fairly sure that most of these factory guys are running a different primary ratio and/or different ratios in some or all transmission gears so it isn't an apples to apples comparison vs your production bike.

Also, when we go to the local amateur race the gates aren't full and there is a much greater skill level disparity on the start.  That skill level disparity is even greater when you have A and B class or C and D class on the same gate drop like some tracks and promotors do.

When the gate is full with 40 or more riders the reaction time and the jump becomes even more important.  Even if starting in 2nd gear is just slightly faster when you factor in the shift, it is likely that the initial jump in 2nd puts your bars a few inches or a foot behind the guys on your left and right who started in 1st gear.   At the pro level, that means you get pinched off just before those other guys shift into 2nd gear.  When there are 15 guys on a gate at a local race, there's enough room that 2nd gear does not pose that problem.