# Thread: how much does air temp effect rpm

1. ## how much does air temp effect rpm

Just wondering how much effect the air temp has on rpm. It is coming to the end of winter here and most days are already around the 75-80deg mark. Once summer gets into full swing it sits around the 85-95deg. It also gets high humidity as well which I know is no good for making power but want to try and work out which ring sizes I should be looking at to compensate for the change in rpm so I can be good to go.

Where I live 85-95deg is from late september till late april so we get alot of riding done and winter only goes down to about 70deg during the day

2. For Me,
from 75* to 95*. IF over 100*, then almost 400 rpm loss.

3. My rough guesstimate based on recording temps and RPMs over the years is roughly 100 RPM per 10 degrees in the same location. Of course, elevation, humidity and all the other air factors come into play, but that's just a rule of thumb I use to loosely predict.

4. ## Re: how much does air temp effect rpm

Chandy,

I just asked this exact same question.

There is great info and links to relative air densitiy calculators. Using the rad calculator you can really see how all the changes effect your rpm.

Sent from my iPhone using Tapatalk

5. I think water temp has a bigger effect because of the Intercooler. Our 87 degree water her makes the Ski run the same all day even when the air temp drops 5 degrees. (after and during a Thunderstorm)

6. RAD not temperature is the biggest factor. Sure temperature plays a role, but not the largest role. Water temperature is important too. Here is a density altitude calculator. http://wahiduddin.net/calc/calc_da.htm

7. wow that's great. thanks guys.now i just have to find something I can use to measure those variables to keep a more accurate log of things.

I have an altimeter that monitors Relative Altitude by measuring barometric pressure with temperature and then comparing it to what it should be at set constant(sea level). With this meter I can be sitting on the ocean on my ski and the Relative Altitude varies quite a bit depending on surrounding weather systems and temp. Would this be the same as this RAD that the calculator comes up with. Hoping it is cause it will save me doing any of the math and this meter is only the size of pack of cigarettes(very portable)

8. Originally Posted by CHANDY
wow that's great. thanks guys.now i just have to find something I can use to measure those variables to keep a more accurate log of things.

I have an altimeter that monitors Relative Altitude by measuring barometric pressure with temperature and then comparing it to what it should be at set constant(sea level). With this meter I can be sitting on the ocean on my ski and the Relative Altitude varies quite a bit depending on surrounding weather systems and temp. Would this be the same as this RAD that the calculator comes up with. Hoping it is cause it will save me doing any of the math and this meter is only the size of pack of cigarettes(very portable)
I'd like to know as well