The Complaint Every Ipoh Rider Has Made
You did the same loop in March that you did last week, at the same effort, and you were four minutes slower. Nothing on the bike changed. You did not sleep badly. You just cooked.
Most cycling advice written about heat comes from places where 30°C is a heatwave and the air is dry. Malaysia is a different problem, and there is now a study that shows exactly why.
Somebody Finally Separated Temperature From Humidity
Almost every heat and performance study confounds the two. Researchers raise the temperature while holding relative humidity constant, which means absolute humidity, the actual amount of water in the air, climbs at the same time. So you never learn which one did the damage.
A 2023 study in Experimental Physiology fixed that. Fourteen trained cyclists rode 45 minutes at 70% of VO2peak followed by a 20km time trial, in four different environments:
- Cool: 18°C
- Moderate: 27°C
- Hot: 36°C
- Hot Humid: 36°C, with double the water content in the air
The first three were held at the same absolute humidity, so the only thing changing was temperature. The fourth added humidity on top of the heat.
The results:
- Cool and Moderate were indistinguishable. Riding at 27°C cost these riders nothing over 20km compared with 18°C.
- Hot cost 3.6 to 6% over the time trial.
- Adding humidity cost a further 3.4% on top of that, and this is the important part, it did it through a different mechanism. Humidity raised core temperature, perceived temperature and discomfort. Temperature alone mostly raised skin temperature, heart rate and sweat rate while barely touching the core.
Per degree of extra air temperature, riders showed skin temperature up 0.5°C, heart rate up about 1 beat per minute, and sweat rate up 0.04 litres per hour.
Why That Matters Specifically Here
The humid condition in the study was 36°C at a water vapour pressure of 3.92 kilopascals.
Run the numbers on a normal Ipoh afternoon, 33°C at 80% relative humidity, and you get roughly 4.0 kilopascals. Slightly more water in the air than the harshest condition those researchers tested, at a lower air temperature.
That is the whole story of riding here in one comparison. Our air temperature is not extreme by world standards. Our absolute humidity is. And humidity is the variable that drives core temperature up, because sweat that does not evaporate does not cool you. It just leaves you.
So when you feel like you are riding badly in Malaysia, you are probably riding fine. The environment is taking a documented 3 to 6% off the top, through a route that generic hot-weather advice does not address, because dry-heat advice is mostly about drinking more and staying in the shade.
The Part That Belongs to a Bike Fitter
We fit bikes, so here is the honest division of what heat does and what we can do about it.
Moisture changes what your saddle does to your skin. Saddle sores are described in the literature as arising from a combination of friction, heat, pressure, moisture and bacteria. A systematic scoping review of saddle sores in female competitive cyclists found the empirical evidence base thin overall, but two things did have some support: handlebar positioning relative to the saddle, and reducing perineal pressure. Both are fit variables. In a climate where you are wet from twenty minutes in, the moisture side of that equation is not optional, so the pressure and position side is where the leverage is.
Fatigue moves you on the bike, and a marginal position stops being tolerable. A position you can hold for two hours in cool air is not automatically a position you can hold for two hours at 4 kilopascals with your core temperature climbing. This is the mechanism behind the most common complaint we hear: the pain that only shows up on hot afternoon rides and never on cool morning ones. The bike did not change. Your capacity to hold the position did. If your fit only works when you are fresh, it is not a fit, it is a best case.
More weight goes through your hands as you tire. Once your core temperature is up and your trunk muscles fatigue, you sag onto the bars. We covered what that does to the ulnar nerve in Numb Hands and Tingling Fingers While Cycling, and heat is the reason it starts at kilometre 50 instead of kilometre 90.
One Claim We Are Not Going To Repeat
You will read on a lot of cycling sites, including in the drafts that led to this article, that your feet swell up to half a shoe size during a hot ride, which shifts your cleats and causes hot foot and numbness.
It is plausible, and it is repeated everywhere. We went looking for the measurement behind it and could not find one for cycling. So we are not going to state it as fact.
What we will say is that foot discomfort in heat is real and common, and that shoe fit and cleat position are worth checking if it happens to you. We just are not going to invent a mechanism with a number attached to make the advice sound more scientific than it is.
What Actually Helps
Ordered by how much difference they make here specifically:
- Ride early. Not a fit tip, just the biggest lever there is. The difference between 7am and 2pm in Ipoh is larger than anything you can buy.
- Recalibrate your expectations. The 3 to 6% is real and measured. Pacing off your cool-morning numbers on a hot afternoon is how riders blow up.
- Get airflow, not just fabric. Evaporation is what cools you, and evaporation needs moving air. This is part of why sitting up in a group at 22km/h feels worse than riding alone at 30km/h.
- Check your position holds when you are tired, not just when you are fresh. A fit assessed only in the first ten minutes tells you very little about hour three in August.
- Address saddle pressure before you address saddle cream. Creams manage the symptom. Pressure distribution and bar-to-saddle relationship are the parts with fit evidence behind them.
The Short Version
Malaysian riding is not hard because it is hot. It is hard because the air is already close to saturated, so your primary cooling system runs at a fraction of its capacity. That costs a measured 3 to 6% on top of what the heat alone takes, and it does it by driving your core temperature up rather than just making you sweat.
You cannot fit your way out of the weather. But a position that only works while you are fresh will fail here much sooner than it would anywhere else, and that part is fixable.
References
- Jenkins, E. J., Campbell, H. A., Lee, J. K. W., Mündel, T., & Cotter, J. D. (2023). Delineating the impacts of air temperature and humidity for endurance exercise. Experimental Physiology, 108(2), 207-220. PMC10103870. The four-environment crossover study and the 3.4% humidity penalty.
- Bury, K., Leavy, J. E., Lan, C., O’Connor, A., & Jancey, J. (2021). Saddle sores among female competitive cyclists: a systematic scoping review. Journal of Science and Medicine in Sport, 24(4), 357-367. PubMed: 33109466. Friction, heat, pressure, moisture and bacteria, and the limited evidence for handlebar position and perineal pressure.
Vapour pressure figures for Ipoh conditions calculated from the Magnus formula at 33°C and 80% relative humidity.
Ready to Ride Better in the Heat?
If your position is fine in the first hour and falls apart in the second, that is a fit problem the weather is exposing rather than a fitness problem. Chat with our AI bike fit expert on WhatsApp for a free assessment. Tell us when in the ride things start hurting and what the conditions were.