K cool. So with that temp swing, speed increase on the second lap is two fold.
Few watts from air density AND a few watts from actual tire rolling resistance getting faster with warmth.
How much total? About 5 watts.
The weather impact is really interesting. Thx for the detail.
Hmm, didnât even think about the rolling resistance change with temp. Makes sense, but I assume that curve is a lot flatter than air density impacts?
Actually the opposite! Air density vs CdA and implied CRR relationship is very much linear where the air temp vs tire CRR relationship is a bit more progressive.
Meaning as it gets colder and colder tires get slower faster than the air around you gets slower.
Thanks for sharing! When you test again Iâd suggest using the Chung method as it doesnât require holding the same power and you can do short tests where the conditions are the same. You can test gravel/pavement/aero bars all separately as well.
Yep, I thought about it. I used to be a big golden chetah user (including the embedded chung testing), just havenât played with it in years. Probably need to reinstall and remind myself how to use it. Or are there better tools these days for doing Chung testing?
Yesterday was just opportunistic with my planned 2 lap ride and near perfect testing conditions. And Iâm usually really flat with wattage on easy endurance rides, so no challenge there. I was checking periodically, but not watching it constantly.
Bad wording on my part, probably should have said non-linear. I was meaning flat like a power curve (once it gets past the early steep part, it gets very flat with additional time). I assume rolling resistance and temp is some thing (a freezing tire is really slow, but once you get past a reasonable temp the curve is pretty flat).
I looked at the study and didnât see a curve and was too lazy to run any numbers, but my assumption is that a 73f tire wouldnât be that much slower than a 82f tire (but thatâs just a guess on my part).
Correct, like 5% slower rolling resistance at 73 degrees. Not much.
BRR had a test on temp also.
Sub freezing is where it really slows down tires, but even at normal rising temps itâs enough to skew tests so itâs often on my mind.
TB 2.1âs successfully mounted on my CruxâŚ.plenty of room because they only measured 49mm once inflated. 
Weâll see if they widen a bit with age / use. @jkarrasch indicated over on the EC Discord that they will and that is my suspicion as well.
But even if they blimp out to 51 or 52mm, there should still be ample room.
What rims did you put them on?
I put them on a 25mm internal and they measured 53mm 
way too little clearance for me personally. Didnât get a small batch 
Enve 3.4âs w/ 25mm IW.
After reading about the Hutchinson Caracal Race 40, Iâm interested in buying them. Iâm wondering though if my 29mm internal, 40mm external Nextie NXT45AGX wheels would âstretchâ these too much since my 42mm Pathfinders are already being stretched to 46mm on these wheels..?
I think it is a bit unfortunate that the BRR tested the rolling resistance only in warmer temperatures. Many northern hemisphere riders spent significant part of the year in temperatures between 5 to 10 degrees C, so it would have been nice to get figures for those temps too.
Looking at the BRR data, the Caracal is very similar to the PF42 in terms of sizing*. The casing width is 2mm smaller, while the tread is 2mm wider. The casing width will translate to roughly 1mm less tire width. The wider tread cover is great because it means less exposed sidewall. I think the Caracal on those wheels sounds like a super fast combination. It will look fantastic too.
If youâre not having problems with the Pathfinders on those wheels, I would definitely try the Caracal Raceâs. You are definitely giving up some puncture protection though.
*The two tires had the exact same measured width on the BRR rim.
Thanks for the detailed explanation, exactly what I was hoping for!
I read about people flatting them quite easily, but the puncture protection is the same as for the Vittoria Mezcal 44s I was running this winter and I havenât flatted those, also not in last weekends race where I hit tree stumps and there were stretches with a lot of pebbles. So not sure how worried I should be here.. The PF42 has been flawless as well, no flats.
Itâs ok. They all get slower as it gets colder. Fast tires are still whatever amount faster than slow tires
It was interesting this winter - I went out on an ice free morning at about minus 8-9c. I was running G-Ones - an Ultrabite on the front and an R on the back. They felt wooden and generally awful, and no faster at all than my usual Suomi studded tyres.
Interesting. Mine were around 51 when first installed on my 27 internal wheels. After leaving them around 30-35 psi for a week and several rides, they now sit around 53-53.5mm. Iâd bet yours will eventually bump to around 51ish. Iâd knock them up another 10 psi over what you will run them while theyâre sitting and itâll probably speed up the process a bit (if you werenât already).
Have you measured that clearance? Looks to be 3-4mm and way more than a lot of pros seem to have. I wouldnât hesitate to run that one bit in dry conditions. Looks similar to my TB on front.
Yeah, they were sitting at 40 psi yesterday and I usually run tires this size ~20psi. Will check them before I ride today to see if there is any change (not likely this soon, but weâll see).
A few thunderstorms rolled through early this AM and dropped a ton of rain, so looks like Iâll be checking mud clearance sooner than I thought! 
Yeah mine have stretched to around 51.5-52 on 23 iw rims. I think they were also sub 50 when I bought them.
I run mine with 3mm clearance, even in mud and rain - no chunky mud around here though. Iâve run this setup throughout the winter with no issues.
I did recently install frame protection tape around the chainstays, seatstays and fork just for peace of mind.
It was 3mm or less including the little hairs. I know pros are running that type of clearance but Iâm not a pro and something tells me they donât care about frame rub as much as I do 
