That took longer to show up here than I thought it would. Also, not sure why anyone would think 55psi is "super low" on a 28mm measured tire.

---

My YouTubes

For this to work out, based on the bumpy in the video, you'd really have to do the math on time spent in each CRR scenario.

This has been covered a thousand times over. There's been lots of videos that are more anecdotal showing riders "thinking" the higher pressure tire doing a roll down test on a gravel road to "feel" faster. Just to be proven wrong.

As for tarmac, I tend to agree you shouldn't pump it up to max.....but......what % of your route will you really benefit form the lower pressure?

My last TT bike ride outdoors was 30ish mi. I pumped up to a pretty solid 80/75 psi on 23/25 combo. I think there was a total of a minute to two minutes total accrued "rough road" that entire ride. The rest was smooth other than minute changes in texture.

It takes a pretty solid screwup in pressure choice to suffer 50w of damage for an entire ride.

Lastly, we're not pro cyclists (I'm not), but the pros on pave' run such high speeds that the spring/mass system isn't in the same ballpark as some bloke doing Paris Roubaix on vacation. Speed matters a lot to spring/mass systems being modeled like a bike tire and rider.

Yeah, agreed on the 50 watt scenario. I base my pressures more off comfort and no loss of speed, i.e. balance. Being that I am on the lighter end of the spectrum for total system weight and I don't run 22s anymore that ends up being 55/55psi front and rear, respectively, on my road bike. I'm running 23/25 schwalbe pro ones (old version) that measure out to 25 and 28 on my 19mm internal Easton wheels. They are setup tubeless. I likely ride some of the nicest pavement in the nation outside of the random broken stuff. But when I do hit that broken stuff it's not a question of am I losing 5 watts or not but how that impact impacts my ride.

Time Trial bike is a whole other animal and I will keep those trade secrets to myself. 😆

ETA: https://www.strava.com/activities/3718362217 This was this past Sunday's ride. If I am losing watts due to "low"pressure(s) then I am likely more aero on my AR than my DA. 😉

---

My YouTubes

And therein lies the rub.

Tubeless sucks, and the pressures they suggest with tubes = boatloads of pinch flats for me.

Ah well. Always a compromise somewhere.

Yeah, I think tubeless is the key here.

fwiw, I have ~5500 miles on my Pro Ones and only flatted once and really surprised it didn't destroy my wheel on impact. another time I picked up a nail and rode ~40 miles (finishing my ride) thinking I was having a bad day, but when I got home I realized pressure had dropped to ~35psi. those tires are still going after I got them sealed back up.

I know many others have not had that experience and I do ride some choice roads.

---

My YouTubes

FIFY

It sounds like you had a bad experience or something. I think you should give it another go. It's been just brilliant for me.

I honestly can't remember the last time I had to pull over on a ride for a flat. Riding is way more comfortable. I'm (apparently) faster.

Okay.

No.

You can just respond in the future. No point in changing my posts.

On a really rough surface and pressure way too high vs just right... I could believe it. Maybe.

I'd like to see some data on torque losses, particularly on a steep climb, with that fat squishy tire on the back.

I just looked at this and am looking for some advice.

I have ZIPP 858 wheels. It seems to be suggest for 303s you want to have your tubes significantly lower in pressure than I do - I perhaps feel like a moron.

What should my pressure be for relatively rough tarmac? I assume not the 100 I set them at.

https://axs.sram.com/tirepressureguide

I would use road and gravel for your surfaces and split the differences.

Lowering the psi on my 25mm TL tires on Zipp 303 NSWs was a revealing experience. I am at about 5.5-6 bar / approx. 85 psi or less.

What size are you running? What's your weight? I kept dropping until I was at 60psi and thought it was the greatest thing. Then I went down to 55psi and found the sweet spot. Such a difference.

---

My YouTubes

What's your weight? Can I assume you're running tubes?

---

My YouTubes

80kg. Yes latex tubes. Thanks in advance

Thank you. Wow I’m way too high

This entire claim should be pretty easy to validate on a real road; the white paper is based on their proprietary testing system, and they didn't actually provide much data from their third party consultant. And there's a gem on page 7.

Forgot to ask the tire width. It's kind of important. if you have a measured width that would be better than what the label says.

Also, good tool to start off is:

https://info.silca.cc/...-pressure-calculator

---

My YouTubes

Is there a better one to start (or finish) off?

Yup!

http://cdacrr.blogspot.com/

---

My YouTubes

The tested power vs speed on a "dirt road" (details on that would certainly be nice) are much less dramatic. ~12W increase going from 50 to 110 psi @35kph. Would be really cool to get this data on a variety of road surfaces.

The "gem" on page 7? Inertia plays a tiny roll as expected.

MTB studies (the Swiss National team sponsored some good ones) have long shown that the lowest "rolling resistance" on dirt comes from the widest tire you can fit and run at the lowest pressure. My suspicion is that this is mostly because, unlike on hard pavement, the surface "softness" starts coming more into play at the tire/ground interface, where a narrow and/or hard tire is going to deform that surface more than a wide/soft tire. Of course, tire measured width is a function of the internal rim width, so that plot isn't exactly an "apples to apples" comparison of the rims.

In other words, that plot shouldn't be surprising in the least :-)

---

http://bikeblather.blogspot.com/

So inertia (wheel, rotating mass) is ~9W or less than 1% in a 1000+W full sprint.

Is it correctly understood:

So the difference in inertia from the Zipp 303 to, say, a lightweight low profile wheel that some people prefer for climbing or crits for “rotating mass reasons” would be much smaller than 9W and almost negligible or at least negligible compared to the aero benefits of a higher profile wheel?

Exactly. I was a bit surprised they devoted as much space as they did in that discussion to inertia. The inertia of the bike+rider system is WAY dominated by the mass of the rider and bike, and other more important properties (such as aero) are vastly more important than any rotational inertia differences between wheels.

Rotational inertia as a performance property is a "red herring"...

---

http://bikeblather.blogspot.com/

Rotational inertia as a performance property is a "red herring"...

Just don't try and convince anyone of that who just bought a new pair of lightweight wheels. I get flamed so often on the Riding Gravel forum for it that I just gave up and let them stew in their ignorance. Even math does not convince them. (I used the Kraig Willet article that is clearly well done.) I like Riding Gravel for a lot of things, but the main writers reviewers are decidedly low-tech, have never used a power meter and say stuff like "the lighter wheel is noticeably quicker" and about tires "it rolls well" without providing any data at all. Other than weighing each component with a super-accurate scale. Of course, they get to test out a lot of top end stuff and no one would send them their gear if they quantified some of that stuff and said, "Your 2000 dollar wheelset" does not really do much.

Super low to me. I know about this breakpoint where increasing pressure causes increasing power on a rough surface, but if I pump up less than 101 psi I get problems wit snake bites (running tubes in my clinchers though, di not have tubeless). Used to pump up upto 122 psi when I still thought the harder the better.

Still with 55 I think I would not get vey far.

I acknowledged in a later post that this is all biased towards Tubeless. Tubeless is the key for running comfortable and still fast pressures. FWIW, I run tubes in my Time Trial setup and am nowhere near 55psi.

---

My YouTubes

Yes I thought that would play a role, tubeless or not.
What strikes me still though is that the article of zipp linked in the first post states:
"The 303 Firecrest has a max tire pressure of 72.5psi (5 bars)"
where I guess that the 303 Firecrest is also suitable for non tubeless use.
5 bars seems to be very low to me, but probably I have to learn and go even lower than the 100 psi I run at the moment.
I'm a bit confused at the moment.
I might try to run 6 bars with conti 5000, I weigh 190 lbs; do you think that would be ok? I would fear flats, especially in a race I rather loose some speed as getting a flat.

Well your issue is the 190lbs. If you're running something like a 28 then yes, you should be fine around 90psi/6bar. I'm a tubular guy that kind of moved on from tubies, but what I loved about my tubies was the ability to not run ridiculous pressures to avoid pinch flats. Now, that phenomenon is much less a concern for someone of my size, but the fear was still there.

In terms of pressure we need to look at volume and the larger the tires obviously the lower the pressure, all things being equal. In my Time Trial setup, which runs latex tubes and 23mm corsa speeds, I'm around the 6bar mark. but bear in mind that my entire system weight is ~30lbs less than just your weight. I also run as high a pressure I can get away with for the pavement I ride. Most of the stuff I ride on is like glass. For some of the Time Trials I do that have a lot more broken pavement I adjust down.

Really you need to experiment. If you're into testing then find a stretch of road that matches what you ride and figure out what works best. Then you'll have to figure out if pinch flats will be a problem. FWIW, I would ride a slightly higher pressure than optimum if it meant I would finish the race instead of taking a wheel from neutral service.

For testing out what works I suggest http://cdacrr.blogspot.com/

---

My YouTubes

I weigh a bit more than you (215 at the moment, have been heavier over the last few years), I haven't run anything above 95psi in years. I can't remember the last time I had a pinch flat. With 23mm GP4Ks (which measure 26mm on my wheels) I'm running around 90psi, and with 25mm GP4Ks (which measure 28mm) I'm running around 80psi. If I were 190 lbs, and/or my tires measured wider, I'd be running even lower pressures...

---

"I'm thinking of a number between 1 and 10, and I don't know why!"

I remember a snake bite when I had a bit lower pressure, anyway I have 23 mm front and 25 rear and as I said I pump up to 100 psi at the moment. You have 80 psi. Isn't it strange that zipp restricts such:
"The 303 Firecrest has a max tire pressure of 72.5psi (5 bars)"

I mean at least me but even you as a rather low pressure rider could not purchase this rim because you can only inflate it up to 72.5. I think, but correct me if I'm wrong, that also Tom A and Josh at Silca talk about pressures of 100 psi on rough roads. Although lower pressures are even faster but more prone to flats. This max of 72.5 psi just feels strange to me as if it is a typing mistake.

Definitely not a typo. The reason is that both the 303S & 303 Firecrest are hookless rims. ETRTO standards only rate any hookless rim up to a max pressure of 72.5psi.

So basically, run higher at your own risk (and no doubt invalidate any warranty cover)

Actually, I could run the recommended pressure, I would just need a tire that measured at least 30mm when installed on those rims. With a 30mm tire, I would be right at the recommended maximum pressure, with 32mm tires I could run in the mid 60s.

How wide are your rims, and how wide do your tires measure when installed on them? If I put a 23mm tire on my old Open Pros, on average the tire is actually going to measure 23mm, and according to Silca's calculator (and my own testing), my ideal pressure would be about 110psi. Put those same tires on my FLO 60s, and now the tire measures 26mm. And according to Silca (and again, my own testing), low 90s is ideal, while 110psi is noticeably slower and harsher riding. Put 25mm tires on the FLOs, and they now measure 28mm, and the ideal pressure drops again to about 80psi. And 110psi rides like crap.

Also keep in mind that tire widths are very inconsistent across brands. I've seen a lot of OEM spec tires that run significantly narrower than labeled, even on wider rims...

---

"I'm thinking of a number between 1 and 10, and I don't know why!"

Thanks for your thoughts. I looked at Silca tire pressure calculator, but that only seems to work in the "professional" version.

Anyway, I measured my sizes:
Front Tire: 23mm 4000 SII measures 24,2 mm Rim: 808FC 27mm running 7 bar 100 psi at the moment
Rear Tire: 25mm 5000 measures 26 mm Rim: Citec 24 mm running 7 bar 100 psi at the moment

In races I run 25mm 5000 on the front, that should aerodynamically still be ok, staying under 27mm of the rim.
Aerodynamically, the rear tire seems to broad for the narrow citec but I think that does not matter because the rear wheel is hidden anyway on the front by the frame. I weigh 85 kg (187 lbs).

longtrousers wrote:

I looked at Silca tire pressure calculator, but that only seems to work in the "professional" version.

You get access to the PRO version by entering your contact info...but if you don't want to do that the results for road bike and Time Trial are below







What I used was a system weight of 207lbs, worn pavement/some cracks, install width of 26mm, and Cat 1/2/3 racing. For my tube setup the calculator comes pretty darn close. For my tubeless setup it misses the mark by ~40%. YMMV

---

My YouTubes

Use latex tubes...

Just an FYI, the full version is actually available without entering an email now: https://silca.cc/pages/sppc-form

Not sure why that specific link is hard to find but I was getting a bit tired of receiving the same thank you email after putting in my info every time haha.

---

Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
Deals on Wheels - Results, schedule, videos, sponsors

I use latex. Yesterday I hit a pothole with 100 psi no problem.

You need high pressure to prevent pinch flats with latex? I even use them in my MTB and I'm always bouncing off the rim...

You have more experience then. I had only once or twice a flat with low pressure, so "n" is too small to make statistical statements, I'm aware of that.

Thanks that works.

I put in my data:
214 lbs system weight;
worn pavement/some cracks
700c/29"
cat1/cat2/cat3 racing
50/50 weight balance

At the moment I have a 23mm in front and a 25mm on the rear. They measure 24 resp. 26.

For 24mm the calculator gives 102,5 psi;
for 26mm 90,5 psi.

I pump at the moment 100psi in both.
So acc. to Silca that's ok whereby I could lower the 25mm a bit.

Yes I read a bit and it seems also that these rims require tubeless ready tires (in which you can still have inner tubes I presume) and there is a table which only has 28 and 30 mm tires.
So these rims do not seem to be suitable for the tire sizes and pressures which I am used to.
Curious to see if this concept will get into the other wheels of Zipp too.

Keep in mind that a huge reason for the push to hookless is because they are dramatically cheaper to manufacture, not because they perform better in any way.

---

-------------
Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
Instagram • Facebook

Same shit as pressfit bearings?

The SILCA calculator works great on all rims including the 303 hookless, you just have to be sure to use the measured tire width on that rim and not the stated sidewall width.

There also seems to be continued belief that tubeless tires need different pressures than when using tubes, but we just have not been able to show this in any testing we have done. I know Zipp talk about inner tubes fighting against the air pressure by as much as 8psi, which if true would lead to a reduction in pressures when running tubeless, but again, we've tested for this and don't see any change in tire spring rates when comparing tubed vs tubeless, only differences in damping characteristics.

---

http://www.SILCA.cc
Check out my podcast, inside stories from more than 20 years of product and tech innovation from inside the Pro Peloton and Pro Triathlon worlds!
http://www.marginalgainspodcast.cc

I do not remember why I wrote at the time that the calculator is not applicable to the 303 hookless, I played a bit and it works. So I deleted that remark in that post #41.