DaveSSS 

Don't forget gauge accuracy. Be sure your gauge reads correctly.

PeteHski

Well if you banged those pressures straight into a 28 mm tubeless setup you would definitely be doing yourself a disservice!

Seattle Forrest

I put 5 psi less in the front than the back. Like you, there's only so far I'm going with this.

Sy Reene

You can simply just take the Zipp calculator and see larger differences than you're showing by simply toggling between tubed, tubeless and hookless tubeless selections.

PeteHski

I see what you mean. I guess the Silca calculator doesn't attempt to account for all those parameters and just by coincidence it spits out much the same recommendations for my specific combination of those parameters. I'm surprised that the Silca calculator doesn't make any differentiation between tubed and tubeless tyres.

Sy Reene

I guess it's just my theory, but can't say I've seen anything contradictory yet, but Silca spits out what they deem 'optimal' (for lack of a better term). Ie. what yields fastest speed for the given parameters for a given power input. That is, what data is out there that, providing an average weight rider would be within safe operating levels regardless, that a tubeless tire should be run at a lower PSI than a tubed tire to yield max speed for provided power?

We know that a tubed tire setup can be run a max pressure higher than Tubeless hooked, which in turn can be maxed at higher value than hookless Tubeless. On the flip side, the tubed setups can't be run at as low of pressures as the TL options without more severe risks of pinch flatting. Perhaps the returned values for Zipp's calculator is to match the marketing if they want to rate a rim as ok for certain max rider weight and the likely tire width that rim is optimized for? On the flip side, Silca seems to disregard any tire, rim or weight ratings, and effectively is telling consumers to figure that part out for themselves.

PeteHski

Come to think of it Pirelli recommend the same tyre pressure for both tubed and tubeless setup of their latest TLR race tyre. But with their endurance focused TLR tyre (Cinturato) they recommend a lower pressure when set up tubeless. So maybe the latter is intended more for optimal comfort.

Iride01 

The only disservice will be if I continued to maintain that PSI for every ride and never tried other pressures to see if I both felt something better in my legs or the handling, and compared that to my metrics collected for those rides.

My use of higher pressures in my tires isn't some stuck mindset as those that only do what formulas and calculators tell them to do. I have on many occasions tried out different pressures. And not just when changing my tire size, but also when changing models or brands that are the same size.

Typically I'll ride six to twelve rides at the same pressure. Then adjust it up or down and ride the same number of rides at that new pressure and then rinse and repeat till I find the PSI I like.

PeteHski

So you assume people who use tyre calculators never adjust their starting pressures?

Out of interest what pressure would you have started at with 28 mm tubeless?

Iride01 

That's what to me your assumption was about people that .....I probably won't know till I get 28 mm tires. I wouldn't expect to run the same pressure as my current tires once I did my trials with them. So as long as I'm within the range suggested by the mfr, what does it matter what PSI I start out with?

Tubed or tubeless, my procedure for finding out what PSI to run them at on the road conditions around me will be the same.

PeteHski

My impression here is that you would grossly underestimate how much to drop from your current pressure for a 28 mm tyre. Not a big deal, but you would end up wasting more time dialling then in.

These calculators would give you a very good idea how much to reduce from your preferred pressure on narrower tyres. They provide a good relative tool in that way.

Koyote

Well, stuff happens.

In a gravel race last month, I was descending, in a forest with dappled sunlight, with my sunglasses' lenses smeared up with sweat and road grime...I thought, "I hope there's not a big pothole or tree root on this trail, 'cause I would not be able to see it." The next moment, BAM! Right through a nasty pothole. The wheels were fine, but the rear tire burped out enough air that I had to stop to pump it up.

At least it was towards the end of the race; three riders passed me as I was pumping up the tire, though I later caught one of them. Yeah, I was really bummed - I ended up in 21st place instead of 19th. It was tragic!

tomato coupe

Yeah, that's rough. You coulda been ... a contender.

Psimet2001 

I was JUST coming in here to drop that one. a couple psi is also a huge difference in these lower pressures as well.

Koyote

Right! I mean, 19th place gets you on the podium, right?

Iride01 

Maybe we could do it like T-Ball and every gets a participation trophy or gets to stand on the podium. And no winners or losers or even timekeeping.

PeteHski

Only for you "proper" roadies! For me I can't tell the difference between 69 and 71 psi.

Chandne

25mm tubed GP4000 that measure a touch over 27 on 19mm (internal) rims. I have been playing with pressures. My roads are usually quite good with a few expansion cracks in sections. I am 175 lbs and have ranged from 70-90 rear and 65-80 front. Recently, it feels like ~70F/80R feels the best and can be slightly faster (per my Strava stats/PRs) than higher pressures on the downhill corners and downhill fast sections too. I definitely feel more confident downhill at slightly lower pressures but have not gone as low as many do. I'll swap to tubeless in September and see what pressures feel the best, with no worrying about pinch flats.

merlinextraligh

but rim damage, and burping still are

PeteHski

I suppose so if you run ridiculously low pressures. Not something I've experienced anyway.

WhyFi

Burping is exceptionally rare with road tubeless.

merlinextraligh

The same physics that cause a tubed tire to compress enough to pinch a tube against the rim, compress a tubeless tire against the rim sufficient to cause rim damage and/ or the bead to separate enough to flat the tire.

The point is that there is no free lunch. If there’s not enough pressure in the tire on a tubeless setup, by definition you can’t pinch flat, but bad things still happen.

So whether, you’re tuned or tubeless, there still needs to be enough air pressure to support the load and forces imposed. The precise math may change as to what is too low, but bad things still happen if the pressure is too low.

Seattle Forrest

So don't run 28 mm tires at 5 psi like a mountain bike. 🙂

WhyFi

Whatever, but burping isn't a thing with road tubeless.

Chandne

The nice thing about hookless rims is that the rim bead area is so much stronger. It takes a lot to hurt those over the hooked-bead rims.