Sy Reene

The sidewall is supposed to indicate the safety margin for the construction of the tire itself, not specifying the ideal inflation from a performance perspective which of course depends on rider weight and road conditions. Schwalbe calls their chart a 'very general guide'

Racing Dan

Me thinks you are the one throwing around basic formulae and charts to appear knowledgeable, and me thinks you are the one putting words and movies in MY mouth, while adding insult after insult.

As I said before no one ever questioned the the basic premise that fatter tyres "require" less pressure, only not that much less. I wasnt the only one mentioning it, but apparently you are such a hot heat you didnt even notice.

Moving on .. Bye!

Cypress

See above.

Cypress

Diameter of 31.54mm gives a cylinder volume of 1679777 ml

The Schwalbe chart sort of implies a 30mm tire to be run at 90 psi, so I used that. Your 31.54mm width would only need a pressure of 81.27 psi to be comparable to the 30mm at 90 psi.

noodle soup

yeah, I understand what the sidewall recommendation is for, but using the chart provided would put me over the max inflation if I put on a little weight.

xroadcharlie

Regardless of what any chart says or the advice of a bike shop tech I would not recommend going more than 10% over or under the tires printed pressure range.

In fact we can use this range to help determine the correct tire pressure for our needs as it includes many variables such as tire casing suppleness, tread compound (for traction), ect.

The heavier you are and more aggressive you ride, the higher up in the range you should use. There is a range of preasures that will likely work well. I start with my best estimate taking into account the pressure range on the tire, the results from a 15% drop based calculator, and riding conditions. Then go from there.

Sy Reene

So, I'm not sure where any of this discussion leaves us.. We have an OP who weighs 190, but with 32mm tires that indicate max of 70psi. We have HED who'd recommend 55-60psi. We have Schwalbe chart who'd generally recommend somewhere around 85psi, and Cypress's calculations around 80psi. Tire inflation calculators seem to indicate a rear inflation somewhere in the 70s. Someone quoted Hunt wheels max of 50psi for 33mm. These don't seem like small disparities.

Cypress

It's a right mess.

I treated it like ammunition loading: Start safe (higher psi) and work your way to whatever pressure "does best" for your uses.

bbbean 

That's a good analogy. There is a lot of "what works best for my application" involved in both. Throw in the fact that current research is changing the way we approach tires/wheels/psi/aero, and you have are trying to hit a moving target.
Ultimately, "find what works best for you" is rarely wrong.

xroadcharlie

I do find it interesting that some tests results show that lower tire pressure then some use as a baseline actually improves speed. I know when I run my 50 mm tires at low (30 - 35 psi) pressure my assumption has always been I should go noticeably faster by increasing it to 40 - 50 psi. Yet when I ride at the higher pressures I can honestly say there is little difference in speed. Mind you I don't do controlled tests, But I was still hoping to feel some improvement. All it did was make my ride uncomfortable. Because the ride is stiffer, I end up having to go slower anyways.

Next season I'm going to keep the tires at the lower end of my range. Kenda recommends 40 - 65 psi. So I think I'll try 35 front and 40 psi rear next time. out. I try to stay within about 10% of what Kenda recommends. These are inexpensive tires, So it comes as no surprise that they are not the most comfortable or fast. But for recreational riders like myself at the lower pressure they make a very good, Dependable tire overall. I will definitely be moving to a better tire next time. One with a semi-slick tread and more supple sidewalls.

Cypress

1:25 in this video shows the GCN crew running 75 psi in their 25c GP4KS tires. *edit* presenter weighs 161 pounds

Sy Reene

Sounds about right (at least for the rear wheel).. 45/55 distribution for descending position (more weight on pedals). Wide rims with notorious GP4Ks wider-than-nominal inflation widths. Added 20lbs for his clothing, water bottle and bike. Perhaps he even took a little air out given intent to bomb down a wet roadway -- ie. for a bit more grip?

tyrion

Really useful info from Josh Poertner here:


Some takeaways:

- the max pressure printed on the tire is simply half the tested blow-out pressure (by law).
- the max pressure spec is almost always too high for optimum rolling resistance.
- smooth looking pavement varies a lot in actual smoothness (Poertner analyzes race course pavement for pros to determine optimal pressure).
- wealthy neighborhoods usually have finer, smoother pavement.
- optimal pressure (for rolling resistance) is almost always lower than you would determine by subjective riding feel - optimal pressure feels subjectively slower!
- generally speaking aero considerations trump rolling resistance in road racing.

Sy Reene

Very interesting.. led me to search Silca's site.. you might find of interest this general white paper. Salient details from this testing was 190lb rider+bike on TT rig to help ensure a close to 50/50 weight distribution on the tires. 25mm GP4Ks
https://blog.silca.cc/part-4b-rollin...-and-impedance

Gconan

noodle soup

Have you figured out what tire pressure works well for you?

Metallifan33

For now, yes. This thread has been extremely enlightening. I found it interesting (from the YouTube video) that the max labeled pressure is around 1/2 the value at which the tire had structural failure (in lab conditions). What's interesting here is this may be more of an issue with wider tires than narrow. For example, a normal road tire may be at 100 to 110 psi (but the degrade point may be 220 or so)... well, you'd never inflate to close to that. But for a 30+ tire, the max being 70 and structural failure at (in the lab) being around 140... well, the 100 psi that the LBS set for me is closer to that (again lab conditions differ from actual road conditions... which could be worse). Further complicating the matter is the recent rise in popularity of wider road bike tires.
Regardless, I learned that its highly subjective and a personal style depending on the road conditions etc. (being an ardent Formula 1 racing fan, I can appreciate the complexities of tire behavior).
I started at 65/70 and dialed it down to 60/65... I'll keep it here for now till I settle in (only 50 miles ridden so far). I also prefer only changing one thing at a time (and currently haven't settled on a saddle yet).
Thanks again for all the comments!

eduskator

Current trend is wider tires at lower pressure! Research suggest they give better performance.

Nonetheless, just run the desired pressure that makes you comfortable and that you prefer. You can go a little below of above the recommended one - it's just numbers

Sy Reene

Please realize that this 2x sidewall pressure thing is speaking ONLY about the tire. There are numerous rim makers that would give you much lower values as safe with their rims. The lab testing I think referenced using a steel walled rim, that is bound to be able to withstand anything (more or less) thrown at it. Not sure also what width rim they use for given sized tire.

Fendertele

Interesting thread. I suspect your bike is a 2020? My SL5 is a (2019) with same tires. The tread is different and inflation labels differ significantly. Makes me wonder how much of the difference is relative to tire engineering vs market trend. Embarrassed to post these pics after seeing how clean your bike is.

Metallifan33

Yeah, it's interesting for sure. I looked up the tire on the Trek website, and the max pressure they show now is 50 psi! You can see how this would thoroughly cornfuse a noob.
https://www.trekbikes.com/us/en_US/e...-tire/p/25927/

My bike is the 2020 version btw.

wallace1973

Hi I realize this thread is a year or two old but I tripped over it whilst Googling.
I have the same bike (Domane DL 5 Disc) and tires (Bontrager R1 700x32 / Hard-Case Lite) as the original poster. I got the new bike a few days ago, ready to take it out for a spin I pumped the pressures up to what I have been used to with my older (thinner rim/tire) bike - 95 to 100 psi range.

I then wondered why the bike shop have given me the bike with lower pressures (seemingly 50-60 psi or so) - then I checked and noticed the "max 70 PSI" warning on the outer tire.
I immediately deflated and reinflated to around 65 PSI.

I did no riding on the tires - is there a chance I did any damage to the tire or rim by pumping temporarily to 95/100 PSI for a few minutes before deflating again? From what I've been reading here *seems* not but just checking!

P.S. I weigh 195lbs and the bike is around 22lbs so guessing 217 ish lbs combined rider + bike weight. From what I can gather it's a question of picking a starting point and adjusting to your own comfort levels from there. I am will be exclusively road riding - no gravel.

WhyFi

Nah, don't worry about it. Ride and be happy.

Badger6

No chance you damaged anything. None. Zero.

As for starting pressure using your bike+rider weight and estimating the speed as a moderate group ride on a worn tarmac surface (some cracks), start out at 62psi (4.3bar) R and 60.5 (4.2bar) F, and adjust up or down based on feel. https://silca.cc/pages/sppc-form

Just for reference, I have a bike that rolls on tires measuring 35mm when inflated, tubeless, and the recommended pressures are about 55psi (3.7bar) and I routinely run them below 50psi (3.2-3.3bar) with no issues.

wallace1973

Hi great, thanks for the reply and advice, and also to WhyFi. Yeah these have tubes, and tbh although my rims are tubeless ready I am unsure if I will go to tubeless tires, so for now going to assume I am sticking with tubes.

I'll take a look at those starting pressures and see how I go. Since my intention is to lose some weight guess I should periodically review the pressures as my weight comes down.