60/65 psi on 25 mm tires?
 

Hi! I weigh around ~56 kg and my bike is just under 9 kg. For the most part, I ride on rough pavement. Using Silca's tire pressure calculator, it recommends around 80 psi front and 85 rear for my 25 mm tires but I find it pretty uncomfortable. Heck, even dropping down to 70/75 is still a bit jarring to me. I've tried running 60/65 a few times and they seem to be a noticeable improvement, but I'm worried if that's too low and I have a higher risk of bottoming out. My internal rim width is pretty narrow at 15 mm, so the 25 mm tires measure to exactly 25 mm, give or take. What do you guys think? Is this a good excuse to ditch these tires and go get 28 mm?

If you can fit 28's on your frame and have a string preference for the pressure you mention, then it's a no brainer. I would not run 25's quite as low as you mention (60/65) for the exact reason you mention. :)

I've ridden 25s at 60-ish psi a few times after fixing flats, because it's a hassle to pump it up to 80-90 using a micro-pump, and I'm 72kg. I don't think a 59kg rider would be in actual trouble at 65 psi unless you plowed full speed into a giant pothole.

However, yeah, sounds like a case for 28s.

Also, better tires feel a bit less harsh at the same pressure.

initially I was gong to write that this is a bit low pressure but given your low body weight, why not, try it and if you end up bottoming out on the rims or flatting a bunch, change things up (pun) a little bit.

Running 28s is a perfectly reasonable option, but if you're not actually bottoming out running 25s at 60/65, then you're probably fine doing that as well.

On 25mm tires on your body weight, for rough pavement, 65r/60f sounds far more reasonable to my ears than 85r/80f. If you start pinching, go wider.

If you're going to play with lower pressures, also pay attention to how they feel when cornering, in addition to the possibility of bottoming out; with narrow ID rims and low pressure, it may get to a point where they don't handle gracefully under aggressive cornering.

You're not going to bottom them out at that pressure. If you aren't getting pinch flats then go ahead and run them lower.

If your frame can fit 28s, I would step up to those and make life easier. If not, I would just try the lower pressures anyway. At 56 kg you will probably be fine.

+1 on tire quality.
https://cimg9.ibsrv.net/gimg/bikefor...1c8e11b417.png
from Silca Blog Part 4B: Tires with More Supple Casings Have Lower Rolling Resistance Everywhere and are More Forgiving of Over/Under Pressure

On going to 28s, if you run 60/65 in 28s it's going to feel harsher than the same in 25s. I don't know what the equivalent under-inflation comfort-level PSI for 28s would be offhand; somewhere in the 50s on 28s I imagine?

I guess nobody wants to just tell OP to HTFU..

What tires are you running? Something like an an “open tubular” with higher thread count casing will give a more forgiving ride. Also in addition to this, latex inner tubes are a good choice for a better ride, the ability to run slightly lower pressures and being more resistant to pinch flats. Even changing to tubeless rim tape can help if you are running Velox. The tubeless tape helps create slightly more air volume for your 25mm tires.

I suppose if you really wanted to go even lower (in pressure) on those same rims you could get those Stan’s tubeless conversion rim tapes that have the presta valve built right in to the rubber rim tape. I bought a set of these on clearance when Performance Bike went out of business but haven’t really had the need to try them since my tire set ups are latex tubed clinchers on one bike and 25mm/28mm road tubeless on the other.

If there is any way to rebuild your current wheels for road tubeless, I highly recommend it. When reading these forums you would think avoidance of flats is all that tubeless is good for. My experience has been an increase compliance on choppy road surfaces which keeps me more relaxed and fresher thanks to less harshness. I can ride in the “gutter” if I want to (still avoiding broken glass and debris) and hang out there comfortably. My road tubeless bike’s pressures could safely be run in the high 60’s front and the mid 70’s rear. I weigh more than you though, currently around 88 kg.

I'd have to ask what tires you are running too.

I went from a discontinued model of Continental Ultra Sports that was uncomfortable at 70 PSI to a Vittoria Rubino Pro (also now discontinued) and it was more comfortable at 125 PSI than the Ultra Sport was at any PSI.

I pay no attention to what a tire pressure calculator says. Just ride the pressure you feel most comfortable on. If you need a starting point then you can start with what the calculator tells you, but then adjust from there both up and down. Eventually you'll know what works for you.

Sorry, but I gotta think there are safety limits that come into play at some point.

Well I didn't see that you addressed safety limits in any of your posts to this thread. Why should I?

All the pressures I wrote about were within the limits of the tires I used them on. The calculators for tire pressure don't tell us what is safe. They just tell us what they think will give us a good enough ride.

Agree with above would be helpful to know what tires you are running.

Based on the data you do provide, I would aim for something like 65F and 70R, much lower and it may get a bit squishy.

Bike and I = 150 lbs combined on 25's, 250 mi/week 55/50 all day long no pinches. For high speed cornering I would bump it a little.

You can feel an underinflated tire bottom out. It's pretty noticeable. If you aren't bottoming out that I say go for it.

​​​​​​​+1. In your position, I'd have no qualms going down a step to 65/70. I'd probably even be happy there, without going to 28s. :thumb:

I don't think relying on having not bottomed out yet is a good idea, unless you have been riding that way for years (sounds like you have not). In the last year I bottomed out twice.. two times too many for me. I didn't get a flat either time but I did warp my brake disc on one hard hit and was probably not far from rim damage. I eventually realized my pump was mis-reading and no bottom-out since I corrected for that.

If you are regularly on rough pavement I would fit the biggest most supple tires you can, set up tubeless for added insurance against pinch flats, and run a bit on the low side of the recommended pressures (say 5-10psi below the SRAM calculator which itself seems lower than the Silca one).

I run 28s at 65/70 with no issue and I'm 50 pounds heavier than the OP. I'm nearly certain that pressure is fine with 25s.

I would never even considerpver inflating my tires as it's such a rare thing actually run into a 'giant' pothole. You'd have to dramatically over-inflate your tires to keep a pinch flat from happening when plowing into the 'giant' pothole and you'd hate the ride quality you'd have the 99.9999% of the time you weren't finding such road hazards.

LaPlace’s law (wall tension = pressure x radius) says this discussion is largely meaningless unless rim width rim is specified.

It was in the OP.. 15mm

Thanks for the information. I started biking for 2 month after my college time, so I'm a beginner.
I'm about the same weight as OP and using 25/28 on my 2 bikes. When I bought my first bike with 28mm tires, I felt the ride were so harsh until I reduce it's tire pressure little by little to a point that the ride is comfortable to me. My 2nd bike with 25mm has much better ride comfort with higher pressure. Since both bike are used, I have no idea how old those tires were. Both have continental Gatorskin tires. I am wondering if the age of tire/tube also contribute to the ride comfort.

Ryan

Different bikes even if both the same frame material can give different ride qualities as to how bumps are felt. Also, tire manufacturers are constantly changing the the methods and materials tires are made from but still re-using the same model name of the tires. My old Continental Ultra Sports from circa 2010 probably don't ride anything like the Continental Ultra Sports today. If you look at the product numbers they aren't the same but the name is.

So I expect the same thing might be happening with your Gatorskins. Unless you find you need them for flat protection, You ought to try GP5000 or some other brands premium road tire. They'll ride better than any puncture resistant tire. And if you are in a place with no goatheads of thorn like me, then you'll go a year or two between punctures.

I definitely will try different tires next time for sure. I am not aware of what's special of" Gatorskins" as you mentioned "Unless you find you need them for flat protection"
I'll dig into it later. Thanks!

Ryan