Choosing tire size

[jrenaut]

I know everyone loves to put their two cents in on threads like this (some of you more than two). So, it’s close to replacement time for my tires. They’re 23mm Gatorskins, and I’m very happy with them. Excellent flat protection (though, anecdotally, slightly less so than Armadillo Elites, but also don’t feel like you’re riding on tank treads) and they’ve held up well. I expect to buy another set.

However, I’m wondering about tire size. When I started, I assumed that you should get the smallest size you were comfortable with, and bought 23mm. I assumed smaller meant faster at the expense of a little grip, but I don’t do a lot of bad weather riding, so no big deal. I gather that this is not really true, so I’m probably going to get a bigger tire. The question is, what size? The bike came with knobby 32s which I rode on once (the trip home from the bike shop). I have Velo Orange fenders that will accept something like 35mm max (Man, I love my fenders).

I’m looking to get a little more comfort for city riding without riding on balloons. How do I decide what size is right?

Topic

[hozn]

@KLizotte 70440 wrote:

I checked my tire sidewalls and it says the recommended psi is 115-125. Do people routinely go less than the manufacturer’s minimum? I’ve always been worried about pinch flats as opposed to speed issues.

Yeah, people do often run less — especially on larger tires. I run 80-85/90-95 (f/r) on 25mm tires. No pinch flats, but I also try not to plow into things. In 23mm I usually run around 100-110psi. I tried lower when running tubeless but ended up cutting my tires against the rim (effectively pinch flatting). For reference I weigh 175-180 lbs.

You probably won’t notice the difference in rolling resistance, but you I’ll notice the difference in comfort. And putting more rubber on the road helps grip. Go too soft and the tires will feel sloppy, though. Play around with pressures to find the sweet spot for you.

[Raymo853]

I think the pressure listed on tires is not the recommended but the recommended highest.

I ran Michelin open pro 2 25c tires for years. Huge 25s. Was so sad when I bought open pro 4 and their 25 are now normal sized. So looking for a good 28c tire. Probably going Schawable

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[ronwalf]

Michelin has an article with a pressure-vs-weight recommendation chart:

Bicycle Quarterly has a decent article on the subject, too.

[mstone]

@ronwalf 70452 wrote:

Michelin has an article with a pressure-vs-weight recommendation chart:

Bicycle Quarterly has a decent article on the subject, too.

The michelin chart has been floating around for a while, but it’s pretty disappointing. 20mm to 23mm is a pretty big difference in air volume, but they treat them the same on the chart. And all the tire sizes have lines with the same slope, even though the increase in tire volume is non-linear. And then they treat everything over 180lbs the same. I suspect it’s more marketing driven than science driven–it needs to look pretty, they’re focused on racers, and they want to be vague about what’s really necessary but outside the limits set by the lawyers. E.g., a 300lb guy on 20mm tires isn’t going to magically be ok riding at the maximum pressure printed on the sidewall. What it should say is “you need X psi, and if that exceeds the tire/wheel max, pick a different tire/wheel”. The BQ article is much more plausible.

[KLizotte]

I’m beginning to think that figuring out one’s correct tire pressure comes down to trial and error. The article referenced above says this “Inflating tires to the maximum pressure recommended by the manufacturer tends to underinflate narrow tires and to overinflate wide tires.” What the?!

My tires are as hard as rocks with no noticeable deflation when I’m sitting on the bike so obviously I’m overinflating so I’m gonna start by putting less air in each day and see how that works. I’m sure taking the bike out of a toasty apartment to freezing cold temps doesn’t help either.

[Raymo853]

@KLizotte 70459 wrote:

The article referenced above says this “Inflating tires to the maximum pressure recommended by the manufacturer tends to underinflate narrow tires and to overinflate wide tires.” What the?!
.

I can translate the first part of this. No one should ride tires smaller than 25c. And 25c should be for racers only.

Even the pro elite teams this year moved away from the tradition of 23 and smaller tires.

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[hozn]

@Raymo853 70467 wrote:

I can translate the first part of this. No one should ride tires smaller than 25c. And 25c should be for racers only.

Even the pro elite teams this year moved away from the tradition of 23 and smaller tires.

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The decision of some teams to move away from 23mm was probably driven as much by the teams using wider rims. The pro teams are predominantly on tubular tires which (from what I have read, anyway) behave fairly differently when mating different width tires and rims — specifically that a narrower tire isn’t going to fill out as it will with a clincher on those 25-27mm wide carbon rims. So I understand that to mean that a clincher 23mm can be wider than a tubular 23mm on wide rims. So it’s not apples-to-apples; 23mm tires definitely feel (and look) different on my 24mm-wide rims (17mm internal) as compared to my traditional 19-20mm wide rims.

I will agree that going smaller than 25mm seems a bit unnecessary — assuming you have wide rims. If you have traditional road rim, I would expect that 23mm will roll less / be less squirmy in corners and that isn’t without value. Not saying that other benefits won’t outweigh the cons still, but seems less of a no-brainer. Of course 25mm tires *barely* clear the rear brakes on my Motobecane frame, so it may not be an option for everyone to run 25mm on their road bike. Certainly running larger than 25mm is not possible on many road frames (so for this and other handling reasons I don’t agree that 25mm is a “pro-only” size). When rims are even wider (20mm internal widths?), disc brakes are standard on road bikes (making clearance easy), and fast tires come standard in 28mm, then 28 might well be the new 25.

[DismalScientist]

@KLizotte 70459 wrote:

I’m beginning to think that figuring out one’s correct tire pressure comes down to trial and error. The article referenced above says this “Inflating tires to the maximum pressure recommended by the manufacturer tends to underinflate narrow tires and to overinflate wide tires.” What the?!

This may be true with respect to a 15% tire drop, which the article states as ideal. Of course, this begs the question as to why 15% is ideal and to what extent performance drops as one moves away from 15%.

If narrow tires are practically routinely underinflated even when blown up to the maximum inflation on the sidewall, I would expect to see a lot more cyclists complaining about pinch flats.:rolleyes:

[vvill]

I rarely inflate past 80-90psi on any of my tires. I have pinch flatted my 23s a few times though out of laziness (not re-inflating after several rides).

I imagine riding 23s on wider rims would be as good as, if not better, than 25s on narrow rims. This is based solely on my experience riding 32mm tires on wider rims (23.2mm external, 20mm internal) on my CX bike.

[KLizotte]

Well, I rode for an hour today with the tires only at about 98ish and I didn’t flat (yeah!) and the ride was noticeably less harsh but not of “unicorn fur” quality. The bumps along the Custis were less painful so I think I’m a convert to lower psi!

[Author]

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