Bicycle Mechanics - tyre width, tyre pressure & comfort

Hi all,

My new bike in planning is going to be a road bike with 700C tyres. I am planning on going for a 28mm wide tyre for a bit of extra comfort, however am I right in saying that comfort really comes from the pressure and not the width. I have some 35mm tyres on one of my bikes which have a pressure rating of 100psi, I want my new bike to be able to handle the bad roads better than my current 23mm tyre'd road bike (120psi).

I guess the 28mm tyres will be around 100psi too, is this the MAX or the recommended?

Is it the case that pressure matters more than width?

My 35mm tyres are specialized armadillo nimbus tyres, would it be possible to run these at less than the rated pressure?

Are there any bombproof tyres that will be more comfortable? (if it comes to it, I would prefer more puncture protection over comfort)

Thanks

Daven

100 psi in a 35mm tire is incredibly overinflated....don't do that unless you want a harsh ride and no benefit to your larger tires.

I weigh 175 and when I ran 28's I put maybe 95-100 psi in the rear and 90 psi in the front....no pinch flats, decently comfortable. My current 37's I run 65 psi in the rear and 60 psi up front....very nice ride.

Are there any bombproof tyres that will be more comfortable? (if it comes to it, I would prefer more puncture protection over comfort)

If this is the case, just run armadillos in whatever size you want and pump them up to the max psi listed on the sidewall of the tire.

People have argued with me on this, but my opinion is that larger tires run at low psi offer FAR FAR more comfort and also additional puncture protection. Most flats I have fixed at bike shops are from people using crappy air pumps and not running the right pressure (pinch flats).

There really is no reason to run 23mm tires unless you are racing, or doing some intense training....if so, go for it. But for commuting and general riding or touring, there is no way to make 23's as comfortable as would be ideal on crappy streets....if you run psi lower you will just bottom out the rims.

I run 28 mm Gatorskins at 90 psi on my retro grouch bike and don't pinch flat. Actually, I haven't had any flats at all with that rig. FWIW, I weigh right at 200 lbs.

Thanks, is there any real-life difference between 100psi and 90psi in terms of comfort?

@Gene2308: 100psi is what the tyre recommends...

Armadillos are my tyre of choice tbh. Would a higher width armadillo at a lower psi be slower? I only commute but I like to go fast!

Thanks

Thanks, is there any real-life difference between 100psi and 90psi in terms of comfort?

Thanks

Do you have a friend who could vary the pressure between multiple rides - and not tell you what the pressure is?
If you would be able to tell the difference more often than not then maybe there is a real-life difference between 100 and 90.

They probably listed 100 psi due to marketing - the thinking that people won't buy a tire unless they think they can fill it up to absurd pressures even when it is completely unnecessary and foolish.


Would a higher width armadillo at a lower psi be slower? I only commute but I like to go fast!

Yes, there is going to be a trade-off between comfort and max speed. It's kind of like clothing that is waterproof and breathable.

The larger the tire width, the less pressure you can use. Ratings on tires don't mean all that much. I use 70-75 psi on some 35mm Forte Metro-K's, they are both fast and comfortable.(They say run 90 psi!) They have less rolling resistance than Turbo Armadillos in a 28 when I used them. They were also very harsh. Are the Forte's "bomproof" ? I don't think there is such a thing unless you ride solid rubber tires. I've had one flat this season, with many miles on a stretch of highway shoulder strewn with crappola galore. The flat was from a fine piece of wire .... the type no tire can be immune to.

my 2 cents ...

There is an article in the Adventure Cycling monthly that talks about air pressure. It is a variable controled by the tire size and system weight. I have 28's on my road Heron and inflate the front to 75 and the rear to 85. My bike and I weigh 221 when fully loaded.
The sidewall pressure is 1/2 the amount necessary to blow the tire off the rim.
http://www.adventurecycling.org/resources/200903_PSIRX_Heine.pdf

Thank all, I guess some experimentation is required!

I go by the chart that Davidad posted, and it's spot on for me.
If you're bellow 200lbs a 32C would handle moderately bad roads very well. Over 200lbs on bad roads? 37C or higher unless ya like feeling the bumps.

Yep I am below 200lbs probably about 175 with me and bike.

The advantage of wider tires is the result of the shape of the contact patch. Tires deflect until the area of the contact patch times the pressure equals the axle load. Narrower tires require higher pressures to avoid having a long narrow contact patch, and the energy loss due to added side wall deflection.

Wider tires running at proportionately lower pressures, have shorter wider contact patches, less energy loss to side wall deflection, and tend to give a more comfortable ride.

Cyclists tend to believe that narrower is faster, but would do well to look at the automotive world where tire size, pressure and footprint are carefully matched to the application.

Hi all,

My new bike in planning is going to be a road bike with 700C tyres. I am planning on going for a 28mm wide tyre for a bit of extra comfort, however am I right in saying that comfort really comes from the pressure and not the width. I have some 35mm tyres on one of my bikes which have a pressure rating of 100psi, I want my new bike to be able to handle the bad roads better than my current 23mm tyre'd road bike (120psi).

I guess the 28mm tyres will be around 100psi too, is this the MAX or the recommended?

Is it the case that pressure matters more than width?

My 35mm tyres are specialized armadillo nimbus tyres, would it be possible to run these at less than the rated pressure?

Are there any bombproof tyres that will be more comfortable? (if it comes to it, I would prefer more puncture protection over comfort)

Thanks

Daven

My view is that comfort comes from reducing pressure, at the expense of rim protection. You can regain rim protection at a comfy pressure by going to a bigger tire size.

Thanks, is there any real-life difference between 100psi and 90psi in terms of comfort?

@Gene2308: 100psi is what the tyre recommends...

Armadillos are my tyre of choice tbh. Would a higher width armadillo at a lower psi be slower? I only commute but I like to go fast!

Thanks

I think small differences in pressure can be significant. I use Conti 28 mm Gatorskins on my Trek, and set at 110/100 they are harsh. Reduced to 100/90 (f/r, sorry) they are just a bit better in vibration, and at 90/85 they are comfortable but I should watch out for bumps. I weigh about 180.

The sidewall pressure is 1/2 the amount necessary to blow the tire off the rim.

I see that comment made all the time, literally for decades, but I've never seen a first person source. Are you aware of a bike tire testing protocol or something similar?

If it were true, I'm thinking there would have to be a standardized test rim because rims aren't all the same. I'm thinking it's one of those things that has gradually worked it's way into the folk lore.

There is an interesting article on this subject in Bicycling Magazine, November 2009, P. 70. The gist of the article is that you should run whatever pressure (above factory recommended minimum) that feels good for you. A pressure guide from Michelin is included, but other charts are available from Schwalbe and Sheldon Brown. Using the pressure guide chart, and inflating my 23c Grand Prix 4000s to 105 psi for my 150 lb weight, I ran my favorite 30-mile, mixed-terrain training course about 2% faster than I did with 23c Diamante Pros the week before, inflated to 135 psi, and I felt more comfortable doing it. Even though I don't take part in organized racing, I'm still a speed freak, so this experiment was a real eye-opener for me.

I run 28s and pressure in the low 80s up front, around 90 in the rear.

Comfort is in low pressure, but also, I believe, in putting a bigger smear of rubber on the road. The 28s tend to float over trouble, instead of bouncing around.

I see that comment made all the time, literally for decades, but I've never seen a first person source. Are you aware of a bike tire testing protocol or something similar?

If it were true, I'm thinking there would have to be a standardized test rim because rims aren't all the same. I'm thinking it's one of those things that has gradually worked it's way into the folk lore.

I agree that it's probably folklore. Tire companies establish maximum pressures consistent with the burst strength of their casings, obviously with some kind of safety margin, but it might not be 2:1. In any case these aren't necessarily ideal pressures.

They must also test the "blow off the rim" pressure, but that's difficult and varies with rim width, bead seat shape, and manufacturing tolerance of the rims. It isn't reasonable that they could take into account all the rim related factors not within their control, and if a tire does blow off, who can say if it was because of defective tire, over inflation, poor mounting, undersized rim or whatever.

Lastly with wired-on (aka clincher) tires, the tire pressure, combined with the section determine the side stress on the rim flange. It isn't a tire problem per se, but can easily become the riders especially as rim flanges thin and weaken with braking wear. (not a factor with disc brakes)

For those wanting ideal pressure, there's quality research indicating rolling resistance bottoms out when the inflated tire compresses about 15% of it's height as it establishes the contact patch. Pressures above that won't lower rolling resistance any more, and will worsen the handling characteristics.

Is puncture resistance (in for example armadillo tyres) lowered at all by using lower pressures?

Thanks for all the informative replies.

Is puncture resistance (in for example armadillo tyres) lowered at all by using lower pressures?

I don't know of any scientific research on this but based on my 40+ years of experience, I guess that if it did, it wouldn't be by enough to consider.

Softer tires seem to pick up more tiny shards of glass, but harder tires ping glass and stones out with more energy and seem to get cut more often. It's six of one and half a dozen of the other. Choose your tire section and pressure according to your weight and it's distribution.

Is puncture resistance (in for example armadillo tyres) lowered at all by using lower pressures?

Thanks for all the informative replies.I've found lower pressure increases risk of pinch flats but decreases risk of punctures. That's because a high-pressure tyre will ride up on glass or nails and your full weight will be exerted at that point. Lower-pressure tyres tend to wrap around the debris and spreads out your weight load across a much larger surface area. You're not pressing on a tiny sharp point any more.