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Should I have soft tires?

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Should I have soft tires?

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Old 07-04-18, 09:43 AM
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Miramooke
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Should I have soft tires?

Hi all!


I have a mixte bike which I use on my short commute to work every day, and for leisure on weekends.


I went to buy a new tire for it yesterday: 27 x 1 14 32mm. The tag says 62-100psi. The guy at the bike shop was adamant that I should be keeping my tire pressure at 45 psi, and that they should be noticeably soft. This goes against what I've always known: that hard tires = faster ride, and I keep my tires around 80-90 psi. This has always felt true to me, especially when I notice my ride feeling sluggish, I check my tires and the pressure is indeed relatively low.


But, he seemed so confident in his stance (and admittedly, I do feel like I get a lot of flat tires), that now I don't know what to do.


I would appreciate your thoughts on this, TIA.
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Old 07-04-18, 11:35 AM
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He is right, unless you are very heavy.

Unless you have perfectly smooth road, the softer tire will take bumps better and not vibrate the bike. the vibration and you moving up and down over bumps cost energy. and comfort also suffers with high pressure.

https://janheine.wordpress.com/2010/...-and-pressure/

A high pressure tire will feel faster because it shakes you around, not necessarily because it is faster.
Again, unless you have perfectly smooth road. Think about how a railway (smooth steel wheel on smooth steel rail) is more efficient.

edit: with skinny tires there is a chance for pinch-flats when going below manufacturer pressure. if possible, install wider tires and/or go tubeless.
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Old 07-04-18, 11:48 AM
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Thank you! I weight 170 and regularly carry 10-20 lbs on my bike. So, call it 190lbs total, and I understand that the back tire should be a little more inflated than the front one.

But... 45psi, though? My tires would feel like marshmallows! Although I do have an old bike with no shock absorption so the prospect of a smoother ride is nice. Sorry, I am not trying to argue with you, still trying to wrap my brain around this.

The tire says 60-100 and the innertube says 80psi. Do you think 80psi is good (on the back tire) or should/can I safely go lower without risking pinch flats? At 80psi they are a little soft, like a ripe avocado.
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Old 07-04-18, 12:34 PM
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Try it at 45psi

Try it at 65, 85, and 95

Which one do YOUlike best? That is the correct tire pressure for your bike. Everything anyone else tells you is wrong. And you don't have to explain yourself.
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Old 07-04-18, 12:53 PM
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Originally Posted by Miramooke View Post
Thank you! I weight 170 and regularly carry 10-20 lbs on my bike. So, call it 190lbs total, and I understand that the back tire should be a little more inflated than the front one.

But... 45psi, though? My tires would feel like marshmallows! Although I do have an old bike with no shock absorption so the prospect of a smoother ride is nice. Sorry, I am not trying to argue with you, still trying to wrap my brain around this.

The tire says 60-100 and the innertube says 80psi. Do you think 80psi is good (on the back tire) or should/can I safely go lower without risking pinch flats? At 80psi they are a little soft, like a ripe avocado.
It's a bit trial and error and personal preference. Cannot be too low to have the road hit the rim or the tube to be pinched, obviously. Having the front lower is reasonable. Less weight and it vibrates your hands less.
Maybe try 50 psi rear and 40 psi front. Or 60 rear and 45psi front and take it from there. Once you ride look at how the tire looks when compressed. the tube rating is a maximum rating. The tire rating range is to avoid pinch flats (when tube goes into the crack between tire and rim). This is a conservative value, with less weight you can go a bit below. With tubeless, obviously the lower rating is less meaningful since there is no tube to be pinched.

How are you measuring pressure, are you sure that is measuring correctly? If you refer to a ripe avocado, my avocados don't feel as hard as my tires at 60 psi (never had 80 psi ever). 60 psi feels pretty hard to me. Obviously we went far away from actual science if we measure pressure in Avocado units

I have 50 mm tires and about your weight. I run 25 psi front ant 40 psi rear, not sure what I would do with 32 mm tires, obviously more. I also have tubeless. Rolls really easily (Schwalbe Almotion tires). 40 psi feels like an Avocado i would eat.
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Old 07-04-18, 12:57 PM
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I have gravitated towards less air in my tires over the past few years. It comes down to personal preference and the tire itself though. Here is an article and chart regarding "tire drop" you may want to look at. It gives you an idea of what pressures to achieve a drop of 15%. The chart shows weight per wheel. In your case, based on the overall weight you stated, the chart seems to show a higher pressure than you were told at the shop.

I do make allowances for different tires and the minimum pressure shown on the sidewall myself, though many disregard the sidewall recommendation. The advantage of running a lower pressure than what many have advocated in the past, is a much nicer ride, and, as someone else mentioned, less rolling resistance on a rough surface. On a perfectly smooth surface, a tire with higher pressure may in fact have less rolling resistance, but we don't ride with those conditions, so a lower pressure, within reason, gives better rolling resistance.

https://www.compasscycle.com/wp-cont...BQTireDrop.pdf

Last edited by phughes; 07-05-18 at 10:45 AM.
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Old 07-04-18, 02:05 PM
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Originally Posted by HerrKaLeun View Post
How are you measuring pressure, are you sure that is measuring correctly? If you refer to a ripe avocado, my avocados don't feel as hard as my tires at 60 psi (never had 80 psi ever). 60 psi feels pretty hard to me. Obviously we went far away from actual science if we measure pressure in Avocado units
Hah! You mean the avocado isn't a scientific unit of measurement? I am using a manual pump thingy with a gauge on it. I have been assuming it's more or less accurate, but I suppose if it's off by 5-10% it could really be impacting my perception.
At 90psi my tires feel like unripe avocados. I.e., totally firm, no give when I push on them.
At 70-80, maybe a near-ripe avocado. Plan to eat it tomorrow. I can dent it a little bit with my thumb if I push pretty hard.
At 65, that's where my ride feels really sluggish and I realize I need to pump my tires. I can really push into them with my thumb. Overripe.
I don't think I've ever gone below 65 so I can't imagine 45. I guess I just have to try and find out.

Thanks all for your thoughts. I guess I will just experiment, with an open mind, and see what I like!
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Old 07-04-18, 02:22 PM
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There have been straight edged inside rims and there are hook edge inside rims ..

a rim without a hook / crochet edge is more subject to having the overinflated tire
be blown off the rim..

So If you have a rim that is less securing of the tire bead,
you would go for a lower inflation.




....
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Old 07-04-18, 05:58 PM
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45 is pretty low for a 32mm tire in my book. personally i think we overthink tire pressure just a tad.
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Old 07-04-18, 08:24 PM
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Bicycle tire pressure calculator - use the second one from the top.
"I weight 170 and regularly carry 10-20 lbs on my bike. So, call it 190lbs total" - you forgot to add the weight of the bike itself. Lets say, 20 lb more, so 210 lb. At 45%/55% weight distribution this calculator recommends 55 psi front and 67 psi rear which sounds about right to me. I agree with @52telecaster that 45 is too low for your weight. Definitely don't go to 80 - 90 psi on 32 mm tires - ride will be extremely harsh. I use 45 / 55 psi on my bike with 32 mm tires but I'm lighter than you and I don't carry with me 20 pounds of this and that.
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Old 07-05-18, 08:37 AM
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I let my 32s get down to 60 psi a couple weekends ago (user error, I forgot to pump them up before the ride). Easy hills turned into leg-burning monsters, and a fairly short ride wiped me out as though I'd been riding for hours. I attributed that exhaustion to the heat until I saw how low the tires were the next morning (when I did get a round tuit to pump them up).

If you want to experiment with low pressure, I'd try the 62 psi on the tire. Note you're going to need to be vigilant to avoid potholes, because you may be getting close to pinch flat territory if you run through a bad pothole (and who can tell how bad they are until you've run over it?). I'd shoot for 80 psi or so if you pump you tires before every ride, maybe 95 if you're going to ride 4-5 days between pumping them up.
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Old 07-05-18, 10:00 AM
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I weigh 170, and I often carry a bit (but not much) on my bike. The bike also has 32mm tires. I like when the tires are at 50 rear and 45 psi. I inflate to a bit more than that, because the pressure seeps out over a couple of weeks. Some tires ride better when they are harder than that, especially if they have stiff sidewalls. My tires have a supple texture, so I don't have to overinflate. It is not true that harder equals faster. You want enough pressure that the tire doesn't bottom out on the rim when you hit bumps. Do experiments to see what feels best. It's best to use a pump with a built-in gauge. Try putting in 10psi more than you like so you can ride for two or three weeks without re-inflating.
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Old 07-05-18, 01:18 PM
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ride your bike the way you want to
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Old 07-05-18, 01:52 PM
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Originally Posted by Miramooke View Post
I went to buy a new tire...27 x 32mm. The tag says 62-100psi. The guy at the bike shop was adamant that I should be keeping my tire pressure at 45 psi, and that they should be noticeably soft... I keep my tires around 80-90 psi
He's wrong that your tires should be "noticeably soft".

They shouldn't be at either end of the spectrum - not hard as a rock, not "noticeably soft". The ideal pressure is somewhere in the middle between the two extremes, even if speed was your only priority.

Most of other comments have already covered the details so I won't go into them again. You're not doing anything "wrong" at 80-90 psi but you might be interested in trying lower pressures and seeing how it feels for you. 45psi at 32mm (assuming I'm reading your post right) seems way to low for me for most riding.
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Old 07-05-18, 06:00 PM
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You should pump your tires up to the pressure that feels right to you. Really doesn’t matter what the internet tells you.

You should also experiment a lot. 28mm tires were my ideal for about a decade, at around 100psi. But I got a new “gravel bike” with 40mm Knards, and although those tires were the first things to go, I did REALLY like the plush ride. After some trial and error, I’ve settled on 35mm tires at 50-60 PSI, and I really like it. I’m every bit as fast as I was on higher pressure tires, but much more comfortable.

For what it’s worth, I also experimented with some nice 40mm tires (not the Knards), and they were not slower either. They were heavier and felt more sluggish speeding up, but my average speed on the commute wasn’t any different than it is with the 35s. In all honesty, I just couldn’t get used to seeing tires that big on the road.
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Old 07-10-18, 03:05 PM
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Originally Posted by Miramooke View Post
This has always felt true to me, especially when I notice my ride feeling sluggish, I check my tires and the pressure is indeed relatively low.
Feeling can be deceptive. Some of what 'feels' faster about harder tires is more road vibration reaching the body, which means the bike is microscopically bouncing off all the little bumps, rather than letting the tires deform around the bumps so the mass of the bike and rider can travel in a straight line. The body and brain perceive this as increased speed though.

This podcast (also with Jan Heine), is pretty convincing that wider tires and lower pressures is better. I've wanted to get around to a timed rolldown test over the same stretch of gentle downhill, at a range of pressures, but haven't yet.

45psi for 32mm tires and a 170lb rider sounds about right to me. I'm down to a svelte 227 lately, plus load, I run 42mm in the front and 50mm in the back. I'll pump them 'up' to 35 or 40, and let them run down for weeks until they feel soft. At that point of 'too soft' they're usually down around 20. So probably 30ish is 'right' for my tires and load.

Last week I rode with my son to the nearby park to play some basketball. I had to tell him to not ride with such low tires. He's about 150 and the road bike he grabbed had 700x23 tires with about 20psi in them. THAT's definitely too low.
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Old 07-10-18, 03:12 PM
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Originally Posted by Miramooke View Post
Hi all!


I have a mixte bike which I use on my short commute to work every day, and for leisure on weekends.


I went to buy a new tire for it yesterday: 27 x 1 14 32mm. The tag says 62-100psi. The guy at the bike shop was adamant that I should be keeping my tire pressure at 45 psi, and that they should be noticeably soft. This goes against what I've always known: that hard tires = faster ride, and I keep my tires around 80-90 psi. This has always felt true to me, especially when I notice my ride feeling sluggish, I check my tires and the pressure is indeed relatively low.


But, he seemed so confident in his stance (and admittedly, I do feel like I get a lot of flat tires), that now I don't know what to do.


I would appreciate your thoughts on this, TIA.
It's a bit low for my taste but as long as you aren't getting a ton of pinch flats and handling isn't compromised, then you should be fine.
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Old 07-11-18, 08:17 AM
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Originally Posted by Miramooke View Post
At 65, that's where my ride feels really sluggish and I realize I need to pump my tires. I can really push into them with my thumb. Overripe.
I don't think I've ever gone below 65 so I can't imagine 45. I guess I just have to try and find out.

Thanks all for your thoughts. I guess I will just experiment, with an open mind, and see what I like!
Good idea on experimenting with an open mind. Read the opinions and do what you like.

Some people like high PSI as it makes the bike handle like a scalpel (although it will be a bit slower over the crappy rough roads I commute on). Some like low PSI because it gives a more supple ride and is easier to pedal over rough surfaces.

Personally I’ll ride 32mm at 60-80psi on the road or with tubes

I’ll do 45-60psi off road tubeless. At 45 they are getting pretty squirmy and risk pinch flats with tubes.

Here is a measurement of a 35mm tires – so you can see the effect of tire pressure (YMMV):

https://www.bicyclerollingresistance...hon-racer-2015

Rolling Resistance 90 psi / 6 Bar 20.9 Watts

Rolling Resistance 75 psi / 5 Bar 22.6 Watts

Rolling Resistance 60 psi / 4 Bar 24.6 Watts

Rolling Resistance 45 psi / 3 Bar 28.8 Watts

Rolling Resistance 30 psi / 2 Bar 38.3 Watts
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