High tire pressure or low pressure?

i2000s

1 W
Joined
Oct 8, 2016
Messages
52
I don't have a suspension system for my ebike. The DD hub is on the front wheel. Should I retain a high pressure on all wheels, or should I find other strategies? I know the feeling to ride in high speed while jumping across road bumps...

When I do the search on Optimal Tire Pressure, I got one result: https://electricbikereview.com/forum/threads/optimal-tire-pressure.577/
But it looks very complicated to calculate for scientific reasons. My bike is 26in normal MTB. I am ~80bl. The commuting road is mostly flat but with some bumps and potholes in some segments. Your thoughts?
 
30 psi or thereabouts will feel better than 60, with a bike that has no suspension.

Going to high pressure matters a ton when human powered, and moderately fit people can only pedal at 100 watts for more than a mile. But if your e bike even has a mere 350w, it's superhuman now. No need to endure a harsh ride with 90 psi tires just for a better roll. Use the motor to overcome the soft tire.
 
Two things I’ve learned/observed to add into this.

1) Pinch flats are something you may struggle with running lower tire pressure. Myself 225lbs riding a 60lbs eBike 30psi often gets me a pinch flat when hitting some potholes or hopping even a small curb.

2) Wider rims with wide tires seem to provide a somewhat “better” ride for the same air pressure compared to thinner rims.

For my weight and normal road conditions I never run under 50psi. Especially on the rear hub motor. 60psi is my personal preference.

I’ve never met a bicycle tire that doesn’t lose some pressure while sitting. And be aware that if you store and inflate indoors but ride in very cold temperatures, tire pressure can change roughly 2psi for every 10F degrees change in ambient temperature.

For example, air a tire up to 35psi in 72F room but ride in 32F temperatures? That 35psi now becomes around 27psi.
 
You can't talk about pressure independent of tire width and vice versa, they are inextricably linked. 30 psi in a 23mm road tyre is effectively flat. 30 psi in a 2.3" mtb tire is reasonably well inflated or even over-inflated depending on conditions. Weight is also a key factor, a pressure that works well for a lightweight rider and bike can be completely unsuited for someone much heavier. I therefore tend to avoid giving specific recommendations for pressure unless I know all the relevant factors. Still, any given tire/weight/pressure combo sits somewhere on the continuum from barely inflated to rock-hard.

My experience is that running at high pressure is only a benefit if you are dealing with exceptionally smooth road surfaces. As soon as you introduce any irregularities lower pressures roll better. Even something as small as a line of paint can be a noticeable jolt on a rock-hard tire while a softer tire cruises smoothly over. I used to run high pressure over some seriously bumpy and potholed roads, the bike (and me) would be bounced all over the place and rattled to bits. As soon as I dropped the pressure those same roads became considerably faster and safer to traverse. A soft squishy tire can seem inefficient and draggy on smooth tarmac but over anything rough the way it insulates you from shocks and jolts more than makes up for that. If you've ever been running very high pressures and hit a bump bad enough to momentarily bounce the wheel(s) up off the ground, that's directly sapping speed from you since the bike is meant to be going forwards, not upwards. Even if the wheels don't break contact with the ground every bump and jolt you feel is draining some power. A softer tyre may 'waste' power by deforming but under many circumstances that's more than made up for by allowing the bike to move forward smoothly. There's a reason you don't see anyone running very skinny high pressure tires off-road, in fact you get the best results by going in the opposite direction with very wide tires running at low pressures. That applies just as well for dealing with rough surfaces on road. You might think as I used to that by running high pressure you get a harsh ride but get speed in return, when in fact by lowering the pressure you gain comfort and speed/efficiency.

Since the roads and paths I deal with are riddled with bumps and holes I've taken to running all my tires as soft as possible. The lower limit is dependent on avoiding pinch flats and on avoiding the tire folding sideways under cornering. On 26x1.75 Marathon Pluses I run 30-35 psi front and 35-40 psi at the rear depending on how much load I'm carrying.
 
Many factors do affect optimal tire PSI. Tire construction, size and gum hardness, riding weight and speed, terrain and temperature...

Then, once you find out your optimal tire PSI, either by math or try and error, you can change it by using a different tire and/or rim. A thicker tire with 2 ply construction will ride lower PSI, and a wider rim does increase tire volume thus making it ride much lower PSI.

Riding lower PSI is not usually done for comfort purpose, although it does help some for that matter. It is to improve traction that we use better tires and wider rims. Comfort is normally achieved via suspension and geometry.
 
Look on the side of the tire for recommended range, 35-50 psi for instance. I ride on mostly smooth, flat, straight surfaces and put 50 psi in every week or so. You might like a smoother ride and use 35 or 40 psi. I've had 100 psi rated tires pop for no reason but were ok at 90. Somewhere within the recommended range should be right for you, or switch to different tires with a higher or lower pressure rating.
 
Thank you for responding. I was always thinking high pressure is better until I read your experiences. Your posts also answered the question why wider tyre is better to use than narrower ones. My tires are normal MTB type. Not very cold in my area but with some potholes and bumps. Maybe I should try lower some pressure on both wheels and find the optimal ones. I guess since most of the load is on the back wheel, maybe I should put a little more pressure on the back tire.
 
Ykick said:
For example, air a tire up to 35psi in 72F room but ride in 32F temperatures? That 35psi now becomes around 27psi.

The difference in thermally driven pressure between true 72F and 32F temperatures is only 8%. Pressure is proportional to absolute temperature, so compare numbers in Kelvin or Rankine degrees to get a sense of the pressure change.

That said, there is some compression heating in a freshly pumped tire's air that causes pressure to diminish a bit as the temperature returns to ambient. It's interesting to check tire pressure right after pumping, then compare half an hour later.

On a tangentially related note, many people advise letting down tire pressure when flying with a bike, because the reduction in ambient pressure causes a rise in apparent pressure in the tire. But it's not important to do so. There are only 14.7psi in the atmosphere at sea level, so that's the maximum gain in your bike's tire pressure if you went from the beach to the vacuum of space. The 8000psi equivalent cabin pressure of an airliner is less than 4 psi below that of sea level.
 
Chalo said:
Ykick said:
The 8000psi equivalent cabin pressure of an airliner is less than 4 psi below that of sea level.
I think that you meant feet. 8000 psi would be the pressure at about 1,500 feet of sea water.
 
LewTwo said:
Chalo said:
Ykick said:
The 8000psi equivalent cabin pressure of an airliner is less than 4 psi below that of sea level.
I think that you meant feet. 8000 psi would be the pressure at about 1,500 feet of sea water.

Yes, that's right. I meant 8000 feet.
 
Chalo said:
LewTwo said:
Ykick said:
The 8000psi equivalent cabin pressure of an airliner is less than 4 psi below that of sea level.
I think that you meant feet. 8000 psi would be the pressure at about 1,500 feet of sea water ... Yes, that's right. I meant 8000 feet.

Hey what happened? I resemble that remark, sorta? LOL...

Looks like some copy/paste typos got mixed up into our replies. No big deal as far as I'm concerned but in case anybody's paying close attention...

Lemme add, I dunno the science but I know from my personal experience bike tires are always room temperature and I ride all winter down to 5F-10F. Once the tires cool to frigid external temps it's a fairly significant change in tire air pressure. I'm sensitive to pinch flats so I usually add a few extra psi when it gets cold outdoors.

Fairly certain AAA and other automotive experts have made the 2psi for 10F degree claim for changes in temperature regarding car/truck tires. But I can only approximate the actual ratio I've experienced in my somewhat unusual (apt dweller) conditions. It can be very noticeable IMO.

But anyway, check your tire pressure and check it often. And if it's warm when you do and it turns cold, check it again. Checking and maintaining tire pressure is the easiest and cheapest thing with possibly the biggest return on such a minimal investment of time/effort.
 
Had a MTB ebike, several road e-bikes, and various e-scooters.

For MTB ebikes, I suggest:

- high PSI with a suspension seatpost that is not just a mere spring (this will raise the seat height)
- tires with anti-flat technology (not just the kevlar strips on the rims)

The key is to avoid bouncing your brain in your skull. Bouncing causes brain fog, and possibly brain lesions.
 
If you're interested in this, I suggest reading bicycle quarterly's research on this. You have to buy some of their back issues, but it's pretty interesting.
They've done a bunch of tests with careful controls and published the data.
Basically they suggest a wide tire with lower pressure but the key is to get a supple sidewall for low rolling resistance. This is a lesser concern with high power ebikes because we aren't limited to leg power alone.
 
Interesting data that the tire pressure doesn't affect the speed that much!
 
But they do affect comfort! Quite a bit, in my experience. The rougher the road surface, the more tire pressure matters, in my experience. Go as low as you can without getting pinch flats when you go over your largest common obstacle, in my case some potholes and railroad tracks.
 
i2000s said:
Interesting data that the tire pressure doesn't affect the speed that much!

It doesn't slow down some tires much, but it has a huge effect on others. Basically, the narrower, coarser, and rubberier the tire, the more lowering its pressure will raise its rolling resistance.

The tires that are least sensitive to changes in pressure are those with thin, fine-threaded sidewalls and thin smooth tread rubber, without protective belts. That's not the kind of tire that most of us are going out of our way for. But the lesson we can take away is that more isn't always better-- thick, coarse, armored tires with heavy tread features are not only slow and harsh riding at high pressure, but they also get even slower if you lower the pressure in pursuit of better ride quality. So it's best to use as thin and flexible a tire as your conditions permit.
 
I have a 29er hybrid that road really harsh at speeds above 30mph due to the thin and hard tires. Swapping them out made an incredible difference. Although it won't be as much for you since you are already on an MTB... play around with what pressure feels best to you without going so low as to cause pinch flats. I have found Schwalbe Big Apples to be the softest riding bicycle tires. Get the largest size that will fit in your frame and get a suspension seat post too. That is about the best you can do unless you get a new bike.
 
Reading this post, i can appreciate high vs low tire pressures, however one thing which baffles me is how some tires can be inflated to the likes of 60psi + or even 80 to 100psi?.

Maybe its an international conversion thing which i am not understanding... I have
- schwalbe MTB tube 26"
- Schwalbe marathon 26" 2"
My weight is 62kg or approx 135lbs

I can barely pump (using foot/hand pump) the tires up to 40psi and it starts to get quite hard to push the pump down.
 
efergy kb said:
Reading this post, i can appreciate high vs low tire pressures, however one thing which baffles me is how some tires can be inflated to the likes of 60psi + or even 80 to 100psi?.

Maybe its an international conversion thing which i am not understanding... I have
- schwalbe MTB tube 26"
- Schwalbe marathon 26" 2"
My weight is 62kg or approx 135lbs

I can barely pump (using foot/hand pump) the tires up to 40psi and it starts to get quite hard to push the pump down.

Its your weight being applied across the width of the tread, so a very thin road bike is not even 1cm width in contact so they use extreme pressures to keep a float, but that same weight across a large MTB tyre with around 1 inch in contact or around 2.5 × the area in contact with the ground needs around 2.5 × less air pressure.
Thats how drag cars run with 8psi or so the weight being displaced by the tyre is very little if it run over your foot I suspect no bones would brake but a transit van with skinny biscuits needs 45psi and will pancake your foot same said for the carbon road bikes with 100psi + the wheels may chop pedestrians toes clean off specially if a big guys riding.
 
parajared...that's just what I run on the front of my trike - two Maxxis Hookwork 20x2". I run them at just around 58 psi on average, which is one-half of their rating (110 psi). The comfort is good, and improves down to 45 psi, and efficiency doesn't suffer much - it does in the 40 psi range. I also found them to be anti-shimmy, compared to the Big Apples I tried originally. Love those tires.
 
I am putting 30-40 psi on the rear tube in the past month, and it works well for me. Especially because my rim's joint was hit on the curb and resulting with sharp edges, I am also lowering the front wheel pressure now.
 
Back
Top