Tire pressure, rolling resistance, battery range

[Stefan Mikes]

Call me stupid.

During the end of the summer, last autumn and now in winter I got so carried away with my new e-bikes I completely forgot the tires needed occasional pumping up Let us start with a quite funny story though.

When I went to the Specialized dealer to pay for and collect Vado 5.0, finally got onto the saddle and rode out, I felt my new bike was unwilling to accelerate. Before I even rode onto the main street, a glimpse of understanding passed through my mind. I instantly returned to the store.

-- Haven't you forgotten to pump up the tires, have you? -- I joyfully addressed the mechanic. He blushed. -- Yes, I have... I was overexcited with your electric bike and overlooked that, sorry! -- He answered. At that time he pumped the tires up to 4 bar (58 psi) telling me that was not the maximum allowable tire pressure but it would give me comfortable, yet fast ride (he was right).

Recently, I noticed my Lovelec e-bike "slowed down"; the battery range also dropped significantly down. I attributed that to strong headwinds. Out of sudden, my eye caught the long forgotten pump (the one with a manometer) down in the garage. As I am obese, I usually tend to pump tires half bar (7 psi) below their maximum allowable pressure. The manometer readout was 3 bar (43 psi). After resupplying the pressure up to 5.5 bar (80 psi), the Lovelec started rolling fast again, and the battery range improved. (I'm sure the same case is with my Vado now).

Of course, it is unwise to forget about the tire pressure; read the first sentence of this post. Yet, I hear from many sources it makes sense to lower the tire pressure well below the maximum, for example, for smoother ride or for winter riding. Questions:

• If the rider and the bike together are near to the allowable maximum weight, would you ever reduce the tire pressure?
• In justified cases of reducing the tire pressure, how would that affect the speed achieved?
• As above, have you found lower tire pressure reducing battery range?

Discuss.

 

[fooferdoggie]

actually you would up the pressure so the tires can support you and protect the rims.

 

[AHicks]

Big guy here too. At max rated inflation shown on the tire, my bike feels like I'm riding a roller skate, with a very harsh ride, while feeling every small pebble I run over. Not enough air would result in frequent rim contact, which is really hard on the tires, not to mention the really draggy feeling while riding. I mess with the pressure a bit the first few hundred miles looking for a compromise that seems to work best - for me!

Noteworthy maybe, is that some people are running a little less air in front. Maybe 10%, which does make the bike ride a bit better IMHO.

 

[EbikeTestLab]

Good observation! I tested the road load vs. tire pressure and then calculated how that would affect range. Here's the post:

Range vs. Tire Pressure

Good Morning EBR folks! I wanted to test the accuracy and repeatability of my road load testing and have some fun with tire pressures. Therefore, I setup my Magnum Metro+ just like the last test, but I aired up the tires to 90 psi and ran the 20 mile per hour road load measurement test. I...

electricbikereview.com

Tire pressure definitely affects range and might affect top speed if the bike is power limited vs. speed limited as more power would be required with lower tire pressure.

 

[fooferdoggie]

I just experienced this I had a slow leak on the way home and my battery was going down faster then usual and I was working harder. I thought I was just tired.

 

[steve mercier]

Someone told me you can expect to lose about 5 psi per month. That seems about right to me. Fortunately I got a brand new JOE BLOW 3 for my birthday and now it is a joy to pump ,pump it up! https://www.outdoorgearlab.com/reviews/biking/bike-pump/topeak-joeblow-sport-iii

 

[fooferdoggie]

It depends on your psi and how fast the world rotates. But the higher the psi the faster they tend to loose. But my tires are 70 or so psi one looses maybe 10 psi every two weeks the other loosed 10 every week.

 

[Stefan Mikes]

Good observation! I tested the road load vs. tire pressure and then calculated how that would affect range. Here's the post:

Range vs. Tire Pressure

Good Morning EBR folks! I wanted to test the accuracy and repeatability of my road load testing and have some fun with tire pressures. Therefore, I setup my Magnum Metro+ just like the last test, but I aired up the tires to 90 psi and ran the 20 mile per hour road load measurement test. I...

electricbikereview.com

Tire pressure definitely affects range and might affect top speed if the bike is power limited vs. speed limited as more power would be required with lower tire pressure.

Very good article!

I just experienced this I had a slow leak on the way home and my battery was going down faster then usual and I was working harder. I thought I was just tired.

I had the same with my acoustic bike a couple of years ago. I was crying from humiliation thinking perhaps I got very ill. Now, after the experience with that puncture, I always took care to regularly inflate tires. Magically, I completely forgot about that with my electrics.

got a brand new JOE BLOW 3

Looks that we have the same brand of pumps!

 

[AHicks]

You can minimize the need for frequent air pressure checks, and some punctures, by running Slime or something similar in your tubes. My tires used to force checks at weekly minimum, despite my years long search for quality inner tubes. Then I decided to try Slime - against a lot of advice given by store clerks and other "experts". Slime made a huge difference. And years into it now, yes, I've suffered through the clean up required in a worst case Slime scenario. Maybe 15 minutes with a wet rag. I'll risk that again any day for the convenience of not having to check my tires for proper air pressure frequently (weekly). -Al

 

[Stefan Mikes]

Thank you @AHicks! I googled Slime, it is available here and YT tutorials exist!

 

[JRA]

Neglecting to check your tire psi before riding is one thing but I find the most important thing is to find the psi that works best for you to begin with. Different diameter wheels with varying tire widths and overall weight of the bike and rider are all across the board. Sure you can pump your tires up to the recommended max and get used to it but it may not be the optimum for the surfaces you mainly ride on and the comfort and control level you can achieve. These days long distance gravel riders routinely use psi in the 30's range as they put more emphasis on the contact patch being larger to help prevent deflection and small bump compliance increasing comfort over long distances without the aid of adding the weight of suspension seat posts and stems.

Personally I go for the comfort and control level to be as high as possible and am willing to get there by using lower psi but I also put a lot of credence to what size tire and rim width I am riding along with expected terrain. My drop bar bikes get used on all surfaces and with 40c tires running tubeless on i25 rims I keep them at 35psi even if I plan on riding lot's of pavement because where I live the pavement is far from smooth unless you happen to run across a section that has been freshly laid down, but for the most part it is older stuff that is not uniform. I ride a lot of gravel logging roads that are far from smooth and that is where lower psi really comes into play.

Do I sacrifice watts to gain comfort? Sure, but I have gotten to know what level of watt hours per mile I can expect and tailor my motor and and human input according to what my goals are. If I think a ride will stretch my batteries capacity to the max I just go out easy on the watts and increase my input. We are not talking race pace here but general all around just having a good time bike riding.

My eMTB is another story altogether as I primarily ride it on softer, yet rougher due to roots/rocks/soil conditions, terrain that put's the emphasis on traction control. To that end over the years I have gone from using 45psi with 26" wheels with 2.1 tires and narrow 20mm rims at 45psi to 29" wheels with 2.1 tires on 20mm rims at 30psi to where I am today running wider, 2.3 front/2.8 rear, on i35 rims tubeless at 15psi.

But the bottom line is that I messed around with my psi at each juncture to figure out what gave me the best level of performance, comfort and control based on my expectations and such that I wasn't running so low as to have issues with pinch flats or rolling the tire off the rim.

 

[AHicks]

JRA, all that advice is great, but for folks to know if all the specifics you list are relevant to something that might work for them, they need to know how big you are! If you don't mind, what do you weigh?

I ask as at my weight (310lbs), I know for a fact that the pressures you list are WAY low!

 

[Stefan Mikes]

I understand and it is a good post @JRA. My point is, if I could easily reach 19 mph with 80 psi tires and I had a hard time to get to 15 mph with 44 psi then my 1.6" tires were certainly very much underinflated.

 

[JRA]

JRA, all that advice is great, but for folks to know if all the specifics you list are relevant to something that might work for them, they need to know how big you are! If you don't mind, what do you weigh?

I ask as at my weight (310lbs), I know for a fact that the pressures you list are WAY low!

I weigh 200 lbs but the point I was trying to make isn't what I use for psi but the fact that I got to those determinations via a process that can be used by anyone of any weight.

 

[JRA]

I understand and it is a good post @JRA. My point is, if I could easily reach 19 mph with 80 psi tires and I had a hard time to get to 15 mph with 44 psi then my 1.6" tires were certainly very much underinflated.

But does that discount the fact that you may be overall more efficient running something in between? You will never know unless you do some trials on your own to find your sweet spot. But I can guarantee that it is there somewhere in the range between. Start at 80 and let a little out at a time until you start to feel like performance has degraded to an unacceptable level and go back up to where it feels right. My point is there is no right tire psi for all.

Certainly for a larger rider I would recommend at least a 2.0 tires also but without wider rims to match just adding them to your bike, given there is clearance, won't be much if any gain.

 

[AHicks]

Another point too, is your objective. Where is your priority? Are you setting up for max efficiency, best ride, best speed, or some sort of compromise? Point being, the right pressure is what works best for YOU, and the only way to find it is with some experimenting. I use 5 psi steps and a couple mile ride with different conditions to figure it out. -Al

 

[slayer1962]

AHicks good call i do the same. I have a fat tire bike. When i ride on the road i use 18 lbs and when i ride in the sand ( i do a lot) i ride with 6-8 lbs.
I am also large 275lbs 6'2" and i am afraid to go lower on the tire pressure even in sand . some recommend less but i worry about a rock or a stick in the sand with too low of pressure.

 

[steve mercier]

It depends on your psi and how fast the world rotates. But the higher the psi the faster they tend to loose. But my tires are 70 or so psi one looses maybe 10 psi every two weeks the other loosed 10 every week.

How fast the world rotates ...what a concept.

 

[indianajo]

Another point too, is your objective. Where is your priority? Are you setting up for max efficiency, best ride, best speed, or some sort of compromise?

My objective is to not dent the rim if I fail to miss a gas valve hole or mis-aligned sidewalk slab. The standard driveway entrance to all the new street pavement is 1" high, I have to slow down for those. **** city, the wheelchair ramps at the corners are dead smooth. My 2.1" tires are mostly limited to 60 psi, I run about 55. I still hit the rim occasionally, especially with a load of groceries. **** LBS sold me a tire last year rated at 40 psi. Sleazebags. Would love to sell me another rim, I suppose. My fault for not looking because they had done me right the last dozen tires.
I get 6 to 8 weeks without adding air without slime. I tried slime tubes once when they were on sale, it went flat on a shred of car tire carcass just like an ordinary tube. Why bother with it?

 

[AHicks]

I hate dealers....