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Old 06-23-07, 05:01 PM   #1
bugmenot
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Going greater than recommended PSI on an ebike?

I might have seen this question posed in one of the other boards, but wanted to put it here in case there was something different about ebikes.

I just transfered over my smooth slick tires from one of my other bikes to this converted MTB ebike. the highest PSI is 65 lbs. Is it safe to go over that?

I seem to remember (from another thread) that it was the legal department of the tire company that wanted you to keep it at the lowest possible high-end PSI. They wanted to avoid you blowing up the tire, killing yourself, then suing the company. The designers/engineers are always pushing for a high psi for smoother ride and so that you won't exert yourself too much during the ride.

I know that there are some 80-90 psi tires, and I'm saving up for those.
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Old 06-23-07, 06:14 PM   #2
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My mountain bikes are rated for 60 PSI and I'm running 65 up front and 70 in the back. I recently had a flat on the rear tire, which is because I was really going to fast to jump the curb, and I suspect that it happened mostly because it was down to 50 PSI.

I took the same curb, a bit slower this time, with 70 PSI in the rear and the tire didn't pop.
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Old 06-23-07, 07:18 PM   #3
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Thanks. I'll rarely jump any curbs.
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Old 06-24-07, 10:39 PM   #4
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One thing to be aware of: overinflating your tires may improve rolling resistance (in some circumstances it won't), but it will make your traction a little worse. I run my tires at about 80% of max psi because that way their softness absorbs more of the bumpiness in the tread and the pavement. I'm a light guy, though, and if I were heavier I'd want to inflate them higher.

If you're ramming your tires into curbs, underinflation is a serious hazard while overinflating by only 12% like zeuser did seems unlikely to cause danger. I sure wouldn't bet my life on a tire overinflated by 50% though.
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Old 06-25-07, 03:13 PM   #5
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Just to obfuscate this post a bit; I bike 250++ kms a week on my ebike and I've discovered that I pop spokes on the rear tire when my tires are inflated to the manufacturers recommendations. I travel on some rough roads and average about 20 kms/hr with top speeds at about 35. My Schwalbe's seem to work best at 35 or less and the ride is a bit softer. After all, this is an ebike and rolling resistance shouldn't be a huge issue, right?

Oh, obfuscate? That just means to make things difficult to understand.
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Old 06-25-07, 06:13 PM   #6
bugmenot
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Thanks. Good responses.

All the ebike related sites say get smooth tires esp. ones with max high end psi's like 70+. This is to have minimal rolling resistance.
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Old 06-25-07, 06:26 PM   #7
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When you have extra watts to help out, I would value traction and handling more than the lowest rolling resistance, which is a small part of the total resistance beyond pedaling speeds.
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Old 06-27-07, 06:52 PM   #8
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After all, this is an ebike and rolling resistance shouldn't be a huge issue, right?
Actually, rolling resistance is a *huge* issue for battery-electric vehicles... because of the tiny (compared to a gas tank) amount of energy EVs have to work with. This is no diff than any higher-end pedal bike, where someone used to a "clunker" hops on and realizes how much easier the high-end machine is to pedal... Low rolling resistance, aerodynamics, and lowest friction is all mechanical systems actually *consume* the thoughts of EVers...

tks

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Old 06-27-07, 07:02 PM   #9
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Originally Posted by Lock
Actually, rolling resistance is a *huge* issue for battery-electric vehicles... because of the tiny (compared to a gas tank) amount of energy EVs have to work with. This is no diff than any higher-end pedal bike, where someone used to a "clunker" hops on and realizes how much easier the high-end machine is to pedal... Low rolling resistance, aerodynamics, and lowest friction is all mechanical systems actually *consume* the thoughts of EVers...

tks

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http://www.sheldonbrown.com/tires.html

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The higher the air pressure, the less the tire will deflect.
The trade-off with this is that if you pump the tire up too hard, you lose the benefits of pneumatic tires: the ride becomes excessively harsh, and traction will be reduced. In addition, extremely high pressures require a stronger (heavier) fabric and stronger (heavier) rim flanges.

Rolling resistance does decrease theoretically with any increase in pressure, but with modern, high-quality tires the rolling resistance at correct inflation pressure is already so low that the infinitesimal reductions gained are more than outweighed by the trade-offs.

An overinflated tire will have slightly less rolling resistance.
An overinflated tire is more prone to damage from sharp rocks and similar road hazards.
An overinflated tire will give a harsh ride on anything but the smoothest pavement.
An overinflated tire can bounce on surface roughnesses. This can cause dangerous interruptions in traction, particularly if it happens during cornering.
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