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Author Topic: Tyres and rolling resistance  (Read 1716 times)

nigezero

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Tyres and rolling resistance
« on: November 27, 2014, 04:08:00 AM »

just wondering if anyone has investigated the most efficient low rolling resistance tyres for electric bikes?

There is very little information on this topic on tyre sites, or anywhere else i can find?
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Richard230

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Re: Tyres and rolling resistance
« Reply #1 on: November 27, 2014, 04:45:31 AM »

The problem with answering your question is that when it comes to motorcycle tires all of the tire manufacturers are more concerned with increasing friction, not reducing rolling resistance.  I am not even sure whether bias-ply or radial motorcycle tires provide the lowest rolling resistance.  All I could do is to guess and that wouldn't be very helpful.  The only thought I have is that more air pressure reduces the rolling resistance, but that will also make your tire more likely to slide when braking or cornering. I am not too sure that the trade-off is worth the risk if you have to make hard cornering or braking during an emergency.   ???  Plus, high air pressure will give you a very unpleasant ride on a rough road.
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Burton

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Re: Tyres and rolling resistance
« Reply #2 on: November 27, 2014, 06:29:49 PM »

The only thought I have is that more air pressure reduces the rolling resistance, but that will also make your tire more likely to slide when braking or cornering.

Could you provide a source for this?

I was always under the impressions the smaller the contact patch the more pressure is in a smaller area and it is in fact harder to loose traction when braking. I ride with my tires at max sidewall pressure and have for the last 47k miles without having any issues described above.
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Richard230

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Re: Tyres and rolling resistance
« Reply #3 on: November 27, 2014, 09:41:27 PM »

My source is my experience and what I have read over the years.  I have been riding for over 52 years and 800K miles and have been reading motorcycle-related articles for longer than that.  I experiment with air pressures in my motorcycle tires (I own 10 air pressure gauges) all the time.  Just slightly different pressures (especially in radial tires) really makes a difference in ride quality and traction.  I ride a lot in the Santa Cruz Mountains near where I live and the corners on these roads are bumpy and tend to be damp, if not actually wet, in the corners.  Lower air pressure in the tires really provide a much better ride and feeling of security (lack of over-steer and slipping) when cornering.  But too low a pressure will result in rapid wear and tire heating - which could result in structural damage to the tire.

The recommended maximum tire pressures are set by the tire manufacturers for the maximum safe speed of the tire (the more pressure, the greater the load the tire can carry at its highest safe speed), typically 130 to 160 mph for most motorcycle tires.  But few people ride at that speed while carrying a passenger and luggage.  A lower tire pressure will accommodate a lighter load at a lower continuous speed and will provide a better ride and handling experience, compared to using the maximum pressure on the tire sidewall.

However, watch out for radial tires as they are very sensitive to tire pressure.  Too much pressure and they over-steer and too little pressure and they under-steer. Plus, they will deform relatively easily under an extreme impact, such as hitting a big pothole or curb if not enough pressure is in the tire.  This can result in damage to the wheel rim.  Radial tires work better with higher pressures that tube-type bias-ply tires.

All in all, it is always better to start with the vehicle manufacturer's recommendations when setting air pressure and then adjust the pressure upward a little at a time to suit your riding conditions and personal riding experience on the roads that you travel.  If your ride starts feeling a little strange or uncomfortable, then lower the pressure to what you were using before.  Trial and error it the best approach in my opinion.
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Richard's motorcycle collection:  2018 16.6 kWh Zero S, 2016 BMW R1200RS, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior.

nigezero

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Re: Tyres and rolling resistance
« Reply #4 on: November 29, 2014, 02:52:15 AM »

Thanks Richard. That's been my experience too, and I get that grip is key; just happened to notice that car tyre manufacturers are now talking about it more and offering tyres aimed at LRR. So, perhaps in time we'll see some similar designs for bikes
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Richard230

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Re: Tyres and rolling resistance
« Reply #5 on: November 29, 2014, 04:28:07 AM »

Thanks Richard. That's been my experience too, and I get that grip is key; just happened to notice that car tyre manufacturers are now talking about it more and offering tyres aimed at LRR. So, perhaps in time we'll see some similar designs for bikes

Right now it seems to me that motorcycle tire manufacturers are more interested in inventing new tire model names and raising prices with every new tire product (which seem to come out about once a year now).  They continue to promote higher mileage, better grip and traction and more technical features with each new tire name.  But I just don't see it for street riding, which is all that I do.  Every new tire is said to have 10% to 20% better grip and tire mileage, along with 10% greater retail price, compared with the previous tire model. At that rate, by now, tires would just about last forever, which they don't do.  But they certainly have managed to at least double in price over the past 15 years.   ::) If you ask me, I am still seeing about the same mileage from the sport-touring radial tires that most of my bikes use, compared with 15 years ago.   ::)

I just don't see any real interest in reducing rolling resistance, improving mileage or reducing prices from the tire companies.  This makes good business sense for them and it would appear that motorcycle magazines seem to be on the same bandwagon when they perform tire reviews or comparison testing. Plus, there doesn't appear to be any real push by motorcycle enthusiasts to change that trend.

But here is a tip:  If you want to get the best mileage from a motorcycle tire, it has been my experience that the dual-sport (typically rated at 80% or 90% street usage and 20% or 10% off-road usage) radial or bias-ply tires provide something like 50% better mileage than similar "sport-touring" or all street tires.  These tires are just as expensive as similar street models, but I think they give you more bang for the buck.  Perhaps because they seem to have a greater tread depth than street-only tires of the same brand.  Unfortunately, I doubt they provide any improvement in lowering rolling resistance (again, due to the deeper tread).
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bigd

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Re: Tyres and rolling resistance
« Reply #6 on: November 29, 2014, 05:04:27 AM »

Richard - would it not be just simple physics. The lower the pressure the more tire surface area in contact with the ground. As you put more air in, the tire actually losses some surface area (when rounding) in contact with the ground. Am I over simplifying it?
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Richard230

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Re: Tyres and rolling resistance
« Reply #7 on: November 29, 2014, 05:58:39 AM »

Richard - would it not be just simple physics. The lower the pressure the more tire surface area in contact with the ground. As you put more air in, the tire actually losses some surface area (when rounding) in contact with the ground. Am I over simplifying it?

No, that is certainly true to an extent.  But it also has to do with the tire profile, width and tread depth. With a motorcycle tire, it is hard to change the profile just by adding air. (Motorcycle tires are pretty tough, with steel or heavy fabric belts and cords that are very resistant to changing profiles when over or under inflated.) If you really want to change the profile, you have to install the tire on a rim that is too narrow or too wide for the tire width.  Mounting a tire on a rim that is too narrow for the width of the tire would result in the tire tread being curved so as to reduce its contact with the pavement, but would also tend to degrade the performance of the tire.

Just check out a racing bicycle tire for a design the provides the lowest rolling resistance.  No tread, very thin and very high air pressure.  Plus, of course, not much resistance to flats, little mileage and a very rough ride.  Not something that most motorcycle riders would appreciate, nor something that a tire manufacture would design and market, except possibly for use on the Bonneville Salt Flats.  (What company needs more product liability law suits, anyway?)
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Richard's motorcycle collection:  2018 16.6 kWh Zero S, 2016 BMW R1200RS, 2011 Royal Enfield Bullet 500 Classic, 2009 BMW F650GS, 2005 Triumph T-100 Bonneville, 2002 Yamaha FZ1 (FZS1000N) and a 1978 Honda Kick 'N Go Senior.

Doug S

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Re: Tyres and rolling resistance
« Reply #8 on: November 29, 2014, 07:09:13 AM »

The lower the pressure the more tire surface area in contact with the ground. As you put more air in, the tire actually losses some surface area (when rounding) in contact with the ground. Am I over simplifying it?

Back in the early days of drag racing, the Physicists predicted that no wheel-driven vehicle could ever break some fixed time in the 1/4-mile (IIRC it was somewhere around 7.2 seconds), because doing so would require better than 1G acceleration for the entire length of the track, which would in turn require a "coefficient of friction" of the wheels on the track surface of greater than 1.0, which the Physicists didn't think was possible. But the hot rodders didn't much care what the Physicists thought, and of course screamed right through the 1G "barrier" without a backward glance. A little research turned up how it was possible: A compliant material, such as tire rubber, fits itself into small irregularities of the pavement surface, forming a mechanical lock, almost a gear holding the two surfaces together. That's how a tire can exceed a coefficient of friction of 1.0, it's not true sliding friction at all. The more compliant the rubber is, the better the effect works. That's why drag racers inflate their tires to like 4 psi, just barely enough to support the weight of the vehicle.

Recent research into gecko toes and how they support the weight of a gecko upside-down even on completely flat, shiny surfaces like polished glass, have revealed a technique that could further increase the traction of a vehicle tire, perhaps by orders of magnitudes, if you could figure out how to manufacture in nano-scale features like the gecko toes have. You should Google it, it's quite a revelation and really warms my heart that ALL the good, basic science hasn't been done yet.
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bigd

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Re: Tyres and rolling resistance
« Reply #9 on: November 29, 2014, 07:23:12 AM »

"No tread, very thin and very high air pressure." Correct, but in essence would adding tread just decrease the surface area and thus decrease the traction. What I am saying is that all other variables the same, greater surface area is more friction thus more traction. Good if stopping or corning but more drag.
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trikester

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Re: Tyres and rolling resistance
« Reply #10 on: November 29, 2014, 11:38:45 PM »

Quote
Back in the early days of drag racing, the Physicists predicted that no wheel-driven vehicle could ever break some fixed time in the 1/4-mile (IIRC it was somewhere around 7.2 seconds), because doing so would require better than 1G acceleration for the entire length of the track, which would in turn require a "coefficient of friction" of the wheels on the track surface of greater than 1.0, which the Physicists didn't think was possible.

Quote
Correct, but in essence would adding tread just decrease the surface area and thus decrease the traction. What I am saying is that all other variables the same, greater surface area is more friction thus more traction. Good if stopping or corning but more drag.

I didn't do the math here but I always remember, back in my high school days, of being told that it would be physically impossible to exceed 150 mph in a 1/4 mile drag due to the physics stated. It seems to me like it was exceeded just before I graduated from HS and the rest is history - as they say.

I remember the drag racer's tires were called "asphalt slicks" because they had no tread, to make for maximum contact area. The rubber was also very soft to go into all of the rough surface of the pavement for good grip. They were also heated to make them even softer. They wouldn't last long in normal street use.

Trikester
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