| iOn Front | 145/65R15 | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Rear | 175/55R15 (source) | ||||||||||||||||
http://myimiev.com/forum/viewtopic.php?t=1656&start=320#p21131 : I found a tire with a very low rolling resistance: Toyo NanoEnergy 2 in 185/55-15.
See http://www.toyotires.eu/tire/pattern/nanoenergy-2
This tire gets an A grade for rolling resistance according to the EU tire labeling system, that means RRC <= 6,5.
For comparison my i-MiEV was delivered with Dunlop Enasave 2030 in 175/55-15, getting a C grade only (7,8 <= RRC <= 9,0), most probably at the lower end of the RRC interval since I've tried some other C grade tires which offered a shorter driving range.
I've ordered a couple of tires for the rear from Germany and expect delivery at the end of next week, I'm very eager to see any improvements and I'll post an update later on.
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Just replaced the stock tires with the Yokohama Avid Envigor and yes there is about a 10% REDUCTION in range. Tried different tire pressures but no significant difference.
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Motor Trend got a Chevy Bolt for a long term test and one of the first things they noticed was lots of tire squeal and understeering when pressed hard in the corners - Sound familiar?? Since they were going to have the car for a year, somebody talked them into putting a set of summer tires on in place of the OE Michelin LRR tires for a couple months
As expected, most every measurable handling parameter showed marked improvement - Braking, cornering (understeer was almost completely gone!) slalom and lateral acceleration (skidpad) tests were all much better. Since the Bolt's power train is programmed not to spin the OE tires under straight line acceleration, 0 to 60 and quarter mile times were unaffected
What *shocked* everybody though was the 'price' you pay for all the improvement. They used sophisticated test equipment to measure mpg-e with both the OEM tires and the BF Goodrich UHP summer tires and the numbers were almost not believable. Chevy claims 119 mpg-e and their tests with the Michelins showed 122.2. When they tested with the summer tires, they had to double check all their measurements before they believed what they were seeing - The summer tires dropped it 27%, down to 89.2 mpg-e which changes the cars range by a like amount. Chevy claims 238, they tested it at 243 with OE tires but only 178 miles with the summer tires!!!
Our iMiEV's understeer something terrible with the stock LRR tires - I always figured it was due to the fact that they kept the tiny front tires the gas version of the car used, despite the fact that the battery made it a much heavier car, with more of the weight on the front tires than the lighter gas version, but it looks like it may be the LRR tires which are the bigger part of the problem . . . . . but I'm not *quite* ready to give away 27% of our modest range to solve it - Back to going slower around the cloverLEAFs!
Rolling resistance is a result of energy loss in the tyre, which can be traced back to the deformation of the area of tyre contact and the damping properties of the rubber. These lead to the transformation of mechanical into thermal energy, contributing to warming of the tyre.
Sixty to 70% of the rolling resistance
is generated in the running tread (Fig. 2.5) and its level is mainly
dependent on the rubber mixture. Low damping running tread mixtures
improve the rolling resistance, but at the same time reduce the coefficient of friction on a wet road surface. It can be said that the ratio is approximately 1:1, which means a 10% reduction in the rolling resistance
leads to a 10% longer braking distance on a wet road surface. The use
of new combinations of materials in the running tread (use of silica)
has led to partial reduction of the conflict between these aims.
(https://www.sciencedirect.com/topics/engineering/rolling-resistance)
https://www.sciencedirect.com/topics/engineering/rolling-resistance:
Fig. 2.32. In town and when the vehicle is travelling at low speeds on rural roads, fuel consumption is determined up to 40% by the rolling resistance, whereas at higher speeds the air drag is the determining factor see Section 2.1 and Section 2.2 in Ref. [3]). The figure shows a study carried out by VW on the Golf. https://ars.els-cdn.com/content/image/3-s2.0-B978075065054050002X-f02-32-9780750650540.jpg?_
Fig. 2.32. In town and when the vehicle is travelling at low speeds on rural roads, fuel consumption is determined up to 40% by the rolling resistance, whereas at higher speeds the air drag is the determining factor see Section 2.1 and Section 2.2 in Ref. [3]). The figure shows a study carried out by VW on the Golf. https://ars.els-cdn.com/content/image/3-s2.0-B978075065054050002X-f02-32-9780750650540.jpg?_
https://ec.europa.eu/energy/sites/ener/files/documents/user_guide_-_tyres_en.pdf
As you drive down the road your tyres rotate, flexing towards and away from the road’s surface, which causes energy to be lost The amount of energy lost depends on the tyres’ rolling resistance.... switching from Class G tyres to Class A tyres can reduce fuel consumption by up to 9%.
https://ec.europa.eu/info/energy-climate-change-environment/standards-tools-and-labels/products-labelling-rules-and-requirements/energy-label-and-ecodesign/energy-efficient-products/tyres_en
a tire bearing a load of 300 kg running at 17 m/s (40 mph) could be expected to experience a heating load of about 500 W on a flat road (Chassis or Rolling-Road Dynamometers A.J. Martyr, M.A. Plint, in Engine Testing (Fourth Edition), 2012)
for a CD car, a delta of 4% in rolling resistance can affect fuel consumption by 0.4 litres per 100 km.(Noise and vibration refinement of chassis and suspension
B. Reff, in Vehicle Noise and Vibration Refinement, 2010)
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ME:
Attualmente monto delle 4 stagioni Vredestein Quatrac 5 145/65 R15 72T M+S (davanti) e 175/65 R15 72T M+S dietro. Secondo Vredestein, le 145/65 hanno resistenza al rotolamento E, comportamento sul bagnato C, rumorosità 68 dB. Idem le 175/65.
Robbiani ad aprile 2019 mi ha proposto delle Continental Ecocontact 6 estive più cerchi in ferro a 1330.- montaggio e Iva compresi.
Su https://www.prezzogomme.it/pneumatici-auto/continental/ecocontact-6/145-65-r15.html quel pneumatico costa circa 62 euro. Totale 248 euro.
Non ho trovato altri pneumatici della stessa classe di efficienza (B) di quella taglia.
Le Ecocontact 6 145/65 (anteriori) hanno queste caratteristiche:
Resistenza al rotolamento: B
Comportamento sul bagnato: B
Classe di rumore: II
Rumore in dB: 70
Le posteriori (175/65)
Resistenza al rotolamento: A
Comportamento sul bagnato: B
Classe di rumore: II
Rumore in dB: 70
https://www.continental-tires.com/car/tires/ecocontact6
Reduced rolling resistance saves fuel and cuts CO2 emissions. Class A tires deliver the best fuel efficiency, with each subsequent class through to G increasing fuel consumption by between 0.42 and 0.56 mpg for a car which does 36 mpg.
The stopping distance between a class A tire and a class F tire can be as much as 18 metres.
