Range in wet weather

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Joined: Wed, 14 Jun 2017, 22:58
Real Name: Ross Tester
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Range in wet weather

Post by Rrrosco »

Something I've noticed: driving in rain or when the roads are wet significantly reduces range. I have an 8km drive to work, which usually "costs" me up to 20km on the GOM - but when it's wet, that can easily double (ie, 8k costs between 30 and 40km).
Does anyone else find this? If so (or even if not!) does anyone have a clue why? I wouldn't have thought wet roads would have increased rolling resistance (and therefore power required) THAT much - but am I wrong?

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Range in wet weather

Post by leighf »

I've certainly noticed the same effect. My daily commute is about 60km and I typically get home with about 30km on the GOM. I mostly drive in ECO and only use the heater coming home. If it's raining it's more likely to be about 15km left (or even Low Battery Warning) when I get home.

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Purchased July 2012.

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Range in wet weather

Post by offgridQLD »

I'm sure there is some physics at play with the tyres needing to displace water on the road though I wouldn't expect it to be very significant.

Just like the stock low RR tyres factory fitted to the Imiev are supposed to help with energy consumption. I now have stock sized replacement tyres but none low RR spec and haven't noticed any measurable difference I consumption....just price to replace


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Re: Range in wet weather

Post by EV2Go »

I noticed this phenomenon probably 30 years ago when driving from QLD to NSW and it rained the whole way. We were driving in a friends LC Torana with a small 161 ci motor, and the fuel consumption absolutely skyrocketed on the trip (circa 50% more), and the car was sluggish and appeared to lack power. When it was dry on the way home the fuel economy returned to normal.

I pondered how varying amounts of rain could affect the economy so badly to the point we suspected something was wrong with the car. I guess there are a few factors that come into play. The first being heavy rain generally does not just fall out of the sky, there is typically some additional wind associated with rain, this wind hitting into the car hampers the drag coefficient. As we mostly all know in basic physics the faster the car goes, the higher the HP required to push it through the air, the higher the HP the more energy (fuel or battery) required to push it.

So if the rain is hitting the front windscreen the additional wind acts like you are driving faster than you really are, causing the first part of the problem. Next involves Newton's third law of motion... For every action, there is an equal and opposite reaction. If the rain is hitting the car then the car is also hitting the rain, this is turn creates some resistance, which requires an overcoming force.

Thirdly when cars are tested for CdA they are tested in a wind tunnel, where the dry air can easily slip off the vehicle, who is to say the just exactly how much the rainy air is affecting the drag coefficient without even factoring in additional air speed or resistance of the rain.

Finally and I think this is the biggy, the water under the tyres... While I don't think the grip level is largely compromised (apart from the numerous hairy aquaplanes we did along the way) the loss of energy to grip would be minimal, but not entirely without some factoring. Where I think the bulk of the energy went was trying to climb over the standing water. In order to aquaplane you need to first get on top of the water, and that requires sufficient water to be compressed in front of the four tyres to get it up on the water.

When we weren't aquaplaning the rest of the journey must have been doing something similar to a lesser degree. If these combined forces can have a noticeable impact on performance, it stands to reason it would have a directly corresponding affect on economy. Electric vehicles make good torque but they don't make good HP (typically) and the less power the vehicle makes the greater the effect these contributing forces will have on the economy.
Last edited by EV2Go on Tue, 08 Aug 2017, 08:19, edited 1 time in total.

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