# Checking Rolling Resistance



## ww321q (Mar 28, 2008)

I was lifting the hood on my 1991 Saturn SC Coupe and reaching for the hood prop and the car started to roll away from me . That was in my shop and the floor is dead flat ! I think this may be a good sign . Anyway I have to set the parking brake to lift the hood or work on it .I can push the car in my shop with one finger .  J.W.


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## khooper (Apr 15, 2008)

I think that tire RR will matter most at low speeds, At highway speeds wind resistance predominates, especially for, shall I say, the square-shaped vehicles.
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## ww321q (Mar 28, 2008)

khooper said:


> I think that tire RR will matter most at low speeds, At highway speeds wind resistance predominates, especially for, shall I say, the square-shaped vehicles.


It matters at all speeds it just doesn't go up much at higher speeds . This car has a Cd of0.330 a CdA of 0.603 which ain't that bad and a curb weight of 2285 , I thought it would be a good place to start . Plus it cost me $800 Also there is a lot more to rolling resistance than just tires  J.W.


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## piersdad (Aug 16, 2008)

the most accurate way to determin rolling resistance is to tow the car using a ute or wagon so that the tow rope can be hauled in to use a suitable scales and actually weigh the force on the tow rope.
choose a level road and no wind and get up to required speed then haul on the tow rope
a mini car could show 50 - 60 lbs pull at 30 mph
this takes into account every thing from brake grab ,wheel bearings,windage,tire sort and pressure and even diff wear


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## sunworksco (Sep 8, 2008)

If you can build a trike car ,motorcycle touring tires and rims have the lowest rolling resistance.There are carbon fiber wheels available,too.The wheels weigh only 6lbs. each compared to 15lb. aluminum automotive wheels.My trike build is the www.blackjackzero.com


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## atzi (Jun 26, 2008)

piersdad said:


> the most accurate way to determin rolling resistance is to tow the car using a ute or wagon so that the tow rope can be hauled in to use a suitable scales and actually weigh the force on the tow rope.
> choose a level road and no wind and get up to required speed then haul on the tow rope
> a mini car could show 50 - 60 lbs pull at 30 mph
> this takes into account every thing from brake grab ,wheel bearings,windage,tire sort and pressure and even diff wear


Very Practical...I like this idea.
Question
What common brand/model car tire is suppose to have low rolling resistance?


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## piersdad (Aug 16, 2008)

from what i know from way back the cross ply is the worst
then is the steel belted radial (common on nearly all cars now)
then the low profile tires
these have a very small height and wide tread
ie the tire outside diameter is only about 2 inches larger than the wheel rim.
these tires are also not so good for comfortable ride and the rims are so close to the ground that they can very easily get damaged if say you brush a curb while parking or turning


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## Drew (Jul 26, 2009)

The easiest way of getting Cd and Crr is by doing a coast down test.

I couldn't remember the exact procedure so I googled it and this one seems to be the best link; http://www.instructables.com/id/Measure-the-drag-coefficient-of-your-car/ 

I don't have a login to instructables so I haven't checked the spreadsheet, but all the maths is on the background page anyway.

You'll need an assistant as well but basically all you do is pick a relatively high initial speed (70km/h is the articles recommended, but higher is better) then accelerate to a little above that speed, knock the car into neutral and get your assistant to start the clock when you reach that speed, then just record the time at each 10km/h of lost speed. You then just take the info you've got and solve for the Cd and Crr values using the guys spreadsheet or the maths which he included 


Make sure you're not near any other vehicles otherwise you'll stuff up your readings and make sure you do runs in both directions otherwise you'll get variation based on slight angling of the road or winds etc.


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## Woodsmith (Jun 5, 2008)

For low speed rolling resistence you could just see how far you are willing to push it before your legs turn to jelly!

Seriously though, place a set of bathroom scales against the back of the boot (trunk?) lid and push against it. It will register the amount of push required to break inertia and then to keep it rolling.

Same as the tow test but without the spring balance on the tow rope.


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## atzi (Jun 26, 2008)

*Chart comparing 77 different tires*

Here is a 2009 Chart comparing 77 different tires RRF.

California Energy Commission (CEC) DATABASE
This is one of the few Databases that rates and compares different makes and model tires. All are size 195/65R15 Tires. They are rated with the new California Energy* RRF *parameter.

The Top 5 are below.


Bridgestone Insignia SE200 

Michelin Energy MXV4 Plus
Goodyear Integrity
Michelin Energy MXV4 S8
Michelin Energy MXV4 Plus


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