# Wheel rolling resistance Idea.



## Chris Sandberg (Sep 13, 2008)

Hello Group, I had a crazy Idea that I wanted to test the waters on. Has anyone tried using the skinny spare tires at a high air pressure for low rolling resistance? I think the same wheel from donor cars of the same type for a total of 4 would not be too cost prohibitive and worth a try. I am still in the planning stages but was wondering if this has been tried or would even help. A newbie/ beginner just trying to think outside of the box.
TX Chris


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## Zemmo (Sep 13, 2007)

One of the guys in our EV Club did this to his Mitsubishi Eclipse. I don't know of the scientific-ness of it but thats what he did. He likes it. It would make sense since the tire is 1/2 as wide so that would mean 1/2 the resistance. But I don't think he did any tests to find out for sure. You can see his EV at: http://www.flickr.com/photos/mbarkley/sets/72157603518876045/


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## Jimdear2 (Oct 12, 2008)

If you mean those skinny, space saver tempory spare tires.

*A VERY UNSAFE IDEA*. 

Read the owners manual and the information on the tire itself. Those temporary spare tires are generally rated for around 500 miles use at under 50 MPH. Then you are supposed to throw them away!!!!

Then think about trying to stop all that extra battery weight with those things. 

EEK . .  . . . crash

Everybody in EV seems to be concerned with putting thinner. harder tires to get an extra mile. Not good.

When you think about it, the OEM bean counters are going to put the minimum acceptible (read cheapest = smallest) tire on a vehicle that the safety engineers will allow. Now here you have an electric vehicle at max GVW with the battery load, and you want to drive it with less tire than that. 

I think I would trade a couple of miles for my life. PUT GOOD TIRES ON THE VEHICLE. UPGRADE THE BRAKES. Live long enough to spend all that gas money your saving.

Jim


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## Zemmo (Sep 13, 2007)

You can get skinnier tires without going to the spare donut tires. Yes those spare donut tires aren't designed for that type of work. But there is skinny tires that are rated for that. An example is a VW Bug, the original, it had skinny tires and was for full service. You just have to find the appropriate tire.


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## ZenDaddy (Jul 22, 2008)

Scary idea.... DONT DO IT!!!!!!!!!!!!!


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## engineer_Bill (Jun 24, 2008)

I'm with the other guys. The small tires on economy cars are already optimised, I wouldn't go any smaller than that. Just run them at max recommended pressure. Look at a chart to get the lowest rolling resistance tire in your size. Then work on getting better batteries.


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## Xtremek (Jun 13, 2009)

The Prius rolls on a fairly thin tire. It has a 185 section width. I don't mind pushing the limits, but there's a point when safety is first. Like everyone else said, run your tires at max recommended pressure. I wouldn't run to bug tires unless your car is close to the beetle in weight. Try to find a economy vehicle with a similar weight and run the smallest section width available that comes on that vehicle. Be careful, this is where economy and safety clash. That's why the big companies stay away from the limits.


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## rillip3 (Jun 19, 2009)

I think you can probably benefit more by buying a similar sized tire in a different style than you can by shrinking the tire. For example, I'm sure a run-flat has a very different rolling resistance than an all-weather tire, which is different from stock tires, etc. You can probably find some performance-designed tires that will give you better handling, lower rolling resistance and better breaking under normal conditions than stock tires, but may be a rougher ride, wear out faster, etc., while still being safe.


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## Guest (Jul 4, 2009)

The tires on my Ghia are damn nice narrow tires and they have done a bang up job holding the weight. I have them at the max recommended pressure and they have not leaked or given me any trouble. Excellent. I'd prefer proper LRR tires but for now they are doing just fine. 

Pete 

Never use those tiny donut spare tires for any thing other emergency use only. Even using them for that it dangerous. They are, if I am not mistaken, no longer used or made. If they are they should be banned.


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## Duncan (Dec 8, 2008)

Just to put my tuppence worth in,
Tyres on modern cars are much wider than they used to be

I believe that this is mostly for looks, 

I remember some track testing using wider tyres giving almost no improvement in lap times
Tyres in America when I lived there were much harder than in the UK with longer life but less grip 

I will be using relatively skinny tyres on my machine and I don't expect to be giving away any grip

165/14 would be my aim (depends on price), even here I am being conservative
145/14 would probably be best but would "Look" too skinny


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## sunworksco (Sep 8, 2008)

Most tire companies are making low rolling resistance tires with high slica content for stiffness.Even some of the low-profile tires are made in this manner.
The best way to change your ev's rolling resistance is to change the hubs,uprights,bearings and wheels with lightweight materials.If you have access to a metal lathe you can make Ducati 1098/GM style center-lock pin-drive hubs in aluminum.You can then use Ducati BST carbon fiber wheels,Brembo calipers and rotors.This more than anything else will reduce the rolling resistance and conserve the battery charge and create more torque off the line.The shocks can be converted to motorcycle type and the suspension will be lighter and better handling with less wear.


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## frederic (Jul 4, 2009)

Fun subject, and here are some fun facts about tires.

The narrower the tire, the less rolling resistance you have and the better mileage your vehicle will get. This is more noticable on heavier vehicles or vehicles that have tremendous downforce (like 150+mph race cars).

On the flip side, you have less braking, accelerating, and turning ability with narrower tires.

For a 150 HP commuter car that "might" take an exit ramp at 35 mph, a narrow tire is more than reasonable. Mileage is more important than "stickyness".

For a Formula 1 car with 700HP taking a corner at 170 MPH, one needs a bit more tire so the car sticks and doesn't spin off into the grass. Mileage is less important than "stickyness".

Narrow tires are also much better in snow and rain, as there is less room between the tire's tread and the road to trap water and snow. Wider tires, well, stink in the wet though the ones specially designed for such are a significant improvement over outright slicks.

You can also mix and match ideas for optimum results for your vehicle. I'll give you an example.

You might notice that heavy duty pickup trucks (Ford F250/350, Dodge 2500/3500, Chevy/GMC 2500/3500) have larger diameter tires than cars, but they are fairly narrow, barely wider than the average full size car. This is by design because the narrower footprint allows the water/snow to escape better than a wider tire, but the larger diameter tire makes the contact patch _longer_ which means while it has a skinny contact patch, it has more surface on the road than a regular car tire of a smaller diameter.

This is important when you're trying to have enough traction to accelerate, stop or turn a a pickup that typically weighs between 5000-7000lbs plus cargo, trailer, and utility features.

This is also why the old VW's - Ghia, Beetle, "Thing" and Bus all had small diameter, skinny tires - there was no power to speak of and they weighed very little therefore less contact patch was necessary for any reason. The skinnier, smaller diameter tires allowed those vehicles to get better mileage and perform very well on dry roads as well as in the wet.

One of my favorite "stock" vehicles to drive in 4" of snow was the old VW Beetle... RWD, rear mounted engine, skinny tires. They were unstoppable until the depth of the snow equaled the height of the floorpan.

Mounting skinnier tires on an EV is perfectly fine, as long as you take the time to calculate out how much accelerating, braking and turning capability your car needs, and select a tire that gives you enough contact patch to do that. If you're going to drive 35 miles per hour tops in heavy commuter traffic, you need less tire than if you're going to take your EV to Limerock CT and burn a few laps off.

All tires have several ratings, including load capacity and traction capability. For any vehicle, especially a heavy EV vehicle, load capacity is important.

The reason why newer "commuter cars" have wider tires is because they have more power than they did 20 years ago. A typical nissan in 1989 had 100-110hp from the factory. Nowadays, you see Altimas with 220HP.

More power, more tire. What has changed as far as OEM's trying to "look cool" is the factory installation of lower profile tires and fancy, nifty rims. 20 years ago most OEMs gave you ugly steel rims with even uglier plastic wheel covers.


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## Guest (Jul 8, 2009)

Most EV's are not F1 Class so skinny tires are just fine. Acceleration is marginal and stopping is with in normal parameters of the average street car. Sure it an F1 those sticky fat tires are needed but they also have the suspension and performance road to drive on too. No street car has that. 

Skinny reasonable stiffness and good tread are fine until you can find a true LRR tire. I'd like some too but until then the narrow tires I have will do. Still working just fine. 

Pete


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## Duncan (Dec 8, 2008)

Hi Frederic,
Not sure if all of your "facts" pass the sniff test.
Modern cars (like always) are more about styling than anything else, 
dedicated track tyres will always win on a track, 
My old Lancia engined mini with 170Hp was fine on the road with 175/14 tyres
On the track with slicks it was fun!
The difference between 165 - 205 road tyres is negligible and more to do with the softness of the rubber than the width

My advice would be to get the narrowest road tyres (that you can live with for looks)
And get some track tyres for any motor sport you do

As a Scotsman this is also a lot cheaper as a single hillclimb or sprint can eat a set of expensive road tyres but good race tyres are available third hand 

I used to use old F3 qualifiers, the first owner would pay tonnes and do one event,
the second owner would pay less and use for a season
I would then use until the canvas showed

These cheap used race tyres were unbelievably better than the most expensive road tyres


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## frederic (Jul 4, 2009)

Duncan said:


> Not sure if all of your "facts" pass the sniff test.


Then hold your nose ;-)



Duncan said:


> Modern cars (like always) are more about styling than anything else, dedicated track tyres will always win on a track,


Yes, however what I said about a need for increased tire patch on newer cars (at least here in the US) is true. 20 years ago a Nissan sentra had skinny tires. The Altima, which replaced it, has wider tires and twice the power. Sure, styling is a huge factor and that's why low profile tires are selected, but you can't run 220 HP with the skinny tires the Sentra had and expect not to spin them.

Put an 200HP Altima engine in a 20 y/o Sentra and ship it to me, I'll prove me point and record the results to Youtube for you ;-)

Actually, you don't have to, because I break my cousin's Hyundai Excel from the asphalt just by shifting at redline until it smokes.



Duncan said:


> My old Lancia engined mini with 170Hp was fine on the road with 175/14 tyres


Wait a minute... a Lancia is not a "commuter car", it has a nice, well tuned suspension so of course your results will be different. Compare that to the modern OEM garbage here in the US and you'll see the difference. While not an out and out race car, your Lancia has racing roots in it's design.



Duncan said:


> On the track with slicks it was fun!


I bet it was!



Duncan said:


> I used to use old F3 qualifiers, the first owner would pay tonnes and do one event,
> the second owner would pay less and use for a season
> I would then use until the canvas showed


I used to race top fuel funny cars and our very poor team did the same. All of our parts, including tires, were "leftovers" and used until the tech inspection crew told us "no freaking way". Then we put on the next, well used set of sticky's.

It's probably why we never won. lol.



Duncan said:


> These cheap used race tyres were unbelievably better than the most expensive road tyres


Absolutely agree.

See, no stink test necessary. The only difference is regarding vehicles, we weren't comparing apples and apples. And unless someone is building an EV specifically for racing purposes, the whole slick thing is irrelevent.

We have tons of Smart Cars and Hybrids around here (NYC/NJ area), and they all have incredibly skinny passenger car tires.


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## Drew (Jul 26, 2009)

tyre width and rolling resistance are not inherently linked, its pretty important to consider the loading that the tyre will be under as well as the tyre pressures and composition as well.

That being said, if you're interested, America should have the equivalent of Australia's Tyre and Rim Handbook which describes what combinations of tyres, rims, loads and pressures are legal with which tyres.

Another thing to consider is that any improvement in rolling resistance will generally come with a reduction in outright performance, which might sound fine until you need to brake for somebody who pulls out in front of you.

If you're after a tyre which has a low rolling resistance then the best place to look is at a commercial vehicle tyre, they're close enough to made of stone, have a capability to be run at very high pressures and have a very high load rating. Expect awful ride quality and appauling handling and braking to go with it.


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## andylaurence (Aug 6, 2009)

frederic said:


> Then hold your nose ;-)
> Yes, however what I said about a need for increased tire patch on newer cars (at least here in the US) is true. 20 years ago a Nissan sentra had skinny tires. The Altima, which replaced it, has wider tires and twice the power. Sure, styling is a huge factor and that's why low profile tires are selected, but you can't run 220 HP with the skinny tires the Sentra had and expect not to spin them.


A wider tyre doesn't have a bigger contact patch. The contact patch is directly related to tyre pressure. Imagine a car weighing 1200lbs. At 40psi, the contact patch will be 1200/40 = 30sq-in. If the car has even weight distribution, that's 7.5 sq-in per tyre. If you reduce tyre pressure to 30psi, then the contact patch increases to 40sq-in, which would be 10sq-in per tyre in an ideal scenario.

Changing the width of the tyre simply changes the shape of the contact patch. A wider tyre will be able to maintain a larger contact patch for the same amount of deformation though, which will be beneficial for tyre temperature management (keeping them cool).


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## piotrsko (Dec 9, 2007)

series of comments: "Bug" tires WERE 5.60 tread width X 85% aspect ratio which is nowadays about a 145 width tire. I haven't been able to locate any except for the lower profile tires for the front of "slammed" bugs and the occasional Firestone whitewall retro tire. Squarebacks TY3 and bussies TY 2 also used a "D" range tire, same size but extra plies, more air pressure and way more expensive. closest to these are trailer tires, but illegal for running on cars.

In America, If you want low rolling resistance, you will be obligated to find a manufacturer that publishes the lowest coefficients for their tire and get the tire sized for the vehicle maximum load. Unfortunately, most manufacturers do not publish rolling resistance data. 

Rule of thumb is the higher pressure the tire normally handles the lower the rolling resistance under STANDARD loads. other things to look at and to GROK are tire durometer hardnesses, tread patterns, ply composition and orientation, and finally sidewall shapes and price. Cheap tires may not be the easiest rolling ones, but OTOH, neither may the expensive ones..


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## andylaurence (Aug 6, 2009)

piotrsko said:


> series of comments: "Bug" tires WERE 5.60 tread width X 85% aspect ratio which is nowadays about a 145 width tire. I haven't been able to locate any except for the lower profile tires for the front of "slammed" bugs and the occasional Firestone whitewall retro tire. Squarebacks TY3 and bussies TY 2 also used a "D" range tire, same size but extra plies, more air pressure and way more expensive. closest to these are trailer tires, but illegal for running on cars.


Clearly it's different over there. Here, the first site I visited had the following:

10" 145/80
12" 135/80
13" 135/80
14" 155/80 & 155/65
15" 135/80 & 135/70


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## rmay635703 (Oct 23, 2008)

Zemmo said:


> You can get skinnier tires without going to the spare donut tires. Yes those spare donut tires aren't designed for that type of work. But there is skinny tires that are rated for that. An example is a VW Bug, the original, it had skinny tires and was for full service. You just have to find the appropriate tire.


All 4 of the tires on my Comutacar are space saver spares on different rims and they are about 8 years old with about 9k-10k of miles on them.

They are not that unsafe so long as you understand how the ratings work and what they really mean.

Generally if the space saver spare is intended for a vehicle at 50mph and at say 1800lbs PER TIRE (which many are) That tire when used on a SIGNIFICANTLY lighter vehicle can handle standard service. The 50mph rating is mainly because of poor ride/handling (aka 60psi-70psi rating along with the speed differential from being the wrong diameter on your gears) and 2ndly because of potential heat buildup at speeds in excess of that speed AND RATED WEIGHT.

The other issue with space savers is that they have about as much traction as a 50% worn summer tread which means they aren't that great in the elements.

So I would say, go for it, especially if your vehicle is well under the weight rating of the tire AKA half or less or if you aren't driving fast. They really do add a significant amount of range.

Cheers
Ryan May


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