Wheel weight and mileage

Hussman · Sep 12, 2018

I did some research and found out the stock rims on my 2003 ALH Jetta weigh 16.5LB before tires. I have some type 25 grey MSW wheels on it and they weigh 20LB before tires. The MSW are also 16s instead of the stock 15 AVON I think they are called.

Do you think that 3.5 pounds and one inch is hurting my mileage? By how much?

Thanks.

KLXD · Sep 12, 2018

What is the rotational inertia of the two wheels?

Hussman · Sep 12, 2018

KLXD said:
What is the rotational inertia of the two wheels?

That’s a good question, do you know how to find that out?

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WildChild80 · Sep 12, 2018

When I went from the 5 blade 15 inch 6.5 inch to the BBS 16 inch 7.5 width tires I lost a point or 2 in the mpg category but I love the look and preserving the BBS wheels because I think they're gorgeous.

I would expect road manners are more affected than mpg. From my sport bike days, your wheel weight dictated how much centrifugal affect on the bike. I realize that the car doesn't act like a bike but the forces are still at work and a heavier wheel takes longer to respond to inputs like bumps and also takes longer to counteract.

I would think it would affect city driving mpg more than highway or constant speed driving if any real difference were able to be noticed.

Contact patch is probably more critical to fuel mileage than wheel weight due to absolute resistance.

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WildChild80 · Sep 12, 2018

Or was it 5.5 to 6.5...the BBS wheels(Wolfsburg) are an inch wider...

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BobnOH · Sep 12, 2018

Tires of a different circumference is an added variable. Different contact patch, even depth of rubber will make a small difference.

But the answer is yes, different weight wheels will affect mileage. I have no data, but the amount must be very small, all but insignificant.

Powder Hound · Sep 12, 2018

Probably the biggest difference will be found when moving from the stock 15" steelies which weigh in at about 23 pounds to the ubiquitous Avus 15" aluminum wheels that weight in at 17.5 pounds. Big mass difference with no appreciable change in any other variable. Well, except the compliance of the wheel itself.

Anyway, usually even those of us in the unwashed masses can tell the difference in such a wheel swap.

Cheers,

PH

joep1234 · Sep 12, 2018

I just went from 16" Key West to 17" Turbo S wheels and the tires went from 205/60/16 to 225/45/17 and my mileage went up .5 mpg's. The car handles way better with the wider tires and the lower aspect ratio.

jettawreck · Sep 12, 2018

joep1234 said:
I just went from 16" Key West to 17" Turbo S wheels and the tires went from 205/60/16 to 225/45/17 and my mileage went up .5 mpg's. The car handles way better with the wider tires and the lower aspect ratio.

My mileage always went down going to the 245/45/17s. About 3 mpg at least in more than one Jetta (sedan and wagon). Wider lower profile almost always means less mpgs.

WildChild80 · Sep 12, 2018

Maybe if one were to go from an aggressive summer tire to a fuel efficiency tire, you might break even...but that's what I've always seen...bigger wider = more fuel used...

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joep1234 · Sep 13, 2018

The side of the tire said max pressure is 50 psi. I am running 45 psi in all 4. Can't answer why it is better but I am happy. The 205/55/16 is the stock size but I got a deal on my last set that had a 60 aspect ratio tires and the 225/45 are pretty close to the stock size on the Turbo S wheels.

Andyinchville1 · Sep 13, 2018

HI,

I went from stock steelies and Ecopia 195 70R 15 tires to Avus rims and Ecopia 205 70 R 15 (I believe that was the size but in any event it was the next size up )....

RPM's at speed definitely went down (speedo is now right with GPS speed) , maybe a little quieter , didn't feel different performance wise .... MPG went up a bit but not alot ... maybe a few tenths over my standard driving route.

I like the meatier tires and the extra ground clearance .....from now on I'll roll on the larger tires.

AndyBees · Sep 13, 2018

I never read every response, so if this was discussed, excuse me.

Changing wheel/tire size can affect the accuracy of your odometer. Smaller tires will rotate more times in a mile and the opposite for larger tires. So, smaller than stock will overstate miles and larger tires will understate miles.

Bottom line, larger tires may slow down the RPMs at a given MPH, but they will under-register the number of miles traveled between fill-ups. So, the improved fuel economy may be understated as those taller tires caused the odometer to understate miles traveled. Thus, an adjustment is necessary to establish base data for the new tires. Example: How much do they understate miles over a long distance? You can get close by using Mile Markers but GPS is much better.

My Jetta always under-stated miles by about 1%. I come to that conclusion years before I got my first GPS. GPS proved the difference to be more like 1.25%. And, a brand new tire will be larger than a worn out tire.

Andyinchville1 · Sep 13, 2018

AndyBees said:
I never read every response, so if this was discussed, excuse me.

Changing wheel/tire size can affect the accuracy of your odometer. Smaller tires will rotate more times in a mile and the opposite for larger tires. So, smaller than stock will overstate miles and larger tires will understate miles.

Bottom line, larger tires may slow down the RPMs at a given MPH, but they will under-register the number of miles traveled between fill-ups. So, the improved fuel economy may be understated as those taller tires caused the odometer to understate miles traveled. Thus, an adjustment is necessary to establish base data for the new tires. Example: How much do they understate miles over a long distance? You can get close by using Mile Markers but GPS is much better.

My Jetta always under-stated miles by about 1%. I come to that conclusion years before I got my first GPS. GPS proved the difference to be more like 1.25%. And, a brand new tire will be larger than a worn out tire.

HI,

That is true and I did scale MPG as a result of the % of increase in tire diameter (smaller tire diameter is more revs per mile than the larger tire).

On the flip side, I have read that while the speedo usually reads slower than actual speed using the stock tire size supposedly the Odometer readings were supposed to be calibrated correctly....

To be honest I did not drive say 10 miles worth of mile posts to see how accurate the odometer is VS highway mile markers...

I may try to do that next time I get a highway run to see how the bigger tires affect actual odometer readings over 10 or so highway miles...

Thanks

jettawreck · Sep 14, 2018

Yes, if your speedo reading became more "accurate" the odometer is now probably under reporting actual distance traveled.
Going from the stock 195/65/15 tires/alloy wheels to 205/65/15 (not running these currently) on the same OEM alloy wheels brings my speedo readings very close to actual and under reported miles about 1.5% IIRC.
Width and full new tread depth seem a major rolling resistance. Almost worn out tread roll easier, but of course, not worth the safety considerations.

ktmkris · Sep 14, 2018

jettawreck said:
My mileage always went down going to the 245/45/17s. About 3 mpg at least in more than one Jetta (sedan and wagon). Wider lower profile almost always means less mpgs.

245 45 17 are substantialy taller than a 225 45 17 tire, I would expect a difference. That would be roughly 7/10 of an inch taller

jettawreck · Sep 14, 2018

ktmkris said:
245 45 17 are substantialy taller than a 225 45 17 tire, I would expect a difference. That would be roughly 7/10 of an inch taller

Tire companies all produce an on-line spec sheet for all their tires that will give you all the measurements. Circumference, revolutions per mile, etc...
Makes for some interesting comparisons. Not all same/similar sizes roll the same measurements.

AndyBees · Sep 14, 2018

Like this one..

https://tiresize.com/calculator/

EDIT: When I was calibrating the Dakota Digital Interface for the Vehicle Speed Sensor data to the Jetta Cluster I installed in my Vanagon, it took several attempts to get it right. I used a GPS unit to make the adjustments. I found that setting the Speedometer about 2 MPH fast, like in the Jetta, resulted in the Odometer being about 99.999% accurate. My wife operated the Interface by pressing up and down buttons to synchronize the vehicle speed on the speedometer at 70 with GPS showing 68 while I did the driving at a steady state speed.

So, at 70 MPH on the Speedometer, the GPS unit says 68 mph as well as those road side Radar Signs that display your speed.

The two long road trips resulted in the GPS and Odometer being less than 0.0001 difference. I'm satisfied with that.

jettawreck · Sep 14, 2018

AndyBees said:
Like this one..

https://tiresize.com/calculator/

EDIT: When I was calibrating the Dakota Digital Interface for the Vehicle Speed Sensor data to the Jetta Cluster I installed in my Vanagon, it took several attempts to get it right. I used a GPS unit to make the adjustments. I found that setting the Speedometer about 2 MPH fast, like in the Jetta, resulted in the Odometer being about 99.999% accurate. My wife operated the Interface by pressing up and down buttons to synchronize the vehicle speed on the speedometer at 70 with GPS showing 68 while I did the driving at a steady state speed.

So, at 70 MPH on the Speedometer, the GPS unit says 68 mph as well as those road side Radar Signs that display your speed.

The two long road trips resulted in the GPS and Odometer being less than 0.0001 difference. I'm satisfied with that.

Even better is go to the web site of your particular tire brand. They have all their SKUs listed and there are differences between versions even in the same sizes.

That's getting as accurate as practical Andy! Does the Jetta cluster fit into the place meant for the original Vanagon's panel?

PakProtector · Sep 16, 2018

hey-Hey!!!
The biggest thing I notice seems to be improved ride from lower unsprung weight. More wheel mass is not a good thing. in MI, I run 205/65's and keep them inflated so as not to succumb to a pot hole induced flat. It seems to be working. If I need more handling, I will find an S1 Esprit to drive...

cheers,
Douglas

ktmkris · Sep 16, 2018

jettawreck said:
Even better is go to the web site of your particular tire brand. They have all their SKUs listed and there are differences between versions even in the same sizes.
That's getting as accurate as practical Andy! Does the Jetta cluster fit into the place meant for the original Vanagon's panel?

Better would be to just measure the tire, if we want to split hairs. That would account for wear

jettawreck · Sep 17, 2018

ktmkris said:
Better would be to just measure the tire, if we want to split hairs. That would account for wear

Except it's sort of difficult to measure the mounted tire prior to or when contemplating a purchase. Think of it as research tools.

ktmkris · Sep 17, 2018

As I said in the beginning. A 245 45 17 is roughly 7/10ths of a inch taller or .71 than a 225 45 17. If there is debate over that than you are splitting hairs.

245 40 17 would be a very comparable tire height to a 225 45 17 if someone wanted to go wider.

Lastly tires should be steel belted. There will be a negligible height difference when mounted.if you are inflating a modern steel belted tire and it is getting taller, than you are also damaging said tire

AndyBees · Sep 18, 2018

jettawreck said:
Does the Jetta cluster fit into the place meant for the original Vanagon's panel?

photos in this link reflect how I customized the Jetta cluster to fit..

http://pics.tdiclub.com/showphoto.php?photo=126562&title=tdi-cluster-in-vanagon&cat=6288

ToxicDoc · Sep 18, 2018

Your tire pressure will also make a difference in the rolling radius.

ktmkris · Sep 18, 2018

ToxicDoc said:
Your tire pressure will also make a difference in the rolling radius.

Yes and no. If the tire is properly inflated there will be no difference in height. A tire with 30 psi and a tire with 40 psi should be the same size. The rebound of the tire would be the difference. Now if you were comparing a 10 psi tire to a 40 psi. The steel belts would keep a tire from getting taller. Rolling resistance would decrease with more air.

ToxicDoc · Sep 18, 2018

ktmkris said:
Yes and no. If the tire is properly inflated there will be no difference in height. A tire with 30 psi and a tire with 40 psi should be the same size. The rebound of the tire would be the difference. Now if you were comparing a 10 psi tire to a 40 psi. The steel belts would keep a tire from getting taller. Rolling resistance would decrease with more air.

Agreed on the tire not getting taller but then can get minimally shorter. The tire needs to be properly inflated as the side walls have varying stiffness too depending on the profile.

Pat Dolan · Sep 18, 2018

ktmkris said:
Yes and no. If the tire is properly inflated there will be no difference in height. A tire with 30 psi and a tire with 40 psi should be the same size. The rebound of the tire would be the difference. Now if you were comparing a 10 psi tire to a 40 psi. The steel belts would keep a tire from getting taller. Rolling resistance would decrease with more air.

The tire diameter is NOT it's rolling radius. Tires are not round when loaded, they have a significant flat spot that defines the tread contact patch - and this patch will decrease in size when air pressure is raised - and rolling radius will change accordingly as will revs/mile. The steel belt flat spot changes with it. This, BTW, is how newer ABS systems doe tire pressure management - by counting the revs Iactually ABS tone ring pulses) of each wheel and alarming with one increases due to lower air pressure.

And, from an earlier comment: 0.7" difference in tire diameter is significant.

ktmkris · Sep 18, 2018

Pat Dolan said:
The tire diameter is NOT it's rolling radius. Tires are not round when loaded, they have a significant flat spot that defines the tread contact patch - and this patch will decrease in size when air pressure is raised - and rolling radius will change accordingly as will revs/mile. The steel belt flat spot changes with it. This, BTW, is how newer ABS systems doe tire pressure management - by counting the revs Iactually ABS tone ring pulses) of each wheel and alarming with one increases due to lower air pressure.

And, from an earlier comment: 0.7" difference in tire diameter is significant.

I agree .71 is a huge difference in tire size. That is what I told the poster. Someone made a comment they lost mpg with 245 45 17. That is a substantialy taller tire.

As to the other comment about radius, I understand weight and air pressure can change that. Which is the reason I said a properly inflated tire will not change radius. If you are changing radius you are either under inflated or over inflated.

Pat Dolan · Sep 18, 2018

ktmkris said:
I agree .71 is a huge difference in tire size. That is what I told the poster. Someone made a comment they lost mpg with 245 45 17. That is a substantialy taller tire.
As to the other comment about radius, I understand weight and air pressure can change that. Which is the reason I said a properly inflated tire will not change radius. If you are changing radius you are either under inflated or over inflated.

Won't change from what? To be precise, won't change from the ROLLING radius as given by mfg - which is NOT 1/2 the tire diameter. What I do not know is what value of loading the OEM uses to establish rolling radius - as, for instance, the same tire on a FWD car will have considerably different deflection from load front vs. rear, and maybe also vs. mfg standard load.

Wheel weight and mileage

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