Wheel/tire (16") weights and fuel economy??

Wheel/tire (16\") weights and fuel economy??

The story:
Last summer I put Montreal II 16" rims on my Jetta and they came with 205/55R16 Bridgestone Turanza. I run the tires at 44PSI and still took like a 4 mpg hit in fuel economy. Looking online I found that the tires weight 25 lbs each. I love the rims, but I want my economy back.
I can get the same size tires that weight between 20 and 21 lbs and could be run as high as 50 PSI.

The question:
Would going with a lighter, higher pressure tire like this gain any of my economy back?

The discussion:
What 16" tires would people recommend for fuel economy? Some of you NB owners must have some opinions?

Wheel/tire (16\") weights and fuel economy??

Yes.

See this thread about light wheel/tire combo's.

Also this if you like numbers:
see the Excel pics in this thread.

Your wheel/tire combo's polar moment of inertia (how hard it is to induce a wheel to spin: ie...angular acceleration)) is dependent on

KMR^2

K= coefficient of angular inertia...it is shape-dependent. A wheel with more mass at the hub will spin up faster than an identically weighing wheel with more of its mass at the rim.

M= mass of wheel. Lighter is always better, provided it can carry the load.

R= radius...smaller is better (lower polar moment.)

A 15" wheel will accelerate better than an identically weighing 18" wheel (both having same tire + wheel combo diameter)



Yes, you will recover your fuel economy, but you should review SUNRG's thread to find the best lightness-per-$ package...you may be able to sell your current wheel set to recoup some expense.


There are some suggestions about 15" and 16" wheels and their corresponding tires which are light weight & nice looking in SUNRG's thread...happy reading

Re: Wheel/tire (16\") weights and fuel economy??

I actually read SUNRG's thread and they didnt actually talk much about 16" tires. And the Nokian they talked heavily about doesnt come in a 16". I love the rims, they arnt going anywhere. There are people with beetles posting amazing fuel economy and they have the same size whee/tire as I do. So I dont really feel I have to give up the rim.

Re: Wheel/tire (16\") weights and fuel economy??

I don't have a vehicle's rolling and drag resistance equations at my tip, but wouldn't these combined friction forces dwarf the (4) wheels inertia force?

Re: Wheel/tire (16\") weights and fuel economy??

56 mpg on my last tank.

Re: Wheel/tire (16\") weights and fuel economy??

VF, but what tires are you running?

Re: Wheel/tire (16\") weights and fuel economy??

Sorry, Michelin Energies. I drive 65 indicated on the highways though. I've used Energies for the 150k miles I've had the car. 40 psi. Delvac1. What was your previous tires/wheels setup and was it OEM? (maybe previous tires were smaller). Have you tried driving slow for a tank and see how much mileage you get?

Re: Wheel/tire (16\") weights and fuel economy??

I've had Montreal IIs on my car in the past. They came with stock Contis. I noticed no difference in mileage compared to the 15" wheels that came on my car. The Contis were replaced with a set of OEM Michelins... take offs that I bought from a Vortexer for $150. No mileage difference. The Montreal IIs & Michelins are currently sitting in the garage, and I'm now running 16" Hakunamattas (sp?) from a 2004 GTI. They came with the Contis, and I noticed no mileage hit. I'm not saying there was absolutely NO mileage loss when I went to the 16s... But... if there was a drop in mileage it was so unremarkable that it was unnoticed. If you go with an OEM Continental or Michelin tire you should get your mileage back.

Wheel/tire (16\") weights and fuel economy??

I fill every tank until fuel's visible and calculate my mileage. My wagon came with 15" steelies and Energys and now I have 16" Montreals and Kumhos ASXs--15" Blizzaks in the winter. I have to say that winter fuel and speed are the only factors that seem to consistently affect my mileage. Under 75=50 MPG. Under 85=47 MPG. Anything goes=44 MPG. Winter, Thule box, teenagers w/snowboards, mountains, driving 80-90=38 MPG. I love the look of the 16s on the wagon, and I love the handling with the larger tires.

Re: Wheel/tire (16\") weights and fuel economy??

Original setup was 15" avus rims with Hercules Plus tires. 195/65R15. My best tank was like 52.5 with them and i could easily get 50. Now I feel good if I get like 46-47.

Re: Wheel/tire (16\") weights and fuel economy??

I had the Jetta 03 15" alloys and the michelins and the weight was 38lbs. I got SSR's 16x7.5 with a 225x50-16 at 35.5lbs and lost 1.5 to 2 mpg. The rims are 11.9lbs the tires where 23.6lbs. So 4 mpg is about right.
The best tire for mpg's would be the michelins energies.

Wheel/tire (16\") weights and fuel economy??

I have to say that winter fuel and speed are the only factors that seem to consistently affect my mileage. Under 75=50 MPG. Under 85=47 MPG. Anything goes=44 MPG. Winter, Thule box, teenagers w/snowboards, mountains, driving 80-90=38 MPG.

Click to expand...

Not to get off track here, but Peter, I noticed as you posted your speed / mpg's that your highest speeds were during winter - uhhh, thats when most of us slow down.......

Re: Wheel/tire (16\") weights and fuel economy??

I actually read SUNRG's thread and they didnt actually talk much about 16" tires. And the Nokian they talked heavily about doesnt come in a 16". I love the rims, they arnt going anywhere. There are people with beetles posting amazing fuel economy and they have the same size whee/tire as I do. So I dont really feel I have to give up the rim.

Click to expand...

ernie rogers opted for a slightly larger 16" tires, 205-60-16, and has had excellent fuel economy as a result. the Nokian WR does come in this size, is considered a "very low rolling resistance" tire and weighs only 21.8 lbs (in the 205-60-16 size).

the Nokian WR in the standard 205-55-16 size weighs a mere 19.8 lbs!

these tires are also very durable / long wearing, and amazingly, Nokian is the "only four-season family of tires that carries the Severe Service Emblem (mountain with snowflake emblem on sidewall) exceeding new government snow condition regulations" and to top it all off, it's environmentally friendly: "manufactured using only purified low-aromatic oils".

Re: Wheel/tire (16\") weights and fuel economy??

At cruising or steady-state, <font color="blue"> the requirement for angular acceleration is zero, so the polar moment matters little.</font> Thus, at cruising, yes, rolling resistance is >0 so it will dwarf it.

But at any other time, speeding up, slowing down, changing lanes, turning (wheel/tire mass also effects gyroscopic torque vector: how hard it is to turn), there is a polar moment (resistance to angular acceleration), and it totally swamps rolling resistance a lot of the time (depends on how hard you want/need to accelerate/deccelerate.)


The lightest tire/wheel combo with the smallest wheel radius that still gets the job done is always best, especially if you do city driving. If you hardly do any city driving or much stop-and-go driving in traffic, you won't notice it much, otherwise you'll notice a dramatic difference.


Edit note: correction in blue. It was late on a Friday... polar moment is never zero.

Wheel/tire (16\") weights and fuel economy??

I have to say that winter fuel and speed are the only factors that seem to consistently affect my mileage. Under 75=50 MPG. Under 85=47 MPG. Anything goes=44 MPG. Winter, Thule box, teenagers w/snowboards, mountains, driving 80-90=38 MPG.

Click to expand...

Not to get off track here, but Peter, I noticed as you posted your speed / mpg's that your highest speeds were during winter - uhhh, thats when most of us slow down.......

Click to expand...

Actually, my lowest mileages are in winter. Highest speeds......

Re: Wheel/tire (16\") weights and fuel economy??

At cruising or steady-state, there is a polar moment of inertia of zero. Thus, at cruising, yes, rolling resistance is >0 so it will dwarf it.

But at any other time, speeding up, slowing down, changing lanes, turning (wheel/tire mass also effects gyroscopic torque vector: how hard it is to turn), there is a polar moment (resistance to angular acceleration), and it totally swamps rolling resistance a lot of the time (depends on how hard you want/need to accelerate/deccelerate.)


The lightest tire/wheel combo with the smallest wheel radius that still gets the job done is always best, especially if you do city driving. If you hardly do any city driving or much stop-and-go driving in traffic, you won't notice it much, otherwise you'll notice a dramatic difference.

Click to expand...

I wonder if driving habits impact the differences between tires as well. If one accellerates gently, resists sudden moves, and overall tries to drive smoothly, will the difference between heavier and lighter tires be less? I try very hard to drive smoothly and I don't accellerate or decellerate hard. This is demonstrated by the fact that I commute to Boston in my wagon frequently and still have the original brakes at 92K--the rears are about 2/3 worn.

So my question is: Can driving style minimize the difference between tire weights?

Re: Wheel/tire (16\") weights and fuel economy??

The lightest tire/wheel combo with the smallest wheel radius that still gets the job done is always best,

Click to expand...

but, all else being equal, the smaller radius requires higher RPMs, and generally, lower RPMs = less fuel consumption.

<font color="red">so the question is - what setup is ideal for optimizing fuel economy in real world TDI driving?</font>

for the sake of this discussion, let's presume the majority of TDI owners are driving 20k+ annually - i.e. NOT using their TDI primarily for short trip, stop-and-go commuting.

Wheel/tire (16\") weights and fuel economy??

Today I went from this:



To this:



The 14" wheel/tire combo weighed 33 lbs., the BBS 16s w/205/45-16 Yokohamas weigh 36 lbs. Ask me if I care about mileage. The difference in handling is amazing (and yes, I'm getting springs that will lower it a bit).

Wheel/tire (16\") weights and fuel economy??

Ask me if I care about mileage.

Click to expand...

Do you care about mileage?

Which of your three MK3 Jettas is that?

And why do you have so many cars?!

Re: Wheel/tire (16\") weights and fuel economy??

IndigoBlueWagon said:

Can driving style minimize the difference between tire weights?

Click to expand...

Yes, a lot. Driving style is the single most important factor in economy.



SUNRG said:

but, all else being equal, the smaller radius requires higher RPMs,

Click to expand...

I said the smallest wheel that gets the job jone. The wheel + tire diameters are unchanged (or you've changed your gear ratio.)

Re: Wheel/tire (16\") weights and fuel economy??

SUNRG said:

but, all else being equal, the smaller radius requires higher RPMs,

Click to expand...

I said the smallest wheel that gets the job jone. The wheel + tire diameters are unchanged (or you've changed your gear ratio.)

Click to expand...

i want to modify the gear ratio by changing the radius to optimize fuel economy. unless we determine the radius achieved with 195-65-15s is ideal.

i don't want to do any other mods, initially, i just want to determine which radius, that can be accomodated with a stock setup, optimizes fuel economy for the typical TDI owner (drives 20k+ annually, <u>not</u> primarily short trips / stop-n-go).

i realize that modifying the radius will effect speedometer/odometer accuracy, but we can determine the percentage and mathematically arrive at actual/adjusted speed and distance.

Wheel/tire (16\") weights and fuel economy??

Ask me if I care about mileage.

Click to expand...

Nice. Did you happen to get those off vwvortex.com?? I saw a set of the 16" BBS RC's 4x100 on there that were for sale. Of course I love the wheels...

And no... I don't care about mileage either, so I won't ask.

Wheel/tire (16\") weights and fuel economy??

Ask me if I care about mileage.

Click to expand...

Do you care about mileage?

Which of your three MK3 Jettas is that?

And why do you have so many cars?!

Click to expand...

Yes I do care about mileage--to a point. What I like about these cars is that they're guilt-free--I can go where I want and if I don't drive like I'm in a mileage competition I still get better mileage than just about anyone.

The black car is the '97 with 36K on it. I bought that one because it was too good an example to pass up. It was owned by an elderly gentleman on Long Island who used Delvac since the first change, garaged it, never let anyone else drive it, and never let anyone in the back seat. However, he also drove it so slow that the intake and exhaust were almost completely plugged.

My son drives the '98 TDI, and my daughter has the 2.slow. And I drive the wagon most of the time. I'm finding that having several of these cars makes life easy--repairs are all familiar.

Re: Wheel/tire (16\") weights and fuel economy??

According to me, the biggest-diameter tire you can stuff in the wheel well will likely give you the best fuel economy. BUT you will have to correct gage readings to know what you saved.

Now, a new speculation-- I suspect some of the engineers here are way ahead of me on this one. On smooth, level pavement, tire+wheel mass shouldn't matter much. We don't have those roads around here. This "unsprung" mass has to follow the bumps. More mass means more energy goes into the wheel and tire when a bump is hit, and you don't get it all back on the other side. So, lighter "unsprung mass" should lead to better fuel economy. I may try calculating this later.

Ernie Rogers

Re: Wheel/tire (16\") weights and fuel economy??

More mass means more energy goes into the wheel and tire when a bump is hit, and you don't get it all back on the other side. So, lighter "unsprung mass" should lead to better fuel economy.

Click to expand...

bigger AND lighter would be ideal

another advantage of bigger is that it rolls more smoothly, due to the angle of impact between the tire and bumps being reduced. when the radius is slightly increased the angle of impact is changed only very slightly - but if we're considering all variables effected by increasing size ...

Re: Wheel/tire (16\") weights and fuel economy??

Ernie is right (again).
Tire (outer) diameter is more important than weight. Bigger diameter has both the advantage to reduce rolling resistance and improving gear ratios.

The weight of the tire/rim combo affects the ride comfort more than fuel economy.