Larger wheels for MPG?

[SentraSE-R]

It's a cool idea, but that tire size doesn't seem to exist.

[arcosine]

The NANKANG 165/80R15 is rated for 44 psi I'd probably get those , I got Kumho Power Star 165/80R15 tires last time from Tire Rack, 35 psi, not very good in snow. The Federal 165/80R15 SS 657 is rated for 35 psi. You car will coast far with this tire size.

[jpoole]

Nankang are the ones I bought

[SentraSE-R]

Originally Posted by arcosine

The NANKANG 165/80R15 is rated for 44 psi I'd probably get those , I got Kumho Power Star 165/80R15 tires last time from Tire Rack, 35 psi, not very good in snow. The Federal 165/80R15 SS 657 is rated for 35 psi. You car will coast far with this tire size.

What are we doing different? I get no tires available in the size I select when I put in 165/80-15 tire size at Tire Rack and 1010tires.com. I also get no hits at Tire Rack for Kumho Power Star tires. Are you smoking funny cigarettes? Are these some weird trailer tire size, or something?

[jpoole]

I bought mine @ discounttiredirect.com

[CapriRacer]

Just be aware of the fact that the type of tire (meaning make and model) may have a pretty large effect on your results.

You'll also be changing tire size which will also have an effect. Not to mention removing worn out tires and replacing with new. So there are 3 variables just in tires. Be careful when you report the results that you don't identify a single item as the change in mpg!

[arcosine]

Tire Rack no longer carries the size. Try Googleing 165/80R15. You might find some used ones on Ebay or Craigslist.

185/65R15 vs 165/80R15:

I took a hand grinder and cut tread blocks in the tire.



rolling resistance of 165/80R15 at 42 psi and 35F:

http://www.youtube.com/watch?v=igrJ_QI9eBg

[LeeD]

Originally Posted by Big Dave

Increasing tire OD almost always backfires and MPG is reduced.

It might work if you were a long-haul trucker who can maintain the same speed hours on end, but most of us have to deal with stop-and-go situations.

Rotational moment of inertia goes up with the square of diameter. That means those four "flywheels" have to absorb more energy to increase their RPM. Until the tire RPM increases road speed doesn't increase.

Another evergreen myth that deserves a sticky.

Big Dave makes a good point that many people miss.

Yes(as many hear already realize), if you were to drive at a constant speed, you will travel a longer distance given the same rpms but with a larger diameter tire.

However,
imagine holding your arm out with a bag of apples in your hands. If your rotate your body and swing the bag around you, you will find it takes some strength (torque) to ACCELERATE it to speed for a full rotation.

Now imagine holding a stick that is the length of your arm with the bag of apples on the end. You will find it takes MORE strength (torque) to get the apples to ACCELERATE up to speed around you.

If you increase the diameter of your tires, the engine now has to deal with FOUR wheels that have increased in diameter and the car will require more torque and rpms to accelerate the same amount to get to speed.


Given that this is gas saving forum, it's safe to say that everybody here is already accelerating slowly. Assuming all other variables are the same, to get the SAME mpg, you would have to accelerate EVEN SLOWER. These are just laws of physics.

You will however gain mpg at steady state speeds. Hope this makes sense.

To actually gain mpg with taller tires, one would have to drive a higher ratio time at steady state than to acceleration.

Each person would be different and it's complicated to say if one did or did not increase that ratio.

To complicate matters more, tire rolling resistance (likely brought up in other threads here) make a difference too and most people change their tire type when changing wheel size so it makes it even more difficult to gauge which made the difference in mileage. Let's not also bring up how much the weather difference changes it too --> http://john1701a.com/prius/images/da...ic-Compare.png

I am considering to upgrade the 14" wheels of my '01 Prius to 15" so I can purchase the ultra fuel efficient Michelin Energy Saver A/S. These have been proven to reduce rolling resistance and increase gas mileage --> Tire Test Results : When Round and Black Becomes Lean and Green Knowing the downside potential of larger wheels, I'm only considering the lightest wheels I can buy. Super lightweight Enkei RPF1 --> Enkei Racing RPF1 Bright Silver Paint

Other downsides to larger wheels in a hybrid that I'm chewing on:
1. Given the same distance traveled on the highway, I likely will get less battery charge from the lower engine rpm.
2. Given the same distance when decelerating, I will likely charge the batteries less.

[mcrews]

LeeD,
sorry if this seem blunt.......

Originally Posted by LeeD

Big Dave makes a good point
*****actually he doesn't...see below*****t
that many people miss.

Yes(as many hear already realize), if you were to drive at a constant speed, you will travel a longer distance given the same rpms but with a larger diameter tire.

However,
imagine holding your arm out with a bag of apples in your hands. If your rotate your body and swing the bag around you, you will find it takes some strength (torque) to ACCELERATE it to speed for a full rotation.

Now imagine holding a stick that is the length of your arm
*****WHAT!!!!!!! the tire size increase is 5-9% not 100% as your example states!!!!!*********
with the bag of apples on the end. You will find it takes MORE strength (torque) to get the apples to ACCELERATE up to speed around you.

If you increase the diameter of your tires, the engine now has to deal with FOUR wheels that have increased in diameter and the car will require more torque and rpms to accelerate the same amount to get to speed.
*******completely false arguement*********
In the first place the issue is weight, not distance.
1. the distance is 5-9% it barely registers!
2. In most up sizes, the tires weigh the same or maybe 1 lb more.
Since your extrme exaple exagerates the lenght it is void.
Iwhen discussing 'energy' reqiuired to get an object in motion, the issue is potential ADDITIONAL weight. (which doesnt happen in this discussion.)

Given that this is gas saving forum, it's safe to say that everybody here is already accelerating slowly. Assuming all other variables are the same, to get the SAME mpg, you would have

******false. you dont "HAVE TO" that voids the test. Given identical pressure on the gas, the car WOULD accelerate slower. (but so what?) The question is "is the trade off worth it"? to accelerate EVEN SLOWER. These are just laws of physics.****funny, you make up an exagerated example, incorrectly state the test , then say "...the law of physics..."******
You will however gain mpg at steady state speeds.
*** That is the whole point. seems simple. what was all the above about???*********

************You remind me of the guys talking about cone air filters and WOT. Hoe often are you at WOT?***********
Hope this makes sense. [
I]*****no*****[/I]
To actually gain mpg with taller tires, one would have to drive a higher ratio time at steady state than to acceleration.
**************This is a false statement! If you actually knew how to ABA test you would unserstand this. You are saying:
TEST A - drive 1/8 mile accelerating and 5 miles at cruise.
TEST B - drive 1/8 mile accelerating and 6 miles at cruise.

That is a false test AB test!
You drive each test the same with the only change being the tire size. And as I and others have shown in true AB testing, you get better mileage with a larger diameter tire.*******

******(please share any actual AB testing you have)*************

******so everybody is 'always' accelerating?????? really!***********

Each person would be different
***that's why each person developes his own tests!!****
and it's complicated to say if one did or did not increase that ratio.


To complicate matters more, tire rolling resistance (likely brought up in other threads here) make a difference too and most people
*****not true!******
change their tire type when changing wheel size so it makes it even more difficult to gauge which made the difference in mileage.
***********I used the same brand AND type of tire.***********
Let's not also bring up how much the weather difference changes it too --> http://john1701a.com/prius/images/da...ic-Compare.png

I amand Black Becomes Lean and Green[/url] Knowing

(REALLYYYY?????? and you 'know' this how????)
the downside potential of larger wheels, I'm only considering the lightest wheels I can buy. Super lightweight Enkei RPF1 --> Enkei Racing RPF1 Bright Silver Paint

Other downsides to larger wheels in a hybrid that I'm chewing on:
1. Given the same distance traveled on the highway, I likely will get less battery charge from the lower engine rpm.
******in a normal car, an alternator hit max charge at a realitively low speed. If you have a scangauge you can see the proof.************
2. Given the same distance when decelerating, I will likely charge the batteries less.
**********Withuot proof of how the charging cycle works, this is really a non-issue and a silly one. what is you get a job closer to home!!!! uppps less charging......really?********

Actually Big Dave's point is the 'myth'. Blanket statement with no facts.

Increasing tire OD almost always backfires and MPG is reduced.


1. PROOF: several threads on my infiniti Q45 245/45/18 UPSIZE to 245/50/18 stock rims. INCREASED MPG! PERIOD. FACT.
2. KIA Sportage 235/60/16 to 235/70/16 Thread posted. INCReased mpg. PERIOD. FACT.
3. Several others have proven the same set of facts.

Here are the STATED facts:
1. Trucks (in general) dont seem to see an improvement in larger tire sizes. With that said, I have yet to see (FACTS) a case study showing FACTORY size being upsized to a 7-12% larger diameter. But I have clearly stated in all threads that trucks are not in the discussion. (big dave is silent on this distinction)
2. As stated many times, you have to do just a fair amount of your driving at 'cruise' (final speed) for larger size to work in your benefit. If your comute is 5 miles in the city then a larger size probably wont work.
3. The whole idea is to reduce the rpms thus reducing your consumption over the same distance.
4. since we all drive 'slow' then the slight loss of acceleration wont be missed as the tires take longer to get rolling. But again, does anybody spend 50% of their drive accelerating??? So it isnt an equal trade off. larger diameter tires should always help mpg
5. the conversation above is about upsizing on the same rim. When you begin to increase the rim size THEN the conversation becomes more complicated because you are moving the weight farther out. Which can begin to effect suspension componets wear and tear.
6. ALL of this was done using a Scangauge and GPS. (not guesing on an inaccurate speedo). As should all testing.
7. I changed sizes on the infiniti Q45 using the same brand KUHMO and type (summer). The wear rating were almost identical.
8. For upsizing to be effective, there needs to be at least a 5% increase in the diameter.
TESTING DEFINED:
1. find a flat stretch of road you can always use (5-10 miles). alwasy drive to the test the same way (so the engine is at the same level of 'warmed up'.
2. try to run at same time of day, during the same season, same weather.
3. get base line runs at 45, 50, 55, 60, 65, 70 etc.
4. now with the larger tires do it again.
5. bake sure scangauge is calibrated w/ gps. for a more exact calibration switch to metric. Then switch back to mph.