Just wondering if anyone actually increased the outside diameter of their tires as a way to smooth the ride out a lil bit on the fit. I have done it before on older cars, use the same factory rim, but run an aspect size taller and one tread width wider. So instead of running a 195/55/15 you run a 205/60/15

OEM tire requires 892 revolutions per mile, while the 205/60/15 only needs 843. Because the OEM is 23.3 inches tall and the 205/60/15 is 24.7 inches tall. I would think an extra 1/2-3/4 inches of ground clearance would help daily driving quite a bit and the extra sidewall and load handling ability would soak up some impacts a bit better.

Plus, when you compare the $97/tire cost from tirerack for OEMs vs the larger 205/60/15 Gforce tires for $74/tire, you are saving money, rolling on a better performing tire, with a longer tread life just barely. And you would effectively change your final drive ratio by 5.5% So your car would be revving 5.5% lower at the same actual freeway speed, and your odometer would read 5.5% lower than real miles put on the car. And any calculations of gas mileage would have to be adjusted for that 5.5%

I think I am gonna try it when I need a new set of tires. Plus it would fill the fender well a lil more without having to drop as low. so a 1.5 inch drop would LOOK like a 2inch. Just curious if anyone switched up their shit.

 

tagged for interest

 

i run 205-50/16 size tires
diameter is 24.1
revs per mile is 838
the new set of tires i have to replace them are 205-45/16 which is same as stock diameter
try www.onlinetires.com for pricing...the new tires i got are bfg gforce sports (same as the old ones im replacing) $71 each and used by skip barber racing schools

also the bfg gforce sports in 195-55/15 are $67 each
they also have the Direzza Z1 Starspec for $88 each and the Direzza DZ101 for $64 each
all are a very good street tire

 

I am kinda ancy, makes me wanna throw on my other wheels but they have a 25 inch diameter and 225 tires, I think it will rub excessively. Should have gotten ground controls

I always run g-force now a days, they are great performance for the buck and they last a long time. Have you noticed any differences running the larger tire? probably much better grip with the g-force

 

i'm curious as to how it would look to have larger diameter tires on.. i do a lot of highway driving so the idea of lowering the revs is nice.

i'm using this as my crutch to visualize all of these tire specs
Wheel / tire size calculator / comparer - RIMS-N-TIRES

 

fyi taller tires put more load on the engine...your tradeoff of lower revs is higher load which means more gas to stay at a constant speed...i didnt get any better gas mileage with taller tires and going over hills had to run in 4th instead of making it over in 5th
this is why im going back to stock diameter

 

Well, one nice thing is my bigger rims are lighter in wieght, and the tires are within 1lb of each other. My only concern is will they clear the fenders and suspension components. I dunno anyone running 225/45/17s on a fit.

 

i ran a 215/35 R18 before i lowered my fit..... i didnt rub, however there wasnt very much clearance in the rear. the rear did also rub a few times when hitting larger bumps.....

 

Clearance will be the biggest issue, unless you get wheels with offsets for it. But going taller and wider at the same time is a bad idea unless you have plenty of clearance. Personally I would go up only a step, maybe 195/60/15 but your speedo will be off like 3.28%.

 

now that i want to see.. .any pics?

 

on my old cell phone....... ill have to see if i cant get it off there and on to the internet........ let me work on that!

 

I wanna see those 18's. My 17s have 42 offset so it should be close. I wont be able to try it for a while because my girl always has my car, and she gets home late.

 

I WAS ABLE TO GET ONE OFF THE OLD CELL PHONE........LIKE I SAID, THIS WAS BEFORE I LOWERED MY FIT. LET ME KNOW WHAT YA THINK! http://img16.imageshack.us/img16/9898/18sfit.jpg

 

***cough***rollerskate***cough***

Seriously, I'm thinking along the same lines as shaggs. Larger diameter = lower RPM's at freeway speed, which should equal better gas mileage. It makes sense also that larger diameter = more load on the engine due to having to turn that larger circle, but a great deal of my commute is steady state on relatively flat roads so I'm hoping for a net gain.

 

You'll probably have very minimal gain, if any. It really depends on the overall weight of your wheels+tires.

 

same thing with my fit, 22k miles in 9 months, even if I get 1mpg outta it over a long period of time it adds up. I had an old truck I oversized the tires and changed my % of tread over 10%, and the odometer still read the same MPG calculations, but I was really covering 10% more ground. The load on the engine didn't do shit to my mileage, but the lower revs helped freeway mileage. So if the truck still showed I was getting 24=25mpg on an odometer that is spinning 10% slower, I was really getting about 27-28mpg. The load shouldn't change signifigantly enough to really tax the fuel system. I am gonna forget about trying to put my 17s on and when my tires wear out I will upsize my tires a lil bit. I am actually getting really good treadwear out of the factory tires, they look like they should last til almost 50k at the rate they are currently wearing, which would be great.

jibbz- nice lookin wheels. If it was lowered it would look super gangster.

 

I run larger tires on the stock steelies, with stock suspension. I forget the tire size but it's plus 2 inches to diameter, and makes about 1% difference in RPM.
I didn't have a scangauge before, so I can't say whether they have an effect on mileage. I consistently get upper 50's MPG using pulse and glide while doing 70-80 MPH, so I'm not dissatisfied with mileage.
I really like the taller tires for driving bumpy dirt roads, hopping curbs, etc.
RE: the RPM argument: If lower RPM=more load=worse mileage, I assume you drive in 3rd gear on the freeway for optimum mileage, right?

 

Significantly larger tires will be harder on your brakes.

Nominal sizes, actual tire size will vary slightly be manufacturer:

Tire size - revs/mile - diameter - sidewall height - speedo diff - notes

175/65 R14 - 906 revs/mile - 23.0" - 4.5" - (-2.1%) - stock GD DX/LX
185/65 R14 - 887 revs/mile - 23.5" - 4.7" - 0.1%
175/70 R14 - 880 revs/mile - 23.6" - 4.8" - 0.9%
185/70 R14 - 860 revs/mile - 24.2" - 5.1" - 3.2%

205/50 R15 - 902 revs/mile - 23.1" - 4.0" - (-1.6%)
195/55 R15 - 887 revs/mile - 23.4" - 4.2" - 0.0% - stock GD Sport - *baseline for comparison*
215/50 R15 - 887 revs/mile - 23.5" - 4.2" - 0.1%
185/60 R15 - 876 revs/mile - 23.7" - 4.4" - 1.3%
205/55 R15 - 871 revs/mile - 23.9" - 4.4" - 1.8%
175/65 R15 - 868 revs/mile - 24.0" - 4.5" - 2.2% - stock GE DX/LX
195/60 R15 - 859 revs/mile - 24.2" - 4.6" - 3.3%
215/55 R15 - 856 revs/mile - 24.3" - 4.7" - 3.7%
185/65 R15 - 850 revs/mile - 24.5" - 4.7" - 4.4% - stock 4 bolt Civic

205/45 R16 - 894 revs/mile - 23.3" - 3.6" - (-0.8%) - stock GD HFP
215/45 R16 - 881 revs/mile - 23.6" - 3.8" - 0.7%
195/50 R16 - 879 revs/mile - 23.7" - 3.8" - 1.0%
225/45 R16 - 868 revs/mile - 24.0" - 4.0" - 2.3%
185/55 R16 - 866 revs/mile - 24.0" - 4.0" - 2.4% - stock GE Sport
205/50 R16 - 864 revs/mile - 24.1" - 4.0" - 2.7%
195/55 R16 - 851 revs/mile - 24.4" - 4.2" - 4.3%
215/50 R16 - 850 revs/mile - 24.5" - 4.2" - 4.4%

225/35 R17 - 896 revs/mile - 23.2" - 3.1" - (-1.0%)
205/40 R17 - 887 revs/mile - 23.5" - 3.2" - 0.1%
215/40 R17 - 875 revs/mile - 23.8" - 3.4" - 1.4%
225/40 R17 - 864 revs/mile - 24.1" - 3.5" - 2.7%
205/45 R17 - 857 revs/mile - 24.3" - 3.6" - 3.5%
215/45 R17 - 845 revs/mile - 24.6" - 3.8" - 5.0%

215/35 R18 - 869 revs/mile - 23.9" - 3.0" - 2.1%
225/35 R18 - 860 revs/mile - 24.2" - 3.1" - 3.2%

I have no idea if all these would fit or not - I suspect the 225s might not.

For better fuel economy it's generally better to get a narrower low rolling resistance tire. I'm going to run 185/60 R15 Michelin Harmonys myself this summer.

 

re: engine load / rpm:

I think part of the confusion stems from the fact that people refer to the pedal on the right as the "gas" pedal, instead of the "accelerator" pedal. This pedal has nothing to do at all with the quantity of fuel entering the engine - it controls the quantity of air entering the engine (via the throttle body). On older cars it was just a cable hooked up to the throttle plate, on newer cars it's done electronically.

The ECU/PCM/computer/what-ever-you-want-to-call-it calculates the quantity of oxygen entering the engine with the air flow sensor, temp sensor, throttle position sensor, etc, injects what it thinks is the right amount of fuel to maintain the ideal air/fuel ratio, and checks the results with O2 sensors. You have no direct control over the quantity of fuel being injected.

The engine itself it a basically a big air pump. At higher speeds it pumps more air. At twice the speed it pumps twice as much air (assuming the intake restriction and back-pressure don't change).

So the quantity of air entering the engine depends on both the speed of the engine and how "open" the throttle body is.

With larger tires the engine spins slower so you have to open the throttle body a little more to allow more air to pass in order to maintain the same overall airflow through the engine (and therefor the same quantity of fuel is burned).

ie (simplified): Your throttle body wide open (foot to the floor - 1 atmosphere of pressure in the intake runners) and your engine running at 2000rpm will pump as much air as your throttle body half open (1/2 atmosphere pressure in intake runners) and the engine running at 4000rpm. So in an ideal world the same quantity of fuel will be burned in both cases.

But at higher engine speeds more energy is wasted accelerating the pistons up and down, and also due to increased friction. So generally a slower turning engine is more efficient.

For example on large ships (oil tankers, container ships, etc) engines typically run in the 80~90rpm range for efficiency (although another reason is due to piston speed).

But if you continually have to downshift in order to get up hills then the engine speed goes way up and you lose your efficiency again.

So generally the best gearing (for efficiency) would allow you to operate the engine at the lowest possible speed without having to downshift all the time to get up hills.

edit: Other thoughts:
- At highway speeds the vast majority of the load is due to aerodynamic drag and so changing engine speed by +/- 3% won't make much difference overall.
- Using taller tires and increasing ground clearence will also increase aerodynamic drag.

 

Any time you add rotating mass, your MPG will suffer. I have no experience on the Fit’s, but on my Tacoma, I went from a 31” tire to a 32” tire (which is a less percentage of change than the 195’s to 205’s), and I lost about 2MPG (20MPG to 18MPG). The MPG figures were calibrated for the bigger size.

My wife’s Corolla, same deal. Snow tires are 205/60/15’s and summer tires are 195/60/15’s. About 3-4MPG loss with the 205’s (maybe due to the winter gas, too, but still, it does show a loss).

IMO, stick to the stock size. The only thing that would be beneficial is to keep the stock size diameter, but go skinnier, thus reducing the rotating mass..