Any comments on how much power you loose when you go up in rim size or put on wider tires??

 

Not sure, but there's a power to weight ratio formula online somewhere.

 

From what I understand, the smaller your wheel, the faster your acceleration. It all has to do with rotational mass. So just because a 17" wheel weighs just as much as a 15" wheel, doesn't mean you're going to accelerate any faster. That 17" wheel as to be so much lighter so that it can outperform the 15" wheel.

For example, sit in a rotating chair with 10lb dumbbells in each hand. Start spinning around and extend your arms fully out and see how long you can last. Then bring them closer to your body and you will see that it's so much easier to spin.

 

Losing unsprung weight is always good. Car will accelerate faster and MPG will improve due to weight loss.

 

not just base on looks but also the weight of the rims. i agree with "super mario" between the ratational spin. also bigger rims Be very, very careful about going with a wider tread. This increases the rubber area exposed directly to the line of motion and can easily impact mileage. Also, there are some reports of wider tires extending out far enought to impact the edges of the wheel wells when going over bumps. Performance will decrease if you get bigger rims. This is because of the additional unsprung weight. Unsprung weight is the weight that the springs on a car does not dampen or control. Since the rims are on the outside of the springs, the springs do not dampen the rims. It will be slower and will not be able to corner as well. Responsiveness in the corners will improve however.

for me i would recommended 15" rims or anything 1 inch above. 15" or 16"

 

I vote 16" cos its so hard to find tires for a fit once it goes to 17" wheels - I'm one of the victims... T.T

 

Given a 15, 16, or 17" rim, are we assuming that the actual tire diameter at the point of contact with the road is exactly the same?

A. If yes, then:

1. If all three sizes have exactly the same mass, then there will be a very slight difference in power loss. The small difference lies in the rotational inertia, as Super Mario pointed out with his example of holding dumbells at varying distances from your body while spinning in a chair. More rotational inertia (resulting from more mass away from the center of the hub) will result in more power loss, while less rotational inertia with that mass closer to the center of the hub will result in less power loss. However, this rule is for a perfect disk and does not account for the myriad variations of spoke design and everything else that comes into play in a typical rim. Therefore it is safe to say that for all practical purposes if all three size rims have the same mass then there will be no discernible difference in power to the pavement (unless you start testing outrageously different rims like a 17" solid "moon" type rim with something like a 15" Volk T1, at which point these differences in rotational inertia due to rim size start to become more measurable).

2. Generally speaking, a larger diameter rim will be heavier than its smaller diameter counterpart. And as I've already explained, the heavier rim will result in more power loss. Let's say that we chose three sizes of an identical model: Let's pick the Enkei Racing RPF1, just becase it has all three sizes that we're looking at. TireRack lists the 15" at 9.5 pounds (which I highly doubt and I think is closer to 12.8), the 16" at 13.7 pounds, and the 17" at 14.6 pounds. The 15" will result in less power less due to its lower rotational mass (and lower rotational inertia as a result.

B. If no, then:

If the outer tire diameter is different for all three sizes then in addition to what I've already discussed, "final gearing" as a result of rolling tire diameter also becomes a factor. And the law here is that a smaller final tire diameter where the rubber meets the road will result in quicker acceleration and lower top speed/speedometer reading due to "lower gearing". Conversely, a larger outer tire diameter will result in slower acceleration and higher top speed (assuming the car isn't already drag-limited)/speedometer reading due to "higher gearing". In short, if you're 15" wheel is wearing a tire with a smaller rolling diameter than a 17" wheel wearing a tire with a larger rolling diameter then you will see better acceleration (and lower top speed/speedo reading) with the 15" and poorer acceleration (and higher top speed/speedo reading) with the 17". This is of course assuming that the rim/tire combinations in both the 15" and 17" sizes have exactly the same mass.

The big caveat here is that there are so many variables at play that it is difficult to clarify a hard and fast rule without stumbling over a bunch of... caveats.

You can always come up with a mismatched set of rims to compare, like a 15" rim that weighs 25 pounds versus a 17" rim that weighs 15 pounds. Given equal tire rolling diameter I'd take the 17" every time.

To make things easier, remember the following:

1. All else being equal, the lighter wheel of a given diameter and width will always win.

2. All else being equal, the smaller outer tire diameter (at the contact patch) will always yield better acceleration/lower top speed than the larger outer tire diameter.

Note: When I use the term "win" in statement A I mean: more power to the ground, better fuel economy, better handling, better braking. Higher unsprung weight is the enemy of handling, and higher rotational mass is the enemy of horsepower, braking, and fuel economy. This thread is focused on power loss so I tried to limit this power to that topic. However there are other benefits of lighter/smaller wheels that I have only touched on (braking, fuel economy, handling) which are for other discussions outside the scope of this thread.


For the record, I'm waiting on the following: A 16x7 rim that matches the 2009 Fit's factory offset and other specs and which weighs less than the stock Sport rim. I want to mount a good set of summer or all-season high performance tires to my 09 Sport MT, as this would be the easiest way to enhance the acceleration (less rotational mass), handling (less unsprung suspension mass) and braking (less rotational mass) without voiding the warranty. Not to mention a bump in fuel economy (less rotational mass), increased brake pad life (less rotational mass) and a softer ride (less unsprung suspension mass).

/all I ever wanted or needed to know about cars I learned in Physics class
//and a little bit at WyoTech

 

bigger rim= more weight, more money, and harder to stop.... 15's... 16 if u REALLLLLLLLY want...

 

15s and 16s are nice and the light options are a bit more affordable for the most part...light 17s would be nice for looks AND performance...but i myself am wary of putting 17s on my car, the roads around my area are horrible and i would for sure end up with a scuffed up, bent rim at some point. the 16s i had on my last car didn't hold up to the roads around here

 

A larger rim requires more torque (tau = F * s) to rotate than a smaller rim of equal mass.

 

and the Fit is reallllllly lacking in the torque department!

 

Some tools to help:
Tire size calculator from miata.net
Tyre Town size calculator
Tyre Calculator from alloywheels.com

Play around with the - the miata.net one is easiest/most straightforward. The others are international so you may have to play around with measurements/values.

basically I think a big thing to consider when up/down sizing tires/rims is your MPHs and how off your speedo may become as you upgrade things. I think in theory the amount of fuel you'd use to travel at say 60mph with 15" rims and 195s (like the oem 07-08 sports) would be the same as about 57mph with 16" rims and 205s (the "common" size upgrade I've seen) So you'll lose fuel efficiency, regardless of weight (unless like mentioned above the bigger wheel is SUPER light, like CF composite or something) because of rotating mass. I'm no mathematician though. Anyway, have fun with the links.

 

I have the 2008 mid-range model with the 14inch tires... If I get some 15in, do I have to get the computer reset so the abs, etc works for the larger size?

 

What about GE8s? 16s or 17s?

 

Typically it won't affect the computer - your speedo will just be off the bigger you go.
Plus the HFP optional bronze alloys are 16's and Honda doesn't reset anything... right?
And the sport model comes with 15's... And the computers are all essentially the same regardless of base, sport (US), or HX, EX, etc. in other markets... Someone please correct me if I'm wrong.

 

The physics applies to all vehicles.

 

Great now I need to buy another set of Rims...lol So good for me, bad for wife..
Thanks for the input offffff with the 17s

 

if the zero bump steer kit would fit with 14's, i'd stay with 14's... but since they only fit with 15"+ wheels, i have to get some 15"ers.

the lightest weight wheel possible is the best option. less unsprung weight.

 

I was asking which would look better. Lol!

 

you will just need to get the correct size tire. the idea is to keep the over all diamter of the wheel/tire the same. on our cars, 14" wheels have fatter side-walls than 15" wheels, but the over all diameter should be the same.