17 Inch Wheels

[Deanh]

Originally Posted by BRGT350

Jon is 100% correct when it comes to the 17" wheels. If you want to increase performance, responsiveness, braking, and handling, you will want a small diameter wheel and tire combo. The rotational mass of the 17" wheel slows the car down in acceleration, harder to stop due the increased intertia, harder to turn due to the PMOI, and the larger diameter effects the gearing. While I love the look of 17" wheels, they do nothing for performance. If you look at the best autocrossers and racers, they run the smallest wheel/tire that will clear the brakes. Since I am not looking for the ultimate fast lap, I will keep my 17" wheels.

question...isnt everything you have noted tied to rotational mass?...in which case there are some extremely light 17 inch wheels tipping the scales at 16-17lbs...how does that weight compare with some of the stock 15-16 inches. As for diameter..all one has to do is the classic 1 plus 1 upgrade and diameters pretty much remain the same.

[Ataru]

Originally Posted by Deanh

question...isnt everything you have noted tied to rotational mass?...in which case there are some extremely light 17 inch wheels tipping the scales at 16-17lbs...how does that weight compare with some of the stock 15-16 inches. As for diameter..all one has to do is the classic 1 plus 1 upgrade and diameters pretty much remain the same.

I went with a 16" from a 17" on my SVTF to save on rotational mass. I dropped about 10 pounds of weight per wheel going with the smaller setup and also got a smaller diameter setup to help with the gearing. Now this is my autocross setup and it makes a WORLD of difference in how the car responds to throttle and steering inputs. It would be great on the street as well, but honestly, I like the look of 17" wheels on my Focus more.

As for the rotational mass, consider this.

A 195/50/16 General Exclaim UHP weighs in at 17 lbs.
A 205/40/17 General Exclaim UHP weighs in at 18 lbs.

Same overall diameter between those two wheels (23.7" vs 23.8"), but the 17" tire is actually heavier even though there is less "rubber" there. Why? My assumption would be more steel cords in the tire to support the weight since there is less sidewall.

Also, even if the weight was the same, it would mean more weight would be towards the outer diameter on the 17" instead of spread over a larger area (towards the center) on the 16" since the sidewall is smaller on the 17" tire. More weight towards the outside = bad.

[JonsZX2SR]

Originally Posted by Deanh

question...isnt everything you have noted tied to rotational mass?...in which case there are some extremely light 17 inch wheels tipping the scales at 16-17lbs...how does that weight compare with some of the stock 15-16 inches. As for diameter..all one has to do is the classic 1 plus 1 upgrade and diameters pretty much remain the same.

It's a little bit more complex than that. It isn't mass, but rotational inertia (mass times radius of rotation) that you need to minimize. A 5 kg ring of steel that is 25 mm thick with a 391 mm (15") mean diameter has 1.5 times the rotational inertia of a 5 kg ring 25 mm thick with a 254 mm (10") mean diameter. (If anyone wonders how that weigh thesame the smaller ring is about 1.5 times the width of the larger ring.)

Since much of the mass is in the outer ring of the wheel the 17" wheel will have to be lighter to match the rotational inertia. One thing that makes differences smaller with a steel reinforced tire is the steel belts contribute to the roattaional inertia. If the tires have the same outer diameter and construction, the contribution from the steel belts is about the same.

however, the optimum compliance of the sidewall to keep the tread on uneven pavement is the more important factor, with tread patter and compound being equal. Although the following articles do not address tire size or profile directly they do give a good background for the physics of tires and handling on a racecar...

The Physics of Racing: Part 1
The Physics of Racing: Part 2
The Physics of Racing: Part 3
The Physics of Racing: Part 4
The Physics of Racing: Part 5
The Physics of Racing: Part 6
The Physics of Racing: Part 7
The Physics of Racing: Part 8
The Physics of Racing: Part 9
The Physics of Racing: Part 10
The Physics of Racing: Part 11
The Physics of Racing: Part 12

[Rubicon_TJ]

While 17" wheels do add to rotational mass by moving weight/mass away from the hub, a one plus one setup doesn't have to weigh more. Even with the limited amount of research I have done so far I have easily found 17 inch tire/wheel combos that weigh the same or less than the stock 15 inch wheel and tire.

Also, the fact that the factory offers 17" wheels at all does show that the combination isn't too detrimental to performance - otherwise it wouldn't be available.

[Casca]

Got my new rims from Tirerack, thanks alot to Mac for helping me complete the order and getting the right hub rings on em as these were not listed as fitting Fiesta's. Not too crazy about having two different bolt patterns, but am sure it's not as noticable after mounting. My first set of rims I got for the Fiesta, right when I saw it in person....didn't like em. These ones, I think the pic doesn't do it justice. Like even more now that I have seen em in person and am sure it'll look great on the Fiesta. Still trying to decide if I paint it though.





Have an industrial oven at work and a powder coating gun and was planning to either powder coat it matte black or maybe do a reflective chrome base with a black tinted clear over that......pretty much like this rim...AKA black chrome / hyper black / hyper silver / hyper dark. In good lighting, looks like that pic, since the reflective chrome will shine through. In poor lighting, looks black or really dark...because you'll mostly only see the black tinted clear.



But I also like the coat/paint scheme thats already on the rim. Thought it was going to be glossy on the machined part, but it's pretty much a matte clear over everything. Or maybe I make it easy and just tape off all the gray paint and spray matte black over the machined parts with my my hvlp spray gun. Not as tough as powder coating, but a simple matter to seemlessly fix problems later.


Anyone able to photoshop the rims on this car flat black?

[D1JL]

I just ordered my 17”s from Ford Racing. I should have them on the car in two weeks.


Dave

[Fiesta33460]

Originally Posted by D1JL

I just ordered my 17”s from Ford Racing. I should have them on the car in two weeks.


Dave

Which 17's did you order?

[timo]

Originally Posted by Rubicon_TJ

While 17" wheels do add to rotational mass by moving weight/mass away from the hub, a one plus one setup doesn't have to weigh more. Even with the limited amount of research I have done so far I have easily found 17 inch tire/wheel combos that weigh the same or less than the stock 15 inch wheel and tire.

Also, the fact that the factory offers 17" wheels at all does show that the combination isn't too detrimental to performance - otherwise it wouldn't be available.

Yes but a 15" combo developed with the same criteria as the 17" combo which is lighter than stock will be lighter still.

A lot of content offered by the factory is detrimental to performance.

[Rubicon_TJ]

Originally Posted by timo

A lot of content offered by the factory is detrimental to performance.

True enough - still, I am convinced that any significant problem stemming from moderate wheel upsizing is more urban legend than fact. I was just saying that even the perceived negative effects of larger wheels can easily be handled with thoughtful planning, (ie. buying light wheels vs. heavy wheels).

I recently read a comparison test that showed moderately larger wheels had only a negligible effect on acceleration and MPG, while actually improving braking and skidpad performance.

Check here to see:
Effects of Upsized Wheels and Tires Tested - Tech Dept. - Auto Reviews - Car and Driver

[D1JL]

I am getting the M-1007-FA


Ford Racing Performance Parts - [Part Details]