I felt this might serve a few here as well. In a nutshell I was asking if anyone had suffered through 18" 35 aspect tires (an option I am entertaining to help wagon issues with rear fender rub). Also, because I am in a NA Wagon, rotating mass is important to me as well (that's the two factors that are pointing me to 18" but with a 35 aspect ratio).

I was on Nabisco and got at least 3-4 of these canned replies as the following. Hence my further research to hush them up. See Below:


>>> Originally Posted by subieworx
If you are really so concerned with unsprung weight why are you getting 18's regardless of the weight when you would be much better with 17's, 16's, or 15's? <<<


I was actually quite reserved in my comments back to you on the 1st reply, until I could PROVE that my time on this planet has not left me an idiot.

Your argument is old and tired and tends to continue to be mouthed by a whole generation of people who type before thiinking.

Sit down boss and I'l tell you a tale:

I just finished a 2 hour search for tire sizes and weights to show you that an 18" wheel does NOT mean it has to be heavier then the 17" counterpart.

These are the rim sizes and their weights, as well as the weight of the lightest tire I could find in each size. I probably went through 25-30 tires for each size to find the lightest available @ the moment.

#1) As suspected:
18"x7.5 Rota Subzeros @ 18.2 lbs.
Hankook Z212 Tire 215x35x18 @ 18.5 lbs
TOTAL WEIGHT ~ 36.7 Lbs Per Corner

#2) 2nd 18" Option:
18"x7.5 Rota Subzeros @ 18.2 lbs.
Dunlop 901's 215x40x18 @ 20.1 lbs
TOTAL WEIGHT ~ 38.3 Lbs Per Corner

#3) The 17" Option:
17"x7.5 Roat Subzeros @ 17.3 Lbs.
Dunlop 901's @ 21.4 Lbs.
Total Weight ~ 38.7 Lbs Per Corner

My point, don't be fooled by "the obvious" think outside the box and for yourself ~ better to be a leader then a follower.

The 17" option is the cheapest tire @ $82 compared to the 18" option @ $114. My 18" rims are costing $615 Shipped vs. the 17" rims costing $575.

Price was not my point, nor my question, if it was, I would go 17's.

My question is, does anybody ride on 18" 35's and is it miserable??? If so, then I would be wise to go to 18x40's. Still lighter at each corner (with tires) then the 17" Rotas or the OEM 16's"

The higher the sidewall (35,40,45,55) the heavier the tire. Very simple...

So, the guy who asked about 19's on the STI just might save rotating mass on each corner by going +2 as well ~ but with 300HP who cares anyway!

 

I have ridden in cars (not a WRX) with 18's and 35 series tires. It was miserable on that. Obviously with wrx (not wrx in your case :-P) but still, YMMV.
I am considering 18"s with 40 series, but is that too large of a series, is that a larger aspect ratio? I know the idea is to keep roughly the same ratio....

 

18's with 40 series on a WRX is a no brainer, I don't think it would look correct any other way

 

I tend to agree with you. The only reason the 35's come into question is for clearence issues for the wagon. BUT, the 215x40x18 is still a 'tad' smaller diameter then the 215x45x17's, so that might be all I need to clear the rears with the Swifts dropping the car and a bit of - camber in back to help me out!

Thanks above for the 35 comment too. I was a bit afraid of that. But, I have a co-worker (another salesman at the Subie dealer) who is running 18x35's on his '03 Rex and says "it's fine" and he has not bent a rim since he has had them on 30,000+ miles...

Since the 17"x45's and the 18"x40's are nearly the same weight, I will probably go in this direction... I'm too old to get beat up by my cars anymore!

Thanks for the input gentlemen :-)

 

I have 225 40 18 on my 04 and it's not bad. I'm riding on prodrives too. 35 seems to small for me but what do I know. Have fun with your new rims and tires.

 

215/35/18 has too low of a profile and will cause you to bend your rim if youre a little low on air. I used to work at a wheel shop and people with 215/35/18's would come in all the time to order a new wheel because theirs got bent going over a pot hole. My younger brother has 215/35/18's on his prelude and he already has a bent rim. Get 215/40 or even 45 if you dont want a bent rim.

 

Thanks. I have decidied to go 215x40x18. Too many problems (ride, bent rims, etc) to bother with the lighter weight of the 35 rubber! Now, just waiting for Mr IRS to send me my check!

 

I still haven't decided for sure.....17.....18.....sigh.


I am leaning heavily towards 18, but I just don't want to have suck ride quality. And...I also drive a bit on the freeways down here, which sorta suck....plus when I am at home.....
have you ever hit a cattle guard doing 85?

 

i roll on 215/40 r18 koing toxxin rims. its fine and looks the best on the wrx in my opinion. 35 or less is for big wheels that go on trucks

 

I appreciate your time looking up those weights, but your reasoning fails to incorrperate a VERY important aspect of wheel weights. The issue is NOT total weight...it is WHERE the weight is. The inertia of a spinning point on a wheel goes up as the square of its distance from the center of the wheel. So if you have a wheel that weighs 4units and all that 4 units is 1 inch from the center, it will be the same as a wheel that is 2units in weight but 2 inches from the center. And since the bulk of a car wheels weight is carried away from the center, going from 17inch to 18 inch, even when losing ~pound, will still increase your rotational inertia and therefore cause worse performance overall.

 

Yes, thanks for the lesson. But, since rims don't come weighed in units ~ it's sounds a bit more like undergraduate studies then real world issues.

The point I am making, is if you go with a rim that is lighter than a riim you are currenty using of a smaller size it will be CLOSE to an 'equal penalty' for unsprung weight between the two. Your truly splitting hairs here!

I raced for almost 20 years and believe me, the trade off in less sidewall flex, larger contact patch and steering input and braking, MORE then make up for a slight weight penalty to +1 or +2 fitment. I never felt at a disadvantage on a track running as much tire as I could...

The worst place, as you said is at the outside of that rotating mass and that is why the TIRE weight is MORE important then the rim weight. Not only can I loose weight from the current rims I run... but with proper shopping and investigation the tires I will use are also close to 4 pounds lighter then stock. So, combine BOTH factors (rims and tires) and the only place I would ever feel the intial moment of inertia penalty would be on a drag strip. I have been there as a spectator only.

For daily runnning and fast canyon work... I bet I can hang with the best that are riding on 16's OR 17's while I make the most of my 'disadvantage' of the proper choice of rim and tire on 18" rims. Go figure.

Cheers!

 

The same applies to a greater extent to heavy tires for the reasons stated above. I am going to run 17x7.5 or 8 on my STi for a lot of the same reasons... rotational mass affects many areas of performance: most notably acceleration and braking, but also MPG. In my research I came across an interesting rough calculation from one of the guys at the Tire Rack for equating rotating mass to physical gross weight. Rotating mass lost x 4 wheels x 10... for instance: my stock '05 BBS weigh about 19.25 lbs., my standard Bridgestones weigh 25 lbs. for a total of 44.25 lbs. A set of SSR's in a 17x7.5 weigh only 13 lbs. and a set of 225/45/17 Kumho's weigh 23 lbs. for a savings of 8.25 lbs./wheel x 4 x 10 = 330 lbs.! That's about 3 tenths in the quarter, not to mention the improved braking! It's a rough formula, but very interesting. I don't feel like carrying Kirstie Alley all over the place wasting my gas and slowing me down.

 

Well put. It's the combined weight savings of the entire unit (wheel and tire) that most people overlook! The pay a gazzilion dollars for lightweight rims and then hang 25lb tires of them in the absolute worse place ther can be for rotational mass. The point? Combnine your choices and look at the weight for EACH corner ~ get each corner as light as you can and use the formula above. As you can see, you will rock, no matter the size of the rim (to a point, yes! No Dubs included.).

 

Yeah the tire weight is definatly important. And I didn't take into account the added benefits of tire side wall stifness and grip and such...but it isn't about unsprung weight (seperate issue that only counts total weight), it's about rotating mass. You have the race experience though, so I'll take your word for it. That formula is cool, it's rough but should work for everyone except the twice a week and more track racers.

 

It definitely caught my interest. Once I find a home for my stock low mileage '05 STi rims and tires, I plan on putting the formula to the test. I'm going to dyno the car again... same dyno, same setup... and see if any power to the wheels is gained. It appears that the biggest gain to be found as far as relative weight loss is concerned could be in a place not many people think about. I'll post with my results, but it could be a while. The '05 STi wheels are 5x114 and only work on '05/'06 STi's... kind of a bummer.