There really is a performance tradeoff between stock rims/tires and 17s
 

Wow. I recently caught a nail in one of my rear S03s (on my 17" Fikses), and upon inspection the rear tires were near the wear bars, so I decided to switch back to my stock wheels while I decided on 17" tires.

The difference was unreal! The perceived throttle response is better, initial jump on the highway is much quicker, the car feels more nimble, and tight turns (p/s deleted) are much easier. Of course, I break the tires loose in 1st and 2nd gear at about 10 psi, so there is a definite traction tradeoff.

Here are the specs on the 2 setups:

16x8 stock wheels with new 245/45 Yoko AVS Intermediates
17x8.5 and 17x10 Fikse FM5s wrapped in 245/40 and 265/40 S03s

Now, the Fikses are billed as lightweight rims, and for the price they sure as hell had better be. The S03s have always seemed very heavy to me, which may account for much of the difference. Rotating weight makes more of a difference than I would have imagined, and heavy ass tires spinning out the outside (away from the center) must exacerbate the problem.

I performed a very unscientific measurement and used a bathroom scale to determine some weights. A rear Fikse and S03 weighed in at 45 pounds. Tire rack lists the S03 at 29 pounds, so by this reasoning the Fikse weighs 16 pounds. I plan on weighing the rim seperately once the tires are off and I'll bet the results will be a few pounds off from that. Tire rack lists BFG KDs in 275/40/17 also at 29 pounds, but I weighed one (my replacement tires that just showed up) and it comes in at only 25 pounds, so go figure.

At any rate, thought you guys would find this interesting. The Fikses sure as hell look a lot better, but I am thinking about leaving them off and ripping around on the stockers for a while now, lol. At the very least for performance driving I plan on swapping the stockers back on :).

great post

problem is, the stockers look like ass; I hate the miata look....I like my 18" five spoke Ro-jas with lowering springs and S-03s, and I'm willing to sacrifice some "nimbleness" to enjoy the sight of the car parked and not cringe :)

Edit: Any rotational inertia toward the outside has a huge influence on acceleration.

The Fikse rims are fairly lightweight, but I doubt they're the lightest for their size. Their real advantage is their precision manufacture and their overall strength.

btw Rich, you forgot to include the weight of the stock rim and Yoko tire, using your carefully calibrated bathroom scale ;)

the smaller sidwalls of the 17" won't help the handling feel of the car ? also aren't larger contact patches always better ?

in terms of outright traction, yes....acceleration and agility? no

you can't have everything

They are on the car right now, silly goose :D

My dad has a spare pair of stock rims with those same tires, so I will get that measurement as well :)

um, how long does it take to pop one wheel off and put it on a scale? :p:

I weighed a FM-5 in 17x10 size at the post office. IIRC it weighed just over 20lbs. This was a new, never mounted wheel, no packaging, just the wheel.

I noticed a huge difference in acceleration with the stock wheels with race tires vs. my Fikses. The weight isn't the only difference, the diameter of the 275/40/17 is roughly 1" larger.

So with the added diameter and weight you can feel it.

The 4.33 gears put it back to about the same acceleration as the stock wheels tires. Of course putting the stockers back on still gives better acceleration:).

About as long as it takes me to make a Hot Pocket and sit down for the beginning of Family Guy.

Rich, just give me your fikse's, thanks.

:)

I doubt that it's the rotational inertia that your feeling. The rotational inertia of your four wheels is tiny compared to the inertia of your car. For example... let's approximate how much energy is stored in the inertias at 80mph:

- Wheel speed (w): 1050 rpm = 110 rad/sec
- Wheel inertia (I): 2 kg m^2 (this is an overestimate... 1.5 is more like it. But, to prove a point, let's use 2)
- Car speed (V): 80 mph = 36 m/s
- Car inertia (m): 2800 lb = 1270 kg

- Wheel energy (of all 4): 4*1/2*I*w^2 = 48,000 J
- Car energy: 1/2*m*V^2 = 823,000 J

Now, if you decreased that wheel inertia by, say, 25% (which is a LOT!), that represents a total change of 12/(48+823) = 1.3%. That's the same as removing about 35 lb from the car. If you're butt dyno notices the difference, then you should sell your butt to science - it's pretty good! :-)

EDIT: Ahh... I see... your DIAMETER changed. That will change your gearing and, therefore, your acceleration. That makes much more sense... the wheel inertia thing is insignificant. The purpose of light wheels is to reduce unsprung weight and therefore increase handling, not to make you accelerate faster.

Take care,
Shad

Shad,

I also run 17's (some heavy *ss 5zigen Typhoons) on the street and 16's on the track (for now). I notice very little if any difference between the rims (as far as acceleration). I'm running RCompound on the 16's so I notice a lot more grip. ;)

"the car feels more nimble, and tight turns (p/s deleted) are much easier:

The AVS has 9.4" thread on is on all four wheels, a balanced setup.
The S03s have 9" thread in front with 9.7" rear which will understeer more.

Can't compare apples to oranges as they say!

hmmm

when i upgraded my wheels to wider than stock on 17" wheel hop dramatically was reduced and the car turn much more stable. of course the turn in on stock wheels was easier, but i wouldnt say handled better, but thats probably due to the model of tire.

I think that both the diameter increase (275/40 17) and the heavy S-03s contributed to the straightline feeling. You are definitely changing your gearing when running 275/40s....and the S-03s are one of the heaviest tires made. Toyo T1-R or Pirellis (or Yokos) are lighter, but have softer sidewalls.

Everything is a trade-off.

But yes, the car will not feel as nimble with bigger wheels and tires. If I didn't track the car, and especially if I didn't have those huge-ass Stoptech front brakes going on, I would stick with the stockers any day for daily driving. They are more fun in street-type driving. Not as much grip on the track and too much oversteer. See, trade offs. :)

exactly. go take one of yours off if you're that impatient :D

Sounds good to me Johno. Come up and get 'em :bigthumb:

Correct. Why are you posting the obvious?

Pretty much hit the nail on the head. When I do back to the Fikses, I hope like hell that removing the S03s and installing the lighter BFG KD's make a measurable impact. Of course, driving in the rain will be compromised. There go those tradeoffs again ;)

Let's face it, most people go to bigger rims and tires for the looks, and they rationalize it as being a performance upgrade.
When you read how the FD was designed you learn that Mazda went to a lot of trouble, including competition among tire manufacturers, to come up with a wheel and tire combo that weighed no more than 38.5 lbs at each wheel.

IMO

SO3s are not that heavy. Probably lighter than the new tires. The Fikses don't weigh 16lbs.

You'll be faster at an autox or on the track with more rubber. If you're driving at the limit that is.

However: I drive around on the street without much rubber so I can have fun at slower speeds hehehe :)