Better to go wider or lighter?
 

Nearly narrowed down my decision on wheel choice but want to ask a question regarding wider vs lighter.

I am looking at the Kosei K4R in both 17x7 and 17x8.

17x7 = 14lbs
17x8 = 15.8lb

With this info, is it better to get lose an inch in width to lose another 1.8lbs per wheel? What other factors should I take into consideration?

I know I need to consider tyre selection, but not very knowledgeable in this area :(

I will be mostly street with occasional track day use when I get my car

Any help much appreciated :thanks:

More width = more tire = more contact patch; basically. Though nearly 8lbs of rotational mass is nothing to be scoffed at. The thing to remember is that both wheels weigh less than stock, so going wider for some extra rubber or aesthetic isn't wrong.

While I would personally go with the 17x8, it really comes down to a personal choice, as I have no real world experience between a 17x7 compared to a 17x8 on a BRZ. However I figure with a sub 2lb weight difference, you may be able to make that up with the brand and model of tire you select. Tirerack.com has great info on all of their tires including weight and diameter etc.. Hope this helps. :)
Thanks,
Rick

Not too stressed on aesthetics to tell the truth. Not too impressed with the look of the RPF1's, though I do love Enkei's ;)

The K4R wheels are quite reasonably priced, which is also a big tick in their favour. Shipping to Australia is going to be killer, but still going to be cheaper than buying local :S

7.2lbs of rotating mass is quite a lot in the scheme of things relative to the 17x8's, but the 24.4lbs saved over stock is incredible!

Given that I will fit a 215/45 to the 17x7 wheels and a 225/45 to the 17x8, that equates to about 1lb on top of the extra weight per wheel at 17x8. (This is based on Michelin PSS which I have researched to be the best option)

That would make the combo (2.8lb x 4) 11.2lb on the whole vehicle.

so I suppose is 11.2lb of unsprung weight better than a little extra (0.5") tread on each wheel? Tough call....

In the Miata world, wider was better at the expense of weight. That's why 949 Racing sells 15"x9" and 15"x10" inch wheels for Miatas.

Not really, though. Contact patch is determined by the weight of the car and the tire pressure.

The dimensional analysis works like this weight/pessure is lbs/ (lbs/inch^2) = inch^2 which is your contact patch.

A wider tire (at the same PSI and vehicle weight) simply makes the contact patch wider at the expense of length. The area stays the same.

Of course there are other factors in play, as real life is not as simple as basic physics. Tire construction and rubber compound play a role in contact patch as well.

That being said, wider wheels/tires do have a positive affect on lateral grip and lap time, but it's not because the contact patch area is increased.



I know you said 'basically', but I just wanted to be more clear.

wider tires will change the shape of the contact patch but the overall surface area is about the same.

anyway, prioritize width for form, or lightweight for function.

Nice work mate. Contact patch does not increase, just changes width/length. A wider contact patch is more beneficial, but only if it does not push weight up too high.

Now looking at Motegi Racing 17x7.5 at 16.2lbs as I like the look of them better. Glad I am not buying them now otherwise I would be fretting over it even more! Lol

Like I said before, 9" wide wheels on the Miatas are faster than 8" wide wheels during HPDE on real tracks. Increasing width for 'form' only and not 'function' is simply not true.

It is possble to put sticky 225/45-17" tires on 17x7" according to Tirerack. That will probably the faster combination of the two on a track where acceleration is important. It is always a compromize. If lap times is your only goal, you should find light 16" wheels that fit over the brakes you need and go with R compound tires.

I'm after a compromise setup as most of my use is street and some 'weekend warrior' track work. I can't afford to have a track set and a street set for a while either :(

Lots of time to mull it over in any event ;)

Wider over weight. Within reason of course. But with the differences you're seeing in weight, I'd get the extra tire width.

Wheel weight is not as big of a factor as tire weight is. You won't likely find any real difference between the two sets of wheels. If you want to keep your weights low and are willing to sacrifice a bit of responsiveness, get Hankook R-S3 tires. They tend to be 1-2lbs lighter than other tires in its class.

I'm in the same boat. I have my FRS which is my DD but I'm interested to try some auto-x and hpde. I've been pondering the exact same wheels.

One question I have on the Kosei 17x8: the offset is 36mm, is that not enough? Any problems with that? Extra stress on bearings? Stick out too far, past fenders?

Any AutoX? Can stay stock class with 17x7, not with 17x8.