I-luv-Doritos

Yup it's another indecisive thread about 17" vs 18" wheels.
What am I looking for? The best performance wheel and tire set up for the track. Ideally I'd like to apply this thread to those with experience between BOTH diameters. I'd like an educated opinion for your recommendation for me and other drivers with similar applications. So share your tire, wheel, and suspension modifications. And explain why you decided to use these parts and what results over the other.
A little about me and my car. Since I bought my RX8 summer of 2013 I've managed to put about 4000 miles on my remanufactured motor. I currently have installed; Mugan rear chamber arms, Koni Yellow shocks, Mazdaspeed Springs, Hotchkis sway bars (F33,R21mm), Racing Beat end links and an upgraded underbody brace I suppose you could call a 12pt. I have some cheap 17x8 +42 MB wheels wrapped with some cheap 225/50 all seasons. I have a Honda Fit I daily so my RX8 is strictly for spirited driving ONLY. I am happy with how my suspension performs but there is always room for improvement. That being said i decided on some enkei wheels and Micheline PSS tires. I want the offset to stay as close to OEM for the best geometry results.
So let's get started,

RPF1 17x9+45 15.65 pounds
245/40R17 tire 23 pounds total weight of 38.65 or 255/40R17 about 2 pounds heavier
VS
PF01 18x9+45 19.20 pounds
255/35R18 tire 25 pounds total weight of 44.20

Difference between 17" and 18" wheels with PSS tires is approximately 5.55 pounds

paimon.soror

iTrader: (15)

17's will cost you less in the long run when it comes to tire prices. 17s also provide you a wider range of tire widths and compounds for the track.

Also, you mention that you want the offset to stay as close to oem for the best geometry, but you already changed several suspension related components .... sounds counter intuitive

I-luv-Doritos

Hey thanks! Yes they are significantly cheaper and that can be a huge factor in making this decision easier. Unfortunately Michelin does not make the PSS in 255/35 or 255/40 for a 17" wheel. Sucks because I've always enjoyed the stiffness and longevity of that tire. The 18s seem to have a larger market in tires. Anyway the Mazdaspeed springs have lowered the car less than an inch. The majority of the suspension arms are factory and I am able to achieve factory recommended alignments. What components I have changed are really not that major. I had Tunabe springs prior and realized they messed with rear chamber. So that's why I had to change those out and I purchased some used chamber arms in case I run into that issue in the future.
I still don't know if 17" wheels will handle better than 18" wheels.

paimon.soror

iTrader: (15)

A 245/45 17" would put you closer to OEM sizing (assuming your oem are 225/45 18"). Neither 255/35 or 255/40 are anywhere close to OEM total diameter on a 17"

Also, consider the 5 lb savings is EACH wheel. And that becomes quite significant when it is factored that it is a savings in unsprung weight.

But I guess I should ask, when you say "handle better", what exactly do you mean? There are so many factors in handling besides wheel diameter. Actually ... wheel diameter is almost a non factor in respect to handling.

I-luv-Doritos

On a 17" wheel the lowest side wall ratio for a 255 tire is 40. 255/40R17 is 636mm tall.
On a 18" wheel the lowest side wall ratio for a 255 tire is 35. 255/35R18 is 635mm tall.
From the top of the tire to the bottom is equivalent! In fact that's 1mm off.
Custom rims, wheel tire packages for your ride - RIMSnTIRES.com
This website allows you to compare wheel/tire sizes. It proves to me there is no hight difference between the two and they both allow the same amount of contact. So what is the difference here? How could one benefit from one size over the other?

J8635621

iTrader: (10)

255/35/18 is not stock sized. 255/40/18 is close to stock diameter.

Paimon is saying that 255/35/17 and 255/40/17 are no where near stock diameter (they aren't) since you are discussing 17" wheels.

I-luv-Doritos

But yes 5.55 lbs is a huge difference in unsprung weight. But so far that is the only clear difference. I am simply interested in the best performance wheel and tire set up. Now I can try and break that down if we want to be very specific. While driving in the canyons and on the track I want there to be a smooth and direct response on straight aways and while cornering. I know there is a lot of factors that could alter the way the car handles. But all of that can be changed in increments while aligning the car and adjust my sway bars.

How does unsprung weight benefit effect things?

I-luv-Doritos

Maybe I haven't made my self clear enough. I am not trying to achieve the stock wheel diameter. I do want to increase the width about 1" so I can have a wider tire contact. Although i do not want to slow my self down by applying too much contact. Ideally 255 is the widest tire I will apply. That being said. 255/40R17 is not different than 255/35R18. They are 1mm apart in hight even with different wheel diameter.

I-luv-Doritos

Where is everyone at?
Who has experience with 17s and 18s on the track? What is your preferred wheel and tires?

J8635621

iTrader: (10)

Sticky 245/40/17 and 17x9 enkei of your choice with +4X offset

/The end

I-luv-Doritos

Anyone else?

Loki

iTrader: (1)

Pretty much what he said. There is no 'best' setup but the above is a very good starting point. It's like asking 'what is best steak'? Most people will probably prefer filet mignon to many other things, but then you get into the aging, preparation and personal tastes. Filet mignon is a really good place to start, but maybe you'll find you want less sidewall flex or more bump tolerance. It's endless.

Btw I track 235/45/17 and was happy for a while but need more contact so will go 245 next.

Btw there are multiple ways to achieve what you're describing through alignment, suspension tuning or even just tire pressure.
I'd say go with 17s and tune for the tire. By the time you're done, you won't need a forum thread to know what changes to make.

I-luv-Doritos

Wow!
235/45? What ratio will you be going with on the 245 tire?

I-luv-Doritos

Does anyone want to discuss what suspension mods they have and wheel/tire set up?

J8635621

iTrader: (10)

There is a whole forum of that. Suffice it to say that the people who have been trying to help you have spent a good bit of time and money on this stuff for their own car. The advice is sound.

I-luv-Doritos

Of course there is. There is practically a thread for every topic in the forums by now. All I ask is for people share there opinion. Drop a comment for the sake discussion. After all this is a forum.