7.5 vs 8 6UL's
 

Ok, so heres what i'm thinking....is there any real advantage from going to a 15x8 wheel? It seems the 15x7.5 are a bit lighter (by about a pound and a half according to 949 racing) I don't plan on running anything wider than a 225, and if i want to put on a bigbrake kit, i can just get some 5mm spacers..... what are your thoughts/experiences?

What are your goals? How are you using the car? Street/AutoX/HPDE? Why do you want bigger brakes?

You are not going to score many points around here talking about mounting a 225 tire on a 7.5" rim. I can't think of any situation where this would be at all beneficial, unless you are trying to stay within some rim size restriction for autocross classing, but then you wouldn't be able to run bigger brakes, and they wouldn't be doing much for you at that point anyway.

To be honest, i don't plan on tracking the car too often. They would be going on my DD (my 99), and i don't want to get into fender rolling, or cutting out fender wells (i know, i don't need to do that with an 8" rim either, though i know some 225's are a close fit) as i will eventually be selling the DD to fund my project. I plan on just running a 205 series tire for the street, but want to have the option of putting on a 225. In the future, these will be transfered to a project i am building (i have an 01 that i will soon be striping down for parts to build an Exocet, hence why i may want bigger brakes at some point). I guess i'm just wondering if a half inch really makes that much of a difference?!?

The only reason you would want a 7.5" wheel is specifically for SCCA STS2 autocross. In every other situation, on every other car, the 8" wheel is superior.

The 8's fit the 99 without any drama:

https://www.miataturbo.net/attachmen...ine=1381801223

I'm going to try a 15x8 +25 wheel for the Exocet though. I think it's going to need lower offset to run without spacers. Cool to see so many other Exocet builds starting. Mine is also an 01. I am not going to use the sport brakes on the Exo -- it won't need them and there's no reason to carry all of that unsprung mass. Probably going to backdate to 1.6 calipers and rotors and save a lot of unsprung mass. Most everyone I know with Locost builds have gone down to 1.6 brakes (unless they aftermarket BBK).

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Ben, thanks for the insight as to the difference in offset that may be needed for the exocet. I guess my idea of just using the wheels for a little while on my DD, then transferring them to the project. I guess i'll be pricing out some 15x8s when the time comes. As far as big brakes, i'm really only thinking that would be a long term idea for the weight savings (though, as you explain it, it may be completely un necessary!)

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If we are talking strictly street tires, I can tell you from personal experience that under stock power on an NB, I was running 205 sDrives on 8's and it was win for a DD combo. A 7.5 with probably work fine, but on an 8 it just felt great plus it will give you more fitment options going forward.

My goal was to run 225s so I sold my 205s, bought a set of 225 RS3s and put them on my 8s. I honestly didn't like them so I said "screwit!" and bought a set of 9s as I knew I wanted to run 225s going forward. I've come to understand the RS3 has a softer sidewall and really does well with the wider 9, but at the time the RS3 was the only real option. The new BFG Rival in 225 is supposed to have a much stiffer sidewall than the RS3 so you may have a better experience with a 225 Rival on an 8.

Right now I'm running 195 sDrives on factory 15x6s and it's aaaaaall kinds of MEH. I really really miss the 205 & 15x8 combo and I'll go back to it once I run out these 195s.

Would you expound on this? I've read about how 205 on 8s is groovy, but I don't think I've ever come across a direct comparison to the stock 195 on 6s, especially on DD UHP rubber. What are the differences on the street? Disadvantages, if any? Specifically, I'm curious about hydroplaning and tramlining.

I'm on 195 BFG Comp2, and it feels very nice compared to the aged 195 S-Drives it replaced, but I've never driven on a wider wheel. Can you describe a rainbow to a blind man?

There's been many an argument in the UK about optional wheel and rubber sizes. General consensus seems to be that you can take advantage of wider wheels and rubber if you have the power to deal with the added grip/friction.

Having said that - you can have softer stickier rubber on 7" wheels that have more grip than harder compounds on 9" wheels.

I run 195 Federals on 7" rims (Kosei or OZ Ultraleggera) and I've out gunned Miatas/MX5's through corners when they're on 9" rims and 225 R888's.

Put it down to luck/skill/car set up/suspension or whatever but it goes to show that you don't need wider wheels and tires to be quick.

Stance and looks are a different thing......

225s on 8s work nicely. And as indicated you really don't need to make any adjustments to the car to fit them.

Everything else being equal, wider tires/wheels generate more grip. Full stop. If you out run a Miata on 225/45 R comps on 9's with your 195 street tires on 7's, the other guy isn't getting everything out of his car. Simple.

They also generate more drag, much like a wing generates grip and drag. It is up to the individual to sort of what the correct ratio of extra grip/drag meets their needs.

We find that at autocross speeds <100kph, the wider the better regardless of power. At racetrack speeds 80-200kph in a <155whp normally aspirated car, 205's on 8's work well. 225/45's on 9's will usually result in lower lap times, particularly if there are no long high speed turns or super long straights. Probably only 5-10% of the tracks in the US will be faster on 205's rather than 225's on a typical 145whp, 2300# Miata. "rovals" high speed ovals with infield road course sections or old style road courses with massive 3/4 mile straights like Road America might be best on 205's

Above about 170whp, 225's on 9's are faster on pretty much any track. Go above about 250whp and 245's on 10's become the fastest combo. On tight tracks with power over 300whp, 275's are faster yet.

The x factor is how much fun either combination is. For many, it's simply more fun to do HPDE (open track days) on the combo that is the easiest to drive and has the most grip. That's invariably 225's on 9's.

I feel like I'm in the minority here. I'm running 225/9 for AX and 205/8 for HPDE shenanigans. Everyone gives me crap about not running the 225/9 combo for track days, but the 205/8 combo is just faster and more fun for me. I'm "<155whp" and this is phone app and "friend with watch" timing, not a transponder so not exactly scientific. 225 are RS3 and 205 are NT-01, so it may not be a fair comparison :giggle:

Well, I wouldn't really consider the S-Drive a UHP tire for starters ;) It makes for a good DD tire but it does not really excell anywhere in particular. All things being equal, in my opinion based on my experience using the same brand/model tires (Yokohama S-Drive) the 195 on a 6 SUCKS compared to a 205 on an 8. The 205/8 combination is just superior in every way. The 205/8 feels locked in and ready to rock whereas the 195/6 comparatively feels vague. Turn in is better, ultimate grip is better, response is better, hell I feel more confident throwing the car into a corner on the 205 than I do on the 195 and not just because of grip (this would be the rainbow you were talking about.) I personally believe its a function of the support of the sidewall. The 8 inch wide rim seems to do a much better job supporting the 205 than the 6 does with the 195. They are a decent DD tire and work as expected in the rain. I wouldn't call them exceptional in the wet but hydroplaning wasn't really an issue with either the 195 or the 205. (The 225 RS3 on the other hand... watch your ass.) I have and would AX the 205/8 combo if I didn't have anything else, but I wouldn't buy them specifically for AX duty, if that makes any sense.

The only miata.net "downside" for the 205/8 I can come up with that might make the 195/6 seem better would be lighter weight/rolling resistance = better gas mileage, but its probably such a miniscule number its not even worth entertaining as a talking point.

Add boost and I would consider any 205 as the minimum for a street car. Even with my "no-area-under-the-curve-Rotrex" :cjerk: I had no problem lighting up the 205 S-Drive. My 225 RS3's were much better in that regard, but I digress.
TL;DR: Other than the STS2 example, there are no issues I am aware of that would cause me to recommend a 7.5" rim over an 8" rim.
You can even run a 225/8 at some later date, if that's your thing. It's not going to be as as ideal as a 225/9, but IMO its going to suck a whole lot less than a 225/7.5 :rofl:

I bought few months ago a set of Rota Shakotan 15x8 +10 and they fit well, I rolled the fenders a little bit because I'm running low (not on the ground). The tyres are Yokohama Parada 195/50 and I'm very happy with the handling that these rims give me. You can feel the car wider, it's hard to describe assuming that english isn't my 1st language (I'm from Spain). Hope it helps!