225/45/17 or 235/45/17 Tyres a good option?
 

Hi all,
I cannot get 15 semi slicks like 225 or 235 15 inch tyres over this part of the world.
My next available option that is available here are 225/45 and 235/45 17" tyres.

Would it be logical for me to go 17" or am I better off staying on 15"? Have anyone ran 235/45/17 competitively? Am I "under-tired" running 195/55/15 Hankook Z221?

The car is running 300bhp with 6spd and 4.1FD. I am using the car for time attack events.


https://www.miataturbo.net/attachmen...ine=1388246311

the problem with running 17" wheels in a track environment is it takes up a lot of available shock travel (not to mention your wheels can hit the fenders/other parts), which we need as much of it as possible.

definitely at 300bhp, you could use more than a 195 tire. I think the performance minded option is to find a dealer for 225 or 205 tires in 15".

Otherwise, its a toss up really, probably do what you find is best.

Ahh...shock travel. I should have thought about that. Thanks.
But having said that, the difference is slightly over 1" of travel between 15" and 17".
Which is the worse of 2 evil? Shock travel or traction?

225/45R15 = 23.1" diameter
205/50R15 = 22.7" diameter
225/45R17 = 25.0" diameter
235/45R17 - 25.3" diameter

definitely the tires making an impact with suspension components and/or the chassis are a concern here. We are talking about limiting your suspension travel by an amount greater than 1" for sure.

Plus there is going to be some performance disadvantages here. You will need to drop the car further to get near the same COG and ideal ride height. You will in that case take out more suspension travel, and put the tires closer to the chassis. Its probably not a linear relationship.
You can try to google info about this or just do some testing with one wheel to see what you would end up with. I would mount the tires on a borrowed 17" and put the shock on the car without a spring. Use a jack to move it around, adjust to your planned ride height and see what you will end up hitting and how much shock travel you will have left.

I don't really know, but I would stick with a 15" personally. Not sure I want to deal with the headache of making sure there is no components colliding, especially because that will lead to premature failure or excessive tire wear. with that said, tires are the most important part right? a tire change could change lap times by seconds. I wouldn't take internet conjecture for this question, definitely go out and run tests. You may hate a 17" as you will end up on the bump stops and lose whatever traction advantage you would gain from running a bigger tire. Plus sticker tires=need more suspension travel (or stiffer springs).

move up to a slick tire if you can find that more easily and run that in your class.

You are right, there are more variables i didnnt think of. Guess I just have to test it on 17 to find out. I don't have an option to go slicks due to regulations....

Yak - What are the import fees like from Japan? I would think there would be plentiful options from there and it is geographically much closer than Europe or the US.

Well, 225/45/15 yokohama 050 would cost me about $300 a piece landed. I could get it 225/45/17 for $200 a piece.

What compound in the 221 are you running? Assuming your running the soft compound you should only be able to get 2 hot laps in. Have you tried running the RS3 in 225/45/15 and experimenting with tire softening? I think you might run similar lap times on a 225 RS3 simply due to consistency and break away characteristics. I would do back to back testing with your 195 z221 vs RS3 225 on a 15x9 rim. I would also spends some time on your front aero, that front bumper is a parachute.

I was running 225/15 Nitto NT01 but even that would be on the limits of over heating at 300hp

I am running c5 compound for the z221. C3 is too soft and overheats by lap 2. Possibly it is also due to me being in a tropical country with 38degree Celsius track temp.
The front bumper does look like it has a lot of drag, but the carnard and splitters made 2s difference consistently in a 2min30s track. This is in Sepang Malaysia. One of the f1 track in the calendar.

I also tried 225/45/15 on rs3. Nowhere near z221 in terms of performance. But I didnt have tyre softener.

Actually what would be really nice to hear from this forum is if anyone had used 17 and find it useful.
I come from a country whereby 90% of the cars goes to the junkyard by year 10 of its lifespan. Its rare for people to be tracking old cars.

If you're looking for more tire than the Z221, and you can get that from a 17" tire, If I were you I'd try to make the 17" wheel work. It's not "ideal" but I think in the real world you can tweak and adjust to get suboptimal setups to do pretty well (I've had to do plenty of this myself).

I'd run really stiff springs, and adjust/swap bump stops as necessary to limit your suspension travel from allowing the tire to drastically hit the inner fenders. Last resort use bump stop spacers or "packers" to engage the bumpstop sooner and reduce suspension travel. I played with such spacers this past season to combat the severe compression I was getting from downforce. There were better ways to address it, but that was what I could do at the time, and I made it work.

-Ryan

The track is quite smooth, i am guessing bumpstop spacer may work. Will give it a shot. Cheers.

I'd rather have a 205/50R15 over any 17" tire. No amount of clusterfuckery you do to the suspension or bumpstops will ever cure the issues caused by putting a tire 2" too tall under the car. We don't have enough suspension travel to start with, and all you're doing is taking 25-30% of it away. The car will be a nightmare to drive and will almost certainly go slower.

My R1R's are 245/35-17, or 23.8" diameter with a 9.4" tread width. These aren't exactly track tires but the mechanical grip I get from this contact patch is pretty impressive.

If you can run slicks, I think that Achilles has a 17" slick that's 600mm in diameter (23 5/8") and good for an 8.5" or 9" rim.

No offense, but don't you think it's worth mentioning that your car is a tube frame with no inner fender wells for the tire to interfere with?

There is that. :) C'mon Savington, you don't have to sugar coat it when I screw up!

Actually, If I had a 300hp Miata and some access to tin snips, and an open rule book, I'd look at the 16" tires that Hoosier makes for the Radicals. Where there's a will there's a way, right?

The Achilles tires aren't that oversized, and if you're running a low offset rim then I bet even Miatas with mild flares can get away with it. I'm running +25. The link below should tell you if I'm blowing smoke up your ass:

Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

I plugged in a 225/45-15x8 with +38 and a 245/35-17x8.5 +25 and the numbers didn't look too bad.

I've had naughty dreams about the 23.5x12x16 Hoosier slicks. Probably the ultimate Miata tire, although it would take an act of god to get them under the car. IIRC they want a 12.5" or 13" wide wheel.

Like I said earlier, the diameter is the issue. Flares will cure all ills when it comes to overall width (to a point - eventually you run into the tub when turning) but flares don't move the inner fender when it comes to diameter. That's why a 225/45R17 would be a nightmare to fit, but a 275/35R15 isn't too big of a deal.

The 245/35-17 is only ~.4 inch larger by radius than the normal 15" wheel options. IMO that might be workable. But with the R1R is a very low temp compound tire so it wouldn't be my first choice on a road course.

lol. Talk about sugar coating...