Help! somewhat urgent, need new tires for Road+Autocross
 

Hey everyone!

So... recently I managed to totally destroy my tires on an open practice Autocross event. I ran for 33 laps in close succession and the the tires got toasted. They're closing in on 3 years of hard driving+ occasional autoX so, if anything I'm impressed they lasted this long.

They're the infamous Michelin Prius tires on my stock 2017 BRZ Performance pack.

I personally liked the lack of grip of the OEMs, it was more fun for me, but now I want to change it up and try the extreme opposite and go for autocross tires.

I have no intention whatsoever of changing out the stock wheels or anything stock for that matter aside from the tires. So whatever it is, it has to work with 2017 PP.

I did my due diligence and narrowed it down to these 3 choices:
215x45x17 Bridgestone Potenza RE71R
225x45x17 Falken Aznis rt660 or rt615k+
235x40x17 Yokohama Advan fleva v701

I know the 3 tire sizes and brands are very different but they're all 3 within $50 of each other and right around my budget.

I apologize for being so broad in choice but I honestly don't know much at all on competition tires.

I'm just curious to know how far I can place in AutoX with more competitive tires and generally what the FT86 feels like with very grippy tires.

I am as of now I'm leaning towards the 215/45/17 RE71R from what I've read online about their steering feel and keeping the car overall light and nimble which is important for me. But I want to hear from others what they experienced...

I'm attending another event I signed up for in less than 2 weeks times and that's more of a road-course than AutoX so I need to make a decision very soon.

Any comments/ideas/suggestions are all welcomed.

Thanks in advance

Help! somewhat urgent, need new tires for Road+Autocross
 

I’d personally go with the 615k+. They will last longer than the stones and will still be in another league of grip compared to what you’re used to. The stones really are kind of wasted without the necessary camber. I know the same can be said for any autocross tire, but it’s especially true for the RE-71s. The falkens are the best bang for the buck, IMO.

Edit: ok so I actually didn’t realize the Falkens 660s were as cheap as they are. At that price, I’d get those. Earlier this year, I was at an SCCA event where some guys were testing them...and they were faster then the re-71. YMMV, but just food for thought.

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My profile picture is the RT615K+. I love this tire. I recommend it for it's grip, life, cost, and size availability.
I have been running the falkens on my cars since the mid 2000s, they've come a long ways. They aren't the best in any single category, but they're pretty awesome all around.

If you're keeping the stock 17x7.5" PP rims then go 225/45R17. Because the tire will not be stretched like 215/45R17 is on a 17x7.5" rim, you'll have more room to play with tire pressures (ie lowering them for grip).
215/45R17 on 17x7.5" is stretched, which requires higher tire pressures to support the sidewall. This makes the tire less compliant and you'll have less grip.

My completely stock Performance Pack BRZ with its recommended 35PSI (cold) felt like it was on hockey pucks in an autoX environment. Lowering the pressures gained grip but it the tire shoulders were taking a beating. Once I switched to 225/45R17 on a 17x8" rim I can go as low as 31F/30R PSI (hot) with a lot of grip and the sidewalls as fine.

As for tire choices, if you really want a proven competitive tire with good response, the RE-71R is the safe choice. The RT-660 is fast but doesn't feel as good as the RE-71R. Read this: https://grassrootsmotorsports.com/ar...oss-and-track/

Hey! thanks a lot for this link :)

Believe it or not, this link persuaded me more towards the RE71R. They mention that the RE71R is "pressure agnostic" as they chose to put it, meaning it doesn't matter much if you lower the pressure.

I am admittedly on the lazy side of things and if I can get away with not needing to change pressure on my tires on race day, I'll take that. I'm only doing this stuff for fun, I'm not really that competitive. I extensively used my stock Pruis tires for two seasons now.

Also, that link suggested that the RE71R are better communication tires than both the Falkons. That's a big deal for me as I really care about how the tire feels. I bought the FT86 for the pleasure of the drive, not the numbers.

That's what I'm thinking right now but I'll keep on reading posts.

If you're concerned with how the tire feels and communicates, I'll also suggest the GT Radial SX2. Super well behaved at and beyond the limit, good feedback and very consistent tire in terms of trend and temperature. They are not as grippy as the tires you originally listed, but they are much more durable, communicate very well, and are CHEAP. Like $80/tire, cheap. In the land of continuous consumables, that means something.

...like more seat time. :)

If I'm daily driving is it true that the Falkens are too stiff? and that the stones are better if you plan for using it as a daily driver as well?

Stones get super loud when they begin wearing in but aside from that and life span I think they're decent street tires. For us at a medium grip concrete site they lasted about 130 runs with sufficient camber, they will get used up more quickly without camber, and we minimized Street driving as only to and from events (<3k Street miles typically) and swapped to daily wheels and tires. Most people expect about a season of local autocross and some light Street driving, as your only tire you may wear them out quicker than one set per season.

Rt615k will have less grip than stones and they'll last much longer, they should still be grippier than the oe tires though. 660 is still new, as a newbie I'd avoid for the moment and let other people figure out their idiosyncracies first and stick with a better known tire.

I've never heard of the v701, at a quick glance looks like a Firestone Indy 500 competitor, I'd expect it to sit between the oe and the 615ks, meh.

IMHO how long do you want this set of tires to last?

This may help. https://grassrootsmotorsports.com/fo.../142264/page1/

I seem to see everyone saying the RT615k last much longer, is it that well known for lasting longer than the stones? I think you're the 3rd poster to say this and even the link that was posted prior said the RT615k last longer...

Hankook R-S4's should also be a contender here, wear is much less a worry than the stones, also not quite as loud if you leave them on for street use. Grip obviously suffers a smidge but if you're not out there after FTD they should suite your needs.

I kind of think the opposite may be more true. But IMO a *lot* of tire "rules" from bias-ply days are still hanging around though less applicable to radials...

IMO a modest "stretch" will lend geometric stability to the sidewalls and could allow more pressure variation. However low pressures combined with "stretch" can be dangerous in certain instances...

For 95% of us with these cars on radial tires, the difference between 215/45 and 225/45 on a 7.5" wheel isn't going to be a big deal. But 225/45 puts more rubber on the road and looks better (subjective), but weighs more and slightly bigger diameter...

I come across the idea that "lower pressure => more grip" all the time, and often at the track it seems like people are actively trying to run pressures as low as they can get away with. I think this is a misguided approach...
Radials are inherently less sensitive to pressure changes than the old bias-ply tires but again the OLD rules seem to die very very hard, if at all...

The linked GRM article shows just how insensitive Extreme Perf radial tire grip is to pressure. This data shows that there is essentially nothing gained or lost in terms of lateral grip at the skidpad, over a very broad range of pressures.

Note that lower pressures should slow you down at autoX and more so at the track as rolling resistance is higher with lower pressures, relative to skidpad testing where it's irrelevant. Also note that with lower pressures tires will generate more heat and will begin to lose grip due to overheating much sooner vs. higher pressure. Higher pressures are safer as well, at least in the range we're talking about...

I've also recently learned last year with the Porsche, with near real-time pressure monitoring, that tire pressures go up much slower than tread temps do. Essentially goes up linearly over a ~12 to 15-minute session. So in my case I was spending a lot more laps at the lower-pressure end of the range than I had thought...

For all these reasons, IMO it is better to err on the side of *higher* pressures, and not get caught up in a "race to the bottom" of seeing how low you can go with tire pressures.

After analyzing this data a bit, I'm sticking to my previous approach of going out at ~28psi cold, coming in at ~36psi hot.

Thanks man! really really good post

Just making sure I understood things correctly: the above post you mean to say for 95% of us the 225 will not produce better lap times than the 215? or I misunderstood?

I sort of change my mind right now and I'm going for 225/45R15 Falken RT615+ just from the posts I've read so far. It's mostly for the cosmetic looks of a 225 and the price tag of the Falkens still being cheaper than the stones even at 215 and have longer life as I understood.

Sorry follow up question as well,

will the 215s "feel" better to drive? I came to learn from reading online that skinnier tires communicate better than fatter tires and generally feel more agile

Is this the case?