Alright, so I've checked out some other threads and sites but I value your guys' feedback more so than lots of the other racecar forums. I'd like your opinions/feedback regarding my tire choice for competition this coming season.

Here's my situation/question: I'm going to be running my NC in NASA TT5 class next year and have decided to get a little more serious about optimizing the car for the class. I'm going to be buying a second set of track-only wheels and tires. Historically, I've just run one wheel/tire setup for street and track, and have gone with whatever super 200TW's were most affordable (V730s, NT05s and RT660s mostly). With this setup, I want to actually get some high-end tires that will net faster lap times than the other aforementioned tires. RE-71rs and A052s were at the top of my short list.

Current wheels are 17x10 and I'm running 235/40/17 NT05s because I can get them on the cheap. I'll still be running this setup on the street. The fast naturally aspirated NC guys around here are all running a little stretch, and the preferred setup actually seems to be 10" wide wheels with 225/45/17 tires.

Here's where things get a little more complicated. The tire choice modifier for TT5 class has a couple choices that seem... a little overpowered. I'm currently running about 175whp (still need to get the car dyno'd for the exact number), which puts me at the bleeding edge of my power limit if running any of the tires listed by NASA for a +1.0 mod factor. If you look at the tires with a +1.6 modifier, though, 100TW RC1s, NT01s and R888s are listed, and the resulting mod factor would up my max HP to 181.



I'm possibly game to run 100TW tires for competition only, and can get R888s and NT01s for a pretty good price. My main question: Are either of these tires quantifiably faster than an RE71 or A052? And how much quicker can I expect them to wear? For reference, I'm currently getting about six track days (maaaaybe seven if I really want to run them to cords) out of a set of NT05s.

I'd like to drop some time if that's what either tire is going to do, but will probably skip them if I'm looking at getting three days out of them as opposed to six. I want to go faster but not bad enough to double my tire expenditures.

Any firsthand experiences/pertinent input is welcome. I'm sure that there's another factor or two that I may not be considering, so feel free to call me out on that as well lol. Thanks again as always, guys.
-Zak

 

It might be close just doing napkin math, but are you sure your competitors with the 225s aren't running that size to fit within the 226mm template for the +0.3 modifier? You should be able to find that out from the classing sheets.

ETA: That would basically offset the penalty of electronic throttle body, and give you the benefit back to have the ability to do a flat power tune.

 

I've double checked, they are not. Actually, the other guys' setup that I'm more or less copying don't actually race NASA TTs at all.

Unfortunately, with 17x10 wheels, the 226mm and under modifier becomes null because the measurement is taken based off of total width at the sidewalls, not tread width. I could drop down to 9's, but from what I've seen, the 10's are faster even at this power level.

 

So let me caveat this by saying it's all based off an ST4 BMW rather than a TT5 Miata. That said, I have a few thoughts:

- NASA uses the same tire balancing rules for ST and TT, which is kind of wrong. For TT you generally only care about pace over the first couple laps of a session (because after that you're in traffic anyway), whereas for ST you need a tire that will last the whole race. Also, extra power is more useful in ST because it makes it easier to pass people, whereas any TT lap where you had to pass someone is probably not going to be your fastest anyway.

- NT01s are slower than RE-71RS over 2-3 laps. I haven't personally used R888Rs but my gut is that they are the same way.

- The fastest tire will depend a bit on the circuit (and driver). For example, in my M3 I am faster at Thunderhill on RC-1s (1.6 factor, so 40 extra hp), but at Sonoma the balance shifts to R7s. The extra 40 hp is much more useful at Thunderhill with the long straights, whereas Sonoma has more turns and (especially) more left/right/left transitions which the RC-1 hates and it's all about the Hoosier.

- Fastest tire is driver dependent because taking full advantage of the extra grip means holding the car right on the edge of traction for the entire lap. This is relatively hard to do (especially with the fastest tires like a Hoosier), whereas taking advantage of extra horsepower just means pushing the throttle all the way down on the straights. So the more skill you have, the more the balance shifts towards the high grip tires.

- Fast tires all suffer significant drop-off in performance after the first few heat cycles. You might get 7 track days before they cord, but TT times will suffer a lot. If you're just doing it for fun then don't worry too much about this, but the top competitors in TT are generally bringing a set of stickers to every event and using them on whatever session is expected to be the fastest one for the weekend (generally the second one on Saturday)

Anyway, to wrap all that up, if it were me I'd probably start with RE-71s. I think they probably offer the best combination of power and speed over the first couple laps. I haven't run the Yokohamas, but from what I've read they're a tiny bit behind the Bridgestones.

--Ian

 

Ian, was kinda hoping you'd chime in. Thanks for the in-depth response. A couple thoughts on my part in regards to what you've brought up:

-I noted what you said the ST vs TT ruleset, and figured that the single ruleset for both competitions allowed for some loopholes to be made. Seems that the cars in TT running lower power and stickier tires generally have an edge.

-I thought there would be a bigger difference in traction between the R888/NT01 and some of the other super 200TW options. Good to know they're not in a totally different class.

-I want to step my game up a reasonable amount (I'm even going to get a pyrometer this season and something for lap data acquisition), but I'm going to start with only one set of track-specific tires at a time. I'll just have to make whatever I go with work at the three main tracks we race down here. As the season progresses, I'll reevaluate, and maybe grab a second set.

-On the coattails of that last thought, I definitely won't be able to run stickers for every event haha. I'll try to get as close as I can, maybe I can just rotate my race tires onto my street wheels once they've gone through a certain number of heat cycles.

I'll probably start with the RE-71rs. Sounds like you really can't go wrong with em. Glad I can rule out a couple of the 100TW options and simplify things a bit.

 

Some large overwhelming majority of the last three or four years of national championships in TT5/ST5 have been won on Maxxis RC1v2. The only other tire(and resulting build theory) that can/could/has won is the Hoosier R7.

The entire 1.0 category is a compromise. You dont get the big modifier to add "lots" of power or remove "lots" of weight, nor do you get the outright fastest tire of the no-modifer R7.

The fastest TT5 car in the country is a second gen BRZ on 255/40/17 RC1 on 17x10. If I was trying to replicate speed in this class, itd be heavy car, tuned for broad flat power, full aero(maximized 4" splitter + high end wing) and the 1.6 modifier Maxxis RC1. Then buy horsepower until you reach class max.

 

One thing to keep in mind when you're looking at national champs results is contingency awards -- fast guys buy tires that they can use to win more tires. Both Hoosier and Maxxis have significant contingency programs while AFAIK Bridgestone does not.

--Ian

 

Thanks again for the responses, guys. Great info, Doward. I've seen your Daily's build thread before and should have asked you about maximizing a car for TT5, seeing as you seem to have done pretty damn well with it.

I've already got a couple of those bases covered. Again, like I said, I'd like to make a concerted effort to be somewhat more competitive this year, although I don't see myself going ***** out with new tires every other event, etc. That being said, I've got a 4' splitter and wing set up already, and the cammed 2.5 has a pretty broad powerband. I don't personally want to add any ballast to the car for the bump in max HP, though. Maybe that makes me undercommitted. If I'm under max power after dyno'ing the car, though, I'm willing to buy a few extra HP (Fab9 intake manifold or FlexFuel should net another ~10 ponies).



Similarly-spec'd cammed 2.5 dyno sheet, albeit on an optimistic dyno.

Ahh, thanks for the reminder. I should've mentioned that I'm definitely going for contingencies this year. Even last year with less power, no aero, and lower-tier tires, I would have been able to cash in on a few programs this year. You're right, Maxxis and Hoosier both have programs but nothing for Bridgestone. I remember Maxxis's program being pretty good but I just went back to the NASA page for it and the minimum driver count and rewards aren't showing up on the website like they used to.

How much faster do the RC1s wear versus the RE71s? They're pretty comparable in price so I'm willing to consider running the RC1s if they don't wear outrageously faster than the Bridgestones.

 

Google can find the current ones:

https://drivenasa.com/contingency-programs/maxxis-tires/

https://drivenasa.com/contingency-programs/hoosier-racing-tire/

That said, the programs are annual and sometimes change from year to year so check back once they've been updated. You probably need to re-register each year as well.

I don't have real data to compare the wear rates of the two-- I ran the RE-71s for a couple track/test days at Thunderhill, whereas I ran the RC-1s in Utah (the 6 hour enduro and then for champs) and Buttonwillow (the last WERC enduro). The amount of tread worn off the RE-71s seems to be higher than that off the RC-1s (and with fewer hours on the Bridgestones to boot), but both of them are heat cycled beyond the point where I'd use them in a competitive setting and they have plenty of tread left. Again though, my M3 is very different to an NC Miata.

--Ian

 

Strange, I had the Maxxis page pulled up earlier on my work computer and the payout schedule wasn't there.

Yeah, I'll keep my eyes glued to it once the season is closer to starting. That's still great info on the wear characteristics as well. If the RC-1s don't lose tread that much quicker than the RE-71s (if at all), that's a pretty big bonus. They're even a couple bucks cheaper in my size. Honestly, I might end up running those due to the potential contingency benefits.