cthomas61

Starting to get back into AutoX with my new (to me) 350Z. I am going to run CS RTR. I used to run a Saturn in STS quite a bit in AutoX years ago and all these wheel choices, not to mention rear wheel drive, and new SCCA rules, is kinda confusing. Please bear with me if these are FAQs. I've been searching around this forum for a few days but still not sure what the answers are.

I currently have 18" stock wheels. After reading these forums I am looking at getting the Enkei RPF1s due to weight and cost. Is there any competitive benefit to AutoX to dropping down to 17's? Will the computer go wonky if I change the wheel size?

The new SCCA stock class proposal will mandate a 200 tread wear which will further limit tire choices. Dropping down to 17 would definitely improve the tire options but if I stick with 18 what are my options to not break the bank and stay competitive? The Sumitomo's HTRZ III are cheap but are they a good AutoX tire?

A lot of people mention the Dunlop Star Spec but they aren't available in 18s. How about the Falken Azenis RT615k? Some threads mention an RS3 but is that a Cooper or Hankook tire?

So many different options, so confused. Any guidance on tires for an SCCA CS stock AutoX car that will still be legal next year would be appreciated. Thanks.

- C. Thomas
350Z 61 CS RTR

PDX_Racer

iTrader: (2)

I know that there are those who think going "street tires" will somehow magically reduce costs -- but I'm not one of them. I drive like a grandma on the street, and still can barely keep a set of tires from turning to plastic after only 12 months.

However, if you're running in RTR, you're stuck with 18" wheels for this year if your car came with 18s (otherwise you're jumping out of stock -- and therefore RTR).

Next year running 17s -- given the current tire economics -- could reduce your tire costs since tire manufacturers are making far more 17" tires than any other size, so they're selling those tires closer to cost than they are for 16" and 18" size -- and therefore 17" tires are *currently* cheaper (they weren't only a couple of years ago).

Right now the "tire to have" is the Dunlop Direzza Zii, but they aren't much cheaper than so-called "R compound" tires.

Personally, I'd focus on learning the car on the cheapest tires that give me what I would want, and worry about the rule changes next year.

cthomas61

I'm a weekend Autocrosser, well, I guess we all are, lol, what I mean is I'm not a national level champion and don't intend to be. If I drop $2K on wheels and tires I better be able to get more than half a season out of them. Since this season is already half over I'm not to worried about what class I end up in this year. Since the new stock class proposal for next year allows for wheel size changes that is something I need to take into consideration.

Is there an advantage in AutoX to running a smaller 17" wheel? Better gearing? more torque? Will it screw up the computer? Can i simply just bolt them on?

If 17's are the way to go it would sure make tire choices much easier, I'd just get get the ZII's. But if it is better to stay at 18s then my tire choices pretty much boil down to Sumitomo unless they are utter crap and I need to spend big dollars on Bridgestones or something.

- C. Thomas
350Z 61 CS RTR

Lubo

iTrader: (3)

You mention you are a weekend auto-x guy. Just how many weekend are we talking about? I have yet to meet a tire that will last me more than 12 events. I usually do 12 - 14 auto-x days and 4-5 track days a year. I need 2 sets of tires to last me the whole season. The car is rarely driven on the street, I am talking around 3k miles a year and most of it is accumulated driving to events. So expecting a set to last you a whole season may not be realistic, unless you will baby the car around track.

As for wheel sizes, I am a firm believer in trying to fit the smallest wheel you can find that fits over your brakes. Up until now I've been running 17x10 Enkei RPF1 with 295/35 17 Kumho XS tire. There aren't too many choices in tires tha wide in 17s anymore short of running Hoosiers or similar. That is the reason why there are new 18x10.5 RPF1 sitting in my garage.

With that said I did not build the car to any class. Last auto-x I ran with SCCA I was by myself in F prepared, thanks to gutted car and SPL bearings and arms all around.

PDX_Racer

iTrader: (2)

The big issue will be the overall tire diameter and the difference between front and rear tires diameters (rear should be the same size or bigger). Of course, making sure that the new wheels clear the brakes is pretty important too.

That all being said, a set of 17" wheels and tires should have a smaller amount of rotational inertia than 18" wheels and tires of the same diameter (since the wheel barrel is smaller). That means that you should be able to accelerate and decelerate a bit quicker, but you'll have more "give" since more of the diameter is flexible rubber. Currently 17" tires are cheaper, but most 17" tire sizes max out at 255 width.

cthomas61

OK, so dropping from 18 to 17 may give a slight performance improvement but the big benefit will be increased tire choices.

That makes tire decisions a bit easier. So 17 Enkei RFP1s with Dunlop Star Spec as wide as possible that still fit.

- C. Thomas
350Z 61 RTR CS

Z1NONLY

iTrader: (2)

ZII's only go up to 255 in 17 but 275 in 18".
http://www.tirerack.com/tires/tires....el=Direzza+ZII

RS3's top out at 255 in 17 also but go up to 285 in 18"
http://www.tirerack.com/tires/tires....el=Ventus+R-S3

Rivals top out at 255 in 17" but go uo to 295 in 18"
http://www.tirerack.com/tires/tires....=g-Force+Rival

RE-11's top out at 255 in 17" and 275 18"
http://www.tirerack.com/tires/tires....=Potenza+RE-11


You actually have more tire sizes available in 18" right now. (17" are still cheaper for a give tread width though)

PDX_Racer

iTrader: (2)

Remember that dropping to 17" wheels takes you out of RTR C Stock.

The proposal for +/- 1 inch change in wheel diameters is just a proposal for now for *next* year.

cthomas61

Right. But if I am going to buy wheels I better get more than one season out of them. I don't mind running Prepared (or wherever smaller wheels put me) for remainder of this year.

That said I am no closer to a decision as to whether to go with 17s or stay on 18s or anywhere near any idea of what tire to get than when I started looking into things. Uggghh, so many options.

- C. Thomas
61 RTR CS

PDX_Racer

iTrader: (2)

Plus, the +/- 1" wheels are a proposal -- there's no guarantee that part of the proposal will go through.

However, if they do eliminate DOT-R tires, they'll just about have to allow people to go up or down 1" in wheel diameter (but not change width or offset from the original stock width or offset), otherwise cars won't be able to find tires. That was one of the advantages of using DOT-R tires -- since they were a "specialty" tire, so it wasn't as difficult to justify building tires for pretty much all wheel sizes.

cthomas61

So, just to close out this thread....

I just placed an order at the Tirerack

Enkei RFP1's with Falken RS3 245/40R18 F 265/40R18 R

I did a lot of research into the 17s but I was still left with to many unanswered questions. When I used to run a FWD econ box in E Stock the car was so much easier to prep, you basically had one choice, you either chose it or not. Now that I have a real car the choices are absolutely mind boggling. Either way I figure I'm never going to be national champion and will be lucky if I can even challenge the top guys regionally so in the end what wheel/tire I have probably won't make that big of a difference. Best to go with something that at least looks good and I know will work.

So now, I have to wait until the end of the month for the RS3s to get here on their boat cause it looks like they are back ordered. great.

- C. Thomas
2005 Yellow M / 61 CS RTR

cthomas61

OK, so I lied, one more post to close out this thread....

Ran the first event on the new tires today. After running on three near bald, 8 yr old, cracked, stock RE040's and one no name full tread all season, I must say there was a marked improvement.

I went from finishing 6 to 8th in class to 2nd place! Beat all the Miata's in RTR and one BMW, the other BMW got me buy .3 tenths. So far just loving the RS3s.

- C. Thomas
2005 Yellow M/ 61 CS RTR