Why 18" vs 19" wheels/tire for track and Auto-X

ConeKilla

Ok, so after doing a obligatory search I cant find any threads discussing performance of 18" vs 19" wheels on the 370z. However, I see a lot of folks talking about running 18" wheels on their track & auto-X cars.

I am assuming that on a track the loss of gearing is more than made up by benefits reaped by...

1.) less rotational mass
2.) bigger better cheaper tire & wheels options

Is that it?

But for auto-x I see guys running 18" too...which is stranger to me since 2nd gear top speed is such a critical factor for most Auto-X cars.

Anyone care to tell me why they choose 18" over 19" for Auto-X?

1st

Cheaper tires to burn...

stuy486

I never found reasonable 18" wheels that would be legal for CS, but if I had, this would've been the main reason for me.

At current prices, RS3s are $400 a set cheaper in 18" sizes. From the looks of things, I'm going to burn through 2.5 sets in one year of autocross in my car.

Granted, that's doing every regional event including practices (in SoCal, so one a month year round), 2 ProSolos, 2 National Tours, and Nationals next week, often with co-drivers.

I'm getting around 120-150 runs out of my RS3s, flipping them and rotating them.

ConeKilla

Noted, that's valuable feedback as I was intending to get RS3's as well.

P.S - Good luck at Nats buddy...now that your picked for a potential CS winner a lot of eyes will be on you.

stuy486

Thanks

gomer_110

Sounds like a reason just to come play in ASP.

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'11 370Z Nismo #528 Fast Intentions | Stillen | Motordyne | Uprev | CSF | Zspeed | Z1 Motorsports | AST | Swift | SPC | SPL | Whiteline | Hotchkis | Bride | Schroth | Robispec | Cusco | Nismo | Volk | Forgestar | Hoosier | RJM
'17 Titan Bone Stock

gomer_110

1. Better tire options for 18" wheels.
2. Weight reduction, although the wider wheels most of us run end up bringing the weight back up.
3. Rotational inertia is better on 18" wheels.
4. Even with 315/30-18's on my car I still redline around 67mph which is plenty for most courses to not need 3rd gear.

__________________
'11 370Z Nismo #528 Fast Intentions | Stillen | Motordyne | Uprev | CSF | Zspeed | Z1 Motorsports | AST | Swift | SPC | SPL | Whiteline | Hotchkis | Bride | Schroth | Robispec | Cusco | Nismo | Volk | Forgestar | Hoosier | RJM
'17 Titan Bone Stock

ConeKilla

Nismo has same gearing as base w/sport? Also, is around 67mph captured with data or just your best SWAG?

gomer_110

GPS reading on data logger for speed capture. Also the gearing (both trans and diff) are the same between the Sport and Nismo.

__________________
'11 370Z Nismo #528 Fast Intentions | Stillen | Motordyne | Uprev | CSF | Zspeed | Z1 Motorsports | AST | Swift | SPC | SPL | Whiteline | Hotchkis | Bride | Schroth | Robispec | Cusco | Nismo | Volk | Forgestar | Hoosier | RJM
'17 Titan Bone Stock

stuy486

My GPS data shows high 68ish MPH top end in 2nd. Captured using RaceTrace ;-)

The two runs displayed are my right side runs at the Crows Landing ProSolo: https://www.youtube.com/watch?v=NFEB...EGGtLCB9guMgJA

ConeKilla

exactly what I was looking to satisfy my curiosity. Thanks! P.S. You ever heard or seen Petrel data logging software? It's basically THE data logger for Auto-Xer's I highly recommend you make the switch. The ability to instantly review a run definitely gives a competitive edge.

stuy486

I'm a developer for RaceTrace, and I'm pretty happy with the software I wrote myself

This screenshot is from my iPhone, and I regularly review data between runs when I'm autocrossing. Plus, the ability to compare my data to co-drivers' on the fly really helps to learn where we're gaining and losing time to each other.

There's a thread from a few weeks ago with some more info on the topic: Lap recording software.

Also, SoloStorm (The Petrel product) is $200 and Android only, RaceTrace is $15 and (currently) iPhone only.

theDreamer

why 18'' wheels more popular on track?

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ConeKilla

Thanks for linking, some good info there. But mainly covers the points I assumed were true between the two options...and a bunch of other typical off topic forum piss matching<sigh>

cossie1600

Yeah I was hitting 69 on the big 285 35 19, the 285 35 18 only hit like 64 or 65