Call it wedneday fever, but I guess I'll give you the extra long answer
.
The Arp wrote:
I am building a car for track day events and occasional autox use. I have no track experience in a car and the car I'm building will most likely be the fastest thing I have ever driven.
I'm using a hayabusa engine so I'm looking at a car with 175 or so hp with a very low weight 1100 lbs or so and significant rear weight bias. I'd like to use 13inch wheels to keep cost down and keep the ride height low with my chosen uprights and without having to mount my lower control are halfway up the chassis.
As Chet pointed out, there are some similarities between our builds, though I have a feeling that my focus on build a racecar makes the choices somewhat more clear in my path.
The highlights of my build are -
Full blown racecar, R1 motor (slightly less powerful than yours), book-ish sized chassis, miata uprights, IRS, full cage.
Warning -
This next part gets into
my decision process and might be downright boring for some.
If you want to avoid it and read answers about tires and setup please proceed to the distinctively marked part 2.
And now, to some design philosophy of mine.
After running a significant number of track days (75+) with my track dedicated turbo miata I got tired of dealing with the fact that the car isn't going to be competitive in any normal racing series unless I poured a metric ton of money into it.
Since I do not have that kind of budget, building a locost was the answer.
However, driving the miata in so many track days, autocross days and competitive time trials has led me to some understandings -
1. I do not feel safe sliding a car at triple digit speeds with just a roll bar above my head, therefore my locost got a full cage.
2. I'll be driving at the track with vehicles that weigh double, triple and maybe even more than my locost - I'll want to be well protected with side bars.
3. I managed to put down to the ground ~250 RWHP and ~230 RWTQ with tires that are probably too narrow, but that tells me that I don't have to load my locost with massive tires that may just slow me down.
Putting down that power wasn't an easy task but I sure learned a lot of car control skills.
4. I seperate grip from handling while a lot of folks don't.
Grip is the amount of traction that you get from the combination of your setup.
Handling is what your car tells you when you're driving at or passed the limit.
It's the feedback that you as the driver get from the car that inspires you (if you get things right, hopefully) where you can keep up the pace, push it harder or back off.
There are plenty of grippy cars out there that don't really have good feedback, I find it annoying and sometimes even scary.
5. Having a fast car with no competitive class to race in sucks.
It's like having a night with Angelina Jolie only to find out that you have erectile disfunction.
If you want to race, build the car legal for a class that it'll have a potential in and that you have the budget to build for.
I am running on a pretty small budget therefore I'm limiting myself to a class that's not ultra fast (NASA ST2) knowing that thecar I'm building isn't going to be the fastest locost I can make - BUT - it'll be the fastest setup I can come up with that fits into the class rules, and that's a big difference.
6. One major decision that I had to take was if I want to make it street legal.
This is a major commitment - if you want it to be street legal you have to put lights in it, windshield, worry about smog, sound, licensing and some basic comfort.
Going with the full blown racecar you'd want to avoid all the above but worry about other stuff like safety gear, towing to the track and more...
The racecar will allow you to build a much more radical car IMHO.
--------------------------------
===== PART 2 =====--------------------------------
Please take any advice here with a grain of salt, I'm expressng here my opinion as I am in the middle of the build process myself and have not driven the car...
The Arp wrote:
1. Is staggering the tires a good idea? I'm not really sure if this is a good idea right off the bat. Should I start with identical tires front and rear and only stagger them if some handling issue dictates it?
Staggering the sizes seems like reasonable idea, probably even a good one, but I chose not to - I'm running 225/45R13 DOT Hoosiers on 7.5" rims.
Why?
Because running the same size means that I can switch between the front and rear wheels if I need to.
That may serve well better usage of the tires I have, maybe not.
I am "compensating" for it by running an aggressive alignment in the front that will generate very good lateral grip while keeping the rear tires more square to the ground will generate better traction.
I'm also planning on resisting body roll in the front using a sway bar while in the back I'd get the springs to take care of thatduty and may not run a sway bar at all to improve traction.
If needed, I can always go for 245 in the back or run the fronts smaller, 205 maybe...
The Arp wrote:
2. Should I start with Dot tires at first to limit grip and increase tire life while sorting the car out? If I go to a dot tire I kind of get stuck with about 7 rims all around or skinner. Is a 225 going to be too narrow in the rear? Will I spin every tire I touch the gas? If I go with slicks i can go as narrow or as wide as i want as there are plenty of options in 13" sizes.
I don't know if this is a good answer, but for me driving for nearly two years on street tires when I started made a huge difference in driving.
Even the Toyo RA-1 which isn't the most impressive DOT race tire generates a ton of grip comparing to street tires.
It tends to cover up for driving mistakes.
Driving on street tires teaches you that the right pedal isn't an on/off switch and you lose grip earlier so you can learn the car's limits without going really fast.
If you don't have any track experience it might be hard for you to even tell what the car does.
I have seen many guys that dropped a bunch of cash into their cars just because they thought that they are curing some handling problem when the reality is that they just can't drive well enough to extract the potential out of their cars.
So in short, don't start with slicks, it won't do much good for your driving.
The Arp wrote:
3. Anyone with just a straight up suggestion as to what they think I should run as far as wheels and tire size.
I know the answer to these question will be somewhat subjective but I really would like to hear the opinions of those who have spent more time at the track than I. Up to this point I have just been guessing.
Thanks
I'm guessing to, maybe with more reasoning behind but still guessing.
For my purpose 13's work great.
If you're planning on some street driving you'll need more ground clearance and 15's have a lot more options for street tires.
HTH,
Moti
BTW, I don't if you noticed, but we're pretty much neighbours at only 30 mins of driving from each other...