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PostPosted: September 24, 2008, 12:10 am 
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Alright so I know this has been discussed in several other threads but I still don't know what to choose.

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.

So to the questions

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?

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.

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


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PostPosted: September 24, 2008, 12:20 am 
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Sounds like you are building something along the lines of what Moti (blackbird) is building. He has put a lot of time and effort into coming up with answers to the same questions you just asked. He'll chime in here eventually I'm sure, but in the meantime here are some thoughts.

You can change stagger front to rear at any point in time by altering wheel offset.

7" wheels can be fitted with wide bias ply racing slicks too. They make cantilever designs for classes that are wheel width limited. How much better ( or are they better for that matter) than a DOT slick is a subject for debate. I like to look at what tires are winning in national level competitions. (although that too might be skewed by contingency programs)

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PostPosted: September 24, 2008, 12:33 pm 
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You are likely talking different rims for street and track. In that case, what I'm trying to think thru is using 15" with taller tires for street and then 13" with slicks for track. I think this needs to be done for ground clearance issues. You need to work this out ahead to get the right wheel offsets. You want the contact patches on the front suspension to be in the same place, so the 13" wheels would need to offset more outwards.

You should aim for something like 2" ground clearance on the track. Don't make your oil pan the low point. I think soft, sticky tires will be much appreciated the first time you go sideways or swap ends at 100 MPH.

If you opt for different front rear tire size, I would try to keep the same aspect ratio. That might be hard...

When you start driving it, work your way up to speed. You will have to adjust to driving something so light and responsive. I spun a couple of times before my brain/spinal cord learned to pick up on all the clues. Now I can see it coming, but not before I put thousands of $ into repairs...

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PostPosted: September 24, 2008, 8:58 pm 
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How bout i shrink the trade space some.

From my observations it seems like 20X9X13s all around a popular setup for sevens that auto cross. Is this too wide for the track? Seems like the sevens setup for the track run something narrower.

I was considering starting with P225/50ZR13 Hoosier dot radials on 7 inch rims front and rear. The P255/40ZR13 is tempting but appear to only be available in the A6 compound which might heat up to much or not last very long at track days (i don't really know this it's just conjecture).

I have also considered just starting with the 20X9X13 Hoosier bias slicks on 10" rims all around and going skinner at the front if needed later?

Goodyear also seems to have some formula car slicks available if a few different widths and compounds in 13" sizes

Will the dot tires last significantly long that the bias slicks? Is there such a thing as too much tire? Should I just buck up and choose something that tickles my fancy and just go from there? All opinions welcome.


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PostPosted: September 25, 2008, 2:12 am 
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Call it wedneday fever, but I guess I'll give you the extra long answer :lol: .
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... 8)

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PostPosted: September 25, 2008, 1:51 pm 
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Moti writes:

Quote:
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.


This answer concerns me. I would recommend limiting your power much more then limiting your traction. Take a couple of thousand RPM off your redline, until you can really drive the car. This goes for you too, Moti.

Open wheel vehicles have been designed for gladiatorial combat since the days of Ben Hur. Serious, serious business. Also maybe the most fun you will ever have.

Being traction limited with full power means you will risk paying a very serious price on the fastest most dangerous parts of a race course. Places like flat-out, WFO, left hand blind turns - you name it. Having the back end step out on you at 110, 120, 130 - will require top notch skills. Driving fast heavy cars will not give them to you. You need to get them in this car or a real formula / sports racer type car.

You guys are talking about Formula Atlantic equivalents, but no wings for traction. I don't think there are any equivalent cars without real aero downforce aids.

Moti got some good advice from the Hoosier tire folks. I would ask them if the slicks or the DOT R tires have more gradual break away. *you want that*!.

You need to learn how to beat on the car's tires to get them hot. If your braking 0.5 seconds early going into a turn, and you can't do a bit of a slide and recover - your probably not up to temp. Ask yourself, do you want to take that flat out, WFO, left hander on coldish tires - and put down 175 HP without a wing?

So I recommend, learn how to drive the car hard and shift early...

I thought I had some time under my belt, was doing pretty well. During practice I had another Formula Ford take a very aggresive line under me thru one of those flat out left handers. It looked really good and I thought I'd give it a try. Made it through and thought I did fine, done the exit and had 8 feet of road on the outside to spare. 110 MPH. Suddenly I realized things were not so good, the car was just floating down the track and not hooked up at all! ( Probably got into marbles when I went a little wider then I should have... )

I was so happy to have sticky tires as I watched the smoke rising from the pavement as my car rotated down the track, I was also happy to be down close to the ground, with no extra ground clearance. Cost me about $1500 for rod ends, radius rods etc. when I hit the wall backwards...

That car had 100 BHP on FF slicks...

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PostPosted: September 25, 2008, 9:35 pm 
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horizenjob wrote:
Moti writes:

Quote:
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.


This answer concerns me. I would recommend limiting your power much more then limiting your traction. Take a couple of thousand RPM off your redline, until you can really drive the car. This goes for you too, Moti.

:D

You, more than many other people, should know that the speed of your FF is a direct result of having a lot of traction and NOT because it has a lot of HP.

Traction allows you to carry more speed into every corner therefore raises your overall speed.
You corner faster, brake later and accelerate sooner.

However, lack of traction doesn't allow you to corner very fast becaus you'll slide.
You'll need to brake earlier and accelerate later and more gradually...

Traction = higher speeds all the time.
HP = faster straight line acceleration.

Which one do you think is safer for a beginner?
IMHO the answer is pretty obvious, especially given that 175 HP isn't really that much.
It'll be quick because it's light, but this isn't brutal power that gets you in trouble, it's less than your average hot hatch has nowadays...

As for myself, I learned how to drive with a lot more HP and a lot less grip than what I'll have in the locost.
Don't worry, I'll be just fine :wink: .

Luckily for the Arp there's a great racetrack in the area called "Street of willow" ,SOW in short, that's a ton of fun and is fairly slow - great learning enviorment!
In-car video of some laps of SOW of my miata, then with only 211 RWHP, can be found here - http://www.youtube.com/watch?v=deW0TyZdP6w

Moti

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PostPosted: September 25, 2008, 11:45 pm 
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I'll be happy to watch your videos, have seen a few of sevens there.

I don't know how much my view is colored by where I drove. I think the 175 will be more of a handful then you expect. And I am am absolutely not talking down to you by the way, you have a lot more variety of driving experience then me.

I've seen this happen though, even to a friend and arch rival who ran an A Production Corvette. I could beat a good number of those, but never beat him. One day he took an FF for the day. Spun big time on the banking of a 1 mile oval track at 120 MPH. *Not a happy camper*.

175 HP, with so little weight on the wheels is my concern. I don't know, yet, if these cars turn around as quick as a mid-engine formula car, but it's hard to be ready fast enough the first time.

I drove that AP Corvette once, and these problems go both ways. I shifted early to be on the safe side, but what messed me up was the inertia of that car. You couldn't fix a mistake quickly and had to drive several hundreds of feet ahead on the track from where you were, compared to my FF.

Quote:
Which one do you think is safer for a beginner?


High power and low traction will test you on those fast flat out turns. It takes time and effort to learn how to get the speed up on a car like my FF. I assumed that power was part of why I spun that day, but maybe the cornering speed alone was a big factor too. But 175 with somewhat less rear weight bias - going to be fun. Much more of a sword then a battle axe.

I do think I've seen more carnage with the faster street cars, then the formula or sports racers.

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PostPosted: September 26, 2008, 1:33 am 
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Having been mainly around cars that started their lives as street cars and then got modified for racing I've seen mainly carnage of that crowd. Anything from Subarus, Bimmers, Vettes, Hondas and so forth...

horizenjob wrote:
if these cars turn around as quick as a mid-engine formula car, but it's hard to be ready fast enough the first time.

My point is, if you don't have sticky tires you're not going to be able to turn anywhere near as fast no matter what you do, there's just not enough grip.

I know what you mean about the inertia of the Corvette having driven a C5 Z06 at the track at speeds nearing 150 MPH.
Damn car pulled like a freight train but the feedback was so lousy that you just can't trust it 100%... it felt like the car wants to throw you off.

Moti

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PostPosted: September 26, 2008, 8:34 am 
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I agree with learning on street tires. Street tires generally give more audio feedback that is also more progressive, which a beginning driver needs to learn their limits, as they likely haven't honed their skills to the point of being able to understand the feedback the race tires are giving them and can't "feel" what the car is doing as well. Granted I've never run a high performance car at a racetrack, and have only run race tires in a Formula SAE car...but I whole heartedly agree that running street tires will prevent you from having the balls to try taking that flat out blind left hander anywhere near flat out. You get a lot of speed up on the straights with the power, but the first time you overcook a corner will shrivel the "big ones" you thought you had and you will learn to mind your braking zones much more conservatively. And of course it will teach you throttle control on corner exit. And while race tires will help you to be carrying more speed when you spin out, once you leave the track race tires do nothing to help you slow down more quickly.

If you have little racing experience in cars like these, I would actually recommend getting comfortable autocrossing on high performance street tires before jumping up to a road courses and race tires. It will teach you the car control (and recovery) skills you need to drive your car at the limit in a fun, affordable, safe, and low speed environment.

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PostPosted: September 27, 2008, 8:22 pm 
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Thanks for the comments so far. I appreciate the the differing opinions presented. Especially since they come people with different backgrounds. The inputs have helped me form an opinion for my self.

So, here is what I'm think I'm gonna do. I'm greedy and ultimately I want the car to be riding on some wide slicks. I'm going to design the cars ride hight, track width, etc. for the use of 13" bias slicks. the car will be built initially with something with less grip. There are plenty of dot Hoosiers in 13" so, maybe some of those or some streetish tires (even though i really don't plan on making the car street leagal). The thing I don't like about using street tires are that there is pretty much nothing available in 13" and it would force me to go to 15" wheels and screw up my ride height and gearing.

The first place I would take the car would be to a few autox practice days just to try to sort myself and the car out. Then as Moti predicted to the streets of willows. I've actually been to that track several times before just on two wheels. :D I have some track experience just none in a car.

Once i feel comfortable and get a little better big fat slicks it is.


Moti, since we are so close, one of these days I would like to take a look at your build and maybe pick you brain a bit. Also, I some point I'm might ask you to allow me to spend some quality time with that bender of yours.

Thanks again


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