pacman1969

i know its not a rx7....but she has the heart of one! wondering on my 70 midget 12a bridg if neg 2.5 all round is a good starting point? running a 7.5 ford irs rear with custom upper a arms frt an upper an lower custom rear,275/35/15 hoosers.

farberio

iTrader: (7)

It is as good as any, though I would suggest using more camber in the front vs the rear.

Ultimately though, every tire, track, and driver would want different setups so your best bet is to get tire temp data right after coming off track and making sure the temps match what the tire manufacturer suggests.

eage8

iTrader: (9)

With hoosiers (I assume their A6s or A7s based on the size) I'd probably go at least -3 up front if you can get it.

in the rear it depends on how much power you have and how much rear spring, but -2.5 isn't a bad starting point for a non-turbo car.

get a decent pyrometer and take some temperatures after each run to see if you're in the ball park with your camber and pressures.

pacman1969

yea forgot to say have adj coilovers all round with 800lb springs up front an 700lb springs in rear.and rufly 200 or so hp(no dyno yet).

mustanghammer

iTrader: (3)

On a strut car, static camber with a Hoosier is 3-3.5 degrees. On a car with double a-arms static camber may be less. It depends on how much camber gain the suspension has. Hoosier should have some guidelines on their site. What ever you end up with you will want to follow their hot tire pressure suggestions. At this p0int, your best bet is to pick a base line, chalk the edges of the tires and drive the car.


You may get better input on car setup from a forum dedicated to the chassis you have. The fact that your car is rotary powered isn't relevant to alignment, spring rate and sway bar choices.

pacman1969

yea im on a mg site....but no one running a custom set up like mine....but i have goton there imput also and ill take everyone advice into account when i try my first set up. i belive in getting all advice i can when im not sure of what needs to be done...then using that to make my base setup.

farberio

iTrader: (7)

Wait I just reread this, 275s on a midget???? What will your total weight be?

Gian

iTrader: (3)

That's petty stiff spring rate on both ends. But that depends on what the ratio is from actual spring rate at the wheel. I'm guessing it's not 1 to 1. Being it's an double A arm on the front.
Still that seems really high.

I know I'm running 300lb on front of my 1st gen (@2345lbs) 150lb to 200lb on the rear, and was running 200 to 250 on the front of the 510 (@1790lbs) with 850 on the rear (rear had a 4 to 1 ratio)

pacman1969

my a arms are probly half the length of yours is why the high spring rate,my car itsself is only a lil over 11 ft long and 4.5 feet wide and thats the outside of the body....in stock form you can almost haul a mg midget in the back of a long wheel base pick up ! everything is really tight everywhere on a midget.my narrow racing seats touch the doors an are only 3.5 inches apart from one another.im 5-10 ft tall an my head sticks above the windsheld 2 inches!! but its a blast to drive!

pacman1969

shooting for 1300lbs and yes running 275/35/15 hoosiers.there 12 inches wide with a low profile.....24.5 inch i think.

23Racer

After spending the last year working with a tire company doing development testing, I will now always listen to their recommendations first. For example, as the tires I am using are closer to a bias ply in construction and seriously lighter in rotational mass and have a totally different sidewall construction. I tried doing a few things then spent some time with their race engineer who told me what to look out for in the way of camber/ caster/ toe/ tire temps etc...

What I am concerned about is that you are talking about a very light, big tired car with heavy springs, unknown shock valving, bars, suspension camber gains etc... You need to get the tires up into their operating temperatures as quickly as possible and not over heat them during a 1 minute run. I saw what was being recommended to a Time Attack guy and there is no way I could run those settings as they would eat the tires up very quickly. They were talking excessive cambers and toe settings just to heat up the tires quickly and to h3ll with tire life. First, get all the information on your car that you can. Then call Hoosier, talk to their race engineers, explain what you want and your goals on tire life and do what he says. Then remember that when you change tires, heat cycle them a few times, everything is going to change. You are talking about short burst, high transitional requirements and straight line accel and braking requirements. Totally different to track racers and I expect very different settings.

We listened to our guy, set the fastest race laps during a race this past fall, led the race overall, set fastest race lap in the first hour then dropped back to second place overall and stabilized there until we screwed up our pitstop.

Eric

pacman1969

275/35/15 hoosers





hers how i solved my coilover mounting problem....its 1 inch tubing with 1/8 inch wall.

pacman1969

made a call to a buddy thats done this for manny years,and won a few nat races in the past.he says to start at neg 2.0 all round an test an adjust acording to car handling. he has built manny a winning cars so ill do it his way....and he has a shop with all the goddies to do it with. years ago he helped build a bugg eyed sprite (basically same as mg midget) with a 13b that was supercharged,they ran it for severial years an won every race i belive....never heard of a supercharged roatry ! anyway...he said it dyno 453hp at wheels an was a beast to drive an 1350lbs!!! car ran great years latter when sold an never had issues (after all sorted anyway) an still hadnt been rebuilt. some one over seas bought it an hiil climb raced it...supposed to be a video somewhere.

farberio

iTrader: (7)

I am with 23racer, good luck getting the tires up to temp!

pacman1969

thanks for all the help.....just gonna start an neg 1 an 0 toe an see what happins...test...turn...repeat! not worried about tire wear because its trak car only an we only run 10 races a year with 6 runs a day....so 60 1 min runs per year,most our guys get 2 seasons per set of tires with agressive settings for such short runs.they run a season an take off an flip on rims and run 2nd season.i can see where i wouldnt need such agresive settings if i was on track longer....but it is what it is!

23Racer

I totally get what you are saying. Let me put it another way. What does Hoosier say about your compounds sweet spot operating temps? Getting the tires into this zone as quickly as possible is what's required. You may want to keep the camber in the -1 to - 2.5 range, but dial in some toe out to get the tires working harder faster. This will also help your turn in, braking while turning, Ackerman etc... Also, you may want to play with your caster to get as much loading on the inside turning tire as possible. This will also heat up the tires quickly. I wouldn't do any of this for a big track car, but for a Solo 2/ Slalom car, I would look into it. All the alignment settings are designed to get the tires onto the temp working zone and not overheating them while on track. This also includes contact patch control, camber gain control and driver feedback.

Eric

pacman1969

thanks Eric ! finaly someone compleatly understands what im doing and how short of time we have to do it in.i understand everyones point of view....but most of it dosent go with exactly what ill be doing on track in such a short time and distance,dont get me wrong...everyone made a good point,but i dont think most quite understood what i was saying about track times ect.our best setup is in a parking lot best described as half the size of a standard wallmart.....verry small!its verry diffacult for us in arkansas to find a spot to run that we can actually afford. if i could only winn the lottery id build us a perm track !!!

j9fd3s

iTrader: (3)

no real auto-x experience here, but i have talked to a tire engineer...

i would start with hoosiers inflation recommendations, and leave it alone. then for the alignment, start with zero toe and then;

for camber, either use temps, or just run it on a skidpad with and find where it grips best.

after that play with toe, we've found that front toe does nothing, but even a miata is twice as big as your car... generally we run zero toe, but again, we're running a huge miata, and we want a little understeer so they can mat the gas a little sooner.

also you may want to either run wider wheels, or skinnier tires, we started with a 7" wheel, and have run and 8 and a 9, and the 9 is better.

pacman1969

yea my buddy jhon runs a 90 miata with 13inch aloy wheels thats 12 inches wide with 1.5 an 2.0 neg camber with a lil toe out...dont remember how much,an also adj coilovers with 450lb an 600lb springs an it sticke like crazzy ! with my 12a bridgy my goal is to stick like him and i should be in the top 5 fastest.

j9fd3s

iTrader: (3)

a happy tire is a fast tire