turbotrks

So I know there are many factors, but I'd like to know what change i could make that you guys think is the most likely to improve the stability of my mustang on the big end of the track. It wasn't an issue when I was running a little less boost and trapping under 150mph, but now that I'm going over 150, its pretty hairy at the end of track.
​​​​​​ Here are the things I'm thinking are likely contributers:

​​​​​1. I have VW sized radials up front (28 x10.5 et drags in the back). I've read for hours about the topic of mixing radials with bias ply tires and many people are adamant that you cannot mix the two, but then there is another crowd who says that it's all wives tales and salesman tactics and they have not had issues mixing the two. Do I need to get some legit bias ply skinnies?

2. Rear wing. I do not know of many if any fox bodies trapping over 150 that don't have a wing, but I really want to keep the car as "streetish" as possible, and don't want to drill holes through a paint and body thats in excellent condition. How much difference do you think a wing would make in the top end stability? Crazy thought, maybe I could brace up the deck lid several inches or more to effectively create additional downforce to see if that improves stability before i get a wing?? Of course it would not have the flat vertical sheet metal capping the sides (as seen on a wing) which probably helps act as a tail and helps stabilize.... Idk

3. Bump steer. I don't think this is the problem, because it actually did have some crazy geometry to the steering that I fixed over the winter. But fixing this did not seem to make any difference with regard to the high speed sketchiness.

Do you think I need to do something about one of these three items or is there something else I'm not thinking of?

Blown06

iTrader: (32)

I had the same issues with my 2006 Chevy Silverado. I used to run the thing with no bed cover, no wing, tail gate installed and a set of 29.5x10.5 ET Drags on 12" wheel. Around 135-140 mph the thing would get just enough lift in the rear that the tires would just start to loose traction and the truck would just start dancing around. Took out the 1000', 1320' and 1320' mph cones and said **** this. Not going back to the track until something is done. No sense in ruining my super nice truck.

Send the truck over to Madman and he built me a killer bed cover and wing out of carbon fiber. While he was doing that, I changed to a 29.5x10.5 stiff sidewall ET Drag and also started using tubes. Once those changes were made, the truck now runs straight as an arrow. So far I have been as fast as 154 mph and it is a joy to drive on the big end.

Here are a couple pics of the bed cover and wing (I like to show it off cause he did such a good job on it and it looks killer). I also like to ***** out pics of the truck. lol

a05c

A radial will stiffen up the rear a ton. You're probably feeling the softness of the sidewall.

Old Geezer

iTrader: (3)

G body here.[86GN]
Wandering about at 140+. MT bias slicks, 215/65's radials ft.
Brought the car to full wt, driver in place, doors closed.
On the align rack. [4 wheel].
Checked specs at rest, printed it. Raised 1", printed it, continued til ft wheels were free.
The loss of caster was significant. Actually went neg. We set max caster, min toe, camber.
resulted in "on a rail" ride.
We shot video @ 660, 1000, and finish line. The ft end was still "up" at the finish. That's when we did the alignment.

turbotrks

You're right, that is some beautiful carbon fiber work! I'm sure a wing would help my situation, but I will leave that as my last resort option since I don't really want to drill holes and my paint/body just yet.

turbotrks

Over the winter I basically did what you are saying but in a more caveman fashion with a jack and my tape measure. That is when I found that even though my toe was properly set while the car was sitting, it was towing in drastically as the front of the car raised up. So I changed the elevation of the tie rod connection to make them parallel with the control arm. Now the tow stays almost identical from when the car is sitting to when it is fully raised. I was shocked that fixing this did not make any improvement on the handling. You mention that your caster was almost going negative. I'm confused, wouldn't it be improvement on the handling. You mention that your caster was almost going negative. I'm confused, wouldn't it effectively be gaining more caster as the front of the car raised up?

turbotrks

Yeah, it's just nice having a slick though and not having to worry about traction issues on some of these poorly prepped tracks. Maybe a stiff side wall slick? Are there any you would recommend?

ATwelveSec02Z28

iTrader: (17)

Exactly

Put real front drag tires on, and radials out back....

My junk is 58% on the nose and still steady as a rock going 148+ to the 1/8. Not getting any signs on top end slippage with driveshaft speed.

ATwelveSec02Z28

iTrader: (17)

3754X

ProDrag Radial

ProBracket Radial (3355R 28x10.5)

There are tons of Radial options. If a Radial isn't working it may need suspension help

turbotrks

OK, thanks for the help. I will start by getting some real front runners and see how much that helps and if it's still an issue I'll get some radials for the rear.

What front runners would you recommend as a good bang for the buck?

turbotrks

I have my eye on the MT ET front runners. The VW tires I currently have are 25 inches tall.
Which of these three sizes would be the most stable?
26x4–15
25x4.5–15 or
24x4.5–15

ATwelveSec02Z28

iTrader: (17)

26 x 4

turbotrks

Really? I'm glad I asked, because I would have assumed a shorter side wall would be more stable. What is the reason a 26 x 4 would be more stable? Not arguing, I'm just curious.

a05c

We use a MT 28x10.5w stiff sidewall slick on low prepped (non radial) OLS events. It's went 4.70's sitting on the SR2 in the BS3, But I wouldn't be opposed to trying the Pro bracket radial for the lower prepped tracks and has been said that it's pretty forgiving as compared to a Radial pro.

Takes a control arm bar change, weight movement to the rear off the nose, shock adjustment, BS3 SR2 (Traction control in BS3) change for the slicks.

I love radial racing. Plant the tire, and ramp the timing in as quick as possible. Definitely different than slick tire racing, and more fun to me.

turbotrks

OK, I'll probably resort to a stiff side wall or a radial if I still have concerns after changing out my front tires.

turbotrks

Does everyone agree with ATwelveSec02Z28? That a 26x4 would be the most stable of the 3 different sizes I posted above? Just want to make sure before I order them.

Nathaninwa

I was running the new etstreets with a radial front runner. Car was solid to 160ish. Having traction issues I went Hoosier 28x10.50 stiff sidewall and car went sketch above 140. Bought the DS2 bias front runner and car is only slightly wiggly above 160 now, I bet a little more rear tire pressure is in order

Though I would like to try the bracket radials

I run a rear wing and some of them vortex generators along the roof line to make the air not separate from the hatch

Do keep in mind, most tires run small. My 28 inch Hoosiers are 27 inches and my 26 inch front runners measure 25

turbotrks

OK, that settles it, I'll order the 26x4s tonight.

As for the air pressure in the rear, I made some black marks this weekend because I wanted to see what the pattern looked like. At the first 5 feet of the black marks you primarily see the edges of the tires laying rubber and then it turns into a solid black stripe. Is this normal for a properly pressurized tire or do I need to increase the pressure a little? I would post a photograph of the stripes, but I don't know how on my phone.

a05c

How much pressure is in the tire?
Sounds like the pressure is low then when the tire grows the pattern changes

Nathaninwa

Another thing was touched on here is attitude at the track. We want the front end down so it's kinda wedged shaped. At launch a pocket of air can get trapped under the body and not really allow the front to settle so the alignment can be off

I've just installed a front suspension sensor to monitor this

But also remember, when lowering the front static stance, it will affect rear suspension setup and change instant center