Drag Radial launch question with Vids

I have been running my truck for the past year trying to sort it out. Took it to our local 1/8th mile track to work on the short times.

Truck is 3,300 with me in it, boost controller, ladder bars, Afco dbl adjustable on back re-valved by Mencer Motorsports for radials and single adj QA1 on front. Fronts are 3 clicks from full loose and Backs are full loose on extension and about middle on bump. Tires are 315/60/15 ET Pro with 17 lbs air.

Prior, I have gone a 1.42 leaving at 3,200 rpm on 4.5 lbs of boost and ran out to 9.91 at 135 on 14lbs of boost. I believe the truck should 1.29 when all said and done. Well, testing didn't get me close and I got worse. The track prep seemed to be pretty good, weather was a little hotter than I thought it would be, but wouldn't affect 60fts much. I tried to leave at 4,200 rpm (first vid) and then lowered it to 3,800 rpm (second vid), leaving the boost controller where it was.

I have an idea of what I think the issue/resolution is, but I would like to hear the experts (as I am know where near that).

First Vid I spun pretty bad and only went a 1.8x 60ft: https://youtu.be/gLF5ay9dIcs
Second Vid I lowered to 3,200 rpms and still spun and went a 1.56 60ft: https://youtu.be/COn8PqhZ2AY

Thanks to Scotty (member here) for the great slowmo vids on his new camera!

I’m not an expert and am just diving into this myself but to me looks like you have to tighten the front to leave at the higher rpm. It is hooked until the front topped out abruptly, before the rear had any real chance to separate.

Good evening:

Maybe a little less air pressure. I am on a 275 MT radial and started at 17 or 18 PSI. I am down to 13.5 PSI now to get the car to hook consistently. Extension on the rear shocks (single adj) are 2 clicks from full loose.

John

Have you treid a bias ply of the same size on your truck yet? If not, I would, and have on less than good tracks

I am far from an expert but you have almost zero separation in the rear and I agree with Blusmbl that the front is to loose. I would tighten the front down some first and see what the rear does from there.

That truck is awesome, I have always like it!

No claims to knowledge here, but I watched your vids multiple times and something doesn't look right to me...

Then I pulled up this NHRA Stock Eliminator video and watched a bunch of cars making passes: https://www.youtube.com/watch?v=htn-mn4lCOk

The only "conclusion" I can come to is your car seems to be wasting a lot of energy off the hit... you can see it jerk on the hit, then it doesn't move cuz it's just wadding up the tire at first. Then the front end kind of bounces like it's too loose on the compression after it extends... and your front wheel looks like it's just flopping around, too.

What size rims are you running? I think they're too narrow for that size tire.

What hole are the ladder bars in in the crossmember? How many are there? Are the ladder bars level or pointing up? I agree with slowing the front rise but you have NO rise in the rear. You have to plant a radial hard and stay on it.

First off this is good video. Others take note. Two things that I see. The front is to loose. There is zero tire spin until the front tire is off the ground. There is very little seperation in the rear. Raise the ladder bars to increase seperation. Then control that seperation by tightening the rear rebound. If you hit the gear icon on You Tube you can watch the video in 1/8 time.
Doug

Again no guru here and different set up but this is my mates RR with 10x29's@17psi, 8" wheel, caltrac/mono's rear with calvert shocks on 7 tight, 20yr old 90/10's up front , 3800lb car, mega block+11" drums and heavy street wheels/tyres, could be much better, some wasted motion there as well but not as bad as your truck when it tops out unloading rear, he's gone 1.42 60 best, and yes hit the tyre harder by moving the bars up and control the rebound with the shocks to keep tyre planted, tighten the front.


https://www.youtube.com/watch?v=9tnu9cSnf2U

You need a lot more rear rise, then you need to maintain the rise some, radials need to be hit hard / planted to the pavement to work best. Are they radial slicks or radial streets ? Can you raise the front eye in the ladder bar ?
My experience is with Caltracs and radial slicks, so no expert at all with ladder bars, but we were hitting a bias ply way to hard with our set up, despite the theoretically least aggressive settings. Changed over to radials and instantly picked up across the ticket. We also have Menscer Radial valved rears, we switched to Santhuff fronts from menscer / afco. The Santhuffs are a superior unit.
Below is a pic from the last pass of the season, basically testing stuff with new 3.73 gears in the dana. We run around 20lbs in the rears, though we have gone as high as 22lb on a hotter track. We've been 1.32 putting the fronts down before the 60ft, and 1.39 on the backs. car weighs over 4000lb w/d.

Nothing to add that hasn't been said already. Agree that the front is definitely too loose. Slow down that front end and it'll drastically affect the launch.

Is it just me or is the rear tire toeing in on the hit? Probably just an optical illusion, but I see it in both videos.

It LOOKS like it is, but it may just be the tire distorting making it appear the rim is moving?

Thanks all who have replied. I will answer the different questions here.

But first, yes, I believe I need to tighten the front shocks! Also want to make sure I am not topping out the rear shocks.

Blusmbl : First post and you nailed it!

gearhead01: I am still playing with pressure a bit but based on what I have tested, air pressure is close.

Cab_Burge : Do not have a desire to ever go back to bias ply!

Bad340fish: Thanks for the compliment! Tighten the front it is!

Brad_Haak : I don't see it wadding up the tire and being a radial, that would be very tough to do at 16.5 lbs of air, but I will double check. The rims are 13". The front "action" you are seeing is the result of bump steer. Not much I can do about it with the stock front end.

fbs63 : I have the bars up as high as they will go but don't remember the plotting. IMO, the rear does separate about 2 inches but then when it starts to spin, it looses the separation. But....I do wonder if I am topping out my shocks. I will check that.

dvw : Yup! Slow the video down even more? lol

rb446 : Maybe the rear shock is too short..have to check that

Tig : You need more help than I do, but for a different issue! They are Radial Pro tires. The front of the ladder bar is as high as it will go. I may need to invest in some good D/A front shocks vs my single adjustable QA1.

an8sec70cuda : Chip!

justinp61 : Illusion. If it is moving at all, I am in big trouble! The truck goes very straight and the beadlocks helped a bunch!

I had two sets of M/T ET Street tires, one set of radials and the others were bias ply, same size, 315x6x15 on both, ten inch rims.
The radials were quicker (from .012 to .18 ET) and faster than the bias were on a GOOD track, not worth a hoot on the average no prep track or on the street, once they started to spin I had to let off to get them to stop spinning and going up in smoke
The bias plys would spin maybe from a 1/4 turn to maybe 1 3/4 turn and the hook on the same tracks or streets that the radials would not hook on at all
I did not try to make that car hook on any surface on the radials , I'm sure that there are cars that will hook well on radials on the street and average tracks but I wasn't one of them
My Duster weighed 3450Lb. with me in it and had 50.3 % weight on the front tires and 49.7 0n the rear tires, ladder bars with Strange Engr. double adjustable coil overs with 300 lbs. springs, stock 6 cylinder torsion bars up front with double adjustable front drag shocks, 1.42 best 60 ft. times
I ran big bias plys only on my last S/P car, 14x32x15 and 15x33x15
My new car will get 16x16 inch rims with either15x33x16 or bigger rear tires

100% without a doubt the fronts are waaaaay too loose.

A good rule of thumb is you should try to get between 1/2 to 1 full rear tire revolution before it starts to pick up the front tire off the ground.


The rear MIGHT need more separation, but start with the front first. You might find the rears don't need any change. It's hitting the tire decent, so it's not too far off.

It'll only need more rear separation if the front's don't fix the issue.


For what it's worth, High boost/low RPM, was WAY WAY WAY better than Low Boost / High RPM in my car. 22PSI was worth 9.50's@142mph on my car @3700lbs. That was leaving on 12-14psi on a 275/60, 3.55 gear, and 727 trans, good for 1.37 60ft.

Here is a good example of DVW's car.

Notice how far out it gets before it's got daylight under the front tire. Watch the stripe on the rear tire for rotation... somewhere between 1/2 and 3/4.

https://www.youtube.com/watch?v=rC7EASI6ihY

As said front is way to lose and for a radial I would think more rear separation would be a good thing. Check to make sure its not topping out in back for sure.

oh yeah I thought you sold this thing

Very True, we are into 5 figures now repairing stuff from several big wheelstands , the car isn't even that quick I don't know if its a Caltrac thing, but we have tried tightening the front up and / or limiting front rise to stop the wheelstand. Always ends up knocking the tyres off or rattling them some.
We can spend most of a qualifying day chasing our tail if we get it wrong. We cant take any more rise (anti squat) out of the car mechanically, it just seems to need to have a loose front and anti squat in the rear to run it's best. We're going to have to get a handle on it quick with potentially an extra 700 hp (bigger engine + 500 hp N2O dual fogger). IF we ever bust out of the 8.50 cage cert, we will make the rear more adjustable for ride height next time round but keep the caltracs and small tyres.

I did! about 5 years ago and then bought it back about 2 years ago and let it sit...again. I just started to play around with it this year and my son is starting to get interested in it so that makes it better.

I am in the process of getting all the measurements, etc., as we speak..

An easy fix...?

Nice videos. It's really spinning which makes me wonder how much you'd gain making it work. What are the incrementals?

Awesome truck, by the way! I should've mentioned that first. Totally agree about the radials, it makes them so much more confidence inspiring to drive. Only drawback is they don't work as well for no prep type stuff but it seems people are getting them to work on those surfaces now too. The guy who won the small tire class at Roadkill nights this year was on a radial!

A couple of weeks ago in ok air (78 degrees, 55% humidity) on 14.5 lbs of boost it went: 1.44, 6.29@109.96, 9.91@134.43. It hooked but I was leaving on only 3,200 rpms (4.5 lbs of boost). On the big end I was experiencing a "slight stammer" which turned out to be spark blow out. I resolved that but these latest passes were only on an 1/8 mile track and I was ok with that since I wanted to work on my 60fts anyway.

The biggest limitations are the small cam (.220/.520) and "cheap" turbo. But then if I upgrade those 2 things, my stock block becomes the limitation! "One Day", I will move to the Gen III Hemi platform.

Once you go Radials, you never go back!

I'm interested in seeing how the ET Street R compares to the original ET Street Radial on my '73. From what I've read, the current S/S is basically the original version w/ additional grooves for water channeling. The "R" is supposed to be the street-legal version of the "Pro" with a different sidewall construction. I still have a couple of new sets of the original 275/60s to burn through first.

Brad, my understanding is that the Pro have the "best" compound. And since the person who does most of the tuning (Eric Stubbs) runs 4.0's on 275 R's, I just copied him! Once I blow through this set which don't have a lot of passes, he wants me to go to a smaller tire.

This was Eric the same day I went:

https://www.facebook.com/100000100240304/videos/875890863412940/

That's my understanding too. The SS and R both have the same compound, but the R has a softer sidewall. The Pro is better than both, and is technically street legal, but has no rain grooves at all.

I had to go dig this up, since I couldn't remember where the differences between the various ET Street versions are: https://www.streetmusclemag.com/news/inside-mts-new-drag-radial-lineup-pro-bracket-et-street-ss-r/

Oh, c'mon, it has TWO, TWO "rain grooves".

Perfectly fine for street driving.

From what I've been reading you need more anti squat not take it out, the more rise you have the more it will tend to push the car forward and keep the front down. fwiw... Same for Duncans 622 Hemi@1000hp+, he tightened the fronts to max and it wasn't enough so he's just staying out of the throttle some to get it to go down from what I see. Try looking at Kevin Wilson on u-tube, the chassis man, could help you some if you sift out the elementary stuff.

Agree - to a point - there is too much anti squat un-intentionally designed into the car and not enough weight over the front, it's just the way it's ended up. Even on the least aggressive rear settings mechanically, it will kill the sidewalls in a bias ply slick, way before the tread is worn out.
It appears current thinking is more weight over the front and plenty of rise for radials, the no prep radial set up you tube vids are quite interesting. I've posted some you tube stuff by Kevin some while ago on my facebook page, I even think you may have commented on it

the no prep radial set up you tube vids are quite interesting.

Yeah was watching one myself where the back of one of those cars rises up some way down track presumably when the power really comes on to stop it going airborn. Hope I'm there to see you runnning1500hp in that car. I know the l/spring Digby Dart has gone 4.24@181 on springs but thats a whole different ball game.

Totally legit, lol

So at drag week this year I wandered over to the Mickey Thompson tent when I was wandering around waiting for things to happen. I asked them why the 275 Pro was directional, he then proceeded to tell me that it is because the rain grooves are only designed to push water out one direction lol. So I assume they Probably up the safe rain driving speed from 9 mph to 11 over a standard slick.

I really like the radials though, they wear good, they hold the same air pressure for MONTHS and the car drives soooo nice.

I drove my Dart to work one day and it rained, when I left it wasn't raining but the roads were still wet. I run the ET Street R's with the two full groves around them, needless to say it was a white knuckle 35mph ride home. I never drove it again if there was a chance of rain. LOL

Gotta drive it like a sprint car!

One of these is not like the others... it's the one that's not legal for street use

The 275 Pro Carries a DOT Number. It is the most illegal looking one of that bunch.

I actually like the 275 Pro a little better than the pro bracket radial. They hold the rim better for some reason and I believe the sidewall is a little stiffer and my car seems to like that.

I was gonna say the ET Street PRO isn't legal. It has the DOT stamp on it, but says on the sidewall not for highway use.

Brad...the ET Street R seems to be better than the old style ET Street. I got the new tire 2 years ago and have been really happy w/ them.
I use the 295-65. The 275-60 looks stupid on my car. I'm used to the look of the bigger tire and the stance of the car doesn't suit the short tire very well. The 315-60 doesn't fit on mine.

X2. Up here nobody cares about the not for highway use on the tire, it’s allowed in any of the street tire classes. It’s the tire all the x275 and LDR people use too, it’s that good!

I've had to point out that DOT number more than once (usually at the track in "street tire" classes). Pont of reference: it is directly under the "M" in Mickey Thompson.

I got caught late one night in a light shower and it was sketchy as hell trying to get home!

I have been pulled over a few times and none of the cops around here even give them a second glance.

They drive nicely on the street, even at 18psi! I used to air them up for street driving but don't bother anymore because they work fine.

My '73 is already going to be ticketable for at least one item per Virginia regs, but I'd rather not have a laundry list of things from which to select, should a local LEO decide to give it a close(r) inspection.

This right there, ^^^^ do what you have to to increase the seperation, use the rear shock to control it.
Front , needs some travel and a really good double adj shock to control it.

You are at the point that GOOD shocks are whats going to make the car/truck work very well. Getting the ladder bars to point up will help a lot with the seperation. Also as mentioned, make sure that the rear shocks have enought travel to let the rear seperate

Thanks! I have 5 1/2" of front travel and about 3" of rear shock travel, both I believe are enough.

Front shocks were on full loose but will tighten to 6 clicks from full loose (only single adjustable but may have to go to double)
Rear shocks were full loose on extension and 6 clicks from full tight on compression

If you do go to D/A get a real good shock. I'd recommend Santhuffs. I had more $'s in a pair afco's after Menscer modified them but the Santhuff's are noticeably better. You wont have to get anything else down the road

And, yet, it looks like you have very little extension. Did I read correctly that your truck has ladder bars that can still be adjusted higher in the front?

3" travel in the rear is borderline. IF you can get more, get it.
Again ill repeat what Monte always preached. " Shocks make or break it." You need a good shock because the rear is loose and extends fairly fast, you need a stiff compression to keep the tire planted (radials like to bounce back up if not held down) The front needs a good rebound to let the front travle at the correct rate to keep the back planted.

You are at the beginning of needing good shocks to make it run really well


One more thing.....with ladder bars the spring rate means a lot also with seperation. The lighter the rate the faster the rear housing will move ( stored energy) SO if you have a 130lb spring now a 110 or 95 will help the suspension seperate

I have ladder bars that are up on the top most hole. The rear shocks are DA Afco modified by Menser. IFIRC, I have 110 lbs springs in the back. I can't get any more travel due to the shock length.

My next move is tighten up the fronts 6 clicks. I will continue to tighten up as needed.

I have been watching a lot of DR cars and while they do have some rear separation, it doesn't appear to be more than an inch or 2.

I'm assuming you have Afco 3850's with 5" total travel. With 2" compression and 3" extension. A weaker spring like a 90# will shorten the compression distance at stationay ride height. Giving the shock more extension distance. Greater stored energy as a dded benifit. I start full tight on the fronts. I've had QA1 stocker star and Afco doubles with stock valving on the front. Both needed to be nearly full tight.
Doug

Just for a baseline . Get a digital angle finder . Put it on the rocker or frame , then check the bottom of the ladder bar

So you have made me think more... I was wondering if 6 clicks from full loose was enough.. Was thinking going at least 8 clicks (which is halfway). Now, I think I will go at least 8 clicks. I have about 1" of compression on the rear shocks so about 4" on extension.

Did that a little while ago. IIRC it was 4 degrees up.

If the chassis is level , and the bar is up 4* the is very good and that thing should have plenty of separation . For comparison, my car is 1.9* up with a level rocker . And it works pretty good on a 275

I checked again and against level ground, it is 3 degrees up.