Tire spin or wheel hop

Discussion in 'SRT Hellcat Racing Forum' started by Top Cat, May 7, 2015.

  1. Top Cat

    Top Cat Gold Member Hellcat Car Club Gold Supporting Member Fastest Cat/Record Holder HCC Charter Member

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    I copied this from a fellow racer on another forum, it is filled with a lot of information most will never read or figure out on their own, thanks MOPAR MAX

    Difference between tire spin and hop, illustrated

    Thought I’d share some tips for folks learning to play at the drag strip with drag radials. There’s a ton of misinformation out there, and I’m sad to say that a lot of it comes from fellow racers. We are very methodical in our approach to racing, we datalog 15 channels through our Diablosport Trinity every pass down the track, we shoot Blu-Ray resolution video of every launch with a high-end pro video camera on a tripod. We track every tiny bit of info in our paper logs for every pass, including laser probe readings of track and tire temps. One reason we do this is because we are so often testing products for reviews in the magazine that we need to have hard data to fairly evaluate the tested product. The other reason is because we like to win. With an engineering background, I want to know exactly what happened on every pass and it will keep me up at night when there’s a pass with a result I can’t quite explain. I usually figure it out eventually.

    One of the most common areas where people make mistakes is with their tires. The burnout and tire pressure are among the most critical variables that impact your launch and thus your RT, ET and consistency. We have tested tires from most of the manufacturers, we have tested street drag radials, track only drag radials, bias ply drag slicks, we have tested 17” rear radials and 17” rear bias ply slicks. We have tested 15” rear radials and bias plies. We have around 1,600 quarter mile passes with detailed computer and paper logs and video. I think I can say that we have more actual experience and data then the average sportsman bracket racer.

    So, some tire basics. You want the widest and tallest tire that will fit your application. Every millimeter of sidewall height you gain can help you launch, you need the sidewall to wrinkle and help absorb some of the initial hit to the pavement. After you break in a new set of tires with that first big, John Force style smoking burnout (always see if a friend or someone can get photos of that for you, you only get to do it once per set of tires!), then reduce your burn outs to the bare minimum. DR tires don't like a lot of heat, some heavy hitters don't even do a burn out; they just dry spin the tires after avoiding the waterbox to scrub them clean. If you do a burnout and you can see near your tires in your sideview mirror, you want to get out of it the instant you see the first wisp of haze off the tires. More than that is overheating DR tires. I know, lots of folks are going to tell you bigger equals hotter which equals better stick. But, we talk regularly with the development engineers at Mickey Thompson tires. We have a close relationship with MT and were even the very first racers to hit the track with their new Pro Bracket Radial back in February—we gathered and shared data with them. So who are you going to believe, the tire engineers or some stranger at the track?

    The fact is, the primary task you’re accomplishing with the burnout is cleaning the tires. You’re scrubbing off the rocks and stones and the thin layer of oxidized rubber that builds up even between rounds of competition. After your burnout, when you stage your tread’s surface temperature should be between 0 and 20 degrees above track temperature on the starting line. Zero is fine, 20 is the maximum. In hot weather closer to zero above track temp, in cold weather up to 20. Anything more is both wasting rubber and risking reducing your traction due to overheating.

    If you’re doing good burnouts and your still losing traction at launch, then one thing to try to ascertain is whether you're spinning right at the hit, or rolling a 1/4 or 1/3 of a tire circumference off the line and then spinning. The difference is if you spin right at the hit, that's true spin. If you spin 8 to 14 inches after the hit, then it's wheel hop. Best way to tell is have a friend video tape up close near the rear wheel. You'll see it if it's true spin right away, it just starts spinning before the car moves. If you see the car start to move just fine, then it spins, that's hop. Hop (which leads to shake) occurs when you "wad" the tire, that is, the tire wrinkles a lot and gets a "fold" running across the tread and that fold rolls under the tire and causes the traction to break loose.

    Most DRs like more tire pressure than people think. On our old MT Street Radial tires, we ran 19-20 lbs of pressure most of the time and 21 on a good track. On our new MT Pro Bracket Radial we run 22-23.5 pounds (and remember, we have a huge sidewall on this 28x10.5/15 tire). If you run too little pressure, you'll be prone to wheel hop. Too much and you're prone to spin. The instinct is to run too little pressure. The best thing you can do is to go to a test session with a friend. Have the friend video each launch and do a series of launches at ever increasing pressures. Start at about 19 pounds, have your friend say out loud what pressure you're at so it's on the record on the video for later. Next pass go to 20 lbs, then 21, 22 and so on. What you're looking for is the pressure point where the tire just spins right at the hit. When you find that point, go back down one pound and try using that as your base pressure.

    When the track is really well prepped, the tire needs more pressure to help it resist wadding up and hopping. On a bad track you can go down from your base pressure if you have to, with less traction the tire is less prone to hop and a pound less pressure will help the car stick. Hope this helps.

    THIS LOOKS LIKE A GOOD LAUNCH, RIGHT?:
    Kathryn_Rau_TNT2_0376_Web1a.jpg

    NOPE, A SPLIT SECOND AFTER THIS PHOTO THE TIRE WENT INTO HOP/SHAKE. THE PRESSURE WAS TOO LOW. AS YOU CAN SEE WHERE THE ARROW IS POINTING, THE TIRE 'WADDED' UP--THERE'S A FOLD WHERE THE ARROW IS POINTING THAT IS SO DEEP IT RAN ACROSS THE TREAD FACE TO THE INNER SIDEWALL AND CAUSED THE TIRE TO SLIP AND STARTED THE WHEEL HOPPING. WE ADDED MORE PRESSURE AND THE NEXT LAUNCH WAS PERFECT:
    Kathryn_Rau_TNT2_0376_web2.jpg
     
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  2. B5 Blue

    B5 Blue Platinum Member

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    this is very good information Top Cat thank you
     
  3. Nycsrt

    Nycsrt BANNED

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    Topcat some info you
    Forget is you need to do
    Few burn outs on different psi to see which has biggest contact patch
     
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  4. PlumTexasCrazy

    PlumTexasCrazy HELLCAT LIFE MEMBER Hellcat Car Club HCC Charter Member

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    Great Read and info Top Cat!! Thank u!!
     
  5. dragrcr

    dragrcr Gold Member

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    I appreciate what this guy is saying. But all the tires he gave examples of are not the same. For instance a Race Drag Radial Pro needs different pressure than a Bias Slick or a radial slick VS a DOT Drag radial etc. Also I have to ask does his car run any kind of timing retard or other strategies to soften the hit? A lot of those cars have completely different starting line ratios (numerically smaller) than we have as well. Plus think about this. I bet his Car is 1000 pounds lighter? I am just guessing because I am not sure what car he has 1600 runs on. I am just saying a MT Pro Bracket Radial is not the same as an ET Street "R".

    I run the MT ET Street "R" 305/45R18 and I can tell you 100% if I use 18 PSI at Irwindale I will be spinning. Also it really does seem to help if I do a more aggressive burnout when the chips are down (late in the day with a Camaro in the other lane).. So, I would not say a big burnout will cause tire spin. It may lessen efficiency slightly and cause unnecessary wear for sure.......I actually called Mickey Thompson and for that tire they recommended a pressure range of 12 to 16 PSI. I will admit they did say one aggressive burnout to start the day and then a much milder burnout after that. And that does seem to work as a general rule.

    Top cat, I have seen you post that the track will go away sometimes when you run. So, that is when I would lower my pressure and do a little better burnout. But you said you just go home for the night. You run 2 psi over what MT told me. Yes you will be faster on a perfectly prepped track as you have demonstrated.

    My BEST 60 foots with that tire I run were at 13.5 PSI and a good burnout later in the evening when the DA was the best. Way more than that article.

    We are talking a stock motor, stock DS, 3.09 gear and the above DR's +350DA , 1.549 and 1.550, just sticks and goes.........
     
  6. Steppenwolf

    Steppenwolf VIP Hellcat Member

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    Interesting article ...

    Didn't see more detail on the above, but can any of you Hellcat tire experts give me a specific example of a "street drag radial" tire versus a "track-only drag radial" tire?

    I'm interested in a pair of large "street" DRs on the rear OEM wheels, if possible.
     
  7. PlumTexasCrazy

    PlumTexasCrazy HELLCAT LIFE MEMBER Hellcat Car Club HCC Charter Member

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    I'm sure Top Cat Can!! He and his wife Linda are in the 9's and not sure what his daughter is running!! All three have hellcats and I'm pretty sure Top Cat has a drag pack challenger also!! I will without a doubt take his advice on anything to to do with the drag strip!!
     
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  8. Steppenwolf

    Steppenwolf VIP Hellcat Member

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    Thanks, but looking for recommendation on "street/highway" DRs, not for strip or track.

    Wanted a pair for the rear that are gripper than the stock Pirelli summers. Also wouldn't mind jacking up the Cat's rear a bit to run larger rears. Want to use the stock wheels, if possible, but I'm willing to switch different rims in to accommodate larger tires.
     
  9. dragrcr

    dragrcr Gold Member

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    Anything that is DOT rated would be OK for street use in a Mickey Thompson or Nitto. The Hoosiers that are DOT rated still say NOT FOR HIGHWAY use. So don't get the Hoosiers. Based on what you are saying I would get the Nitto NT555R in a 305/35R20 for the stock rims. Better yet would be a 305/45R18 on a Weld 18X10 RTS S77B rim. NONE of these tires are going to dead hook on the street. But the tires I suggested will be way better than the stock tires.

    No need to jack the car up for the 305's on stock rims or the other setup I suggested. At most you will need the wheel tub mod and for the 18X10's you would need shorter sway bar end links from HHP that are not too hard to install.

    .
     
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  10. Steppenwolf

    Steppenwolf VIP Hellcat Member

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    Great info - thanks!
     

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