Fighting For Traction - Tuning Tire Contact Patch With Air Pressure For Max Bite With Street Rubber
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- Опубліковано 21 вер 2024
- While Slicks and Drag Radials will always have a specific pressure range in which they are intended function for max drag strip performance, normal street tires are constructed for doing things like stopping and turning, so determining the pressure for best starting line bite is all about trial and error
We ballparked the best pressure for the tires on our Mission Improbable Jeep XJ based on their rolling contact patch, but as it turns out, the tires react much differently under load, and our numbers were way off. Here's the process we went through to find out.
#automobile #tuning #street
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Policeman, "Do you know how fast your were going?"
Jeep Driver, "No sir officer, the speedometer only goes up to 85."
@@FerdinandAkin What speedo only goes to 85?!?! 😂
My boat of a Fury shows 110 on the dash and it's half a century older than the XJ...
Correct answer, "About 160"!!! Quote Bert Munro😂😂😂
@@jseal21
See video 7:56
@@paulhoogeveen7353 Worlds Fastest Indian! One of my most favorite movies. Anthony Hopkins hit that one out of the ballpark.
@@FerdinandAkin Thanks. I was about to walk outside and look at my XJ's speedometer. You saved me the walk. 😂
It's comforting to know the WELCOME signs south of the border are still in English 😅
Haha
The buildings look like they were built to US Spec as well.
@@mexicanspec Ole Mexico is really catching up. Good for them 😁
NAFTA. They even took 'r signs!
The signs are still in English close to the border. You have to get further in before everything goes to Espanolish
Can’t get over the induction sound when going WOT 👌🏻
I saw that Cherry Bomb muffler under there,.... Cat delete?
Circa 1972 @ Fremont Raceway driving my parents almost new 1971 Road Runner 383 auto with open 3.23 rear end and Goodyear Polyglas GT G60-15 tires on 7 inch factory rims I was naturally experiencing wheel spin (mostly right rear tire) when a spectator approached me with some advice. He suggested I over-inflate the rear tires to reduce tire spin. The air hose at the drag strip was for low pressure drag slicks so I needed to go outside the raceway to a service station to pump up the rear tires. Don't remember the exact PSI but must have been 40 psi or more. When I returned I found I could leave the starting line at full throttle with minimal tire spin, an improvement from before. Don't remember the exact ET's but very low 15's with the 1971 low compression 383 rated at 300 hp gross. Of course, these are bias ply tires we are talking about. On the other hand, with my 1965 Valiant four-speed bracket racer with sure-grip 4.56 rear end and 10" M & H slicks with inner tubes and rim screws I would only use 10 psi.
I remember back around 70-71 a major car magazine making the same claim about Polyglass tires while they were doing a drag test on a new car. I wonder if any of the guys racing in the FAST Series where they still run Polyglass tires still follow that advice.
What a Polyglass Bias Ply needs, A Polyglass Bias Ply Gets.
22 psi was always my favorite
Pays for the whole speedometer and uses the whole speedometer.
What a fun project, I've historically had a ton of fun in some of the slower cars...
Good job brother
Sounds like my Australian made R/T Charger with 265 HEMI 6 and triple webers on full song , that induction roar is addictive for sure aye Uncle Tony .
In the day, we ran 26-28 psi on 60 series tires and 22-24 psi on 50 series tires for street grudges. 70 and 78 series tires were hit and miss, 28-30 psi was the norm. Like you said, we still had to drive home😂
Freeze frame @11:26. See how far forward your axle has moved. I would carefully inspect the leaf spring bushings.
Probably more axle wrap in the springs than bushing distortion.
My own car on it's street Toyos ran down to 12 psi! But it's running 195/50x15s on a car that's only 760 kg kerb weight (1672lbs) and very light at the rear. So i'm not really surprised!
On the last burnout it still looked like the center of the tire was still swelling out 😮😂😂❤
Stock cars, road racers often use tire pyrometer to measure temperature across the tread (at 3 points of more). the goal is to get even temperature across the tread which indicates the entire contact patch is working equally. - FWIW.
A few pounds down on the left will drop the inner shoulder on the right to even the footprint and the front gets psi to the max for minimum rolling resistance. P.S. Don't forget to have fun like Uncle Tony 🏎️
Story of my life. I should have had 9" but really only have 6" 🤣
@@bw3506 You been talking to my old lady again???
I had 9", but they circumscribed me... out of jealousy.
@@jseal21 LMAO
@@AdamA-pm3yn Ha good one. 👍
I think that should’ve been centimeters
Not a whole lot of weight out back to start with, open diff. and its the side that goes lighter under torque. Makes a lot more sense why it needs lower tire pressures. And dang it Tony, you are making me wish I had bought the 2 door, 2 wheel drive automatic I test drove used down in Galveston back in 2003!
It might sound crazy but try Toyo tires. I was impressed by the grip that they had.
As a former gauge man - and I stress NOT a tire man - what I picked up was that you want to go down in pressure until the middle of the patch just starts to get light and then put a couple of pounds back in.
Hi Tony! Actually, you should also mark the alignment of the tire to the rim. That way, you can check if there’s any slippage of the tire on the rim when you're running such low tire pressures. Peace out.
Not bad advice, easy as a quick swipe.
However its torque output even with these modifications is probably just just under 200 at the rear wheels in 2nd gear. The amount of weight launching and transferring back is pretty low. And the total traction patch isn't too large either.
I mean it possible... but what does it matter if it does move 1/8" on that vehicle? 🤷♂️
When I was in Mexico BURNOUTS were on the menu everywhere...
The only thing everywhere on Mexican roads are speed bumps
That frame rate was perfect
I love it's ( Tony the one man show, no film crew necessary)
I remember some story about my father putting only 9 psi and an ounce of water in some tires at a drag strip.
He was worried about my uncle getting wiped out by a sketchy vehicle.
My uncle said it was loads of traction but nearly uncontrollable once he let off.
I won't leave home without my Ryobi 18v tire inflator.
I think that makes sense doesn't your tire swell at high speeds I'm not sure. Love your videos Tony keep up the awesome work
I've never been a SUV fan. But a 2WD manual anything is fun. If I had it, I would lower it and make it more car-like
Haha yup 😂
I go riding motorcycles with my dad,as he's got a spare Yamaha wr250. It's an on/off road bike and the dry pavement handling is absolutely awesome!
Not that I want to find its limit, but it doesn't do anything squirrelly.
I'd like to drop it about 6" and see how much better it is. That's not going to really compromise the dirt roads that we ride, and it doesn't see a lot of trail use either.
@@MrTheHillfolk the dual sport converted to SuperMoto (street tires & rims) are a dream to drive
Up here, we have to go to Canada to do burnouts. The closest crossing is 127 miles, but if you gotta do a burn out, you gotta grab your passport and head north.
Xj sounds great....and that tune makes it run hard
Practice makes perfect details.
And good tools also
Good Afternoon,
Grasping at straws or teaching us how to get the most out of the only part actually touching the ground? This is useless knowledge to me right now, but I am going to be happy about it later.
Thank you for the wisdom!
Lowering the pressure on one tire tilts the rear axel, moving away from the center to the edge of the tire. Also, the tire, by centrifugation, the center will bulge outwards. I say way lower pressures, like closed to 15psi. The center will cavitate and expand outward with rotational speeds.
In another words, those are street tires, no traction and they are designed for fuel economy.
I will hit the junk yard and get LSD for cheap and a couple of decent drag radials for the track. Swap back with street radials to drive around.
Looks like there is more time to get the fuel adjustments taken care of. Im sure you already have the ignition pretty close because you know the compression ratio, and bore.
(And remember when porting to open that throttle up, its all about that side profile at wide open throttle)
Imagine shorter rear tires. Weight transfer on launch, shorter final gearing, lighter rotational weight, lighter non-sprung weight, and lighter total weight. (And thats not even touching the weight of the rims yet)
3 inch shorter tires than stock made my 91 Jetta diesel drop it's 0-60 from like 15-16 seconds down to 11.5.
It's got 52hp and needs all the help it can get. I'm shocked it can do a high 17 in the 1/4 now.
No rocket ,but it's been improved tenfold.
Uncle, maybe if you lower both tyres, it will bite better on the inner part of the Tyre... I think it behieve like if it was wedged
Mexico, its his story and he's sticking to it.... lol
I use a pyrometer to set tire pressure to try to equalize grip across the contact patch.
Eye opening experience
Thanx , Tony !
Maybe you are at minimum recommended rim width for those tires?
Seriously that runs good, it has no traction but it runs strong.
Tire pressure is just a number. The gauge has it's own calibration, the pressure goes up and down as the burnout advances, if the staging takes long and the air is cold, the pressure drops. Then there's the tire itself. How much thread pattern, how old tire, what type of sidewall. What you really need is three fingers. Your thumb can tell you if your street tire is full enough to go around corners and your fore and middle fingers can tell you if your tire is soft enough to leave the line. Then there's visual. As you drop the pressure the tire sinks. At some point it stops sinking even though the pressure is still dropping. You are now resting the tire on it's sidewall. This means you don't have enough pressure to push the middle part of your thread into the surface. Now put enough air to rise the rim just a hair. Then you'll have about 6-8 pounds to play with, and I whole heartedly recommend to screw the tire onto the wheel one way or another. The sidewall feel part comes at this point. Sticky track, stiffer sidewall, looser track, softer sidewall. This applies to DOT "hard tire". Bias ply "slick" needs temp probes and a lot more pressure than most people think. The flat slick myth comes from hard tail era and continues as folk sets up their 4-links to hard tail. After you've learned how to tune your suspension properly, you don't need to use your tires as shock absorbers. In this particular case, 17 psi starts to create noticeable effect.
Being a ol poor boy from east tn........and no...a 11 second stock mopar......I ran 295/50/15 with around 20 pounds and oh yes....she had the high speed wobbles around 100 in my small block 70 chevelle......never ran slicks but would run 13;20,s at 103-4 street car i drove to auto zone and back to work...tire pressure was the key i only had when i went to bristol on street fights back in early 90,sCar was heavy...3600 easy/full frame/not unibody....but would drop the clutch at 3500/3800.....all on used parts.....the ol chevelle would wobble like jello from rocking at the tailend sitting stile.
I like how the lady in the Ford was still pulling away through the first rip luckily the Mexican border is right at the end of my driveway so I don't have to go far
Very interesting, thanks Tony
That XJ gets awesome gas milage I could never get my Xj Mexico under a a tank of gas . Lol
Next time you get to run at the track just set them at 16 psi and see what happens. I don’t think you’ll have to worry about them peeling off the bead. The sidewalls are probably really stiff on those things
I would have figured around 16 as the best number. That vehicle is very light in the rear with a wider than stock tire and there's not much overhang past the rear wheels to multiply the weight.
Also remember the profile of the tire makes a big difference. Had some tires that have really flat profile across the tire then i have had some that a slight convex to the tread.
Fill the diff with Trans fluid overfill. Get it warm an it will lock up nicely 👌
Depending on weight per tire, rim size, tire width, suspension design, all contribute to the tire pressure
It took me 7 hours of scanning satellite images of Mexico from space to find the secret South of the border testing location. 1522 Sarah Court, Murfreesboro, Tennessee.
Damn bro that's rough.🤠
How timely :D. I got the new slick mounted and down to the sawmill today, slid the turbo 6 cyl deutz and pto output with a 12x12" steel flat belt pulley over to mount the slick on the saw shaft. This is to reverse rotation of the sawmill shaft from the engine and the 30.5" slick should give me about 2.5:1 final drive ratio for the blade. Not much contact opportunity so I was pondering tire pressure, stikum and how hard to side the engine up to the steel pulley. With my 1st try with an old street tire it was losing rpms and rolling smoke before I could bury the blade in a log. I'm not sure how to test and dial it in yet but was picking up some ideas. Anyway, thought you'd get a kick out of other applications.
explains burning rubber smell...greetings from mexico
You are forgetting the contact patch expands length ways as well. So you want the lowest pressure that doesn't compromise the contact at the centre of the tire. Not the other way around.
I once did a skid that went for two weeks.
When the wife is doing laundry she said I've got some pretty good skids 😂
thanks
How is this going to translate when you go to the track ? Because you drove it
a long ways to get to Mexico, and built up a lot of heat. If you drive it a long ways
to the track and build up a lot of heat, and then it sits for a long time while you are
waiting to run, you will lose most of that heat and have cooler tires.
You can get a little heat back by doing a burnout but I don't think that the tire temp
will be the same with just a little burnout.
I used to use a pyrometer to check tire temperatures, not just for overall temp, but for
sectional temps too because it does change across the surface of the tire.
A pyrometer is a great tuning tool for tires.
Take out the bench seat part that's removable! if not removed already or keep it cos load up the people I donno.
When I had 235/75r15 LT tires which are light truck tires meant for half-ton pickups and vans. and Yeah, I had to air down to high teens or 20's to get them to contact patch on the snow and ice where I'm at. Light Truck tires being a stiffer thing with extra layers helps resist rocks and nails. But sometimes with a slow leak I would only notice them low when it's 5 psi! Heeps be Light!
I think possible that the tires in the first few rotations and the last few rotations, the centrifugal force is not as great and the tire has a wider contact area. In the first few rotations of the tire it may not have enough force yet to make the tires taller so to speak and once the wheels gain some momentum the center humps up in the middle more. If you were to give it to many rpms once the pressure is dialed, as a result you would probably get less contact patch because of more centrifugal force would be applied. So I think that's what was happening when they weren't air down as much and they looked like it made contact. I bet the wide of the tracks changed really until a steady rpm is achieved for a second or two.
😎👍🇺🇲
Mexico hu, 🤔?
Looks a lot like Puerto Rico to me.
Can't fool us.
😏
16:42 I think the steel belt radial is playing games with you.
Wish you had a fabric radial.
Only deflating the right side, wouldn't that effectively put more weight on the left side?
275/60's, those are big tires for a fairly light vehicle so the pressure will have to be kinda low especially with stiff street radials.
Have you got a spare wheel in the empty spare wheel well? [It's placed where the extra weight does more good]
wonder if the drag at high speed is worth the traction off the line
At least you only have to let down one tyre😂🚀
On Wrenching with Kenny he said Mexico border was closed. Guess you found another way in.
How far is UTG from Mexico? Isn't Canada closer?
Seems like a long trip with one tire low on air. 😉
On a budget, use winter tires. They are softer and sell for low prices used. I wouldn't use them on a fast car but on the Jeep they would be fine.
I suspect that these tires are molded into a specific shape & aren't as flexible at the corners as we'd hope.. I'm betting in 12-15 is where it flattens out but does't help grip much when it tarts hopping more & harder with the pegleg. You need some Cooper Cobras at 35-45psi or McCreary's..(edit: I don't think the McCrearys are around anymore?)
I'm surprised that the tire didn't start cupping in the center. I'm also curious if you keep making the right tire hook better ,how much will it make the left contribute to the launch?Maybe tighter shock setting on the right or a little stronger right rear spring?
It's not a sure grip, it's a track lock. You can find one at the junkyard.
Am I the only one hearing Thunder or Fireworks "booming" in the background ?
No CO2/Smoke-Detector sounds in the background though now...
I don’t know if it can be done but i had a Nissan Frontier and the ABS system would work as a simulated limited slip. When one wheel would spin the abs would apply brake to that wheel and the other would kick in. Is it possible to do that to the jeep? It would be free or cheap.
Air shock fitted to RHR a la Bottle rocket??
Difference between bias ply and radials would be set different, too
Should have dropped pressure in both rear tires. Put it on the scales and see what happens when you let air out of just one side.
Would stiffer rear shocks help with the contact?
If your can put 500hp down on 2 tires, you should be able to put 250hp down on 1 right?
Geezus just get some some posi traction already and let’s see what this thing can run
You dont understand the concept
Plus you can't make as many videos if you skip ahead. More importantly you don't learn a damn thing or get to play.
It should have been the 1st mod the weight etc... to see what actually worked
@hansosl if it was the 1st mod we could have seen consistent gains then took out weight showed more increases etc.
@@zeeptollbooth4129 we aren’t learning anything not getting traction. No clue how much the weight reduction or cold air induction or anything helped. Why spend all this time trying to figure out how to get a single wheel rear to hook when that’s not what he’s going to have in it
Just curious what the offset on the wheels are.I like them centered 2 plant.All the weight in the middle of the tire
Tony were you lowering the air in the other tire on the other side?
How wide are the wheels?
Wheel width impacts tire traction patch. Hence why radial drag cars run VERY wide wheels.
Hey Tony... What's the black XJ?
the Flying Brick
8:44 doing 85 and still getting gapped on the freeway? Is the guage off, or do people drive fast there ?
Some people drive fast. Some are oblivious and will keep going faster if you keep going faster.
check engine light on!
That’s just from removing the vapor canister crap.
I would think that having all 3 of the other tires being higher pressure would have the same effect as a chair with one short leg , and leaving less weight on the lower pressure tire. Especially when the weight of the driver is on the other side of the vehicle.
Ive seen evidence on the street where guys have been burning out and the tread is cupping, the outer edges have good contact but very little toward the centre. I expect it’s a tire pressure, rim width, side wall construction dynamic.
That's what I expected to see on the last try
Would a winter ice compound be stickier?
At a certain point won't tires start cupping in the center ?
Waiting for the positraction to be installed
So burnouts in Mexico is legal? How long did it take you to get there.
I was told when running street tires you went up on the tire pressure, years ago…
That axle is short for life with the one wheel burnouts.
Super hard sidewalls? No flex?
Know whats easier... paint a chalk line across the threads and then drive it for a minute. Where the chalk is worn off is your contact.
Threads? My tires don’t even wear clothes.
@@davidleonard8369
He's got a speech impediment. Be nice.
@@AdamA-pm3yn I’m old and have no filter.
@@davidleonard8369
I'm old, and was joking.
He likes to do burnouts for video, easy not goal
"in Mexico" 🤣
The more you deflate the tire the less pressure internally to hold tire shape.
When you spin the tires the center tread shoots out further than the sides narrowing the patch.
Watch the tires on a real drag car and the tires loose 1/3 their width when spinning up.
Did you even watch the video? I went into that in detail
@@UncleTonysGarage Sorry no, listening and working at the same time, you must have stated that when my concentration was elsewhere.
Proper drag tires are a much softer structure. That’s why they’ll squat so much on launch and grow so much at speed.
Regular street tires like this have a pretty stiff tread section and sidewall. They won’t grow like drag tires do.
My concern is breaking the bead around a corner🙂mid 30s