Previous Thread
Next Thread
Print Thread
Page 1 of 2 1 2
Air pressure and reaction time #2286476
04/12/17 04:42 PM
04/12/17 04:42 PM
Joined: Apr 2007
Posts: 220
Wichita,ks.
jst19600 Offline OP
enthusiast
jst19600  Offline OP
enthusiast

Joined: Apr 2007
Posts: 220
Wichita,ks.
Does anyone had a general rule of thumb as to how much a pound of air pressure in the front tire equates to reaction time increase or decrease,specifically with a 27.5 tire?

Re: Air pressure and reaction time [Re: jst19600] #2286482
04/12/17 05:01 PM
04/12/17 05:01 PM
Joined: Oct 2003
Posts: 3,999
South Park, Pa.
68LAR Offline
master
68LAR  Offline
master

Joined: Oct 2003
Posts: 3,999
South Park, Pa.
Not sure if it affects R/T that much. I thought that the increase in front tire air pressure was to decrease rolling resistance, thus lowering ET.


4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
Re: Air pressure and reaction time [Re: 68LAR] #2286490
04/12/17 05:30 PM
04/12/17 05:30 PM
Joined: Jan 2003
Posts: 5,892
Florida
Locomotion Offline
master
Locomotion  Offline
master

Joined: Jan 2003
Posts: 5,892
Florida
It does. I've had to vary it between 50 and 26 lbs. Somebody told me the rough average, but I forgot. But the higher you go, there are diminishing returns - i.e.: 30-35 lbs will make more difference than 35-40 lbs.

Re: Air pressure and reaction time [Re: Locomotion] #2286541
04/12/17 06:44 PM
04/12/17 06:44 PM
Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY Offline
Master
MR_P_BODY  Offline
Master

Joined: Jun 2003
Posts: 52,972
Romeo MI
Originally Posted By Locomotion
It does. I've had to vary it between 50 and 26 lbs. Somebody told me the rough average, but I forgot. But the higher you go, there are diminishing returns - i.e.: 30-35 lbs will make more difference than 35-40 lbs.


True.. as the pressure goes up the dia will change
less at some point.. I could get a small amount of
change inn reaction time.. but not much at all...
I changed from 30-50 psi
wave

Re: Air pressure and reaction time [Re: MR_P_BODY] #2286552
04/12/17 07:02 PM
04/12/17 07:02 PM
Joined: Oct 2003
Posts: 3,999
South Park, Pa.
68LAR Offline
master
68LAR  Offline
master

Joined: Oct 2003
Posts: 3,999
South Park, Pa.
Originally Posted By MR_P_BODY
Originally Posted By Locomotion
It does. I've had to vary it between 50 and 26 lbs. Somebody told me the rough average, but I forgot. But the higher you go, there are diminishing returns - i.e.: 30-35 lbs will make more difference than 35-40 lbs.


True.. as the pressure goes up the dia will change
less at some point.. I could get a small amount of
change inn reaction time.. but not much at all...
I changed from 30-50 psi
wave


Well, today wasn't wasted. I learned something new...Thanks..I personally can't see the diameter changing more than an 1/4" at best going from recommended psi to 40 or 50 psi, but evidently I'm not getting it.. Thanks for the info. I run my fronts at 40 psi when racing, 32 on the street.


4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
Re: Air pressure and reaction time [Re: jst19600] #2286569
04/12/17 07:41 PM
04/12/17 07:41 PM
Joined: Mar 2006
Posts: 9,791
MI, usa
dvw Offline
master
dvw  Offline
master

Joined: Mar 2006
Posts: 9,791
MI, usa
I can't see any difference. Ive tried numerous times.
Doug

Re: Air pressure and reaction time [Re: jst19600] #2286843
04/13/17 03:10 AM
04/13/17 03:10 AM
Joined: Dec 2007
Posts: 12,587
Great Neck,LI,new york
hemi-itis Offline
I Live Here
hemi-itis  Offline
I Live Here

Joined: Dec 2007
Posts: 12,587
Great Neck,LI,new york
What TP is the manufacturers rec when you pump them up to 40 or 50 PSI?


HEMI-ITIS has no cure.
My condition is fully BLOWN!!
Re: Air pressure and reaction time [Re: jst19600] #2286844
04/13/17 03:29 AM
04/13/17 03:29 AM
Joined: Jun 2005
Posts: 6,257
gulfport, ms, west mi
rowin4 Offline
master
rowin4  Offline
master

Joined: Jun 2005
Posts: 6,257
gulfport, ms, west mi
There's a couple of guy's at the track that play the tire pressure game, one runs one front tire so low the starting line guy has backed him off. He claims he can leave as the 3 yellow comes on . I've watched , he does, he also red lights a lot. Another uses his tire pressure pounds to rpm launch 26 pounds =2600 rpm etc. . Just one mans theory but he wins a lot. Go figure. I just run 35 psi, pull the wheels out of the light on launch and red light.


it's ok to butt heads, just don't do it with a butthead
Re: Air pressure and reaction time [Re: jst19600] #2286900
04/13/17 09:54 AM
04/13/17 09:54 AM
Joined: Jan 2005
Posts: 1,768
Keymar, MD
DusterKid Offline
top fuel
DusterKid  Offline
top fuel

Joined: Jan 2005
Posts: 1,768
Keymar, MD
I used a 2x4 (laid with 4" side down) and a square to figure out how much roll out my tires had with X amount of air. I started at 25 psi and went up to 35 psi, in 5 lb increments. There was a bigger difference between 25-30 than 30-35. I forget the exact measurements but there was 3/32" difference with 5 lbs of air change. Also a "race" tire may change differently than a "street" tire.

Re: Air pressure and reaction time [Re: jst19600] #2286985
04/13/17 12:30 PM
04/13/17 12:30 PM
Joined: Apr 2003
Posts: 3,496
Tulsa, Oklahoma
340Cuda Offline
master
340Cuda  Offline
master

Joined: Apr 2003
Posts: 3,496
Tulsa, Oklahoma
I would guess this would make more difference with a bias ply tire than a radial.

Re: Air pressure and reaction time [Re: jst19600] #2286990
04/13/17 12:41 PM
04/13/17 12:41 PM
Joined: Apr 2003
Posts: 3,496
Tulsa, Oklahoma
340Cuda Offline
master
340Cuda  Offline
master

Joined: Apr 2003
Posts: 3,496
Tulsa, Oklahoma
I would guess this would make more difference with a bias ply tire than a radial.

Re: Air pressure and reaction time [Re: jst19600] #2287095
04/13/17 03:39 PM
04/13/17 03:39 PM
Joined: Mar 2004
Posts: 826
Georgia
66coronet Offline
super stock
66coronet  Offline
super stock

Joined: Mar 2004
Posts: 826
Georgia
rear tire pressure has had more of an affect on our cars. we tried it in .25 lb increments. We run 29.5x10.5 W tires on those cars.

Re: Air pressure and reaction time [Re: 66coronet] #2287183
04/13/17 06:36 PM
04/13/17 06:36 PM
Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY Offline
Master
MR_P_BODY  Offline
Master

Joined: Jun 2003
Posts: 52,972
Romeo MI
I was gonna try 20psi on my race car but after
lowering it to the 20 I looked at the tires..
I was afraid it would hit the rims on the way
back down from the normal wheel stand.. they
were low.. also on my car I had 3/4" of stagger
on the front end.. the right tire was set back
the 3/4" to give me a littler longer time in the
lights to slow the reaction time.. I used a 24.5"
tall tire and the car reacted very quick.. I was
running a 1.19 60' on a normal basis unless the
tires were getting old(70-70 passes).. the rear
tires were MOST of the time set at 6 7/8 to 7 1/8
psi.. depending on the track.. this pic is with a
lower rpm launch and between the rpm and tire psi
it started rolling/folding the tires
wave

5-108.JPG
Re: Air pressure and reaction time [Re: DusterKid] #2287346
04/13/17 11:16 PM
04/13/17 11:16 PM
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
C
Cab_Burge Offline
I Win
Cab_Burge  Offline
I Win
C

Joined: Aug 2003
Posts: 43,007
Bend,OR USA
Originally Posted By DusterKid
I used a 2x4 (laid with 4" side down) and a square to figure out how much roll out my tires had with X amount of air. I started at 25 psi and went up to 35 psi, in 5 lb increments. There was a bigger difference between 25-30 than 30-35. I forget the exact measurements but there was 3/32" difference with 5 lbs of air change. Also a "race" tire may change differently than a "street" tire.

I bought a 10 ft. cloth seemstress tape to check tire circumferences on both my front and rear tires at different tire pressures thumbs scope
I shoot for 1/4 inch vareince on the rear tires, inflate as needed to get that thumbs


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Air pressure and reaction time [Re: jst19600] #2287634
04/14/17 12:57 PM
04/14/17 12:57 PM
Joined: Apr 2007
Posts: 220
Wichita,ks.
jst19600 Offline OP
enthusiast
jst19600  Offline OP
enthusiast

Joined: Apr 2007
Posts: 220
Wichita,ks.
Im at my limit on front tire size now running 27.5 on my dart.I just put a Gerst tubular front suspension on it and i have the rebound set as soft as i can on the viking shocks to allow for most rise.Im looking to slow things down aprox. .030.I run 28.0 x 10.5 in the back usually at 10 3/4 pressure.I footbrake the car and it reacts very quick.I may try backing off the timing kill it a little off launch.If i tighten the front shocks im assuming that would make it react quicker with less movement up?

Re: Air pressure and reaction time [Re: 68LAR] #2287736
04/14/17 04:18 PM
04/14/17 04:18 PM
Joined: Jan 2003
Posts: 27,421
Balt. Md
3
383man Offline
Too Many Posts
383man  Offline
Too Many Posts
3

Joined: Jan 2003
Posts: 27,421
Balt. Md
Originally Posted By 68LAR
Originally Posted By MR_P_BODY
Originally Posted By Locomotion
It does. I've had to vary it between 50 and 26 lbs. Somebody told me the rough average, but I forgot. But the higher you go, there are diminishing returns - i.e.: 30-35 lbs will make more difference than 35-40 lbs.


True.. as the pressure goes up the dia will change
less at some point.. I could get a small amount of
change inn reaction time.. but not much at all...
I changed from 30-50 psi
wave


Well, today wasn't wasted. I learned something new...Thanks..I personally can't see the diameter changing more than an 1/4" at best going from recommended psi to 40 or 50 psi, but evidently I'm not getting it.. Thanks for the info. I run my fronts at 40 psi when racing, 32 on the street.



I do about the same as I run about 35 on the street and 40 at the track. Does it help any ?? Most likely not much if any. Ron

Last edited by 383man; 04/14/17 04:19 PM.
Re: Air pressure and reaction time [Re: jst19600] #2288442
04/15/17 09:46 PM
04/15/17 09:46 PM
Joined: Apr 2011
Posts: 319
jonestown,pa
D
dmking Offline
enthusiast
dmking  Offline
enthusiast
D

Joined: Apr 2011
Posts: 319
jonestown,pa
i also was bulbing a lot and someone told me about slowing my car down reaction time wise with air so i went down to 30 in the front and down 2 in the back and boom i'm at .015. it seems to work. i am on regular bias tires . the rear must wind up the sidewall a little bit more before it rotates the tire and lower in the fromt must make the contact patch a little bit longer.

Re: Air pressure and reaction time [Re: dmking] #2288663
04/16/17 11:28 AM
04/16/17 11:28 AM
Joined: Jan 2003
Posts: 5,892
Florida
Locomotion Offline
master
Locomotion  Offline
master

Joined: Jan 2003
Posts: 5,892
Florida
Originally Posted By dmking
i also was bulbing a lot and someone told me about slowing my car down reaction time wise with air so i went down to 30 in the front and down 2 in the back and boom i'm at .015. it seems to work. i am on regular bias tires . the rear must wind up the sidewall a little bit more before it rotates the tire and lower in the fromt must make the contact patch a little bit longer.


Exactly! It does make a difference. There are variables that often make it difficult to see. A major variable is a driver's "margin of error". i.e.: If a driver can consistently stay within a .03 spread in reaction times, than a change in air pressure that should make an .01 difference may not be obvious. But keeping very detailed, long-term records of all variables will help. This includes different tracks, day/night, possible lane differences & more.

Re: Air pressure and reaction time [Re: jst19600] #2288691
04/16/17 11:57 AM
04/16/17 11:57 AM
Joined: Mar 2006
Posts: 9,791
MI, usa
dvw Offline
master
dvw  Offline
master

Joined: Mar 2006
Posts: 9,791
MI, usa
In my opinion most foot brake guys trying to slow down R/T should look at the driver. Try a pro tree and see where your at. See if you're minus on the full tree and plus on the pro (take out the .100 if its .400 Pro). If so you are anticipating the bottom bulb. You should be within .010 or less difference.
Doug

Re: Air pressure and reaction time [Re: dvw] #2295932
04/29/17 04:19 AM
04/29/17 04:19 AM
Joined: Apr 2007
Posts: 220
Wichita,ks.
jst19600 Offline OP
enthusiast
jst19600  Offline OP
enthusiast

Joined: Apr 2007
Posts: 220
Wichita,ks.
Thanks to my new Gerst suspension i have staggered the front tires 1/4 inch.Havent had a chance to take it to the track yet to see the results in reaction time.

Page 1 of 2 1 2






Powered by UBB.threads™ PHP Forum Software 7.7.1