tire pressure 18/39.5 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mapco · 04-25-2005, 02:24 AM

I have a set of mickey thomson baja belted on my chevy now they are 18/39.5/16.5. I am wondering what tire pressure people are running these type of tires, mud I am thinking around 15, highway I run 25. Do these numbers sound ok or am I hurting my tires? Any input would be great, thanks...

ryanroo · 04-25-2005, 11:05 AM

i have 39-15/16.5s and they are on a 9.75 wide wheel. i run 20-22 in them for the street on a 3/4 ton chevy, they get a good foot print that way. it depends on the width of your wheel a little, because a real narrow wheel will pull the sidewalls in and you will have to run lower pressure to let the whole footprint of the tire contact, but then you might have to little air in them and they will get hot going down the road. the thing is the tires will look about the same at 25 psi as they do at 12(i fiddled with mine just for kicks) so you have to keep enough air in the tire to keep it from flexing to much on the road, not so much that you run on the center only and wear them out to fast. so, for your street pressure you will be fine at 25 in my opinion, as for mud, its as low as you can without blowing a bead. good luck
Ryan

Hoods69BadBowTie · 04-25-2005, 12:06 PM

Yeah I run my 39.5x15x16.5 Swamper TSL's at like 22 psi on the street and then just fiddle with them and take a little air out when I got mudding.
-Later

Mudder · 04-25-2005, 03:29 PM

I run my 35" swampers at 25 in the front and 22 in the rear for Hwy. Too much air and its all over the road..........

mapco · 04-26-2005, 03:20 AM

well my rims I am running are 12 or 14, been lazy and haven't messured them will do so tomarrow. does it help that much to air down in the mud? I just don't see how airing down would help you out if you are going to risk bead breakage. I can see airing down to a flat tread patch on the dirt or ice more coverage of the imediate traction, but mud seems odd to me. I guess I will have to try different things and see how it works out. Thanks for the hlep..

Hoods69BadBowTie · 04-26-2005, 07:33 PM

I lower mine a little bit but not to drastically. I put mine a little under 20 psi. I know for rock climbing and sand and other stuff you want to air way down but I don't know why you would way air down for mud either?
-Later

ABHaulR · 05-01-2005, 01:41 AM

i run 25 on the road and 15 on the sand or mud. oh

i have 18x39.5x16.5
boggers.
Dwayne

LONGHAIR · 05-01-2005, 06:36 AM

Beware of running the pressure too low on the street, especially on the front. The natural tilt of the tire/wheel when turning puts more pressure on the lugs on the edges of the tires during sharp turns. This is what wears the tread to make them look like a saw blade, instead of the square that they were made to be. Wider wheels (greater off-set) exaggerate this problem. You need to run just enough pressure to ride to the center tread, slightly holding the edges off of the pavement (when the wheels are straight). The rear can take less, first because it is not carrying as much weight (unladen) and second because they stand straight all of the time. Just remember to adjust the pressure when you rotate the tires.

Another thing that will make them last longer, ride better....and be quieter is to have them "trued". There is usually a "big tire" store in major cities that can do this. You may be surprised at how out-of-round these tires can be.
They are far easier to balance after this too.

04-25-2005, 02:24 AM	#1
mapco Registered User Join Date: Feb 2005 Location: Anchorage, AK Posts: 10	tire pressure 18/39.5 I have a set of mickey thomson baja belted on my chevy now they are 18/39.5/16.5. I am wondering what tire pressure people are running these type of tires, mud I am thinking around 15, highway I run 25. Do these numbers sound ok or am I hurting my tires? Any input would be great, thanks...

04-25-2005, 11:05 AM	#2
ryanroo Senior Member Join Date: Apr 2004 Location: sw colorado Posts: 2,720	i have 39-15/16.5s and they are on a 9.75 wide wheel. i run 20-22 in them for the street on a 3/4 ton chevy, they get a good foot print that way. it depends on the width of your wheel a little, because a real narrow wheel will pull the sidewalls in and you will have to run lower pressure to let the whole footprint of the tire contact, but then you might have to little air in them and they will get hot going down the road. the thing is the tires will look about the same at 25 psi as they do at 12(i fiddled with mine just for kicks) so you have to keep enough air in the tire to keep it from flexing to much on the road, not so much that you run on the center only and wear them out to fast. so, for your street pressure you will be fine at 25 in my opinion, as for mud, its as low as you can without blowing a bead. good luck Ryan __________________ 72 K20 12v build 72 K20 "parts truck" A place for your diesel swap questions

04-25-2005, 12:06 PM	#3
Hoods69BadBowTie Chevys Kick A$$ Join Date: Jan 2005 Location: Zootown, MT Posts: 12,699	Yeah I run my 39.5x15x16.5 Swamper TSL's at like 22 psi on the street and then just fiddle with them and take a little air out when I got mudding. -Later __________________ HOODS is what I answer too -'79, '77, '88 Pickup Sold, '85 Camaro, '83 T/A, '81,'83,'90 K5 Blazer All Sold -'79 3/4 ton "Big Yellow Bananna" Lifted 4spd. 39.5 TSL Swampers, The money Pit -'86 K5 Blazer Silverado 6.2 4" lift 35"s -'95 Ext. Cab Shorty 4" Tuff Country rolling 35" M/T's -'83 Monte Carlo T-Tops. 126,500 Original Miles -LATER I would rather push a Chevy then drive a ford!!

04-26-2005, 07:33 PM	#6
Hoods69BadBowTie Chevys Kick A$$ Join Date: Jan 2005 Location: Zootown, MT Posts: 12,699	I lower mine a little bit but not to drastically. I put mine a little under 20 psi. I know for rock climbing and sand and other stuff you want to air way down but I don't know why you would way air down for mud either? -Later __________________ HOODS is what I answer too -'79, '77, '88 Pickup Sold, '85 Camaro, '83 T/A, '81,'83,'90 K5 Blazer All Sold -'79 3/4 ton "Big Yellow Bananna" Lifted 4spd. 39.5 TSL Swampers, The money Pit -'86 K5 Blazer Silverado 6.2 4" lift 35"s -'95 Ext. Cab Shorty 4" Tuff Country rolling 35" M/T's -'83 Monte Carlo T-Tops. 126,500 Original Miles -LATER I would rather push a Chevy then drive a ford!!

05-01-2005, 01:41 AM	#7
ABHaulR Registered User Join Date: Jun 2003 Location: West Valley City, Ut Posts: 311	psi i run 25 on the road and 15 on the sand or mud. oh i have 18x39.5x16.5 boggers. Dwayne __________________ 72' GMC Suburban 10 1/2" of Lift, 40" Tires! Waiting for restoration 67' Chevy, What to do??? And Bad Ass American Bulldogs!

04-25-2005, 03:29 PM	#4
Mudder Registered User Join Date: Feb 2001 Location: East Central, MO Posts: 11,336	I run my 35" swampers at 25 in the front and 22 in the rear for Hwy. Too much air and its all over the road..........

04-26-2005, 03:20 AM	#5
mapco Registered User Join Date: Feb 2005 Location: Anchorage, AK Posts: 10	well my rims I am running are 12 or 14, been lazy and haven't messured them will do so tomarrow. does it help that much to air down in the mud? I just don't see how airing down would help you out if you are going to risk bead breakage. I can see airing down to a flat tread patch on the dirt or ice more coverage of the imediate traction, but mud seems odd to me. I guess I will have to try different things and see how it works out. Thanks for the hlep..

05-01-2005, 06:36 AM	#8
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Beware of running the pressure too low on the street, especially on the front. The natural tilt of the tire/wheel when turning puts more pressure on the lugs on the edges of the tires during sharp turns. This is what wears the tread to make them look like a saw blade, instead of the square that they were made to be. Wider wheels (greater off-set) exaggerate this problem. You need to run just enough pressure to ride to the center tread, slightly holding the edges off of the pavement (when the wheels are straight). The rear can take less, first because it is not carrying as much weight (unladen) and second because they stand straight all of the time. Just remember to adjust the pressure when you rotate the tires. Another thing that will make them last longer, ride better....and be quieter is to have them "trued". There is usually a "big tire" store in major cities that can do this. You may be surprised at how out-of-round these tires can be. They are far easier to balance after this too.



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