Air down tires over rough roads?

Tabaz

This last trip included 4 miles of very rough forest service road leading to and from the campsite.  It took me an hour to go the 4 miles! I've read where serious four-wheelers will drop their tire pressures while in the rough.  I carry a portable generator, so airing the tires back up at the pavement's edge would not be a problem.  Any thoughts?

jkjenn

OutbackAZ said:

This last trip included 4 miles of very rough forest service road leading to and from the campsite.  It took me an hour to go the 4 miles! I've read where serious four-wheelers will drop their tire pressures while in the rough.  I carry a portable generator, so airing the tires back up at the pavement's edge would not be a problem.  Any thoughts?

I don't think I would do it as the proper inflation of trailer tires is needed to prevent the damage. I think better to risk a punctured tire than wheel or axle damage. I have thought about the same question, though.

DurangoTaB

Although common practice on beaches, I agree with Jenn...I'd be worried about sidewalls.  

Nomad

Agree - Good for four-wheelin on sand or mud - Not really meant for a better ride.

ericnliz

I wouldn't. The air gives the tire sidewall strength. If you let air out, you are more susceptible to punctures in the sidewall of the tire.

T@Buhura

ericnliz said:

I wouldn't. The air gives the tire sidewall strength. If you let air out, you are more susceptible to punctures in the sidewall of the tire.

While this may be true depending on the tire... the issue with keeping tire pressures up off-road or on rocky/rough FS roads is you're in fact more likely to puncture or pop your tires like a taught balloon that touches a hard edge. The reason we air down off-road varies on conditions and determines how much air to let out. Sure on mud/thick snow/sand off road is to improve flotation and maintain as large a contact patch and for this reason lower pressures are better. On rough roads, it's mainly to keep tires from popping on sharp rocks or to help them deform better around rough surfaces, for comfort, and to let the tires take more of the abuse than the suspension components of the vehicle - tires are far less expensive and easier to fix (especially in the field) - and if you note the tires are a part of the suspension system, it contributes to comfort as a side benefit.

This is what you'd rather see, proper deformation depending on the terrain as opposed to popped bead or worse, popped tire. I have a better image of one from this weekend that I still have on my camera. It looks flat but it's actually at 25psi (cold, I aired down from hot, coming off highway to 30psi) and due to the position of our car vs. the terrain coming around an off camber descent this helped maintain balance.



As for deflating tires on the T@B, that would really depend on the conditions. Given that most off road is at very slow speeds, deflating won't affect the integrity. The biggest concern is with heat and when traveling slow, especially at the 4-15mph range, heat won't be an issue. Plus if the roads look like anything we did this weekend, I probably would especially if on regular road tires (non-Outback model ones) since they don't have as much flex as the General Grabber AT2 that the Outback come with. Speaking of which, he picture is of a General Grabber AT2 - on our XC90. And back to the damage situation, a more cushioned ride will help protect many of the components inside the T@B, like fridge, cabinets, etc while off-road.

jkjenn

T@Buhura said:

ericnliz said:

I wouldn't. The air gives the tire sidewall strength. If you let air out, you are more susceptible to punctures in the sidewall of the tire.

While this may be true depending on the tire... the issue with keeping tire pressures up off-road or on rocky/rough FS roads is you're in fact more likely to puncture or pop your tires like a taught balloon that touches a hard edge. The reason we air down off-road varies on conditions and determines how much air to let out. Sure on mud/thick snow/sand off road is to improve flotation and maintain as large a contact patch and for this reason lower pressures are better. On rough roads, it's mainly to keep tires from popping on sharp rocks or to help them deform better around rough surfaces, for comfort, and to let the tires take more of the abuse than the suspension components of the vehicle - tires are far less expensive and easier to fix (especially in the field) - and if you note the tires are a part of the suspension system, it contributes to comfort as a side benefit.

This is what you'd rather see, proper deformation depending on the terrain as opposed to popped bead or worse, popped tire. I have a better image of one from this weekend that I still have on my camera. It looks flat but it's actually at 25psi (cold) and due to the position of our car vs. the terrain coming around an off camber descent this helped maintain balance.



As for deflating tires on the T@B, that would really depend on the conditions. Given that most off road is at very slow speeds, deflating won't affect the integrity. The biggest concern is with heat and when traveling slow, especially at the 4-15mph range, heat won't be an issue. Plus if the roads look like anything we did this weekend, I probably would especially if on regular road tires (non-Outback model ones) since they don't have as much flex as the General Grabber AT2 that the Outback come with. Speaking of which, he picture is of a General Grabber AT2 - on our XC90. And back to the damage situation, a more cushioned ride will help protect many of the components inside the T@B, like fridge, cabinets, etc while off-road.

I get that. My point is that a trailer is d8fferent than a passenger vehicle. The trailer depending dsplogic@neatstreet.com on tire inflation differently.

T@Buhura

jkjenn said:

I get that. My point is that a trailer is d8fferent than a passenger vehicle. The trailer depending dsplogic@neatstreet.com on tire inflation differently.

I agree, I have had the same dilemma, the one time (last summer) over several hundred miles that we had was whether to deflate. I ended up not, mostly because even off paved road (still very rough) we were mostly traveling at highway speeds. For that trip I had lowered to 30psi hot also on our XC90. I kept the T@B at 44psi. Cabinets didn't like it so much and I'm not sure at speed a lower PSI would have helped them without sacrificing the tires which we needed to last the 7000 mile trip (we only had one spare for the T@B and 2 full size for the XC90). Thankfully we didn't need any but along the way we met several travelers with caravans that on one road went through 2 spares. Another T@Ber we met went through 2 new tires on his T@B alone, and fortunately while he was still "close" to civilization.

ericnliz

It's still a trailer tire, and NOT meant to be deflated. Springs, shocks, and torsion bars are considered suspension, not tires. Sorry to humbly disagree, but I did this for 30 some years, and trailer tires are an animal all in themselves.

Ratkity

I'm really glad of this discussion and prior tire topics. I've learned quite a lot. I've also learned a lot about how axles on small trailers can be problematic on trailer tire wear. Something I didn't even consider. I wonder if axle alignment is an issue on the land yachts? 

T@Buhura

ericnliz said:

It's still a trailer tire, and NOT meant to be deflated. Springs, shocks, and torsion bars are considered suspension, not tires. Sorry to humbly disagree, but I did this for 30 some years, and trailer tires are an animal all in themselves.

I believe we were discussing T@Bs with automotive tires. Outback T@Bs come with General Grabber AT2 - which aren't trailer tires; considering the OP name and that the discussion was for off-road/FS road use.

On ours in particular too, it comes with standard car tires in the 205/50x16 size (full Euro-design including axle - pre LG T@B) - which was the reason behind my consideration for lowering PSI on our trips too.

jkjenn

T@Buhura said:

ericnliz said:

It's still a trailer tire, and NOT meant to be deflated. Springs, shocks, and torsion bars are considered suspension, not tires. Sorry to humbly disagree, but I did this for 30 some years, and trailer tires are an animal all in themselves.

I believe we were discussing T@Bs with automotive tires. Outback T@Bs come with General Grabber AT2 - which aren't trailer tires; considering the OP name and that the discussion was for off-road/FS road use.

On ours in particular too, it comes with standard car tires in the 205/50x16 size (full Euro-design including axle - pre LG T@B) - which was the reason behind my consideration for lowering PSI on our trips too.

Although they are of-road tires, trailer needs are still different  than a car, truck, or SUV. As a matter of fact, I have always been curious I have always been curious about the use of off-road tires with the T@b. (I have them) you read the various literature about tires for trailers, there is a lot of detail about the need for stronger sidewalls. Do the General Tires sidewalls meet the same standards as trailer tires or is it that the T@b is so light that there is not as great of a need for stronger sidewalls?

When I went to have my trailer bearings packed, the guy thought it needed a PA inspection and said it would not pass due to having passenger tires before he realized I did not not need an inspection due to being under the required weight.

T@Buhura

jkjenn said:

Although they are of-road tires, trailer needs are still different  than a car, truck, or SUV. As a matter of fact, I have always been curious I have always been curious about the use of off-road tires with the T@b. (I have them) you read the various literature about tires for trailers, there is a lot of detail about the need for stronger sidewalls. Do the General Tires sidewalls meet the same standards as trailer tires or is it that the T@b is so light that there is not as great of a need for stronger sidewalls?

When I went to have my trailer bearings packed, the guy thought it needed a PA inspection and said it would not pass due to having passenger tires before he realized I did not not need an inspection due to being under the required weight.

That's along the lines of what I've learned about traditional trailer tires, and that the main issue has to do with how static they are relative to autos with the requirement they function as supports while standing. The need for stronger side walls is mainly to handle the extended periods of being parked, having loads vary while having to support the weight. Tire flex from rotation is what keeps them "fresh" (elastomers), too and with lower use, they need reinforcement. Plus helps minimize flat spots that occur with prolonged storage. The upside with T@Bs is they're light relative to other trailers, minimizing the load its tires have to withstand and even the alternate automotive tires aren't necessarily soft (Grabber AT2 or even the H rated tires the old T@Bs came with). With that in mind I use the stabilizers to partially relieve the load on our tires while stored (typical for autos that are stored to preserve their tires as well).

Tabaz

Thanks for the info everyone! My original goal was to go faster along rough roads with the deflated tires (TV and TAB). After reading your posts, it dawned on me to factor the time needed to deflate 6 tires and then reinflate them. 

ericnliz

T@Buhura, This conversation has really sparked my curiosity, especially some of your comments about tires in general. Do you know what load range your Grabber AT2 tires are? H rating is not only for the speed rating of the tire, and rubber compounding,[slightly softer than an "S", or "R" rated tire"] but also for load rating as well. The higher speed rating requires a stronger sidewall for high speed turns. What vehicle are the 205/50R16 tires on? Your Volvo? Would almost bet they are at least an H rating, if not perhaps V.

tabasco

A lot of the problems with sidewall failures comes from the twisting moment during tight turns with duel axle trailers, witch of course does not apply to T@Bs.
We have ordinary car radials on our 2005 T#B, at about 1700 lb loaded (minus 160 tongue weight) that works out to 770 lb per tire, the load rating for a 205/55/16/r
is 1350 lb.  At just over half the recommended max weight per tire, our loading is very modest. We have played around with tire pressures on everything from high speed
on hot freeways to some real rough back road tracks, and despite the original handbook recommending 44psi, have ended up at 35psi with no overheating, and
no sidewall problems on the tracks that are called logging roads here in B.C. Still very stable at speed and much less stuff strewn around inside the T@B on the rough roads!
The original tires lasted a full 10 years according to the  sidewall date without any problems, only changed them because they were 10 years old.
So far so good, Jen and Bern, 2005 T@Basco and 2005 Subaru Forester.                   

ericnliz

Thanks, have fun!

T@Buhura

ericnliz said:

T@Buhura, This conversation has really sparked my curiosity, especially some of your comments about tires in general. Do you know what load range your Grabber AT2 tires are? H rating is not only for the speed rating of the tire, and rubber compounding,[slightly softer than an "S", or "R" rated tire"] but also for load rating as well. The higher speed rating requires a stronger sidewall for high speed turns. What vehicle are the 205/50R16 tires on? Your Volvo? Would almost bet they are at least an H rating, if not perhaps V.

Hi Eric n Liz. The load rating on our General Grabber AT2 255/55x18 is 109, they are H speed rated - not really a high speed tire . Our XC90 originally shipped with 107, Y rated XL - great for prolonged runs at >120mph while driving in Germany . The T@B's are 205/55x16 91T - still on the original tires which are now a ripe10yrs old.

I'm not sure, but I think given that the Outback T@B models come with 14" General Grabber AT2 they are likely the 27x8.5x14LT which are 95Q.

Related I found a great article at tirerack.com that talks about the differences between trailer tires and passenger vehicle tires. What's particularly interesting is that passenger vehicle tires are acceptable on trailers but you cannot assume loading to capacity of the tire load rating - reduce is capacity by 9% for use on a trailer.
TireRack Trailer Tires vs. Passenger Vehicle Tires

XC: and I just noticed the chunk on the sidewall next to the H - likely from our last overland adventure, thankfully we're carrying one full size spare.


T@B: still muddy from finding beautiful recreation area deep in farm land over the weekend.

ericnliz

T@Buhura, The "H" rating is up to 110 mph, the "Y", in excess of 149 mph. The important part is the designated load carrying capacity of each tire which is also stamped on the sidewall. The chunk out of your tire doesn't look too serious as long as it is not down to the sidewall cords. Thanks for the response and info, oh, and Happy Trails to you and yours!

T@Buhura

ericnliz said:

T@Buhura, The "H" rating is up to 110 mph, the "Y", in excess of 149 mph. The important part is the designated load carrying capacity of each tire which is also stamped on the sidewall. The chunk out of your tire doesn't look too serious as long as it is not down to the sidewall cords. Thanks for the response and info, oh, and Happy Trails to you and yours!

Yeah, Y is max of 186mph, Z was the old 149+mph, I think from the 70s or at least that what I recall from when I first put a set of Pirelli P700z on my Integra and those were OEM on old 911s. They were a great tire but I learned they were definitely not a modern tire and needed to be hand balanced rather machine balanced, mostly because they were often out of round from the old molding technology Pirelli was still using to manufacture them in the 90s. Sorry, I didn't realize you were looking to get the info from me to help me. I'm fine, I thought it was more to get a sense of what's what between the old T@Bs on passenger car tires and the new Outback on AT LT tires vs. the ST tires regular T@Bs get now. Actually when I looked up the original specs on the Pirelli Scorpion Zeros our 90 came with I was surprised they were Y, I expected V (<149mph) - that's what Cayennes come with and a little sticker, required by law in Germany, to remind you not to exceed your tires' 150mph rating.

Fun stuff! Sad many people don't really appreciate the importance of getting quality tires for the right use/application. It sounds like your keen on the importance of good tires!

ericnliz

Michelins on Porsches every time! Used to live in Germany, Mainz and Wiesbaden  both with a lot of trips all over Europe. Actually P7's were the original Porsche tires, worse than the P700's. I started switching folks to Michelin tires as they were used stock on the older 911's. The P5's used for Jaguars were the WORST! Your next tire purchase, check out a set of Michelins, you won't be dissapointed. Bridgestone also makes a good tire, and the Falken brand is the lesser expensive of the group with a still good reliable product. Enjoyed sharing with you, and have fun!

ScottG

T@Buhura said:

...
Fun stuff! Sad many people don't really appreciate the importance of getting quality tires for the right use/application. It sounds like your keen on the importance of good tires!

Fun stuff indeed (at least for those of us with a peculiar fascination with technical details...) Thanks for the info and the link--it clears up much of the "special trailer" tire mystery!

T@Buhura

ericnliz said:

Michelins on Porsches every time! Used to live in Germany, Mainz and Wiesbaden  both with a lot of trips all over Europe. Actually P7's were the original Porsche tires, worse than the P700's. I started switching folks to Michelin tires as they were used stock on the older 911's. The P5's used for Jaguars were the WORST! Your next tire purchase, check out a set of Michelins, you won't be dissapointed. Bridgestone also makes a good tire, and the Falken brand is the lesser expensive of the group with a still good reliable product. Enjoyed sharing with you, and have fun!

Haha! Totally - the PS2 that mine came with were great but I have say Bridgestone makes an amazing set of N rated (P-car) tires. For street max performance I've really loved the RE050A. Their great even on track but as I went further down the rabbit hole I fell in love with their RE-11.

One weekend I had the chance to try a friend's Michelin PS2 that were on the wheels I'd bought from him and then the next day I switched to my RE-11 and on the road course the Bridgestone were a good 10s quicker for me around VIR. 

On the more pedestrian tire on the all season spectrum that's really spectacular is the Continental ExtremeContact DWS. It's a really good Ultra High Performance tire that has serious bite in snow and ice. They're not as crisp as the Pirelli Scorpion Zero for initial turn in but other than that versions tire. I've used both also on our XC90. Started using the Grabber recently for winter mountain use and our new overland addiction.

ericnliz

I had the RE71's on my '89 Honda CRX SI. Went to Sonoma for the day, a absolutely blew my boss's '78 911 off the track. The next day he put a set on his Porsche and loved 'em! He liked them so well, he installed a set on his BMW M1! Of course what I didn't tell him was I also put a computer chip in the CRX! Fun Stuff!

Nomad

Tire P0rn

ericnliz

  

ericnliz

PXL, you should see the center fold in the new tire mag!

T@Buhura

ericnliz said:

I had the RE71's on my '89 Honda CRX SI. Went to Sonoma for the day, a absolutely blew my boss's '78 911 off the track. The next day he put a set on his Porsche and loved 'em! He liked them so well, he installed a set on his BMW M1! Of course what I didn't tell him was I also put a computer chip in the CRX! Fun Stuff!

Ha, yeah after I tried the P700z on the Integra (which were really great for the Integra GS 4door - made it far more grounded with it's grip and helped control it's surprise oversteer, yes front wheel drive with a twitchy tail it had a 68/32 front/rear balance) I found the Bridgestone RE950 which ended up being excellent as well but far more modern and sophisticated version. I use them, well now the RE960 on our V40 - great handling made super fun with the RE960 Ultra high performance summers.

I need to try some of the tracks in the west! Laguna Seca would be fun! Too bad I can't tow the T@B (back on topic ) behind the Boxster. One of my instructors used to tow a little tire and tools trailer to the track behind his GT3 which was always fun to see.

Nomad

Can't recall what my 928 had on it but rode/handled like a dream.
Never was into the details.

ScottG

Yeah, my 928 handled like a dream, too.

Oh wait, it was a dream. Shucks...

Nomad

It was a dream car. Then I got over my car period.