put my 19.5s on today

twodownzero wrote:


Depending on how far you can air down, airing down a tire can triple the size of its contact patch by making it longer rather than wider. 20% is nothing compared to that.

I have run many sets of tires in the 4-7 psi range for rock crawling and playing off road. I have never seen a contact patch triple, unless it's wrapped around a rock or tree.

Airing down is great and does wonders for traction, but the contact patch is just part of that equation the rest is how the softer tire effects traction.

Buzzcut1 wrote:
bill

my 19.5s are the same circumference as the 285/75R16s I was running and a hair narrower. slightly better mileage and way less rollong resistance and noise. negligible difference except the 19.5s have way less sway to them and 1300 pounds more load capacity.

Thanx buzz...good info...
Safe travels, B

I have been running 19.5's, for several years. I also have a 4x4 Samurai I run off road. I played with Sandrails, Baja Bugs and Dune Buggies for years. While I agree, you can get more places with a bigger footprint, I have seen too many people get obsessed with it.

In all the years I have played off road, mud or sand, the only time I have had a flat was when I followed someones advice on airing down to the point of being too low. Different applications have different requirements. When we frequented Pismo Beach, it was in a 2WD vehicle, and never aired down. Never had a problem. Fair to say, do not drive out into the dunes, stay close to the ocean.

I have been on the Rubicon Trail with a group of wheelers, most with 34 to 40 inch tires almost flat, and have one of them tell me 30 inch tires are to small on my Samurai and I should let more air out of the tires. I point out, they may recall I just came on the same trail as they did, traveling with them. Maybe they should have smaller tires with more air.

To be fair, if I frequently ran in the desert off road I would rethink my tires. Probably would go with something like Jefe is running. I would also get a smaller TC, and 4x4 truck.

2down...I totally understand the physics and I would not air down my 19.5's. Your explanation is spot on as far as I am concerned. I still would like 805 to explain his statemement or maybe he should relate the issues he had and under the circumstance he endured those issues, so we all may be enlightened. It may be helpful to me and those of us who drive 19.5's so we can avoid those situations. So far I have not had any issues, but his expereinces may enlighten me on how far I can push my rig. Maybe I was not plain enuf in my original post request. Happy driving to everyone.

pjay9 wrote:
SO 805 your statement "Wait until you hit soft sand or mud, those pizza cutters will really dig in and not in a good way"...I don't understand! The vehicle basically has not increased its pressure per sq inch on the road as the surface area contact with the road is maybe a little bigger with the 19.5, why would it dig in any worse then the lessor diameter tire with the same surface contact area??

Making a contact patch longer by airing down makes a greater marginal difference than making it wider by going with wider tires. Most of us who go with a wider tire increase the width by 10% or so when we go up one size and perhaps 20% when we go from a stock 265 to a 315.

Depending on how far you can air down, airing down a tire can triple the size of its contact patch by making it longer rather than wider. 20% is nothing compared to that.

For the record, I have nothing against 19.5s for pickups; they seem to work fine for some. I do think for most purposes desiring traction, a regular light truck tire is superior. For the highway, especially when it's hot and the truck is overloaded--especially a SRW--the 19.5s are a major improvement.

On my truck braking feels generally the same, as does mileage. I'll be honest that mileage is hard to track with only 10K miles a year and I am always varying loads. I have seen some pretty low tanks while towing and some fairly high tanks while empty, which isn't a lot different than OEM wheels tires. I don't have much to back it up, other than observation and feeling, but highway mileage may be up a hair and city mileage may be down a hair.

Braking heavy when empty does make a lot more tire noise than my old tires thou.

bill

my 19.5s are the same circumference as the 285/75R16s I was running and a hair narrower. slightly better mileage and way less rollong resistance and noise. negligible difference except the 19.5s have way less sway to them and 1300 pounds more load capacity.

hey buzz...what is delta in mpg and braking distance vs OE wheels?

Thanx.

so after 1100 miles of pavement I threw it in 4x4 for five miles of twisty wet dirt mt road with some nice steep ups and downs with a 24 foot length restriction to go camp at the beach in the redwoods and watch bull elk stroll by. piece of cake.

I am not sure the narrower tread pattern will matter too much in the grand scheme of things. They are not a lot narrower than the OEM 265 on my truck, and with a ±5000lb front axle I am going to sink regardless... unless I go to monster truck tires.

Sinking down is better in many cases as well.