235's vs 31's

[91Woody]

Last year I ran 31" Definity M/T's through the winter and they seemed to do just fine even in 2WD. This year I work 35 miles away in MA so I downsized to 235 BFG AT's and notice a big difference in winter traction. The BFG's are 3 old school and one KO- just the luck of the draw since I got them used. Anyone else have a similar experience with downsizing in general- probably not common since I am going backwards in the upgrade process. I am uncertain I want to put MT's back on with the highway driving. Opinions/Comments?
BTW, I have stock D30/35 with 3.55's.
Is this simply the "torque loss" due to the larger tire making it less prone to spinning?
Thanks

 

[88JeepXJ]

I'm assuming you are saying the 235s were worse? Sort of hard to read into...

 

[mjma]

I would guess that the increased torque with the smaller tires makes them easier to spin. How much tread to they have left??

How did the switch down to 235s effect your mpg?

 

[91Woody]

I'm assuming you are saying the 235s were worse? Sort of hard to read into...

:dunce:
I wrote while at work...
you are correct in assuming the traction got worse.
The BFG's are decent enough in tread depth, I don't have a gauge but I would guess about 70%. which was the same for m/t's- which have a deeper tread to begin with though.
The MPG's went from 15-16 up to 17-18mpg switching from 31's to 235's.

 

[sidriptide]

Is this simply the "torque loss" due to the larger tire making it less prone to spinning?
Thanks

BINGO!!!! that, and the different tires have different traction characteristics. a few years back i had what might be called an opposite experience.. i switched from 235s to 31s and one slippery day on the highway climbing a steep mountain curve and with the automatic it was lugging the RPM so i pushed it farther down and when it downshifted, it broke loose and the rear end came around on me and i nearly wrecked right in front of a flatbed loaded with Xmas trees. learned my lesson about mismatched tires and gears that day.. even though they were still relatively small tires it still changed the operating RPM..

 

[91Woody]

I just didn't think it made much sense being that the tires and gears are now back to factory specs that it would be worse. Damn, stocker XJ's must be not so much fun in the snow.
Thanks for the input.
Looks like it's back to the 31's for me- gas mileage isn't that good anyway. Won't hurt that I have been dying to get my 4.5" put on anyway- if only I could get my air compressor to work properly now to play with my new air tools:laugh3:

 

[mjma]

it's not worse, you're just used to giving it too much skinny pedal!!

 

[91Woody]

I do tend to be a bit heavy on the skinny pedal for highway merges and on ramps, but other than that i am a fairly average driver now. I am cautious in the snow and ice as I do not want to wreck my Jeep- you know the insurance value on a 91 sucks- need to notify the insurance co of my mods just in case.

 

[BBeach]

The torque's the same, its just the tangental force that changes. I think it could be that but more of the different tires as sidriptide said.

 

[91Woody]

I realize the torque output is still the same, which is why I placed it in quotes- more of a mechanical advantage lost due to the larger tire requiring more effort to begin rotating. ( I didn't google tangental force yet ) Who would have thought that Pep Boys tires (although made by Cooper with some similarities to the STT's) would be better than the BFG's.....perhaps if the BFG's were 31's it would be a much more appropriate comparison.
Thanks

 

[CheapXJ]

BFG ATs huh?

that's the problem right there.

I still don't know why they have such a grear reputation when they make such a shitty tire

 

[91Woody]

Perhaps it all the mall crawlers that upgraded from the Sears Guardsmen that were on the Jeep when the proverbial old woman around the corner sold it to them. :shhh:

 

[91Woody]

Well, I got my 31 Definity M/T's on before the storm and what a world of difference. These tires inspire so much more confidence than the A/T's, I had NO issues with the snow yesterday afternoon- i even went out to play
The only down side is carrying my spare on the roof with a ratchet tie down and factory load bars- holds plenty well, but eventually i'll need a better setup.

 

[Serveck]

i'd have to say the same thing, i swaped from my 235 all season's to my 31" mud's and it was a HUGE difference i was just destroying everything snow wise that i went through. i would definately recomend it. however, i would get the siped, because muds are not known for their cooperation with the rain.

 

[91Woody]

I bought these tires because they do have siping, albeit only as much as Pro Comp Mt's, but they have done very well over the last year with the exception of treadwear.