Report on new 255/85/R16 bfg M/T

[1leg]

I went on a drive today. Here is my report.
On a scale of 1-10, 5 being stock 225/75/16 tires

Freeway:
Handling = 7
Power = 5
Passing power = 3
Noise = 4.5 with soft-top i could barely hear them

Street:
Handling = 6
Power = 5
entering traffic = 5
Noise = 5

My first impression is that overall the driving improved. Handling on the freeway greatly improved(that really surprised me). Power loss is barely noticeable until i went to pass a slow truck on the freeway. around town you couldn't even notice a loss in power. Noise isn't even an issue with a soft-top. i can't comment on a hard-top. I would recommend this size for anyone not wanting to do a gear change or lift on Jeep JK with 4:11 gear. I will report MPG when I go through a few tanks. My guess is it wont change much. I drive slow. which helps.

 

[maximumrob]

My first impression is that overall the driving improved.

Taller tires increase your caster if you don't manually compensate for it by making adjustments. Increasing caster will make for a dartier feeling, which isn't so bad when starting with a relatively slow-steering vehicle like a Wrangler.

Glad to hear you like the way the tires feel. I'm heading to that brand and size very, very soon.

 

[Scott Brady]

Taller tires increase your caster if you don't manually compensate for it by making adjustments.

Are you sure about that?

 

[Redline]

x2.

Lifts generally reduce caster, but just tires?

Are you sure about that?

 

[1leg]

Actually the taller tires made the Jeep less darty. I don't have a lift.

 

[madizell]

I think he is right, that increasing tire size increases effective caster. The angle stays the same, but the distance between vertical and angular intersection of a line though the kingpin increases as a function of distance from the kingpin. Assuming caster to be not the angle of the kingpin per se, but the distance that the vertical point of contact lags behind the angular intersection of the kingpin angle and the road in front of the tire contact patch, larger tires would necessarily increase this distance. When I increased my tire size from 33 to 37, I had to take 2 degrees of caster out of the front end, from 7 degrees down to 5.

 

[Redline]

Interesting...

A couple years ago my alignment guy was telling me how sometimes he needed to take a little caster out on some lifted Jeeps to make them drive better. We tried it on my TJ with shims but it didn't help, made it worse/twitchy. Later I added adjustable lower control arms to put the caster back to stock. But it only had 3-in. of lift and 33s.

I think he is right, that increasing tire size increases effective caster. The angle stays the same, but the distance between vertical and angular intersection of a line though the kingpin increases as a function of distance from the kingpin. Assuming caster to be not the angle of the kingpin per se, but the distance that the vertical point of contact lags behind the angular intersection of the kingpin angle and the road in front of the tire contact patch, larger tires would necessarily increase this distance. When I increased my tire size from 33 to 37, I had to take 2 degrees of caster out of the front end, from 7 degrees down to 5.

 

[madizell]

Try this discussion in Wikipedia

http://en.wikipedia.org/wiki/Caster_angle

Perhaps the correct observation is that increasing tire size increases trail, while caster stays the same.

 

[Pskhaat]

I think he is right, that increasing tire size increases effective caster.

Hmmm, it shouldn't. It does adjust the steering geometry due to as you said the kingpin angle/road intersection, but should have more steering trail. Adjusting the caster should only adjust for that trail, though at least it's off in the `right' direction...

 

[Pskhaat]

increasing tire size increases trail, while caster stays the same.

Woops, sorry you already effectively posted that.