CJ-3B

[Bob W]

About 3/8". At first I wasn't being careful enough and when I came out of the rubber doing the inner lugs I accidentally made some slices in between the lugs on the outer half of the tire. 

[athawk11]

Thanks!
I've never siped a tire before.  If there is an advantage, it seems like NDTs and NDCCs would be the perfect tire for this modification.

I've read that with today's modern tread designs, siping doesn't offer a significant advantage.  What do you think?

Tim

[Bob W]

I'm not a tire guy but additional siping on a modern tire probably offers no benefit, they are already siped from the factory. NDTs are not so modern�

[oldtime]

I'm certainly not a tire expert either but I'll make a few comments.
On Bob's tires we only see a transverse siping direction and not a longitudinal cut.
I think that his transverse siping will do little to stop side slipping on wet pavement.
However his transverse siping should certainly help with fore/aft grip.
Because the siping is a fine slip it theoretically should not pick up any stones.
Also the transverse siping should actually decrease tread wear by allowing increased tire flex.

In theory longitudinal siping would help with sidling traction and also tire wear.

With Bob's siping he still maintains large treads blocks.
 
Large tread blocks will reduce any tendency for the tread to "chunk off" under pressure.
That's why you never see an NDT with missing chunks of tread .

[jpet]

I find that odd that your NDTs are only 30-1/2" tall.  I wonder what they measure without weight.  My 700-16s are 30-1/2".  I am considering going with 750s for more clearance.  Coker has 750-16 advertised as 31.6' diameter.

[Bob W]

These are Firestone from Summit Racing.

[Bob W]

On the Coker website my tires are listed as 31.6" tall. Maybe my tape measure is broken?

[jpet]

Wonder what they measure left to right or without weight?

[oldtime]

Seems to me that there exists no common industry standard for measuring tire height.
I find that to be very frustrating.
For example the Interco tires always measure notably shorter than they indicate..
That's one good thing about the STA's they actually measure taller than suggested.
The only real test I know of is to get actual mounted/inflated tire diameter from someone who owns the tire in question

I did a short study on various tire heights and I estimate that the average 7.50 x 16" bias jeep tire (new with full tread) measures around 31.5" tall after inflation and mounted on the narrow rims.
I figure the diameter loss due to GVWR averages .97 times the un weighted tire height.
Approximate .03 diameter loss due to 2250 GVWR.

Regardless I prefer to use tires that are the same diameter as the rear wheelhouse opening.
For the stock Willys CJ that's 31" tall.

[Bob W]

I went on a cool Willys Run today in Central NY state. I set my tires at 12psi and I'm happy to say they performed very well! May try 10psi next time.

[aboyandhisdog]

Nice!  Bob, why such a low psi in the tires?

[Bob W]

Low pressure allows the tire to flex better giving more traction
When the pressure gets too low the tire bead can unseat, then all the air escapes 

[athawk11]

That X98 looks to be in its element.  Nice.

I dropped tire pressure to 20lbs at the FCT.  I'll try a lower pressure next time.

Tim

[Bob W]

On-road pressure should be higher than off-road pressure. Tough choice for the FCT. There was no on-road driving at the NY event.

[Bob W]

So, in June at the Willys Picnic I purchased a T90C for X98. I'm planning to put it together over the winter and have it ready for spring wheelin. I like to build transmissions with serviceable used parts because of the quality issues with some of the reproduction stuff. Unfortunately I'm out of good used parts. Anyone put a T90 together in the past year with new parts that actually work good? If so where did you get them? Looks like I'm going to need at least a 2nd gear and a small parts kit.