Rolling Radius With A 33” Tire

Yes the wheel speed changes just enough from lower pressure for the speed sensor to pick it up. If you have traction control on the newer cars they sometimes go nuts when going around a corner with a little to much power and set off the traction control from speed sensor input varying from side to side.

 

Probably a combination of both. As the diameter changes the friction will increase as well as the axle slowing down from the rolling radius changing.

 

I believe this is correct.

 

I’ll have 30 minutes tomorrow morning while waiting for seam sealer to set up.

 

You guys and your math!
I used a GPS app on my phone. 40= 42
That’s all I need to know.

 

If nobody gets to the math, I’ll do it later... I’ve got a build to get back to.

This is the 33x12.50 tire(s) mentioned earlier.
I started with this baseline. If I backed up and it didn’t line up perfectly, I jacked it up and repositioned the tire.



Results. I did three tire rotations so I’d get definitive results. Divide the distances by three to get numbers for a single rotation.

 

You guys are funny. I just let some air out of the tires and go wheeling.

 

Interesting result. Did you measure the overall height of the tire at each pressure? That's where the math comes in.

I think the main point here is not that you can detect a change, but what people attribute that change to. The change in footprint due to lower pressure brings the axle closer to the ground, but I would contend that's not what's changing. Instead, the tread is lengthening because the entire tire is blowing up like a balloon.

A 33" tire has a nominal circumference of ca 104". A one inch change in 3 revolutions is a change in circumference of 1/3 of an inch, or about 0.32%. If the height of the tire changes by an inch that's a reduction in rolling length by about 3", and over 3 revolutions you'd see a difference of 9" or so, nearly an order of magnitude different.

 

I didn’t. I was trying to hurry because my jeep was leaking oil all over the pavement.

While I was doing this, I kept thinking about a tank. If you took tank tracks and expanded them into a circle, what would the test results show?

 

Bien sur, mon ami! (Been talking to a French colleague... puts my mind in that frame.)

 

Glen and Howard
The vehicle I’m working has some details as noted in my “signature”.

Unfortunately its about 3 hours to Glamis, or about the same to the dunes at Devil’s Playground or Joshua Tree, about 2 hours to Ocotillo Wells area.

Around here - sand, dirt roads, sandy roads and in rare moments possibly some snow. Highway tire pressure and higher rpm for hours to get anywhere!

I will be spending significant time on highways here in So Cal.
Just trying to obtain enough info to decide (brand x right now) if it is to be a 33” or 33.5” or 33.8” tire to start to hit my optimum numbers.
Will likely guess in the end.....note my vehicle is probably heavier w the frame boxing, full cage, dana 44 front and dana 60 rear than most( too much left of my SCORE racing in the 70s I guess)

Dennis

 

Moi aussi.

But our jeeps are not products of the digital age with nano-particle binary yes/no answers.

Close is Good Enough, IMHO. Better, even...if you understand the concept of 'Anti-Fragility' and its value in these times of upheaval.