It's all about tire pressure. If you sacrifice some traction for higher air pressure, the tire won't move. On a bike with tubes and no rimlock, depending on the bike, tire, surface conditions, and pressure, you'll find a point where any tire will move on the rim. Apparently you've been running sufficient pressure to avoid this.

 

Off-road, I'm usually at 12-15. I don't spin the rear tire a lot, but I am pretty hard on the front brakes.

I wonder if there are things that can assure a better bond between wheel/tire, such as making sure surfaces are CLEAN when mounting tires, and using the "Windex" lube on the tire bead. I noticed that the Windex makes the rubber real sticky where it contacts the rim. I understand the concept of an aired-down tire potentially rotating, but in reality theres a lot of contact area (around the rim). I'm guessing there's other factors involved, like dirt getting between the bead and rim.

 

Yeah, that's true that factors like you mention can influence how well the bead grips the rim...tire compound, bead/sidewall flexibility, rim design, etc. Without a rim lock, the interface between the bead is the critical element, and it does change a bit depending on some of those factors I mentioned. However, it is more likely than not that you will experience a rotating tire on a dirt bike in some instances by running lower pressures without a rim lock. At what pressure that will occur is about as clear as mud, but it exists. In your case, you apparently have hit upon a combination of factors that have worked for you. However, it could happen on a cold day where your pressure is a hair lower...or you cross a creek and hit a submerged rock that flexes the bead just a hair which allows the bead to creep a bit more because of the water.

I'm not saying that you're claiming that one shouldn't run rim locks, but history shows strong evidence that one probably should run rim locks if you're going to do any aggressive dirt riding with a relatively low pressure. Of course the next question is, "what is too low a pressure?" Who knows?

 

YOU WILL know when it happens!

I'm reading an book about dirt biking way back in the olden days of the 60's and 70's and the writer mentions using FOUR rim locks on some races.

 

Oh, talk about sticking the knife in and twisting!

I was desert racing in district 37 and 38 in the 70's...

Ron

 

Oh, the good ol' days of wooden wheels and steam engine dirtbikes.

 

Got to twist the knife while I still have a chance...

Were you out there against Super Hunky?

 

It is my opinion that the tire rotates on the rim over time due to a 'kneading' action that occurs as we are riding. The rubber hits the road and compresses over and over and over while riding thus causing the tire to 'walk' on the rim.

I wonder if the bike owners that are not experiencing this movement of their tire(s) (w/o rim locks installed) are either

A) not riding
or
B) have their locking nuts on the tube stem screwed down tight, hence they don't even know it is occuring.

I couldnt prevent the slipping of the tires on my rims no matter what pressures I rode, street or dirt, until the installation of TWO rimlocks per wheel.

 

Even though the bikes at the time were state of the art, they sure look antique today!

You can see some in the Carlsbad Grand Prix.

I was in that race, BTW.

Ron

 

I raced for about 10 years in the desert east San Diego. That was district 38. I was actually only in one race in district 37 (the Los Angeles district). That was a combo district 37/38 race held to help finance the anti BLM movement. I don't know if Super Hunky was there or not.

He lived in the Los Angeles area at the time. I'm not sure how much desert stuff he did. I think he was mostly a MX guy. BTW, he lives here in the Phoenix area now.

Ron