“Could you please tell us what you believe to be a safe air pressure range for the stu 26" blasters on a rzr ? When does it start to 'wrinkle' on the rzr ?”
I understand you want a specific number however, and as I said before the calibration of your gauge can be one of the variables here. Let me venture into the weeds a little with some of the other reasons one might want a different air pressure besides the wrinkle issue. They might include wheel tire fitment, driver input, sand conditions and wheel damage are just a few more and will speak to the first question, Safe Air Pressure.
The key word here is SAFE!!! When I started as an employee with this company in 1975, I was introduced to the sand tire/wheel combination and how the two different pieces (tire & wheel) work as a single unit. Without going into too much detail and saving myself about 15 paragraphs and doing my best not to bore you, I’ll just give you the fifteen cent tour for now.
When I started with this company back then there were no bead-lock wheels and our society had a different tort system. We could do things to wheels in those days we don’t dare do today. As a result, I can’t offer today the type of wheel that would make me feel better about safety and why I don’t sell wheels any longer. You see the specs. that the tire & wheel manufactures are forced to use are more suitable for street applications i.e. D.O.T. and with much higher pressures than we use in the sand.
(1) The Tire Fitment Variable:
Here’s the nuts and bolts of the matter, I can’t roll a safety bead in a wheel today like in the good old days to increase its size so that the tire fits the wheel really tight. And the tire manufacture won’t reduce the bead size of the tire beyond what the Tire & Wheel Safety people say is safe (for liability reasons) so now we could have tires going on wheels easier than I would like in some cases and possibly coming off easier in other cases and our hands are tied. This brings me back to air pressure requirements. More air pressure can mean it becomes harder to dismount a safety beaded wheel, therefore more safe. However, more air pressure can also mean less performance. There is at times a trade-off of safety for performance and vise versa. Think of the steel cable inside the tire bead like you would a hose clamp on your radiator hose. The hump on the end of the radiator hose fitting keeps the hose clamp from sliding off, right? The fit between the tire bead and the wheel bead seat and the safety bead hump is similar accept there’s no adjustment to make the tire squeeze the wheel tighter.
Are you asleep yet? No!!! Lets keep going then. Now lets add another variable to the mix and this is where it gets fun. Listen up, not all tire manufactures use the same specs. and not all wheel manufactures use the same specs. What this can mean is that one company’s tire fits tighter on a specific wheel than another, and why one company’s wheel fits tighter on a specific tire than another. This has a lot to do with why I’m getting old. By the way print all this out and keep it by the toilet, it will help you relax.
(2) The Driver Input Variable:
Depending on how aggressive you drive or the mistakes you make behind the wheel also speak to air pressure settings. If you slide the car, if you jump the car, these are variables that require more or less pressure.
(3) The Sand Condition Variable:
Those of you that dune in the Southwest i.e. Glamis know that wet sand is the exception and not the rule. Those that dune in the Northwest i.e. Oregon might consider dry sand the exception and not the rule. Either way wet sand is heavier and can have an unfortunate result of debeading a tire (on a non bead-lock wheel) during a turning maneuver, that you’ve done in dry sand many times without a mishap. Wet heavier sand has more resistance to moving out of the way during a slide, and the path of least resistance could find you with a tire off the wheel.
(4) The Wheel Damage Variable:
This is the one that I really think people don’t give enough thought too. Stay with me folks we’re almost to the finish line. Yes, I did lie, you got the 50 cent tour. Many times I don’t think people really consider how a tire is a big suspension component to the vehicle and this is what I mean. Think of your tire as a pneumatic spring and say for example you go over whoops at a high rate of speed or you jump the car off of a 5 foot razor back. Then lets say you bottom the car out, your tire is being compressed and without enough air pressure the wheel/s could impact the ground and bend. As long as you have the smallest of an air cushion between the wheel and the ground you won’t flat spot your wheel or worse fold it up like a can.
Now with all the above damage I’ve just done, and in a perfect world with perfect gauges, wheels, drivers and conditions maybe 5 to 6 on the low end (be careful here) and 10 psi on the high end. You won’t hurt the tire with 15 psi however, I can’t foresee a reason to run that much. Try not to use CO2, the expansion and contraction rates are wild. Make it a habit every time you get out of your car to put you fist, thumb or knee into your tires and check to make sure you haven’t lost any pressure. You will get to a point that you’ll be able feel a half a pound difference between tires and this might save you from spending more money with one of my dealers. We’ll have a conversation about tire sealant another day.
To the last question and regarding the wrinkling of the sidewall, I’ll give you a couple of things to think about. First of all weight or the lack there of speaks to the question. The heavier i.e. 4-seat cars, big fat guys like me ect. require more pressure so as not to wrinkle the sidewalls. The more horsepower you have can cause wrinkling and therefore require more air pressure. When your driving the car and you transfer torque through the wheel to the tire this is when the damage is being done if there’s a wrinkle. I feel confident no one will have wrinkle related issues at 10 psi however at 5 psi in a 4-seat car with 4 Mark Harmsis and a turbo on the XP maybe??? Have your wing man in his RZR run next to you as to give you a base line on pressure. I’m personally a fan of about 2 psi above a wrinkle unless I’m racing. If I’m racing all bets are off.
Now a little side bar to this posting thing. I really enjoy helping people with their tire related questions. My problem can be I get overwhelmed here at STU when I’m really busy like right now. So the only time I can really spend time and not all the time replying to your questions is after hours. Sometimes I need to leave here in a hurry and can’t get to your question right away. Be patient and I’ll get back to you sooner or later. Again understand I’ll do my best to answer your questions with a thing or two I’ve learned over the years but I’m not coming to this community to promote my business because that’s what I agreed to when I registered for this forum.
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Thanks for the replies.
