QuestionQUESTION: Hi Barry,
I am building a high mpg 3-wheel vehicle, with two wheels in the front like a car, and a small motorcycle in the rear. The objective to get maximum mpg by using lightweight ATV parts for the front wheels and the motorcycle parts for the rear, and the streamline the whole thing using tear-drop body components (foam and fiberglass). Think IndyCar with the tire/wheels covered as well, and you get an idea of what is looks like.
I have purchased some suspension components from a large ATV including spindles, hubs, disc brakes, calipers and such. This guarantees that these parts can take a beating off-road and hold up on the highway with no safety issues. I would also like to purchase an aluminum ATV wheel and mount some type of street going DOT approved tire to the ATV wheel, but am not sure if tire bead specs for road tires are the same as those for ATV's.
Several emails and calls to ATV parts handlers has come up with few ATV tires that first, have a very high air pressure callout (>12psi), and second, a tread pattern designed for street use. That leaves small car tires like the Geo Metro or boat trailer tires.
If all else fails, my remaining option is to buy a car wheel and modify the bolt mounting pattern to fit the ATV hub, which will require the services of a certified welder as part of the conversion process. I understand the DOT is rather particular about how this is done.
So that in a nutshell is the situation. Have you others asking about this? I would think with the higher energy costs we had earlier this year, this topic would be getting more attention.
As before, any and all information you can give will undoubtedly be very enlightening since you worked in this industry so long!!
Thanks, Jim.
ANSWER: Jim,
Bead specs for tires vary considerably. The specs are highly dependent on the rim they are designed for.
All tire standardizing organizations specify the shape and size of the rim in this area and it is up to the tire manufacturer to make the bead area "fit" the rim. Needles to say, this varies considerably amoung all the tire manufacturers.
It took a bit of research, but I found ATV tires listed in JATMA (Japanese Automobile Tyre Manufacturers Association). It looks like the bead area dimensions for ATV rims are reasonably close to both small passenger car tires and tires designed for trailers.
Looking over the ATV tire specs I notice a couple of things:
1) The pressure of ATV tires is a maximum of 40 kPa (6 psi), while passenger car tires and trailer tires is considerably higher (35 psi / up to 80 psi) This means that rims designed for ATV's are not going to be strong enough.
2) The speed of the vehicle becomes important and using ATV tires for regular highway speed usage - particularly long term usage - would not be advisable. On the other hand, trailer tires aren't designed to be used in powered or handling situations. This leaves us with regular car tires. I think this means getting someone to fabricate rims with the proper bolt pattern - or finding a rim that matches the existing bolt pattern.
As you can see, designing a vehicle is pretty complex, particularly when you are trying to use existing components - and components designed for a different usage. This is quite an obstacle to overcome and not many folks are willing to work to overcome those types of obstacles - so I wish you luck.
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QUESTION: Actually, the ATV rims must be stronger than what first meets the eye, since ITP, who makes ATV tires and rims, uses up to 12 psi in their off road applications for heavier ATV's. That gets us closer to 30 psi for auto applications.
The other thing that gave me hope for using an ATV rim is the high impacting they take on the trail when jumping logs, rocks, cliffs,etc. You may have been commenting on the rim's ability to hold higher air pressure (6 to 35psi) when mounting a trailer tire on it. ITP does have a cast aluminum wheel which I suspect would be much stronger than the rather thin "rolled" wheels.
I suppose the only way to really be safe about this is simply go ahead with a modified car rim and alter the bolt pattern to fit the ATV hub.
Any comments?? Thanks again, Jim.
AnswerJim,
One of the things that rims do is resist the sideways force generated within the tire by the inflation pressure. Needless to say this force is 3 times as high at 36 psi compared to 12 psi.
To put some idea of the size of the force:
A P145/80R12 (which is the smallest passenger car tire I could find) has a diameter of 21.14”. That means the pressure is generating a sideways force of 21.14”-12” = 9.14” squared = 85.5 X pi (3.14159) = 262 square inches X 36 psi = 9,450 pounds. This would be the force trying to separate the 2 halves of the rim.
The problem here isn’t one time events like impacts, it’s the fatigue due to the number of cycles. Taking the P145/80R12 used above: When this tire goes 50K miles, that’s the same as 50 million cycles. (and probably ought to be designed to withstand 200 million cycles.) S-N diagrams say that for something to withstand 50 million cycles the stress has to be 20% of one time events.
By comparison, impacts are one time events, and while repeated impacts – such as off road usage – the number of cycles is small compared to each revolution – keeping in mind that the tire is absorbing most of the impact force and spreading it out over the entire rim surface.
As a way to compare the difference, I think you ought to look at the difference in rim thickness. This is going to be difficult because aluminum rims are cast or forged, while steel rims are formed by rollers (meaning steel rims start as a flat piece of steel). Obviously you shouldn’t compare steel and aluminum rims – and the area to be compared is difficult to describe without look at both rims, but I’m thinking the flat of the rim is the best place.
A side thought: You could start off with the ATV rims and watch the rim flange to see if cracks develop – replacing the rims when they do. Hopefully, you’ll see the cracks before the rims start to leak. A tire failure at high speed can have tragic results.
I would not draw the conclusion that a cast rim is better and than a roll formed rim. Cast rims tend to be porous, while roll forming work hardens the metal.
Those are my thoughts so far. Good luck with this project.
