Wheel Load Ratings vs actual vehicle weight

[titanmax]

I am trying to determine how a Wheel Load Rating actually relates to the weight of a given vehicle. This would be related to selecting aftermarket wheels for passenger cars and SUV's in general on road use. Also, relating to dedicated track wheels where the actual vehicle curb weight plus driver can be calculated accurately.

The literature I have read basically states to divide GVWR by 4 and then make sure the Wheel Load Rating meets or exceeds this number. One issue I see is that many cars do not have a perfect 50/50 weight split to the front and rear axles so dividing by four does not seem very accurate. The other obvious issue is that this only looks at the static load and does not take into account potholes, curbs, etc. This leads me to believe that the Wheel Load Rating is not necessarily an exact figure and that it is more of a range? Is there a standardized way to determine this range?

Relating to dedicated track use wheels where the actual curb weight plus the driver can be calculated precisely. In most situations vehicle owners simply do not know the exact curb weight of the vehicle plus passengers and cargo can vary over the course of a day so it makes sense to stick to the GVWR. With dedicated track wheels on the other hand where the driver will not have any cargo and can get a more precise weight of the vehicle and driver how would Wheel Load Rating be used in this situation?

Thank you in advance for any input.

 

[GregLocock]

I'll let you into a little secret. With the best will in the world wheel designers cannot predict the loads their wheels will see, so the load rating you get is very much a ballpark figure. If the wheel gave a load rating that was tire sidewall height and tire pressure dependent that would be a start.

I'm not really convinced that track racers are that much better off, what load does a wheel see when it hits a kerb, every lap, for 70 laps, on one particular corner?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[CapriRacer]

I think you are going to find that the rating of a wheel is larger than the worst case of loading by wheel position. That applies to tires as well.

In both tires and wheels, there is more to designing these than just the static load.

Yes, dividing the GVW by 4 is inherently wrong - and seems so obviously wrong that you wonder why this was even cited by anyone ever!

But if your ultimate goal is buying wheels, you can be assured that quality wheel manufacturers take the effort. If you buy low end stuff, do not depend on it.

But if you are looking at wheels for track usage - consider that at the top end of the sport, wheels are considered expendable. An accident should result in throwing the wheel away.

 

[CapriRacer]

And one further thought:

Because of the bolt patterns, wheels can be designed more specifically. Wheels that fit SUV's will not fit passenger cars (except by design) and vice versa.

 

[Xwheelguy]

For OEM, the customer would more often than not supply the wheel design loads (it was based off the axle rating and had a safety factor added into it). If the wheel was to be used on multiple vehicles, then the highest rated axle loading was used to determine the design loads. For the most part, aftermarket wheels used the highest design load rating of a tire that would fit the particular rim size. The design load rating was taken from the tire & rim books. I believe the idea was that the tire was to fail before the wheel (since there was a safety factor thrown into the wheel test load calculations). Whether this was good or bad practice is probably up for debate.

Tim Flater
NX Designer
NX 7.5.4.4 MP8
WinXP Pro x64 SP2
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

 

[titanmax]

Thank you very much for the replies, VERY much appreciated.

If I am understanding all this correctly the number given as a wheel load rating is based on the highest static weight vehicle that the particular wheel is intended to go on not the static weight that the wheel can handle determined by testing?

Regarding the bolt patterns controlling whether or not a wheel be a match for a car or SUV, I have also read about this. In fact this is one of the reasons I am trying to understand the meaning of aftermarket wheel manufacturer supplied wheel load ratings. I think this may no longer be a means to determine wheel load rating. I think this is because many SUV's are very car like in this day and age. I think this may still be possible with some car lines such as Ford where the heavier vehicles use higher number of wheel bolts. My knowledge is mainly in European car lines and there is a pretty large difference in vehicle weight for a given bolt pattern. An example of this would be BMW 5x120 bolt pattern which is on the X5 SUV that has a curb weight of around 5,000 lbs and the 1 Series coupe which has a curb weight of around 3500 lbs. This same bolt pattern is used pretty much throughout the BMW range.

How can a consumer use the Wheel Load Rating provided by a wheel manufacturer to choose a wheel that is a good match for their application? It seems like the wheel load rating is really a ball park or range, I guess what I am asking is what would be a safe range to use when trying to match aftermarket wheels to a car or suv for street use and also for dedicated track use? Is it safe to say that as long as the wheel load rating is within say +/- 30% of the actual curb weight the wheel will be a good match?

Thanks again!

 

[Xwheelguy]

I can't speak for all wheel manufacturer's - but if I were still working for my former employer and I was asked to design a wheel to fit similar vehicles which all had different load ratings, I'd do just as I outlined above. I'd find the highest rated tire design load that would fit the rim size being used and base my wheel load on that (make note that we did not usually publish or cast-in the wheel load ratings - some manufacturer's do).

Again, I cannot speak for all consumers, but I don't feel that most consumers pay much attention to the wheel load ratings, as those are usually higher than the applicable vehicle. Those might be put on there to help distinguish between different sized rims that have similar designs (i.e. a spoke design is common for a series of wheels made for SUVs, light trucks, 1/2 ton trucks and 3/4 ton trucks). The rim sizes and bolt patterns might vary from the SUV up to the 3/4 ton truck, but the overall design of the wheels might appear identical. This could be to help someone distinguish the wheel that's meant for the SUV from the wheel meant to be used on the 3/4 ton truck.

Typically, the wheel manufacturers publish the target vehicles for the wheels for what I assume is to help the consumer simplify the process of picking a wheel for a specific vehicle. Unless you're going to be racing on these wheels or using the vehicle in any other manner than typical on the road driving, I'd say just pick what is intended to fit your car and don't get too worried about the wheel's load rating. Please elaborate about your planned vehicle usage if you're still concerned.

Tim Flater
NX Designer
NX 7.5.4.4 MP8
WinXP Pro x64 SP2
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB

 

[GregLocock]

In practice what will happen is that you'll hit a pothole and either the wheel will break or bend to an unacceptable amount, or it won't. The test condition is very poorly defined, as is what is acceptable to the customer. Oddly enough one of my jobs is estimating that load, and to make the process bearable we have invented a standard series of wheel smashing tests. But the customer doesn't know what our tests are, and would not be able to drive to that profile.

In Australia a long time ago we had a a particular imported wheel that caused unacceptably high warranty returns, so we have since added extra tests for wheels for the Australian market as well. Imported wheels still regularly cause problems.

When you add in tire profile, pressure, and suspension tune, to the mix then the best bet is to do as Tim says and overdesign it.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[titanmax]

Thanks again for the replies. Lots of great information.

I understand that when a manufacturer, especially one that has been around for a long time states that a certain wheel will work properly with a certain car or suv that all should be fine. I think we can pretty much take their word for it.

I am wondering though in applications where trying different combinations within a bolt pattern for track use to try to optimize size, weight, etc...many manufacturers of off the shelf wheels do provide load ratings for their wheels as well as many custom wheel companies (that build wheels to order).

I will provide an example. Let's say a particular suv has a GVW of say 6700 lbs, actual weighed curb weight with driver is about 5800 lbs.

One wheel manufacturer offers wheels with Load Ratings of 1350 lbs , 1500 lbs, and 1980 lbs (depending on diameter and width). Some sellers of the wheels state that wheels with all three load ratings will work with said vehicle without issue. Some say that only the 1980 lbs load rating will work.

Another example with a different manufacturer of custom made to order wheels has wheels with 1600 lbs load rating and manufacturer states they are compatible with said vehicle.

Would it be possible to use all 4 of these load rated wheels on the vehicle in question? In other words do these wheels all fall within the range of the load ratings?

Thanks again!!!

 

[GregLocock]

I'd go with the 1980 recommendation myself, the others won't break as soon as you fit them, but may suffer early fatigue failure or failure in potholes. The SAE test for wheels is rather more taxing fr steel wheels than alloys, I can't remember a fatigue failure on alloys.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[CapriRacer]

Titanmax,

There are some issues with what you've posted. I'm struggling to imagine why a wheel manufacturer would say it is OK for a particular wheel to be applied to a car where the wheel's rated load is less than the curb weight. That does not make sense. I'll bet there is some tidbit of information that is missing that will make everything work out. So let's get to specifics:

What wheel manufacturer are we talking about? Which wheel in particular? What vehicle?

 

[titanmax]

The first three weights from the off the shelf wheels are the same model/style wheel in various diameters. Only the largest diameter carries the 1980 lbs load rating. The manufacturer suggests only the 1980 lb load rated version for the vehicle in question. The sellers/dealers are the ones that offer all three load ratings (sizes) for that vehicle.

As for the custom wheel with the 1600 lb load rating, the actual manufacturer along with the sellers/dealers recommend the wheel for the application.

Thanks!

 

[CapriRacer]

Titanmax,

This still doesn't make sense. I would like to verify your info, so could you please post the exact wheel part number (a link would be very helpful.) And we need to be specific about the exact vehicle these are being applied to.

I strongly suspect there is an issue that is not being identified that will clear this whole matter up.