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18 Posts

Posted - 04/20/2004 :  8:14:59 PM  Show Profile  Reply with Quote
Hey, y'all! :-)

Everyone was so much help with the wheel FAQ discussion, and I appreciate it greatly. I have finally gotten round to putting together an FAQ of sorts, but it's still a bit rough. PLEASE feel free to critique or add anything missing. There are a few unanswered questions still in the piece, so if you have the answers, fire away!


Eric von Kleist

A Wheel FAQ that started as a request for one.

I was confused about wheels. I had read many different things, but was still confused. I asked about wheels on a couple of the school bus groups, and the answers are incorporated here.

Brad Barker, Administrator of the fora provides these resources on the net for information about wheels and tires:

See article in back issue. June/July SBF [School Bus Fleet] magazine [], 'All wheels are not created equal'. This should give answers. Contact They will send you free of charge everything you need to know about all types of wheels including wall charts, training manuals and video tapes.

General Rim Types

Rims vs. Split Rims

With regard to the mounting of tires on the wheel, there are two types of rims: solid rims and split rims. Solid rims take tubeless radial tires. Split rims take tires with inner tubes, and can use either radial or bias-ply tires. (Note: it seems that most tires nowadays are radial tires, although bias-ply tires are still available but not as good in some respects as the radials.) Rims are welcome at tire repair centers, and it is easy to mount tires on them. Split rims are a bit harder to get serviced because they require special mounting equipment and there are serious dangers with their potential "explosively" to come apart as tires are mounted. Split rims seem to have the reputation of a loosely packed cannon. Most of what I have read recommends replacing split rims with rims, if not immediately, then as soon as it is time to replace tires. Note: this dire warning regarding split rims seems to apply mainly to the very old type of split rims, although it does apply to some smaller degree modern split rims. From what I read and have been told, many, if not most, tire stores that cater to the trucking industry can, and will, handle either type the Goodyear place down the street might not handle the split rims, but the truck center out on the interstate is likely to be able to tackle the job.

Question: How can one tell which kind of wheel is on a bus? I have seen tire sizes referred to as 9.5Rx20 or 10.5Rx22. The smaller number is the tire width. The larger number indicates the wheel diameter. The "R" indicates a Radial tire. Is it safe to assume that a bus described as having tires with an R in the tire description has rims (NOT split rims) since split rims do not work with radial tires?

ModMech at answers:

"20" or "22" is TUBE type, 19.5, 22.5, 24.5 would all be tubeLESS.

EDITORIAL QUESTION: Im still not clear on this. Do radial tires ONLY go on non-split rims? I think the answer is, yes, but I would like verification. Sorry if Im being dense on this.

Are split rims and rims ever mixed on the used busses that are sold? That does not seem to be a wise thing to do, from my limited experience with mixing radials and bias-ply tires on automobiles.

ModMech at answers:

Technically, it IS ALLOWED, but the tires must have the same rolling radius, capacity and MUST be Radial or Not (you CANNOT mix types).

Brad Barker, Administrator of the fora provides this information about split rim types:

There were wheels (rims) that had a manufactured split that went all the way across the wheel and had a solid locking ring that held the tire onto the rim. They were [used] prior to the 1960's. They used the Dayton style center spoke system to hold them onto the axle.

As far as so called regular wheels, or disc wheels as they are truly called, there are three main styles with some variations of the multi piece wheel and locking ring. Locking ring wheels have a solid wheel and rim and use either a two piece locking assembly which consists of a split locking ring and a solid outer ring or the single piece split locking ring. There may be even more variations than that as in the solid ring that had an oblong center cut hole.

These multi piece wheel and ring assemblies used tube type tires in sizes such as but not limited to 9.00x20, 10.00x20, etc. with smaller and larger sizes.
When manufacturers started using tubeless tires the wheels changed, as an example, 10.00x20 was equivalent to a 11.00x22.5. Each has the same or nearly the same weight rating. What Joe recommends is good. Refer to a tire data book, easily available from any tire supplier, free of charge. These will give you all of the technical data that you are requesting. Again Accuride Corporation will also give you, free of charge, all the technical data about all types of wheels. All you have to do is go on-line to and ask for them to send you the information.

WHE8913 at adds some more history and information:

First, I think it is important to note that the dangerous types of split rims that no one wants to work on anymore is what Brad mentioned [as in use prior to the 1960s]. Those rims could completely blow apart if they weren't fastened securely.

The split rims that people are more familiar with today are the single rim with the locking ring type. While becoming obsolete, it has been my experience that tire shops have no problem with mounting a tire on them, but you do hear some "grumbles" from them about having to "true up" the wheel on the "Dayton" type spoke assembly.

To answer a couple of questions from the original post

First, you should not (and I think it is illegal to) mount a spoke type, split rim and a spoke type tubeless rim ON THE SAME AXLE. I think, however (since I have seen it), that you can put split type rims on the back axle and have updated the front steer tires to tubeless rims.

Second- They DO make radial tires for split rims, though they are getting harder to find. To distinguish between a radial and a bias-ply tire, the R was put in between the wheel width and the rim size, and a dash (-) is used to denote a bias-ply split rim tire. I.E: 9.00-20 would be a tire that is made of bias- ply construction, while a tire with 9R20 is a tire made with radial construction.

A final note- they also make 20 inch split rims with a "Budd" configuration. This is the locking ring type with the 10 hole mounting, rather than the 5-6 lugs, or "dogs" as I have heard them referred to.

IMHO, the 11R22.5 "Budd" hub-piloted wheel is the most advanced in the truck and bus industry in a long time, and that is what should be ordered with new buses, finances permitting.

Spoked Wheels vs. Disk Wheels

Once past the rim style, there are to be two kinds of wheels, spoked wheels and disk wheels. Each kind uses a different hub design. In order to switch from one kind to the other the axle has to have a different hub and brake system installed, and changing hubs is not really economically practical. If you are desirous of a particular wheel type on your bus, buy the bus with that kind of wheel on it: changing wheel types would involve some costly work to change the hub and the brake system.

There are two types of disk wheels, hub piloted and stud piloted. The hub piloted wheels are more like car wheels in that they are centered on the axle by the hole that fits over the hub assembly. The stud piloted wheels fit over the hub, but are centered on the axle by the studs that attach the wheel to the hub instead of by the hub itself.

The terms "Daytons" and "Budds" are used when talking about wheel styles, and the terms refer to whether the wheels are disk or spoke wheels.

Question: What are "Daytons" and what are "Budds"?

ModMech at answers:

Dayton = spoke
Budd = disc

Question: If the front wheels on a bus are spoked wheels, are the back wheels spoked as well?

ModMech at answers:

No, not REQUIRED, but almost all are manufactured that way.

Question: How hard is it to change a spoked wheel as opposed to a disk wheel? Is the difference worth worrying about...that is, is it as big a difference in terms of service and repair as the difference between split rims and rims?

ModMech at answers:

In MY opinion, for Disc brake vehicles, Spoke (dayton) wheels are preferred. Also, if you do your own tire work, Dayton wheels are much lighter and are LESS of an injury problem.

Question: If one had a flat tire out in the boondocks, would it be possible to change a spoked wheel on his own? Would it be possible to change a disk wheel on his own?

ModMech at answers:

Definately, easier [to change a Dayton rim] than with a Budd.

Number of Wheels

How many wheels do busses need? Obviously this must vary from bus to bus, and is probably dependant on the size of the bus and its loaded weight. Some busses I have seen have 4 wheels, 2 front and 2 back. Some have 6 wheels, 2 front and 4 back (dual wheels). It appears that the longer/larger busses have dual wheels in the back.

How can one tell whether a bus has dual wheels in the back from a written advertisement that has no picture. Is there some standard to go by?

ModMech at answers:

All vehicles (except motorcycles) need at least 4 wheels. Most vehicles over 10,00 GVW have SIX tires.

(Apparently I was mistaken about seeing a bus with two single wheels on the rear end. It was a picture that I was looking at, taken from an angle.)

Wheel Size

I have seen tire sizes from 16 inches to 24 inches mentioned. Are these measurements used in the same way that car tire measurements are used, that is the size indicates the size of the wheel, or do these (particularly 22.5" and 24.5" tire sizes) fit a common wheel size and just have higher/lower sidewalls?

ModMech at answers:

Yes, RIM diameters.

What are the common wheel sizes for busses?

ModMech at answers:

10R22.5, 11R22.5 are the most common "standard" sizes on Full-size units.

Note: These are tire sizes, but the second number indicates the rim diameter. The wheel sizes are described in the answer relating to rim diameters.

Question: What are the advantages to each? (I have seen it recommended that a partial "fix" for an undesireably high geared rear end is to increase the wheel size.

ModMech at answers:

Smaller tires (10R22.5):
Advantages: Tighter turning cicrle, lighter, lower step-in heights, very slightly cheaper.
Disadvantages: Lower load capacity, less resistant to impact damage (potholes), wear out more quickly, less room under vehicle for servicing, no (or negative) residiual value.

Larger tires (11R22.5)
Advantages: Lots of room under vehicle, long life, durable, high residual value, most common "truck tire", high load capacity.
Disadvantages: Slightly higher cost, greater weight, higher step-in height, wider turning radius.

Is it possible to change wheel sizes on a bus?

Is it EASY to change wheel sizes on a bus?

ModMech at answers:

Yes. But you need to correct the speedo. On '89 up Navistars, that's EASY. Older units can be less cooperative.

Note: Changing the wheel diameter on a vehicle alters the final drive ratio of the vehicle slightly, which affects the real speed of the vehicle, but unless the speedometer is modified (by changing a part) it will reflect the speed based on the old drive-train set up.

Question: Say one found a bus that met his requirements with regard to size, engine, transmission, rear end, but it had smaller/larger wheels than he wanted.

Is changing wheel sizes on a bus as easy as changing wheel sizes on a car?

Could 20 inch wheels simply be replaced with 24 inch wheels?

ModMech at answers:

With "Budd" wheels, anything is "easy" and possible. With Daytons, you WILL have 20/22.5" rims (a 20" Tube-type = 22.5" tubeless, they are completely interchangeable).

EDITORIAL QUESTION: Are there ONLY 20/22.5 rims available for Daytons? Is that what this means?

I know that changing wheel sizes can raise issues of clearance within the wheel wells and with the steering gear, but are there some common "universal" changes that can be made?

ModMech at answers:

10.00-20.00 to 11R22.5, 9.00-20.00 to 10R22.5 are the most common.

Is it necessary to have the same sized wheels on the front and rear of the bus? Is it desireable to have the same sized wheels on the front and rear?

ModMech at answers:

1. No, not on a private vehicle. On a school bus, YES - mandatory in most States.
2. Without question. Tire inventory, vehicle stability.

Tire Sizes

With cars, there is some latitude in the width of tires that a given wheel can handle.

What size tires can be put on what size wheels?

ModMech at answers:

A 10R22.5 should have a 7.5" rim, a 11R22.5 tire should have an 8.25" rim. You *can* put a 11R on a 7.5" rim, but DO NOT put a 10R on a 8.25" rim.

Can a bus with 9.5 inch wide wheels take a 10.5 inch wide tire?

Is it possible to increase the tire width on dual wheels without running into clearance issues between the tires?

If anyone can answer some or all of these questions, it would be a big help to me (and others, I'd bet) in understanding bus wheels and evaluating busses.

Please feel free to add any information or considerations that I have left out through beginner's ignorance.


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948 Posts

Posted - 04/21/2004 :  10:06:22 AM  Show Profile  Visit ModMech's Homepage  Reply with Quote
EDITORIAL QUESTION: Im still not clear on this. Do radial tires ONLY go on non-split rims? I think the answer is, yes, but I would like verification. Sorry if Im being dense on this.

Answer: Radial tires are available for ALL rim choices, and in most sizes.

EDITORIAL QUESTION: Are there ONLY 20/22.5 rims available for Daytons? Is that what this means?

Answer: "Dayton" hubs are avaialable in 20" and 22" hub diameters. The 20" hub will accept 20" (tube-type) or 22.5" (tubeless) rims, while the 22" hub will accept 22" (tube-type) or 24.5" (tubeless) rims.

By far the most common configuration is the 20" hub, which as mentioned will accept either a 20" tube-type, or a 22.5" tubeless rim.

Can a bus with 9.5 inch wide wheels take a 10.5 inch wide tire?

Answer: It depends on the Tire Manufacturer's recomendation for rim width. You can "safely" install a wider tire on a norrow rim, but NOT a narrow tire on a wide rim. Generally you will have either a 7.5" or a 8.25" wide rim (either spoke or disc). NEVER attempt to install a 9.00-20 or 10R22.5 tire on the wider (8.25") rim. Now, you should know that the tire "width" is the first number (9,10,11 or 12). These "widths" are NOT the measurements of the rim, but of the tread (or cross section). 9" and 10" nominal tires can use a 7.5" rim, 11" tires can use EITHER a 7.5" or a 8.25" rim (8.25" is the preferred), 11" and 12" tires use a 8.25" wide rim.

Is it possible to increase the tire width on dual wheels without running into clearance issues between the tires?

Answer: Yes and no. With "disc" wheels, almost any tire size will fit if the rim is of proper width for the particluar tire. With "spoke" wheels, there are differences in spacer width and wedge profiles to consider. My expierence has shown that *most often* 9.00-20.00/10.00-20.00 tires are completely interchangeable if you use the narrower 7.5" rims, just as 10R22.5/11R22.5 are. I have routinely "upgraded" from the 10R22.5 "minimum spec" tires to 11R22.5s without a rim, specer, or wedge change. There are no interfearance issues on our primarily Navister fleet.

If you want customer service, you NEED an International!
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853 Posts

Posted - 04/21/2004 :  2:39:40 PM  Show Profile  Reply with Quote
Just a comment or 2: "split rim" can be a confusing term, especially to those not familiar with the nuances of multi-piece wheels. Early versions had split bases with solid rings, later versions had solid bases with either a 1 piece split ring, or a 2 piece ring setup where the outer ring was solid and the inner ring was split. There are also wheel assemblies where both the wheel and the "ring" are solid.

When I started in the school bus business years ago, I came from the truck tire business. This was about the time when most fleets had completed the migration from tube-type bias-ply to tubeless radials. The district I work at had not completed this process. They had a mix of bias and radial tires, all mounted on 20" multi-piece wheels from 3 different wheel companies. They had mixed up parts from Goodyear/Motorwheel, Firestone, and Budd and managed not to kill themselves! So a word of caution to those who may want to work with these: Don't assume anything just because the wheels fit together. Make sure the parts match. You could have a Goodyear Ledge-Weld base, with a 5 degree Firestone Commander ring set. They were not designed to interchange.

"Is it safe to assume that a bus described as having tires with an R in the tire description has rims (NOT split rims) since split rims do not work with radial tires?"

Answer: NO, Multi-piece wheels work with radial tires. Example:1000R20 could be mounted on a 20X7.5" rim or wheel.

EDITORIAL QUESTION: Im still not clear on this. Do radial tires ONLY go on non-split rims? I think the answer is, yes, but I would like verification. Sorry if Im being dense on this.

Answer:There are still many tubetype radials (10R20, 11R20, 12R20, 10R22) around, especially on old buses. These would be mounted on multi-piece disc wheels,often refered to as "Budd" wheels, and on demountable rims, sometimes known as "Dayton" and out West, "California-wheels." These are the wheels being called "split-rims."

As far as wheel preference goes, mine is disc-type. This could be a regional thing, but either system works fine. In Washington State's minimum school bus specs, only disc-type wheels are allowed on school buses.

Common wheel sizes: most common is 8.25X22.5.

What size tires can be put on what size wheels?

Answer: same as ModMech with this addition, we use 12R22.5's on our class D pushers on 8.25X225 wheels.

Hope this helps some...

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