Is wheel center bore critical?

[LyleB]

I'm having a new axle installed on my Scamp 13 in a few weeks. The axle was purchased from Scamp directly. As a result, I need to replace my 4 lug wheels with 5 lug wheels.

In researching, I find that the standard lug pattern seems to be 5 on 4 1/2, but that the wheels have differing center bore dimensions.

I also find that on some axles, the center bore only needs to be large enough to fit over the hub (lug centric) on other axles the center bore must be an exact fit (hub centric).

My question, does anyone know, off hand, which Scamp uses? Is the center bore critical when replacing Scamp wheels?

[redbarron55]

There are basically two kinds of wheels. Hub centric and lug centric.
My VW has hub centric wheels and that means that the wheel is kept centered by the fit to the hub.
My Scamp and all of the trailers I know about are lug centric which means that they are centered by the cones in the lug holes and the cones on the inside of the lugnuts.
The center has to have enough clearance time fit over the hub in this case.

Sent from my SCH-I605 using Fiberglass RV mobile app

[Steve L.]

Obviously it's critical that the center bore is greater than the hub diameter. Other than that it makes matching up the wheel holes to the studs easier when mounting the wheel to the drum, (if you just hang the wheel on the pilot then rotate the wheel only until the stud and hole line up) but once you snug up the first conical lug nut it's pretty much served its purpose.

[getaway1]

Wheel center hole that just fits the hub is stronger, and should the nuts loosen, it may help the wheel stay on until you can stop safely.
If the wheel is held only by the lug nuts they can pull through the holes in the rim very quickly if there is much of a load involved. Measure the hub diameter with a caliper or dividers and shop around for rims that fit your new axle properly. I lost a wheel one time and never want to relive that experience. A trailer wheel that loosens may not be heard or felt in the tow vehicle at all !

[Jack L]

If you want hub centric wheels, I think you are limited to steel very plain wheels only. Every "fancy" steel or alloy wheel I've seen has been lug centric so the decorative cap can be used.


There are thousands of lug centric wheels in use. I've used lug centric wheels on many vehicles without a problem.

[Steve L.]

The studs/nuts are got going to pull through the wheel holes. The studs will break first. I have nothing against hub centric or bolt centric wheels but that's not one of the issues to concern yourself with.

[mary and bob]

Originally Posted by Steve L.

The studs/nuts are got going to pull through the wheel holes. The studs will break first. I have nothing against hub centric or bolt centric wheels but that's not one of the issues to concern yourself with.

There is a photo that was recently posted on a Casita group of a wheel that did exactly that, but the stud holes cracked out to the spoke holes in the rim. This was caused by a sway condition. Must have been a real serious sway, as it tore one wheel right off and cracked the other at the stud holes. An unusual extreme case for sure, and amazingly the trailer stayed upright.

[redbarron55]

Originally Posted by mary and bob

There is a photo that was recently posted on a Casita group of a wheel that did exactly that, but the stud holes cracked out to the spoke holes in the rim. This was caused by a sway condition. Must have been a real serious sway, as it tore one wheel right off and cracked the other at the stud holes. An unusual extreme case for sure, and amazingly the trailer stayed upright.

This is most likely a problem with loose lug nuts causing localized stress at the lug holes.
There may have been incorrect nuts or wheels, but the lug nuts will not pull out under anything resembling normal operations.
I noticed that my Flexiride axle calls for 90 ft.lbs on the lug nuts and cautions that these need to be retorqued regularly especially with new rims that have not had the paint worn off where the lug nuts seat and the back of the rim where it mates to the hub.
Cracking is normally an indication of repetitive stress and not a single event.
I have not found the picture, but I have a lot of industrial experience at looking at all modes of failures.

[Donna D.]

Originally Posted by mary and bob

There is a photo that was recently posted on a Casita group of a wheel that did exactly that, but the stud holes cracked out to the spoke holes in the rim. This was caused by a sway condition. Must have been a real serious sway, as it tore one wheel right off and cracked the other at the stud holes. An unusual extreme case for sure, and amazingly the trailer stayed upright.

I scooped those pictures from Facebook

[redbarron55]

Loose lugnuts are to blame here. You can see where the holes were wallowed out.
The repetitive stress caused the cracking before the wheel came off.
Looking at the surviving one is a better indication.
These are safety wheels that have the compression ridge around the inner and outer part of the clamping zone and if they are not torqued properly this can happen.
This is why you are cautioned to torque the wheels!
The inner part of the wheel is made to deform slightly to allow for the proper stress to be built up between the lug nuts and the wheel and not get loose, but it depends on the nuts being tight enough in the first place.
This is actually safer and more reliable than a flat surface in this area.

Check the torque on the lug nuts like the manufacturer says!

Sway did not cause this, but I guarantee that the trailer swayed a lot when it lost a wheel.

[mary and bob]

Thanks Donna, kinda looks like loose nuts on the wheel that is still on the trailer. May have contributed to the uncontrollable sway. I'll let the other analysts decide. Certainly an extreme condition whatever happened.

[mary and bob]

Owner stated sway occurred when they were passed by a big truck. No report of speed

[redbarron55]

The passing truck could have been what put the side load on the trailer to precipitate the sway, but those wheels were ready to come off anyway.
I have seen a lot of race car wheels that had lugnuts not tightened properly and in the car the vibration is very noticeable. but on the trailer not so much. Which is why many do not bother to balance their trailer tires.
No passing truck caused the sway that damaged these wheels!
This was an accident looking for a place to happen

[Jack L]

Lug nuts can also be over torqued putting excess stress on a small area of the wheel. I have seen steel wheels with spider web like cracks around all the lug holes and there was rust in between some of the cracks indicating they were old. This could have been caused by over torqueing. An air impact wrench, used improperly can easily overtighten something. The purpose of using a torque wrench is to get it right. Not too loose but not too tight.

[redbarron55]

Normally the excess torque might lead to the lugs breaking.
These trailer wheels need to be torqued properly due to the design of the center of the wheel.
The lugs are located in an area that is dished slightly so that the nuts will deform the steel in that area and make a more secure mounting. They will hold torque better than a flat wheel.
The wheels are either painted or powder coated and until this coating is either worn off or compressed the wheels need to be retorqued often.
If a new wheel is installed this is of particular importance.
The wheel and hub should be cleaned at the mating surfaces and the nuts and lugs NOT lubricated.
After the wheel mating surface and the cones where the nuts fir into the wheel have been scoured of paint the lugnuts will hold torque.
Until that occurs the wheels need to be checked. Best is to use a click stop torque wrench and back off the nut a little so that you can turn the nut until it clicks. If you check it by just pulling on a tight nut it will click alright, but the torque may not be correct since the torque is a dynamic thing.

[Donna D.]

This is the text to go with the pics I posted:

Heading east on I-40, just before Albuquerque, we hit a bump coming off a bridge, while passing a semi. The casita fish tailed and wouldn't recover. The tire rim tore thru the lug nuts and sent the tire flying at at least 60 miles an hour across the lane, down the side, across an access road and about 10 ft into a field. After getting the spare on, we noticed the other side tire rim tearing out. We hobbled to camping world. PLZ be super careful out there, we truly have been watched over by angels

[FRED SMAILES]

Did you see how much stuff is hanging off the back of that trailer?
I too have a lot of experience with wheels and tires I have worked in a custom wheel shop, raced circle track and drag strip mounted and dismounted my own tires my whole life. I agree with Red baron.
Plus the stuff on the back of the Casita acts as a pendulum once that weight gets moving it takes more tongue weight to overcome it. Improperly torqued wheels plus all the factors stated and most likely speed as they were passing,, like they said "their angels" had to step in to save the day.

[sokhapkin]

"while passing a semi" says it all. Semi trucks on I-40 in Albuquerque area usually run at 75+ mph speed.

[Steve L.]

If the lug nuts were ever grossly overtightened at some point the bolt threads can stretch so that the next time you tighten the nuts you get a false torque reading before the wheel has been clamped down properly. Hard to tell after the fact. Just a general observation. Like tires, studs don't "heal". Treat them badly once...

"Grossly over tightened" means different levels that depend on stud size and the grade of the studs. 1/2 (and M12) studs are troublesome. The torque to yield is not much higher than the usage torque. There are other considerations as well.

There are only a few thousands of an inch of elastic stretch (not "yield" which is a plastic deformation, i.e. permanent) in a properly torqued stud. As alluded to earlier, wearing away of paint can easily "relax" the joint to virtually finger tight. Retorque often on new wheels.

[BillE]

Well..to answer the question with a question...is it critical?

First...if the bore was not there at all would it assemble to the trailer...IS IT CRITICAL?

If the bore was too small....would it assemble to the trailer...IS IT CRITICAL??

If the bore was so large that it left a thin wall by the lug nuts causing a failure...IS IT CRITICAL???

You also have to take into consideration the clearance for the bearing hub

I'll let you decide