Tubeless tires on rims without hump

Shocks, Springs, Brakes, Frame, Body Work, etc

Moderator: Team

Post Reply
german4inline
Member
Member
Posts: 157
Joined: Tue May 20, 2014 5:09 pm

Tubeless tires on rims without hump

Post by german4inline » Wed Jul 19, 2017 6:43 am

Guys,
on my Renault Alpine sportscar, I´m using tubeless tires with rims without hump. But the car is just since some 100 kms on the road, not really hard pushed in corners and straight. We ´ve had some interesting discussions here in Germany about the risk to use tires without tubes on rims without a hump. Some guys are claiming that the tire might be pulled off the rims once hard cornering without even trying to do that even when the pressure is ok. Others claim that the risk is only present once the tire pressure is way to low, thats as well my opinion. I can´t believe that the hump prevents the tire from pulling of once the pressure is ok. In Germany at least it´s sometimes claimed that the use of tubes is generally forbidden due to the internal friction on the tire and the danger of rubbing them to break. Doesn´t matter for me, I definitly wouldn´t use tubes anyway. My tires on the rear are 235/45-13 and I can´t suggest that the low cross section area of the tire would accept a round CSA of the tube without bending the tire patch outside in an unacceptable way.

I could suggest that the invention of humps was 50 years ago ok to give some more security for tires which are not frequently checked for correct pressure and maybe someone might have a patent on it and made good money with. But what I´m missing is a straight statement of maybe a tire manufacturer who states that the safety margin with a hump by DEFINITLY CORRECT TIRE PRESSURE is not needed. Everyone has a feeling that it might be required or even not - but I`m missing a straight statement from experts or maybe from racers with various cars which are using tubeless tires on no hump rims for long times. Please tell me about your experiences.

I´m very curious about your statements.

midnightbluS10
Member
Member
Posts: 195
Joined: Sun Oct 20, 2013 8:41 am

Re: Tubeless tires on rims without hump

Post by midnightbluS10 » Sat Jul 22, 2017 6:10 am

What are rims without hump?


Is this correct?
The hump is a protuberance within the channel that keeps the tyre bead in place even when the pressure is zero.
From:

http://www.bartubeless.it/en/bartubeless/rim-hump

german4inline
Member
Member
Posts: 157
Joined: Tue May 20, 2014 5:09 pm

Re: Tubeless tires on rims without hump

Post by german4inline » Sat Jul 22, 2017 1:13 pm

Yes, the link you´ve attached declares the hump function. To my opinion, for a daily driver all arguments for humps are ok. On a car, what you doesn´t check the tire pressure daily, the hump is an additional safety to prevent from pulling the tire off with low pressure. But I think if the pressure is dropped for a critical amount, one should notice that after the first corners or even by strange steering feeling. But that wasn´t my inital question:

If the pressure is ok, could it be possible to pull down a tubeless tire from a rim without hump? Or vice versa: Needs an tubeless tire an additional safety of an hump to be sure not being pulled off the rim ( of course when quick cornering with big side loads) even once the pressure is ok?

My car is no daily driver, it´s used for track days or sometimes fast road use and when I intend to go fast, I will check the tire pressure before starting.
If there´s a sudden pressure loss, I think it´s relativly no matter if you have an hump or not. You will loose control over the car when the tire has no pressure at all, but stays on the rim. But the discussion is: Is it possible WITH CORRECT PRESSURE that whilst hard cornering the tire moves a bit because no hump holds it in place, the tire starts to leak air pressure, pressure drops down, tire moves more and leaks more and pressure drops down even more. The initial question is if it´s possible initially that a tire looses pressure because it could move more without a hump.

In Germany, lots of guys telling various stories : In no case you should go with tubeless tires without humps. But the other way round: it´s been warned about using tubes because they will warm up inside the tires by rubbing against each other.Some tire dealers are refusing to mount tubes basically because it´s a historic technology. So in consequence, rims without humps ought to be scrapped because there are no tires for. Therefore I`m going to discuss this topic this way....

PackardV8
Guru
Guru
Posts: 5069
Joined: Sun Jul 30, 2006 2:03 pm

Re: Tubeless tires on rims without hump

Post by PackardV8 » Sat Jul 22, 2017 2:29 pm

Just personal experience, but for many years I've run both street and race tires on straight-bottom wheels (no hump) and never thought twice about it and never had any problem whatsoever.

OTH, Germany has much more strict TUV (TTechnischer Überwachungsverein, English translation: Technical Inspection Association) certification for aftermarket wheels than does the US. Many wheels sold here are not allowed in Germany and several other Eurozone countries.

At a guess, any wheel without a hump was sold prior to TUV standards. And this will reopen the discussion of "are old magnesium wheels safe to use?"
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering

german4inline
Member
Member
Posts: 157
Joined: Tue May 20, 2014 5:09 pm

Re: Tubeless tires on rims without hump

Post by german4inline » Sun Jul 23, 2017 6:19 am

Thats a statement what supports my opinion =D> more would be appreciated, but as well negativ experiences with pulled off tires....

The wheels without hump were legal for use with tube tires - in the past anyway. Tube tires has a smooth, slippery surface on the inside opposite to tubeless ones to make sure that the tubes will "bed in" properly to avoid any risk of folding and crinkle. With the rough surface of tubeless is this not provided and the tubes maybe rubbing and potentially damage the surface even to wear through. Due to this considerations, almost no tire manufacturer is interested in the old tube tires with low quantities. However, with nowadays high performance cars those issues will come up much more than with the old classic with less than 100 hp, and to my knowledge, it´s even not advisible to join low section tires with tubes. I can´t imagine that the round cross section area of the tube will be accepted by a 45 cross section of a tire. This problem comes up mainly with classic cars which are modified to modern power output by using the old wheels ( without hump) and modern tires which are not intended to use with tubes. Furthermore, a high performance car will spin the wheel inside the tire and there are longitudinal forces along the tubes that the valve (whats part of the tube) will be prone to be sheered..

As far as I know, there are no "hard" rules from whatever institutions what defines that tubeless tires may not be installed on wheels without humps.
I don´t know as well if tubes are definitly forbidden to install in tires what are refered as tubeless ones. There´s a big scope of discretion even in Germany and at German TÜV, in other respects some classic cars has to be taken off the road. If you catch an TÜV-operator whats an $%&}²?=)`?, bad luck....But most guys are ok and not less are owing classic cars by themselves.

To my experience, the TÜV never checked out for having tube tires at all if the hump is missing. Maybe the younger engineer generation of the TÜV operators does not know the existence of wheels without humps.... :lol:

chimpvalet
Member
Member
Posts: 94
Joined: Wed Jun 04, 2014 2:02 am

Re: Tubeless tires on rims without hump

Post by chimpvalet » Mon Jul 24, 2017 12:12 pm

A close friend equipped his Lotus Esprit with BBS 3 piece race wheels for the same sort of use as our German friend's Renault. Front rims were "flat band", as BBS calls them, "non-drop center" as known in North America. No troubles at all in hard track day use, nor on long cross-country touring. Changing a tire is more involved because the tire cannot be extracted with a typical mounting machine, one must disassemble the rim shells from the center to remove then reassemble when new tire is in place. The drop center is designed to be a failsafe feature for the ordinary driver who may not have the slightest idea that air pressure is what keeps their tires securely in place. Flat band should be no problem for an attentive operator like our friend.
Steve

chimpvalet
Member
Member
Posts: 94
Joined: Wed Jun 04, 2014 2:02 am

Re: Tubeless tires on rims without hump

Post by chimpvalet » Tue Jul 25, 2017 12:29 am

On reflection I believe it was for ease of mounting tires that rims are usually drop center. Regarding safety in the case of loss of pressure the "hump" referred to, known as a "safety bead" in North America, is to restrain the tire from separating quickly from the rim, correct?

german4inline
Member
Member
Posts: 157
Joined: Tue May 20, 2014 5:09 pm

Re: Tubeless tires on rims without hump

Post by german4inline » Mon Aug 14, 2017 9:54 am

Yes, the "hump" is visible as an circular groove from the outside of the wheel if it´s a pressed steel or aluminium rim. From the inside it´s of course a hump. On an alloy cast wheel, the hump is not visible from the outside. It has nothing to do with "drop center". This is only for easy mounting. So we do not know if the Lotus Esprit has had an hump, the drop center doesn´t influence the tendency to pull the tire off at all.

chimpvalet
Member
Member
Posts: 94
Joined: Wed Jun 04, 2014 2:02 am

Re: Tubeless tires on rims without hump

Post by chimpvalet » Wed Aug 16, 2017 1:32 pm

Yes, my friend, we do know whether this Lotus has a hump in its front rims as they were custom order, race wheel assemblies in 3 piece form. To be more clear these fronts were built up using 15 inch, 20 bolt BBS shells in spun aluminum with no hump known as " flatband ". They use a centre of the type " E50 " in magnesium and are not the cast 1 piece wheels from BBS which were fitted as standard on Esprit from about '82 onward.
Steve

german4inline
Member
Member
Posts: 157
Joined: Tue May 20, 2014 5:09 pm

Re: Tubeless tires on rims without hump

Post by german4inline » Sun Aug 20, 2017 5:04 am

Steve.,
thanks for clarifying this detail. I know these 3-part wheels, I have a set of them for my Alpine, very,very rare, and as well without hump and drop center. Sorry if I was confused about your posting from 25th July 4:29am, it sound a bit like a question :wink: Anyway the message for me is important that other guys are confirming that a hump is not needed as long as tire pressure is ok.

peejay
Guru
Guru
Posts: 1227
Joined: Tue Aug 10, 2010 9:16 pm

Re: Tubeless tires on rims without hump

Post by peejay » Sun Aug 20, 2017 12:17 pm

There are a lot of tubeless 16.5/19.5/22.5 tires and wheels on the road.

Not only do they not have the safety bead, the angle of the bead seat is MUCH different, originally to accomodate the use of inner tubes.

Image

(This is why every 16" tire, as well as 14" and 19" and 22", has "Not for use with xx.5" wheel" moulded into the sidewall. The bead shape is quite different)

dwilliams
Expert
Expert
Posts: 927
Joined: Sun Oct 15, 2006 10:00 am

Post by dwilliams » Sat Sep 02, 2017 1:05 pm

Back in the early '80s we were racing a Chevy Monza in SCCA Solo I. We had a local company called Saber Wheels make us up a set of 13x9 wheels with the correct offset and bolt pattern. The wheels were spun aluminum halves bolted together. They had no bead retention humps, and we raced the car for several years with no problem on either slicks or street tires. The salesman made a particular point that the wheels did not meet DOT(?) standards due to the lack of retention humps, and were therefore not intended for street use.

chimpvalet
Member
Member
Posts: 94
Joined: Wed Jun 04, 2014 2:02 am

Re: Tubeless tires on rims without hump

Post by chimpvalet » Mon Sep 11, 2017 6:59 pm

Question for German4 regarding BBS race wheel source - can you suggest a vendor with large selection of centres like the E50 and E52? Also a vendor for good selection of rimshells?
Steve

Post Reply