Weld spacer to a rim - Solved.

[o_man_ra23]

Go with your instincts... its safer and better engineering practice

[Mooro]

Welding = Localised heating, distortion, internal stresses and destruction of factory heat treatment*. Just not a good thing to do to a wheel..

* - I've read about wheels bending more easily after powder coating...

Just thinking about this a bit more cos I'm possibly gonna have to go down this path. My thinking is that the HAZ (heat affected zone) is only going to be 5-10mm deep at the most and with correct pre-heat you can minimise residual stress so the majority of the wheel will be unaffected.

I'd love to see something like an FEA plot with the typical stress distributions through a rim but I'd hazard a guess that the outer corner of the inner mounting face of the wheel is not an area of high stress, keeping in mind that by adding the spacer you will be adding additional metal in this area anyway.

It's not something I would want to bust out the oxy and have a shot but I reckon with a bit of planning and research, welding can still be a good option.

Thoughts?

[Ben Wilson]

Yeah - But you don't know what heat treatment (if any) the wheel originally had.

The only way I can think of to be sure you are doing it right is to normalise the entire wheel after welding and then heat treat it again. Without knowing exactly what heat treatment was originally applied, you'd be playing with fire..

Bolt on spacers have none of these problems...

[CrUZida]

I see no reason why it can't phyiscally and safely be done (assuming its done correctly as you've stated)

However, getting someone to sign a legal document stating that its 100% safe may be another matter.

[o_man_ra23]

The outer part of where you would weld a spacer IS a high stress point. You have all the torque from the lateral forces on the tyre pushing on that point. Its the most probable fail point (from a stress point of view, not taking into account areas of weaker material) of the entire wheel, due to the fact that the lateral forces get multiplied by the distance from the tyre outer to the outer point of contact of the rim. This is why this area is typically thicker than the spokes of the rim.

I would be against welding a rim... as Ben said, you need to normalise and re-heat treat the rim afterwards for it to be safe, and then as Cruzida said, youve gotta find an Engineer willing to put his balls on the line to say its safe (rim manufacturers pay their engineers to put their balls on the line, its cheaper just to buy a correct fitting rim)

Also, NCOP section LS states that no spacer is legal (unless fitted by manufacturer), and doesnt mention an exception for bolted spacers, so if your engineer is to apply the NCOP as they should, it would mean that it needs to be either factory fitted or an ICV for a spacer to be legal.

[Mooro]

Just trying to understand your description of why it is a high stress point. Just thinking aloud So by lateral forces you are referring to sideways loads which would be present during cornering?

So this load acts at the point of contact between tyre and road so you have a moment applied through the spokes and reacted where the spokes attach to the wheel hub...to my why of thinking this is the critical area in resisting these stresses...I don't see how this then translates to high stresses at the back of the hub? Obviously there will be stresses present, maybe some compression loads to resist the moment acting on the hub but I don't see how it is a high stress area...I guess it depends on what we consider a "high stress area" though.

I certainly wouldn't go fiddling around anywahere near the spokes and their attachment to the hub but on a lot of the lightweight rims I see the back of the hub is not continuous and actually has metal removed as a weight saving measure....it is reinforced around the bolt holes which is obviously a high stress region.

I wish I had some good photos to illustrate what I'm talking about cos it's bloody hard to describe .

I wonder if manufacturers would ever release FEA images showing stress distributions...I might search on the web and see if I can find something.

[Mooro]

This doesn't really add anything to the current discussion but here is an interesting couple of pictures showing an FEA of a wheel but who know what loads have been considered and unfortunately it doesn't show the back of the hub,

http://img232.imageshack.us/img232/5554/4spokegz7.jpg
http://img232.imageshack.us/img232/2...v3a1200rj0.jpg

[Mooro]

Here is something a bit more like it,

http://img482.imageshack.us/img482/1710/wheel1zj9.gif
http://img206.imageshack.us/img206/7258/wheel2tj9.gif

Shows the high stress where the spoke attaches to the hub as expected to resist any lateral forces...whether those stresses extend right to the mounting face at the back of the hub depends on each wheel design. Also the size of the heat affected zone from the welding is up to debate. Personally I think it will only be 5-10mm deep as the heat will dissipate pretty quickly but I may be wrong

[Ben Wilson]

Very nice - Notice the stress concentrations around the studs in the second picture? Do you really want to be welding anywhere near that area?

[Mooro]

Yeh but my interpretation is that that is at the front of the rim and the stresses are due to the attachment of the spoke to the hub at that point. Depending on the design of the wheel obviously but the mounting face at the back of the hub is a fair distance from this area...I don't actually think the corner of the mounting face will actually be doing much to resist these stresses as the stress concentration will be at the corner between the spoke and the hub....definitely don't do anything if it is near this area.

[Gibbon]

You actually need a 30mm positive offset rim, to get rid of the 5mm spacer.

cheers Chuck.

I'm having a prick of a time trying to locate some 17x7 < 30mm offset rims. I need that size so I can reuse my existing tyres. Checked all the forum sponsors - but no luck - I don't really want to pay RRP if I can avoid it.

If I went with a greater than 50mm offset rim, and used a 20mm bolt-on spacer (*) - would that achieve the same effect?



(*) Assuming the engineer is happy with this and will sign the paperwork saying so....

[Mooro]

+50mm offset with a 20mm spacer is effectively a +30mm offset rim. Have you thought about importing some rims of yahoo Japan?

Also what car is it going on and what stud pattern? if it is 4x114.3 or 5x114.3 you should easily be able to find decent offset rims by looking at the silvia/skyline forums.

[o_man_ra23]

Gibbon, try BSA rims, I looked through their site and was pleasantly surprised at the range of wheels they have with +25ish offset.

Mooro,
Think of it this way. Grab a plastic ruler and hang it off your desk, about half on the desk and half off. Hold the ruler firmly to the desk with one hand near the edge of the desk, and with the other hand, push down on the ruler from the very end of it. Where is the greatest amount of stress applied?? Well if you keep pushing the ruler, it will break where it meets the desk. Any 10 year old who has gone too far with the musical ruler game can tell you this.

So, translate that, your hand was the studs, I hope your hand wasnt at the very edge of the desk, but rather a bit in, like a stud would be. The desk is the hub, solid cast steel, not going to break from road stresses, and made of much stronger material than your rims. The ruler is the rim, alloy is flexible, and so the plastic ruler does an ok job of representing it. You apply pressure at the end, like where the tyre contacts the road... the ruler bends more the closer to the desk it goes, and less at the end where you are applying the pressure. This is due to torque being a multiple of force applied, by the leverage distance.

Can you see what I am getting at?? From engineering basics (without having to go into FEA), its pretty easy to see that the high stress point of the rim is where it meets the hub. This is why rims are thicker there. They are then recessed for weight saving and a number of other reasons, but ribs are left in place for rigidity.

Clear as mud??

[wilbo666]

Also, NCOP section LS states that no spacer is legal (unless fitted by manufacturer), and doesnt mention an exception for bolted spacers, so if your engineer is to apply the NCOP as they should, it would mean that it needs to be either factory fitted or an ICV for a spacer to be legal.

One can look at this in a number of different ways...

If it bolts in is it a spacer? Or an adapter? One could say that as it bolts on it isn't a 'spacer'...

Also by the letter of the law you aren't allowed to change a car that has rear mount front disks to disk over hat...the disk is a spacer now isn't it... and its between the hub and wheel which the NCOP says is a no-no unless the manufacture made it like that! ...in my example the manufacture didn't make it like that, they made the disk rear mount to the hub... So how does that work?

Seeing as everyone seems to have no dramas with disk over hat brakes, and spacers under disks even it seems to me that the laws are a bit vague / open to interpretation...?

Cheers
Wilbo

[o_man_ra23]

But it isnt a spacer, its a disk rotor. A spacer has no other purpose than to move the rim outwards... the disk rotor has the purpose of... well being a disk rotor, so it is not a spacer. So yeah, using my interpretation, the letter of the law allows hat type rotors to be used.

Back to the bolted on spacer, it is up to the engineer's interpretation of the devices use. Technically its illegal, but if you claim it is an adaptor, then its legal... very much a grey area.