Seat Spacer Mod
- Thread starter v8z4
- Start date
i wouldnt worry too much, if you see what holds the seats down on a westfield then im sure what you have done isnt going to make a huge difference.
assuming the runners are about 30 cm long then youve only raised them by angle of ~3 deg i doubt very much this will exceed the tensile strength of the bolt. i would be more concerned withthem bending but as its already been stated they dont sit supported over their whole length anyway
assuming the runners are about 30 cm long then youve only raised them by angle of ~3 deg i doubt very much this will exceed the tensile strength of the bolt. i would be more concerned withthem bending but as its already been stated they dont sit supported over their whole length anyway
There is no doubt that this mod decreases the ultimate strength of the seat anchorage in a collision scenario. If you don't think so, you are deluding yourself. Was the original design overdone? I don't think so, auto engineers are not known for overkill. A 10mm bolt doesn't cost much more than an 8, until you have to buy many thousands of them. So the unchanged rear bolts are unlikely to be adequate on their own.
The lack of intermediate support or angle of the runner has nothing to do with it either way, all stress is transmitted horizontally through the bolts in a collision. Yes the problem is bending. The bolt was originally in shear, it is not intended to resist bending in any way. Any joint where the fastener is in bending is a poorly designed joint. To correctly raise the seat so that it is connected with OEM strength would entail building up a platform on the floor so that the bolt stays in pure shear.
I'm not saying don't do this mod. If it saves you serious back pain, I can see one would consider the reduction in safety for an unlikely event worth the diminished daily pain. But do not rationalise there are no consequences of this mod. You are trading safety for comfort. That is a fact.
The lack of intermediate support or angle of the runner has nothing to do with it either way, all stress is transmitted horizontally through the bolts in a collision. Yes the problem is bending. The bolt was originally in shear, it is not intended to resist bending in any way. Any joint where the fastener is in bending is a poorly designed joint. To correctly raise the seat so that it is connected with OEM strength would entail building up a platform on the floor so that the bolt stays in pure shear.
I'm not saying don't do this mod. If it saves you serious back pain, I can see one would consider the reduction in safety for an unlikely event worth the diminished daily pain. But do not rationalise there are no consequences of this mod. You are trading safety for comfort. That is a fact.
Because a lot of people keep asking me "does this raise the seat?" and obviously not getting a clear understanding of what is happening, I made a quick and dirty drawing:
This should help clear up/end the confusion.
The seat is NOT being "raised", it is being tipped back. Using my quick and dirty drawing, note that ONLY the front of the seat gets any higher. The back/butt area remains at the same height. So doing this will get the seat front up under the legs to support them.
Even though my picture shows the back rest going further back (ala gangster/gheto setting), this is only a result of my picture. The seat back still has enough adjustment to still get straight vertical is you so desire.
note: NOTHING in this picture is to scale. The spacer is not nearly as large as it seems in this picture and the angles are not nearly as severe. I just got tired of getting asked the same (should be obvious) questions over and over again so I wanted to exaggerate the change to make it clear.
This should help clear up/end the confusion.
The seat is NOT being "raised", it is being tipped back. Using my quick and dirty drawing, note that ONLY the front of the seat gets any higher. The back/butt area remains at the same height. So doing this will get the seat front up under the legs to support them.
Even though my picture shows the back rest going further back (ala gangster/gheto setting), this is only a result of my picture. The seat back still has enough adjustment to still get straight vertical is you so desire.
note: NOTHING in this picture is to scale. The spacer is not nearly as large as it seems in this picture and the angles are not nearly as severe. I just got tired of getting asked the same (should be obvious) questions over and over again so I wanted to exaggerate the change to make it clear.
This is something I have planned for my Z3 as the seat position is appealing, combined wither the offset angled steering wheel and badly positioned pedals. Certainly has been done to quite a few Z3's in the past.
As for the safety element, I'm not sure from and engineering point of view... But from a "not getting cramp in my right thigh in the fast lane of the motorway" point of view, hopefully it will be well worth it!
The best thing about the M seats in my Z4 is the seat base tilt adjust, if only they would easily fit in the Z3 I would buy another set...
As for the safety element, I'm not sure from and engineering point of view... But from a "not getting cramp in my right thigh in the fast lane of the motorway" point of view, hopefully it will be well worth it!
The best thing about the M seats in my Z4 is the seat base tilt adjust, if only they would easily fit in the Z3 I would buy another set...
DR-Z said:
If you're saying you only have three threads of engagement, that's either 3mm or 4.5mm, depending on what you mean by three threads. Either way, it's not enough on its own - your weld will have to be very good.
To explain: To place your tightened bolt into tension, which is required for a sound fastening, a 10mm (grade 8.8 ) bolt needs a torque of 50Nm. This puts a preload of 25.5kN into the bolt. But 3mm engagement will strip the thread at just 11kN, and 4.5mm at 16kN. To avoid stripping thread with the correct preload, you need 7mm engagement minumum - that's 5 threads.
Hence your weld is taking the load. Fine if it's a good weld, rather than just surface 'glue'. PS sorry about the metric units!
After a long drive this weekend I also found the sets uncomfortable. So I am going to try the seat mod. As my user name implies I have access to a few machines. It's no hardship to make a few sets. So if you want some pm me all I ask is you pay the p+p. and if you need anything else made I work for beer money 
Machine monkey said:After a long drive this weekend I also found the sets uncomfortable. So I am going to try the seat mod. As my user name implies I have access to a few machines. It's no hardship to make a few sets. So if you want some pm me all I ask is you pay the p+p. and if you need anything else made I work for beer money
Interested to see how you go about making your set. Are you going to use coupling nuts and studs (like I did) or machine a solid/billet unit?
Hi v8z4
I will probably do the same as you. If it ent broke don't fix it saying goes. I will probably just use some stock hex bar drill and tap it. Then weld the studs in. I find it quicker than brazing. Could make it out of a solid lump but seems pointless? Lots of extra work. for the same result.
I will probably do the same as you. If it ent broke don't fix it saying goes. I will probably just use some stock hex bar drill and tap it. Then weld the studs in. I find it quicker than brazing. Could make it out of a solid lump but seems pointless? Lots of extra work. for the same result.
Adamski said:
x2
Machine monkey said:After a long drive this weekend I also found the sets uncomfortable. So I am going to try the seat mod. As my user name implies I have access to a few machines. It's no hardship to make a few sets. So if you want some pm me all I ask is you pay the p+p. and if you need anything else made I work for beer money
Would certainly be interested in some of these, please, but need to make sure there's plenty of thread engagement before welding . To be honest, I'm absolutely clear as to why welding (or brazing) is needed - is it because of limited thread engagement?
After reading the hole post again. I will be making the hole thing from either hex bar BMS bright mild steel. Or round 303 st/st. I will turn down to the correct diameter and screw cut or you use a split die to cut the thread. I will mill a couple of flats onto the round if st/st. If BMS i will run it thro our blacking plant to help stop them going rusty? Any questions? Any one want any?
Sorry didn't relay explain that very well. Its to try and avoid the the limited thread engagement issue DR-Z. Dose any one know how long/ Deep the thread is in the back. I.e. the hole not the stud?
I guess you just need to measure hoe much the current stud is protruding - i.e. thickness of bottom rail (say, 2mm) plus thickness of nut plus however much the thread extends above the nut (not checked, but probably just a small amount). Maybe a total of 10-12mm? Should be easy enough to measure it.
Not that mild steel is a third of the strength of a grade 8.8 bolt. But I work for a heat treatment company! So maybe could get them strengthened.
Not that mild steel is a third of the strength of a grade 8.8 bolt. But I work for a heat treatment company! So maybe could get them strengthened.
Thanks DR-Z explains all the technical know how. And informed comments on the subject. Right then grade 303 st/st it is unless DR-Z has better ideas your the man who knows.
I didn't fancy taking a seat out to measure. And then make them so shall we say 12mm deep taped hole. I will probably make them next week. I will take pictures if i remember.
I didn't fancy taking a seat out to measure. And then make them so shall we say 12mm deep taped hole. I will probably make them next week. I will take pictures if i remember.
The initial idea of using a coupling nut and stud is actually a better option if enough thread is located. Why? Because mild steel and 303 stainless steel both have a much lower strength (about a third!) than grade 6 or 8 bolts and nuts.
In practice, this means that you wouldn't be able to torque up the mild steel bolts without snapping them.
In practice, this means that you wouldn't be able to torque up the mild steel bolts without snapping them.