Lowering Seat Height

[MickyG]

I know it’s been talked about since Z3s came out, but I like a challenge and wonder whether lowering the rear of the seat by 25mm is worth the significant effort it will require?

By adapting a standard seat base mechanism - cutting out the height adjust mechanism and some welding - it would be physically possible to lower the rear of a standard seat by a maximum of 25mm whilst retaining Fore/Aft electrically operated adjustment: also retaining the front seat mounting points will tilt the base which has been reported as useful to do by those who have used spacers at the front.

25mm doesn’t sound much, yet an annoying little worm in my ear says “ But it will feel like a lot! - Have a go!”

Will it?
Worth it?

 

[Trevor /chedder]

It would be interesting to see if you can pull it off. Would love mine lower.

 

[MickyG]

It would be interesting to see if you can pull it off. Would love mine lower.

Many have said they want it lower, but is 25mm enough?
Technically it is possible: dropping the right runner of the drivers seat base is easy. Dropping the left is much more difficult for two/three reasons.
Unlike the right seat side the left sits substantially over the slide runner beneath limiting the maximum drop to 25mm - and that is only possible if a crank section of the runner is removed. Even if all this is dealt with the seat base would lower and foul the seat belt anchorage point. This can be cut, extended and welded, which physically I would have no issue with, but suspect it might not be technically acceptable to an MOT tester. Whether they would ever pick it up is highly questionable.

But my question remains - is 25mm worth the effort?

 

[shera25]

Lowering the seat 25mm isn’t huge, but you’ll definitely notice the difference in feel and driving position. If you enjoy a hands-on challenge and don’t mind the effort, it could be worth it just make sure any welding/mods are safe and secure.

 

[GZed]

Many have said they want it lower, but is 25mm enough?
Technically it is possible: dropping the right runner of the drivers seat base is easy. Dropping the left is much more difficult for two/three reasons.
Unlike the right seat side the left sits substantially over the slide runner beneath limiting the maximum drop to 25mm - and that is only possible if a crank section of the runner is removed. Even if all this is dealt with the seat base would lower and foul the seat belt anchorage point. This can be cut, extended and welded, which physically I would have no issue with, but suspect it might not be technically acceptable to an MOT tester. Whether they would ever pick it up is highly questionable.

But my question remains - is 25mm worth the effort?

Why do you want to lower it? Is it because you’re too tall/ legs too long, or is it because you want to lower the centre of gravity?
If you’re too tall, then ironically a tried & tested solution is to raise the front of the seat, which has the effect of tilting the seat base backwards, and giving the backs of your thighs more support. I think it was Aceman and T-tony (RIP) who used to sell these ‘seat tilters’ or ‘seat lifters’ ( can’t remember exactly their name). My silver 2.8 has them and my red one doesn’t and they make a real difference. I’m just over 6 feet tall by the way, and have plenty of headroom.
And they’re perfectly MOT compliant

If you want to lower the centre of gravity for handling purposes, as advocated by the likes of Chris Harris, then lowering the seat by 25mm doesn’t sounds like much to me. It will depend how heavy you are - you could probably do some calcs based on your weight & the centres of mass of your body and the car to judge any effect. I say ‘probably’ - I can’t

 

[MickyG]

Why do you want to lower it? Is it because you’re too tall/ legs too long, or is it because you want to lower the centre of gravity?
If you’re too tall, then ironically a tried & tested solution is to raise the front of the seat, which has the effect of tilting the seat base backwards, and giving the backs of your thighs more support. I think it was Aceman and T-tony (RIP) who used to sell these ‘seat tilters’ or ‘seat lifters’ ( can’t remember exactly their name). My silver 2.8 has them and my red one doesn’t and they make a real difference. I’m just over 6 feet tall by the way, and have plenty of headroom.
And they’re perfectly MOT compliant

If you want to lower the centre of gravity for handling purposes, as advocated by the likes of Chris Harris, then lowering the seat by 25mm doesn’t sounds like much to me. It will depend how heavy you are - you could probably do some calcs based on your weight & the centres of mass of your body and the car to judge any effect. I say ‘probably’ - I can’t

An interesting perspective.
I would like to lower my eye level vis-a-vis the windscreen and doors. I suspect the latter has more to do with modern cars having glass much higher than previous iterations so is a relativity issue. However looking out through the top of the front windscreen is not comfortable.
I’m not particularly tall, but do have a long back ( ok I admit I’ve got short legs) and invariably have a car s seat set to it lowest.
Your point about raising the front is a double positive. If raising it whilst the rear remains at its standard height, then lowering the back achieves both a physical lowering of the seat and benefits front the tilt backwards by leaving the front in its standard position.
I had not given a moments thought to centre of gravity. I’m too old to drive to those margins, but would be fitting much lower and side supportive bucket seats were that the goal.
Thanks for the reply - it’s beginning to clarify my thoughts and that it may well be worth it.

 

[Ade33]

I bought a set of "Southernboys's" seat tilt solution a few years back and they transformed the ride for a 5ft 8" driver..and the passenger too..I would struggle to drive a Z3 without them..That's why in the unlikely event I ever sell my car I will be keeping them in case I ever purchase another Z3!

They are really engineered to top quality. Unfortunately I am not sure he is selling these anymore although worth checking...

 

[MickyG]

I bought a set of "Southernboys's" seat tilt solution a few years back and they transformed the ride for a 5ft 8" driver..and the passenger too..I would struggle to drive a Z3 without them..That's why in the unlikely event I ever sell my car I will be keeping them in case I ever purchase another Z3!

They are really engineered to top quality. Unfortunately I am not sure he is selling these anymore although worth checking...

Hi Ade33
Thanks for the reference.
Southernboy kit has been well received by many: unfortunately I’ve had no response to my DM to him and sadly assume he is no longer on this forum.
Raising the front of the seat 20-25mm relative to rear improves the support from both the squab and the bolsters , however it does not address the issue of long backed people having their eyeline too high relative to the front screen, and head to the roof.
Nonetheless all this fuels my belief that lowering the rear relative to the front by the same gives me the best of both : the same tilt gain but all 25mm lower.

 

[IainP]

You can’t lower the rear of the seat more than 10mm, the seat rail would hit the frame rail, this bit here

It’s the saddle the backrest cable goes through so you can’t just chop it out unless you want the backrest fixed. An alternative would be to chop the mechanism out, raise the front and weld the rear solid, but that’s a bit of work and still only lowers the rear 10mm.

The front seat raise bits are just M8 threaded rod joiners from Screwfix/Toolstation and a couple of M8 bolts. I have plenty of them if you want to try a pair, it allows you to recline the seat one click which lowers the eyeline a tad.

 

[IainP]

Hi Ade33
Thanks for the reference.
Southernboy kit has been well received by many: unfortunately I’ve had no response to my DM to him and sadly assume he is no longer on this forum.
Raising the front of the seat 20-25mm relative to rear improves the support from both the squab and the bolsters , however it does not address the issue of long backed people having their eyeline too high relative to the front screen, and head to the roof.
Nonetheless all this fuels my belief that lowering the rear relative to the front by the same gives me the best of both : the same tilt gain but all 25mm lower.

Chopping out the raise mechanism gives ou this

Only minor lowering at the rear, if you raise the front though, you get to this


The rear of the seat rail touches the frame rail. Obviously it’s a weld job, and if were me I’d add a triangular fillet for strength.
Before you weld you’d need to remember to tack weld a nut to hold the fore/aft worm gear. I’d also weld the front pivot.

 

[MickyG]

Hi Iain
Thank you very much for all your comments - they are very pertinent to what I had been looking at.
Support wise, I felt I could make lowering the rear 25mm work with some degree of fabrication/welding. However, following up on your initial comment regarding the tilt cable I think I’ve met one obstacle too many.
I believe it would have been possible to remove the crank section but be able to find a path for the tilt cable. Unfortunately whilst looking at this I notice the other end of this cables exits the seat side (from the handle) and already projects down through 90 degrees and comes into contact with the seat runner at its lowest.

Lowering this further looks like it will mean losing the tilt mechanism, which is not acceptable.

You’ve obviously been round this loop too!

I’m going to have another look!!

 

[MickyG]

I’ve had a bit more of an explore with the passenger base as a prototype to see what could be possible.
The most extreme would be to remove the rear pivot bar and bush, reduce the crank depth of the main runner, and cut off the nuts/fixings for the seatbelt anchor bracket to allow the maximum lowering of the seat runner.
This could then all be welded to create a structure that would be stronger than the original ( though I’m slightly unsure if it would be legal with welded fixings in place of bolted connections?)

Edit:
(Quick Google suggests welded connections are permissible).

The base measurement of the original seat mechanism was 65mm from underside of the sliders to the top of the seat runner at the rear.

By taking it to the extreme I’ve reduced this to around 40mm.

This last photo shows the gain possible vs the original.

Picking up on Iain’s comments/photos and suggestions I think it might be possible to achieve a 20mm reduction without the need for so much drastic cutting and welding by raising the front 5mm. This will hopefully allow the original fixings for the seatbelt anchor bracket to remain standard.

 

[IainP]

Just a thought since I saw them on the garage floor today.
There are plastic rods inside the frame rails, so need to be careful if welding, best to weld in stages and chill with an airline, or wet cloth.

 

[MickyG]

Just a thought since I saw them on the garage floor today.
There are plastic rods inside the frame rails, so need to be careful if welding, best to weld in stages and chill with an airline, or wet cloth.

Again, very useful information: I was not aware, thank you.
When I can get away from re-tiling our bathroom, I plan on experimenting with the drivers side next, with a view to minimising ( but not eliminating) the amount of welding necessary.