Under seat cross member... thing

My coop interior has been completely stripped in preparation for a roll cage at some point this year. I've been doing my reading through anything I can find on lowering the seats on here but there's one thing I can't find. The cross member / tunnel that runs across the width of the Coupe's floor (that the front bolts of the front seats fix to) - what is it? What does it do?

The rear mounts could easily be chopped out to make the seat a LOT lower but this front thing appears to be the cause the 'issue' of high aftermarket seats.

I would presume that it adds fairly substantially to the structural rigidity of the car. It could be modified but consideration of full reinstatement of structural integrity taken out would be needed - the cage would help but works in a different way.

When I put an OMP seat in my car earlier this year I put some extra holes in the side mounts to enable it to be mounted lower, I think it is now slightly higher than the standard seat, but only very slightly and I do have a full slider with ability to suit different height drivers. Bolting directly to the floor is the other solution, without sliders, if no one else is going to drive the car.

I too assumed this but can't for the life of me see how? It's box section and runs directly across the car? It doesn't look like any form of bracing I've seen anywhere else... There are no clear mounting points, it's the 'wrong' shape and it doesn't do the whole 'triangles' thing...

Are you going to do track days mate?

It's my intention to chop that transom and the two rear mounting pillar points out and start again with my track car. Will be done properly with some box section and by a coded welder but will try to get the seat a lot lower, and at the same time will make the mounting areas/points more in the 'standardised' position most aftermarket seats use.

It's my intention to chop that transom and the two rear mounting pillar points out and start again with my track car. Will be done properly with some box section and by a coded welder but will try to get the seat a lot lower, and at the same time will make the mounting areas/points more in the 'standardised' position most aftermarket seats use.

I will do, yes. I'm not creating a stripped out noisy track car though - I want the cage to improve the ride and handling but I'm going to sound out the sound deadening while I'm at it. Carpets back in and also new carpet in the rear to replace the seats. I'll start a project at some point.

I'd be interested to see how this goes as I'm thinking the same. I'd have it done when the cage goes in along with a harness bar and decent mounting plates for the seats.

It's been a while since my carpets have been up so hopefully I'm remembering the right thing, but I should think it's a 4th side to square essentially. Think like a shoe box. Adding the lid stiffens the box in X, Y, and Z

Quite a lot of cars have similar sections which I think add strength in the way szkom says - it is a central brace which also helps with a mounting for the seats. Certainly the classic Mini has a very similar section (I've welded floors and patches on them many times!!) and they are generally seen as safety critical.

Apart from anything else, the rear mounting points on the Coupe are lower than the front ones which gets the seat at the right angle so removing the cross member and lowering it could mean you have to find a way to lower the rear mounting bolts and there isn't a lot of space for that.

I've done a bit more searching for this sort of thing and came across a very good rally car prep series by 'Dirty Garage' on youtube. Two videos in particular are relevant to this discussion.

Subaru GC8 Stage Rally Build EP. 5: Cutting out the Stock Seat Mounts

GC8 Rally Car - OMP Race Seats Mounts - FIA Stage Rally Roll Cage Build

I've watched lots of videos showing roll cage installations and, although I haven't seen the actual removal and rebuild of the 'seat mounts' before, I've seen plenty with a similar finish to mount the seats to. Seems a very easy way to drop the seats in the Coupe, especially while you're going to all of effort of installing a roll cage

I'm still dubious about the wisdom of removing them - just because someone else has doesn't mean it is right! Watching the video you linked to of removing the original seat mounts showed to me how they create a box section which would add massively to the integrity of the car if involved in a side impact. At least he has replaced that with the mounts he fitted in the second video but it doesn't look like they ended up any lower than the originals, just provided a way to mount a fixed seat that would suit one driver only. If it was me doing that I'd want to weld those cross braces to the lower member of the roll cage that runs along the inside of the sill. In the Coupe any similar bars would only enable the seat to be very slightly lower than standard.

I had a quick look to see if I could see what any professionals do and found these images of a WRC Skoda shell which clearly has cross members included, although they don't look like the sort of design that the original road car would have:
https://www.motorsportauctions.com/user_images/3769450.jpg
https://www.motorsportauctions.com/user_images/9636640.jpg

Alternatively, here is an image showing inside the 2010 Fiesta WRC
https://cdn.motor1.com/images/mgl/3QN1L/s1/2010-212378-ford-fiesta-wrc-30-09-20101.jpg

I'm not suggesting anything is 'right'. I was hoping to throw out an idea to lower the seats by referring to work carried out by others

I find it encouraging that the professionals who carried out the WRC conversions on both of the cars you linked to had the same idea as this 'Dirty Garage' chap. As I said, I've seen it done like this a number of times (a touring car was another example) - the videos I linked just showed it being carried out.

I agree that it would seem ideal to attach any replacement steelwork to the lower half of the roll cage but, given that the OMP cage at least, mounts to the chassis at the same height as the top of these existing seat mounts, that isn't going to help us. Besides, neither the DIY chap nor the two WRC teams here have done so, so I think it would be fair to say that it's as safe to mount it to the points they have all chosen. This could easily lead to a mount as much three inches lower by my estimation.

Just worth mentioning I think, but notice how the cage picks up on all the suspension points in the second pic andyps linked. For me that makes it a cage with something car shaped hanging off it. Any cage suitable for the road I suspect wouldn't replace the strength you'll lose from removing/altering that box section.

Edit to add, I'd look at custom seat mounts to lower any aftermarket seat. Presumably you'll be using harnesses so the seat mounting itself doesn't need to be anything too special

If you wanted to add strength you could add several (3 or 4) cross members out of say 40 or 50mm box section in say 3mm thickness, utilising two as 'standardised' seat mounting points. There is only the one as standard from the factory, and if you wanted it to be really trick you could have a decent fabricator fashion some kick-up ends so it spreads the load over the entire height of the inner sill and tunnel, or weld on some spreader plates perhaps.

Dont forget though that lowering the seat down will alter your viewpoint through the steering wheel to the instrument panel........so then you may have to lower the column, restricting access if you have door bars on the cage, and the safety issue of dropping the column itself.

It seems from looking at the photo of the coupe that you could just remove the driver side. Passenger side doesn't matter really.Then just strengthen up driver side once sure of the new seat and under frame position.

Here is another video I have since found that offers perhaps the most 'official' solution yet. Good series too actually
How To Fit My Big Head In This Porsche (FIA Seat Mounts)

Not too far from the solutions discussed earlier in the thread.



This is something I have considered. More important still is the height of the floor / pedals essentially being raised. I've no idea what the position used to be like as I haven't driven it in nearly two years but I can't see it being an improvement...

Interesting film and good to see the FIA recommendation. I'd need to go out and look at my car but to me it looks like using a bar of that size positioned as he has wouldn't lower the seat particularly in the Coupe compared to the cross member.

A quick point to consider - if fitting a 5 or 6 point harness you would need somewhere to mount the crotch straps. I've not fitted mine but plan to mount them through the cross member.

Any good?

Well I just gained a few inches!

2 or 3 cms were gained on that project.

If you think you are getting the seat anywhere near the floor,then it's going to be almost undriveable without a pedal box,let alone the steering wheel position and drivers view.

Is that 2-3cms lower in the top of the mounting point or sat in the seat? If the latter, is that with a seat directly bolted down or with side mounts and or rails?

That looks an amazing job by the way. Is that your second roll cage fitted coop?

Not my coupe but a French pals. It's an extremely well prepared car. I'm not sure of the mounting to be honest. But he is lower than stock for sure.