Racing with a hardtop vs roofless

Magpie · Postby **Magpie** » Sat Feb 03, 2018 1:00 pm

I would like to install a much lighter seat soon.

Your best bet maybe to cut out the existing floor mounts and go direct to the floor. Provided you use the same backing plates as used for CAMS eye bolts there should be be no issue.

I'm going to test this theory out on my shell sometime this year when I find a suitable seat.

CrazyRacer · Postby **CrazyRacer** » Sun Feb 04, 2018 12:56 am

Magpie wrote:Your best bet maybe to cut out the existing floor mounts and go direct to the floor. Provided you use the same backing plates as used for CAMS eye bolts there should be be no issue.

I have already removed the rear seat mount brackets, using a spot weld cutter which looks like a miniature hole saw. I got a bit carried away on a couple though and went all the way through, but generally it seemed to do a pretty decent job.

The pressings in the floor don't help though. Not going to be able to get a large enough underside counterplate to sit flat without bashing the floor flat or cutting a section out and welding a flat section in. An alternative might be to weld some flat in between the side mounts and and run the plates laterally.

lightyear · Postby **lightyear** » Mon Feb 05, 2018 7:07 am

How tall are you? I am 6'2" and fit in my car with a roof and full cage using a Velo seat bolted to the floor. The better way to make more room is to cut the floor out and lower it to the chassis rail box height. Most guys just cut the sides and back, then lower the back of the floor about 50mm or whatever it is. On my very mild NB8B I was 2 seconds faster with the roof up at P.I. I would never consider no roof, unless you just want to have some fun.

Nuddy · Postby **Nuddy** » Mon Feb 05, 2018 10:06 am

Nuddy wrote:Get the best roll cage you can then build a custom soft top to go over it. You dont need a rear window.

This is not mine and you could probably do it better but this is the idea:

soft top MX-5.jpg

Tim_cyc03 · Postby **Tim_cyc03** » Mon Feb 05, 2018 8:56 pm

I'm 188cm or so and have managed to find a solution that seems to be comfortable now with a roof, cage and no cutting thus far to the seating position.

I have no input on what is best, as I have always run a roof.

I have a lightyear CF roof and the cage was built to fit perfectly under that. So much so that a standard roof has no chance of fitting. I'm not sure if you can gut a standard one enough to make it fit.

Yes I understand that you have said that a CF roof might not be in budget, but having to redo a cage would probably be much more expensive than the initial outlay.

Flat bottom sparco wheel, OMP removable wheel kit, bride VIOS III with all the padding removed, and Procar Race Seat mount from Kazespec engineering is the combination I've used.

Magpie · Postby **Magpie** » Tue Feb 06, 2018 7:33 am

Tim_cyc03 wrote: bride VIOS III

Does it contact the window? Looking at the specs they are 550mm wide at the 'wings' whereas the Sparco Sprint is 520mm.

CrazyRacer · Postby **CrazyRacer** » Tue Feb 06, 2018 12:20 pm

lightyear wrote:How tall are you? I am 6'2" and fit in my car with a roof and full cage using a Velo seat bolted to the floor. The better way to make more room is to cut the floor out and lower it to the chassis rail box height. Most guys just cut the sides and back, then lower the back of the floor about 50mm or whatever it is. On my very mild NB8B I was 2 seconds faster with the roof up at P.I. I would never consider no roof, unless you just want to have some fun.

I'm only a little over 6' but with very long legs. It means I like to sit back as far as I can get, which is where the roof line of the hardtop starts to drop away. I would have thought that it means I'm shorter in the torso, but its still a problem.

The way I'm mounting the seat means it is only a few mm above floor as it is, and the design of the seat would mean to get it much lower would require cutting into the chassis rail. Something I'm not all that keen to do.

The BD bar I currently have in the car sits a fair way back and with the seat where I'd like it to be, it just kisses the bar. The problem is that the top of my helmet sits 40mm+ above the top of the roll bar. I know AGI bars (as an example) are a bit higher because they sit about 75-100mm further forward, but I'm not sure I could drive the car with the seat moved that far forward. If I'm going to get a custom cage anyway, I might need to see if I can come up with a compromise between leg room and roof height.

Dave, do your CF hardtops offer more headroom? Are they a different profile, or just thinner due to material and lack of hood lining etc?

neilh · Postby **neilh** » Tue Feb 06, 2018 1:11 pm

Is the car a purpose built track or road registered

I am 6ft 4 and had the same issue with my race car.

After a few seasons of looking at different option I actually lowered the drivers side floor. I ended up making it level with the bottom of the chassis rail. I have a full roll cage in the car, with a carbon fibre hardtop and still get the correct role cage clearance above my head.

It is a fair bit of work though as you need to re run brake lines etc, but defiantly worth the effort

CrazyRacer · Postby **CrazyRacer** » Tue Feb 06, 2018 2:56 pm

neilh wrote:Is the car a purpose built track or road registered

I am 6ft 4 and had the same issue with my race car.

After a few seasons of looking at different option I actually lowered the drivers side floor. I ended up making it level with the bottom of the chassis rail. I have a full roll cage in the car, with a carbon fibre hardtop and still get the correct role cage clearance above my head.

It is a fair bit of work though as you need to re run brake lines etc, but defiantly worth the effort

It's a dedicated track car, a stat write off so its never going to be registered again.

Did you have to cut through the inner chassis rail to do it?

Could you please post some pics of what you've done with the floor?

neilh · Postby **neilh** » Tue Feb 06, 2018 4:06 pm

I will take some pics and put them up.

I thought there was a thread by colster3 on how to actually do this, as he was one of the first people to do it, but I can not seem to find it.

CrazyRacer · Postby **CrazyRacer** » Tue Feb 06, 2018 6:26 pm

I found these pics of cutting out and lowering the floor to get the seat lower on miataturbo.

This would probably do the trick, but surely taking a significant box section main chassis rail and turning it into essentially a flat strip of steel like that has to have a significant detrimental impact on the strength of the car?

greenMachine · Postby **greenMachine** » Tue Feb 06, 2018 7:48 pm

First up, that box (at least its sides) will add strength, how much compared to the lost rail I don't know.

Secondly, a cage will add LOTS of strength, especially if it is designed with structural strengthening as a goal.

Don't sweat it.

:mrgreen:

neilh · Postby **neilh** » Tue Feb 06, 2018 9:45 pm

I had the same concerns about losing chassis stiffness when I was looking at doing this. Ultimately after much research this is why I left this job to the experts ( I generally do most of the work myself) and got a someone with significant motorsport experience and fabrication skills to help with this.

Basically greenmachine is correct, the box section can actually add rigidity to the chassis, provided it is built correctly. I have attached some pics of mine (not the greatest of quality, sorry. the first two are from underneath the car, the third is from the inside) You will notice my box section is slightly different to the one shown above as it has ribs etc in it to try and add additional strength, and is not just flat. But beyond this, if you are running a full cage setup then you will have heaps of rigidity, they really do strengthen the car up.

Based on lap times and race results before and after getting this done I can honestly say there have been no negative impacts by doing this

Again I should point out, I ended up getting this professionally done, and the job was much more involved than even the experts thought it would be. While this is the best way to meet the objectives of running a hardtop with a full cage and getting the correct head clearance, it is by no means a quick job.

CrazyRacer · Postby **CrazyRacer** » Wed Feb 07, 2018 12:23 am

Thanks for posting those Neil

I think I'll save lowering the floor as a last resort. It sounds like I'm a good 2 to 4 inches shorter than most of you who have had to do this so I've been playing with the seat position some more tonight.

I've found that if I...

remove all padding from my seat, so I'm sitting straight on the fibreglass shell
modify the bought side mounts so the seat sits right at the bottom of the frame
sacrifice some leg room so that I can tilt the seat back further (which is actually more comfortable on my back)

I can just squeak in under the current BD rollbar.

I also finally got around to removing the hardtop from the road car and fitting to the race car. The BD bar in the road car is hard up against the hardtop, but with the bar in the race car (which I think is a fair bit older) there's a good 20-25mm of clearance. I'd assumed they would have the same clearance, but apparently not. I guess this means that with a CF or stripped out hardtop I might get 40mm of extra clearance for a custom cage which would be enough now.

So it looks like the job for this weekend is seat mount mk3.

neilh · Postby **neilh** » Wed Feb 07, 2018 9:05 am

No problem. It was a last resort for me as well. CAMS (at state level racing anyway) get really picky on head clearance with MX5 races

Everything you said sounds reasonable (looking at different seats, mountings etc.). Also to get and extra few CM, consider racking the seat back, so you are in more of a laying down position (similar to an open wheeler seating position). it is surprising how much extra clearance this gives