Now that the bike's mostly finished I can move forwards on the Spit again

"BiTurbo228 - Dr Frankenstein of Spitfires" (biturbo228)
08/09/2017 at 06:10 • Filed to: spit6

Fitted the diff, mock spring, VL and wishbone to check what I needed to cut out of the chassis. Turns out...quite a lot.

I certainly wouldn’t recommend this wishbone placement on a non-reinforced chassis. At the moment I’m weighing up whether I’ll need further reinforcement (either internal gussets inside the chassis, a double-thickness plate on the outside vertical face of the chassis, more substantial gussets to the bodyshell, or a combination thereof).

DISCUSSION (16)

BvdV - The Dutch Engineer > BiTurbo228 - Dr Frankenstein of Spitfires
08/09/2017 at 07:23

That’s quite a lot of metal that needed removing. I’m sure you’ll be able to reinforce it enough to cope with the change, though.

BiTurbo228 - Dr Frankenstein of Spitfires > BvdV - The Dutch Engineer
08/09/2017 at 07:38

It is a worrying amount of metal. There’s more that needs to come out too as I expect it’ll need more clearance to cover the suspension travel.

I’ll definitely figure something out :) the whole area is a lot more braced already as the chassis is welded to the body, which also has the backstays for the roll hoop welded to the same point (which will also be welded into the roof for added stiffness).

With all that, I’m not even sure I’d need to add anything funky like internal gussets...

RamblinRover Luxury-Yacht > BiTurbo228 - Dr Frankenstein of Spitfires
08/09/2017 at 09:07

I’ve only got sawing out to do/done in two crossmembers and under the steering box. Not anywhere close to this much out of a major fore and aft member. That being said, the extreme tail of the chassis doesn’t have much to do outside of driveline support here anyway, so your big concerns are resistance to twist and shear, not any sort of beam loads. Shear is much easier to get sorted.

BiTurbo228 - Dr Frankenstein of Spitfires > RamblinRover Luxury-Yacht
08/09/2017 at 09:38

Very good point :) I suppose it would be useful to vaguely map out where the actual forces will be going at this point in the chassis and if any bits actually need reinforcing.

There’s going to be vertical load put upwards through the diff mounts from the spring. That’s sorted as it gets put directly into the bodyshell and roll hoop, or is in front of the cutouts.

There’s going to be fore-aft load from the wishbones under acceleration and braking, but I don’t think that’d be much of a problem.

Lastly there will be lateral load from cornering which I suppose would try to rotate the narrow section of the chassis along its length. Not much I can do about that I don’t think :S

RamblinRover Luxury-Yacht > BiTurbo228 - Dr Frankenstein of Spitfires
08/09/2017 at 09:52

The thing about the lateral loads from cornering is that they’re acting on a very short moment arm, so the amount of twist is rather small overall. Two big difficulties seen on a box section chassis are the distributed load over a length supported at both ends, and the poor resistance to twist - both of which result from long unsupported spans and to an extent a long “lever”. There’s where you see the greatest advantage in a full box, but for simple shear, very little matters other than total cross-section.

BiTurbo228 - Dr Frankenstein of Spitfires > RamblinRover Luxury-Yacht
08/09/2017 at 10:02

Should be pretty peachy then! So long as shear’s sorted I can’t see anywhere where cutting into the chassis to clear the wishbones will actually reduce stiffness in actual use :)

BvdV - The Dutch Engineer > BiTurbo228 - Dr Frankenstein of Spitfires
08/09/2017 at 10:12

Yeah, I’m guessing the car being unibody now does help a lot. On the other hand, better to be safe than sorry I guess.

RamblinRover Luxury-Yacht > BiTurbo228 - Dr Frankenstein of Spitfires
08/09/2017 at 10:28

As long as you lay in enough “reversed” boxes into holes to close the chassis with and to reduce the effects of sharp corners, you should do a’right. I rather wish you were right down the road from me, as I could bend you up a few pieces for that with me new brake.

CaptDale - is secretly British > BiTurbo228 - Dr Frankenstein of Spitfires
08/09/2017 at 12:14

Jesus it has been so long I forgot you had that

BiTurbo228 - Dr Frankenstein of Spitfires > CaptDale - is secretly British
08/10/2017 at 19:16

Yeah it’s been a while :S too many projects really, but I’m getting there...

BiTurbo228 - Dr Frankenstein of Spitfires > RamblinRover Luxury-Yacht
08/10/2017 at 19:18

Yeah the chassis will be all closed up :)

A proper brake is something that I really want to have. Not enough to actually buy one, but definitely enough to try and make one at some point ;)

RamblinRover Luxury-Yacht > BiTurbo228 - Dr Frankenstein of Spitfires
08/10/2017 at 19:23

Well, you know how it was for me. Proper fix on the Galaxie trunk with a cost well in excess of a proper brake, need to make assorted channels for the Ranchero, whole thing sort of insisted on itself. Even setting aside a vast number of Land Rover things needed as well...

BiTurbo228 - Dr Frankenstein of Spitfires > RamblinRover Luxury-Yacht
08/10/2017 at 19:42

Now that’s a justification I should pull out more often ;)

CaptDale - is secretly British > BiTurbo228 - Dr Frankenstein of Spitfires
08/10/2017 at 20:20

Good, congrats.

BiTurbo228 - Dr Frankenstein of Spitfires > CaptDale - is secretly British
08/10/2017 at 20:23

I was weighing up whether to make a little friendly wager as to who would finish their dinky little Brit sportscar first...but I don’t exactly fancy my odds ;)

CaptDale - is secretly British > BiTurbo228 - Dr Frankenstein of Spitfires
08/11/2017 at 11:11

I would make a friendly wager because I too don’t like my odds. Though mine is technically further along.