Marko's GTD (I think) 40

[Terry Oxandale]

My thoughts were more along the distribution of that force through a small triangular gusset (or thin plate as you've noted) connecting the two longitudinal tubes, with the heavier lateral cross bar. I've always attempted to place the point of force at the joint itself, and if displaced off the joint (as done with the two longitudinal tubes), then reinforce that area to re-distribute the loading. Photos don't show it all, so you may be fine with what you've got. Perhaps I overbuild too much.

 

[Marko S.]

Got it. I wasn't sure what gusset meant but now I understand and that's what I'll do. Here's a photo of the both shocks in position. I'll have v to grind everything off though cause I'm not completely happy with the weld quality. I'm using some shitty 170 mig machine now and I'm getting my Fronius back soon so I'll redo the whole thing then and do the reinforcing plates as well.

Cheers
Marko

 

[Marko S.]

Hi again

I was working some more on the rocker. I added one more bracket on it for the anti roll bar. Each rocker weights about 280g if the math is right.

I was thinking about the shock mounts and other modifications I've done and will do and how it all effects its integrity and decided to make a CAD model of the chassis. Today I managed to finish the front end. It's not completely right (some angles are a nightmare) but it's more or less within one centimeter. When I finish the whole thing I'll use it to do a stress analysis on the complete chassis.

Cheers
Marko

 

[Marko S.]

Hi guys

Finished with the modelling of the chassis. Well I have to make a few changes to the front end and confirm the height of the bulkhead but other than that it's done. Now I have to add the mounting points and apply all the forces and materials in the FEA software and hopefully then I'll have a baseline for all the future (and past) modifications. I'm thinking about modelling the suspension as well. I was planning to replace the Granada wishbones anyway so I might just model em first before fabricating.

If someone needs the model feel free to ask. I'm all about sharing

Cheers,
Marko

 

[Mike Pass]

Hi Marko,
Maybe add some angled struts from the end of the engine bay to support the rear bulkhead frame in event of a roll over. After all it's your head it is protecting!
Cheers
Mike

 

[Marko S.]

Yup they're definitely going on there. First time I've seen the struts on other people's cars I decided to put them on. Thanks for taking care of my scalp

Cheers
Marko

 

[Marko S.]

Hi guys

Since I dropped the "as original as possible" route, I decided to abandon the standard replica wheels as well. Instead I came across these American Racing wheels. I'm definitely going for the arctic camo paint job and I think these will look good with the white and grey scheme. I might have the lip or something painted in white. They have that "stealth fighter" feel to them. I was thinking 15x10 with 275 tyres in the rear and 15x8 with 235 tyres in the front. Rears have -62 offset I think so a lovely deep dish to them as well and that will give me enough clearance for everything. A third of the price of BRMs too, meaning I can afford to have them under the Christmas tree

Btw, has anyone heard of Galaxy radials? Found those tyres for under 100 pounds each for the rears and I was wondering if anyone has any info on them. All I can find online is Galaxy tractor tyres.

P.S. couldn't resist posting that sacrilege. That guy ought to be connected to life support and tortured indefinitely.

 

[Marko S.]

Hi guys

After temporarily addressing my uncontrollable drooling issue, I managed to finally upload this photoshopped picture of what my GT40 should look like. Now if you'll excuse me, I need some tissues.

Cheers
Marko

 

[Ryan L]

reminds me of this

 

[Marko S.]

Haha yes it does. I'm trying to think of a good place to put those RAF circles too, and perhaps a 1950's lady in a bikini named Harrier.

 

[Marko S.]

Hi there

I've been fiddling with the suspension geometry a lot since the last post. The wheels I like, the black ones with the large offset, turn out to be a problem. The offset it too big. This got me thinking. I didn't like the arms and wishbones I had in the first place and wanted to make new ones, and also the uprights, so I decided to make everything from scratch. I was trying to get some info on this but couldn't find anything decent. What are the effects, apart from the scrub radius difference, in fabricating shorter wishbones and A arms / radius rods (the lateral ones)? The moment would be lower, meaning the stress on the bearings would be lower, but are there any negative effects to it?

Cheers
Marko

 

[Terry Oxandale]

I believe scrub radius is independent of arm lengths, and instead related primarily to wheel offset and kingpin inclination. Personally, I prefer using the longest arms possible, which for me, keeps the arm angles smaller for the same suspension travel. If the large angles are required to produce the camber gain you need, then longer arms may not suit your needs. My scrub radius was reasonable, but I'm also using wheels with a lot of positive wheel offset (it's at the limit of the manufacturer).

 

[Marko S.]

Hi Terry

From what I gather, scrub radius is the angle between the shock centreline and wheel centerline, therefore if the wishbone is shorter and the upper shock mount isn't moved, the shock centreline changes and so does the scrub radius. This is true of coarse only if the wishbone shock mount changes along with the wishbone length. Thanks for the camber gain thought, that never crossed my mind. The shorter the wishbone, the more significant the camber gain is due to the lower radius between the chassis mount and the wheel centerline. Correct?

Cheers
Marko

 

[Terry Oxandale]

For a true dual A-arm suspension (front), shock positioning or alignment does nothing to affect scrub radius, but rather changes the effective spring/dampening rate. For our type of suspensions, the scrub radius is the distance between the axis of the two ball joints (upper to lower) intersecting the road surface, and the center of the contact patch from the tire. It then becomes a compromise of how much you want. More improves driver feedback, but at increased steering effort. Going with shorter arms, and a negative offset (or none to very little positive) wheel will increase the scrub quite a bit, but again, the kingpin inclination will recover some of this depending on the design of the upright.

 

[Marko S.]

I stand corrected. The shock inclination does affect scrub radius on a McPhearson type suspension though, doesn't it?

 

[Ryan L]

The red line represent an axis intersecting the top and bottom ball joints on the front spindle/knuckle. this has been positioned on an axis that includes the Camber, Caster and Kingpin inclination. I am designing my own upright so i have positioned this as far out as possible. this is limited by caliper selection and needing to clear the back of the wheel, which then positions the disc. You should be able to see that i have some contact issues between the axis, disc and wheel.

the 3 groves in the perimeter of the tyre represent the centre of the tyre.

the centre of the contact patch will be somewhere between the inner edge of the tyre and the centre of the tyre. i am assuming 1/3rd in from the inner edge.

"scrub", as your asking, will be the distance between the centre of the contact patch and the point of intersection of the red axis on the ground.

Regards Ryan

 

[Terry Oxandale]

Ryan,

Your diagram shows a very similar situation with my recently fabricated front uprights. Even though a high positive-offset wheel (similar to what is considered a "FWD" wheel) is not visually appealing to our era of cars, it did provide me with the ability to tighten up on the scrub radius, and utilize other aspects of front suspension geometry (caster for example) in providing feedback.

I stand corrected. The shock inclination does affect scrub radius on a McPhearson type suspension though, doesn't it?

Marko, I'd say in concept, yes. But then you've got to have a strut that has adjustable camber at the bottom of the strut in order to apply this thinking, else you change the camber each time you adjust the top of the strut.

 

[Ryan L]

I agree, Lots of options to play with here. I will be trying to keep some of the original look and feel to the car, no point building it if it drives like a Prius.I’m sure they are great cars, but I have no idea how Toyota manage to engineer all soul out of a vehicle. That must take some serious skill!
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I will add some more details to my build diary in due course. I was planning on having the wheel hub axle slightly behind the king pin axis to reduce the amount of mechanical trial.The benefit of this is that the pneumatic trail will become more pronounced.

Ryan<o></o>

 

[Marko S.]

Hi guys

Thanks a bunch for the input. Cleared up a thing or two for me. Talking about cars without soul, I have a 2000 Suzuki Alto. I'm using it as means of transporting oily differentials, not getting in fight with kids over chocolate smudged seats and staying perfectly relaxed after breaking half a rear bumper upon close encounters with short walls. People say it's an utter piece of excrement and that it has no soul whatsoever, but I think that while it might not have soul, it has tons of character. It's such a rubbish that that fact alone makes it stand out above other cars. Well, below maybe, not above. Anyways I love it and no one understand why. I was hoping someone here will.