Mythbuster: continuing project thread of my 1303 '75

[70Turbobug]

Maybe you could build a diffusor that bolts up to the rear bumper mounts inside the fenderwell? Then you could do away completely with the spoiler and have full effectiveness of your IC.

[Steve C]

Hi Wally

I wasn't saying it was ugly, I think it looks very good, your being too hard on yourself, a big change to cars looks can do that.

Steve

[NO_H2O]

Awesome stuff as always Wally. Lots of changes this time and much quicker lap times. That is why I always look forward to updates from Wally.

[owdlvr]

Not to derail Wally's thread, but it really depends on alignment as well. My Audi in track trim was running -4 deg of camber, it would eat up a set of tires driving from Richmond Hill to Shannonville and back, assuming I spent the day on the track. I could get two days out of set by popping them off the rims and putting the inside edge to the outside.

A bug, though, is relatively light and easy on tires so I wouldn't expect it to be a problem.

-Dave

[70Turbobug]

4WD drive cars eat tires also.A guy I work with has an WRX STi and he runs Bridgestone Semi Slicks and gets about 10Tkm out of them,which is great.Dave made a good point about alignment though.If you have an aggressive camber or a heavy car it´s obvious that the tires will wear more quickly than a light car.Everyone has their own preference for which tire is best.Driving style,damper selection and engine performance also plays a role in which tire works the best.There are just so many factors that depend on each individual needs or preference that you can´t really say "this tire works best" and you have try which tire you think is best for you.Some put more emphasis on stability during braking because they prefer to brake later,generally they give up corner speed for it or those that brake less but therefore earlier use a little more corner speed and prefer traction during acceleration out of the corner.It´s not a coincidence that tires are a huge issue in racing and decide each race.Most of us I would think need a comprimise since we´re not Sebastian Vettel and don´t have tire sponsors and require a tire that is also good on the street.If you have the luxury of beeing able to take a second set of rims+tires to the track with you,than it´s a different story.It would suck however,if you have really sticky semi slicks that are great for the track and then it rains or it rains on the way home,then you´re even slower than if you were to run a good street tire.

[Cam]

Hi Walter,

Great to see the continued development of your car!
I'm sure the LSD has made a world of different, I bet you can't wait to get back to the 'ring and give it a try ;-)
Keep the updates coming mate.

Cheers,
Cam

[vdubzack]

If you are not runnig a relay to the fuel pump to get dirrect battery voltage you can try to use a voltage stabilizer to maintain constant voltage regardless of input. Used this one before and worked great even with the generator. Headights dont flicker with voltage or engine speed change. Just bright all the time. Should make the electrical items last longer, as it also controlls spikes in system voltage.
http://www.jacobselectronics.com.au/

[Wally]

Originally Posted by vdubzack

If you are not runnig a relay to the fuel pump to get dirrect battery voltage you can try to use a voltage stabilizer to maintain constant voltage regardless of input. Used this one before and worked great even with the generator. Headights dont flicker with voltage or engine speed change. Just bright all the time. Should make the electrical items last longer, as it also controlls spikes in system voltage.
http://www.jacobselectronics.com.au/

Interesting!
Wasn't Jacobs electronics a US based company?

[vdubzack]

Originally Posted by Wally

Interesting!
Wasn't Jacobs electronics a US based company?

Yes. And still is but was sold to the company that does Summit racing and the like.(I do believe) The Aussie jacobs is the only direct site.

[Wally]

Looked at my suspension geometry this weekend and as I remembered, the tca is almost parallel with the steering rod (good thing):



Futhermore, for the camber to get more negative, the tca must become rectangular with the imaginary line through the top of the strut and the ball joint, right?
It seems I am still pretty good with the current angle, even when fully suspended inbound (this pic is taken with the wheel/tca-end supported, so in resting position):


My idea to use a ball joint extender will probably give more bump-steer since tca and steering rod won't be parallel anymore and isnt needed from a camber point of view, so I think I don't want to do that after all.

Next action will be to see what my 'scrub radius' actually is:


Haven't done this part (ran out of time), but will do as well

[Wally]

I actually did already indeed Rich, just like you described, but think I got the wrong points connected...
With your answer I am a little confused even more what KPI and scrub radius is. MotoIQ had a great article about it the other day, using tie rod(?) and the lower ball joint of our Mc Pherson suspension system. Or is that just the upper and lower suspension point in the picture? Thought the upper one was the tie rod of the steering in the schematic?


However, I took the line through the upper Mc Pherson strut connection with the body and the lower ball joint. Thought afterwards I did it wrong and it needed be through the tie rod and lower ball joint. Maybe I did it correct after all?
Anyways, that gave me a scrub distance of +18mm. Still not sure now if that was correctly measured or not...
Mike specified a distance between 3/4" and 3". With 18mm I am right at the lower bandwidth of that.. a bit more might help. I have a little room in the wheel arch, but I think 17" might be better for track driving anyways, mostly because of wheelweight you feel the negative effect of it most on the front. 7x17" is half an inch less wide and with a few mm more spacer, might just give that added scrub we're after?

Tire centerline above is right against the rim contact path, which is somewhat confusing too. It doesn't seem to be the exact tire centerline..?

I'll post some of the pics I took of that tonight.

[Steve C]

Hi Wally

Do you have any issues with the tie rod touching the chassis rail / inner mudguard?

Steve

[Wally]

No, but... I have squared the spare wheel well (for easier battery placement and such) and the tie rod could hit the edge or so it seemed, so I made a recess for it.
The tie rod never hit anything fortunately and now with the stiffer springs even less chance.

[ricola]

Wally: I'm in the process of correcting poor scrub geometry. The high offset porsche wheels make the scrub radius massively negative. I was desperate to try and avoid wider wings but the compromises just weren't worth it. From memory my scrub offset measured about 38mm -ve. A quick test with the rear 944 wheel spacers have made the steering feel much nicer and more confidence inspiring, it isn't to far off stock now I believe. Most RWD cars have +ve scrub but some late (including 2 bolt strut supers) are designed with -ve.
Rich

[Wally]

I hear you Rich; I run the 21mm spacers up front as well, but more because I couldn't fit the high ET wheels; this was before I ran the slimmer AVO struts. Now the spacers help to have full steering without hitting the inner fenders...

My theory is that the 944 spindles are bad for scrub radius. I think their tie rod ends are located further outwards then the originel VW 2-bolt spindles, which curve more towards the inner side of the car? Not sure though. Whats your take on my theory?