CR Rear suspension mods

[Aussie Mike]

Peter from Ozwheel just sent me a couple of pics of my new rear wheels. Hopefully I should have them by Thursday.

It's only 50mm more dish than the old setup but I reckon it makes quite a difference in the look. The spinner is almost all inside the wheel now and not sticking out like Ben Hur's Charriot.



I ordered them with the centers un coated as I plan to get all 4 centers recoated together and wanted them all to match.



Cheers

[acecob]

Awsome wheels Mike they look magic.
what colour are they going to be

[Aussie Mike]

The centers are going to be HPC coated silver the same as the side pipes.

I restored Garrett's (Justbetter)wheels a little while back. I stripped them down and had the rims re polished and sent the centers away to be HPC coated. They came up magic. Probably as close as you'll get one of these cast centers to looking like polished aluminum.

I'll see if I took a pic of them. Otherwise I'll call in and see Garrett and snap a pic. I think he's using them as a fancy coffee table

Cheers

[Aussie Mike]

Well I had an interesting evening in the shed. I decided since I had one side all together that I should see if my geometry theories were going in the right direction.

I built a Bump steer guage to check what the rear end is really doing. The guage uses 2 dial indicators spaced 600mm apart. This is roughly the diameter of a tyre. To measure the bump steer I moved the suspension up 10mm at a time and calculated the difference between the readings on the 2 dial indicators. This shows how much the rear upright is rotating. I then put all the data in an excell spread sheet that let me calculate the change in toe in mm




I first measured the rear bump steer on the stock setup with the donor Falcon arms to see how much toe in they added as the suspension compressed. I was shocked to see about 41mm of toe in added from fully relaxed to fully compressed. It's no wonder my tyres keep rubbing on the inner tub as the suspension compresses.

Next I measured my chrome molly arms with the Murphy track locator. On my first pass I the rear suspension went from zero toe to 14mm of toe in from relaxed to compressed. A definite improvement plus I also gained 20mm in wheel travel with the new setup.

This graph shows the comparison between the stock setup and the 4130 arms with a 54mm clevis.



I designed the rear bump steer to be adjustable by changing the height of the rod end where it attaches to the clevis on the upright. My initial setup has a 54mm clevis length so I thought I'd try a shorter length to see what happens. I set it at 21mm and ran the measurments again. The results were horrible with 22mm of toe out being added from relaxed to compressed. Well it proves the adjustment works at least.

Here's the graph



OK how about a length somewhere in between. I tried 41mm next and measured the bump. This time it only added 7mm of toe out when fully compressed. I'm heading in the right direction.



It was getting to late to try another clevis length but I reckon about 48mm will be about spot on.

It's all good fun and I'm learning heaps.

Cheers