Rear camber findings and adjustment recomendations

[ALLAN]

OK, after my last post and not getting any answers I dug into the camber adjustment question. What I came up with applies to the Goodpart adjustable brackets or the stock-notched brackets, through logical deduction, some measurments and other post and web sites--this is what I think will work best. First you cant have different adjustments or notches on all four mounting points--that would definetly screw up the geometry (pivot points)causing the swing arms to arch at different angles, In my case this is exactly what I had and Im sure was causing my quirky handling problems.------I laid out a swimg arm on the shop floor and took measurments based on tilting the the swing arm from side to side simulating a camber change and height adjustment. The results of this showed,--adjusting the inside effects camber more than the outside, adjusting the outside effects the height more than camber. As Ive stated before I doubt if there are many Triumphs with perfectly straight frames and the adjustment will probably end up different on each side because of it, so in most cases there will have to be a compromise in the adjustment to keep the rear swing arm geometry close. Here is my recomendation for adjustment and keeping the geometry within reason.----Adjust the height first using outside(only)adjustments/notched brackets, this is the adjustment that should be the same on each side no matter what, by either using the same notched brackets or with the Good parts adjusters the sliding block should be in the same position on each side. After this adjustment if the ride height is unequal then you need to use spring spacers to dial in the ride height-but wait to do this untill after you adjust the camber because the camber adjustment will slightly change the ride height.---- Now for the camber adjustment. Using the inside (only) adjusters/notched brackets -adjust the side that is already closest to your desired camber then adjust the other side, if its obvious that with the second side the adjustment is not going to be in the same position then my recomendation is not to go more than 3/8" different than the first adjusted side. 3/8" is the same as one notch on the stock brackets. It is better to have that second side off on the camber than to go beyond the 3/8"/one notch difference because as I have already learned keeping the overall geometry close to the same is more important than having the camber the same.----Im not an engineer or alignment guy and I am not that good at composing stuff like this, but I do have alot of automotive experience and because of a lack of info on this subject I thought I would give it my best stab.------I know--I know, I live in California and I am not one of you easterners----but I was born in Massachusetts-does that count!!??

 

[swift6]

Good info. Possibly a knowledge base entry?

 

[bobh]

Allan,
You may want to but Herb Adams' book on chassis setup and handling. I've only read part of the book but it does explain things.
The rear suspension in the TR6 is a compromise. The trailing arms are semi trailing arms. The geometry is oddball. All of this was done to accomodate IRS to the existing chassis with as little cost increase as possible.
Weight differences on each corner of the car will affect handling. The Miata was designed for 50/50 front to rear weight distribution as well as side to side including the driver. (I'm sure they used an average weight for the driver) I think the weight on each wheel is very close to the weight on the other wheels. This balance along with correct geometry is why they handle so well.
Crucify me as a heretic, but I doubt that you will ever get a TR6 to handle as well as a Miata. I think the best thing you can do is to try and equalize the weight on each wheel as close as possible. Including yourself in the drivers seat. You may want to sit in the car when you get it aligned. I recall something in the Roger Williams book on improving the TR250 and TR6 about the camber on the front wheels. I can't remember if there is anything on the rear.
With the information you have gathered you may want to contact someone who races or has raced a TR with IRS. Neil Revington may be a good source. My guess is that a racer who sees that you are attempting to understand the geometry and have taken the initiative to measure, postulate and gather data will be glad to offer information.
BTW I plan to go to the Mitty at Road Atlanta during the last weekend in April. I hope to find one or two IRS TRs in the paddock. I want to take pictures and attempt to suck the drivers and mechanics brains dry. I'll let you know what I find.
BOBH

 

[ALLAN]

bobh, I agree about the semi trailing arms, I think the Tr6 should have come with a rear wishbone set up. I also agree with the weight distribution, but to do that and not mess up the geometry is tough. I originally sent this topic out to the racing forum but I didnt get any feedback. That would be great about the pictures and getting more info. Thanks,

 

[Brosky]

Re: Rear camber findings and adjustment recomendat

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I know--I know, I live in California and I am not one of you easterners----but I was born in Massachusetts-does that count!!?? [/QUOTE]

I knew that there was something that I liked about you.

Thanks for the great explanation.