'71 front suspension / scrub radius / wheel setup

[71rs]

I've got a 71 which I'm running a 16x8 4.5" BS wheel (vintage wheel works V45) and 255-50-16 all the way around (Toyo RA1's). No rubbing and everything is pretty much ok so far. The rears are a perfect fit, the fronts are a tiny bit offset to the outside more than I'd like, in terms of looks.

This post is about the scrub radius though - I think geometry-wise, I have the front wheels too far out. there was a noticable difference from my old 15x7 stock setup, in terms of a rough roads' ability to kind of grab the car i.e. hitting a moderate pothole with RF tends to "steer" car to the right. The old 15x7 with BFG radials didn't seem to do this. Suspension is rebuilt so it's not old bushings or anything like that.

I've reset the front suspension to around 4* caster / -0.5* camber (max caster I could get with the stock A-arms with just about no shims in the front and a fairly thick stack of shims in the rear). This has helped a decent amount (and was a great benefit to overall steering feel), but has not eliminated the problem.

I've done some searching and looking, but I haven't been able to find a real solution to this problem (outside of going to 17" wheels with more backspacing). It seems like what I need is a spindle that brings the entire wheel assembly closer to the spindle by about half an inch or so. The complications are that, if the wheel assembly is half an inch more in, I think it would hit the stock steering tierod end and possibly the A-arms as well. So I'd need this imaginary spindle to also push the outer tierod end hole towards the center of the car a 1/2" or so (and the obligatory tubular A-arms).

I have no idea what either of these suspension changes would do to my geometry. I don't think moving the wheel in would affect anything (other than to reduces reduce scrub radius), but no idea what the tie-rod end move would do to my bump steer/ackerman etc.

I know that 17's would give me more clearance and solve the problem, but I rather like the look of these 16's and the toyo ra1's in 255-50-16.

So, I'm wondering if anyone knows of any options to improve upon the situation or has any ideas?

Attached a few pictures, quality is not so good and I'm sure we all know what it's like to have a car in the "project" stage. :)

[79T/Aman]

what are you comparing this feel to ? what was your old tire size? an 8" wheel with 4.5 BC will give you a stock scrub radius I suspect you had smaler tires on the car before, and now the wider lower profile tire is giving you more fead back from the road.

[baz67]

By your explination it seems more like a bumpsteer issue. You stated that it only happens on one side during suspension compression and it seems that your caster angle has some effect on it. That tells me bumpsteer. What was the BS and tire size on your old rims? How about your static toe settings.

[Mean 69]

This post is about the scrub radius though - I think geometry-wise, I have the front wheels too far out. there was a noticable difference from my old 15x7 stock setup, in terms of a rough roads' ability to kind of grab the car i.e. hitting a moderate pothole with RF tends to "steer" car to the right. The old 15x7 with BFG radials didn't seem to do this. Suspension is rebuilt so it's not old bushings or anything like that.

I think it is likely that you have two issues here, and one is making the other more pronounced. You made two very big changes (relative) at the same time. One, you increased the scrub radius, as you pointed out, with the new wheels you put on, and this is not in the correct direction (obviously), and as youpointed out, there isn't anything simple you'll be able to do about it. The other big thing is the new choice in tires: RA1's are VERY different tires than the old radials you hade on the car, and my guess is that the RA1's have a wider contact patch to boot. The combination of those two things is creating the situation that you describe. I'd bet that there is a bump steer issue too, but here again, the difference you are feeling from the old wheel and tires to the new is the dramatic difference in the tires, pronounced by the slightly wider overall track/increased scrub radius. You never felt the issue as such before because the tires masked the problems that the suspension setup had/has.

When I switched from a 245 tire, to a 275 tire on the front of my 69, I experienced the same thing that you describe, the car will track to funky grooves in the road, etc. In my car's case, the tire change in terms of construction was not that different (Toyo street radials to BFG KD's), the difference came in terms of the very slight increase in track/scrub. It was actually pretty dramatic. And again, in my case, not a whole lot can be done short of significant suspension changes, nothing free here. The good news is that I have a lot more front grip, and I am guessing that you do as well, and that to me at least, is more important than the by-products, at least for now until the new front goes on the car.

Mark

[71rs]

To answer the questions:

Yes, I had somewhat smaller tires before. BFG radial T/A in 245-60-15 on 15x7 stock steel wheels.

I should clarify my statement about the feedback only occuring during suspension movement. in reality, it occurs whenever something changes the load on a front tire - such as a suspension movement, -or- one tire going over ridged pavement, or grooved pavement (no suspension movement, just altered contact patch) or something along those lines.

I'm pretty sure the BS on my old rims was 4.25".

toe is 0 for the time being, measured by comparing distance from center of tire on "front" sides to distance from center of tire on "rear" sides.

thanks for the input.

[jeffandre]

71rs,
How did this story turn out? Did you change wheels to reduce scrub? Any alignment changes to help it out?

Anybody else battling with front geometry problems?

I have a 71 with B-body spindles (only wanted larger outer bearing, plus they were from 95, so less years of abuse). I used a Kore3 hub with 14mm studs, and a Wilwood 6-piston setup. I know people sometimes have a hard time thinking of 19" wheels as performance-oriented, but running 19" wheels allowed me to backspace the wheel almost over the center of the upper ball joint, and with a wheel width of 11" I have a scrub radius of about 1". Also figured my roll center last night to be about 1.75". I still have a decent turing radius (same as a 3rd Gen), and only rub the sway bar when turning sharply in slow speed situations.