Track width alignment

[JohnUlaszek]

On my 72 Nova I will have 285's on the rear and 245's up front. Ignoring packaging and cosmetic factors, what is the preffered location for maximum handling capability? Do I align the centerlines of the tread or align the outside faces of the tires?



Opinions are fine but I would really like to know what the standard accepted practice is, so this might be a Katz or Pozzi question

[Salt Racer]

So you're asking where you should go by when you do alignment?

Ideally you want to use rims or hubs for reference for camber and caster. Longacre and other places sell nice alignment gage that register off of rims. I'm sure you guys can duplicate that.

I've done toe setting hooking up a tape measure on tread grooves, but it's not recommended b/c you should measure the difference between the leading edge and trailing edge of tires, which is near impossible with sheetmetal and engine in place. You can use tire sidewall for toe alignment, as long as you butt the straight edges high enough so they won't butt against the bottom area of sidewall where they're bulging due to vehicle weight. But this is also difficult to measure. Toe-gage is recommended if you want to do it right. I'm cheap and I don't have a toe-gage, so I use tread groove method combined with some trigonometry.

When I'm not in hurry...
First, I measure the height of rocker panel at ride heigt, as well as the distance from the ground to the center of wheel - all with full weight on vehicle, including the driver weight and half tank of gas. At this point, I check the toe using tread groove and see if it's roughly close to what I want.

Then take the tires and springs off, and disconnect sta bar. Set the car on wood blocks so that the rocker will be at the ride height, and put some blocks under LCAs so the hub will be at the same height as the rolling radius of the tire.

Center the steering, and check camber on hub face with a digital protractor. There are usually machined faces on knuckles that are symmetrical left & right, and perpendicular to the steering axis. Deburr the surface and place the protractor there to check caster.

Then I measure the tie rod length to make sure both are at the same length. Run the bumpsteer check at this point, and adjust tie rod height if necessary.

Put everything back together, drive around a parking lot to have the springs settled. Then I re-check the toe.

Drive the car on level road, and if it pulls one side, I increase camber and/or caster on the side it was pulling towards. If steering wheel is off center, I re-clock the U-joint on steering box/R&P or re-clock the wheel if possible.

I'm probably being too anal, but the car feels very nice afterwards.

As for alignment specs, David probably can give you better answer for F/X-body suspension. But my guess is -1.5~2.0*ish camber, +4.0~5.0* caster and 1/16"ish toe-out.

P.S. Nice valves you got in your plastic engine block.

[JohnUlaszek]

Katz,
Thanks for the wonderful and informative answer, unfortuneately I didn't make my question very clear.

I am trying to determine the relationship between the front and rear track width in regards to axle width and wheel offset. Do I want the rear track width wider than the front to compensate for the wider tires or do I offset the rear wheels such that the outside tire faces are co-planer?

Thanks for your earlier post, you answered questions I would have had later.

I am working on another set of "valves" right now

[MrQuick]

yeah those are great but wait they are all intakes! he he I think I just heard Katz go DOHHHHHH!!!!!!!!!!!!!!!!!!!!!!!

[Salt Racer]

No Vince, it must be some kind of his secret new siamesed valve system. There are only six of them on one bank. Hollow glass valves are light, and allow easy inspection of piston tops simply by taking the valve covers off. Or maybe his inner ricer-self subconciously forced himself to add extra fake exhaust ports so he can claim he has a V8 when in fact all he has is a V6.

JohnU,
I see. Now you explained it, it finally made sense in my head. Perhaps I need some siamesed valves myself to clear up my head.

I have to admit that I don't have much experience/knowledge with this one. The reason is on production-based cars, which I have been dealing with 99.99% of the time, tires need to go where they need to go. I wish I had experience with open wheel cars where you can change track width easily, but unfortunately I don't.

But my gut feeling tells me you want front track to be slightly wider than rear especially on a nose-heavy car. It probably would make the car more stable in straight line, and I'd think it will be more responsive to steering (better turn in).

Since you're retaining stock spindles, you also need to consider scrub radius. If you slap on a pair of 8" wide 3" BS wheels just to make the track wider, it will severely hurt the stability of steering over rough pavement as well as under braking, not to mention increase in spindle stress.

I had 245/45R17s on 8" rims with 4.875" BS on my '69 Nova. With factory discs, the tires rubbed on the top bolt on inner fender slightly during turn even with G-mod style modification (button head screw solved this problem), so you probably can't use 3" BS anyway. I never drove this car on track, so I cannot comment on balance and whatnot.

Sorry, I can't back up these statements with scientific proofs (other than scrub radius). I'll do some checking.

[David Pozzi]

For max cornering traction the wider the better on either end.
On an autocross car, the width will hurt you on linked turns or slaloms especially.
Go-Karts adjust understeer/oversteer balance by spacers behind the wheels, widen the front track, more traction on that end.

As far as F/R track, I can't remember reading anything about it. making the front wider would affect tire scrub radius and the car wouldn't steer as well, especially going straight down the road. I think I'd try to keep the front as close to on center as possible. By on-center, I mean draw a line through the balljoints, where it touches the ground should be between zero and an inch inboard of the tire tread center. I don't have a definite figure, I just picked an inch as a number that would "sounds good" to me.

I don't think you want the rear way wider than the front, but if it were an inch or two wider I don't see any harm. The front has the most weight and would benefit from a wider track for better corner entry, but the rear helps you accelerate out of a turn and wider helps that.
In the end I'd make the tires fit the bodywork, try to make the front tires have a low scrub radius so it's easy to drive and brake without swerving around. I don't think an inch different backspace on one end or the other will be felt. On a go-kart it would since it's a larger percentage of the chassis width.

[JohnUlaszek]

Thanks David and Katz.

I need to keep working on that special valvetrain, maybe something bigger next time.....

Katz,
I keep forgetting you have a little Nova project of your own, any advice you can give me regarding balljoint location etc is much appreciated. Cutting up arms or moving things around is not a problem.

I am trying to get as much tire up front as possible, it looks like the Vintage Wheel Works V45 is limited to 4.75" backspace, hopefully this will allow the 245 up front. I don't mind working the sheetmetal to allow the widest tire up front as possible.

So, it looks like the 4.75" backspace is the driver here. The car is mini-tubbed and will have trucks arms so there is a ton of room out back to move the 285's wherever I want them. Appearance may become a factor. Ideally it sounds like I don't want the rear width any wider than front.

I will have a 2" engine setback in addition, so hopefully that will give the 245's up front a fighting chance.

[Salt Racer]

Actually, I'll be using JP IFS for my Nova and I didn't do any development on the car so to speak, so I can't comment much on the stock-based suspension.

But I punched in pickup point locations of G-mod'ed 1st gen suspension provided by David in WinGeo a while ago, and it actually looks pretty good save for bumpsteer curve. But I'm guessing you'll need some kind of drop spindles if you want to lower the car. I know mine was f'ed up, with subframe at 4" off the ground.

IIRC, the front outside sidewall-to-sidewall on my Nova measured about 69ish, while rear measured 70ish. 245s BFG Comp T/As (do they still make these tires?) measured 9-11/16", and 275s measured 11-3/16". So front track was like 0.5" wider than rear. I'm sure yours will end up about the same.

IF I were to modify stock IFS, I'd get a pair of custom drop spindles from SCP (since now I know they can make spindles with LBJ much lower than spindle pin), and build longer arms and use rims with more BS. Longer arms, better. Less scrub radius, better. The only down side is decrease in installation ratio.

But this obviously is not an option if you're set on VWW wheels. You could make something like Wilwood hubs (hub face is 3/8~1/2" closer to king pin axis), and make 1/2" longer arms, but that wouldn't be worth the effort.

Can you get 8.5" rims instead of 8", possibly with slightly more positive offset? (like 5.25" BS). That will helps reduce scrub radius, and wider rims make the tires work better.

[Salt Racer]

...Go-Karts adjust understeer/oversteer balance by spacers behind the wheels, widen the front track, more traction on that end....

Speaking of Go-karts, Brian Zales (baz67) and I went to an indoor kart track on Saturday. Within 3.5 hours, I spent more money than I had ever spent on a date (that's probably why I repel women). They have about 8~10 karts, and we tried almost all of them in an effort to find a good one.

Current track record is 22.22 sec, and I somehow managed 22.90 in a good neutral-steer kart


Sorry off topic. But, it's a really good for learning throttle steering so it's somewhat PT related.

[Fuelie Fan]

We're insane about finding the fastest kart when we go to Speedzone. There is ALWAYS a ringer, for whatever reason. We fight each other for it.

One time, we went early in the morning for an all-day jaunt, and it was sprinkling outside, but we hung around and ended up with the place pretty much all to ourselves when it let up.

For the question at hand, when we built the formula sae car in college, the front was wider than the rear, but it was also designed for really tight courses. As others have said, the front track is "pretty much" fixed by the geometry of the front suspension.

[JohnUlaszek]

Katz,
Thanks for the detailed response. I am going to see about a 8.5" wheel. I am starting to think I need to buy the wheels that give me the offset I need and to hell with the look for track use at least. I can always do a 315 rear and 235 front if I want to do the car show thing.

You mention longer arms, what do you think about moving the ball joing out a 1/4 inch further on the stock arms?

[Salt Racer]

Yes, if you're serious about track use, you're better off giving up looks. I personally prefer the look of light/rigid flat-faced front wheels that screams "F'ck hot rod looks, function first!!", like on JP's car. I can't afford a set of Kinesis right now, so I'm eye-balling at a set of AFS 18x9.5 C5 replicas (21ish pounds and plenty of room for big calipers).

My philosophy is every little bit counts (at least for production-based cars). If you can move the LBJs out 0.25" w/o too much trouble, I'd go for it. But the gain is minimal. I'd leave it alone if that requires significant amount of fab work.

[JohnUlaszek]

Moving the ball joint out is not that big a deal as I am converting over to screw-ins on the bottom anyway.

The only problem I see with the C5 and 4th gen wheels is they are 9.5". BBS's would be nice too I just don't see how I can package a 9.5" up front with the stock subframe.

[Salt Racer]

You can get C5 rims in 17x8.5, but it probably wouldn't work unless you make the hub width wider by fair amount. +0.375" offset, 8" wide rims fit good on my car, and non-Z06 C5 front rims have +56ish mm offset (~+2.205"). Assuming the section width of tire stays the same, 2.205-0.375 = 1.83" per side.

[Salt Racer]

Just some additional info about C5 replica rims...

There was a set of 18x9.5s with cosmetic blems on e-bay for $495. I wasn't sure what kind of load rating these things have, so I sent e-mail to the manufacturer. I hadn't received the reply but I bought them anyway thinking they'd at least make good mockup wheels.

I got the reply a day after I bought them. The rims are rated at 1400lb. Marginal at best for my car, as each front wheel carry 1200lb or so. Not too many people here have cars as heavy as mine, but it's another thing that shouldn't be overlooked if you intend to run your car at the track.

I think I'll live with my billet wheels until I can afford a set of Kinesis K18s.

[baz67]

Katz I think it is time for you to start thinking about an all alum. sbc for that Buick. That alone should take, what, 400 lbs off of that nailhead.

Brian

[Salt Racer]

Nailhead: 685 lbs carb-to-pan (not sure if it's correct, I read it somewhere)

Bill Mitchell's all alum 427 SBC: 435 lbs carb-to-pan

Not quite 400 lbs, but it still is a big deal.

Unfortunatly, the swap won't happen anytime soon. I need to start saving some money, especially with potential relocation and whatnot....
Speaking of which, my potential new employer should be starting his business soon.

I think I'll just buy a set of good tires that would fit on my current rims (255/45R18s, probably GY GS-D3), build rear sta bar and call it good for this season.