Wheel Offset

[Bill Blue]

In the past I've made several posts about maintaining the original Alpine wheel offset, mostly in the interest of steering effort, not that anyone seems to care as long as the wheel looked good and would otherwise "fit".

Surprisingly, over on the H.A.M.B., steering has recently been a very popular subject. I just saw this paragraph and thought I'd share it for the benefit of anyone having steering issues. Guess what, it is about scrub radius, which is all about wheel offset! Unless, of course, you are building a car. then it becomes an exercise of matching wheels and front suspension design. I have known about scrub radius for about a zillion years, but never understood why it was so important. I would assume about 90% of the Alpiners are in the same situation. So here goes:

"You want some Scrub radius either positive or negative. You don't want zero scrub because steering will feel loose and will have an oscillating effect on the loads. Squirrelly steering would best describe a car with zero scrub radius. You also don't want more than 2" scrub radius, steering will feel heavy and result in having a car that wants to dart when the natural forces combine with your steering wheel Input while negotiating curves or braking. Especially braking in curves and cornering maneuvers even road irregularities. (Ever drive with one wheel on the smooth road and the other on the scarification surface)"

I have no idea what the stock Alpine scrub radius is.

Bill

 

[MikeH]

https://en.m.wikipedia.org/wiki/Scrub_radius

 

[Bill Blue]

Anybody seen data for the Alpine scrub radius? Is it possible the Alpine was designed with negative scrub radius? Why else would it use such a weird (1 1/4") offset wheel?

Bill

 

[Barry]

Bill,

No data, but I seriously doubt that a stock Alpine with stock width wheels has negative scrub radius even with the narrow factory wheels. One of the many weird aspects of the Alpine front suspension is that the steering axis inclination is only 5.5 degrees (very vertical) . Combine that with the upper ball joint being completely inside (laterally) the wheel and it seems likely that even the narrow (4 or 4.5") factory wheels probably resulted in a significant positive scrub radius. Wider aftermarket wheels have to go outward to avoid hitting the upper ball joint and that further increases the positive scrub radius.

My best guess is that the weird wheel offset (1-1/4" offset is a lot for a 4 or 4-1/2" wide wheel) was an effort to minimize positive scrub radius resulting from the very vertical steering axis.

You have to remember that this is a really old suspension design. My research indicates that the basic chassis dimensions and front suspension geometry of the Alpine are the same as the post war 1945 Hillman and I would not be surprised if the post war Hillman suspension was copied from a 1930-something Humber or whatever.

 

[Bill Blue]

Okay.
Bill

 

[DanR]

"You want some Scrub radius either positive or negative. You don't want zero scrub because steering will feel loose and will have an oscillating effect on the loads. Squirrelly steering would best describe a car with zero scrub radius. You also don't want more than 2" scrub radius, steering will feel heavy and result in having a car that wants to dart when the natural forces combine with your steering wheel Input while negotiating curves or braking. Especially braking in curves and cornering maneuvers even road irregularities. (Ever drive with one wheel on the smooth road and the other on the scarification surface)"

SO? What is the answer to the "Squirrelly and Darting" Steering?

I have the new springs I ordered, I want to test them before I install. Hope against hope they will be part of the answer,

 

[Bill Blue]

I don't know. I thought there was a chance the Alpine, with it's weird offset, was setup with negative scrub. As wheels with more offset are used, negative scrub would become zero scrub (bad), but even more offset would produce positive scrub (good). Barry thinks the Alpine has positive scrub from the factory, so that could not happen. Barry knows a LOT more about this stuff than I do.

It appears that extreme positive scrub does not produce squirrely, darty handling. Instead, the steering becomes sensitive to one wheel bumps and unequal front braking.

I do know this:
With considerable negative camber and toe, my car was very darty, but would settle down nicely in a turn. Hated it.
With about 30" positive camber (the most I can get on both sides) and 1/8" toe, it handled okay, still like to wander.
Increased caster from about 2' 45", to about 3' 30", it did okay. Not really good, but okay.

Then I bought some General RT 41 tires. The car was all over the road. Increased caster to the currant (about 5 degrees) it once again settled down. If there is a lesson here, I think it is try stuff until you hit the proper combination. Fortunately, caster and camber are easily changed in your garage. Don't really need to know exact numbers, just keep things even, side to side.

Oh yes, I have discovered it can be damned hard to get honest, exact numbers from alignment guys. I think they don't like to change anything on an Alpine except toe, so let a lot of stuff that is really iffy, slide by and tell you it is okay, or "close enough".

Bill

 

[Barry]

Bill,

I used some large graph paper and made a full scale plot of the key dimensions of the Alpine front suspension.

The best I can tell, the scrub radius with stock 13 x 4.5 wheels and 23" diameter tires is about positive 2-3/8".

With 13 x 6 aftermarket wheels and 23" diameter tires, the scrub radius increases to about positive 3-1/8".

I was pretty sure the Alpine scrub radius was significantly positive, but I had no idea the values would be that large.

 

[Bill Blue]

Thanks Barry, don't know what I'd do without you keeping my head on straight.

BTW, how's things going on your cross member redo?

Bill

 

[todd reid]

If I am understanding the diagram in Mike's wikipedia attachment, it appears that increasing wheel diameter would decrease the amount of positive scrub radius, so 15x6 wheels are probably closer to stock than 13x6 wheels?

 

[Barry]

Thanks Barry, don't know what I'd do without you keeping my head on straight.

BTW, how's things going on your cross member redo?

Bill

Bill,

I thought it was going pretty well, but gremlins have appeared. I built an alignment fixture (a big, heavy gizmo) to make sure the crossmember fits the car and was starting to build the first unit when I found a small dimensional error. Correctly rebuilding the alignment fixture to prevent the same problem has turned out to be harder than I expected.

 

[Barry]

If I am understanding the diagram in Mike's wikipedia attachment, it appears that increasing wheel diameter would decrease the amount of positive scrub radius, so 15x6 wheels are probably closer to stock than 13x6 wheels?

Todd,

Increasing the tire diameter does decrease positive scrub radius, but the effect is very small. A 1" increase in tire diameter only reduces the positive scrub radius by about 1/16".

 

[Bill Blue]

Bill,

I thought it was going pretty well, but gremlins have appeared. I built an alignment fixture (a big, heavy gizmo) to make sure the crossmember fits the car and was starting to build the first unit when I found a small dimensional error. Correctly rebuilding the alignment fixture to prevent the same problem has turned out to be harder than I expected.

Barry, I have recently decided the alligators and gremlins rule everything we do. No matter the project, it always has to be made in a way that pleases them.

Bill

 

[Barry]

I would gladly welcome any 'gator that can locate four 5/8" holes in a 3/8" steel plate within 1/32" horizontally and 1 degree vertically.

 

[Bill Blue]

In high school machine shop, the tolerance was +/_ 1/64" for all fractional work. Layout dye, scriber, steel rule, prick punch and compass should do the job. Maybe you need younger eyes.

Bill

 

[Barry]

Vision was 20/12 at last check and there is no problem doing the layout to +/- 1/64". Locating the holes to +/- 1/64" would require better equipment than I have.

 

[Bill Blue]

If the problem is locating the punch marks, try this. Use a complete coat of layout dye. After the intersections have been established, hold the prick punch lightly in your off-hand. Drag the punch into one of the interesting lines. You will be able to feel it drop into the line. Move along the line until it drops into the intersection. You will be able to feel it. Straighten the punch to vertical and tap with a small hammer. Check to make sure of location, then punch with an ordinary center punch. Use a small center drill (like the ones used on lathes) to start the holes. The first drill should be about 1/4" diameter.

Bill

 

[Charles Johns]

I just got back from a 2275 mile drive in my 65 Mustang SIX and had a question about suspension. However, you guys have given me so much to think about my brain hurts! Fortunately, it is small and I already take aspirin for thinning my blood. My question was relating to softening the ride without hurting cornering, which may involve a rear sway-bar. Bill I know you are not generally in favor of these devices, but while dodging semi's at 80 MPH on uneven lanes, my stiffer-than-normal Pony suspension became obvious to the wife of 52 years. Now 53 is not looking as obvious as before! With a much shorter wheelbase than the Mustang, the Beam could be a real challenge to drive if the suspension were to be made too soft. Remember, I am new to the sportscar field but built many a Hot Rod. Unless I stretch the wheelbase 40" anti-roll devices or tricks, proper caster, camber and springing seem to be my best bet for a good ride. You guys probably do not have smartass friends like I do who suggest "Training-Wheels" attached like out-riggers. OH, what seats work? Air-Ride 18 wheeler seats will NOT fit I am sure. That also came up during our trip on ROAD REPAIR traveling. All ideas appreciated.

 

[Bill Blue]

Charles, I hear you. My wife hears you. Here is the truth as seen after 6,000 miles @ 75 (years old).
Softening the ride.
1. Use stock rubber suspension bushings.
2. Be sure the rear suspension is free to work as intended.
3.Keep unsprung weight as low as possible.
a.Small wheels and tires
b.Stock brakes or lightweight aftermarket brakes
c.Stock rear axle. Consider using the Pinto 6 3/4" unit. Weighs 20 pounds less and is plenty tough enough for a cruiser.
4. Gas shocks, not "performance".
5. Seats
6. Colorado Highways
Improved handling
7. Springing
8. Roll bars
9. Shocks

Comments
1. I used "performance" bushings. Wrong - very harsh
2. Best money spent on ride and handling. It is hard to keep the rear end behind you when it is 6" off the road.
3a. I went to 175 X 15 tires. Not good for ride improvement as it causes a huge change in unspring weight. This is a subject that needs very thorough consideration.
3b. Stockers are good enough for what you propose. I went to monster brakes, got'em, but there is a ride penalty. If you have to change brakes, make sure they are not heavier.
3c. I do not regret going to the 8" with its 10 lb weight penalty, but often wonder if I should have used the 6 3/4", which is much lighter and would be adequate. I don't know if it would have survived my "hot rodder" phase.
4. No regrets on using the stock Camaro shocks as it was a major improvement over the stock shock, but wonder if there is a gas shock that has softer valving.
5. Seats. Use a good firm, not plush seat. I think a major problem with Alpines is your restricted movement. You get in, adjust the seat, wheel, mirrors and drive. You do not move much after that initial adjustment. The bod gets tired. A seat that is comfortable for you and yours is mandatory.
6. Keep off of them! They seem to build them to be rough riding.
7. Proceed carefully! I would not go there unless your springs are obviously bad or too stiff. The stock setup, when properly maintained is not bad. Don't make the mistake of thinking the solution to a worn suspension is a new design.
8. I think the Tiger front roll bar is a great upgrade. I know it has to make the ride stiffer, but you'd never know it. It is also hard for me to see how a rear bar can help the ride. Beyond that, all I will say is that I see no need for a rear bar in my car.
9. No comment. My car was never seen as a corner carver, so I never went down the performance shock route

 

[Bill Blue]

Charles, it is disturbing that you find the Mustang to be uncomfortable for long trips. Just how stiff is the rear suspension on a Pony? If it can't be made comfortable, I don't think there is any realistic chance the Alpine will be better. The things I mentioned are well known and will help, but are not transformative. It is hard to get past the fact the Alpine is a little British sports car. I think you would have to go to a more modern design rear end. There are several seen on Tigers and Alpines, but they are performance oriented and use heavy American car/truck components.

Might want to poke around here, probably the best technical automotive website you will ever find. I can't keep up with them, but they don't seem to mind. A great bunch of gearheads.
:http://www.locostusa.com/forums/viewforum.php?f=5&sid=b49091c8bd71d5ada9bd37b34c160dad

Bill