SCCA EMod MGB GT V12 Build

The steering effort is less and better 'cause you are using less steering input.....Ask me how I know....

Rog

Curmudgeon wrote: Cool! Wonder why the steering effort would feel different? Maybe something was binding before?

You know what? Maybe there was something binding with the front sway bar because it was all pretty tight in there and both sway bars are now gone. Whatever the case, the steering is light to the touch now, which is good for my wife.

Umm,if you didn't change the front suspension and the understeer is now gone doesn't that mean the rear lost grip?(assumming it wasn't a welded diff before and lsd now or something)

kevlarcorolla wrote: Umm,if you didn't change the front suspension and the understeer is now gone doesn't that mean the rear lost grip?(assumming it wasn't a welded diff before and lsd now or something)

The balance was changed, not neccessarily a reduction in overall grip. There were lots of changes, both sway bars were removed, motion ratios changed front and back and rear roll center dropped from 14" to 7". The roll center was not adjustable before and I'm betting that if I raised it back up to 14", the car would understeer again despite the other changes.

loosecannon wrote: Project update: I drove it for the first time with the new rear suspension and it feels completely different. The terminal understeer of before is completely gone and I no longer have to punch the throttle to get around the tight kart track. Somehow the steering effort is much reduced and I haven't quite figured that out. I will be tinkering with camber, roll center and track width so there is more testing to do. I took a video of the rear suspension while I did some laps and even with two lights on it, the GoPro is still a little dim-I included the video if you want to see it. http://www.youtube.com/watch?v=l-K5dMyHfRg

Getting rid of the bars on my Daewoo really improved the steering feel. Maybe you're getting the same thing.

kevlarcorolla wrote: Umm,if you didn't change the front suspension and the understeer is now gone doesn't that mean the rear lost grip?(assumming it wasn't a welded diff before and lsd now or something)

Roll center axis inclination would have an effect on balance. Getting rid of the bars would also increase the grip available to the system, I think.

Right, you use sway bars to 'loosen' one end or the other. For example: if you want the car to oversteer, add rear bar (more rear roll stiffness). Ditching both bars would drastically change how well each end grips, much more so than the roll axis inclination although it does play a part.

It's possible to control body roll with spring stiffness (not to be confused with spring preload) and thus eliminate the sway bars but that usually means a lot of disassembly to swap springs. Sway bars are much easier to swap/tune.

I'm just curious as to what would have changed the steering effort. emodspitfire may be on to something: less input required = less effort.

The reason I'd said that was because you'd stated you'd driven it for the 1st time with the new rear suspension which implies only the rear was changed.I didn't go and reread all 21 pages.Lowering the rear roll center should make more rear grip due to reduced weight transfer at the rear no?.I know roll axis inclination changes balance and all but I would think no other changes other than raising the rear roll center would increase rear weight transfer and reduce rear grip.

Curmudgeon wrote: Right, you use sway bars to 'loosen' one end or the other. For example: if you want the car to oversteer, add rear bar (more rear roll stiffness). Ditching both bars would drastically change how well each end grips, much more so than the roll axis inclination although it does play a part. It's possible to control body roll with spring stiffness (not to be confused with spring preload) and thus eliminate the sway bars but that usually means a lot of disassembly to swap springs. Sway bars are much easier to swap/tune. I'm just curious as to what would have changed the steering effort. emodspitfire may be on to something: less input required = less effort.

Except that I don't have to swap springs, I just have to adjust the motion at the rocker arm. I make either end super soft or stiff, stiff, stiff and not even throw the damping out of wack. I still have the sway bars but the ability to adjust roll center makes them unnecessary unless I run out of adjustment, so they have been removed.

How much scrub radius do you have? It's possible if your scrub radius is high that removing the swaybar resulted in less steering induced weight jacking because the suspension moves easier.

There is still a place for swaybars even with perfect roll centers. If you are relying only on springrate for roll stiffness you don't have the flexibility to pick your ride rate separate from roll stiffness. To achieve a high enough roll stifness you may end up with an undesireable ride rate.

kevlarcorolla wrote: The reason I'd said that was because you'd stated you'd driven it for the 1st time with the new rear suspension which implies only the rear was changed.I didn't go and reread all 21 pages.Lowering the rear roll center should make more rear grip due to reduced weight transfer at the rear no?.I know roll axis inclination changes balance and all but I would think no other changes other than raising the rear roll center would increase rear weight transfer and reduce rear grip.

I was fiddling with numbers in my suspension program and it looks like if I raise the rear spring rate, I need to lower the rear roll center. I had that wrong at first but I looked at it again and that seems to make sense. Although it shows how much changes to motion ratio affect balance because I cut my roll center in half and still lost the understeer. This is a good thing because I only have an inch higher to go on roll center but have 3 inches lower, so curing overtseer should be easy.

nocones wrote: How much scrub radius do you have? It's possible if your scrub radius is high that removing the swaybar resulted in less steering induced weight jacking because the suspension moves easier. There is still a place for swaybars even with perfect roll centers. If you are relying only on springrate for roll stiffness you don't have the flexibility to pick your ride rate separate from roll stiffness. To achieve a high enough roll stifness you may end up with an undesireable ride rate.

If I had to guess, it would be 4" positive scrub radius. I am reducing the negative camber by a bunch and widening the track width soon so that may or may not change.

I needed to find my center of gravity so I followed the directions on Longacres website http://www.longacreracing.com/articles/art.asp?ARTID=22 and punched in the numbers. I inflated the tires to 40 psi and put the car on the scales with me in the car. I wrote down what the total weight and front weight was then lifted the rear of the car up exactly 12 inches and checked the front weight again. Once I punched in these numbers as well as front tire circumference and wheelbase, the calculator told me that my center of gravity is 17.35 inches off the ground.

Trigonometry ftw. The higher you can get that angle, the more accurate your figures. Tilting it on its side is usually easier, and just as accurate.

As most of you know, I put 15" wheels on the car because I needed to clear the brakes. Then I found out that the radial slicks I planned on running were actually no good for autocross because the radials don't like rapid turning (such as a slalom) like the bias ply slicks. The only tire company which has 15" bias ply slicks in the right widths is Avon, and they are more expensive than Hoosiers or Goodyears and have no contingency.

The price difference between 13's and 15's will pay for a set of new rims so, I broke down and ordered a set of 13" rims from Diamond Racing wheels. I took a chance that I would be able to modify the brakes to fit. The wheels arrived and with some minor tweeking, I got them to fit over the brakes. Then it came time to order tires, and problems arose. The Goodyear or Hoosier tires that are supposed to be the hot ticket in D/EMod are actually designed for Formula Atlantic cars. This means the front tires are 9.5 inches wide and the rear are 13 inches wide. This is not a problem for cars like a certain green Bugeye which has only 41% of it's 1850 lbs on the front tires, but I have 49% of 2250 lbs on my front tires.

Now, I can make the car work on these skinny front tires, provided that I don't overload tires designed for a car 650 lbs lighter than my own, but they would be a compromise. I started to look again at the Avons, which to be fair to Avon, cost about the same as Goodyears or Hoosiers as long as you stick to 13 inch wheels. However, the Avon rep advised me that the 13 inch tires are designed for cars up to 1600 lbs and the 15 inch tires would work better for me. So, I decided to go with the Avon 10.7/21.5-15 in front and 11/23.5-15 in back. At some point I may want some rain tires and I can put those on the 13 inch wheels.

Curmudgeon wrote: Right, you use sway bars to 'loosen' one end or the other. For example: if you want the car to oversteer, add rear bar (more rear roll stiffness). Ditching both bars would drastically change how well each end grips, much more so than the roll axis inclination although it does play a part. It's possible to control body roll with spring stiffness (not to be confused with spring preload) and thus eliminate the sway bars but that usually means a lot of disassembly to swap springs. Sway bars are much easier to swap/tune. I'm just curious as to what would have changed the steering effort. emodspitfire may be on to something: less input required = less effort.

I would think it has at least something to do with keeping the weight more evenly distributed between the front two tires, although he probably is using less steering angle as well.

BTW, I'm using the no bars setup on my project and haven't swapped springs once. Part of that is I got lucky and wasn't far off from the start, but part of it is also that I can just change the roll centers to adjust balance.

@ loosecannon,

Do you have any idea on where I can go to learn how a woblink works? I'm interested in using one on my next project.

DaewooOfDeath wrote: @ loosecannon, Do you have any idea on where I can go to learn how a woblink works? I'm interested in using one on my next project.

Sure, try this one: http://www.fordcapri.co.nz/images/technicalpage/mallocksuspension.pdf

Despite my best efforts to move the steering rack back more, I couldn't move it enough to get any Ackerman out of it. Ackerman is when the inside front tire turns sharper than the outside front tire which is important in tight turns. The solution was to make the steering arms a little longer, which increases my turn radius (in theory) but will actually make the car turn better and easier (Briget will like that). I started by taking the MGB steering arms off and making a template:

Then I moved the part where the tie rod bolts to over one inch and clamped it in place. I used 1/2 inch wall tubing and flat bar to make the new arm:

Here are all the pieces, ready for welding:

And installed on the car:

I haven't driven it yet but now I can push the car with one hand when the wheels are cranked.

The steering arms look great!.

I'm switching to Avons for this year,after some e-mails with Chris Raglin and seeing how much more resistant to heat cycling the Avons are over hoosiers the sligh increase in cost per tire is outweighed by useful life.

kevlarcorolla wrote: The steering arms look great!. I'm switching to Avons for this year,after some e-mails with Chris Raglin and seeing how much more resistant to heat cycling the Avons are over hoosiers the sligh increase in cost per tire is outweighed by useful life.

I have used Hoosiers for a few years and like them, except for how they go off after 50 runs. The Avons are supposed to last a while and the A15 in particular because it has a deeper tread. It's actually an ungrooved rain tire.

The steering arms are cool. I've been wondering if a similar fix could be done to the Spitfire/GT6 steering.

loosecannon wrote:

kevlarcorolla wrote: The steering arms look great!. I'm switching to Avons for this year,after some e-mails with Chris Raglin and seeing how much more resistant to heat cycling the Avons are over hoosiers the sligh increase in cost per tire is outweighed by useful life.

I have used Hoosiers for a few years and like them, except for how they go off after 50 runs. The Avons are supposed to last a while and the A15 in particular because it has a deeper tread. It's actually an ungrooved rain tire.

Exactly my experience,Chris tells me they did a same day same car/driver comparison with a set of approx 90 run avons agaisn't a new set-the old set was 2/10's slower.Try that with an R25b and it'll be more like 2 seconds slower than a fresh set.

Ian F wrote: The steering arms are cool. I've been wondering if a similar fix could be done to the Spitfire/GT6 steering.

You would be suprised what British parts will swap around. My steering arms were MGB parts that bolted directly onto the Jag upright, no mods required.

damnit I love this thread

4cylndrfury wrote: damnit I love this thread

And I love building this car. I want to sell it so I can start another one. How about a Subaru STi powered Midget? ;)