GM trucks use progressive bump stops...if you look at Hummer front suspension, the bump stops are only 1/2" away from contact with the frame...

 

same for the multilink rear on the Subaru Legacy. A cone shaped bumpstop sitting close to a flat plate on the rear control arms.

 

Matt and the others,

The bumpsteer comes from not altering the steering rack mounting when you raise the inner ball joint mounting point that 3/8". One approach to the bumpsteer correction would be to do what I did, that is, lower the attachment point for the tie rod at the steering knuckle to make the tie rod approximately parallel to the "new" (old) control arm angle. Another approach would be to raise the entire steering rack about the same amount, 3/8", and the tie rod would again be approximately parallel to the tie rod again. Either would probably work fine.

Real world experience with the correction? Well, nothing has failed, fallen off, or leaked after about 1000 miles of track duty over 2 1/2 years. The experience is about what hasn't happened. I feel that I haven't lost the modest stock camber gain in corners. The car continues to roll like stock, I'm not tempted to add a stiffer front anti-roll bar, and the inside front wheel stays pretty planted on corner exits. I'm happy.

Where I am not happy is that I have been trying to add more and more front caster to increase the camber gain in corners and high speed stability. Frustrating, cannot easily find more than 5.5 degrees. This winter I'm going to take another run at the problem. There's got to be a way........

Did I answer all your questions?

My best,
John Petrich in Seattle

 

can be installed for more caster (or castor or whatever)..... Anyway, PM Don (DMH), I think he was getting some race Minis to about 7 degrees, if memory serves....

Matt

 

I'm going to see if I can raise the steering rack to decrease bump-steer, as I can't see a simple solution in the knuckle end.

John, do you have a link or info on the Bimmerworld Z3 extensions? I can't seem to find them in their webstore.

Matt: The PSRS can increase anti-dive, or kick-up, but it's not the same as caster. Caster is the longitudinal inclination of the strut or steering axis pivot. To increase caster, you have to pull the top of the struts aft of their stock positions. Use your air tool to enlongate the strut tower holes!

 

Ryan;
Telephone Bimmerworld and ask to speak to the owner, James Clay. He's "the man". The Z-3 bumpsteer correction components started out as an internal thing for their race car. Don't know if he still has spares or not

Have you any experience at getting up to 7 degrees of caster out of MINI? Your idea about moving the top strut mounting point makes a lot of sense to me. However, I've already done some minor surgery to the tower tops and stopped when it seemed to me that I was removing a lot of metal and getting only fractions of a degree increases in caster. Left me wondering at the time and haven't had the motivation to take another run at the problem. Is there anything I can do at the lower end, near the steering knuckle, to move the knuckle forward? I've tried levering the knuckle forward with a bar, but it didn't want to move. A penny for your thoughts.

Matt;
I will contact Don as you suggested. Appreciate the suggestion as always.

Regards,
John Petrich in Seattle

 

Had a very senior moment about caster and decided to erase my suggestions. I might have given you all reason to laugh well today...

 

Michael, Matt, Ryan and the rest,

At Matt's suggestion I had a little chat with Don (MTH) about the suspension modifications we've been talking about. He was supportive of some modest modifications such as lowering and camber plates for a track oriented, dual purpose, car. His main point was (Why am I not surprised?) "the key is to keep in a little understeer and learn to drive a FWD car". In other words, he diminished the performance advantages of suspension modifications, except camber, and emphasized the advantages of driving technique. He drew a distinction between setting up a chassis to pull G's in a turn, or setting up a chassis to go fast around the entire track.

I know this. I've heard it before. But, it is instructive to hear it again from the voice of experience.

So, back to the topic of lowering: most of the initial posts were similar to each other and similar to Don's comment. It was felt that any performance gains, just from lowering were modest at best, and came at the cost of some potential compromises of the overall suspension geometry. Are there any serious differences of opinion?

John Petrich in Seattle

 

Not from me...we might be better served by removing as much weight as possible...

 

John; I have not actually put effort forth to achieve much more than stock caster. IIRC, the stock suspension has about 4 degrees of caster, which certainly isn't very much for a current production car. That said, I'd wager it's one reason it does so well on auto-x circuits where speeds are low; low caster usually translates into good low-speed mechanical grip. To get more caster for high speed setups, you're essentially trying to incline the strut as much as you can. There are only two places to do this; on the top at the strut mount, or on the bottom where it attaches to the control arm. ALTA's PSRS allows the user to add caster my essentially being an offset bushing for the rear locater pin for the control arm. This pivots the arm around the middle ball joint, pushing the knuckle forward, creating more caster. The combination of an offset bushing like ALTA PSRS and slotting the upper strut tower sheetmetal will give as much caster as you can get out the MINI without major surgery. If a manufacturer was inclined, control arms that push the lower ball joint forward [thus increasing caster and wheelbase] would help the goal. The downside there is running your tire into the front panel!

Oh I almost forgot; the easiest way to increase caster is to shorten the strut! With adjustable length coilovers, spin it all the way short and the caster will increase slightly at that lower ride height.

Back to the topic; I also agree that anything more than about a 1" lowering starts getting into a too-low state with stock suspension geometry. This is why I'm modifying everything; so I can get my car to sit lower while still having decent geometry! To tangent, I did manage to successfully get the steering rack spaced up off the subframe about a 1/4" and not run into any clearance issues. It's still about 1/8" not enough to compensate for my spindle drop, but it's better than no change at all.

To go back a few posts; I do understand how bumpstops are an active part of the MINI's suspension; as they are with many cars. My point was that with my new setup I'll have more free up-travel before beginning to compress the active bump stops.

Michael: I 100% agree with you, weight removal rules!

Cheers,
Ryan

 

Ryan,

Very lucid and thanks. Raising the rack, huh? Very good approach. Boy, how did you get access to those mounting bolts? They are sure buried in there.

I think that I'll elongate my strut tower tops a bit more and call it good. I see what you are saying about the effort required to push the knuckle forward and the trade off from reducing strut travel.

Regards,
John Petrich in Seattle

 

I already had my subframe off the car because I'm in the middle of replacing almost everything! This gave me plenty of room to measure changes desired and install the spacers and longer bolts as needed.

Do you have the PSRS's? That's what I'd suggest if you aren't pleased with how much caster you can squeeze out of the strut tower.

Good luck!
Ryan

 

...just keep an eye on outer ball joint articulation. We don't want thing to bind...but I think we're still well within reasonable limits???

 

That's all part of my modification to make the "drop spindle". I machined a pair of spacers out of 6061 aluminum to push the ball joint down in reference to the axle. The outer ball joint for the control arm is in the exact same location, so articulation is maintained. Now I just have to hope the CV's articulate enough! [bites nails]

 

Dammitttt! Here comes the talk of a diet again! Grrrrrr.....

If they don't at first, they will after a bit!

Matt

ps, I wouldn't worry. There are those that have dropped that much, and the CVs weren't a problem. But they didn't have the extension you will have.... I guess time will tell!

 

I've never been inside the Mini's CV joints, but these seem a wee bit more sensitive to lowering than any I have previously experienced.

diet...just feed your car good quality complex carbs and give it a work out twice a day

 

someone who really knows suspensions (Bruce Griggs) designed the stuff on my mustang. While I didn't put it in myself (Wayy to big a job for my skill level then, and probably now as well, even if I could weld well), I've learned the benefit of good suspension desgin. I upped HP, got more aggressive rear gears with good clutches in the traction loc clutch pack and the like, and with a the set up that's on the car now, I went to a softer suspension with much, much better traction. I can come out of turns and lay power down like no Mustang of my cars vintage can (The guy who builds a lot of Griggs equipped cars calls in the "Griggs Grip"). It's amazing. Scares the living crap out of passengers who own old Mustangs with stock suspensions. Tons of fun..... And because of good design, I get better cornering, better grip, more complience over rough surfaces, overall a better performing more comfortable ride. A win all around (Except for the bank account, that took a big hit!)

I'm totally stoked to see the transition from the standard bolt ons to really well thought out suspension modification techniques. While they won't be for many, it's good to know they're out there.

Way to go! Could this be "Team OpenSource"

Matt

 

...I'm still trying to figure out how to get the upper control arms from my 99 Si to work with the Mini's lower arms...been thinking about that one for a while. Figuring out the knuckle is the tuff part; the splins on the axle and bearing may or may not work...adapting the Si's outer CV joint might work...lots of little things to consider, but a double wishbone Mini would be nice.

 

FYI

On my car, the Bavarian Autosport offset front control arm bushings gave me close to 1° of added caster (from ~4.5° to ~5.5°).

http://www.bavauto.com/

Their site doesn't allow linking directly to products, but it's in there.

 

Agree. The R56 was missing character...I still prefer my R53...maybe it is just the pulley, the software, exhaust system and etc that enhanced the experience ;0)

 

This is the photo... $50 per bushing....

Matt