raising spindle height on struts

jmz · jmz's Garage

I know most people raise the spindle heigt on their race cars. It seems to me for lowered street cars this would be the way to go as well. It should give you more suspension travel and help to alleviate bump steer. Is there any reason why this would be a bad idea? It costs a few bucks to do but everything does.

Wil Ferch · 08:55 AM

It's the "best" way to do this...for the reasons you state. It keeps the full suspension travel, it doesn't alter the camber curve...etc, etc.
This was done for the original RSR's...the elevation was typically 12-18 mm..but today you can raise the spindle much more, some do as much as 35mm, but the lower ball joint interference must be checked for the wheel diameter you choose to use.
However, it was my understanding this can only be done on Bilstein ( housing) struts...because the "collar" can be moved upward easily for this design. The Boge and Koni shock/struts have a body "bulge" right above the spindle collar...not allowing any upward relocation. However, Chris Bennet informs me that some enterprising souls have actually done it with struts other than Bilstein. Do a search.
---Wil Ferch

ChrisBennet · ChrisBennet's Garage

On a lowered street car or track/street car, raising the spindles really isn't necessary. Of course, if your car is "slammed" to the ground you have other problems (emotional and suspension) to deal with.
Like Wil Said, a (very clever) friend of mine raised the spindles on his Boge struts. Last I knew, he had modified his A-arms to get more camber.
-Chris

jmz · jmz's Garage

chris, I know it isn't necessary but it seems it would improve handling and ride quality. wrong or right?

Wil Ferch · 03-05-2003, 09:00 AM

If you limit the lowering to 1" or thereabouts...you're on the "edge" of whether this is a nicety or a necessity. Many have had good results with rack spacers and/or ERP kits to keep bump steer in check. As to camber curve aspects and such...without getting overly anal...as long as the lower control arms are "still" angled downward slightly toward the ball joints ( or at most...are horizontal at static ride height)...you should be OK for a street or street/track combo car. Never lower so far as to have the inboard pivot points of the lower A-arm... lower than the ball joints. Then you'd really have wacko camber curve / ride / handling problems !!
--Wil Ferch

ChrisBennet · ChrisBennet's Garage

JMZ,
It wouldn't improve handling or ride quality. The car has to be lowered further (IMO) than you should on a street car in order to get to the point where raising the spindles would "fix" anything.
As a data point, I run larger torsion bars and my car's ride height is 25f/24.5 rear. I don't use anything to correct bump steer.
-Chris

RallyJon · 10:53 AM

Every suspension has an ideal ride height dictated by the damper. The piston should be right in the middle of its travel (or at another predetermined point dictated by its design) and there is only one ride height where this happens. The ONLY way to change the ride height without screwing this up is to move the spindle. I'm not saying moderate lowering without moving the spindle isn't acceptable--but it is not optimal.

The same logic applies to the steering angle. At ideal ride height, the tie rod is horizontal. At any other ride height, it won't be unless you move the spindle, shim the rack or use an expensive bump steer kit. Edit: that's not quite right. Moving the spindle wouldn't mitigate the effect of lowering on the steering angle.

The only question is how far from ideal geometry you want to go while still considering it "acceptable". Raising the spindle just gives you that much free lowering before you have to start worrying.

Jeff Jagusch · 03-05-2003, 10:40 AM

I understand the concept, but am curious who does the modifications? and what could the expected cost be?
lastly, can I do it myself with the help of a confident fabricator/welder?

RallyJon · 03-05-2003, 10:52 AM

Rennsport Systems charges $425/pr

Dart Auto charges $250/pr

I saw another 914-oriented vendor who wanted mid-$200s

I believe that, for the extra cost, Rennsport also bends the steering arm so it matches up with the steering rack better.

Chuck Moreland · 03-05-2003, 11:02 AM

Why not do it? It is illegal for some club classes, if that is a consideration.

You can also purchase RSR struts that have the raised spindle, then sell your old struts to help offset the cost.

dad911 · 03-05-2003, 11:02 AM

I had a strut failure after this mod was done. Cracked where it was re-welded. At the end of the long straight at mid-ohio. I bought the RSR strut housings to replace them, not very expensive, and I have a lot more confidence in a factory proven part. For a street car I don't think you would need more lowering than the rsr strut housing provides.

Jack Olsen · 11:32 AM

So long as it's well-done, I can't see a down side to raising the spindles, other than cost. The 911's front suspension geometry, through the years, involved a lot of weird compromises to keep manufacturing costs reasonable. American ride height (about 1 inch higher than ROW) isn't what the susupension was designed for. Then again, lowering down close to 24 inches will produce bump steer, whether or not a driver claims to 'feel it.' Spacers only make up for about half an inch of lowering beyond Euro height. The ERP kit will correct things beyond that.

And that's only bump steer. Suspension travel is the bigger consideration. My 24-inch-high front end was bottoming out all the time, even with 21mm torsion bars on it. And once you've run out of spring, your chassis is absorbing all the energy of the impact with the road, which isn't good at all.

Some guys (or so I've been told) get really carried away with this stuff.

JRZ puts the strut together to whatever specifications (spindle height, static camber) you request, with the final cost in the same neighborhood (well, kind of) as the RSR Bilsteins.

Does any of that make a big difference when it comes to street driving? Probably not. But if we were all sensible about the demands of ordinary street driving, we'd all have Toyotas in our driveways and a lot more money in our bank accounts.

jluetjen · jluetjen's Garage

The other issue with the geometry that Wil Firch alludes to is the roll center which is on a plane with the lower A-arm in MacPherson strut suspensions (there's more to it then that ...). In a nut-shell, if the roll gets too low strange suspension stuff starts to happen.

This month's issue of Grass Root's Motorsport has an interesting article about suspension set-up on Mustangs (which share the strut style front suspension design) and the significant compromises involved in that car's suspension. The example is not exactly the same since the Mustang has engine's weight fairly high in the front of the car while a 911's engine is fairly high in the back.

Some things to keep in mind though when lowering a strut equiped car...

1) Camber curve - usually you want a car to gain negative camber as a wheel goes up, so that it keeps the wheel vertical when the car rolls. Once the inside of the A-arm drops below horizontal, strut suspensions gain POSITIVE camber with bump. So the wheel will start to lean out like the 1950's F1 cars. That will increase understeer drastically.
2) Roll center - This is the imaginary point around which the body rolls when cornering. It is one part of the Roll-Axis defined by the front and rear roll centers. Roll centers always move, but ideally oll centers should stay fairly consistant compared to the center of gravity and generally above the surface of the road. This will result in a car that handles consistantly. If the roll center goes below the tires' contact patches by much, it can suddenly cause the roll and camber curves to get strange. The result will be a car that can "lurch" suddenly from understeer to oversteer or vice versa.

This is why the handling of drastically lowered rice racers is often suspect at best, and dangerous at worse.

Anyway -- this is why lowering the spindle is preferable since it neatly sidesteps all of these geometry issues. The only issue then becomes do you have enough suspension travel to keep the chassis off the ground and the spoiler off the road when exiting service stations?

RallyJon - You should be able to resolve the strut travel issue just by shortening the shaft on the strut by the same amount as the car is lowered. Voila - the piston is centered again.

Wil Ferch · 03-06-2003, 04:08 AM

jluetjen:
Excellent explanation... !
For the sake of correct archiving , however,...I think you meant to say "raising" ( not lowering) the spindle in the later paragraphs....

---Wil Ferch

RallyJon · 03-06-2003, 06:07 AM

Quote:

You should be able to resolve the strut travel issue just by shortening the shaft on the strut by the same amount as the car is lowered.

Makes sense. How is this usually implemented on a street car? I've been broswing around a lot lately for struts and haven't found anyone offering different length shafts or a service to cut shafts to length and presumably rethread the tops.

One other possibility--several higher-end Japanese strut manufacturers who cater to the slammed Honda crowd offer struts where the lower mount is threaded. You can "raise your spindle" and adjust ride height from the bottom without affecting the damper travel. Pretty clever, but the only applications are for those cars.

I would LOVE to see a scale drawing of the 911 suspension (and steering rack) from the front--does anyone have one? It sure would make estimating the effects of lowering much easier to visualize.

Wil Ferch · 03-06-2003, 07:45 AM

RallyJon:
I've done this in a crude way by taking measurements of the front A-arm ( about 11" swing length as I recall)....and drew it on graph paper. Using basic trigonometry and noting something like ( ?) a 10 degree angle for the A-arm ( factory spec)...I deduced that you can go about 1-1.5" lower from this configuration before you're in danger of going "beyond flat" for the lower A-arms.
I drew three front views alongside one another on the same graph paper to the same scale..to also help me visualize what happens stock... vs lowered ( not changing spindle height) ...and lowered raising spindle height.
Just pour yourself a coffee...and doodle with this...it'll all come clear ( at least it did for me )

--Wil Ferch

Jeff Jagusch · 03-06-2003, 08:55 AM

I'm still curious how the spindles are raised on the strut?
from memory the spindle collar is fastened to the strut tube in some manner, this needs to be "unfastenend and raised????
Just curious, as I have a friend that is a superb fabricator that I may ask to help!
Thanks

CarreraCab · 03-06-2003, 09:37 AM

Jeff, on the last set of RSR struts I used, the spindle/collar/brake attachment ears portion of the strut is a casting, with the strut tube body attached to the tube by welding. The trick on modifying stock struts is being able the remove the attachment weld to allow you to raise the spindle collar further up on the strut tube, and then rewelding. The RSR struts also have an additional gusset welded in to the attachment point. Doug

jluetjen · jluetjen's Garage

RallyJon;
I believe Truechoice can shorten your strut shaft. Basically you need to hacksaw off the required amount and then rethread the top of the remaining shaft.

Wil -- Thanks!

beamonk · 03-06-2003, 04:09 PM

We raised mine 15mm. In the back of the strut is a hole welded in from the factory. We got a die grinder and ground it out. Then cut a vertical slit right up the middle of the hole. We scribed lines to be sure we didn't mess up the alignment. We got the collar loose and them raised it. We then welded up the hole, the top and bottom of the collar and the cut line. 10k hard street miles and no problems. A good welder can make it a forever weld. You can safely go to 18mm I think, but we didn't want to go too far so we did 15. It is fine for 16" wheels.