How to make widebody 911 steering feel like a narrowbody 911?

[PcarPhil]

Hello Pelicans,

For the past 7 years or so I've been playing with aircooled widebody 911s. During this time I haven't spent much time driving narrowbody 911s except on vary rare occasions. Each time I did drive a narrow 911 I recall walking away thinking "hmm...the steering feel on a narrow 911 seems more precise - a lot less kickback from the steering wheel on bumpy back roads". I recall thinking this is probably due to widebodies having 1" wheel hub spacers attached to the hubs and low offset wide wheels messing with the steering geometry.

Last year I purchased a '88 911 narrowbody cabriolet that has Ruf 8" +30.4 ET front wheels and 9" +17.7 ET rear wheels. Overall it also has a nicely dialed in suspension. I've come to realize this '88 cabriolet has the best steering feel (for me anyways) of any aircooled 911 I've ever driven!

So... now I want to figure out how to make widebody 911s steering feel like my '88 cab. How do I do this? For this discussion lets assume both narrow and wide cars are running the same 8" +30.4 et front wheels with 235/40/17 tires. The widebody has 1" wheel spacers to make up the difference in the fenders.

I have searched on the subject and came across a few threads on lengthening front control arms:

Extended Front Control Arms ?

Lengthening A-arms - by how much?

Question about scrub radius

I think I've wrapped my brain around the idea of lengthening the stock front control arms 36mm, raising and resetting the spindle to accommodate a mild 1.5 degrees of negative camber and low ride height, removing the front wheel spacers, and running wheels with 30 to 36mm of + offset. By the way +36 happens to be the offset of 6x16" Fuchs.

Does this sound like a good idea? Will the end result be worth the effort? I think so.

I do have a few additional questions revolving around this idea:

1. Can stock ball joints accommodate the increased strut angle resulting from lengthening the control arms? Or will I run into binding issues?

2. If the end result allows eliminating the front 1" wheel spacers but keeping the overall front track width the same, will I need to make any changes to the rear track width to keep the overall balance of the car the same as before the front end changes?

3. I'll need to also lengthen the tie rods. In one of the above links Chuck at ER says he can provide the correct length tie rods. Are there any other alternatives? Perhaps modify stock turbo tie rods? Or is there another tie rod part number that would work?

4. If done properly is modifying the strut/spindles/control arms safe? I especially wonder about repositioning the spindle on the strut to allow proper camber positioning.

5. I believe lengthening the front control arms will make the effective wheel spring rate lower, so I may need to bump up the front torsion bar rates a bit. If I lengthen the control arms by 36mm does anyone have any idea by what % the wheel spring rate goes down?

Thank you in advance for any help you can provide on making a widebody 911 steering feel like a narrowbody 911!

[bpu699]

I have a 930 with 8 and 9 inch rims like you. Due to the offset, one of the tires was rubbing under hard cornering. To solve this I narrowed the front tires by 10mm. I think I went from a 225 to a 215 If I recall...

Made a world of difference. Steering is super light...

Bo

[javadog]

Suggestions:

Raise the front ride height.
Raise the spindles on the struts to suit whatever amount of reduction in ride height from factory specs that you end up with.
Run less castor and camber.

JR

[PcarPhil]

Guys,

To be clear I'm trying to get rid of the steering kickback in widebody cars that is caused by (IMO) inferior steering geometry vs. the steering geometry of narrow 911s.

I don't see any way to truly make widebody steering feel as good or better than narrowbody 911s without correcting the steering geometry. And yes JR raising the spindles is part of this process!

Below is an example of a widebody car that the builders optimized the front steering geometry.

[john walker's workshop]

Fuchs wheels make a big difference as opposed to heavy RUF wheels (unsprung weight). I really noticed a difference on my 77 930 after going from RUFs back to fuchs. I had 8" fuchs all around at one time. Looked cool, but lots of feedback. Just going to 7s in front made a big difference.

[David Borden]

If you lengthen your lower control arms but leave your upper strut location stock, you will increase your SAI(steering axis inclination) or kingpin angle. As you raise your SAI, you create issues like camber loss as you turn in, which counteracts caster. It also increase jacking.

How these changes feel on the 911, its hard to say. I can tell you that I went to great pains reducing SAI on a different kind of car and it made a tremendous improvement on how the car felt and handled. Im not suggesting the same for the 911, just dont have experience there yet.

You may want to do you best to eliminate scrub with an optimal wheel offset, and eliminate bump steer the best you can and see how the car feels then. Regardless, looking forward to seeing how this works out for you. Ive been thinking about this very subject as I decide which way to go with my 73 911.

[javadog]

Having owned a few 930's, in my opinion, if you leave the suspension and wheels stock, you won't experience more kickback than on a regular 911. Lowering one into the weeds will create a lot of that. Altering the wheel/tire size, offset, camber and castor can also make for heavier steering.

It almost sounds like you are looking for an excuse to re-invent your front suspension. What Tyson did to Jack's car might be somewhat irrelevant to your quest.

My .02,
JR

[Fly911]

When Porsche came out with the 930, they completely changed the rear suspension, with shorter control arms, situated further back and further out than the traditional narrow body. This changed the geometry of the wheel travel under load, in an effort to correct the Turbo's wild oversteer when the turbo kicked in. So 930 rear control arms are a nice upgrade on NB cars...

On the front suspension however, they did virtually NOTHING. To fill the wider fenders, they put 21mm spacers, and to avoid a too wobling steering, they designed the Turbo tie rods, a "must have" for all NB cars.

If you look at any modern car, the pivot point of the front wheels are pretty much in the vertical center axis of the wheel. If you look at older 911's, this pivot point is much further in. With the 21mm spacers, the Turbo front wheels don't pivot, they roll back and forth as the wheel turns. The further the distance from the pivot point (the MacPearson struts) to the tire center, the more force the wheel will induce on the steering arms/tie rods. So bumps in the roiad will give a much more kick than a NB car, or a moden car with a different steering geometry.

There are to my knowledge three ways of "fixing" this issue; lengthen the existing front A-arms by 21mm on each side, buy a set of adjustable 935 front control arms, or buy a set of Elephant Racing GT3 style front suspension. In order not to get a too crazy negatiuve camber, you have to move the top of the strut outwards at the same time. And possibly also have longer tie rods.

With the 935 style or GT3 style front suspension, you can get an even more accurate steering feel than a NB 911, on a 930. Both these suspension types require coil over struts. Obviously, the coil overs take up more space than the old torsion bar struts, and inner wheel rubbing might be an issue. So front wheel offset and tire width have to be considered in the total solution.

[Bill Verburg]

Originally Posted by Kaefer

Guys,

To be clear I'm trying to get rid of the steering kickback in widebody cars that is caused by (IMO) inferior steering geometry vs. the steering geometry of narrow 911s.

I don't see any way to truly make widebody steering feel as good or better than narrowbody 911s without correcting the steering geometry. And yes JR raising the spindles is part of this process!

Below is an example of a widebody car that the builders optimized the front steering geometry.

By far the biggest thing influencing steering wheel feedback is the scrub radius, if the scrub radius is too big feedback becomes kickback.

It's just in the nature off the beast that scrub radius gets bigger when the track is widened, the top of the shock is fixed you can move the bottom out by lengthening the front control arm but then you have camber issues that will need to be controlled.

The factory has run into his issue w/ every RSR they have ever raced. Their solution is a combination of wheel o/s and moving the lower control arm outboard and camber plates, sometimes shims as well. I don't believe that they are overly concerned about the feel or amount of feedback as long as the drivers can control it.

You can further help the feel by using alignment settings, for instance less caster, less camber etc.

[PcarPhil]

Here are a few more links on the subject. I suggest paying extra attention to what Tyson Schmidt is saying about Jack's car:

Widebody handling question for gurus..

Suspension considerations and all these RS/RSR clones...JackO you may be of help

Driving a narrow vs. wide body 911

BB2 Sighting! Roof rack!?


The following quotes summarize the issues nicely:

Originally Posted by Tyson Schmidt

The problem with the Turbo's is their positive srcrub-radius. This is the distance between the wheels centerline at the ground, and the steering axis centerline where it meets the ground. The greater the distance, the greater the scrub-radius. This radius acts like a lever-arm on the car's steering, and fights against the driver. It also introduces greater side-loads on the sliding members of the suspension.

So in effect, a Turbo-bodied car can actually improve the steering characteristics by going to a wider wheel up front with greater back-spacing. With Jack's car, I was able to achieve even less scrub radius than a narrow-bodied car with 6" Fuchs, due to the geometry changes. That's why the car can be driven with much less steering effort, and more predictable behavior, particularly on uneven pavement and during hard braking.

Yes, the increase in steering axis inclination does make the wheels move in an upside down arc when turned. This is compensated for by increasing the caster.

Increasing the caster, and the steering axis inclination both increase the straight line stability and self-centering effect of the steering, at the expense of steering effort. But the increase in steering effort is more than compensated for by the reduction in scrub-radius. The end result is a very well-mannered car that seems to know what you are thinking. That "intuitive" handling that has been talked about in regards to the '73 Carrera RS.

Originally Posted by Tyson Schmidt

On Jack's car, I changed the front control arm length. (longer)

Raised the spindles beyond what was possible on the RSR, due to utilizing 17" wheels versus the RSR's 15's.

Changed the steering axis inclination with custom geometry front struts for better scrub-radius in conjunction with deeper offset front wheels. (The altered geometry allowed deeper offset while retaining the wider track.)

These changes result in improved steering balance, particularly under hard braking. (from the reduced scrub-radius)

Higher front roll-center height, for more built-in resistance to body roll- also keeps camber curve in the proper range when car is set very low. (raised spindles)

Less roll-center height change as the suspension moves through it's travel, for more consistent/predictable handling. (longer control arms)

Reduced scrub-radius also benefits tire clearance during turns, since the wheel pivots closer it's center-line instead of swinging forward and rearward in the wheel-well. (Notice how oblong the front flares are on an original RSR, which were necessary for tire clearance with it's very positive scrub radius, combined with it's 9" wide wheels).

Originally Posted by Tyson Schmidt

The increase in caster on Jack's car was simply to work with (offset) the SAI increase.

When you increase SAI, the wheels go into more positive camber when turned. This is fine on the inside wheel, since that is beneficial, but bad on the outside wheel. Increasing caster does just the opposite. It increases negative camber on the outside wheel when turned. This compensates for the SAI. None of this was changed on the Factory RSR.

[PcarPhil]

Originally Posted by Fly911

When Porsche came out with the 930, they completely changed the rear suspension, with shorter control arms, situated further back and further out than the traditional narrow body. This changed the geometry of the wheel travel under load, in an effort to correct the Turbo's wild oversteer when the turbo kicked in. So 930 rear control arms are a nice upgrade on NB cars...

On the front suspension however, they did virtually NOTHING. To fill the wider fenders, they put 21mm spacers, and to avoid a too wobling steering, they designed the Turbo tie rods, a "must have" for all NB cars.

If you look at any modern car, the pivot point of the front wheels are pretty much in the vertical center axis of the wheel. If you look at older 911's, this pivot point is much further in. With the 21mm spacers, the Turbo front wheels don't pivot, they roll back and forth as the wheel turns. The further the distance from the pivot point (the MacPearson struts) to the tire center, the more force the wheel will induce on the steering arms/tie rods. So bumps in the roiad will give a much more kick than a NB car, or a moden car with a different steering geometry.

There are to my knowledge three ways of "fixing" this issue; lengthen the existing front A-arms by 21mm on each side, buy a set of adjustable 935 front control arms, or buy a set of Elephant Racing GT3 style front suspension. In order not to get a too crazy negatiuve camber, you have to move the top of the strut outwards at the same time. And possibly also have longer tie rods.

With the 935 style or GT3 style front suspension, you can get an even more accurate steering feel than a NB 911, on a 930. Both these suspension types require coil over struts. Obviously, the coil overs take up more space than the old torsion bar struts, and inner wheel rubbing might be an issue. So front wheel offset and tire width have to be considered in the total solution.

Fly911,

Thank you for this informative post.

My preference is to come up with a solution that does not requiring modifying the chassis (in this case an '87 930 chassis) so I'm thinking I should stay away from coilovers. It's my understanding to install front coilovers I should reinforce the strut towers. I'd rather leave this 930 chassis 'stock' and stick to bolt on mods, which means no coilovers due to possibly needing chassis reinforcements as well.

So... most likely I won't be going with the 935 or GT3 front suspension system since I'll be staying with torsion bars. I believe by lengthening stock front control arms ~36mm (not the 21mm you mentioned) I can do away with the 21mm wheel spacers used on the front of turbos. Also by staying with torsion bars I won't have interference between coilovers and the insides of the wheels/tires, allowing more optimal wheel offsets to be used.

[javadog]

How are you going to lengthen the control arms by 36mm and maintain a decent camber angle without modifying the strut towers? Have you measured how much room you haveto play with? Offset upper strut mounts?

JR

[PcarPhil]

Originally Posted by javadog

How are you going to lengthen the control arms by 36mm and maintain a decent camber angle without modifying the strut towers? Have you measured how much room you haveto play with? Offset upper strut mounts?

JR

I'm not 100% sure yet. The solution will probably be a combination of running offset camber plates flipped side to side for increased positive camber and spindles that have been raised and repositioned at a better camber angle on the strut tubes.

[Ferrino]

Great thread. I'm currently putting together a 930-bodied 911 and am eager not to lose the nimble 911 steering through my aesthetic need to fill the flares. I have picked up a set of modular wheels, so I have a little room to tinker with wheel widths and spacing.

What are you using as your "gold standard" for scrub radius? i.e. with the standard control arm and 911 hub, which wheel width/offset is known to make people happy? You mentioned an 8ET30 RUF wheel above (which effectively grows to 8ET5 with your 1" spacer on a widebody). Is that a good place to be? I currently have an 8ET6 for my front too (no spacer: 4.75" backspace in the wheel itself).

How much of the lightened steering is down to the tire itself? You said you're running a 235 tire on that 8" RUF wheel. What if you were to take that right down to a 215 (like the RUF CTR did)? I was actually thinking of running 215/255 on an 8/10 wheel setup on my widebody for the street. If it worked on a Yellowbird with 460 BHP, I'm sure my humble 3.2 won't complain!

What about compromising wheel/tire weight to improve scrub radius? For example, it would appear that if you had room to grow your wheel/tire inwards, you would decrease the scrub radius by half the increase in width. But would you not suffer from having increased unsprung weight? I'm guessing a lot of it is down to intended application...

[PcarPhil]

Originally Posted by Ferrino

What are you using as your "gold standard" for scrub radius? i.e. with the standard control arm and 911 hub, which wheel width/offset is known to make people happy?

Currently there are two "gold standards" that I am considering:

1. The standard 911 control arm, standard SC/Carrera 911 hub (no spacers), 8x17" +30.4 et Ruf wheel, and 225/45/17 tire.

2. The standard 911 control arm, standard SC/Carrera 911 hub (no spacers), 6x16" +36 et Fuchs wheel with 205/55/16 tire.

I'd like to make my 930 have a steering feel equal to or better than "gold standard" #1 or #2 above. #1 is probably the most realistic. This concept would also apply to widebody 911s as the end result geometry would be the same (within reason). Strictly street use vs. strictly track use may have slightly different geometry.

Gotta run. More later...

[PcarPhil]

Originally Posted by Ferrino

How much of the lightened steering is down to the tire itself?

If it worked on a Yellowbird with 460 BHP, I'm sure my humble 3.2 won't complain!

What about compromising wheel/tire weight to improve scrub radius? For example, it would appear that if you had room to grow your wheel/tire inwards, you would decrease the scrub radius by half the increase in width. But would you not suffer from having increased unsprung weight? I'm guessing a lot of it is down to intended application...

I'm not looking for lightened steering. I'm looking for much less kickback and better overall tracking due to eliminating 21mm front spacers via extended control arms and repositioned spindles.

I agree 1000% - what works for Ruf works for me! Another solution to this idea is for someone to straight trade me a real Yellowbird for my 930! This would get me my "gold standard #1" overall steering feel!

Another approach would be stock 930 front geometry with a 10" +34 wheel and 255 tire.... but I don't want to do that.

[Tyson Schmidt]

How strange it is for me to read things I wrote 10+ years ago.

Anyway Kaefer, if you want the numbers and specs I used when I designed the front geometry for Jack Olsen's front suspension, PM me.

[PcarPhil]

Originally Posted by Tyson Schmidt

How strange it is for me to read things I wrote 10+ years ago.

Anyway Kaefer, if you want the numbers and specs I used when I designed the front geometry for Jack Olsen's front suspension, PM me.

Thank you Tyson, I really appreciate it. I've been gathering tidbits of info recently trying to wrap my head around this whole idea. Then my plan was to contact you to see if you would be willing to discuss this further.

edit: PM sent.

[PcarPhil]

Update 2/9/15:

I found some time yesterday to really look over the front suspension and start putting together a parts list of what could be needed to successfully perform this project. Since the car I'm working on is a late 930 I'll need to change the front brake setup a bit:

- Remove the stock '87 930 hubs and brake rotors. My existing rotors have the 21mm (22?) spacer built in.
- Source new rotors with flat hats and 911 hubs.
- Figure out how to get my existing 930 calipers to center properly over the new rotors/hats/hubs.

The flat hats and 911 hubs are the key to getting rid of the 21mm spacer. I test fitted my 8x17 +30 Zuffenhaus Fuchs wheel on a friend's car with the '78-'80 930 brake setup and my wheel fits great without a spacer. There was maybe 4mm clearance between the wheel and 930 caliper.

What I have now:


What I need to have to allow the project to move forward:


Another option would be to rob my 3.6 cab of it's 993TT brake setup and install them on my 930, then revert back to 3.2 Carrera brakes on the cab. Then put the 930 brakes in storage with the rest of my take-off stock 930 parts.

Good times...

[Bill Verburg]

Are you sure it's a 993tt setup?

At least some of the Racetechnology 993 BBks came w/ 993 RS brakes which is a much better way to go than the 993TT because of the additional 993RS rear bias.

I run 993RS setup on both of my cars, for street use it is totally unnecessary but does look cool. For track use it is the nuts.

If you have 993tt oe 993RS it's main advantage over 930 is it's increased thermal capacity

the 930 has much better bias than the 993tt but the 993RS is best of the 3

both 993tt and 993RS will give you more brake torque but you don't really need it.