steering geometry

[allessence]

Looking for info/books on steering geometry.

I am thinking of making the front and rear track 4-6" wider.

Front longer axle shafts will just be machined and spacers welded in.

Rear axle cut and fitted with inner piece and then rewelded.

The info I'm looking for is how does distance from spring centers and over all travel effect what it is I am doing.

Yes, I do know this will void any race venues, but this seems like and easy thing to do with little money.

Also, does someone have the measurements needed for front bushing upper and lower? I am looking at matching something up.

[Luke]

Jen,

I really respect you as a fabricator and I know you've done some really nice work, but I think you are opening a major can of worms here! These types of day-dreams are usually reserved for 17 year old boys working at advance auto.
But.. I do have some good books, I'll get the ISBN's for you.

[Crazyswede]

The things that come to mind off the top of my head are bump steer issues, road tracking issues, and steering difficulty. But if you did everything correctly it could be ok. The problem I see is that to do everything correctly the project quickly moves from the not a lot of money realm to the lots of money realm.

[allessence]

Thanks for the info. And Luke's very kind comments.

I guess the problems I face are the same for any front wheel drive car.

How do you get the power to the ground and still have good steering. The answers I have come up with are good shocks, proper springs, and wider tires.

The other thing is I would say I've always been different or have had different perspectives of what I'd like to see in a car.

I know I'll never be a car designer or engineer, but having the ability to run wider than stock tires would be a nice feature and if the SAAB handles as well as it does with regular track width then wouldn't it handle better with a wider track width?


As usual it's probably more a fantasy than anything else, but if nothing more than that maybe I'll at least add more useless info to my all ready mostly filled with useless info brain.

Okay, so here are some of the answers I have come up with since Crazyswede asked:

Bump steer is controlled via steering rack, depending on axles length would translate to lengthened steering rack tie rod end adapters.

Tracking. If all the parts are machined/welded straight then there wouldn't be really any change in tracking distance/stance front to rear.

The welding I can do myself. The drive axles to lenghten are about 180.00 for both. This includes machining and fab of press fit thick wall tube to fit over the axles and weld in and again I would weld them myself. I had to do this to a HP V4 I built. I used 99 inner drivers with 96 outer CV's.

Front wishbones are the only real problem and this can be remedied by re angling the end where they fit at the bushings and then welding on longer box sections back to where the factory ball joint would be put in.

The other factor is as the tire/hub moves away from the spring the spring rate as I understand it goes down. So, I would need stronger springs or move the springs closer to the ends (ball joints).

Just think it would be kind of a neat project. Or at least my warped sensability seems to think so.

And again, probly more a fantasy than anything else. I figured it would run about 300.00 to do everything except the springs. Not including labor of course. I guess I have to much free time.

[Crazyswede]

[Crazyswede]

[Crazyswede]

Bump steer is a result of poorly setup suspension geometry, wheel width, and wheel offset. The further the wheel center line moves from the pivot line made up by a line passing through the hub pivot points the worse the bump steer will be. Basically the further off it is the more the road can leverage the wheel and steering and the harder you will have to work to keep things pointed correctly. Camber, Caster, and toe can play into this as well as steering acrimen, steering axis of inclination, and a slew of other things.

By road tracking I am referring to the manner in which the car is affected by every crack or low spot in the road. The lower profile wider tires and cars with wider stances tend to be more easily affected by irregularities in the road.

a good book with diagrams and explanations should walk you through your design. Another good resource is Charlie North.

[Geoff]

SAAB actually experimented with a wider track in the '80s. The results weren't too impressive though. They called it the 9000.

What would you do about wheel/fender clearance? Cutting them out and making something like the Austrailian Enduro kit would be pretty slick. If you were going to go through with elongating the A-arms, it would just make sense to put in some of the coil-overs like Luke has done. That way you can experiment with springs and the force of the spring is closer to the ball joint (there are some carnage shots of bent up a-arms and busted ball joints from having the spring mount too far from the ball joint and not having enough strength in the a-arm).

[Crazyswede]

If you keep the stock Saab hubs and you fabricate new longer A arms and choose your wheels appropriately you will minimize bump steer problems. With longer A arms you may have to analyze the swing path to make sure that the longer arms don't change something for the worse. Doing the track on the rear should be very easy but you may have to beef the axle tube up a bit to support the leveraging effect of having the wheels further out from the trailing arm mount point.

[allessence]

SAAB actually experimented with a wider track in the '80s. The results weren't too impressive though. They called it the 9000.

What would you do about wheel/fender clearance? Cutting them out and making something like the Austrailian Enduro kit would be pretty slick. If you were going to go through with elongating the A-arms, it would just make sense to put in some of the coil-overs like Luke has done. That way you can experiment with springs and the force of the spring is closer to the ball joint (there are some carnage shots of bent up a-arms and busted ball joints from having the spring mount too far from the ball joint and not having enough strength in the a-arm).

I would cut out the stock metal fender flairs and run a lip from the underneath so as to be able to spot weld the out and inner fender pieces back together. I've planned on this anyhow even with the Aero 16" rims I run now.

I think the pictures CrazyS posted would be about right. I have an SPG so would blend the fibertglass/carbon fiber so it would be right as rain with the airflow kit and look just about factory.

Sorry, I didn't understand the bump steer to begin with. I do now since it was explained well. I always thought bump steer is when you turn it from lock to lock.

Makes perfect sense though and this is one reason I was looking at putting in the stiffer delrin or poly bushings.

I was thinking of doing coil overs as well, but will wait for the time being. As for steering geometry I was very intrequed by the fact that it would have longer suspension travel as well. Better for the big bumps.

So, any good books any body.

[allessence]

Was this a Factory kit?

[DeLorean]

Pretty sure Saab-AU made that themselves. you might could call it quasi-factory. You won't see one in the US though. Pretty sure all it is is fender flares, wide wheels and some spacers. Also, AFAIR, that;s an 8 valve. supposed to make 190 some HP (or something close to that). There is someone on SC who has one and has a thread all about it.