Steering Rack Location-Opinions Needed Please

[LafayetteFSAE]

Hey guys,

My name is Will, and I'm a Junior at Lafayette College in Easton, PA. We competed last year at VIR, finished about middle of the pack IIRC...well anyway, myself and another Junior MechE student are doing a chassis/suspension design for a technical elective(since we do not have a team for this year).

One thing I'm wondering about is where some of you guys place the steering rack to eliminate bump steer and keep it out of the way of the drivers shins. On our current car it is hard for tall drivers like me (6'2") to drive it due to my shins hitting the shield that is on the rack.

So we are looking into a floor mounted rack, and we are not sure since our school has always done the rack mounted high up with the tie rod running about 1/2" above the upper a-arm, and basically parallel to that a-arm.

Another thing, I was reading in Milliken that for a floor mounted rack you want the tie rod to attach on the front side of the upright, and the opposite for a high mounted rack. Any truth to this, or does it not matter?

FWIW we will be running a Planar front suspension for next year. We are a very new team, so any thoughts/ideas would be greatly appreciated

Thanks,

Will

[LafayetteFSAE]

Hey guys,

My name is Will, and I'm a Junior at Lafayette College in Easton, PA. We competed last year at VIR, finished about middle of the pack IIRC...well anyway, myself and another Junior MechE student are doing a chassis/suspension design for a technical elective(since we do not have a team for this year).

One thing I'm wondering about is where some of you guys place the steering rack to eliminate bump steer and keep it out of the way of the drivers shins. On our current car it is hard for tall drivers like me (6'2") to drive it due to my shins hitting the shield that is on the rack.

So we are looking into a floor mounted rack, and we are not sure since our school has always done the rack mounted high up with the tie rod running about 1/2" above the upper a-arm, and basically parallel to that a-arm.

Another thing, I was reading in Milliken that for a floor mounted rack you want the tie rod to attach on the front side of the upright, and the opposite for a high mounted rack. Any truth to this, or does it not matter?

FWIW we will be running a Planar front suspension for next year. We are a very new team, so any thoughts/ideas would be greatly appreciated

Thanks,

Will

[LafayetteFSAE]

Some pics from our 07-08 car:

[JamesWolak]

Your going to have a hard time trying to mount that rack on the top side of your chassis with the new template rules (the whole point of the rule was to prevent teams from being able to do it).

You are correct Milliken does suggest that the rack should be on the front side of the upright. But then with traditional rack suppliers for FSAE your steering input would be backwards (you would be turning left and the car would turn right). This can be easily fixed but most teams with lower mounted racks mount it on the backside for simplicity.

The judges (and we have had Claude the last two years) haven't called us out for having it on the backside. What i would worry more about is your bump steer and that you have linear steering inputs. It looks that your input isn't liner on last years car.

But I am just a lowly power train boy though so take this with a gain of salt.

[Mike Macie]

Last year we had a "high nose" setup with a low rear steer rack. Basically our foot pan was a couple inches higher than our lower wishbone frame mounts which left plenty of room for the rack and master cylinders. The RCVD book suggests those locations so that any camber compliance will cause an understeer reaction. I think a low rear steer rack is easier to package, pro ackermann geometry easier(more so with 10's), tie rods are more protected from cones, and you have more options with your pedal assembly.

[LafayetteFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JamesWolak:
Your going to have a hard time trying to mount that rack on the top side of your chassis with the new template rules (the whole point of the rule was to prevent teams from being able to do it).

You are correct Milliken does suggest that the rack should be on the front side of the upright. But then with traditional rack suppliers for FSAE your steering input would be backwards (you would be turning left and the car would turn right). This can be easily fixed but most teams with lower mounted racks mount it on the backside for simplicity.

The judges (and we have had Claude the last two years) haven't called us out for having it on the backside. What i would worry more about is your bump steer and that you have linear steering inputs. It looks that your input isn't liner on last years car.

But I am just a lowly power train boy though so take this with a gain of salt. </div></BLOCKQUOTE>

Would you be able to tell me the rule # that pertains to the steering rack?

Also, can you explain more about how our steering inputs aren't linear on last years car?

Another thing I'm concerned about is if the rack is mounted on the floor and attaches to the back side of the upright(so a standard rack w/out modification would work), how can you get the steering shaft down at such a steep angle, I feel that a single u joint would lock up due to the large angle

[RBbugBITme]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Another thing, I was reading in Milliken that for a floor mounted rack you want the tie rod to attach on the front side of the upright, and the opposite for a high mounted rack. Any truth to this, or does it not matter? </div></BLOCKQUOTE>
You shouldn't have enough compliance to worry about this, its for rubber suspensions on road cars.

You shouldn't use just one u-joint and I'd bet with the steering wheel angle you'd be comfortable with it will be impossible. Two high quality u-joints can get you about 60 degrees though. We attempted to do a rack ahead of the pedals/behind the FBH to keep the solid shaft but we couldn't get the ackermann we wanted with our wheelbase so we'll be a high nose low rear steer car as well.

[LafayetteFSAE]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RBbugBITme:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Another thing, I was reading in Milliken that for a floor mounted rack you want the tie rod to attach on the front side of the upright, and the opposite for a high mounted rack. Any truth to this, or does it not matter? </div></BLOCKQUOTE>
You shouldn't have enough compliance to worry about this, its for rubber suspensions on road cars.

You shouldn't use just one u-joint and I'd bet with the steering wheel angle you'd be comfortable with it will be impossible. Two high quality u-joints can get you about 60 degrees though. We attempted to do a rack ahead of the pedals/behind the FBH to keep the solid shaft but we couldn't get the ackermann we wanted with our wheelbase so we'll be a high nose low rear steer car as well. </div></BLOCKQUOTE>

Ok thanks a lot, using 2 U-Joints makes sense for sure.

[Zac]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RBbugBITme:
You shouldn't have enough compliance to worry about this, its for rubber suspensions on road cars. </div></BLOCKQUOTE>

Are you sure about this?

[RBbugBITme]

Yes.