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View Full Version : Center Load/End Load rack & pinion?



moto1
02-10-2009, 05:32 PM
Center Load rack & pinion, End Load Rack & pinion. I did a little search on this subject, but would like some input, I`m not to clear on this??
thanks
Moto1

Gene
02-10-2009, 08:34 PM
Good question and I'm sure there answers vary. One opinion is that end load racks are less expensive than center load racks and another is that end load racks undergo more stress than a centerload rack.

Hang tie rods off the end of an end load rack and it must be harder on the rack than hanging tie rods from the center. Alo it is easier to design a bracket that cancels out bump steer using a center load rack than an end load rack.

I've used both types. I won't use an end load rack again for those reasons.

Opinions vary.

plkracer
02-10-2009, 09:01 PM
You can always make an end load work though. For me, it was due to limited space, and the end load was the right width to begin with.

ProtoDie
02-11-2009, 05:35 AM
Depends on your frame width & a arm pivots points width.


Center load tie rod ends are closer together, so your A arm mount points need to be closer together

End load tie rods are farther apart, so the A arms also need to be farther apart.

I have 16" wide end load rack, 19" of travel & less than an 1/8" of bumpsteer

Gene
02-11-2009, 08:41 PM
That is very interesting. If I understand this correctly a center load rack is more agreeable with a center pivot design than an end load rack and an end load rack is more agreeable with A-arms that are not center pivot.

Is that correct?

Did anyone see the recent Glamis Dunes post of the Sonic car that needed end load pivot rack bracket modification that seeme - extraordinary?

In any case, if designed in CAD it seems that either rack is good. I can only relate my experience and that is limited to a single car using both racks with different suspension systems.

Artie on Edge
02-11-2009, 08:56 PM
Just a quick reply, ProtoDie is completely correct. The pivot point for the steering arms is dictated by the arc the upper and lower arms describe and their (combined) linear length change as they describe this arc.

With a long lower and shorter upper arm they are each going to have a different arc and different length changes therefore requiring something of a compromise (to a degree) in the positioning of the rack ends.

Saying that you prefer this or that unit because this is easier to mount etc ignores the principle of bump steer and its minimisation. Bump steer isnt nice stuff and while some claim to have 'eliminated' it in their machines it is much more likely that they have minimised it.

IMO :D

nutz4sand
02-12-2009, 10:36 AM
Just a quick reply, ProtoDie is completely correct. The pivot point for the steering arms is dictated by the arc the upper and lower arms describe and their (combined) linear length change as they describe this arc.

With a long lower and shorter upper arm they are each going to have a different arc and different length changes therefore requiring something of a compromise (to a degree) in the positioning of the rack ends.

Saying that you prefer this or that unit because this is easier to mount etc ignores the principle of bump steer and its minimisation. Bump steer isnt nice stuff and while some claim to have 'eliminated' it in their machines it is much more likely that they have minimised it.

IMO :D

I agree that with a rack that bumpsteer is just minimized. Being that as the wheel pivots on its kingpin axis the part of the spindle where the tierod connects moves forwards and backwards as it moves side to side (it might not move much depending on the design but it does still move forward and backwards.) With this motion no rack will ever have "zero" bumpsteer.
You would need swingset steering like many cars and trucks have/had. The kind with idler arms holding the center steering link so that it pivots with the same arc that the steering knuckles do.

But this adds cost and complexity and as stated above with proper setup it can be mimimzed with a rack to where its practically not a concern. A rack in comparison is easy to mount and pretty small and light. So they get used a lot.

I HAVE seen cars (normal street cars) with idler arms that actually pivot the opposite ways of the steering knuckles. Lotsa weird stuff (geometry) going on there. But for a vehicle with 6 inchs of travel or less its not near as noticeable if somethings not perfect. Going for big travel exagerates any problems if your setup has them.

The length of the rack is not a good thing to choose after you have a frame and such. You should look at different racks then locate a rack that will put its tierod mounts as close as you can match up to where you are gonna put tha A-arm pivots for a frmae you are considering buying. If your building the frame then you get the rack 1st (or at least its measuremnts) and build to meet its width.

Its why many people say its a good idea to get your wheels and spindles first. Then build inward with the arms and then the steering. Once you know where thats all going you build the frame to hold it.

Going from the frame out (pick anyones frame you like) you have to adapt to its measurements or the car will be screwy (as in not right).

You can add an adaptor to a rack to get different widths thats its factory mounts in some cases. It basically bolts to the place where the tierods should and you make new tierod mounting holes where you need them. Not always easy to do with all racks. Plus the rack has to be able to deal with the loads imposed on it if they are far from what the maker made it to take.

ProtoDie
02-12-2009, 11:05 AM
Very well said.
That is a question posted often,,,,,,"I bought a frame,,now I need to figure out supension & steering"

Like you mentioned,,,there are a lot of frames built without having the suspension & steering figured out.

For those buying frames, maybe they can ask the manufacturer what rack & suspension they designed the rollcage for.
Ask for specific A arm mounting point locations

If they designed the roll cage with suspension, they should be able to provide this info.

It may not be realistic though,,,,,,,,,,,,,,,maybe just design & build from the wheels in.