Difference in 18 1/4" rack and 19 1/4" rack

[Cranky]

Besides the actual length difference, what is the difference in the 2 differnt size racks? If a chassis manufacturer recommends an 18 1/4" rack, can a 19 1/4" rack be used in its place with shorter tie rod tubes? Why are cars built with a certain length rack in mind? Just something ive wondered for awhile??

[billetbirdcage]

Besides the actual length difference, what is the difference in the 2 differnt size racks? If a chassis manufacturer recommends an 18 1/4" rack, can a 19 1/4" rack be used in its place with shorter tie rod tubes? Why are cars built with a certain length rack in mind? Just something ive wondered for awhile??

http://www.longacreracing.com/articles/text/bsdrawing.jpg

Normally on a LM since the tie rod ends up between the upper and lower arms (between lines 3 and 4 in drawing not where they show it - due to steering arm location needing to be higher then the lower arm to clear the wheel): You can see to be on that line (line 2 in picture) the rack end needs to be outside the lower control arm mounting bolt, so the rack needs to be longer then the distance between the lower arm holes. Typically this is about 3/4 to 1 1/4 over the lower arm spread.

Hope that makes sense, but basically with the wheels straight both inner tie rods at the rack should be outside the lower control arm mounting point about 1/4" to 1/2" on each side.

[Ltemodel]

What billet said was perfect. I just wanted to add a little more. There is also the aspect to raise the rack to get more ground clearance. We are all trying to get the front end lower while still getting the geometry correct.
The rack is the big hindrance now. So we raise it up and need to put a longer rack in to get the geometry to come out.
The stopping point now has become the fan and radiator clearance. That is why we are seeing short radiators. The next problem becomes these large 19” fans to pull enough but’s off these 800 to 900 hp motors. The ultimate is trying to figure and get away with a sprint car style drag link steering system.

[Ltemodel]

It’s not letting me edit the above post. I meant to say “pull enough btu’s off these motors.” Darn autocorrect.

[reinhart]

auto incorrect