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How to get low


Mattt

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So some of you may have seen my new project thread on my 1970 RT80 corona. I finally got around to doing some measurements today and it has occurred to me that I’m going to have issues with gravity. Details in short:

Requires 50mm drop front and 60mm drop rear to bring guard in line with tyres. Wheels are 14”X6 and 7 wrapped in 195/45 tyres

Front engine cross member sits about 110-115mm off the ground

Sills sit about 130mm off the ground

Front springs are aftermarket lowering springs. Not sure if they’re correct or off something else but they’re certififed

Rear is hilux diff with what seem to be fairly flat leafs and 2” lowering blocks

 

I expect to require Cert for anything I do. 
 

What have people done to sort out this sort of gravitational issue? I don’t really want to run 17s. I was planning to replace these wheels with some Oldschool jdm wheels but wanted to stick with 14s. If I have to I could go to 15s which would mean I could get around 15mm drop front springs. Could probably get 20mm if I made up new hangers for the rear leafs. Then if I go to 15s I may be able to go with a slightly bigger tyre and get add 10mm which would bring my gap down to 25/35 which I still feel is too much. This is my first time dealing with dropping a small old school Car on 14s so sorry if this all seems a bit noob. I am a fabricator by trade so I can happily cut and mess with things but just want some advise from the voices of experience. 0DCF990B-D9A8-46A1-A27C-EB3AE587A6F8.jpeg.3fb32171f4b50b60d3f3f47a64e069fc.jpeg

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If you do all of that, you are looking at crossmember 80mm of the ground, is that right?

Technically you can get certed for less than 100mm ride height, but my understanding is that it's hard/unlikely. 

Also have to look at what happens if you get a flat tyre, make sure nothing hits the ground. 

Can you cut up the crossmember and reduce it's size while replacing the strength?

/4-link the rear and airbags.

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80mm seems about right. I’m not keen on bags unfortunately. I need to actually measure exactly and get some accurate figures on paper but these are pretty close. I had considered looking at a GTIR rear set up which will convert to IRS at the same time but I won’t have time for that for quite a while and it doesn’t really solve the problem of the sill height.

I had thought about cutting up the front cross member. I’ll have to talk to a certifier about what they would want me to put back into it to keep them happy.

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Something to keep in mind is you need a minimum 40mm suspension droop and bump. Starts getting hard the lower you go as you have to get pretty specific with spring rates used vs car weight, to keep that travel. Also comes down to budget. I am almost at the right bump/droop figure with my setup, and because front and rear are adjustable platform height, changing ride height doesn't affect those figures. It just changes steering geometry / bump steer which is also measured come cert time. 

 

To quote Cletus

Quote

40mm bump 40mm droop from ride height. 

Depending on the car and suspension and bumpstop type,  can include some bumpstop compression in that figure

 

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try find some factory or already cut springs - put them in and work out how low you want it - cut more to suit the ride height at the front you want.

Then look at what has changed underneath the car - clearances, travel, angles etc.  Figure out if this stuff is an easy fix and go from there.

 

 

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