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How to plan your suspension upgrades

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jtmcinder

DSM Wiseman
5,403
82
Nov 4, 2003
Iowa City, Iowa
The first step to modifying your suspension is to have a clear goal. The second step is to go back and modify your goal because your first draft asked for things that are mutually incompatible. For example, you cannot set up your suspension to be perfect for both drag-racing and autocrossing; you also cannot set up your suspension to be perfect for autocrossing and cause minimal tread-wear on the street. That does not mean that you can't set up the car with, e.g., both drag-racing and autocrossing in mind. It only means that you can't optimize for both at the same time. Digest what this means, rank your priorities, and be ready for compromise if you are asking for more than one thing.

The second step is to declare a budget. This will guide all of your specific decisions. If you do not set a budget (or if you change it too often), then you could well end up with a set-up that is less than what you could have gotten for the same money if you had had a better plan. Alternatively, it might cause you to spend a lot of time trying to sell off parts on eBay when you decide that something you bought was not good enough or doesn't work well with some of the short-cut parts that you used elsewhere in the system.

The third step is to develop a clear plan with your goal (step one) and budget (step two) in mind. This is when you need to do a lot of research, ask questions when you can't find the answers, and be ready to start over from step one when your goals and budget are not compatible.

With regard to the specifics, my suggestion is to start with the driveline and then do the suspension. This may seem strange, given that this is the suspension forum, not the driveline forum, but I say this because the choices that you make with regard to the suspension depend on the driveline and not the other way around.

By "driveline" I mean the following: (a) FWD with open diff, (b) FWD with LSD, (c) AWD with open front diff and stock VC center, or (d) AWD with aftermarket diffs. Keep in mind that each diff that you upgrade will cost around $1000, give or take. For most people, therefore, this is a huge decision, but it really ought to be made first. You do not want to optimize the suspension for a stock driveline and then have to do it over when you get a Quaife or Kaaz. (Ask me how I know ;) .)

Once you have a plan for your driveline, you are ready to plan the suspension. The first issue here concerns ride-height and its adjustability. The second issue is springrates and swaybars, along with the shocks to match them. The third issue is whether to replace your bushings. The fourth issue is how you will adjust your alignment to what it will need to be.

When you are ready to start planning your specific suspension modification, start by reading everything that you can find on "weight transfer," especially if your main goal is autocrossing or road-racing. Drag-racers need to know about weight-transfer, too, but it isn't quite as important and you have other things to worry about, such as "wheel hop." Save alignment issues for later. They are the easiest to deal with, anyway.

One other complication needs to be mentioned (probably earlier, but I wasn't sure where): tire size. In general, there are two options: tires that can tuck inside the fenders and tires that can't. Extremely few people [that need to read this, at least] will end up with springrates and/or rideheights that allow for tires that will not tuck in, so most people are limited to tires that are about 245mm wide. If that is not enough for you, then you have to plan your suspension such that the rear tires will not hit the lip of the fender. If 245s will be enough for you, then you can put off thinking in detail about your tires and wheels until later.

Comments and suggestions welcome, but please do not ask specific questions in this thread. Thanks.

- Jtoby
 
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