Hey guys.

It's been awhile since I've posted, good to be back.

I had a nagging question regarding dynamics/stability that I've been curious about that I thought I'd ask here.

So when you replace your stock springs with sport or race springs and do not concurrently replace the shocks, the stock shock's damping coefficient is too low for the stiffer springs, and therefore the suspension is underdamped which will lead to unnecessarily far rebounding of the spring and a potentially rougher ride and less traction due to the fact that the tires are not matching the road perfectly. (Sorry about the run-on.)

My question is, what happens dynamically to the handling of the car if you only replace, say, the front shocks when you replace all 4 springs?

My first impulse is to say that due to the underdamping that would happen in the rear and the critical damping (more solid suspension) in the front, oversteer would be more prevalent. Anybody have any thoughts? Anybody have any experience?

If this is the case, and there are no / negligable side-effects, lets face it... oversteer is fun and it may be a cost-effective way of lowering your car (if you're poor like me) without dropping 1200 on coilovers or 800+ for a spring/shock set... just get a $200 spring set and $250 for front shocks only.

I love responses... but please don't tell me 'StoP beeing a duma$$, d0 iT RITE'. I'm not saying I'm going to do this, it was just a curious physics problem, and since I'm an engineer, I need to know the answer.

Cheers, thanks in advance.

Rob

 

Well Rob your assumption is correct. You missed one minnor thing. Tire Ware is going to be very uneaven to an almost dangours extent. Think of it this way Audi front in with a Kia tail = Not Safe. The overall way is save and do it in one shot you will be pushing dangours grounds when you mix and match there are slim odds that it would turn out ok and meet the safety requirments.

I have driven a few cars that were setup like that. I know a few people that did the general setup with Civics and Accords modded eather front of back first and still took them on the street. They started to ware out brushing on control arms and couldnt figure out why. The added weight going to the top sections isnt meet to take it 100% of the time you should know that.

If you want a true answer run the quick load test say thru comos on the angles and meterials that would be used watch the strees points. Be safe do it all at once. $800 isnt bad at all I spend more in renting a crappy apartment I could well justify a safe setup for even $1300.

But considering its a question and the answer is What do you want to do and How do you acomplish it. Just run a quick example and find out. Other then that I might get someone in our engineering department to do the strees anaylist on it for fun. What parts where you looking at I'll probley get the stuff toghter that they need and hand it off.

Good Question btw interesting to see the truth.

 

Thanks, excellent point. I hadn't thought about tire wear.

Anybody else have anything?

 

Actually having just front shocks will make you understeer more. The rear will be softer, causing the front to loose traction before the rear, which will make for an interesting ride since the rear will be swaying all over the place, and the front will stay level-ish. I'm imagining it will look like a dog who tries to run really fast and turn on hardwood floors.

If you were really going to do this, it'd be better to replace the rear shocks for oversteer. That would keep the rear stiffer, and make the car slide a little easier. The Vogtland club spec springs have a stiffer rear spring just for that reason.

Another thing it sounds like you haven't thought of is how bad the ride quality will be. A lot of normal spring/shock combos ride on the bumpstops most of the time, so with the stock shocks, it'll be even worse.

I think you may enjoy reading these threads, grab some popcorn, one is 10 pages. It has some great input from Dick Shine (he designs suspension setups, very nice ones at that).

http://www.passatworld.com/forums/sh...d.php?t=205178

http://grassrootsmotorsports.com/archives/shocks.html

http://audizine.com/forum/showthread.php?t=147185

Should give you a bit more information about how the shocks will affect your handling.

Kyle

 

thanks kyle.

wouldn't it be the same stiffness in all 4 corners, but only the fronts will actually be damped correctly, while the rears will be bumping around, losing traction? I'm not arguing, I just think it's an interesting problem