josh99ta

iTrader: (1)

For my front suspension I'm going to end up running cut stock springs (1.5-1.75 coils for a 26-26.25" front ride height) with the upper mod mount and 40mm Koni bumpstops to regain most of the suspension travel I've lost with the lower springs.

For the rear suspension I'm going to end up running cut stock springs (2 coils for a 26.25" rear ride height) with the rubber isolator in, which should make them 150 lb/in springs from the research I've done. My main question is in the rear since I checked out my factory bumpstops today.

One was completely rotted away (driver's side) and the other was in marginally okay shape (passenger's side). I went ahead and removed the spacers on each side (measured 1" thick each), then I trimmed the stop that was in decent shape down another 1/2" and added a taper back into it. As it was obvious the driver's side made contact more frequently and I only had one bumpstop, I chose to put it on the driver's side, although I think I probably should have reinstalled it on the passenger's side just in case the axle gets up into the exhaust piping (thoughts? leave on driver's side temporarily or move back to passenger's side ASAP?). By straightforward measurements that should have gained back 1.5" of suspension travel in the rear, and I am currently lowered 1.5" in the rear, so I should be back to stock suspension travel specs in the rear (theoretically).

Right now I'm at a 26.5" rear ride height and with the suspension fully loaded on level ground I have approximately 2.5" before the rear axle will make contact with the bumpstop that I trimmed and put on the driver's side of the car. On the passenger's side where I completely removed the bumpstop I have a measured 3" before the axle comes into contact with the area where the bumpstop used to be.

Are these numbers sufficient? I've never measured a stock height car to see what kind of travel they have.

josh99ta

iTrader: (1)

Also it's worth noting that I do see a huge difference between the more blocky SS bumpstops and the more tapered Z28 bumpstops. I have a set of Z28 bumpstops on the way that I may trim down some and reshape to keep maximum travel with the most progressive rates (unless I should just leave the Z28 stops alone as they're good as-is).

JamRWS6

Cutting stock springs isn't going to help you. The stock springs don't have enough spring rate when their travel is reduced to keep you off of the bumpstops.

My advice on the rear? Put bumpstops on both sides and stop worrying about bumpstops. Bumpstops are the end of the road in protecting expensive parts from getting torn up. What kind of shocks are you running? That will make a HUGE difference compared to whatever you are trying to accomplish now.

Bottom line is if the car is lowered and you hit some nasty potholes you WILL be hitting the bumpstops. Another .2" isn't going to help...if anything it gives the axle more time to speed up before slamming into the stop.

Bottom line is these cars weren't designed to be lowered and however you decide to do it is a compromise of some sorts. The best option is to always find a spring w/ enough rate to keep you off of the bumpstops paired w/ a quality shock that can control the spring and body motion of the car.

josh99ta

iTrader: (1)

I'll be running Bilsteins, which are valved for the stock spring rates. These will work very well up front since my rates will be close to stock, and with the UMM I'll have very close to stock suspension travel, with better bumpstops in the Koni 40mm units, so it should ride just as well as stock, handle better from the upgraded shocks + lower center of gravity, and the height will be where I want it from an appearance standpoint.

Have you cut stock springs? Do you know that cut stock springs have the same rate as most aftermarket lowering springs? Look up some of JustinWW's posts. I won't go into the details since he's already laid out the math. 1 coil off the stock rear springs = 130 lbs springs. 2 coils = 150 lbs springs. Now look up Strano's or BMR's rear spring rates (150 & 160 lbs springs, neither in a coil bind situation).

Also your idea of what the purpose of bumpstops are is completely flawed. I don't mean to be rude, but when I said tech talk I meant tech talk, not rehashing misconceptions. Springs are probably the single most simplistic piece of the suspension puzzle. It doesn't matter whether they're cut stock springs or huge, thick aftermarket springs, if the height is right and the rate is right you're fine. It's been proven than you're more than fine cutting the stock springs and getting exceptional results when paired with good shocks, which I'm doing, and when the steps are taken to properly use and take advantage of the progressive nature of the right bumpstops for the purposes of ride quality and handling, not just a stop-gap for avoiding tearing stuff up.

I want the most progressive bumpstops I can get for handling purposes, but I also want the most travel I can get before getting on the bumpstops for ride quality. It's obviously going to be compromises, and I know I wont get the whole cake, but I want as much of the cake that I can get while I'm eating it too. The rear will be every bit comparable to an aftermarket spring setup. I am giving up some rate and some handling up front for lower rates and a smoother ride, and also better weight transfer during straight line acceleration. Having a softer front and stiffer rear will induce oversteer. In order to compensate for what I'm doing on the front suspension I'll be adding a 35mm bar up front and leaving the stock bar in the rear, which should help to make the car perform more neutral.

I've got a good plan. I was running stock untouched springs on Koni SAs on my old Trans Am and out of over half a dozen suspension setups it was my favorite for a balance between ride and handling. Effectively I'm trying to do the same on this car without as much cost invested, and comparable results. The extra lengths I'm going to in order to maintain maximum suspension travel while still setting the car up to ride well and handle better and more neutrally will pay off. Spring-cutting-naysayers or not. The one piece of the puzzle I'm unclear on is the rear bumpstops and suspension travel. More travel + quicker ramping rates on the stops, or less travel and more progressive stops? I have to imagine less travel with more progressive stops is the best for handling, but which is best for ride quality, and which side of the tradeoff do I want to lean towards in my particular application? I'd rather ask and get some input than spend a ton of money on two sets of bumpstops.

Sam Strano

iTrader: (41)

It's really not that simple.

You are missing a lot of points here. Among them are:

Stock front bumpstops give more free travel than Koni stops do (but Koni stops are softer and more progressive). You are not comparing apples and oranges.

The valving of the shocks is different, and if you ran Koni's anything beyond full soft plus a touch more, then you won't like the Bilstein valving as it will be too soft in comparison--regardless of what springs. Shocks aren't only about controlling the spring rate, but also the mass of the car and how it responds. Most anyone who likes a crisp controlled car runs the car technically overdamped compared to what they springs would require.

Balance wise adding a big front bar with a stock rear isn't recommended, and I only do it where rules preclude us from running a rear bar to match (and then we do other things for balance which aren't very street or tire wear friendly). If you up the front roll stiffness a lot, and don't touch the rear, the car becomes more disjointed at the limit and the rear will feel like a trailer tagging behind. It will be stable because it won't be balanced it will be pushy when driven hard.

On the rear, the best is more travel and progressive stops.

I applaud the thinking here, but there are a lot of assumptions being made that are a big off base. And cutting springs is horrible idea. You don't know exactly what kind of drop you will get, and because of the nature of the springs, you generally end up dropping more height than you add back rate and end up with----well, Sportlines. Something that looks good but isn't functionally good at all.

josh99ta

iTrader: (1)

Sam, when I was daily driving the car I ran all four Konis at full soft with stock untouched springs (lower perch in front, hose mod in rear) and loved the ride. Best riding setup I've ran out of all the suspensions I've had to date. For track duty and very spirited street driving it's obviously far from ideal, but I don't track my daily drivers much if at all, and I don't drive very hard on the street either (never know what could happen on the street). I drive spiritedly at times to enjoy the car, but never push the car that hard.

If I'm not mistaken the Bilsteins should have a comparable level of control that the Konis had on full soft, my spring rates will be up slightly over my old setup as my springs are cut a bit, but my travel should be nearly the same with the UMM in the front and the measures I'm going to in the rear to ensure as much suspension travel as possible. I'd love to go with Konis, but I have other budget-priorities in life right now with getting married and buying a house, so I'm attempting to attain a similar setup for a bit less cost. I also don't feel that Konis are the answer for me even if budget wasn't a concern. The more I look over things, the more I feel like the ideal setup is the IAS shocks (if they do indeed work as advertised) and air springs all around. Again, the budget doesn't allow for that right now. Maybe a few years down the road.


Good to know. Come to think of it I never noticed my old setup handling poorly (stock bars all around, Konis, stock springs, 245 tires up front). Maybe that had something to do with the 245s. For daily driving I like 245s up front for a number of reasons (less tracking, more hydroplane-resistant, less rolling mass, less cost to replace), but also tend to push sooner under spirited driving. That could be what balanced out my old setup so well and may work pretty good on this setup also. It's something I'll be experimenting with.

Very good to know. I'll continue to try to maximize travel then once I get these Z28 bumpstops in. They're very tall and very progressive. I think I'll trim 1/2" off of them initially, reshape the taper to maintain the progressive rates, then drill a hole through the middle of each one to help soften them up a bit also.

Thanks Sam. I think my front rates are going to end up being pretty close to what the Sportlines are, but my rear rates will be much more ideal. I couldn't believe the rates they use in the rear for the drop you get. According to what I've seen I'll be at a 150 lbs spring in the rear. I'm cutting with a die grinder, a little at a time, to avoid heating and changing the springs' properties. I've got a ballpark figure of the rates I'll be at, and I'm not drastically dumping the car, just getting a better stance than stock. The goal is to lower the car ~1.5" while gaining back nearly all of that in suspension travel while maintaining stock-like ride comfort. I'm pretty close now. I think swapping the Bilsteins in with the UMM and working on the rear bumpstops will get me where I hope to be. I'm so close now it's crazy. Those few things should be the icing on the cake.

camaroextra

iTrader: (10)

Thread Hijack:

I actually have a Strano Front Sway bar that I picked up used, I love it.

Sam have I handicapped my car by keeping the stock rear sway bar on?

therealcreeper

iTrader: (37)

I ran a 35/19 combo for a few weeks. wasn't too bad. when i went up to a 21 in the rear it definitely balanced it out better though. the rear actually helped the front do what it wanted to do instead of just hanging out behind there and following. accelerating around tight turns the rear bar is especially noticeable.

I'm not sam, but I wouldn't say your handicapping the car. seems sort of silly to leave it like that forever but it's not absolutely ruining performance at the moment. definitely worth it to upgrade though.

Sam Strano

iTrader: (41)

Running a bigger front only is not the way the bars were developed. Yes, you are giving up balance and performance running a stock rear bar.

I've done it, but only when I had to when rules precluded me from changing the rear bar (and I'd run a lot more shock and tire pressure than ideal to balance the car).

If there are no rules (you don't race, or do and don't care on the class) then you should absolutely have a matching rear bar to the front. Not having is is akin to having a nice set of heads with a stock cam and valve springs.

As much as the front bar helps response on it's own, the set makes the car feel more as one, and better balanced. realcreeper describes the difference well, the rear can almost feel a little trailer like with a stock rear bar, with a matching rear like our Hollow 22 that goes with the Hollow 35 the car feels more like a piece of billet than tin-foil.