3 questions about bump stops. #1 What is the point of the 17" spacer?
10-08-2008, 06:34 AM
#1
3 questions about bump stops. #1 What is the point of the 17" spacer? If it helps to know, my car has 17x11's with 315/35 Nitto DR's. I have an adj PHR. and LCA's with relocation brackets. I am on stock shocks (haven't got Koni SA's in the rear yet to match the front) and also lowered about 1.5-2 inches because I barely have 2.5 inches of clearance between the tire and quarter panel (maybe if the tank is empty)
Question 1: I see that SLP put spacers on all SS/WS6 models because of 17" rims. It is suppossed to keep the tire from hitting the wheelwell. I don't understand this. A tire for a 17" rim isn't any taller than a tire on a 16" rim if you get the correct sidewall height. Can someone help me understand this. I am going to remove the spacer because I've been slamming the bumpstop on the rearend for the last 46k miles and I'm tired of it. It hits on even the smallest bumps and makes A LOT of racket. Which leads me to question 2.
Question 2: Some people say they remove them completely with no ill effects. Then I've heard they crush the over the axle exhaust pipe or they hit the fenderwells and slice the tires. My problem is that I have Fikse FM-5s and the offset on all Fikse's is custom to an fbody so that the wheels come towards the outside of the car more; they don't tuck in like ZR1's. I don't touch the bumpstops on the inside until I jack up the car, then they just barely scrape. On the outside however is another story. I'm worried that if I remove them completely, they may severely damage the quarter panels by coming into contact with them.
Question 3: So I'm relunctant to remove them completely but I've been told and have read on here that the Z28 bumpstops are better or have more cushion so that there is less of an impact when they hit. IS THIS TRUE? Do they use a softer rubber or something? COULD SOMEONE PLEASE POST A PICTURE OF A Z28 BUMPSTOP so I could see the difference? Any input is much appreciated. Thanks.
Question 1: I see that SLP put spacers on all SS/WS6 models because of 17" rims. It is suppossed to keep the tire from hitting the wheelwell. I don't understand this. A tire for a 17" rim isn't any taller than a tire on a 16" rim if you get the correct sidewall height. Can someone help me understand this. I am going to remove the spacer because I've been slamming the bumpstop on the rearend for the last 46k miles and I'm tired of it. It hits on even the smallest bumps and makes A LOT of racket. Which leads me to question 2.
Question 2: Some people say they remove them completely with no ill effects. Then I've heard they crush the over the axle exhaust pipe or they hit the fenderwells and slice the tires. My problem is that I have Fikse FM-5s and the offset on all Fikse's is custom to an fbody so that the wheels come towards the outside of the car more; they don't tuck in like ZR1's. I don't touch the bumpstops on the inside until I jack up the car, then they just barely scrape. On the outside however is another story. I'm worried that if I remove them completely, they may severely damage the quarter panels by coming into contact with them.
Question 3: So I'm relunctant to remove them completely but I've been told and have read on here that the Z28 bumpstops are better or have more cushion so that there is less of an impact when they hit. IS THIS TRUE? Do they use a softer rubber or something? COULD SOMEONE PLEASE POST A PICTURE OF A Z28 BUMPSTOP so I could see the difference? Any input is much appreciated. Thanks.
10-08-2008, 08:19 AM
#2
It's not called a 17" spacer, it's called the "SLP spacer" or something and they added that because some of those cars got lowering springs and they wanted to play things safe. I didn't know what you were talking about at first. 
This is the rear bumpstop you need:
It's a stock piece and is used on many more models than just the Z28. It is long and tapered with a foam like construction. Even these are a bit too stiff and long for these cars. Now if you haul heavy things in the back, it may be just fine.
Slp sometimes used a hard rubber bumpstop and they are known to ride harsher. I would recommend you ditch the spacer and get new, stock bumpstops for the regular cars.
A lot of what your asking depends on the amount the car is lowered. If at stock height, you can remove the bumpstops altogether with no problems.
Once you decrease ride height a lot of other factors come into play. By allowing the rear of the car to compress more, it brings those fat tires closer to the sharp fender lip. This is more likely on a dip rather than when the car leans. When it leans the other wheel extends and can angle the top of the inner tire inward. But on a dip, both tires go straight up. Plus the PHR design forces the axle to move towards the passenger side under compression.
If you want to know what will hit first as the rear end compresses, just put the axle on jack stands and get under there and look. Measure the gap at the bumpstops, plus maybe 1/2"-3/4" more as the bumpstop gets compressed.
I have a thread on this when I did all these measurements on my car. Long story short, the stock exhaust pipe will usually touch first, but just barely. There's usually enough play in the exhaust system that it will just get pushed up. No big deal there.
I would also recommend a PHR with rod ends. Under heavy cornering a poly bushed PHR is still going to let the axle move left and right some and that's all it takes to rub or cut a tire. When I was running the 315 GSD3's (really wide for their size) I had to roll the fender lips as well as swap my poly PHR to a rod-ended one. That was the only way I could get my very lowered car to not rub anywhere.
Something else to consider is spring rate. A lot of aftermarket rear springs can be pretty soft and allow the rear to compress more than a firmer spring would. I tend to prefer 150-170lb/in. springs for my daily driver. Not only do they keep you off the bumpstops more, they made the car feel more nimble.
Once you swap over to the Koni SA rear shocks, you'll notice that they will also reduce bumpstop contact. The DeCarbon shocks are just valved too soft all around. No control.
This is the rear bumpstop you need:
It's a stock piece and is used on many more models than just the Z28. It is long and tapered with a foam like construction. Even these are a bit too stiff and long for these cars. Now if you haul heavy things in the back, it may be just fine.
Slp sometimes used a hard rubber bumpstop and they are known to ride harsher. I would recommend you ditch the spacer and get new, stock bumpstops for the regular cars.
A lot of what your asking depends on the amount the car is lowered. If at stock height, you can remove the bumpstops altogether with no problems.
Once you decrease ride height a lot of other factors come into play. By allowing the rear of the car to compress more, it brings those fat tires closer to the sharp fender lip. This is more likely on a dip rather than when the car leans. When it leans the other wheel extends and can angle the top of the inner tire inward. But on a dip, both tires go straight up. Plus the PHR design forces the axle to move towards the passenger side under compression.
If you want to know what will hit first as the rear end compresses, just put the axle on jack stands and get under there and look. Measure the gap at the bumpstops, plus maybe 1/2"-3/4" more as the bumpstop gets compressed.
I have a thread on this when I did all these measurements on my car. Long story short, the stock exhaust pipe will usually touch first, but just barely. There's usually enough play in the exhaust system that it will just get pushed up. No big deal there.
I would also recommend a PHR with rod ends. Under heavy cornering a poly bushed PHR is still going to let the axle move left and right some and that's all it takes to rub or cut a tire. When I was running the 315 GSD3's (really wide for their size) I had to roll the fender lips as well as swap my poly PHR to a rod-ended one. That was the only way I could get my very lowered car to not rub anywhere.
Something else to consider is spring rate. A lot of aftermarket rear springs can be pretty soft and allow the rear to compress more than a firmer spring would. I tend to prefer 150-170lb/in. springs for my daily driver. Not only do they keep you off the bumpstops more, they made the car feel more nimble.
Once you swap over to the Koni SA rear shocks, you'll notice that they will also reduce bumpstop contact. The DeCarbon shocks are just valved too soft all around. No control.
Last edited by JasonWW; 10-08-2008 at 08:27 AM.
