Ride height discussion
Joined: Sep 2006
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From: ATL
^Any idea how much he cut them down? I'm going to be starting with 700/600 spring rates but I also have a full set of 800lb springs so I might play around with 800/700 as well. I know as is the rear travel is definitely limited and cutting the bumpstops would probably help a little but I also don't want to trim them down too far.
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Also wondering what is the best way to choose bump stops with a low ride height with limited travel, ie 12.5" rear with full length shock body. Do have GC extended top hats for an extra 1/2" bump travel.
What's the minimum useful length for the bump stop, 1/2"?
What's the minimum useful length for the bump stop, 1/2"?
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Joined: Jun 2010
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From: Michigan
^Any idea how much he cut them down? I'm going to be starting with 700/600 spring rates but I also have a full set of 800lb springs so I might play around with 800/700 as well. I know as is the rear travel is definitely limited and cutting the bumpstops would probably help a little but I also don't want to trim them down too far.
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From: Arizona
At 13.3" rear with the kw club sport I think 7" 650 # or 700# springs are spot on. I will be confirming this weekend with some close measurement of how my 5.5" 650s perform. They might fully compress under extreme load but we will c!
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From: Emmett
Rear bump is something I've learned to take seriously, it can be the difference of a car that's unpredictable (not having enough) to a car that's super easy to drive.
Bump stop length is super important as well as density, a shorter stop is not always better and in some cases might make things worse. They basically work just like springs, if you cut them down their rate increases. I tried many times to get PSI to dyno their stops but they were always too busy but RE Suspension has dyno's of their stops http://www.resuspension.com/index.html
Just a guess here but I think a stock length rear damper assembly running at 13.25" height with 800lb springs with a 30mm stop is probably over the edge depending on grip level. Anything less than this and it'll be really bad, I swapped over to 20mm stops and 700lb springs and this is where my dilemma really started. I thought maybe my back problem had something to do with my poor driving but after driving different cars at Buttonwillow and being able to carry a bit more corner speed through riverside I knew something was up with my car. I thought it was my damper settings so I started getting crazy with them and oddly enough the car was much more predictable, I was at around 4 out from full stiff and at my last track day I was at around 14 out just to give an idea of how stiff it was. I reduced the springs from 700 to 650lb and lowered the car a tad to like 13" and that was all bad again. I took some video of the car with the cam mounted to the quarter panel but it was hard to see what was happening, I later installed an Eibach rear bar and things got better so I knew it had to be bump related since the increase in roll rate helped. I took video of the actual damper with the Eibach bar and sure enough I was squashing the stop. I sent the video to PSI and they didn't see a problem with it but said they could shorten to STR spec if I wanted. I had them shortened and the difference in drivability was night and day.
My findings as far as measurements go
measurements are taken from center of clevis mounting hole to top of top hat chassis mounting point with damper compressed. Slight stop compression just means that the bump stop might be compressed like a 1/16th inch or so. It's not a super duper precise measurement.
Factory rear damper and top hat bottomed out with slight bump stop compression
13 3/4
Cut down 30mm rear TTX w/AST top hat bottomed out with slight bump stop compression 20mm
12 3/8
Bottoming out isn't all that big of a deal if the bump stop is matched up to the ride height, spring rate, roll rate/grip level.
I'm trying to compile some measurements of dampers but with all the different top hats/spring perches it makes it harder. It would be nice to have measurements of the different damper assembly lengths.
KW V3's center clevis hole to top cap is 11 1/4" so I just need to measure the stock damper to get an idea of their overall assembly length for V3's
Bilstein PSS is 11 1/2" center clevis hole to top cap
Anywhere around 12 3/8 with 650lb springs, 20mm bump stop, Eibach rear bar, 3000lb chassis and driver and RS3's is enough. Anything less or more and you'll need to adjust spring rate or roll rate or both.
Hope this info is clear and makes sense
Bump stop length is super important as well as density, a shorter stop is not always better and in some cases might make things worse. They basically work just like springs, if you cut them down their rate increases. I tried many times to get PSI to dyno their stops but they were always too busy but RE Suspension has dyno's of their stops http://www.resuspension.com/index.html
Just a guess here but I think a stock length rear damper assembly running at 13.25" height with 800lb springs with a 30mm stop is probably over the edge depending on grip level. Anything less than this and it'll be really bad, I swapped over to 20mm stops and 700lb springs and this is where my dilemma really started. I thought maybe my back problem had something to do with my poor driving but after driving different cars at Buttonwillow and being able to carry a bit more corner speed through riverside I knew something was up with my car. I thought it was my damper settings so I started getting crazy with them and oddly enough the car was much more predictable, I was at around 4 out from full stiff and at my last track day I was at around 14 out just to give an idea of how stiff it was. I reduced the springs from 700 to 650lb and lowered the car a tad to like 13" and that was all bad again. I took some video of the car with the cam mounted to the quarter panel but it was hard to see what was happening, I later installed an Eibach rear bar and things got better so I knew it had to be bump related since the increase in roll rate helped. I took video of the actual damper with the Eibach bar and sure enough I was squashing the stop. I sent the video to PSI and they didn't see a problem with it but said they could shorten to STR spec if I wanted. I had them shortened and the difference in drivability was night and day.
My findings as far as measurements go
measurements are taken from center of clevis mounting hole to top of top hat chassis mounting point with damper compressed. Slight stop compression just means that the bump stop might be compressed like a 1/16th inch or so. It's not a super duper precise measurement.
Factory rear damper and top hat bottomed out with slight bump stop compression
13 3/4
Cut down 30mm rear TTX w/AST top hat bottomed out with slight bump stop compression 20mm
12 3/8
Bottoming out isn't all that big of a deal if the bump stop is matched up to the ride height, spring rate, roll rate/grip level.
I'm trying to compile some measurements of dampers but with all the different top hats/spring perches it makes it harder. It would be nice to have measurements of the different damper assembly lengths.
KW V3's center clevis hole to top cap is 11 1/4" so I just need to measure the stock damper to get an idea of their overall assembly length for V3's
Bilstein PSS is 11 1/2" center clevis hole to top cap
Anywhere around 12 3/8 with 650lb springs, 20mm bump stop, Eibach rear bar, 3000lb chassis and driver and RS3's is enough. Anything less or more and you'll need to adjust spring rate or roll rate or both.
Hope this info is clear and makes sense
Former Moderator
Joined: May 2006
Posts: 14,847
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From: Emmett
First video, slowed to like 1/15
http://www.youtube.com/watch?v=UEkxC...e_gdata_player
Second video
http://www.youtube.com/watch?v=t0O6Y...e_gdata_player
http://www.youtube.com/watch?v=UEkxC...e_gdata_player
Second video
http://www.youtube.com/watch?v=t0O6Y...e_gdata_player
Former Moderator
Joined: May 2006
Posts: 14,847
Likes: 10
From: Emmett
