Lowering springs and suspension travel. You ARE hitting the bumpstops.
Dec 9, 2009, 07:35 PM
#1
Lowering springs and suspension travel. You ARE hitting the bumpstops.
This is going to be long and ugly. Sorry. 
A lot of people understand that you can't drop an EVO (or most cars) 2 inches and expect the car to handle well. You lose bump travel and suspension geometry goes to hell. These drops are mostly for show unless the car has coilovers designed for that drop and geometry correction kits/parts.
But I don't think a lot of people understand how limited bump travel really is on these cars and how close these cars are to the bumpstops at even stock ride height.
(remember you have the weight of the car on these, and a big honking rubber/foam bumpstop in there too taking up space. bump travel gets used up quick even before you hit a bump or the car starts rolling in a turn.)
A big thanks to Ludikraut and funks for helping me get these measurements again off their cars after my old laptop was stolen.
These are approximate numbers....not measured by me first hand but should be good. Also 1 inch of wheel travel is not exactly 1 inch of strut travel, but it's very close with a mcpherson strut.
Total stroke (bump + droop travel) is 155.6 mm or 6.125 inches.
Bump is 88.9 mm or 3.5 inches at stock ride height.
This is NOT including the bumpstop....which is about 2 or 2.5 inches long i think (anyone got an exact measurement? stupid moron that broke into my place has a LOT of useless info that probably doesn't make any sense).
So that means that (calling the bumpstop 2 inches), you have 1.5 inches of bump travel before hitting the bumpstop. And you are hitting them....1.5 inches of movement is not much.
What happens when you "hit" the bumpstop? You probably don't feel the initial impact to be honest. They're actually designed to be engaged. Spring rate progressively increases....more and more rapidly, which means understeer. You can end up pretty far into the bumpstop actually, and the spring rates just keeps going up and up and up....
On my MINI and on a few other cars, the car is essentially on the bumpstops at rest. This means that the second the wheel turns, the car rolls onto progressively stiffer bumpstops. So you get AWESOME turn in, quick reactions and good feeling transitions. Similar to an EVO or Subaru with a HUGE front sway bar....awesome at up to 7/10ths or auto-x situations where steady state cornering isn't quite as important.
But this sucks *** (layman's terms) at the limit or anything beyond 7/10ths, as the spring rate spikes to infinity up front, you get massive understeer. Good for engineers designing a sporty car to "feel" good to most people and yet still be safe from underwear ruining oversteer. My MINI in stock form was kinda crappy when pushed really hard, but a total blast the rest of the time. It also sucks when hitting bumps.
Back to the EVO.....1.5 inches (assuming a 2 inch bumpstop, it could be bigger) before the bumpstop is engaged is not THAT bad compared to some other cars. You are hitting it at times stock, but as I said it's gradual at first. True bottoming out is when you actually bottom out the shock, which is pretty darn harsh and that's what you're feeling on big potholes.
(a stock EVO....very much on the bumpstops in a corner. world is not ending, but the car could do better.)
Now drop the car more than 1.5 inches and you're on the bumpstops before the car starts moving. And every EVO I've seen with a spring that drops the car that much has understeered massively. Not only that, but bumps, whether it's curbing at the track, mid corner bumps, or simple bumps on the street....seriously upset the car.
Cutting the bumpstops is an option, but it does have it's drawbacks. They're progressive....so cutting them means the impact when you do hit them (which you will) is going to be more abrupt and probably not pleasant. You do need the bumpstops there for those times when you DO bottom out the damper (which is obviously more likely when you lower the car 1.5 inches).
Added spring rate helps to keep the car off the bumpstops a little more. And added rear rate helps keep the balance in check to an extent. This is why Swift springs are actually pretty decent when pushed (see SmikeEVO) and also why Swift Spec R's have ride quality that is not far off the Swift Sports....the Spec R's added spring rate at the same height means you're off the bumpstops a little more. But you're still on them, and you get on them fast.
Our GTWORX springs sometimes get crap because they only lower the car 20mm (about 3/4 inch) up front....and the cool "look" is more popular than better handling. Many people think we did it for ground clearance or suspension geometry....these were a concern but they were far behind maintaining bump travel. I wanted the suspension to be able to "work" and control the car with the springs as much as I could and avoid the super progressive bumpstops that ramp up super fast to inifinity lbs/in. Lowering the car just 20mm front and 15mm rear with a higher spring rate then Swifts means you are letting the dampers and springs "do their thing" as opposed to having the bumpstops come in and ruin the fun. It's more compliant and it handles better.
Good track suspensions are designed to avoid the bumpstops when possible....and to let the spring rate come from the spring. Better handling, better chassis control, more compliance.
Time for a beer. I had been meaning to post something like this for a while. Let me know your thoughts, observations, tell me i'm full of crap, questions, etc.
- Andrew
A lot of people understand that you can't drop an EVO (or most cars) 2 inches and expect the car to handle well. You lose bump travel and suspension geometry goes to hell. These drops are mostly for show unless the car has coilovers designed for that drop and geometry correction kits/parts.
But I don't think a lot of people understand how limited bump travel really is on these cars and how close these cars are to the bumpstops at even stock ride height.
(remember you have the weight of the car on these, and a big honking rubber/foam bumpstop in there too taking up space. bump travel gets used up quick even before you hit a bump or the car starts rolling in a turn.)
A big thanks to Ludikraut and funks for helping me get these measurements again off their cars after my old laptop was stolen.
These are approximate numbers....not measured by me first hand but should be good. Also 1 inch of wheel travel is not exactly 1 inch of strut travel, but it's very close with a mcpherson strut.
Total stroke (bump + droop travel) is 155.6 mm or 6.125 inches.
Bump is 88.9 mm or 3.5 inches at stock ride height.
This is NOT including the bumpstop....which is about 2 or 2.5 inches long i think (anyone got an exact measurement? stupid moron that broke into my place has a LOT of useless info that probably doesn't make any sense
). So that means that (calling the bumpstop 2 inches), you have 1.5 inches of bump travel before hitting the bumpstop. And you are hitting them....1.5 inches of movement is not much.
What happens when you "hit" the bumpstop? You probably don't feel the initial impact to be honest. They're actually designed to be engaged. Spring rate progressively increases....more and more rapidly, which means understeer. You can end up pretty far into the bumpstop actually, and the spring rates just keeps going up and up and up....
On my MINI and on a few other cars, the car is essentially on the bumpstops at rest. This means that the second the wheel turns, the car rolls onto progressively stiffer bumpstops. So you get AWESOME turn in, quick reactions and good feeling transitions. Similar to an EVO or Subaru with a HUGE front sway bar....awesome at up to 7/10ths or auto-x situations where steady state cornering isn't quite as important.
But this sucks *** (layman's terms) at the limit or anything beyond 7/10ths, as the spring rate spikes to infinity up front, you get massive understeer. Good for engineers designing a sporty car to "feel" good to most people and yet still be safe from underwear ruining oversteer. My MINI in stock form was kinda crappy when pushed really hard, but a total blast the rest of the time. It also sucks when hitting bumps.
Back to the EVO.....1.5 inches (assuming a 2 inch bumpstop, it could be bigger) before the bumpstop is engaged is not THAT bad compared to some other cars. You are hitting it at times stock, but as I said it's gradual at first. True bottoming out is when you actually bottom out the shock, which is pretty darn harsh and that's what you're feeling on big potholes.
(a stock EVO....very much on the bumpstops in a corner. world is not ending, but the car could do better.)
Now drop the car more than 1.5 inches and you're on the bumpstops before the car starts moving. And every EVO I've seen with a spring that drops the car that much has understeered massively. Not only that, but bumps, whether it's curbing at the track, mid corner bumps, or simple bumps on the street....seriously upset the car.
Cutting the bumpstops is an option, but it does have it's drawbacks. They're progressive....so cutting them means the impact when you do hit them (which you will) is going to be more abrupt and probably not pleasant. You do need the bumpstops there for those times when you DO bottom out the damper (which is obviously more likely when you lower the car 1.5 inches).
Added spring rate helps to keep the car off the bumpstops a little more. And added rear rate helps keep the balance in check to an extent. This is why Swift springs are actually pretty decent when pushed (see SmikeEVO) and also why Swift Spec R's have ride quality that is not far off the Swift Sports....the Spec R's added spring rate at the same height means you're off the bumpstops a little more. But you're still on them, and you get on them fast.
Our GTWORX springs sometimes get crap because they only lower the car 20mm (about 3/4 inch) up front....and the cool "look" is more popular than better handling. Many people think we did it for ground clearance or suspension geometry....these were a concern but they were far behind maintaining bump travel. I wanted the suspension to be able to "work" and control the car with the springs as much as I could and avoid the super progressive bumpstops that ramp up super fast to inifinity lbs/in. Lowering the car just 20mm front and 15mm rear with a higher spring rate then Swifts means you are letting the dampers and springs "do their thing" as opposed to having the bumpstops come in and ruin the fun. It's more compliant and it handles better.
Good track suspensions are designed to avoid the bumpstops when possible....and to let the spring rate come from the spring. Better handling, better chassis control, more compliance.
Time for a beer. I had been meaning to post something like this for a while. Let me know your thoughts, observations, tell me i'm full of crap, questions, etc.
- Andrew
Last edited by GTWORX.com; May 11, 2012 at 12:34 PM.
Dec 9, 2009, 08:53 PM
#3
^ nice pic!
there was a great article i read recently interviewing a Prodrive engineer about different car's handling "feel." How a Mini would feel awesome on the streets of Monaco, and a BMW M5 wouldn't be as great....but it would be reversed on the race track. both great cars with high limits, just the way they got there and what happens when you reach that limit. and talked about how they dialed these sorts of things into the car when working with manufacturers. of course i can't find the article or remember what mag it was.
there was a great article i read recently interviewing a Prodrive engineer about different car's handling "feel." How a Mini would feel awesome on the streets of Monaco, and a BMW M5 wouldn't be as great....but it would be reversed on the race track. both great cars with high limits, just the way they got there and what happens when you reach that limit. and talked about how they dialed these sorts of things into the car when working with manufacturers. of course i can't find the article or remember what mag it was.
Dec 9, 2009, 09:12 PM
#4
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This is why I am on the waiting list to purchase your GTWORX Springs. This information is great. This completly explains the engineering and purpose behind your product as well as others on the market in a clear way even a dunce like me can understand. I never knew they were this much information involving bumpstops and spring design. A+ job in educating the evo community. More write up's like this will make anyone a suspension guru
Dec 10, 2009, 04:48 AM
#5
^ nice pic!
there was a great article i read recently interviewing a Prodrive engineer about different car's handling "feel." How a Mini would feel awesome on the streets of Monaco, and a BMW M5 wouldn't be as great....but it would be reversed on the race track. both great cars with high limits, just the way they got there and what happens when you reach that limit. and talked about how they dialed these sorts of things into the car when working with manufacturers. of course i can't find the article or remember what mag it was.
there was a great article i read recently interviewing a Prodrive engineer about different car's handling "feel." How a Mini would feel awesome on the streets of Monaco, and a BMW M5 wouldn't be as great....but it would be reversed on the race track. both great cars with high limits, just the way they got there and what happens when you reach that limit. and talked about how they dialed these sorts of things into the car when working with manufacturers. of course i can't find the article or remember what mag it was.
Exactly. Focus is great to 7/10ths, like you mentioned, but once past that...she becomes one unhappy beast! Still fun to throw around the corners though
Funny side note, my SVTFs original owner...now has an M3
Trending Topics
Dec 13, 2009, 01:09 AM
#10
you mentioned in ur thread "These drops are mostly for show unless the car has coilovers designed for that drop and geometry correction kits/parts."
what coilovers fall into this category?? Where can u get that "look" but also "performance" too. Im trying to find that medium ground
what coilovers fall into this category?? Where can u get that "look" but also "performance" too. Im trying to find that medium ground
Dec 13, 2009, 02:41 PM
#11
thanks everyone....glad to see some people are reading it!
You need firm spring rates when you're dropped low and coilovers often have rates that are firm enough. But when you have firm rates, you need better damping or the car will be rough on the street and track.
Coilovers that adjust ride height separate from preload do not sacrifice bump travel when you lower it....but they generally don't have much travel to begin with so again you need those firm spring rates when going low.
Low and a smooth ride or good handling is difficult to do, but possible.
- andrew
you mentioned in ur thread "These drops are mostly for show unless the car has coilovers designed for that drop and geometry correction kits/parts."
what coilovers fall into this category?? Where can u get that "look" but also "performance" too. Im trying to find that medium ground
what coilovers fall into this category?? Where can u get that "look" but also "performance" too. Im trying to find that medium ground
Coilovers that adjust ride height separate from preload do not sacrifice bump travel when you lower it....but they generally don't have much travel to begin with so again you need those firm spring rates when going low.
Low and a smooth ride or good handling is difficult to do, but possible.
- andrew
Dec 13, 2009, 03:42 PM
#14
thanks everyone....glad to see some people are reading it!
You need firm spring rates when you're dropped low and coilovers often have rates that are firm enough. But when you have firm rates, you need better damping or the car will be rough on the street and track.
Coilovers that adjust ride height separate from preload do not sacrifice bump travel when you lower it....but they generally don't have much travel to begin with so again you need those firm spring rates when going low.
Low and a smooth ride or good handling is difficult to do, but possible.
- andrew
You need firm spring rates when you're dropped low and coilovers often have rates that are firm enough. But when you have firm rates, you need better damping or the car will be rough on the street and track.
Coilovers that adjust ride height separate from preload do not sacrifice bump travel when you lower it....but they generally don't have much travel to begin with so again you need those firm spring rates when going low.
Low and a smooth ride or good handling is difficult to do, but possible.
- andrew
I had a shop setup my preload on the Ohlins as well as ride height. Do you think if I raised the car about a 1/2in and messed with the preload some that I could get my back tires not to lift as much? I would much appreciate some suggestions.
Dec 13, 2009, 07:38 PM
#15
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When I got my second Evo, it already had junk Tanabe's GFwhatever's installed. I was having trouble choosing between Swifts (had Swift on my last Evo.. I loved them), GTWORX or RobiSpec's. I always knew why the springs GTWORX didn't drop much and I know for a fact that they are the best spring that you can get for an Evo. The Swifts did have a better look to them, so I wanted a compromise. I wanted a lower look, but didn't want to go as low as the Swifts again and didn't want to compromise performance. So I chose the RobiSpec springs and RSB. I just need some Bilstein's and a FSB then I should be pretty happy.
At times I look back and wish I had gotten the GTWORX springs. I'm trying to talk my dad into a set for his MR Anytime I recommend springs I always mention GTWORX first.
Very good read.
At times I look back and wish I had gotten the GTWORX springs. I'm trying to talk my dad into a set for his MR
Anytime I recommend springs I always mention GTWORX first.Very good read.
