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Lowering springs and suspension travel. You ARE hitting the bumpstops.

11343 Views 7 Replies 7 Participants Last post by  Litespeed08
Taken from the EVOM Forum, just something to think about before you lower your car. Make sure you get higher rate springs or a spring/shock combo engineered together so you do not have any bump-stop issues.


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.)

I measured bump and droop travel back when we designed our GTWORX lowering springs, but unfortunately lost all that data when my laptop was stolen last year.

A big thanks to Ludikraut and funks for helping me get these measurements again off their cars.

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 ass (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 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).

Swift springs lower the car 1.4 inches, which is more than I'm personally comfortable with....BUT they do add a some amount of spring rate over stock so even though you have a tenth of an inch or so before the bumpstop (need to double check that length), the added spring rate helps to keep the car off the bumpstops a little more. And the added rear rate helps keep the balance in check to an extent. This is why they 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
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STI's and EVO's are known for this issue. Plus the TSX has a totally different suspension than both those cars. As long as you cut the bump stops in half, with any spring, you will never have a problem unless the shock is blown. In addition, STI suspensions are engineered to incorporate the bump stops in the suspension travel to benefit the handling like progressive springs.
^ exactly. not only that, but cutting bump stops is not exact science. some springs are engineered with this in mind and the instructions will specifically say DONT CUT or CUT ONLY REARS etc.
just remember if your using stock struts or even aftermarket, if the springs lower the car beyond its specd range of movement, you will severely cut the life of your struts
This applies to most cars, cutting the Bump stops makes things worse since you remove the progressive nature of bump stops so you go from soft to Hard this means Snap oversteer! Watch this!
So does cutting bump stops alone, essentially lower a vehicle regardless of springs being used, stock or aftermarket?
Lowering springs and suspension travel can affect your vehicle's performance in various ways, but it's important to ensure that your car's modifications comply with legal requirements. If you're a car enthusiast and want to modify your car's suspension, make sure you have the appropriate licensing such as a freelance license in Dubai. Lowering springs can provide a sleek and aggressive look to your vehicle, but can also affect the suspension travel causing it to hit the bumpstops. It's important to take into account the type of driving you'll be doing and consider the impact of the modifications on your car's handling and safety.
To answer your question, cutting bump stops does not lower a stock car. They provide some cushioning so that when a car compresses to it's lower limit there is reduced harshness on impact. When you hit a bump too hard and your car's suspension compresses all the way down, the bump stops prevent metal on metal impact.
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