Bump springs

[Mr.Kennedy777]

I ran bump springs before I ran bump stops and my experience was this: Running bump springs you get an instant jump to a higher cross setup when it contacts the bump spring in the first corner. They are also a little harder to control with the shock rebound than a bump stop in my experience. I ended up rebuilding my shock on the RF about half a dozen times before I was happy with corner exit. It would tighten up in the middle, but I would lose drive on exit super early as it would lift off the bump to soon. At least I think I didn't have strong enough rebound control and it kept lifting off the bump spring too early. I ended up needed a really really heavy valve stack inside the shock to keep the corner down on the bump spring long enough to gain drive on exit. Once I had it figured out it was great. The nice thing is they come in so many different rates and usually leave you decent amount of room for going over ruts and bumps on the track before you bind. Biggest things are having a ball park idea of how much loading your cornering forces create so that you can select the right combination of ride spring and bump spring rate, how much clearance you have when you get on the bump spring (they're usually 2"-2.5" so usually have decent clearance), and rebound speed to keep the corner on the bump spring when you exit the corner lol. Running bump stops I really really liked when the track was smooth, I never ran them on a rough track but if the track is smooth they are waaaaay better than bump springs IMO. The reason I like them is that they tend to give you a more progressive feel, the harder the car gets on the bump the tighter it gets which is something I really liked in the middle, it felt like I could drive the car a harder in without it busting loose or sliding. It was really nice when changing my line to the inside when the cushion got used up, I was able to move down and run the low line and not worry about the back end sliding out at the apex. At this point I had already found a shock valve stack that worked for the bump spring and used it on the bump stop. So here's my two cents on bump springs and bump stops. Bump springs I feel are better on hooked up fast tracks and I think work better running the car down on the bump for the entire race. Once it engages running a shock that is strong enough to keep it down on the bump helps load the RF tire contact patch sooner coming in. Usually need to run a much stiffer RR spring to keep the car neutral in the middle. Biggest benefit in my eyes is the aero platform, lower front, limited camber change, and increased LR loading when utilized properly. Bump stops are better on a dry smooth surface, when it helps to have the car become tighter as you get deeper into the corner or drive the car harder in. They don't need quite as much rebound control because they are progressive, usually helps to have a slightly stiffer ride spring in my experience. I guess it does depend on the type of bump you run. Some load like crazy and some are relatively soft. I think for dirt it's best to run softer bumps with somewhat stiffer ride springs to avoid spiking the load on the tires unless the track is like really really fast and really smooth, then I'd run super soft ride spring with a small stiff bump and lots of gap. That's just me though and I'm sure there are varying opinions on this.

[fastford]

very good analysis Mr Kennedy, ive never ran a bump spring, but in the conditions you described using one, i use the 2 stage set up. I was concerned about the little spring coil binding. I was wandering about stacking to real stiff ones together to get the rate i want, but dont think theres room without going with a longer shock, have you tried this?

[Mr.Kennedy777]

I haven't no. What rate are you looking for?

[fastford]

im on 500 when i hit the lock out on 2 stage, thats what i was thinking about two 1000s because i think a single 500 spring might coil bind. I will say the only reason i was thinking about this is to reduce the weight of the 2 stage which i only run on a heavy and or rough track,

[Mr.Kennedy777]

The only issue with that is your bump spring setup doesn't lock out the ride spring. So if you had for example a 300 ride spring and a 850 bump spring, your final rate would be 1150. If you wanted 500 for a final number, you'd have to run a really soft ride spring, like a 225 ride spring and then two 550 bump springs (for a final rate of 275 for bump springs). Which to me is kinda crazy. You would need enough room in the 225 spring to take up enough rate to avoid binding the 2 550 springs that have a combined 2.2" travel taking up 4.5"+ caps and a coupler, so let's just say 5". I'm not sure how much travel your RF has, but to make sense of that application let's just for instance say, you had 2400 lbs of force in a corner, with 7" of shock travel, and pre-load of let's say 500#.. your ride spring would take up 2" of travel before it got on the bump springs, so 550# plus 500# of force, that's 1050#. There is a remaining 1350# of force that needs to be taken up by the combined rate of the bump springs and ride springs, which would require an additional 2.5" of travel, and leave you with nothing before bind. It could be made to work eventually but is it really that much lighter to run a taller shock with a taller spring with different mounting points now to increase available shock travel to accommodate these tall bump springs? It would be a lot of work and then here is the next step... is that 2" before the bump springs going to be enough room for you to achieve the transition of handling at the right part in the turn? I mean you could play with your compression speed I guess.

[Mr.Kennedy777]

I had to edit that.. I'm tired and my math sucked lol!

[fastford]

my 2 stage set up is 2 500# springs, which is a 250# rate until it reaches the lock out, then it goes to the full 500# rate, this is what i would want to achieve with the bump spring , keep in mind this is for a heavy rough condition. in the smooth slick im on a medium cone bump stop and a single spring between 175 and 225 # . I realize the need for more clearance but you could use a 9" shock instead of a 7" and travel should not be affected. I doubt i will ever try this because we stay on the bump most of the time, just thinking out loud and wandering if this could take advantage of both set ups combined into one......

[Mr.Kennedy777]

you mean like a three stage spring?

[fastford]

no, at static height, your just on the primary and at your desired travel you hit the bump, but on a rough track you have more travel than being on a rubber bump or just one short bump spring , like i said i think this could combine the advantages of both type set ups( bump stop and 2 stage) into one. I know there is probably some one on here reading this with more experience than me so maybe we can get some useful input. To me this is the best part about 4M because i have gained a lot of knowledge from here.

[Mr.Kennedy777]

Have you ever ran the dual stage on the RR as a digressive stack? I am wondering how well that works out. You would think it would be a nice way to tune entry and exit just wasn't sure how touchy the adjustments are.

[zeroracing]

Mr. Kennedy, I think this is an interesting thought, digressive type spring set ups on any wheel honestly. I think the issue you may run into on some cars if bottoming the RR tire into the deck or birdcage into the frame rail with a real soft spring once it compresses down. This is an issue we have ran into with some cars, that we get the wheel rate we want, but run out of travel when we hit a bump.

[fastford]

Have you ever ran the dual stage on the RR as a digressive stack? I am wondering how well that works out. You would think it would be a nice way to tune entry and exit just wasn't sure how touchy the adjustments are.

no, but i would think you could control the dynamic load on that tire better, might be touchy on dry slick though.

[Mr.Kennedy777]

I was thinking also on the topic of bump devices. And the bump washers. On the LR corner when it hiked up a lot of the loading is being supported by the bars. Would it be beneficial to use some sort of bump device built into the rod itself, either at the chassis mount or on the birdcage. I was thinking something like a pull bar design, but much smaller, having the heim end cut and welded onto a plate with four bolts, and two other plates in the system... the bolts pass through one plate so that it can slide separating two stacks of the washers and the last plate is secured with the nuts on the other end of the bolts. The bar is connected to the threads and the threads pass through the last plate into the second plate allowing you to pre load the bottom section. One side pre loaded to near full compression and the other side semi pre loaded for a bit of give when it gets up on the bars. We aren't talking a whole lot of travel, maybe 0.25" or so, either way. I was thinking this could help the tire out a little bit at least. Any thoughts??

[MasterSbilt_Racer]

I was thinking also on the topic of bump devices. And the bump washers. On the LR corner when it hiked up a lot of the loading is being supported by the bars. Would it be beneficial to use some sort of bump device built into the rod itself, either at the chassis mount or on the birdcage. I was thinking something like a pull bar design, but much smaller, having the heim end cut and welded onto a plate with four bolts, and two other plates in the system... the bolts pass through one plate so that it can slide separating two stacks of the washers and the last plate is secured with the nuts on the other end of the bolts. The bar is connected to the threads and the threads pass through the last plate into the second plate allowing you to pre load the bottom section. One side pre loaded to near full compression and the other side semi pre loaded for a bit of give when it gets up on the bars. We aren't talking a whole lot of travel, maybe 0.25" or so, either way. I was thinking this could help the tire out a little bit at least. Any thoughts??

That ain't legal... Lol

[Mr.Kennedy777]

Why did they make it so that you can't cushion the LR through either the rod or the birdcage assembly? Is it a possibile safety issue or what is it? Scared of trying new things? If we're talking unfair advantage this piece would cost maybe 200 to make at home lol.