Bump stops

[Havoc5]

I'm new to using these and the series I run basically only allow a 1/2 inch rubber. To clarify this is a modified are running but I thought I'd get better answers here. We went to a 400lb rf spring and driver said he couldn't get off the corner. We were running a 3-12 shock and I don't know if we need more rebound to stay into the bump or less with a softer spring. Does anyone have any starting recommendations with these?

[Keepittacky]

More spring. We run a 600 rf. 1/2 material won’t do much. It’s a limiter not a typical bump stop.

[Matt49]

The first thing you need to know is whether or not you're getting on the bump at all in the first place. So you need a travel indicator for starters.

[ZERO25]

The first thing you need to know is whether or not you're getting on the bump at all in the first place. So you need a travel indicator for starters.

Then, he could possibly lower the upper shock mount to use a bump like its meant to!

[Havoc5]

I agree it isn't much material but essentially shouldn't it work the same? According to the indicator we were on the bump but I guess my question is can you create more drive with rebound in the shock holding it in the bump?

[RaceEngineer]

I agree it isn't much material but essentially shouldn't it work the same? According to the indicator we were on the bump but I guess my question is can you create more drive with rebound in the shock holding it in the bump?

"Drive" as you describe it, is dynamic wedge. It comes from the LR pushing against the RF, or weight transfer from front to rear upon acceleration. Trying to hold the car on a really short bump is nearly impossible in practice and not how it works anyway.

[Austin34471]

Then, he could possibly lower the upper shock mount to use a bump like its meant to!

Or.. if you don’t like chopping up your frame and welding on new mounts.. you could add some packers!

[Havoc5]

Race engineer- it won't allow me to quote but relating to your response how would it be any different from running a coil bind set up? Wouldn't the two work fairly similar but the bump obviously won't go completely solid? I could be wrong but I'm just trying to figure out how to utilize it better

[CCHIEF]

Yeah, that would only serve for overtravel safety, I see no way to get enough compliance from it.But someone may have figured a way to Make good use of it.Non coilover.....I got no clue what to do. Chuck it up in a crusher and see how much it increases load, based on travel the shock will see?

[billetbirdcage]

1. Since your only allowed a 1/2" bumpstop, then you should be using an Apollo style bump and probably the 15 degree under washer (10 degree at least) to give it more compliance.

2. Assuming you had a 1/2 bump of some sort there before you softened the RF spring and it was at least at some point getting on it, then YES loosing drive off the corner is exactly what I'd expect. (also assuming you have the same 1/2" bump and packer/exposed shaft length)

[ZERO25]

He could get really slick with the lower mount and make one using the replaceable slugs, which would hide it from his competitors.

[riddle28]

add some turns to the right front jack screw and tune with that, works decent in a mod with a softer rf esp since youve got such a tie down shock

[RaceEngineer]

Race engineer- it won't allow me to quote but relating to your response how would it be any different from running a coil bind set up? Wouldn't the two work fairly similar but the bump obviously won't go completely solid? I could be wrong but I'm just trying to figure out how to utilize it better

Billet explained much better than I. You can't generate load until you compress the bump if your spring is weak.

[Havoc5]

Is there a point where a softer spring should end up creating more drive? Assuming it allows the car to get into the bump harder? My thinking is the bump would gain rate quickly which would tighten off the corner. Taking it to an extreme say I put a 200 in the rf it should fall into the bump to wedge up instead of relying on spring pressure. I could be way out in left field here

[riddle28]

say its a 5 lb spring with your bump, just because its laid over and looks cool doesnt make drive. youll hit that small bump so fast itll sheer traction on that small tire

[Matt49]

Is there a point where a softer spring should end up creating more drive? Assuming it allows the car to get into the bump harder?

Kinda. But you have to be able to keep it there. As soon as you unload off the bump, your dynamic wedge falls off a cliff. And to billet's point, that's where "forward bite" is coming from.

[Havoc5]

Kinda. But you have to be able to keep it there. As soon as you unload off the bump, your dynamic wedge falls off a cliff. And to billet's point, that's where "forward bite" is coming from.

In that sense couldn't you tie the corner down harder with rebound to keep it from coming off

[95shaw]

Or just remove a bunch of cross, so spring doesn't try to hold the car up.

Lots of ways to skin the cat.

Just need to end up with the correct balance of traction to minimize time for the 360 degree turn that is 1 lap.
Thhen repeat until you see checkers. Lol

[fastford]

say its a 5 lb spring with your bump, just because its laid over and looks cool doesnt make drive. youll hit that small bump so fast itll sheer traction on that small tire

it has a lot to do with left rear bar angles , the thrust load against that bump stop will keep drive in the left rear , the trick for me when i started with the bump was to get just enough dynamic rear steer to stay just below a throttle push , or the sweet spot , it was amazing what moving the upper bar up one hole did........

[Matt49]

it has a lot to do with left rear bar angles , the thrust load against that bump stop will keep drive in the left rear , the trick for me when i started with the bump was to get just enough dynamic rear steer to stay just below a throttle push , or the sweet spot , it was amazing what moving the upper bar up one hole did........

Watching the touring guys it appears that all of them are basically on the verge of a throttle push when they launch really hard off the corner. Especially if they happen to under-rotate the entry. Of course they are very good at driving around that (so to speak) without lighting the rear tires up...probably one of the most common driving mistakes that cost you on the stop watch.