Bump stops seem to confuse alot of people. I feel most forget about the Stop part of bump stop. If your frame or crossmember is in the dirt, nothing else will matter at that point and you will need to add packers until you are out of the dirt but you don't want to race at that number, let's day 3000, because the only compliance left in your suspention is the sidewall of the tire. I like an "All In" number. Spring load and bump load at Dynamic. Let's say 1500 on the spring and 400 on the bump to shoot for. The bump will spike from there to keep you out of the dirt but if you can hover at that sweet spot , 1/4 above when the bump spikes solid, you still have compliance for the RF to work against the LR to add traction. The videos are great Jay, I appreciate all the effort you put into them to help people.
Thanks for your response, this is correct and in today's market, I think we are seeing the bump used more as a stop than a load. Understanding how it makes load is what is hard to understand for most people. Very we said and thanks for your input.
Great question and I will answer it in both directions. What I mean for those not aware of what you are talking about. You can use your shock to stop the up travel in the shock by preloading your spring against it. This allows you to run a softer spring with load without having your car above ride height and I think this works very well. As always it sucks in the rough because it is not enough spring to manage the rough, also not legal in most scansion anymore. The 2nd option is to bottom out your shock and use it for a bump stop. This will work to a degree and better when you have softer springs, but you will hear me say this is bad. I am not a fan of bottoming out or “coil-binding” a setup on dirt as I think it is going to shear traction on the tire. It all depends on the grip level of the track. So, like one and not the other.
When knowing your bump load, where should the car be "racing" at in the bump curve? Let's say you wanna be at your dynamic state at 4" of travel. How far into the bump should you be at full compression? And to clarify, full compression isn't bottoming out, but where you want to be racing dynamicly.
Okay, we will go with what we know in this case and make up some stuff too. RF shock travel is 4” which is our desired down number in inches or dynamic position. At 4” we want 3000 lbs. load number, and we are using a foam bump (speedthan soft), we want our travel to be as light as it can be as it travels down and then makes the most load it can, or the load we are looking for, in this case, 3000 pounds. So here is what that would look like, load on spring at ride height (650), spring rate 500 pounds, on a Chevelle lower control arm standard length. • Ride height (650) • 1” (870) • 2” (1090) • 2.375 top of bump (1172) • 3” (1310) (75lbs) = (1385) • 3.9” (1508) + (650) = (2158) • 4” (1530) + (1500) = (3030) total load This is based on a couple of things that are going to change in real life, so you need to do this to test it on your car. 1st we are using a 220 pound per inch spring rate gain and a 650-load number. 2nd the Chevelle arm gains a lot of number in the last inch of travel, and it may change from car to car. Hope this helps thanks
@jaynealgofast , yes, it does. Another question is, like above, if we want to hit 3000 at 4" and to get that, we need to be at the top of bump at 2.375. But let's say we soften the bump, with your top of bump being at the same 2.375 and you'll turn spring rate in the car to get the 3000 load at 4", but you could lower the upper shock mount so top of bump is 2.25 or whatever that number is to get 3000 lbs at 4". I'm guessing that decision is based on issues on track and if you need a more or less progressive load graph?
Yes, this is true, a bump rubber (foam style) is very progressive and is ideal for what you want in a race platform. I have used springs in the past with great success under certain conditions, but for the most part the bump foam in a cup is really good.
I wish someone would explain how the laws of physics work on a hydraulic device with a bump on the outside vs a bump on the inside. All I can come up with is one is a load device and one is a stop device.
Bump stops seem to confuse alot of people. I feel most forget about the Stop part of bump stop. If your frame or crossmember is in the dirt, nothing else will matter at that point and you will need to add packers until you are out of the dirt but you don't want to race at that number, let's day 3000, because the only compliance left in your suspention is the sidewall of the tire. I like an "All In" number. Spring load and bump load at Dynamic. Let's say 1500 on the spring and 400 on the bump to shoot for. The bump will spike from there to keep you out of the dirt but if you can hover at that sweet spot , 1/4 above when the bump spikes solid, you still have compliance for the RF to work against the LR to add traction. The videos are great Jay, I appreciate all the effort you put into them to help people.
Thanks for your response, this is correct and in today's market, I think we are seeing the bump used more as a stop than a load. Understanding how it makes load is what is hard to understand for most people. Very we said and thanks for your input.
Good stuff Jay thank you.
Thanks a ton.
Great video as always, what is your opinion on the guys in imca using the shock to limit travel on the right front?
Great question and I will answer it in both directions. What I mean for those not aware of what you are talking about. You can use your shock to stop the up travel in the shock by preloading your spring against it. This allows you to run a softer spring with load without having your car above ride height and I think this works very well. As always it sucks in the rough because it is not enough spring to manage the rough, also not legal in most scansion anymore. The 2nd option is to bottom out your shock and use it for a bump stop. This will work to a degree and better when you have softer springs, but you will hear me say this is bad. I am not a fan of bottoming out or “coil-binding” a setup on dirt as I think it is going to shear traction on the tire. It all depends on the grip level of the track. So, like one and not the other.
When knowing your bump load, where should the car be "racing" at in the bump curve? Let's say you wanna be at your dynamic state at 4" of travel. How far into the bump should you be at full compression? And to clarify, full compression isn't bottoming out, but where you want to be racing dynamicly.
Okay, we will go with what we know in this case and make up some stuff too. RF shock travel is 4” which is our desired down number in inches or dynamic position. At 4” we want 3000 lbs. load number, and we are using a foam bump (speedthan soft), we want our travel to be as light as it can be as it travels down and then makes the most load it can, or the load we are looking for, in this case, 3000 pounds. So here is what that would look like, load on spring at ride height (650), spring rate 500 pounds, on a Chevelle lower control arm standard length.
• Ride height (650)
• 1” (870)
• 2” (1090)
• 2.375 top of bump (1172)
• 3” (1310) (75lbs) = (1385)
• 3.9” (1508) + (650) = (2158)
• 4” (1530) + (1500) = (3030) total load
This is based on a couple of things that are going to change in real life, so you need to do this to test it on your car. 1st we are using a 220 pound per inch spring rate gain and a 650-load number. 2nd the Chevelle arm gains a lot of number in the last inch of travel, and it may change from car to car. Hope this helps thanks
@jaynealgofast , yes, it does. Another question is, like above, if we want to hit 3000 at 4" and to get that, we need to be at the top of bump at 2.375. But let's say we soften the bump, with your top of bump being at the same 2.375 and you'll turn spring rate in the car to get the 3000 load at 4", but you could lower the upper shock mount so top of bump is 2.25 or whatever that number is to get 3000 lbs at 4". I'm guessing that decision is based on issues on track and if you need a more or less progressive load graph?
Jay,is it true,bump rubbers don't try and unload themselves when compressed vs a bump spring tries to unload as soon as its compressed?
Yes, this is true, a bump rubber (foam style) is very progressive and is ideal for what you want in a race platform. I have used springs in the past with great success under certain conditions, but for the most part the bump foam in a cup is really good.
shock that over travels and destroys the bump stop which adjustment is needed comp or rebound?
It would be compression, but the real factor could be in the spring rate of the car.
Crusa street stocks outlawed bumps, any suggestions on getting the same effect without actually having a bump in place?
Buy shocks with the bumps inside or chain right side at ride height then crank preload into rr and rf
I wish someone would explain how the laws of physics work on a hydraulic device with a bump on the outside vs a bump on the inside. All I can come up with is one is a load device and one is a stop device.