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#1 bump stop timeing
junior01

Posts: 6
rating

08/22/2011 7:18 AM

I've got a Howe Ss car I race in the Midwest at a 3rd mile semibanked track 2750 lbs I have both fronts onbump stops and I here a lot of different ways to set them before you go to the track and I'm not sure which is correct last week the car was rolling over and i came to a conclusion that it wasn't getting on the right bump stop wondering if someone here can help. Also wondering how to set the sway bar some push them down to set and some people set them at ride heighto
 
#2  
Rock

Posts: 2590
rating

08/22/2011 3:16 PM

There is tons of info on this site about bump stops.
But I'll give you my quick reply.
Put in 4 175lb spring if on coil overs, if it's a big spring car then I would put in a pair of 400's in the front, a pair of 175's in the rear.
Now get the car race ready ride heights, all your bar angles, cam & cas, etc.
Take the front springs off/out put something under the cross member 1.1/4" to 1.1/2" thick set the car down on that, mark both front shock shafts with a sharpie at the shock body where the shaft would go in.
For the right side fill that amount of shaft to the line using 1 bump stop and the rest with spacers & shims/packers.
For the left side do the same thing except leave about a 1/2" of shaft before the marked line, in other words you will have a 1/2" of gap before the shock body.
If it is done correctly the car will not rollover at all.
Now the LR with the car race ready and the driver in the car fill the shock shaft with 1 bump stop, spacers & shims, (always use about a 1/2" of shims on all 3 shocks) but like the LF shock but leave about 1/4" to 3/8" of shaft showing.
To set the bar have 2 to 3 people push the car down and set the bar neutral and then preload the bar two turns.
I noticed you did not mention anything about the LR bump stop, in my opinion it is more important to bump stop the LR, if you had to choose between the front and rear, do the LR over the RF.
Rock
 
#3 Re:Bump setup
curtis7

Posts: 36
rating

08/22/2011 4:21 PM

Rock can you explain why you put 4 175s in car before
When you set the bumps. And do you put your regular springs in before you do the lr ?
And do you set the swaybar while we are holding it down? Or let it come up
Thanks Curtis
 
#4 Re:Bump setup
crewchief99

Posts: 162
rating

08/22/2011 6:38 PM

Curtis, with the setup he's recommending, the 4 175s are the regular springs. He's just talking about taking them out to get the car down to determine the bump stop and spacer height.
 
#5  
Rock

Posts: 2590
rating

08/22/2011 10:40 PM

crewchief99 is correct.
The 4 175's are the springs you will be running all the time.
The sway bar, yes set the bar to neutral when you are holding the car down and then put two turns of preload you can do that at the same time or after the car comes back up, always put in two turns of preload, do not use the bar to adjust the chassis. And do not change any springs to adjust the car.
Use the bump stops, rear roll center and cross to adjust the chassis, after you get the car dialed in then you will only need to use the bump stop packers to adjust the car, for a given day.
Rock
 
#6 Bump setup
curtis7

Posts: 36
rating

08/23/2011 3:39 AM

Hi Guys thanks so much for all the help!
How do you know what to adjust first? Cross, panard bar? I've learned on here that if your rrr is hottest and car is tight that the panard bar is to low? But what about other senarios, what if it is not yhe hottest and you are tight in middle? When would you adjust cross? Sorry for all the questions.

Curtis
 
#7  
junior01

Posts: 6
rating

08/23/2011 7:08 AM

Why do you put the 175 on the right rear. Also why is it so important to bump the lr I have before and it made me tight off is there something else that it does for you.do you run it ahead or behind the axle.
 
#8 Re:
Stage1

Posts: 157
rating

08/23/2011 7:42 AM

You are on the LR bump too quick if tight off. Thats why you shim it to tune.Reduce the bump height 1/16" at a time.
 
#9 Re:
Rock

Posts: 2590
rating

08/23/2011 10:18 PM

Quote posted by junior01:Why do you put the 175 on the right rear. Also why is it so important to bump the lr I have before and it made me tight off is there something else that it does for you.do you run it ahead or behind the axle.
The reason for the 175RR is so the car can come down and get on the LR bump stop and give you drive off, now if your car is tight off, and somebody answered this above, this is the reason I tell everybody to always use about a 1/2" of shims/packers so you have something to tune with, you needed to take shims out so it doesn't get on the bump stop to soon/hard because the LR bump stop adds cross weight, but you run mush less static cross so the car will turn in the center and then when you get on the throttle you get the cross and drive off.
The thing is it's not in stone you need 4-175's it could be 4-165's 4-185's etc. once you put in, lets just say 4-175's you will never have to change a spring to adjust your chassis because the bump stops do all the work for handling, before I started running bump stops I must have had almost a 100 springs, now they just sit on my shelf collecting dust.
I'm not sure what you mean about ahead or behind the axle, it's wherever your shock is mounted and the effect will be the same at either location.
Rock
 
#10 Re:Bump setup
Rock

Posts: 2590
rating

08/23/2011 10:40 PM

Quote posted by curtis7:Hi Guys thanks so much for all the help!
How do you know what to adjust first? Cross, panard bar? I've learned on here that if your rrr is hottest and car is tight that the panard bar is to low? But what about other senarios, what if it is not yhe hottest and you are tight in middle? When would you adjust cross? Sorry for all the questions.

Curtis

This is a very good question.
OK so at least you learned one thing on here, LOL
This is not that easy to explain, I'm assuming your not running bump stops.
Tire temps tell you everything about how the car is handling, but it's another tool you need to know how to use, it's like a tire pressure gage lets say you put the gage on one of your tires and it reads 18, now if you don't know
what that number means you would not know if you need more psi or less psi, just an example.
OK lets say the car is tight in the middle and your RF is the hottest tire, there would be several things you could adjust, my first choice would be to put in a smaller sway bar and preload it several turns maybe 4 to 6 turns, preloading a smaller sway bar will help the entry and exit and not hurt the center, a bigger sway bar will tighten up the complete corner.
You could also take out some cross to free up the center but normally that will free up the exit also, this is the reason to have very good tire temps,
you could also have a camber caster problem, it could also be a shock problem more RF compression will also help the car turn in the center, I'm out of ideas, I'm sure there are other things you could adjust.
Rock
 
#11 Re:
Rock

Posts: 2590
rating

08/23/2011 10:49 PM

Quote posted by junior01:Why do you put the 175 on the right rear. Also why is it so important to bump the lr I have before and it made me tight off is there something else that it does for you.do you run it ahead or behind the axle.
The problem you had is more then likely a problem everybody would want if they had a problem, it is by far the easiest problem to correct.
More often then not you would have a car tight in the middle and loose off a very difficult problem to fix without running bump stops.
Again this is just me.
Rock
 
#12  
junior01

Posts: 6
rating

08/24/2011 6:12 AM

Thank for the help I understand now what you are getting at.the other question I would have is I'm running around 58% cross now how much would you take out for a good starting point.
 
#13  
Rock

Posts: 2590
rating

08/24/2011 9:15 AM

I would start with around 50% static and then preload the sway bar 2 turns or more.
Rock
 
#14  
junior01

Posts: 6
rating

08/24/2011 12:16 PM

Thank you Rock you have been very helpful
 
#15 Re:
bigman21

Posts: 157
rating

08/24/2011 12:17 PM

Just out of curiosity what kind of rr shock travel are you seeing with this setup?
 
#16  
timothy29

Posts: 21
rating

08/24/2011 7:32 PM

i see you say 11 inch rear roll center, so is that 11 on both sides.
 
#17  
Rock

Posts: 2590
rating

08/24/2011 10:47 PM

It could be, the roll center is the middle of the two ends, 11" and 11" is 11" roll center,
12" and 10" is also 11" roll center, 13" and 9" is also 11" roll center, etc.
Remember the 11" roll center is just a starting point, only the tire temps can tell you where it ultimately should be.

 
#18 Re:
Rock

Posts: 2590
rating

08/24/2011 10:52 PM

Quote posted by bigman21:Just out of curiosity what kind of rr shock travel are you seeing with this setup?
Are you just asking a general question for everybody or is it aimed for someone
in particular.
Rock
 
#19 Re:
Rock

Posts: 2590
rating

08/24/2011 10:56 PM

Quote posted by bigman21:Just out of curiosity what kind of rr shock travel are you seeing with this setup?
Are you just asking a general question for everybody or is it aimed for someone
in particular.
Rock
 
#20 Rock
curtis7

Posts: 36
rating

08/25/2011 3:37 AM

Rock can you explain why you keep the crossmember up 1 1/4 to 1 1/2 off floor when setting up bumps. And not lower? Is it because of suspention travel? Or somthing else. Also why do you use 4 175 and not softer say 150s? I know there's a reason just curious.
Thanks for all the previous posts.
Curtis
 
#21  
bigman21

Posts: 157
rating

08/25/2011 4:11 AM

Rock I was directing towards you with 4 175 springs how much rr shock travel do you generally see?
 
#22 Re:Rock
Rock

Posts: 2590
rating

08/25/2011 11:14 PM

Quote posted by curtis7:Rock can you explain why you keep the crossmember up 1 1/4 to 1 1/2 off floor when setting up bumps. And not lower? Is it because of suspention travel? Or somthing else. Also why do you use 4 175 and not softer say 150s? I know there's a reason just curious.
Thanks for all the previous posts.
Curtis

I used to have people use, let say a 1X6 piece of wood because it's easy and most people have something like that laying around, but the problem was that a lot of people just don't really understand the concept of bump stops and would have problems with the chassis hitting the track, and some people just didn't know how to adjust for that, so it is just easier at least for me to have people start higher 2 piece of 1X6 wood or something like that will give you an 1.1/2" off the ground at your cross member.
There is a lot of flex in all the components dealing with this, tire flex, bump stop flex, chassis flex, etc.
You also have to keep in mind that most of the stuff I post about is more geared towards the less experienced racer so I try to keep things on the
conserved side, and once people get more conferable they can start trying different things to fit their needs, I don't want anybody to get discouraged so I try to get them something that will work right off, it may not be the best for everybody.
The 175's yes you can go softer, it has been my experience that if you go to soft that you will hit the the bump stop to hard and you have a chance of over loading the suspension, the 175's seem to smooth out the transition of getting onto the bump stop.
There is a range with everything you should try to stay within and that is more important with the beginner or less experienced with this type of setup.
I try to keep the transition of the bump stop setup less involved for most.
I'm not sure if this will help but I did my best, everybody does things in there own way and you just can't give one answer that will fit everybody's needs, I do a lot of guess work as it is on what I think people are trying to ask, or want to know.
Rock
 
#23 Re:
Rock

Posts: 2590
rating

08/25/2011 11:30 PM

Quote posted by bigman21:Rock I was directing towards you with 4 175 springs how much rr shock travel do you generally see?
You know I just don't worry about shock travel, but if I were to guess, it would not be a lot maybe around 1" to 2" again just guessing, it may only be a 1/2" don't know, it's not important at least to me, it's what ever it takes to win, everybody knows your not going to win every race but you at least want to have a shot at it.
We got closed to it so far this season, won 5 out of 7 races and the 2 we didn't win we were leading and got taken out by a lapped car, it's not alway if you have a winning car, you will also need a little luck, at least that's the way I see it.
I do all my adjustment based on tire temps the tires are the only thing that's on the track, and if all 4 tires aren't happy then you will have an ill handling car.
Rock
 
#24 Re:
Rock

Posts: 2590
rating

08/25/2011 11:55 PM

Quote posted by bigman21:Rock I was directing towards you with 4 175 springs how much rr shock travel do you generally see?
This has nothing to do with your post but I though it is worth talking about it could be giving some people problems, I have not though about this but somebody called me the other day and ask me about this and it is very very important, I talked about this a little the another day on a different topic,
but this topic on bump stops seem to be getting a lot of interest.
OK here it is.
If your running bump stop on the LR (nothing to do with the front bump stops) you need to run a solid upper third link, no spring or rubber biscuit style upper links, here's what happens with something other then a solid upper link as you get on the throttle the rear end wants to wrap up and that is pulling the shock open and getting off the LR bump stop and losing some cross.
There is no way for sure to know how much so you don't know how to adjust for it and even if you did know and you put in extra shims in to compensate for it you would be adding static cross and that could make the car tight on entry.
Just run a solid upper link and keep your life simple, there's enough things to chase as it is.
This is if the shocks are mounted behind the axle tube.
Rock
 
#25 Re:
bigman21

Posts: 157
rating

08/27/2011 5:28 AM

Rock do you run the same 175 springs at all tracks banked or flat? Reason I ask we are going to a really flat 1/3 mile track under 5 degrees and a lot of people run 150 and 125 on bumps stops do you think with the 175 you would get enough travel to make the front bumps effective.we are thinking if trying this setup and seeing if this track was a good place to try it!
 
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