The Mustang Forum for Track & Racing Enthusiasts

Taking your Mustang to an open track/HPDE event for the first time? Do you race competitively? This forum is for you! Log in to remove most ads.

  • Welcome to the Ford Mustang forum built for owners of the Mustang GT350, BOSS 302, GT500, and all other S550, S197, SN95, Fox Body and older Mustangs set up for open track days, road racing, and/or autocross. Join our forum, interact with others, share your build, and help us strengthen this community!

Min Bump Travel Recommendations

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

17
10
Exp. Type
HPDE
Exp. Level
3-5 Years
FL
Setting up my suspension for track and some street use and wonder what others are running for bump travel (static ride height to full compression travel). I have about 1.45" of bump travel in the front before it gets into the jounce bump stop pretty hard (shorty FP jounce bumper).

Using the Ford Performance struts and BMR handling springs (250 lbs/in spring rate). My calculations show this will lower the front by a little less than 1", which is consistent with what BMR states. So that is my starting point for the bump travel.

I was doing some checks last night w/o the spring installed and measured 1.45" of bump travel. Seems low to me ... but wanted to get some input from more experienced track guys. Thoughts? Thanks in advance for your help.
 
6,363
8,188
I would not overthink the bump travel issue, whatever you do, it will affect toe, and rarely does the car bounce up and down in a straight line, even braking on turn in is dynamic in that it loads the car differently at all 4 corners. You can raise and lower the car on a chassis plate, to check the bump, and there are things like the extensions to the tie rod ends that can help with that, but ultimately, you are going to pick a toe in setting and live with it. The S197s used tons of ground clearance and tons of spring travel to handle, the S550s, not so much, (I think the GT4 cars only have about 3 inches of travel, tops) and more and more cars are designed to "ride the bump stops" during cornering these days. As an example, in the LMP classes, between the 2 inches of suspension travel, and the cars riding the bumps, shock development has completely stalled.
I tired finding a pic af a late model stock car as an example, but the left front on those is cambered out at the top so the tire looks like it has about 30 degrees of positive camber, but in cornering the tire rolls across the pavement using all of its' surface area until it lays against the bumps, in the center of the corner. So those guys set their toe at full chassis load, which is still somewhat of a guess.
 
77
56
Exp. Type
HPDE
Exp. Level
Under 3 Years
TX
3-4" of travel is the ideal number you want. So I wouldn't say 1.45" is low, maybe below avg. You can always use a more progressive rubber, or an even smaller bump rubber in general.
 
17
10
Exp. Type
HPDE
Exp. Level
3-5 Years
FL
I would not overthink the bump travel issue, whatever you do, it will affect toe, and rarely does the car bounce up and down in a straight line, even braking on turn in is dynamic in that it loads the car differently at all 4 corners. You can raise and lower the car on a chassis plate, to check the bump, and there are things like the extensions to the tie rod ends that can help with that, but ultimately, you are going to pick a toe in setting and live with it. The S197s used tons of ground clearance and tons of spring travel to handle, the S550s, not so much, (I think the GT4 cars only have about 3 inches of travel, tops) and more and more cars are designed to "ride the bump stops" during cornering these days. As an example, in the LMP classes, between the 2 inches of suspension travel, and the cars riding the bumps, shock development has completely stalled.
I tired finding a pic af a late model stock car as an example, but the left front on those is cambered out at the top so the tire looks like it has about 30 degrees of positive camber, but in cornering the tire rolls across the pavement using all of its' surface area until it lays against the bumps, in the center of the corner. So those guys set their toe at full chassis load, which is still somewhat of a guess.
Thanks for sharing your experience. Interesting that manufacturers are engaging the bump stops that intensely. I guess they don't worry about controlling or specifying a roll stiffness once travel exceeds a certain amount. I haven't figured out the bump steer yet. Need to make a gauge and don't want to slow done too much right now.

At this point, I will take your advice and not worry about the ~1.5'" of bump travel too much. Thanks. Looking at the OEM PP1 strut, it has 2" less overall strut travel as compared to the Ford Perf strut (3" vs. 5") . See attached photo for illustration. I had no idea there was this difference between the struts. So guaranteed the track events I have run to date with the OEM PP1 struts have engaged the bump stops (jounce rubber) hard. So should be no worse with the Upgrade Ford Performance struts (although I will est the OEM bump travel and compare).

The FP struts are now installed w/ the BMR front springs. Can dropped 0.8 - 1.0" depending on where I measure (before/after). The distance from the fender lip to center of the hub is 14.5" (ave left/right) ... ie. not that low. I believe the real serious track guys run 13.75", but not 100% sure of that. Thoughts? The right side sits higher by about 3/16", so to level it, I would need to add a shim plate to the left side. Note that the right side was higher w/ all the stock OEM PP1 parts as well. Wonder if this is by design or just manufacturing tolerances. Thoughts?

I measured the camber change as a function of suspension travel. Also have the angle of the lower control arm (lateral link) and tie rod, so all 3 angles vs. travel. Need to clean-up the data a bit but will post it when it's clean. It's interesting. Definitely more camber change than I expected for a strut design. Thanks for the input guys. Cheers.

PP1 vs FP Struts.jpg
 

TMO Supporting Vendors

Top