How much shock travel is enough before hitting bumpstop

[alcyon]

I just changed the rear shocks on my car . I couldn't get OEM bump stops for my car so I cut down a BMW e36 bumpstop from 110mm down to 65mm. I thought this was okay but when I installed the shock to my car, I did not check its rest height.Now I realize at rest height, the bump stops will hit at an eyeball measurement 30mm of shock travel. The car has not been lowered at all and i reused the stock springs, the ride height is standard.
It just seems to me 30mm of total travel is too little? Eyeball measurement of total travel the bumpstop is limiting is about 70mm, which is total end travel of the shaft, which we do not want.
Its possible to cut the bumpstop from the outside, so should I cut off another 15 to 20mm of the top of the bumpstop ?

 

[HangFire]

The anwer is "depends"... how much of the 65mm is usable? What is the spring rate and vehicle weight? Is the new stop the same compliance as OEM?

 

[Cujet]

Shock travel and wheel travel may be wildly different or exactly the same, depending on the mechanical setup. Struts travel the same as the wheel. Shocks mounted well inboard of the upright can move far less. Shocks on a live rear axle may or may not move as much as the axle, depending on shock angle.

At this point, I'd suggest that you try it and see. It's easy to tell when hitting the bump stop from the jarring ride. You can also look at the bump itself, as it will show signs of use.

A motocross bike may have 12 inches (30cm) wheel travel, but only 3 inches rear shock travel, and only 2 inches before it hits the bumper.

 

[alcyon]

Originally Posted by Cujet
Shock travel and wheel travel may be wildly different or exactly the same, depending on the mechanical setup. Struts travel the same as the wheel. Shocks mounted well inboard of the upright can move far less. Shocks on a live rear axle may or may not move as much as the axle, depending on shock angle.

At this point, I'd suggest that you try it and see. It's easy to tell when hitting the bump stop from the jarring ride. You can also look at the bump itself, as it will show signs of use.

A motocross bike may have 12 inches (30cm) wheel travel, but only 3 inches rear shock travel, and only 2 inches before it hits the bumper.


The reason I ask is because with the new rear shocks but same old original spring, I am now feeling a bit of a stiff ride, kinda jittery, like the damper is stiffer than the old one. I feel this when driving over non highway roads that have small imperfections and dips, I just wonder if perhaps I it is already hitting the bumpstops even though with no big dips. Body roll is also noticably less, again maybe because it already hit the bumpstop ?

 

[ctechbob]

Now this depends on the car, but. Some suspension designs factor in the bumpstop as part of the spring rate. Instead of just slamming into a hard stop, they will hit a nice progressive bumpstop, in effect a rising rate spring. People that swap them out or shorten them end up with a harsh ride because the car was meant in some part to ride on the stop.


NA/NB Miata's are known for this in the rear. People lower the car, and then cut the bumpstop to gain back travel and end up worse off. The solution for them is a higher spring perch and a progressive bumpstop that restores some of the travel and lessens the impact of hard suspension travel.

 

[alcyon]

Originally Posted by ctechbob
Now this depends on the car, but. Some suspension designs factor in the bumpstop as part of the spring rate. Instead of just slamming into a hard stop, they will hit a nice progressive bumpstop, in effect a rising rate spring. People that swap them out or shorten them end up with a harsh ride because the car was meant in some part to ride on the stop.


NA/NB Miata's are known for this in the rear. People lower the car, and then cut the bumpstop to gain back travel and end up worse off. The solution for them is a higher spring perch and a progressive bumpstop that restores some of the travel and lessens the impact of hard suspension travel.

Pretty sure a 1980s supra is not designed this way. And I was running the car for almost 3 years with a completely perished/evaporated into thin air rear bumpstop, it actually rode quite well except for lots of body roll in hard corners, and some rubbing noises when both rear shocks rebound to to ride height after going over a large road hump.Strangely the old shocks doesnt make any noise when cornering hard.