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View Full Version : Bump stop question...


corsair23
11-01-2006, 11:25 PM
For those that know suspension setups better than I :)

Currently I'm running 35" BFGs but I will be dropping down to 33" MT/Rs in the near future. My front bump stops are 2", 3.5" overall with the bracket. By dropping down to 33" tires should I therefore increase or decrease my bump stop length? In my frazzled brain it makes sense that with a reduction in tire size I should decrease my overall bump stop length by about an inch or so, assuming I won't bottom out the shocks.

I ask because my PS bump stop is pretty well shot and needs to be replaced. I was just going to get the same size but then I started wondering...

TIA

Red_Chili
11-02-2006, 07:21 AM
Ideally, bumpstops are determined by things other than tire size, like the amount of reverse flex that is acceptable, tie rod/drag link clearance, etc. Nevertheless some folks use them to limit body contact (not the best rationale, but hey, whatever works). Which situation are you in?

nakman
11-02-2006, 08:58 AM
All things remaining constant, going to smaller tires would mean you need less bump stop. If their purpose is to prevent tire rubbing, like Red Chili said. If you aren't rubbing 35's, you shurely won't rub 33's.. IMO. only change the BS if you have more upward travel in your shocks, won't interfere other components, etc. otherwise keep them the same. :)

corsair23
11-02-2006, 12:49 PM
Thanks guys...

I am sad to admit that since buying the FJ40 last fall I have not had it out to test the flex. My assumption is that the bump stops are in place to prevent rubbing of the 35s (given it is SUA with only a mild lift) but the PO didn't do the work so he doesn't know for sure either. At this point in time my best course of action then will be to wait until I get the 33's on and can test out the flex and see what sort of travel the shocks have and go from there.

At my snail pace for getting stuff done I have plenty of time to figure out which way to go :)

nakman
11-02-2006, 01:02 PM
Here's an idea: put a zip tie or something on the metal shaft of each shock, then find a hill or loading dock or something to flex 'er out, until the opposite wheel is airborne... then see where your zip tie is. That should at least give you a rough idea of available shock travel, maybe have a buddy watch who can yell at you if you start to bottom out a shock.

There are really only a couple things that will limit your travel- your springs will stop flexing (and there's not enough weight to get them to arch further) or something smacks into something- like a tire on the fender, or axle on a bump stop, tie rod on a driveshaft, shock fully compressed, etc. find out what's limiting your travel, then worry if you need to limit it further.

corsair23
11-02-2006, 04:27 PM
Good advice Nakman...

My hope is that the 40 is setup well. The PPO owned it for years and ran the Rubicon in it many times. The PO bought it because he thought it was "cool" and he could use it to drive from his home in San Francisco to his home in Tahoe on the weekends. I think the cool factor wore off real quickly for him though after making the trip just once :)

I'm really not new to off roading, I've just been out of it for a long time and never gained the experience setting up my own rig really. I owned a built up black '82 Toy SR5 PU a long time ago and took that all over the place...Took a hiatus for about 15 years and now trying to get back into the fun :)