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  • steronz

    June 3, 2011 1:33 p.m. steronz New Reader

    I'm still relatively new to car setup, but my understanding from the Honda world has always been that bump stops are there to protect the shocks from damage, and that's about it. When lowering a car, you're supposed to get stiffer springs, cut the bump stops, and not go too low; the idea of course is to avoid the bump stops at all costs and let the suspension do it's thing.

    Well, today someone introduced me to this company called Fat Cat and the concept of bump stops as a suspension component. Apparently some cars are constantly corning on the bump stops by design. This sounds crazy to me, but there's enough activity about bump stop design over on miata.net that I can't help but realize there must be some truth to this.

    Set me straight. Is this something unique to certain cars? Or have Honda people been doing it wrong all these years by cutting the bump stops in half?

  • oldtin

    June 3, 2011 2:04 p.m. oldtin Dork

    Quite a few bump stops serve as an end-of-the-line, progressive rate spring. Having axles come to a hard stop on a chassis rail can make for some nasty handling traits often involving off road excursions.

  • steronz

    June 3, 2011 2:10 p.m. steronz New Reader

    True, I suppose they can protect more than just the shock bodies. By "end of the line," though, do you mean the suspension has exceeded it's "normal" range of travel, or that you're just hammering it around the oak tree at VIR?

  • oldtin

    June 3, 2011 2:25 p.m. oldtin Dork

    Kind of a suspension designer's choice how it acts, but if you are on the bump stops you are pretty much past normal travel and probably closing in on 10/10th of the suspension parameters - perhaps grip exceeding suspension. They are a good solution to reaching the end of suspension travel as opposed to a hard stop. When there is flex or progressiveness, it is by default part of the suspension. If you can't max out your suspension, you need more grip or to optimize the geometry.

    If you think of the rubber suspended classic mini - basically four bumpstops served as progressive springs.

  • stafford1500

    June 3, 2011 2:47 p.m. stafford1500 New Reader

    Steronz: If you plan for engaging bump stops you should make the trasition from the spring to the bumpstop a smooth as possible. Generally, tapered bump stops are more 'progressive' in there spring rate than constant sections. If you simply cut the bump stops off to make clearance, the wheel rate of the spring before bump stop contact to after will be a very steep increase. There is a ton of work done to shape the bump stops used in numerous forms of motorsports. Unfortunately most of that work is not available to the public... If I had to modify the bump stops of a production based car, I would try to use the top end (first engagement) and modify the trimmed bottom to connect back to the stock location. Basically this allows the suspension to travel further, but keeps the same engagement 'progressiveness'.

  • erohslc

    June 3, 2011 5:51 p.m. erohslc Reader

    The factory racing prep manual for Nissan 1600/2000 roadsters featured different bump stop trimming profiles for fine tuning the suspension ;) I still have that thing somewhere. For Sebring (1973?), we had lined up a car, an ex-works motor from the factory, tires, some gas money, and race sponsorship from 'Big Daddy's Lounge'. Unfortunately, the car and trailer were stolen in North Miami Beach when a flat trailer tire forced us to leave the rig on the side of the road for 30 minutes to fetch a spare. When we returned, it was gone!.

    No Sebring for us.

    Carter

  • SkinnyG

    June 3, 2011 7:37 p.m. SkinnyG HalfDork

    My last two daily drivers were Nissans, and Nissan doesn't seem to like "real" suspension travel to begin with. In lowering them, I drilled a series of holes through the bumpstops to "soften" them, not shorten them. This made the progression from "too low" to "on the bumpstops" a bit more gradual.

  • novaderrik

    June 3, 2011 8:12 p.m. novaderrik Dork

    some people setting up GM G bodies to corner use a certain S10 truck front bumpstop as a final tuning device. it has a progressive rate to it that softens the final "hit" when the suspension is getting near it's travel limit.

    NASCAR Cup teams set up the cars to ride on the bumpstops around the corners on some high speed tracks- they set them so the front splitter is just off the ground for max downforce and minimum drag. Chad Knaus (crew chief for Jimmy Johnson) has been known to move the bumpstops up or down .030" to get it "just right". i learned this on NASCAR Performance on SPEED- a show that everyone who cares about race car technology should watch. i also learned that they don't use bumpstops in the Nationwide series at all, and instead the teams set the cars up to bind up the coil springs (rated up to 2500 lb/in on the right front!!!) around corners.

  • chaparral

    June 3, 2011 9:00 p.m. chaparral Reader

    Koni cellasto progressive bumpstops are around $20 for a set. They work very well as long as you remember that one of the main reasons they're progressive is the gradually increasing cross-section.

  • jrw1621

    June 4, 2011 7:13 a.m. jrw1621 SuperDork

  • Dr. Hess

    June 4, 2011 7:24 a.m. Dr. Hess SuperDork

    Don't quote the canoe, Rio. When the mod sinks the canoe, you quote is still around with the links. The links are why they canoe.

    Smith mentions modifying the bump stop shape to adjust the progressiveness of the end of travel spring rate.

  • jrw1621

    June 4, 2011 7:26 a.m. jrw1621 SuperDork

    The mods will kill Rio's post as well and maybe my asian canoe picture.

  • mad_machine

    June 4, 2011 11:13 a.m. mad_machine SuperDork

    mmmrmm.. asian canoes.

    The Idea of drilling a bumpstop to soften it is an unusual one.. but I like it:)

  • Tom Heath

    June 4, 2011 1:41 p.m. Tom Heath Web Manager

    Dr. Hess wrote:

    Don't quote the canoe, Rio. When the mod sinks the canoe, you quote is still around with the links. The links are why they canoe.

    Smith mentions modifying the bump stop shape to adjust the progressiveness of the end of travel spring rate.

    This is sooo painfully true. (about the canoes, at least.)

    Regarding bump stops-

    Material, shape, and size definitely play a part. The only reason manufacturers use rubber is because it's cheap.

    The poly material that FCM (and now some others) use really seems to help; they're popular among autocrossers and spec miata folks. I have FCM coilovers (that use the same bumpstop material) on my turbo Miata and I am completely in love.

    I haven't driven cars back-to-back to compare bump stops specifically, but I've talked with Shaikh at Fat Cat for enough time to decide he knows more about suspensions (specifically Miata suspensions) than I ever want to know. I'd trust him.

    I've heard of people having success with drilling holes as well; I'd probably rather do that than shorten them if it's an option.

  • mad_machine

    June 4, 2011 8:29 p.m. mad_machine SuperDork

    If you think about it.. drilling makes perfect sense.

    I remember the rear bumpstops on my Fiat spider are factory drilled.. they are LARGE triangular bit of rubber with a hole or two molded into them

  • nicksta43

    June 4, 2011 9:20 p.m. nicksta43 Reader

    I put the zq8 s10 bump stops on my Impala ss, less than 1/4" of clearance before they touched. Made a huge difference on turn in, felt much better around a auto x course.

 
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