What is gained when they use bump stops instead of coil binding?

RobsanX - 10 March 2008 08:20 PM

What is gained when they use bump stops instead of coil binding?

The bump stops are mandated by NASCAR in order to eliminate coil binding. Apparently, it didn't work because the boys use a combo of spring rates and bump rubber rates that nail the splitter to the track in the corners. The bump rubbers are compressed throughout and there is still some space between the coils. Net effect - nearly the same as a coil bound front suspension. Crazy stuff.

A few years ago everybody was complaining that they wanted the Bump Stops back because coil binding was "Dangerous", now they give them the Bump Stops back and are complaining that they are "Dangerous" and they want Coil Binding back...

No coil binding. No bump stops. Find a rule that does that and you'll still have a bunch of whiney primadonnas complaing about how terrible the cars handle. Its a racer thing.

RobsanX - 10 March 2008 08:20 PM

What is gained when they use bump stops instead of coil binding?

Actually using assorted bump rubbers of different rates (they are actually springs) for the last 1/2 inch of travel of the suspension before coil bind.
Once coil bind is achieved there is no more movement in the suspension, at least the bump rubber can slow or prevent coil bind by a "sudden" increase in the spring rate (say the main spring is 400 lbs and the bump rubber is 1000 lbs for the last .5 inch of travel before coil bind.
This allows the spoiler to get closer to the ground and still have some dampening of the movement with spring rate before reaching infinity (turning the car into a go kart with no suspension).
Without the bump rubber the car would literally "crash" into coil bind.

I agree with you speedsense except that I think it's more like the last 1/4 inch and the spring rates on the rubbers are probably double 1000 lbs.

The problem is at that point the main suspension absorbtion has moved to the tires. And that is where the problem is. Goodyear is trying to design a tire that has to act as a suspension part as well as it's normal function. Granted it acts as a suspension part under the best of conditions, but I am talking about it becoming a major suspension part.

In the last 1/4 inch of travel there is mute difference between coil binding and bump stops. In both cases the tire is being over used.

What if NASCAR came up with a different means of measuring splitter height? Maybe they could apply weight to the car to simulate downforce and create a dynamic height rules.

Isn't the issue that no matter what, the fast way around is to have the splitter (or spoiler/nose in the old cars) just about kissing the track. Yet, if the cars have to much suspension travel or is too soft the rigid splitter will bottom-out on the track and take the weight off the front wheels which results in an immediate crash into the outside wall.
The solution could be a more flexible splitter mounting, letting it drag on the track while maintaining some suspension travel - but NASCAR needs to approve and they seem a bit overwhelmed these days.

speedsense - 10 March 2008 11:49 PM

RobsanX - 10 March 2008 08:20 PM

What is gained when they use bump stops instead of coil binding?

Actually using assorted bump rubbers of different rates (they are actually springs) for the last 1/2 inch of travel of the suspension before coil bind.
Once coil bind is achieved there is no more movement in the suspension, at least the bump rubber can slow or prevent coil bind by a "sudden" increase in the spring rate (say the main spring is 400 lbs and the bump rubber is 1000 lbs for the last .5 inch of travel before coil bind.
This allows the spoiler to get closer to the ground and still have some dampening of the movement with spring rate before reaching infinity (turning the car into a go kart with no suspension).
Without the bump rubber the car would literally "crash" into coil bind.

You don't think the teams don't have the shocks tuned for every millimeter of travel until the car bottoms out against the bump rubbers? What you are describing is exactly what the shock takes care of or at least what the teams are striving it to take care of.

RED376 your description and explanation are excellent, thanks. What I was reacting to is that some of the drivers are complaining about what sounds like very, very stuff or nearly fully compressed rubber bump stops, but as you point out they may have missed the set-up with the interaction with the shocks.

part of the current problem is that the reduced shock travel from 7-8 inches to 4-5 inches