Bumpstop Tuning

[xBlueStreakx]

Gents,

I have a track built 135i. Noticed the most track-oriented action is here so I figured I'd ask here.

Anybody look into tuning the suspension with bumpstops in addition to springs?

[roastbeef]

first i've heard of it on this particular forum. wouldn't you want to avoid it? i mean, if you're not riding on springs and dampening with your valving, isn't something wrong?

[xBlueStreakx]

I believe the theory behind it is that it compliments low and high speed corners with aero. With a progressive bumpstop, say 100lbs/in bump stop, you can run softer springs to be quick in the low speed corners and have the bumpstops add 'spring rate' in the higher speed corners where your aero would otherwise overpower your spring setup alone.

As an example, a time attack racer local to me, James Houghton runs this setup. He's been setting/resetting records across Ontario, Canada as well as at GridLife and Superlap battle alongside Will Au Yeung (another fellow Canadian - he's going to the World Time Attack event in Australia this year; pretty cool). I have yet to meet these guys in person so I haven't had a chance to pick their brains. Don't know how forthcoming they'd be about their setups tho.

James Houghton Motoiq Article

If you go to page 4, the article touches on the use of bumpstops to compliment the aero. Funny thing about his setup is his spring rates and the resulting wheel rates. They come out lower (softer) than what 'conventional wisdom' calls for in the BMW scene. Granted, the DC2 Integra has a double wishbone suspension whereas BMW is McPhereson and that plays into spring/wheel rate/wheel frequency choice. I still can't throw the theory away, though.

Short video on his car.

Searched google but unfortunately there doesn't seem to be much out there that pertains to road circuits.

[Richbot]

Originally Posted by roastbeef

first i've heard of it on this particular forum. wouldn't you want to avoid it? i mean, if you're not riding on springs and dampening with your valving, isn't something wrong?

The M3 corners on the bumpstops from the factory, as do many many cars that come with soft springs from the factory but still handle reasonably well with reasonably controlled body roll. There's no other way to get the compliance trade-off cheaply

[Richbot]

Originally Posted by xBlueStreakx

I believe the theory behind it is that it compliments low and high speed corners with aero. With a progressive bumpstop, say 100lbs/in bump stop, you can run softer springs to be quick in the low speed corners and have the bumpstops add 'spring rate' in the higher speed corners where your aero would otherwise overpower your spring setup alone.

As an example, a time attack racer local to me, James Houghton runs this setup. He's been setting/resetting records across Ontario, Canada as well as at GridLife and Superlap battle alongside Will Au Yeung (another fellow Canadian - he's going to the World Time Attack event in Australia this year; pretty cool). I have yet to meet these guys in person so I haven't had a chance to pick their brains. Don't know how forthcoming they'd be about their setups tho.

James Houghton Motoiq Article

If you go to page 4, the article touches on the use of bumpstops to compliment the aero. Funny thing about his setup is his spring rates and the resulting wheel rates. They come out lower (softer) than what 'conventional wisdom' calls for in the BMW scene. Granted, the DC2 Integra has a double wishbone suspension whereas BMW is McPhereson and that plays into spring/wheel rate/wheel frequency choice. I still can't throw the theory away, though.

Short video on his car.

Searched google but unfortunately there doesn't seem to be much out there that pertains to road circuits.

Yep what he said. Bump stops are hard to damp so you need good dampers to avoid chasing your tail but it's a great tool, one way to think of it is as the opposite of the low-rate "helper" springs that collapse as soon as any meaningful weight is on the car; on a race setup they only get involved when you've used up the bump travel the primary springs give you over a curb, etc.

I think conventional wisdom in BMW world still bears the scars of some of the crappy suspension geometry of earlier platforms.

I think there are much lower hanging fruit on most setups though

[xBlueStreakx]

Originally Posted by Richbot

I think there are much lower hanging fruit on most setups though

What do you mean? Other things that can be done before looking into using bump stops?

[leo95se]

tuning in lieu of a good shock setup? I think if you have an appropriately tuned shock, with bump and rebound appropriately dialed in, you can run a softer spring to achieve the same goal.

[spxxx]

James Houghton is a badass. That Integra he drives is a monster, think he set the FWD record at Buttonwillow?

This must be his trick... lol

[xBlueStreakx]

Originally Posted by leo95se

tuning in lieu of a good shock setup? I think if you have an appropriately tuned shock, with bump and rebound appropriately dialed in, you can run a softer spring to achieve the same goal.

I don't think its in lieu of a good shock setup; its in addition to. Personally, I can't just write off a setup when someone uses it and is setting records.

Not saying the records are being set because of the bumpstops but I'm sure its doing its incremental job within the entire package.

[Richbot]

Originally Posted by xBlueStreakx

What do you mean? Other things that can be done before looking into using bump stops?

Yes. For instance, almost everyone with a track car still has a ton of rubber left in the suspension that makes it sticky and deflection-prone. Houghton's car is making a shload of aero corner weight at the front end in high speed corners, on a car that already needs the front end to do 95% of the work. I would caution you against taking too many lessons from his car if yours isn't, the demands of a front-drive car on its front tires are what they are. Besides, we are all already using some sort of bumpstop already. The stock ones are a major, working part of the suspension, they don't just sit there, and all aftermarket damper setups use one in some form as well.

EDIT: I think this falls into the category of the only way to know for sure is to take copious amounts of data from the driver and the car and see if you like it. If you're doing it on your car, I would think a progressive stop on the rear with a softer rear spring could ease the torque hit coming out of corners and make it a little easier to drive

[xBlueStreakx]

Originally Posted by Richbot

Yes. For instance, almost everyone with a track car still has a ton of rubber left in the suspension that makes it sticky and deflection-prone. Houghton's car is making a shload of aero corner weight at the front end in high speed corners, on a car that already needs the front end to do 95% of the work. I would caution you against taking too many lessons from his car if yours isn't, the demands of a front-drive car on its front tires are what they are. Besides, we are all already using some sort of bumpstop already. The stock ones are a major, working part of the suspension, they don't just sit there, and all aftermarket damper setups use one in some form as well.

EDIT: I think this falls into the category of the only way to know for sure is to take copious amounts of data from the driver and the car and see if you like it. If you're doing it on your car, I would think a progressive stop on the rear with a softer rear spring could ease the torque hit coming out of corners and make it a little easier to drive

Agreed. The purpose of the original post (though in hindsight, not very descriptive) was to ask if someone has tried this and then to what extent they have experience. There's not much out there to work with, it seems, so if I do decide to give it a go, I'm basically on my own.

I think the prevailing perceived utility of bumpstops is to prevent smashing struts/dampers to the chassis or bottoming out. Bumpstops are worth so much more than that (to which you've indicated).