BC Racing BR type coilovers

[green_comet]

Is this sh*t for real??



That ones for you Ben..

Not enough travel for the rears? Just get some better tophats, problem solved.



http://www.iscracing.net/miata_suspension.html

or



http://www.dp6061.com/?view=tophats

My brain hurts just from reading this merda...

[ricky-pinky]

Hi green_comet,

No, the problem is that the damper piston rod is not long enough. I have asked if a longer piston rod can be fitted to the damper body. I'm still awaiting a reply.

If they can only provide a longer rod by using a longer damper body, then the higher tophat would be a solution.

[ricky-pinky]

Hi broady,

Do you know that for a fact, or is it just paddock talk. I somehow doubt that Mazda would have designed it that way, although some drivers may have lowered their cars so far that they do ride up against the bumpstops during cornering.

According to Carroll Smith's publication "Engineer in Your Pocket - A practical guide to tuning the race car chassis and suspension", understeer and oversteer may be caused by the following conditions at the front or rear of the car respectively:
# Insufficient inside wheel droop;
# car body rolling onto the bumpstops;
# a too high relative spring rate;
And bumpstops are essentially a very high rate spring.

I Guess if it seems to work for them who am I to decry it, but it goes against Carroll Smith's philosophy and I tend to give him a fair bit of credence. I would be inclined to raise the ride height and/or fit stiffer springs and/or anti-roll bars to avoid it.

[bretauto]

there seems to be a little misunderstanding, travel has not been lost due to lowering the car , but is limited by the design of the shock .
Bump stops are not springs, they are a saftey item, there to cushion the effect of running out of suspension travel and keep component damage to a minimum . the material bump stops are made from deteriorates quickly when compressed all the time, it has a very limited life compared to a steel spring.
I hear of people changing springs and shocks all the time , reusing the bump stops
Simple fact If you are using the bump stops as a helper springs, then your spring rates are not stiff enough!
Brett

[GS]

Hi broady,

Do you know that for a fact, or is it just paddock talk. I somehow doubt that Mazda would have designed it that way, although some drivers may have lowered their cars so far that they do ride up against the bumpstops during cornering.

According to Carroll Smith's publication "Engineer in Your Pocket - A practical guide to tuning the race car chassis and suspension", understeer and oversteer may be caused by the following conditions at the front or rear of the car respectively:
# Insufficient inside wheel droop;
# car body rolling onto the bumpstops;
# a too high relative spring rate;
And bumpstops are essentially a very high rate spring.

I Guess if it seems to work for them who am I to decry it, but it goes against Carroll Smith's philosophy and I tend to give him a fair bit of credence. I would be inclined to raise the ride height and/or fit stiffer springs and/or anti-roll bars to avoid it.

"The bump stops are an integral part of the suspension travel in the Miata. They offer a progressive spring rate, additive to whatever spring rate the spring itself may have. Finding a ride height which does not "bottom out" onto the bumpstops (which I tried to do for the initial coilover installation) is not only not necessary, but impossible.

A Miata even with its stock suspension corners on the bumpstops essentially all the time. While driving in a straight line, the soft springs provide a nice ride. As soon as cornering forces go beyond suburban commuting, the bump stops add from several hundred to a thousand lbs/in of spring rate to the equation, giving nice handling."

Copied from this page on the web:
http://virkki.com/jyri/miata/bumps.html

The pics in that link indicate how much travel the stock suspension has before hitting the bumpstops.

[broady]

Thanks GS! That's an awesome resource!

[meanmx]

I'm just thinking that the people on this thread with the lower post counts (ie bretauto and rinky-pinky) should maybe be listening to some of our more experienced members. As GS pointed out, the mx5 does indeed use the bumpstop as part of it's suspension layout and it is a very normal thing. Maybe the reason that noone has complained about the bc coilovers before is that people don't overthink the situation and just install their coilovers. I am sure they are fine. BC is a big company with many satisfied customers. In fact I just purchased some BC coilovers for another car and when I get them I will just install them and see how they feel before deciding anything

[zorak]

Maybe the reason that noone has complained about the bc coilovers before is that people don't overthink the situation and just install their coilovers.

Yep! Installed mine, left the preload @ 5mm, upped the damper setting a few clicks and haven't looked back. Absoultely love my BCs after a few 1000ks, better than my king/koni setup.

[mattah]

Maybe the reason that noone has complained about the bc coilovers before is that people don't overthink the situation and just install their coilovers.

Yep! Installed mine, left the preload @ 5mm, upped the damper setting a few clicks and haven't looked back. Absoultely love my BCs after a few 1000ks, better than my king/koni setup.

Hi Zorak, are your BCs riding on the bumpstops all the time?

And GS, maybe you should have quoted more from the same reference. Further down that page the author says:

How much to cut?

It is easy to conclude from the above pictures and numbers that if the car is to be lowered by any non-trivial amount, the bumpstops probably need to be cut. With 'old' style bumpstops a ride height any lower than 12.5F/12.75R will be permanently riding on the bumps, quickly leading to a very harsh ride on anything but glass-smooth roads.

Before going on to write:

Based on the above analysis I decided to keep full length 'new' style bumpstops and a stock ride height. As documented in my GC page, the results have been very good.

The issue isn't necessarily that the MX5 uses the bumpstops as aids when cornering, it is the amount that they are used when fitting coilovers to lower the car.

Checking links from GS' reference also shows,

Fat Cat Motorsport, where they offer bumpstops from 12mm to 76mm. From the 12mm page:

# Benefits

Shortest bump stops available! Lets your springs do their job!

And from the 36mm page:

If you've lowered your car or are using a coil-over kit, these stops are the ideal choice and a great value. Don't risk damage by running too short a stop, or lose travel using one that's too long! Our kits are perfectly sized.

From their PDF on suspension:

Bump stops are also key to proper suspension performance. Which is ironic since many people (including me at first) considered them a necessary evil or afterthought.
Cutting stock bumpers has been and remains popular but such convenience comes at a price in terms of reliability, safety, and performance.

I have only just bought an MX5, and it's been interesting to read about this. Like a lot of others I assumed that the bump stops were only used to prevent damage, and not as an active suspension component. From what I have read so far they are important in their own right, and that maybe we really need to be looking at a combination shock/bumpstop that will ultimately give the desired performance. How many cars out there are still running around on stock bumpstops?

Can anyone comment more on this?

[Steampunk]

A good mate had a set of these at today's track-day, and he had his set to very hard.
I think he said 5 clicks from full hard front and rear. Although there was hardly any compression on the dampers if you push the car down, bugger me they sure worked!
Where I get away from him on the straights, he comes right back in the corners.

These now have a very high probability of being my next set of damper/spring setup

[ricky-pinky]

Hi All.

This is a progress report.

Thanks to all who responded to this post. It gave me someting to think about. Although I am not convinced that MX5's are supposed to ride around on their bumpstops, I'll accept that bumpstops are a little more high tech than I might have at first thought.

So, since I wanted more rear suspension travel, I went through the BC Racing catalogue to see what might fit. BC Racing have plenty of dampers with a longer stroke, however, the damper bodies are considerably longer than that supplied for the MX5 rear end. I eventually settled on one that had 30mm more travel and a 30mm longer body. BC Racing confirmed that they would fit, but they weren't particularly happy about the modification. They wouldn't do an exchange deal, so I had to buy them separately. It cost $300 for the pair, so I guess you could say I'm really puting my money where my mouth is. I have now fitted them to the rear coilovers ready for installation on the car. It might take a few days before I can get around to doing this.

Two issues arise.
1) The extra damper body length means the car will ride higher, so I will need to use a good amount of the ride height adjustment just to bring the car back down to current height. In the long term I will get some higher top-hats, but only when I am satisfied that this modification is successful.
2) The rear springs will now potentially be required to accommodate a larger deflection. The free length is only 160mm, and I reckon they can take about 90mm compression before they become coil bound. With 77mm of travel before the bumpstop is impacted, this will only occur after 13mm of bumpstop compression. If I determine this to be a problem, I'll get some longer springs, but again, only when I am satisfied that this modification is worth spending more money on.

I'll provide a further update after I have installed them on the car.

[meanmx]

You should have just put the ones that came with the kit on and tried them out first. Then if you weren't happy change them later. Seems a bit backwards to be spending all this money based on your own calculations that go against all the so called experts. As I said you are overthinking rather than spending the couple of hours it takes to install them and giving them a go. But it is your money and your time. You obviously have too much of both at the moment

[broady]

You should have just put the ones that came with the kit on and tried them out first. Then if you weren't happy change them later. Seems a bit backwards to be spending all this money based on your own calculations that go against all the so called experts. As I said you are overthinking rather than spending the couple of hours it takes to install them and giving them a go. But it is your money and your time. You obviously have too much of both at the moment

qft

[Fabio]

I certainly would have tried them first, but I think it is a good thing when people try to think about things like this. You never know, this may be the next BIG thing in MX5 suspension.

[ricky-pinky]

Hi All.

I don't know whether anyone is interested in this thread any more, but I may as well finish it off.

When I installed these shocks the car didn't settle as far as I expected under static load. Just out of interest I checked the spring rate with a Rate Calculator I found on-line and the front was 9.6kg/mm and the rear 7.4kg/mm. However, these can only be ball-park figures since spring rates are very dependant on steel properties and the heat treatment process. I back calculated the spring rates from the distance the car settled under static load and the front came out to be 9.1kg/mm and the rear 7.6kg/mm. Maybe the torsion of the bushes and the pressure in the gas filled shock also contribute. But if this is the case then the original shocks would have had 6mm clearance between the bumpstop and shock when set up with the 5mm of preload as recommended by BC Racing.

I am currently running the front of the car 25mm lower than stock. Since my rear damper body is 30mm longer than the usual damper supplied with these shocks, I can only get the rear 20mm lower than stock using mimimal preload and the height adjuster on maximum low. I am in the process of getting a couple of high-hats fabricated for the rear to allow the shock to sit 30mm higher in the chassis.

I was pleasantly suprised at the ride with these springs - firm but not excessively so. In fact, with the damper rate set to full soft, you would barely be able to tell that the car has non-standard shocks. There are a couple of speed humps around my way which used to cause the suspension to crash against the bumpstops at anything over 50kph. I can now hit them at 70kph and the car just goes up and over and down the other side with the minimum of fuss, although this is probably more to do with the higher spring rate than the longer damper travel.

I am happy with these shocks, but whether the modification was neccessary I accept is a moot point. But I do like having plenty of travel.

And just for interest, while I had the springs out of the car, I checked the motion ratios and found the front to be 1.5 (i.e. when the damper piston moves 10mm the wheel moves 15mm) and the rear to be 1.4 around normal ride height. These figures do change toward the extreme of travel, but not by much.

Also, I when I examined one of the rear shocks, I noted that the bump rubber was pretty long. Also, it was quite worn on the end, I guess from regular contact with the shock. So I accept that MX5's do use their bump stops as part of their normal suspension movement. Mine won't, though!