Gen 4 fork travel

[CJC]

Hi,


I would like to ask for the views of anyone who uses their Gen 4 on the track and, more particularly, about whether anyone is struggling to stop the forks from bottoming out.

By way of background, I weigh about 95kg plus kit, and typically ride somewhere towards the top of the inters group. I bought the bike new, performed the initial 600 miles on the road, and then have used the bike exclusively as a track bike and covered about another 1400 miles. Further, I am not a suspension expert ? in the past, I have tended to find a setting which works, and leave it there as my riding was probably the greater limiting factor - but have avidly viewed the number of YT videos on, and around, this topic.

Right from the get-go of going to the track, I?ve been unable to avoid using all of the available fork stanchion travel. Over time, I?ve upped the pre-load to almost max, and then increased the front damping to close to max also. With these settings, the suspension provides more confidence under heavy braking, but I?m always cognisant that I may have bottomed out the suspension leaving only tyre deformation to give the bike an ability to absorb bumps during phases of heavy braking. Taking the bike away from the current front suspension settings tends to give a less confidence inspiring ride under heavy braking.

I was wondering if anyone recognizes this situation, and if so how it was resolved? I understand that stiffer springs are not easy to come by for the Gen 4. I?ve seen heavier, quicker riders using stock suspension and not using all of the fork travel, so it might well be my riding style if I?m too hard on the brakes initially. Indeed, if all of the heavy braking is done with the bike vertical, it may not be such an issue, but nevertheless I have an uncomfortable feeling about this at present. (I don't have the necessary sensor on the bike to analyse actual fork travel.)

I?ve had discussions with a suspension tuner over this which helped slightly by changing geometry but didn?t come to a fully satisfactory conclusion as I was still using all the travel, and will be having more of these discussions to work out the extent of the issue and any required resolution.

In the meantime, I would welcome any input from anyone else who recognises this. At the very least, I'm trying to differentiate whether the "problem" is more down to me (weight, riding style) or the bike suspension set-up/configuration.

As ever, thanks in advance for any input you can provide,

CJC

 

[alex]

Which mode are you in? Race Pro's need to be used to make the suspension less 'active'.
Have you wound up the rebound on the rear to slow the weight transfer?

 

[CJC]

Which mode are you in? Race Pro's need to be used to make the suspension less 'active'.
Have you wound up the rebound on the rear to slow the weight transfer?

Hi Alex,

Thanks.

Yes, I'm using Race Mode Pro with rear rebound at 10.

CJC

 

[alex]

I guess my next question is, how do you know you're using all the travel?

Reason I ask is that I chased zip ties for a while.
I have a Gen 3 with Ohlins. I wound the thing up (preload and compression), only to work out it was either slipping or ending up 'squashed flat' due to bumps under braking. I stopped using a zip tie and wound everything back to where HM Racing put them. I was able to turn much better for having softer suspension and in some ways that meant less braking too...even at Snetterton which has some proper braking zones. I've never felt the front end out of control for going back to a softer front end.

If you really want to know what you are using. Get a camera, mount it somewhere you can see a fork, and record a session. If 99% of the time you're not using the full stroke under braking you're probably too stiff on the front.

 

[CJC]

I guess my next question is, how do you know you're using all the travel?

Reason I ask is that I chased zip ties for a while.
I have a Gen 3 with Ohlins. I wound the thing up (preload and compression), only to work out it was either slipping or ending up 'squashed flat' due to bumps under braking. I stopped using a zip tie and wound everything back to where HM Racing put them. I was able to turn much better for having softer suspension and in some ways that meant less braking too...even at Snetterton which has some proper braking zones. I've never felt the front end out of control for going back to a softer front end.

If you really want to know what you are using. Get a camera, mount it somewhere you can see a fork, and record a session. If 99% of the time you're not using the full stroke under braking you're probably too stiff on the front.

I'm using the ubiquitous zip tie too. In fact, I'm using one on both legs since I wanted to check the the first one wasn't somehow slipping down the stanchion rather than being pushed down. Both are telling the same story.

I think we are going heading along the same lines though. Whether you use a camera or a sensor, the key thing is to understand where/if full travel is being used and what the significance of that is. This is a question to which I don't currently know the answer, but I like your camera suggestion. I'm also suspicious that my braking technique may well be sub-optimal, but this is something I'm working on.

I also tried to back off the pre-load slightly, my thinking being that by lengthening the stroke, there is more time for the compression damping to act and hold up the bike away from the end of the fork travel. That actually make the make squirm a lot more under heavy braking, and I soon dialled it back in.

The one thing which the tuner did was to push the forks through the triple clamp so that the top of the forks sat flush with the top of the triple clamp. That helped.

Thanks for the on-going thoughts Alex. They're much appreciated. I find this whole topic of geometry and suspension setting way more complex that it should be for someone of my level. Therefore I'm off to suspension school later in the week so I hope that will shed further light.

CJC

 

[fmo]

Having the same problem. 85 kg without gear, bottoming out even with preload almost on max. Original DDC with 2D-potentiometer in the front for separating rebound and compression. Had Ohlins on my previous K46 but wanted to give the new DDC-system a chance, but will install aftermarket suspension during this winter. Mainly because of poor front end feeling.

 

[bananaman]

I'm prob 95k, my cable tie is approx 3mm from bottom just back from Portimao. I'm more of a light at first then heavy on the brakes as opposed to jamming them on.

 

[JamieMac]

Yep, if the initial braking is too aggressive it unsettles the bike with the big pitch forward and the bike's back end is likely to leave the ground. Better a little less aggressive and then build. More control. IMHO

 

[CJC]

I'm prob 95k, my cable tie is approx 3mm from bottom just back from Portimao. I'm more of a light at first then heavy on the brakes as opposed to jamming them on.

Are you using stock suspension? I was told by BMW that bottom out was 10mm from the bottom of the stanchion???

 

[bananaman]

Are you using stock suspension? I was told by BMW that bottom out was 10mm from the bottom of the stanchion???

Yep, stock sussies. I'm certainly not feeling any bottoming out.

 

[bananaman]

Are you using stock suspension? I was told by BMW that bottom out was 10mm from the bottom of the stanchion???

By bottom of the stanchion you mean lower dust seal or distance between bottom of upper and top of lower?

 

[alex]

8mm was the Gen3 Sachs bottom out.
Not sure if the Mazzochi Gen4's are more or less

Sent from my SM-G965F using Tapatalk

 

[SCM]

Hi
I?m 75kg with gear. I can?t get the front to work properly. Do you get fault codes if you revert to a manual set up. Failing that I?m seriously considering a M1000
Steve.

 

[fast_ryan]

Aftermarket Suspension

Do you get fault codes if you revert to a manual set up. Failing that I?m seriously considering a M1000

You need to have the DDC deactivated within the ECU prior to removal and fitting aftermarket suspension on the Gen 4. Your BMW dealership can do this for you as can others like Crowe Performance. By all accounts the M1000RR?s standard suspension isn?t much better as BMW fitted cheap kit knowing that the race teams would strip and fit ?hlins or K-Tech items as soon as the bikes were delivered.

 

[CJC]

By bottom of the stanchion you mean lower dust seal or distance between bottom of upper and top of lower?

Apologies for the delay in replying Bananaman....

I mean the minimum distance between the dust seal and the top of the "silver fork bottom" which holds the wheel. Put another way, if you were to put a very thin keeper/zip tie on the bottom of the fork, this keeper would be 10mm from the top of the silver fork bottom. Hence, 10mm of the fork stanchion would be showing and cannot be used by the suspension.

I hope this makes sense - my lack of engineering vocabulary makes this feel like a clumsy answer. Oh, for a diagram...

I'd also flag that I was asking the question whether the fork uses all the stanchion travel, so there may be small finessing of the detail with regards the width of the dust seal etc.

Hope that helps to some degree,

CJC

 

[bananaman]

Apologies for the delay in replying Bananaman....

I mean the minimum distance between the dust seal and the top of the "silver fork bottom" which holds the wheel. Put another way, if you were to put a very thin keeper/zip tie on the bottom of the fork, this keeper would be 10mm from the top of the silver fork bottom. Hence, 10mm of the fork stanchion would be showing and cannot be used by the suspension.

I hope this makes sense - my lack of engineering vocabulary makes this feel like a clumsy answer. Oh, for a diagram...

I'd also flag that I was asking the question whether the fork uses all the stanchion travel, so there may be small finessing of the detail with regards the width of the dust seal etc.

Hope that helps to some degree,

CJC

No probs.... On reflection, that few mil would be plus the width of the zip tie. Also thats at my extreme breaking on track, not to say that it's not working in the optimum area in general.

 

[CJC]

Aftermarket Fork Spring Suppliers

Hi,

Has anyone come across a supplier of aftermarket springs for the K67 front? I?ve asked a couple of suspension specialists and so far have drawn a blank. The internet hasn?t been forthcoming either unless you want to go down the Alpha racing cartridge kit route or replace the front end entirely with the associated mega bucks cost.

CJC

 

[fast_ryan]

Aftermarket Fork Spring Suppliers

Hi,Has anyone come across a supplier of aftermarket springs for the K67 front? I?ve asked a couple of suspension specialists and so far have drawn a blank. The internet hasn?t been forthcoming either unless you want to go down the Alpha racing cartridge kit route or replace the front end entirely with the associated mega bucks cost.

The only options to date are cartridge kits which are available from Ohlins, K-Tech, Bitubo and Mupo. The last time I spoke to reps from both Ohlins and K-Tech neither had any plans to release springs for the K67 to suit DDC equipped bikes.