Serotta F3 6.5 vs 8.5

[Joachim]

Has anyone ridden both a 6.5 and 8.5 Serotta F3 fork? I enquired about the MeiVici SG 55cm and it has 8.5 tubes with a 6.5 fork. Interested if there is a real world "feel" difference between the two.

[spamjoshua]

I recall a member of the Serotta staff noting that in testing the 6.5 has less deflection under equal loads than did the Edge 2.0, so I believe the question of "Serotta defined stiffness" versus what you may be familiar with as a "stiff fork", is as relevant as the Serotta specific designations.

[Joachim]

I recall a member of the Serotta staff noting that in testing the 6.5 has less deflection under equal loads than did the Edge 2.0, so I believe the question of "Serotta defined stiffness" versus what you may be familiar with as a "stiff fork", is as relevant as the Serotta specific designations.

Good point. I remember Mike Lopez said the 6.5 was 19%(?) stiffer than an Enve 2.0. So yes, I agree, someone who rode an Enve 2.0 and F3 6.5 and or 8.5 will be a good comparison too.

[happycampyer]

The "Serotta staff" you are referring to is Mike Lopez. As Mike explained a while back, he and Jim Pfeil were founding partners of Reynolds Composites, and they sold the company to MacLean Quality Composites (MQC). Mike Lopez designed the Ouzo Pro, and also started collaborating with Serotta on its fork designs while he was still at Reynolds. He then left Reynolds to work for Serotta full time, and Serotta purchased from Reynolds the facility in California where Mike was/is based. That facility, which Mike runs, is the source of Serotta's carbon production. Sometime later still, MQC restructured Reynolds (to focus on wheels), and Jim Phiel and others left to form Edge Composites (now Enve).

To give you some points of reference that may or may not be helpful, according to Mike the 6.5 fork is 19% stiffer than the Enve 2.0 (http://forums.thepaceline.net/showpost.php?p=1196319&postcount=4), and the layup of the 8.5 is similar in ride characteristics to the Ouzo Pro (http://forums.thepaceline.net/showthread.php?p=1151273#post1151273).

As I posted in the thread linked above, in my experience, the difference between the 6.5 and 8.5 forks is pretty subtle, and your ability to notice differences between the two will probably be a function of your weight and how aggressively you ride. My full post is here (http://forums.thepaceline.net/showpost.php?p=1151397&postcount=27) from this (http://forums.thepaceline.net/showthread.php?t=110789) thread.

[11.4]

I have all three, plus a few others. I was curious some time back and tried to figure out the differences. As far as I can tell, the fork blades are identical between the 6.5 and 8.5. The steer wall thickness is quite different, and since that's supposedly where most of the actual flex occurs in a fork anyway, you aren't changing basic vibration suppression (which is what the fork blades are for) but are getting less flex from weight on the bike or big bumps that would seriously flex the steer.

In that regard, I find that the overall stiffness of the Enve 2.0 is highest of any of them, although it has more vibration suppression in the fork blades themselves. Comparing the forks on a track bike shows quite a lot of difference in flex with the Enve 2.0 at the stiffest end, the 8.5 still very stiff, the 6.5 quite a bit less so, and the Ouzo Pro least. The Easton's are pretty much at the bottom of the scale, and the Alpina track fork is the stiffest of anything I've found anywhere (and can be downright uncomfortable even on the track). Different people are looking for different things, and looking for vibration suppression and that kind of fork flex is different from looking for a fork that doesn't flex under the stress of a track standing start. I suspect Serotta has an interest in both perspectives -- the vibration suppression for the usual rider and the overall rigidity when Serotta is building for a larger rider. There are great options for all of them and frankly both the 6.5 and 8.5 are superb forks. As I said, I have both, as well as Enve 2.0's, and I don't see any reason to switch any of them for any of the others. We are in a great fork world these days. Now if Enve would only bring back their track fork ... .

[Joachim]

Thanks for the great info! I am seriously considering the MeiVici SG and this really helps. My Ottrott has a F2 fork and that is less stiff than my Enve 2.0. Not bad less stiff, since I wouldn't swop it for another fork.

[bigreen505]

I have all three, plus a few others. I was curious some time back and tried to figure out the differences.

Did you do a real world road test of these forks and possibly an Alpha-Q and post the results on Weightweenies sometime back? If you did, could you post the link? I remember the thread being very informative, but can't find the link.

[Serotta_Carbon]

I have all three, plus a few others. I was curious some time back and tried to figure out the differences. As far as I can tell, the fork blades are identical between the 6.5 and 8.5. The steer wall thickness is quite different, and since that's supposedly where most of the actual flex occurs in a fork anyway, you aren't changing basic vibration suppression (which is what the fork blades are for) but are getting less flex from weight on the bike or big bumps that would seriously flex the steer.

In that regard, I find that the overall stiffness of the Enve 2.0 is highest of any of them, although it has more vibration suppression in the fork blades themselves. Comparing the forks on a track bike shows quite a lot of difference in flex with the Enve 2.0 at the stiffest end, the 8.5 still very stiff, the 6.5 quite a bit less so, and the Ouzo Pro least. The Easton's are pretty much at the bottom of the scale, and the Alpina track fork is the stiffest of anything I've found anywhere (and can be downright uncomfortable even on the track). Different people are looking for different things, and looking for vibration suppression and that kind of fork flex is different from looking for a fork that doesn't flex under the stress of a track standing start. I suspect Serotta has an interest in both perspectives -- the vibration suppression for the usual rider and the overall rigidity when Serotta is building for a larger rider. There are great options for all of them and frankly both the 6.5 and 8.5 are superb forks. As I said, I have both, as well as Enve 2.0's, and I don't see any reason to switch any of them for any of the others. We are in a great fork world these days. Now if Enve would only bring back their track fork ... .

Interesting feedback. In your opening statement do you really mean the Serotta 6.5 & 8.5 forks or perhaps do you mean the Enve 1.0 & 2.0? The reason I ask is that the steer tubes in the Serotta forks do in fact have the same wall thickness but in my recent obserbations of the Enve line the 1.0 & 2.0 do not.

In your observation of the Enve 2.0 being the stiffest are you basing this on the way it rides or have you fixtured them up and loaded/deflected them in the lab as we do? (Our data suggests differently) I'm not being argumentative... I'm truly curious as I'm always seeking rider feedback in order to improve our products...

Thanks!

[clweed]

Mike,

What determines the choice of fork between the 6.5 and the 8.5, is it strictly rider weight ?

Thanks,

Lee

[11.4]

Interesting feedback. In your opening statement do you really mean the Serotta 6.5 & 8.5 forks or perhaps do you mean the Enve 1.0 & 2.0? The reason I ask is that the steer tubes in the Serotta forks do in fact have the same wall thickness but in my recent obserbations of the Enve line the 1.0 & 2.0 do not.

In your observation of the Enve 2.0 being the stiffest are you basing this on the way it rides or have you fixtured them up and loaded/deflected them in the lab as we do? (Our data suggests differently) I'm not being argumentative... I'm truly curious as I'm always seeking rider feedback in order to improve our products...

Thanks!

I was part of a team evaluating design concepts for a high-end monocoque track frame. As part of this we looked at forks to understand what the stress and failure issues were, and to understand design strategies better.

I don't have the precise data available, but to your questions, first, yes, we fixtured forks. Typically they were fixtured in a large block of steel with a milled hole in an upper section to emulate a steer tube, then mounted with a Cane Creek 110 integrated headset (so any issues in the fork brought about by the headset's support of the fork would be incorporated in the results), and a lower section to slide up and lock the fork tips in place. Not perfect, but our primary interest was in the steer end of the fork and we got the kind of results we needed. Three holes were drilled into the milled shaft so that lasers outside the fixture could measure deflection inside the head tube, as well as above. Because track forks often are ridden with quite a bit of steer extending beyond the head tube, we measured head tubes that were, I believe, 12 cm and extensions of about 8 cm to the top of the steer. We applied torque in different tests at the clamping point at the top of the steer and also at the fork tips, to see the effect not only of surface induced deflection but also the leverage of a rider flexing on the bars. The entire fixture was dovetailed and bolted solidly together and at no point measured less than 4x4 inches of solid steel. We learned a lot that could have improved the fixture, but we also got the info we needed and didn't have time to do more.

We measured a lot of fork steers and did get both different steer wall thicknesses and different measures for eccentric compression of the steer for the two Serotta forks. Eccentric compression became an important parameter for us, especially as we saw how fork steers flexed in real time track use. We didn't tested numerous samples, but these results coincided with our experience that internal plugs tended to deform the 6.5 more than the 8.5. Again, only one of each fork. We definitely saw a huge difference in wall thickness between the Enve forks, enough to rule out the 1.0 almost immediately. For sprinters it was downright scary. The 2.0 and the track forks were what we used as final design parameters.

We didn't focus as much on ride quality because we were looking at track use, but tracks aren't as smooth as people like to think and a track fork does have to deal with that problem. Issues can range from irregularities in concrete or asphalt surfaces to joints in wood tracks to the often huge joints in demountable tracks. Some of the European six-day tracks are particularly bad in this regard. We limited our testing to a single ping on the fork end with the fork steer held in the fixture, with no flex applied elsewhere, and a laser monitored the oscillations of the fork end as the fork damped the initial deflection. This was pretty crude, especially since we just assumed that rapid damping would translate to a rougher ride. However, we were designing a complete monocoque frame and fork and needed to figure out the basic design issues. I'd also mention that we were comparing internal fork steers with external steers such as Look and Felt and others use on their high-end track and TT frames. We found that those allowed us much greater rigidity and control, at the expense of comfort. They also tended not to be as reliable in crashes.

There was a lot more that I'd need the lab notebooks to remember, but I hope that gives you a sense of where our comments came from. I'm not clear why steer wall thicknesses were different. We of course measured deeper inside the steer and not at the cut, but couldn't rule out irregularities inside the steer. There are so many variables in fork design that we didn't try to cover everything. I probably don't have to say that to you, Mike.

[Serotta_Carbon]

Mike,

What determines the choice of fork between the 6.5 and the 8.5, is it strictly rider weight ?

Thanks,

Lee

Rider weight is not necessarily the main factor. During the fit interview there's also supposed to be discussion regarding the intended use. Is the rider looking more for performance or comfort? A big person is not going to break a 6.5 but it might be a bit more compliant that desired under certain riding conditions.

I had mentioned recently in a previous thread that this system probably applies better to the custom fitting process where time is spent between the fitter and customer discussing the application.

[Serotta_Carbon]

11.4,

Sounds like you did some interesting testing.

We also fixture the fork in a massive block using Cane Creek headsets and then apply a load to a dummy axle and measure the deflection at that point. We're not necessarily trying to isolate the steerer tube as it sounds like you may be. We're trying to look at the whole fork/steerer as a system. We do however quantify the properties of the steerer in both torsional & 3 point loading but these are in different fixtures.

We're in the midst of designing some new products and I just ran these tests on several Enve products side by side with ours and found the Enve forks to be less stiff. This isn't to say bad... Just less stiff.

The exception was the disk/cross fork with the tapered steerer. It was plenty stiff! Were you testing tapered steerers or straight 1-1/8" forks?

Also. Depending on which version of the Ouzo Pro you tried you may have gotten different results. There were at least 3 different lay-ups over the years each having unique stiffness characteristics.

Your measurements on the F3 steerer tube walls intrigues me. The tubes are made on steel mandrels and then centerless ground to tight specifications. The walls shouldn't vary more than a few thousandths at best...

All good info. I like trading notes with other lab rats!

Thanks!

[11.4]

11.4,

Sounds like you did some interesting testing.

We also fixture the fork in a massive block using Cane Creek headsets and then apply a load to a dummy axle and measure the deflection at that point. We're not necessarily trying to isolate the steerer tube as it sounds like you may be. We're trying to look at the whole fork/steerer as a system. We do however quantify the properties of the steerer in both torsional & 3 point loading but these are in different fixtures.

We're in the midst of designing some new products and I just ran these tests on several Enve products side by side with ours and found the Enve forks to be less stiff. This isn't to say bad... Just less stiff.

The exception was the disk/cross fork with the tapered steerer. It was plenty stiff! Were you testing tapered steerers or straight 1-1/8" forks?

Also. Depending on which version of the Ouzo Pro you tried you may have gotten different results. There were at least 3 different lay-ups over the years each having unique stiffness characteristics.

Your measurements on the F3 steerer tube walls intrigues me. The tubes are made on steel mandrels and then centerless ground to tight specifications. The walls shouldn't vary more than a few thousandths at best...

All good info. I like trading notes with other lab rats!

Thanks!

The ping testing I described in the fourth paragraph was about testing the behavior with regard to track surface aberrations and was necessarily brief. We did much more testing looking at deflection caused by immobilizing the fork tips and then torquing the top of the steer -- this at least roughly modeled the effect of a start or a rapid acceleration. We used ping testing to emulate rapid hits rather than simply deflecting the fork tips at a slower rate because we found that a ping (we actually hit the fork tips with the hammer of a modified pneumatic finish nailer -- it gave the rapid hit that resembled hitting a bump at speed and we did find that it gave quite different results from a slower controlled deflection (possibly due to modulus of elasticity, etc.). The hard ping gave us a chance to watch the fork stabilize by watching a dot move back and forth through a laser beam so we got very precise cycle and amplitude readings. These were quite useful and were used again when we actually had the whole bike together and were trying to figure where to add extra carbon to the frame to control oscillations that potentially limited high-speed stability of the bike.

We tested straight 1-1/8" steers and external steers only. And we didn't test enough units to see the variations among different versions of any fork, but we are aware that there have been at least a couple versions of the Enve forks and the same for Reynolds.

Appreciate your comments. It's nice to see someone who appreciates actually trying to get real answers rather than speculate. On this forum we've tried to do this with tubular gluing, rim spoke tension, methods for tensioning discs, etc. It isn't hard and it saves a lot of wasted talk.