2manyoranges
Old School Grand Master
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The thread this week about overforking (eg 100mm travel on a bike designed for 60mmm) got mE considering this thread.
I had a bit of a problem in the 90s, since people would get very upset with the way I had my suspension set up … basically 30% sag, so softer than anyone else. This was the same on all my bikes, Proflex, bikes with Judy’s etc. This simply came from my experience in MX, where sag was an important parameter. Why? Because when your bike is sitting in the 70/30 (middle-ish) range of the suspension it allows a wheel to track the ground, dropping into holes as well as compressing over the bumps. If you set the bike up with the mass sitting at the top of the travel it will top out on return, most likely be too bouncy because oversprung, and not track the ground.
So….that’s the first thing…SAG.
But those old elastomer or spring forks had no way of changing the SPRING RATE other than changing out the elastomers or spring. It was perfectly common to have forks which eat through the travel and then bottomed out, or were too hard and bouncy. That’s where air forks began to help with management of SPRING RATE, particularly those with both an upper chamber and a lower chamber (eg Rockshox Dual Air SIDs) Now it was possible to adjust easily the small bump compliance and RETURN RATE.
Compression (compression and return rates) were uncontrolled on early forks, and then things like the cartridge in Judys appreared. An improvement, but with a fixed performance - no way of adjusting COMPRESSION RATE. So the forks would pack down after repeated hits or be too compliant on bit hits, again blowing through the travel.
This is where modern forks have finally used the insights from the F1 and MX world. Hurrah.
Want a fork where the SPRING RATE ramps up so that at the beginning of the travel the forks can cope with small hits (low SPRING RATE) while they also can handle big hits (high SPRING RATE) - then use an air fork into which you put tokens if you are heavy and fewer if you are light. This changes the RATE CURVE to suit your weight, style of riding and terrain. Set up therefore needs a shock pump (to vary pressure to suit) and tokens (to fit in fork). If you have COIL rather than AIR forks, then you will tend to want longer travel forks (eg if a bike says 120-140mm forks then I would go 140-150mm and over fork slightly) and do very careful work on which WEIGHT spring is needed. Some coils have variable coils to allow different RATE characteristics. Getting the right weight spring can be fiddly, experimental process - and you may need to buy three or four springs to really tune things. With growing groms we use air shocks which avoid this problem.
Air shocks are non linear, since the spring rate increases with compression. Coils are more or less linear. Air weighs less than spring steel or ti - but a well set-up long travel coil can be a magic carpet ride with amazing small bump compliance. Air shocks need heavy duty seals, and this introduces friction - and thus initiation forces have to be higher, which reduces small bump compliance. We run both, and with careful set-up the problems of each can be mitigated.
So far so good. That sorts SPRING RATE But then the compression control/damping needs sorting. And all this shows that the early generations of forks were very limited in their adjustment, which seriously limited performance.
Now COMPRESSION. The adjustment is usually expressed in the form of CLICKS. Dials on the tops or bottoms of fork legs (depending on make and model) allows the RATE OF OIL FLOW in the forks to be adjusted, thus tuning COMPRESSION RATES. This was not available in early forks and really is as crucial as SPRING RATE. Modern forks have up to forty clicks, and often two circuits - HIGH SPEED COMPRESSION and LOW SPEED COMPRESSION. Modern valving (compared to the couple-of-holes-in-a-washer in the early cartridges) is sophisticated. The idea is to give good small hit compliance, good RECOVERY RATES to the suspension (to avoid packing down over multiple hits) and HIGHER RESISTANCE during big hits - allowing big hits to be handled as a smooth curve of force rather than a big spike. We tune a fork for compression by starting in the middle of the CLICK RANGE and turn up or down as successive rides indicate we should. It’s a very empirical process. Repetitions on a known ride really helps. Once right, you write them down.
ANTI-SQUAT is a big thing for FS, and that’s to do with the way in which the physical path of the rear suspension interacts with the SPRING RATE and COMPRESSION DAMPING of the rear shock - good ANTI-SQUAT is designed into well-designed rear suspension.
On a hardtail, compression of the forks radically changes the geometry and centre of mass of the bike, shifting the wheelbase measurement. In an old bike with a long stem and small- or mid- travel (50-100mm) blowing through the travel on a steep drop gave a terrifying shift of CoG and reduction of wheelbase - with over-the-bar accident a very real risk. For modern hardtails such as the BfEMAX, having such a slack HEAD ANGLE (62deg static) and short stem (eg 35mm) means that this huge shift in handling dynamics as the forks compress is reduced massively. Bikes work as COMPLEX SYSTEMS and that’s one of the reason why slapping a longer fork (eg 100mm) on a bike for a short travel fork (eg 60mm) gives a horribly handling bike. I had an Orange O2 Evo with a 60mm fork - rode well, nicely balanced. I stuck a 90mm fork on and it gave weird steering, an incredibly slack seat angle that couldn’t be mitigated by moving the saddle forward, and an unhelpfully raised bottom bracket. Awful. Was just an experiment but a complete waste of time.
This adjustment of SPRING RATE and LOW SPEED and HIGH SPEED COMPRESSION RATE is crucial to the astonishing performance of modern forks (just look at a RED BULL slo-mo of DH bikes) and the absence explains why early forks were an advance, but offered very little true performance - whilst modern forks are astonishing (and expensive).
I have capitalised key things to bear in mind when setting up modern forks, and I hope that this has been helpful. Really useful ideas to help with fork setup:
SAG
SPRING RATE
RETURN RATE
COMPRESSION RATE (low speed and high speed)
(thanks WOZ…and then there are fiddly additions such as LOCKOUT (including remote lockout - as if your handlebars were not busy enough already, with shifters, dropper remote, levers and Garmin gubbins) - a feature which people say is helpful for climbing and ‘road work’ (what this thing called ‘road?) but which never gets used and messes up climbing anyway - use lockout, climb, climb, hit root, fall over - while the rider next to you has lockout off and just absorbs the bump from the root and carries on. And some forks have additional fiddly tuning bits (eg DVO’s OTT which notionally allows tuning of small bump compliance but seems to actually affect things differently on different people‘s forks of the same year and model….so it’s an enigma).
Very nice write up below by Novocaine of the design of open bath Marzocchi forks,…
I had a bit of a problem in the 90s, since people would get very upset with the way I had my suspension set up … basically 30% sag, so softer than anyone else. This was the same on all my bikes, Proflex, bikes with Judy’s etc. This simply came from my experience in MX, where sag was an important parameter. Why? Because when your bike is sitting in the 70/30 (middle-ish) range of the suspension it allows a wheel to track the ground, dropping into holes as well as compressing over the bumps. If you set the bike up with the mass sitting at the top of the travel it will top out on return, most likely be too bouncy because oversprung, and not track the ground.
So….that’s the first thing…SAG.
But those old elastomer or spring forks had no way of changing the SPRING RATE other than changing out the elastomers or spring. It was perfectly common to have forks which eat through the travel and then bottomed out, or were too hard and bouncy. That’s where air forks began to help with management of SPRING RATE, particularly those with both an upper chamber and a lower chamber (eg Rockshox Dual Air SIDs) Now it was possible to adjust easily the small bump compliance and RETURN RATE.
Compression (compression and return rates) were uncontrolled on early forks, and then things like the cartridge in Judys appreared. An improvement, but with a fixed performance - no way of adjusting COMPRESSION RATE. So the forks would pack down after repeated hits or be too compliant on bit hits, again blowing through the travel.
This is where modern forks have finally used the insights from the F1 and MX world. Hurrah.
Want a fork where the SPRING RATE ramps up so that at the beginning of the travel the forks can cope with small hits (low SPRING RATE) while they also can handle big hits (high SPRING RATE) - then use an air fork into which you put tokens if you are heavy and fewer if you are light. This changes the RATE CURVE to suit your weight, style of riding and terrain. Set up therefore needs a shock pump (to vary pressure to suit) and tokens (to fit in fork). If you have COIL rather than AIR forks, then you will tend to want longer travel forks (eg if a bike says 120-140mm forks then I would go 140-150mm and over fork slightly) and do very careful work on which WEIGHT spring is needed. Some coils have variable coils to allow different RATE characteristics. Getting the right weight spring can be fiddly, experimental process - and you may need to buy three or four springs to really tune things. With growing groms we use air shocks which avoid this problem.
Air shocks are non linear, since the spring rate increases with compression. Coils are more or less linear. Air weighs less than spring steel or ti - but a well set-up long travel coil can be a magic carpet ride with amazing small bump compliance. Air shocks need heavy duty seals, and this introduces friction - and thus initiation forces have to be higher, which reduces small bump compliance. We run both, and with careful set-up the problems of each can be mitigated.
So far so good. That sorts SPRING RATE But then the compression control/damping needs sorting. And all this shows that the early generations of forks were very limited in their adjustment, which seriously limited performance.
Now COMPRESSION. The adjustment is usually expressed in the form of CLICKS. Dials on the tops or bottoms of fork legs (depending on make and model) allows the RATE OF OIL FLOW in the forks to be adjusted, thus tuning COMPRESSION RATES. This was not available in early forks and really is as crucial as SPRING RATE. Modern forks have up to forty clicks, and often two circuits - HIGH SPEED COMPRESSION and LOW SPEED COMPRESSION. Modern valving (compared to the couple-of-holes-in-a-washer in the early cartridges) is sophisticated. The idea is to give good small hit compliance, good RECOVERY RATES to the suspension (to avoid packing down over multiple hits) and HIGHER RESISTANCE during big hits - allowing big hits to be handled as a smooth curve of force rather than a big spike. We tune a fork for compression by starting in the middle of the CLICK RANGE and turn up or down as successive rides indicate we should. It’s a very empirical process. Repetitions on a known ride really helps. Once right, you write them down.
ANTI-SQUAT is a big thing for FS, and that’s to do with the way in which the physical path of the rear suspension interacts with the SPRING RATE and COMPRESSION DAMPING of the rear shock - good ANTI-SQUAT is designed into well-designed rear suspension.
On a hardtail, compression of the forks radically changes the geometry and centre of mass of the bike, shifting the wheelbase measurement. In an old bike with a long stem and small- or mid- travel (50-100mm) blowing through the travel on a steep drop gave a terrifying shift of CoG and reduction of wheelbase - with over-the-bar accident a very real risk. For modern hardtails such as the BfEMAX, having such a slack HEAD ANGLE (62deg static) and short stem (eg 35mm) means that this huge shift in handling dynamics as the forks compress is reduced massively. Bikes work as COMPLEX SYSTEMS and that’s one of the reason why slapping a longer fork (eg 100mm) on a bike for a short travel fork (eg 60mm) gives a horribly handling bike. I had an Orange O2 Evo with a 60mm fork - rode well, nicely balanced. I stuck a 90mm fork on and it gave weird steering, an incredibly slack seat angle that couldn’t be mitigated by moving the saddle forward, and an unhelpfully raised bottom bracket. Awful. Was just an experiment but a complete waste of time.
This adjustment of SPRING RATE and LOW SPEED and HIGH SPEED COMPRESSION RATE is crucial to the astonishing performance of modern forks (just look at a RED BULL slo-mo of DH bikes) and the absence explains why early forks were an advance, but offered very little true performance - whilst modern forks are astonishing (and expensive).
I have capitalised key things to bear in mind when setting up modern forks, and I hope that this has been helpful. Really useful ideas to help with fork setup:
SAG
SPRING RATE
RETURN RATE
COMPRESSION RATE (low speed and high speed)
(thanks WOZ…and then there are fiddly additions such as LOCKOUT (including remote lockout - as if your handlebars were not busy enough already, with shifters, dropper remote, levers and Garmin gubbins) - a feature which people say is helpful for climbing and ‘road work’ (what this thing called ‘road?) but which never gets used and messes up climbing anyway - use lockout, climb, climb, hit root, fall over - while the rider next to you has lockout off and just absorbs the bump from the root and carries on. And some forks have additional fiddly tuning bits (eg DVO’s OTT which notionally allows tuning of small bump compliance but seems to actually affect things differently on different people‘s forks of the same year and model….so it’s an enigma).
Very nice write up below by Novocaine of the design of open bath Marzocchi forks,…
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