[Closed] What happens if you do this (fork offset)

It’ll speed the steering up a bit and make it a bit harder to weight the front wheel - swap the stem for one 10mm longer and that’ll balance things out. But you might not even notice!

No! I couldn’t tell when I swapped from one to the other.

The big issue is that you'll know- if you didn't, you probably wouldn't notice but when you do, all bets are off 😉

My understanding is that a higher offset will make the front wheel a bit flip-floppy. Kind of like a supermarket trolley castor. Speeds up the steering and makes it feel a bit more twitchy. Current trend for reduced offset (<40mm) helps make bikes feel more stable going downhill at the expense of being very slow to turn on tight and twisty stuff.

Wouldn't more floppy floppy be less twitchy at speed?

you'll not notice, compared to the variation as the fork compresses

Wouldn’t more floppy floppy be less twitchy at speed?

Think of trying to push a supermarket trolley which has the wheels forward of the steering pivot.

“My understanding is that a higher offset will make the front wheel a bit flip-floppy.”

No, it’s the opposite.

At low speed the shorter offset fork turns more quickly because the head tube drops more as you turn the bars. At high speed it turns more slowly because of the increased castor effect from the increased trail. And vice versa for longer offset.

After yet another F1-style pit stop at Mojo, it was back up the hill with a medium offset of 44mm – the same as a standard 650b fork from Fox. As you might expect, the handling was somewhere in-between the standard and super-short offsets used previously - not as calm and lazy as the 37mm, not as twitchy as the 51mm. After another trial run to get a feel for the 44mm offset fork, the stopwatch was applied once more.

Shorter offset also reduces the ‘floppy’ feeling that can occur when tackling tight corners, where the wheel can feel like it wants to tuck under.

From here: https://www.bikeradar.com/mtb/gear/article/pushing-the-limits-of-fork-offset-an-experiment-45343/

It's just one tiny variable amongst a load of other variables you will be getting into on the new frame.

I bet you could provoke far, far more difference in feel by messing about with different length stems and bars.

I wouldn't give it a seconds thought personally mate.👍

Fork offset is just the new "long, low and slack" as I think people are bored of hearing that phrase now.lol

Different example as on track bike but I swapped a 30mm offset fork for a 45m offset fork.
Trail was decreased and steering felt lighter/less stable for the first few minutes. After that I didn't notice it and it made no real difference to actual riding (other than removing toe overlap)

Cheers folks.

Can't believe how cheap these are in aluminium form? What's the catch.... weight?

Interview with the guy from Pole bikes said in blind testing they couldn't tell the difference.

I'd like to see a bunch of bike journos do the same & see if they could quantify the hype in some way.

"Interview with the guy from Pole bikes said in blind testing they couldn’t tell the difference."

Not very sensitive testers?

I know there's more to bicycle steering than the trail figure, but on the Sentinel which has a 64 degree head angle, a 42mm offset fork gives you 136mm of trail. To get the same amount of trail with a 51mm offset fork you'd have to reduce the head angle to 62.7 deg.

http://www.kreuzotter.de/english/elenk.htm

Can anyone show me a diagram that clearly shows why reduced offset increases trail please?, my head says it should be the other way around.... which means I have a misconception of what trail is!

first hit in google for 'bicycle trail measurement'

EDIT - or the one above with more words

There was a thread on here about it.

Interview with the guy from Pole bikes said in blind testing they couldn’t tell the difference.

Probably 'cos their heads hurt too much after crashing from trying to ride a bike blindfolded 🙂

TBF Pole bikes don't need blindfolds their heads are stuck so firmly up their own arseholes

Seems mtb HA can be seen to be vital ie +/- 1 deg is a potential deal breaker to some while offset effect is often dismissed, yet makes similar levels of difference. Only been an option on mtbs in recent years granted, but on drop bar bikes the effect/use offset has been understood and valued for a long time - easier to adjust a steel fork of course and you feel differences a lot easier on a rigid bike.

You probably won't be able to tell any difference. I couldn't when I swapped between a 51 & 44 fork.

What you probably will notice is the super low BB is another bit lower with a fork too short for the bike.

Can’t believe how cheap these are in aluminium form? What’s the catch…. weight?

They are heavy, but not outrageously so, given their intended use. Catches> Limited tyre clearance, sh*t paint quality, rubbish bearings & a rear shock that is a bit of a pain to find a balance with & they only really make sense when you are absolutely hauling on it.

Only been an option on mtbs in recent years granted

It's been an option since the beginning of mtb. It's only recently certain companies realised how easily marketable it is an angle to get a fool to part with their money twice for the same thing.

Thanks folks. Lots of really useful responses.

Think this is the first time I've posted a question and not got half the responses full of sarcastic dribble!

The fork I have is a top end Lyric and I can swap the air shaft out to different lengths.

I've gone part time so £3k carbon frames are out these days, trying to find something to have as my one "do everything except xc" bike.

Really want it to be 29, long and slack. But not too fussed on travel if it's light. But big travel and heavy isn't really an option.

Anything else I should look at?

If you can find a 2017 Smuggler frame the Large weighs 7.3lb 2018/19 8.8lb for medium. But run better with 140mm forks, very capable bike.

Really want it to be 29, long and slack. But not too fussed on travel if it’s light. But big travel and heavy isn’t really an option.

I guess the obvious question is what do you define as long, slack & light?

As always there are plenty of owners of bikes on here that seem to defy the laws of gravity which doesn't help when trying to potentially pick something new...

470 reach+ on a frame with a sub 460mm seat tube. Slack 66 or less.

Travel & weight aspirations?

Not that fuased about travel. 125-160 as I can change the travel of my Lyrics. Sounds vague I know but will have trade offs depending on whether I'm hauling it around the peak district or using a ski lift.

I can get a Sentinal for a touch over a grand new with warranty. Maybe I should lose 2kg and then it'll be light?

To be honest if it wasn't the fork Ofsett being marketed so much eaving a doubt over if it will ride funny I'd just buy it.

Shameless plug I am selling some 2019 performance 36's with 44 offset which will get round the issue. Pm me if of interest.

Weight is a consideration for sure, but people do place a lot of emphasis on it, possibly even too much, unless you're racing XC. When you take into account the entire 'system' weight of the bike, rider & associated paraphernalia, 1-2kg on the bike is going to make little to no difference.

I have an 11.8kg Fuel 9.9 EX, 140/130mm travel 29er, which is just over 66 degrees in the low setting & ~465mm reach, it's a very lively, playful bike which I have in the past built up heavier & raced enduro's on & even the odd regional DH.

I also have a 15.2kg coil sprung 160/160 29er, 64 degree HA, 500mm reach. I could maybe save 500g. If I ride it on local stuff, it feels massive, sluggish, heavy & dead - but it's my race bike. it's built to go fast & be taken abroad to ride & race which it's perfect for.

When I get back on the Fuel after riding the Raaw, it feels scary light, twitchy & deflects off everything & when I swap back, the other bike feels just like the above. It doesn't take long to adapt to either & I find my riding gravitates to the bike i'm on at the time. The thing I do find with the big bike is, you really do have to ride it hard for it to make sense & to do that, you need the terrain for it to work. I found the same with my Sentinel, as does one of the guys I ride with who has a carbon one.

Wonder how the Stooge Mk4 will feel.
That will be running 80mm offset rigids with 66' headangle.
Look forward to trying it!

Hob nob. I'm not so sure. Think of how heavy a camelbak feels with 2litres. You know about it when you put it on.

If you strap that to the frame then you've got that permanently on the frame.

It’s been an option since the beginning of mtb.

Well yes, when forks were rigid. Since sus came out there wasn't the option. RE marketing, maybe, companies can only market meaningless guff for so long though.

Hob nob. I’m not so sure. Think of how heavy a camelbak feels with 2litres. You know about it when you put it on.

If you strap that to the frame then you’ve got that permanently on the frame.

Absolutely you can feel the difference, i've got just over 3kg between my two bikes, it's certainly noticeable (although less so when on the bike). Then it become geometry & suspension that make a bigger difference IMO.

But, much like I don't want to ride my big bike around my local spots, I equally don't want to take my Fuel out to race the EWS's i've entered this year, nor do I want to take it to Whistler, because I want to keep it (and myself) in one piece!

The weight is the price I pay for increased durability & performance (in that area). You can't have it all, so it comes down to where you are prepared to compromise.

Although the new Scott Ransom 900 gets close I think 🙂

Well yes, when forks were rigid

Nope.

Go measure the offset of the varoius suspension fork manufacturers throughout the entire history of mtb suspension forkage too.
not all brands used the same offset. infact look at DH forks and you'll see offset between manufacturers/model year varied wildly

Go measure the offset of the varoius suspension fork manufacturers throughout the entire history of mtb suspension forkage too.

Oh no doubt, and there's never been a standard offset of any sort. I meant only fairly recently would you have the same sus fork with a choice of offsets, lower leg castings in different offsets. I guess you could have varied fork brand to get that change but it wasn't much of a like for like swap.

geex

Member

It’s been an option since the beginning of mtb. It’s only recently certain companies realised how easily marketable it is an angle to get a fool to part with their money twice for the same thing.

Absolutely.👍

I guess you could have varied fork brand to get that change but it wasn’t much of a like for like swap.

The only mtb riders I knew who actually cared about the offset difference were geeky downhillers like me interested in playing with geometry. All most punters cared about was what brand, colour and weight the fork was when infact many of the less popular cheaper forks (often with different offset) were actually more advanced and better performing than those more popular more expensive brands full of plastic shite to control damping and spring rates.

Why look for like for like when you could have had something that actually worked?

Looking at the numbers posted half way down this thread (link here) I would disagree that there was much of a range of offsets back in the day or "since the beginning of MTB" (i.e. 26" forks)

The range is pretty much 5mm with most being around 41mm. Can't see 2mm either way being noticeable to anyone (especially not on a suspension fork where the head angle is changing continually)

Anyone remember the dude on a specialized I think who ran his forks backwards? Ahead of the game...

"Looking at the numbers posted half way down this thread (link here) I would disagree that there was much of a range of offsets back in the day or “since the beginning of MTB” (i.e. 26″ forks)"

The numbers there are within quite a narrow range. But that wasn't long ago, I don't know what forks were like nearer the turn of the century.

I went with short offset (42mm) 160mm Lyriks on my Turbo Levo, which as stock comes with 150mm standard offset (51mm) forks. Weren't 29er forks 46mm offset as standard until fairly recently, with 51mm being the new improved quicker steering variety?

Nearer the turn of the century offset wasn't much of an issue for single crown suspension forks, probably the number was published somewhere deep in the technical specification. I am pretty sure it was around the 40mm mark for a 100mm fork. The first I remember hearing about it was with the Gary Fisher "Genesis" gemoetry for 29ers.

Dual crown forks were different because offset can be changed more easily. I have found on my computer a manual for Marzocchi forks 2004. The drawings show the offset of the stanchions, but not of the axle. Eyeballing it, it looks around 40mm for the 100mm forks, a bit more for the longer travel ones.

Just found a manual for 2002 Marzocchi Marathons (which are still on my wife's bike) and it gives 18mm of stanchion offset and 25mm offset from the stanchion to the axle, giving 43mm. That is a 100mm 26" fork.

This was Pinkbikes take from a Sentinel review....

I've been answering all sorts of questions about offset lately, many from riders who are worried about getting left behind by some sort of new “standard.” Should you rush out and buy a fork with the least amount of offset you can find? Well, no. The amount of offset does make a noticeable handling difference, but it's not as cut and dry as saying that X amount of offset is bad and Y amount of offset is good – there's more to it than that, and installing a fork with the least amount of offset possible isn't going to automatically turn your bike into a magical shred sled.

I spent a day in the bike park switching back and forth between two Fox 36 forks, the one that came on the Sentinel, which has 44mm of offset, and one with 51mm of offset, which is what the majority of 29ers are currently spec'd with. I started off by taking three laps on the stock fork, and then made the switch to the fork with 51mm of offset. The difference is very noticeable – the increased offset felt more like what I'm used to, and the bike felt livelier, but it was also easier to oversteer and wash out the front wheel – the feeling of unlimited front wheel traction that the 44mm offset fork delivered wasn't there anymore.

I timed all of my runs, but the numbers didn't end up indicating any statistically significant difference between the two offsets; I felt like I was able to adapt my riding style fairly quickly to both forks. After swapping back and forth between the two offsets it was clear that there are benefits to the stock, reduced offset fork on the Sentinel – namely better front wheel grip and more stability – but the bike works just fine with a 'regular' 51mm offset fork as well.

Is there any reason you would want a different offset on a fork, other than to adjust the trail?

I was thinking about this, and unless I'm missing something, it's like this...

Steering speed is really just a function of trail (?)
Trail is a function of head angle (slacker = more trail), rake (more rake = less trail) and wheel size (bigger wheel = more trail)
The affect of a small change in rake on trail is pretty small compared to the other two factors...

e.g. The Sentinel has a 64 degree head angle, and with a 2.4 on the front, has an overall radius of 372mm (using BikeCalc's handy table https://www.bikecalc.com/wheel_size_math). Some basic trigonometry tells you that's a trail of 181mm with zero rake [372/tan(64)].

The rake reduces the trail by rake/sin(head angle), so a 51mm rake reduces the trail by about 73mm - OK, about 40% of the above. But reducing the rake by 7mm increases the trail by just 7.8mm, or 2% of the trail.

So I guess the question is why not just reduce the head angle to have the same effect? I make it almost exactly a degree of head angle to balance it out. Is there another limit on head angle? Stresses on the frame/headset? As far as I can see it's going to have exactly the same effect on handling.

I guess you could it's easier to reduce the offset than slacken the head tube (in which case why didn't we start there?) but it does seem like the bike industry changing something else to make it more complicated for everyone - and how do we make it less complicated? Easy, buy a new frame/fork/bike 😀

Steering feel isn’t just a function of trail. The trail dominates at high speed. At low speed the way the front of the bike drops as you turn the bars has a big effect. With high steering angles the movement of the front contact patch to the inside of the turning arc destabilises things. I’m sure there’s more from the wheel/fork end of things.

And there’s wheelbase, reach, front-rear centre ratio, bars and stem to consider.

But if all you’re thinking about is trail, front centre and reach, to get the same trail with 51mm and 42mm offset, the 51mm bike needs a 1.3 deg slacker head angle. That change adds 23mm of front centre length. Do you then shorten the reach by that much whilst increasing the stem by the same? But that’s going to change the steering feel too.

Can anyone tell me in basic terms what running this wrong ofset on a sentinel is likely to feel like at low and high speeds?

I think the word you’re looking for is: “fine”.

The quote above from that Pinkbike review sums it up pretty neatly.

to get the same trail with 51mm and 42mm offset, the 51mm bike needs a 1.3 deg slacker head angle. That change adds 23mm of front centre length. Do you then shorten the reach by that much whilst increasing the stem by the same?

Dafuq you on abah't NAO Chief?

You can't quantify what trail increase/decrease will result from H/A or offset change without tyre diameter (axle height from ground).
And you can't quantify the front centre increase/decrease from any of the above without first quantifying axle to crown length.
Wihout these quantities your post above is just number vomit

Stick with "fine" and ride your bike moar

“Dafuq you on abah’t NAO Chief?

You can’t quantify what trail increase/decrease will result from H/A or offset change without tyre diameter (axle height from ground).
And you can’t quantify the front centre increase/decrease from any of the above without first quantifying axle to crown length.”

Sorry, that was for a Sentinel, or indeed my Turbo Levo. So 29” tyre and 570mm A2C (160mm fork). Obviously head tube length has a small effect too.

“Stick with “fine” and ride your bike moar”

Certainly doing that with electric power to speed and extend the commute!

And there’s wheelbase, reach, front-rear centre ratio, bars and stem to consider.

I guess you're right. My thinking was that reach can be adjusted quite easily with bars and stems.

Thinking about whether there's an effect on front-centre and wheelbase is making my head hurt. If the axle's in the same place there isn't, and you could increase the trail by slackening the head angle and keep the axle in the same place.

What head tube length, A2C length, wheel size and reach is that for?

Thing is, if you're changing the frame design to change the head angle, you could also move it back (shorten the top tube) to give the same front centre and wheelbase.

"Thing is, if you’re changing the frame design to change the head angle, you could also move it back (shorten the top tube) to give the same front centre and wheelbase."

Yes, but then you shorten the reach, which changes the fit. And if you add stem length to get the effective reach back then you change the steering feel.

Head tube 120 including allowance for headset
A2C 497
Wheel diameter 770 (29er)
Reach 507

I drew it up on CAD just to get a picture of how trail changes with head angle change, and how that compared to offset change.

Yes, but then you shorten the reach, which changes the fit. And if you add stem length to get the effective reach back then you change the steering feel.

Yeah, true.

Why look for like for like when you could have had something that actually worked?

Yes look for a better performing product at the same time if you're setting up the best bike you can.
What I was talking about was changing the offset of a rigid or sus fork and keeping all else constant, or close to, to see what offset changes alone does for a bike - or looking at offset and HA combos etc. Purely geo experimentation.