Quantcast

Explain fork offsets to me

norbar

norbar

KESSLER PROBLEM. Just cause
Jun 7, 2007
11,369
1,605
Warsaw :/
So I've been out of the information loop for a while and now I learn that the whole new hot thing is shorter fork offsets. Any companies adjusting geo to it already? Is the difference noticeable or is it just a way to help superlong bikes from companies that hate posting geo numbers keep the front end weighted (which isn't completely necessary of course ;) ) ?
 
Flo33

Flo33

Turbo Monkey
Mar 3, 2015
2,066
1,306
Styria
Tranny has it in their marketing speech.

To me it is noticeably, going from my 26" 36 to the 650b one feels quite different, a2c height is nearly the same. The 650b feels like driving a bus compared to the shorter offset 26" one like a "normal" car, if that sounds not too stupid...
 
norbar

norbar

KESSLER PROBLEM. Just cause
Jun 7, 2007
11,369
1,605
Warsaw :/
Flo33 said:
Tranny has it in their marketing speech.

To me it is noticeably, going from my 26" 36 to the 650b one feels quite different, a2c height is nearly the same. The 650b feels like driving a bus compared to the shorter offset 26" one like a "normal" car, if that sounds not too stupid...
Click to expand...
I'm mostly talking about same wheel size, diffferent fork offset.
 
Happymtb.fr

Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,916
1,270
SWE
I went from 51 to 42mm on my trail bike, everything else was the same, same travel, same fork model, etc... I did not notice much of a difference except for slightly more grip on the front which could basically be explained by the shorter front centre.
 
Sandwich

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,073
5,985
borcester rhymes
I'm not going to get into the techno babble gobbledy gook. I'll reply with my opinions and experiences-

When mfgs went to big wheels, they found that they handled slowly (naturally cause big wheels). To combat that, gary fisher came up with the idea to increase fork offset (from 42/45 to 52ish) in order to speed up handling at low speed and make big wheelers feel like 26ers. This pleased the MTBR crowd as now they could MORE ROLLOVER as well as still navigate spaghetti trails. All was well in the world

Until people who go fast got involved. Suddenly they realized that shorter offset slowed down steering and made it more direct. This allowed more control at higher speeds (as well as shortening the wheelbase [which seems ridic @ like 7mm]). Transition has claims about moving the wheel back under the rider despite the longer front center due to every growing reach measurements, but again, 7mm.

In my experience, longer offset does indeed speed up handling at low speed, but it makes things twitchy at higher speeds which is unwanted if you visit higher speeds, ever. I've also found other weirder aspects of increased offset, like wheel flop at low speeds (and sometimes higher speeds too) and ruts having a bigger impact on steering. Some of this may be imagined, but I would hop back onto a low offset fork if they were more readily available in an instant. My experience comes from both 26ers downhilling and 29ers on trail.

I think it's largely a matter of taste, and I think that it's worth considering if you're building a bike from scratch, but unlikely to matter if you're happy on your current gear.
 
englertracing

englertracing

you owe me a sandwich
Mar 5, 2012
1,580
1,074
La Verne
Ive tested different offset on mx bikes, supermoto, and mountain bikes. I have tried it at the tripple clamps with different clamps, at the axle with a rekluse e axle for quick back to back testing, and adjustable insert tripple clamps.

In mx the offset is subjective and usually not changed more than + or - 2mm from stock but sometimes as much as 4mm.

I find, more too much offset/too little trail has a lighter feel, or floppy, or swappy perhaps, quicker perhaps good for making quick steers around unexpexted junk. When grip limits are exceeded it washes and provides a neutral feedback where the bars get lighter when it pushes, or it tried to straighten up. May have slightly less grip.



Too little offset/too much trail heavier steering, but also more planted, but also slower and harder to avoid unexpected stuff. When grip limits are exceeded it tucks, so the bars actually turn in when your loosing it making it worse. May have slightly more grip.

Now endurobro mag wants to help fox sell 36 29er owners 27.5 crowns and 27.5 owners 26" crowns.

Now i havent tried anything with my 36.
But with my 40, ive tried
With 27.5" wheels
45mm offset 26" lowers
52mm offset 27.5" lowers
And now i have an outsider adjustable offset crown kit and have tried 53mm, 51mm, 49mm

For myself, 52mm was flompy,
45mm heavy and slow, but not really tucky,
53mm outrageously bad
51mm meh, 49mm ok.
Would prefer a range of probably 47-49mm personally, so rockshox nailed the offset, but ive always ran fox 40s.

The best way to figure it out is to head over to outsiderbikes.com and buy a pair of aaron bland's beautifully machined adjustable clamp and figure out what offset suits you best.
 
norbar

norbar

KESSLER PROBLEM. Just cause
Jun 7, 2007
11,369
1,605
Warsaw :/
Sandwich said:
I'm not going to get into the techno babble gobbledy gook. I'll reply with my opinions and experiences-

When mfgs went to big wheels, they found that they handled slowly (naturally cause big wheels). To combat that, gary fisher came up with the idea to increase fork offset (from 42/45 to 52ish) in order to speed up handling at low speed and make big wheelers feel like 26ers. This pleased the MTBR crowd as now they could MORE ROLLOVER as well as still navigate spaghetti trails. All was well in the world

Until people who go fast got involved. Suddenly they realized that shorter offset slowed down steering and made it more direct. This allowed more control at higher speeds (as well as shortening the wheelbase [which seems ridic @ like 7mm]). Transition has claims about moving the wheel back under the rider despite the longer front center due to every growing reach measurements, but again, 7mm.

In my experience, longer offset does indeed speed up handling at low speed, but it makes things twitchy at higher speeds which is unwanted if you visit higher speeds, ever. I've also found other weirder aspects of increased offset, like wheel flop at low speeds (and sometimes higher speeds too) and ruts having a bigger impact on steering. Some of this may be imagined, but I would hop back onto a low offset fork if they were more readily available in an instant. My experience comes from both 26ers downhilling and 29ers on trail.

I think it's largely a matter of taste, and I think that it's worth considering if you're building a bike from scratch, but unlikely to matter if you're happy on your current gear.
Click to expand...
Wait so what you feel longer offset speeds up handling and creates wheel flop? Isn't it simply changing the effective head angle and FC?

I will probably buy complete but I will also probably go back to obsessive tinkering which is why I'm asking.
 
Sandwich

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,073
5,985
borcester rhymes
I feel that greater offset increases steering speed (or agility), particularly at low forward speed. I have heard that increased offset contributes to greater stability at speed, but I think you need very high speeds and less aggressive turning angles (ie wide arcs). Shorter offset creates a more direct feeling between your hands and the wheels, slowly down steering and making it more direct. I think it's similar to stem length, but there are certainly additional components.

Wheel flop is something that I first noticed with my avalanche DHF back in the 00s. That fork had 65mm offset and I struggled with wheel flop at speed often. I would be mid-berm and the bike would just "snap" over and throw me OTB. There are a lot of factors here, but when I switched to a boxxer on a sunday frame, I never experienced that sensation again. At least part of it was due to the reduced 20mm of offset (as well as slacker HA and wide bars), but I noticed similar traits with a 36 @ 51mm vs, rebas and others at 45mm.

There was an article floating around where a guy tested 37, 45, and 51mm forks on the same bike with the same fork, and he was significantly faster on the lowest offset fork. He also reported similar things to what I've seen, with slower and more direct handling.
 
ChrisRobin

ChrisRobin

Turbo Monkey
Jan 30, 2002
3,351
193
Vancouver
I think the biggest difference I noticed going to 44mm offset from 51mm on my 29er, was the slow speed twitchiness. With 51mm, I found rocks and roots knocked the front wheel around, especially on climbs. The results of going to 44mm was more subtle...not exactly earth shattering but still noticeable. I'll be sticking with 44-46mm moving forward.
 
C

Cerberus75

Monkey
Feb 18, 2017
520
194
In my experience it has a lot to do with the length of the front center of the bike. On my Riot I played with different offsets. On the size small the shorter offset would tuck to easily, which wasn't worth the stability. I just upsized and prefer the offset shorter.
 
HAB

HAB

Chelsea from Seattle
Apr 28, 2007
11,580
2,006
Seattle
norbar said:
Wait so what you feel longer offset speeds up handling and creates wheel flop? Isn't it simply changing the effective head angle?
Click to expand...
It's different than changing the effective head angle, because the axis about which the steering turns doesn't change. Larger offset does speed up steering and increase wheel flop, it feels quite different than reducing head angle.

I've experimented with various combination of 37mm, 44mm (26 and 650b 36 uppers, respectively) and 45mm (26 40, which clears a 650b comfortably) on two different bikes, with both 26" and 650b wheels. It's worth noting that both bikes in question are very long and slack. 37mm on a 650b wheel is definitely my favorite combo from a steering perspective. I keep thinking about making some crowns for the 40 to get down to a similar number, but haven't gotten around to it.

To me, bigger offsets feel most detrimental at medium speeds, where you're moving out a bit, but not going so fast that you're no longer making significant steering input. The effect fades as you hit warp speed, and the size of the steering inputs you can make drops to near zero. Bigger offsets feel twitchier/floppier and less precise. The effect is noticeable at slow speeds too (e.g. climbing), I just don't really care that much one way or the other, because handing at 3mph simply isn't a priority.
 
F

FarkinRyan

Monkey
Dec 15, 2003
611
192
Pemberton, BC
The difference between the two generations of Transition Patrol from a steeper head angle, longer offset fork to slacker head angle, shorter offset fork is definitely noticeable when riding the two bikes back to back. The newer bike has 10mm more travel up front and a 64 degree head angle but as soon as you jump on you notice that the front wheel isn't as far out in front of you as it 'should' be.

To me the most noticeable difference on the trail is the newer bike feels like you can find front wheel grip while cornering without the need to get your weight as far forward, allowing you to ride the bike in a more neutral position that allows for more overall grip. The older bike is a hilariously fun drifting machine but the newer bike is likely faster in the corners.

Edit: This is comparing an older large to a new medium, which have pretty comparable reach numbers.
 
Last edited:
You must log in or register to reply here.
Top Bottom