MTB frames and their maximum fork length versus the fork length you actually run

If I were to stick some 160mm Lyriks on my LT hardtail frame (which has a theoretical maximum supported fork length of 150mm) will the sky cave in and demons rise up from beneath the earth's crust?

I should probably just stick with my 140mm Pikes.

How far have you pushed the manufacturer's guidance on your bikes?

it'll be fine

(running 180mm domains on a dialled alpine)

120mm in 100mm Lynskey for a few months and it rode a lot better for it.

160mm on a hardtail frame is probably a bit pointless. unless you're bottoming out the 140mm you'll not see much benefit. running longer forks will also straign the head tube welding a bit more than intended – how you ride will determine if this is trouble or not.

It can break your frame

The original Giant Trance was a lot better on a 130mm fork than the 100mm supplied/recomended.

If your frame's still in warranty, I'd think twice but other than that I'd crack ( 😉 ) on.

If your frame's still in warranty, I'd think twice but other than that I'd crack ( ) on.

It's a Commencal, so I may be tempting fate!

I ride an Alpine with Lyriks, but very rarely use them at full travel. If you have u-turns there is no reason why you can't run them at 140mm or 150mm. Unless you are pointing downhill the handling gets worse the longer your forks get.

can't really see the point in running 160mm in a hardtail frame TBH…. if it's rated to 150, I imagine it'll be ok with 160, but there will obviously be a warranty issue and you'll slacken the front up quite a bit.

If you put Lyrik u-turns in it, you can always dial them down to 145 or something, but then you may as well stick with the pikes for that.

Assuming your Pikes are 20mm axle, can't remember if they all are or not, I don't think there's much point in changing unless you're pushing the limits of your pikes and botteming them a lot (a number of times during each ride) as said above.

cynic-al – Member

It can break your frame

Will it tho? its such a small % increase in the leverage and there must be a safety margin. So unless you are hooning off huge jumps and weigh as much as wales then I don't buy this argument.

The frame is safe for a 100 mm fork – thats A-C of what – 450 mm (ish)

Go to a 130 mm fork thats 480mm A-c – an increase of 7% in length so 7% greater leverage. Thats not a lot. 7% greater forces.

stooo – Member

if it's rated to 150, I imagine it'll be ok with 160, but there will obviously be a warranty issue and you'll slacken the front up quite a bit.
10mm – not even a half a degree of slackening.

I run a bike designed for 80 mm forks with a set of u turn pikes at 95 – 140

At 95 it rides just fine. at 110 the weight shift backwards is starting to effect things – it doesn't climb well but the steering is still ok. At 140 mm it is only any good for steep downhills and is totally wheelietastic and a bit sluggish steering

I suspect it was a steep angled sharp steering frame originally.

Would love to hear mike@dialled, brant or cy's view on this

I replaced 435mm a-c rigid forks with 545mm a-c 150mm travel suspension forks.

noticeably higher at the front but by god it makes the bike a much better ride 😉 I am running about 50% sag though 😛

I expect manuals are easier now nbt…

TJ – I said it "can" break your frame – soulrider did exactly this.

As to whether it will, that depends on numerous factors in the OP's riding that you and I know nothing about. It's clearly not just about fork length % increase. The fork will likely be most compressed at maximum stress. Folk will tend to ride more hardcore on a longer fork and it is likely to be stiffer, transferring more force to the frame.

As TJ aludes to its all about the A-C lenght. Take my bike, i am running the 2010 Revelations on my P7 which at 150mm are supposed to be too long for my frame (max 140mm) but the A-C length on the 2010 revs is the same as the 140mm 2009 model…

Don't buy the stiffness of the fork having any significant impact, most modern trail forks are a lot less flexy than the used to be and even more so with bolt thru axles. I reckon she`ll be right 🙂 , with the appropriate amount of sag the real length of fork will be less anyhow.

Folk will tend to ride more hardcore on a longer fork

I'm guessing thats the critical factor – not the increased fork length putting more stress on the frame but the harder riding that becomes possible.

I put the pike on mine as an experiment and was fascinated by the apparent results – in that the slackening off of the head angle made little difference that I could feel in terms of the steering ( perhaps because of the decreased trail??? or steep angle to start with) But the alteration in the centre of gravity was very noticeable. The weight going backwards and higher alters the feel remarkabley.

If you think bolt-through axles are relevant, you haven't thought this through have you?

160 lyriks on an old (03ish) rocky ridge frame, have done for a while. Given the franky pisspoor way I ride I'm most concerned about the chainstays.

Not so much relevant, just in relation to stiffness. All modern forks are stiff as hell unless you go for XC specific. I was saying that i'm not so sure the forks stiffness (i asume u meant lateral stiffness) is a significant factor in the forces on the frame. Certainly not in relation to the leverage of the fork itself as the majority of impact will be inline with the frame from the wheel hitting obstructions in the trail, thats why gussetng sits on the down tub surely.

Go to a 130 mm fork thats 480mm A-c – an increase of 7% in length so 7% greater leverage. Thats not a lot. 7% greater forces.

Yes, but if we're talking fatigue damage is it necessarily a linear relationship?

I was saying that i'm not so sure the forks stiffness (i asume u meant lateral stiffness) is a significant factor in the forces on the frame.

I mean back and forth stiffness. A lyric is going to deflect way less than a 32mm fork for instance. Lateral stifnfness is irrelevant.

130mm menja's on a 456 so still 20mm off the 'maximum'.

I tried 150mm once on a hardtial, the problem is as TJ said, the bigger forks push weight back, and make it harder to put weight on the fork and off the unsuspended rear wheel. With 130mm-140mm forks I can get the bars low enough to keep weight on the front wheel, any more and I start to wish for some rear suspension.

Ever since the favourite buzzword in magazines became "slack" there seem to be a lot of people who are convinced that bike designers don't know what they're talking about. I once put 100mm forks (with no preload to maximise sag) on my old Kona – after the honeymoon period I was forced to admit that it wasn't better, and in fact was quite annoying, because you had to get all over the front of the bike to get it to turn.

I prefer a neutral handling bike that you can drive from the middle, pretty much like the designer had in mind in the first place.

I'm running a '03 100mm Superlight with 130m Revs. It has made going down much more fun but climbing is more difficult. No cracks yet.

Longer forks push seat angle back, as well as head angle backwards, so you're sat further over the back wheel, which makes the bike wheelie more on climbs.

It also lifts the BB, which in most cases, isn't really what you want to happen to maintain nice handling, and also means the bike is more wheelie prone.

Frames designed for long forks (hopefully) have things in the right place when those long forks are fitted.

I can see how shorter riders can struggle with the height of the front of a long travel hardtail, but there's not a lot anyone can do about that. Suggesting perhaps a shorter fork, and slacker head angle is one, but… For a small rider wanting a great ride, the On-One Summer Season with an 100mm fork is still a standout buy.

To answer the OP, it'll probably be fine. I agree with Cynic-al's sentiments about

Folk will tend to ride more hardcore on a longer fork and it is likely to be stiffer, transferring more force to the frame

, but the change from a tough 150mm fork to a tough 160mm one isn't too great.

Yay! I wuz right!

Anyway, a 10mm longer fork (for the same A-C) isn't actually 10mm longer, as you'll have 30% of that as sag, so it's more like 7mm longer. If that makes a difference I'll be surprised.

cynic-al – Member
Yay! I wuz right!

lol, nothing like only reading what you want to read al! 😀

How so tree?

if a fork has the same a-c but has 10mm more travel won't it actually be 3mm shorter than the other fork with 30% sag dialed in?

not sure it matters, as I rarely slam the front end of a bike into things when sitting at sag, normally fully extended or fully compressed when i crash 😀

i ride 140 pikes on an Intense meant for 100 mm forks not died yet. Wind them down for all but downhill and they have a lot of sag as well so possibly only 20mm longer than 100mm not dies yet.

Al

To answer the OP, it'll probably be fine. I agree with Cynic-al's sentiments about

Folk will tend to ride more hardcore on a longer fork and it is likely to be stiffer, transferring more force to the frame
, but the change from a tough 150mm fork to a tough 160mm one isn't too reat.
he agrees with you – italics- but the says it makes f all difference- bold. Either side could claim victory from that statement

Aye well the design guru/hero quoted me, so I am taking it as my victory

Anyways soulrider recently broke his soul running wound down lyrics so there has to be something to it.

Anyway, a 10mm longer fork (for the same A-C) isn't actually 10mm longer, as you'll have 30% of that as sag, so it's more like 7mm longer. If that makes a difference I'll be surprised.

Good point.

However, one to watch is that manufacturer tolerances on forks are quite wide- Fox for instance spec +/-5mm for length on their forks! I only found out as I mentioned to Cy that rear shocks have +/- 2mm on their length (which is quite a lot at a 3.25/1 ratio!

ps – cynic-al – I can now use this quote about myself 🙂

design guru/hero

Bottom line: If the longer fork rips the headstock off, would you be happy just buying another frame? 'cos you'll be out of pocket.

Yes: do it!

No: relax, don't do it.

Its that bottom line that's stopped me putting pikes on my tandem and 160mm forks on my 5-spot.

160mm Lyriks on a Dialled Alpine

140mm Pikes on a Meta 4.2

180mm 66s on a Spesh Pitch

No snapped headtubes so far

Anyways soulrider recently broke his soul running wound down lyrics so there has to be something to it

yes you've got me there as no one has ever snapped a frame with the correct length forks on their bike…you have swayed me with your impressive use of a massive amount of statistics now 😉

ADH – having used the term "headstock" I can no longer take you seriously in technical matters. See also "cross-bar"

brant – Member
ps – cynic-al – I can now use this quote about myself

If you credit me (as internet fan-boy), I will allow it.

Setting aside the frame breaking, surely the best reason to not bother is that it is unlikely to be better? If the designers worked out all the angles, built and tested prototypes and in all likelihood based the design on tried and tested previous years' models, how likely is it that they got all of that wrong?

Personal preference may mean someone prefers a different set up to the designer's.

As for statistics – I've not heard of any soul breaking there (if at all), and all I ever said was that it was possible.

i was joking – you did see the wink didnt you? I would be certain it makes it marginally more likely as you are outside "normal " tolerances but the increase/difference is marginal and the small increase in risk is acceotable IMHO.

Braking frames is probably more due to rider style/terrain than fork length per se. A mincer will never break a frame where as a balls our rad to the sic jumping god will be far more likely even if they are smooth