On my bike I have a set of talas that go from 120 to 160 I thought this would be the perfect combo for the riding I do but whenever I switch to 120 it feels like I have put the brakes on or something is dragging, I met someone on a trail yesterday and he had the same problem with a 100 to 140 travel bike. Is it to do with the geometry of the bike or because my front tyre is pretty meaty and more weight is on that? Anyone else come across it? I have a blur LT.

I remember a saga about this in MBA magazine last year. They even got Dave Weagle of DW link fame on the case. I don't remember the reason as I don't have travel adjustable forks but I think there was some geometric reason why this is the case.

linky

It's prolly your front tyre rubbing the downtube. 😉

It tips you forward on the bike, which affects the way the gyroscopic stability of the rotating wheels interacts with your bodies inertia, slowing you down. It's a bit like the way you can't eat a banana on a merry-go-round because the end is always pointing away from your mouth.

Had the same on my old Giant NRS with bombers on the front, if I used the eta to lower the front for really steep climbs it felt like the brakes were on, was easier to cope with the light front than the increased resistance

Seat angle becomes too steep so your no longer at the optimum position for pedaling efficiency.

Dropping the fork one inch is about one degree on head and seat angle as a rule of thumb. Dropping 4 inches of your fork is therefore about 4 degrees. If the gradient is only 4 degrees, I doubt you'd need to drop the fork travel. I doubt very much it's anything to do with seat angle and pedalling efficiency. Besides, that could open up the whole Keith Bontrager/KOPS can of worms.

More weight over the front of the bike, coupled with the tendency to run the front tyre soft, making the bike feel slower?

set your bike up with the fork in 120mm, ie. bar angle, seat position, brake angle. When you flip to 160mm itll be like riding a chopper, horrid, unless your pointing down a steep trail in which case you might actually se some of the 160mm.

Dropping 4 inches of your fork is therefore about 4 degrees.

40mm isn't quite the same as 4 inches!

At a guess probably a combo of more weight over the front and the tyre hitting obstacles and stalling (very slightly) rather than rolling over them with the longer travel.

jim, exactly, so the effect is even less if you're only dropping 40mm. Certainly not enough to start upsetting seat tube angles.

i think it is to do with head angle and more specifically trail angle.

as you lower the fork the trail decreases. I find this most noticable on bumpy but flat terrain, fire roads etc. the bike feels much easier to pedal at 140mm than 100mm.

There has been discussion of this on MTBR.com. Sometimes I think it's happening to me… (honest).

which affects the way the gyroscopic stability of the rotating wheels interacts with your bodies inertia, slowing you down

Blimey 😯

Can't say I've noticed this with my Fox Talas forks when lowered.

The theory is along the lines that with a steeper head angle, a greater proportion of the force pushes into the face of the hill with less vertical component. Guess it makes sense. It's the flip side of too much vertical component where the bike starts to wheelie.

It's a bit like the way you can't eat a banana on a merry-go-round because the end is always pointing away from your mouth.

I know this is rubbish but I want to try it now.

So does that mean you are still using the same amount of energy/force to pedalbut it just feels different?

force times distance per unit time. If none of this varies (and you don't waste a load more energy as heat) I guess it's the same but feels different.