[Closed] Wandery handling

It's likely to be insufficient weight bias to the front.

Longer stem, lower bars, move saddle forward.

Depending on how the bike fits you, the will be effective, or not, and may compromise comfort.

BTwin bikes are good value but they don't wear very well. Is the headset loose or siezed? That would explain the wandering handling.

Or headset too tight, even?

I had that exact problem and the cure for me was as simple as lowering the stem by one 5mm spacer .

what do you ride at home, for comparison?

Tyre pressure too high

It may be that you don't ride super steep fire roads in the UK? I've encountered silly steep fire roads in Europe that we don't usually make here.

You could try saddle further forward, bars lower, or longer stem - all of which are cheap to try. But it could just be technique - you need to perch on the nose of the saddle for silly steep stuff. Or stand up.

If the bike constantly feels as if it wants to dive across to the side of the road and feels generally insecure it's because the headset bearing is seized or over-tight.

The geometry sounds fine for ascending. Try and chew the stem when you're climbing steep stuff. On steep stuff it will wander, you've no weight over the front wheel so it's not the forks flexing, just the bike doesn't respond to your inputs so well due to the low speed and rearward weight bias.

Obviously a general check that everything is set up right is worthwhile too. And lower/lengthen the front end if you want to achieve this stem biting position with less elbow flex.

Does it feel most vague on roads and smooth surfaces? Ie take it off-road and it feels fine?

Or is it vague all the time on all terrain?

How does it behave when you take your hands off the bars?

Have you checked the swing arm pivots?
Had a weird handling problem which turned out to be the rear end but felt like headset.
Whenever I checked the rear axle was clamped tight but by accident - I was cleaning the frame with the rear wheel off - I discovered that what the wheel clamps to was loose.

I know Decathlon have a reputation for producing amazing value bikes but you are not going to get swingarm pivots on a 650 euro MTB , it's a hardtail .

mismatched tyre pressures?

Thanks everyone for the input, much appreciated.

For info: at home I ride a Specialized Chisel Comp 2018, so another XC-focused bike. On the B'Twin I am running a 100mm stem with a 0 degree rise, bar ends and no spacers. Tyre pressures are usually around 30 front / 35 rear since the tyres (50-584 Hutchinson Cobras on 584 x 19c rims) are tubed.

Does it feel most vague on roads and smooth surfaces? Ie take it off-road and it feels fine?

Yes, this is exactly it. It's great off road but vague and wandery on the road, even on the flat or descending. What were you getting at, spacemonkey?

If the bike constantly feels as if it wants to dive across to the side of the road and feels generally insecure it’s because the headset bearing is seized or over-tight.

This has been suggested a few times which leads me to feel it may be the issue. Unfortunately I'm nowhere near the bike at the minute. Will check the headset out when August rolls around!