Is there such thing as a 'perfect weight' for a XC bike?

swelsbyuk

This might seem like a strange and possibly unanswerable question, but it’s a genuine one nonetheless.

A friend I go riding with in roughly the same weight as me (13 stone) but considerably fitter. I ride a £700, 12kg hardtail and he rides a £2.5k, 9.5kg carb whippet.

Given the extra fitness levels and lighter bike he thrashes me going uphill. However, going downhill over rocky terrain he bounces all over the place and I can bomb past him.

I am looking to upgrade my hardtail in the coming months and want something lighter but don’t want to get to the stage of bouncing around like a jack-in-a-box on the downhills.

So, is it possible to work out at what point a lighter bike will be just too light for XC downhills?

S

cooldad

Maybe it has nothing to do with the bike and you just pick better lines.

.blitz

Everything that makes a bike good at downhill makes it worse uphill.

njee20

Not that clear cut is it.

A short travel FS will beat a rigid bike of the same weight on technical terrain up or down.

I'd say not. I really like my 9kg FS bike, some folk would no doubt find it too light, but I like how it rides. Lively I think the term probably is!

nicklouse

the weight of the bike has little to do with it.

set up and terain has more. (except climbing).

andy_welch

It depends on what you are after I suspect.

Given that you spend a lot more time climbing than going down and even though the light bike is bouncing around more it probably isn't losing that much time, I'd guess that the light bike will still be faster overall. So, if the goal is to beat your mate (or even beat your own PB around a course) then lighter is probably always better (until you reach levels that hardly any of us could afford). However, if your aim is to enjoy the descents as much as possible then a lighter bike may not be any good for you.

I do find this question interesting though as I've recently re-started a bit of off-road riding after many years of being a roadie, where lighter is usually better as long as you don't lose stiffness. So, I'll be interested to hear the comments from those more knowledgeable than me.

Cheers,

Andy

andy_welch

Just trying to think why the lighter bike bounces around more. Presumably it's because, when the heavier bike hits a bump the tyre compresses more. So, can you not just drop the tyre pressure on the lighter bike so it doesn't bounce around any more than the lighter bike but is still faster up the hills?

Cheers,

Andy

Rushmore

Get a full Susser that weighs around the 12kg mark... You won't really notice the weight... As you'll just cruise over everything pretty much...

bails87

I think the OP should swap bikes with his mate.

I bet it's down to the rider, not the bike. Although fork and tyre setup can have a massive impact, they're easy to change (assuming air forks).

njee20

Get a full Susser that weighs around the 12kg mark... You won't really notice the weight... As you'll just cruise over everything pretty much...

I would. I notice when I swap to my 'normal' wheels, which are less than a kilo heavier than my race wheels. Sod adding another 2kg on that.

Weight isn't the be all and end all, the style of bike is a bigger factor. Heavy hardtail vs light FS or light rigid vs heavy FS will yield rather different results in different situations!

Northwind

A really light bike can be a wee bit more of a handful- less momentum basically, which makes it easier to knock around. But also easier for the rider to move it around. If you're a rockplough then a really light bike won't give you the benefits that it'll give a more subtle rider and might have some drawbacks.

swelsbyuk

I already have a 2011 Canyon Nerve XC 6.0 full suss which is about 12.5kg, just fancied a HT at around 11kg and wondered whether that might be too light and likely to 'bounce'.

andy_welch

swelsbyuk wrote:

I already have a 2011 Canyon Nerve XC 6.0 full suss which is about 12.5kg, just fancied a HT at around 11kg and wondered whether that might be too light and likely to 'bounce'.

So, can you keep up with your mate on the Canyon?

Cheers

Andy

swelsbyuk

I've yet to try - we're out on Thursday so maybe I'll give it a go.

njee20

just fancied a HT at around 11kg and wondered whether that might be too light and likely to 'bounce'.

The weight is pretty irrelevant in that - it's how you ride it. But yes, if you ride it the same way (primarily because it's a hardtail) you will have a rougher ride than on your FS.

11kg is hardly featherweight.

The Rookie

njee20 wrote:

11kg is hardly featherweight.

This !

Simon

supersonic

I like riding light bikes as I can ride faster and further on them, or use less energy for the same speed or distance. I especially find them easier to hop and manoevre under my body.

However... the kit I have falls on the sensible side of light. There is an eye on strength and durability. This costs though.

jehosophat

There are a few different things here. Firstly I have found that speed downhill and over technical terrain is more down to the rider than the bike, within reason. Some of the guys I ride with I have known since school (I left school 19 years ago...............) and have ridden with, on and off, since. The rider makes the main difference.

The heavier you are, the less difference saving a fixed amount of weight off the bike will make. A 60kg rider is going to notice a 1kg saving more than a 100kg one, just as he/she would notice a 1kg saving in a rucksack more than the heavier rider if walking or running.

In terms of how the lighter weight affects downhill performance, it depends on how the weight is saved. I don't think you'll go any slower changing from an SLX to an XTR groupset, or from a set of heavy 2.3" heavily treaded tyres to a lightweight equally heavily treaded 2.3" set of tyres. But go for a shorter travel or weaker fork with inferior damping, bendy light wheels, controls and brakes that are so light they don't inspire confidence, or narrower, less treaded tyres and you will be slower.

I have two full suss bikes, a Superlight with 100mm travel and very light slightly bendy 100mm forks, weighing 26 and a bit pounds and a Blur Classic weighing about a pound more with 115mm travel (but from a more active VPP setup - feels like more of a difference) and a set of very stiff 130mm forks with better damping than the lightweights. Wheels, transmission, brakes and finishing kit are near identical. The Superlight is set up fairly stiff, the Blur (my "trail" bike) so that I use full travel on the bumpy stuff. I feel like I am losing a bit on the hills on the Blur, the suspension remains more active and 130mm forks bob more even when seated. But it more than makes up for it on the downhills where it is far more stable and secure. That's the main difference I have noticed going from a hardtail to the Superlight to the Blur as main bike over the last decade - my speed downhill vs the people I ride with remains much the same, whatever we are all riding, but longer travel, less flex, and wider tyres means more confidence, security, fewer crashes, and less fatigue.