Stem length

[Jarred]

Grrrrrr... My pet hate. 

 

IMO the fit "charts" are still way off, based upon historic adaptation from road cycling fit characteristics, which are vastly different to MTB. I won't go into the reasons here, but they are many.

 

Also - our body compositions are vastly different to each other - that's why I suggest a range of stem lengths, so that you can adapt over 2 frame sizes given certain parameters, and rule out the inapplicable frame size based on either reach requirements, inseam length (important when considering a dropper post) and desired application and current weaknesses. 

 

Yes, at 178 you would be borderline medium / large on most frame charts. But a medium is not a medium is not a medium. It's a generic term based on seat tube length. Which is a totally random way of sizing an MTB, which is not nearly static when riding (unlike a roadbike)

 

An answer to yoiur desire to get it set up like your road bike... Yes and no. 

 

ITO Seating position - absolutely. That's a function of your biomechanical stature (hip position, hip rotation, leg length etc) and shouldn't change between your road and MTB. If you're seated, you want the same pedalling position across both. 

 

ITO bar position - it's slightly different. The wider bars will pull you further forward, which means that your bar to seat post length can be slightly shorter (shorter stem) which consequently means better handling at speed and more confidence in the rough stuff... In short, short stems rule. Long stems make you drool. 'Cos they pitch you over the bars and make you eat through a straw. 

 

So ja. Adapt, adopt, improve (yes, it's the Round Table motto, but it fits. Pinetown 10 member, here...) until you get it just right. It's not an exact science, but it has a few general parameters which can be tweaked according to your circumstances / measurements. 

 

But yes. If you're feeling cramped on a 740mm bar & 90mm stem then you are DEFINITELY on the wrong size frame. 

In general you have a number of good points here, but some of it could be tweaked a little.

 

Inseam is actually not that important because it doesn't give you a proper biomechanical measurement of leg length. Rather concern yourself with greater trochanter (femur to hip attachment) to the bottom of the ankle length. 

 

The measurements of frame sizes are not standardised as you mentioned, and specifically with Mountain bikes where the seat tube runs at all sorts of angles to shorten the wheel base while accommodating 29" wheels. For instance our ErgoFit system uses 2 varying angles to compare Fram size (either a 73 or 90 degree angle). In general your saddle setback should be ~10% of saddle height (when measuring with a 73 degree angle).

 

In general you want your saddle setback to be very similar on the road bike or MTB, but having them exactly would not relate to the exact same pedal stroke as we generally see slightly shorter cranks as a standard on road bikes compared to MTB's.

 

Wider bars may also reduce your reach due to the sweep on the bar. Your shoulder angle is also more important than stem length. The notion that a shorter stem is better for handling is also not always true

[rudi-h]

I am in the opposite situation.

 

I have a 90's 26" mountain bike which is as close as I could get to my roadbike in terms of the distance between the handlebar grips and the back of the saddle. The saddle BB position is the same on both bikes.

 

In December I bought a 29" and started by getting the saddle BB measurements exactly the same. There is however a massive discrepancy on the measurement from back of the saddle to handlebar (120mm).

 

I understand (and have not done any races with the new bike yet) that you sit more upright on the mountain bike versus the roadbike. I feel cramped on the bike however as I want to get into a more aero-dynamic position but cannot. I have lowered a the handlebars as much as I could by removing the spacers and turning the the stem around.

 

Can I install a longer than standard stem and what will be the effect off road? I favour more the jeep track type of roads rather than the tight bits.

 

Thanks

 

Johan

 

IMO the  advancements in MTB geometry (and associated handling improvement) over the past two decades far overshadow the advancements that were made in frame, wheel, fork, brake and drivertrain tech, and these advancements were no doubt significant each in their own right.

 

If all you want in an MTB is essentially a road bike that can ride off-road, i.e. no intention of every riding anything technical, then you can fit a longer stem or do whatever necessary.  Just know that you will compromise handling for aerodynamics, comfort or whatever outcome you are trying to achieve.

 

However if you want to use an MTB to ride MTB, then you SHOULD NOT fit a long stem, nor should you get rid of the handlebar spacers and nor should you fit one of those negative angle stems...

[Jacoo]

IMO the advancements in MTB geometry (and associated handling improvement) over the past two decades far overshadow the advancements that were made in frame, wheel, fork, brake and drivertrain tech, and these advancements were no doubt significant each in their own right.

 

If all you want in an MTB is essentially a road bike that can ride off-road, i.e. no intention of every riding anything technical, then you can fit a longer stem or do whatever necessary. Just know that you will compromise handling for aerodynamics, comfort or whatever outcome you are trying to achieve.

 

However if you want to use an MTB to ride MTB, then you SHOULD NOT fit a long stem, nor should you get rid of the handlebar spacers and nor should you fit one of those negative angle stems...

Wide bars with short, inverted, dropped stem works perfectly for me. Seat height slightly above handlebars.

[DieselnDust]

In general you have a number of good points here, but some of it could be tweaked a little.

 

Inseam is actually not that important because it doesn't give you a proper biomechanical measurement of leg length. Rather concern yourself with greater trochanter (femur to hip attachment) to the bottom of the ankle length. 

 

 

Bingo, femur length and lower back angle is more important to determine the seats position in space.

 

The measurements of frame sizes are not standardised as you mentioned, and specifically with Mountain bikes where the seat tube runs at all sorts of angles to shorten the wheel base while accommodating 29" wheels. For instance our ErgoFit system uses 2 varying angles to compare Fram size (either a 73 or 90 degree angle). In general your saddle setback should be ~10% of saddle height (when measuring with a 73 degree angle).

 

10% of saddle height measured from where? pedal or bb axle centre?

 

In general you want your saddle setback to be very similar on the road bike or MTB, but having them exactly would not relate to the exact same pedal stroke as we generally see slightly shorter cranks as a standard on road bikes compared to MTB's.

 

Yip , i'l subscribe to that. makes fitting across bikes easier and standard

 

Wider bars may also reduce your reach due to the sweep on the bar. Your shoulder angle is also more important than stem length. The notion that a shorter stem is better for handling is also not always true

 

Wider bars can also increase your reach when the bar is too wide It really depends on shoulder width and neck shoulder flexibility, arm length and torso length and flexibility.

 

Hence I always prefer to start with getting the saddle in the right space, then adjust the stem length and bar width according to the riders flexibility. There are no hard and fast rules here. Physical  variances between people can be great within the same height

[Jarred]

 

In general you have a number of good points here, but some of it could be tweaked a little.

 

Inseam is actually not that important because it doesn't give you a proper biomechanical measurement of leg length. Rather concern yourself with greater trochanter (femur to hip attachment) to the bottom of the ankle length. 

 

 

Bingo, femur length and lower back angle is more important to determine the seats position in space.

 

The measurements of frame sizes are not standardised as you mentioned, and specifically with Mountain bikes where the seat tube runs at all sorts of angles to shorten the wheel base while accommodating 29" wheels. For instance our ErgoFit system uses 2 varying angles to compare Fram size (either a 73 or 90 degree angle). In general your saddle setback should be ~10% of saddle height (when measuring with a 73 degree angle).

 

10% of saddle height measured from where? pedal or bb axle centre?

From centre of the BB 

 

In general you want your saddle setback to be very similar on the road bike or MTB, but having them exactly would not relate to the exact same pedal stroke as we generally see slightly shorter cranks as a standard on road bikes compared to MTB's.

 

Yip , i'l subscribe to that. makes fitting across bikes easier and standard

 

Wider bars may also reduce your reach due to the sweep on the bar. Your shoulder angle is also more important than stem length. The notion that a shorter stem is better for handling is also not always true

 

Wider bars can also increase your reach when the bar is too wide It really depends on shoulder width and neck shoulder flexibility, arm length and torso length and flexibility.

 

Hence I always prefer to start with getting the saddle in the right space, then adjust the stem length and bar width according to the riders flexibility. There are no hard and fast rules here. Physical  variances between people can be great within the same height