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-   -   Xc mtb fit conpared to cx (https://forums.thepaceline.net/showthread.php?t=282171)

catchourbreath 05-02-2022 06:08 AM

Xc mtb fit conpared to cx
 
Trying to figure out why my arms/wrist/hands felt so horrible riding my mtb for the first time this season. Only got the bike last year and never really set things up totally.
My question is to get ballpark saddle setback and reach is there any correlation from a cx fitting? I read somewhere to match saddle setback (all saddles the same) among different bikes and using your forearm length for a rough reach measure. Using those metrics I was way too compact in the cockpit.

bewheels 05-02-2022 07:45 AM

You could start here - https://www.leelikesbikes.com/dynamic-mtb-fit
It is worth the $25 to buy the downloadable book.

Part of the issue with asking about mtb fit is that it can vary greatly depending on:
- Your geography ...east coast tech single track with steep ups/downs, big up/downs of the Rockies, etc
- How you ride ...XC racer, freerider, down hiller, trials rider, groomed bike parks, etc
- New bike with new geometry, older bike with older geometry
- Limitation to your body ...beat up hands, wrists, elbows, shoulders, etc

Bars with a lot of sweep back can also help hand/wrist/elbow issues. Some brands and models sweep forward and then sweep back so that it doesn't turn into a calculus-based project to sort out stems. https://www.sq-lab.com/en/products/handlebars/

catchourbreath 05-02-2022 08:01 AM

East coast, xc, 2021 Top Fuel (moderately new geometry).
I'm sure there are various body limitations.
That link looks interesting.
I was thinking/hoping there might be some correlations to work off my fit from cx or road to set things up on the bike to see how I feel from there. I do have an idea now just matching setback and forearm but was curious if that's even a good metric.

bewheels 05-02-2022 08:41 AM

Quote:

Originally Posted by catchourbreath (Post 3087345)
East coast, xc, 2021 Top Fuel (moderately new geometry).
I'm sure there are various body limitations.
That link looks interesting.
I was thinking/hoping there might be some correlations to work off my fit from cx or road to set things up on the bike to see how I feel from there. I do have an idea now just matching setback and forearm but was curious if that's even a good metric.

Consume the various videos/articles/eBook from the link above. It will cover what you want to know.

The issue with trying to directly match your road/cross setback to your modern mtb are multi-fold:
- The seat tube angle on your Top Fuel is going to be a lot steeper than your road/cx bikes. If you try to match the setback you are going to be looking for a dropper seat post with extreme amounts of setback and most dropper posts have very little (or no) setback.
- The seat tube angle of a dual suspension bike changes as it moves through its travel.
- The steeper seat tube angle is part of the overall geometry evolution of mtbs which has evolved to align with how the bikes are used.

But the setback you know can certainly be used as a starting point. Just don't get hung up on it for all the reasons listed above.

The use of your forearm to determine reach:
- This is a very old method to narrow in on a range when starting on a very wide range. asking how tall someone is gets you to the same range
- It is not reliable
- You could use your forearm as a measuring tool when comparing one of your bikes to another but there are much more accurate measuring devices to do this :)

But...you are not trying to match a road/cx bike's reach to a modern mtb to be ridden in east coast terrain (assuming rocks/roots/steep ups and downs). If you plan on riding any level of technical trails and want to be dynamic in your riding vs just hanging on to the bars, look over the info in that link and do a search for Lee McCormack to find more of his fitting info...or just buy the eBook.

catchourbreath 05-02-2022 08:46 AM

That's very useful info, thanks.

benb 05-02-2022 09:07 AM

Make sure you think about tire & suspension sag affecting the seat angle as you set your seat up. Not real easy but the fork sagging can tilt the saddle forward and pitch you onto the bars and also shift you forward relative to the BB. It's not like road where you're holding a stationary position all the time but it's still a thing.

Also make sure your brake & shift levers are positioned so you can keep a neutral angle with your wrist... check your seated chugging along position and your out of the saddle "attack" position.

The suspension & tire setup itself also plays into wrist comfort. Bar shape/size has been mentioned already of course.

Reach is going to be shorter AFAICT on a modern MTB compared to an older one due to the wider bars, and much shorter than a road bar that's almost 1/2 the width of the widest MTB setups. Shorter reach is beneficial when riding technical downhill terrain anyway as excessively long reach makes it harder to shift your weight back when out of the saddle.

catchourbreath 05-02-2022 10:05 AM

I found some info on the RAD/RAAD so will mess with that then continue on to maybe buying the Dialed Book if that still doesn't do it. Preliminary measurements making it seem like things I was thinking might be on the right course. Will have to revisit setback and associated bar angle/lever angle for sure.

sblackmacken 05-02-2022 01:45 PM

You're bound to feel some aches and pains after your first MTB ride of the season, esp. if you are moving from indoor/road/cx courses. If I were you, I'd do a couple more rides on your current set up and think about what hurts/when etc. before you start making changes. A good carbon handlebar and silicone grips like ESI (or Ergon grips if they work for you) can do a good bit for comfort.

John H. 05-02-2022 04:04 PM

Matching CX to MTB
 
Not many things apply to matching a CX to MTB. Especially a full suspension MTB with modern geometry. The seat angles on modern mountain bikes tend to be steeper, also a zero offset dropper post greatly limits how far back you can get the saddle. To compound that- measuring saddle setback on a suspension bike may not be the same in a static position as when weighted.
All that said, I think there are 2 things you can roughly apply.
1.) Saddle height. Make this close to CX saddle height correcting for any differences in crank length, shoe stack, pedal stack (if pedals are different), and any small fudge factor of you like to keep the mountain bike saddle slightly lower than the CX bike (I keep mine the same).
2.) Reach. Should be longer than CX bike reach to bar, but shorter than reach to the hoods.

Drop- I didn't include this as essential because I find that some people like their mtb bars to be as high as possible. I think a good place to start is to have the bars at about half the amount of drop you are used to using on CX. Adjust up or down from there.

None of these are rules- Just things to consider and look at.

catchourbreath 05-02-2022 05:46 PM

This is all very helpful, I realized that after picking up the bike and riding only a couple months last year that I never properly set things up for starters. Now I'll have something in the wheelhouse.

catchourbreath 05-21-2022 08:41 PM

I adjusted things accordingly and by golly the bike felt so much better today, more lively and fun. Granted it wasn't the most insane ride but very excited.


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