Setting up a MTB to match a road bike

Equipment
1

Hi All
I’ve two road bikes that are set up identically and feel that my position is as good as its going to get for someone not blessed with flexibility. I’ve set the saddle relative to the BB exactly the same on my trail bike however after going for a ride yesterday it felt horrible, legs felt heavey and sluggish.
Is there a general rule that people follow to convert a road position to mtb?
Thanks for any help you can send my way

2

Couple of issues.

  1. If you measure from center of BB to top of saddle, did you also account for changes like Crank Length, Shoe and Pedal Stack Height, Saddle Fore-Aft Position?

    • Every one of those can be and is likely different from a road bike to MTB.

  2. Don’t assume that what is right for road is also right for MTB. Plenty of reasons to have subtle differences in saddle height, fore-aft saddle position and bar drop. You might use them as a starting point, but using them without consideration to the huge differences in use, is not likely the best approach.

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3

I would not relate one to the other. So many things are different; the bike geometries, how you move your body, suspension settings, etc. I recommend a mountain bike-specific bike fit.

4

Do you not even aim for the same knee bend?

5

Leg extension is typically set around 30-35*, and varies with each rider and/or bike use.

Just note that matching a BB to Saddle height is only part of the total equation when you factor in equipment differences we outlined above. It’s not as simple as some people think sometimes.

6

I use a dropper post on my mtnbike. But even at its maximum height, the saddle is closer to the bottom bracket than on my road bike.

7

So far as an MTB newbie I’ve found that the position is just not translatable at all.
I’ve got 165 cranks on the road bike and can’t go any longer due to hip/knee issues. But 175 cranks on the MTB seems to be fine. Maybe this is just due to doing a lot less constant pedalling and a lot more out of the saddle efforts than on the road bike?

You’re also sitting I’m going to assume a lot more upright and the bars are in a totally different position.

8

You must also consider the difference in rolling resistance. Even between different MTB tires there is a huge difference. I have a fast rolling tire on my HT and a very aggressive tire on my FS and I was shocked at how much of a difference that made when just pedaling along on hardpack. I felt lethargic the first time I had to lug those heavy knobs up a climb!

9

Hadn’t thought about rolling resistance in terms of pedalling. Are me now into the discussions of gear options in erg mode and inertia? More effort required over the top on a MTB, oval chainring?
Riding MTB on Sunday am for first time in 8 weeks so going to check setup in terms of knee bend before and see what I feel and report back.
Thanks for the input everyone

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10

I use the same crank length (175mm) on my road and MTB and the same saddle, however with the MTB i drop it by 1cm (don’t use a dropper) and move it forward slightly.

Over the past 25 years ive have had matching positions at times and it never works out, steep techy climbs are extremely difficult when set the same (for me anyway).

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