MTB Setup relative to Road Setup

Diesel6

I'm new to MTB but absolutely loving it. I've bought a new Trance 2 (2008) 20" frame. I've set up the sag properly on both shocks. My question is.... should I be measuring saddle height relative to the BB when I'm sitting on the bike with it sagged to the correct level? My saddle to BB height on the road bike is 82cm. Should this be the same sitting on the MTB with the shock sagged?

Love it if someone could help.

j.r.hawkins

Assuming your cranks are the same length, an XC MTB saddle should be 1-2cm lower relative to your roadie. This is to allow you to slide off the back of the seat for the technical downhills, ladder drops and such without snagging your shorts or - worse - your gonads on the saddle, yet still give you good power and look after your knees on the flats and climbs.

As my local trail has quite a wide variety of terrain sections, I move my seatpost height around a lot during the course of hte ride, but if I was racing I'd probably set it up as above and leave it.

For downhill or 4-Cross you'd have it much lower, like sitting on the frame, to get it out of the way. The pro downhillers never pedal in the saddle anyway, from the little I've seen on DVD.

Diesel6

Thanks for the reply. That makes a lot of sense to me and I like the answer since it means I won't have to buy another seat post as I'm at the limit.

I do have the same crank length as the road bike. I'm assuming that 'couple of centermetres lower' is the measurement taken when I'm sitting on the bike and taking up the sag?

threaded

Sagged when in your normal riding position. Yeah, the next next problem is like how to measure it... Tottering with one foot on a fruit crate, other foot clipped in, significant other lurking below with a tape measure...

First off set the suspension and tyre pressures you think you'll need.

Also you want to wear your riding gear, especially shoes, and if you use a camelback fill it up half way. You want to thump the suspension down and wait for it to fully rebound before measuring, as the sag from the top is often different from the sag from the bottom. Only a few mm, but I can feel it.

Go out for a few rides, fine tune the suspension and tire pressures.

Then when you're happy, lay the bike down and measure everything, so when you're forced to move stuff, i.e. you take a tumble and knock your seat out of line, you can set it back up without needing anyone else to help.

__________________
threadeds website, threadeds blog

Diesel6

Great tips thank. Have done so with the roady but hadn't thought to measure everything with the MTB. So my 82cm on the roady should be about 80 on the MTB when sitting on and sagged?

threaded

It's like everything, you go for as good a starting point as possible and then fine tune.

Another thing to remember is seat angle. You may want it sloping a little futher down on the MTB, so you don't catch your shorts when sliding back, but not so far you can't get yourself behind it for a steep downhill when tired.

__________________
threadeds website, threadeds blog

j.r.hawkins

Sorry, if I've got this wrong, but I thought the BB on the Trance was built into the front triangle and not the lower suspension link? In that case, is not the distance from seatpost to BB unaffected by what the suspension is doing?

The other factor I forgot to mention is the seatpost angle, whihc will impact on how high and how far back you mount the saddle to get the ergonomics right. It's unlikely the MTB and roadie will be the same. Your final riding position will be determined only by riding the thing, but the guidelines here will at least get you close enough for some meaningful fine-tuning.