saddle setback road versus mtb

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zmjones
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by zmjones

so i am relatively new to mtb and have a epic evo w/ an axs dropper (which is zero offset). measured off the bike even with the saddle pushed all the way back, i can't get my normal setback. is this normal that you have much less setback than on a road bike? or did i get the wrong frame size? the mtb is a 2020 epic evo large and i normally ride a 54 or 56 road bike w/ 21ish cm of setback. saddle height is usually 73cm or so.

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Cleaner
Posts: 213
Joined: Wed Oct 28, 2009 7:13 pm

by Cleaner

Setback is measured from the bottom bracket. The seat tube angle will affect this measurement as well as other frame geometry. Unless the frame has the same geometry I would not expect your contact points to be the same measured relative to the bottom bracket.

In general I would not try to match my road position to a mountain bike frame when setting it up.

zmjones
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by zmjones

Cleaner wrote:
Thu Nov 04, 2021 9:57 pm
Setback is measured from the bottom bracket. The seat tube angle will affect this measurement as well as other frame geometry. Unless the frame has the same geometry I would not expect your contact points to be the same measured relative to the bottom bracket.

In general I would not try to match my road position to a mountain bike frame when setting it up.
sure obviously the geometry affects it.

why would you not recommend matching position? and what would you suggest as a modification? it seems like the frame geometry is suggesting i should be more forward which i guess makes sense on steep single track and so on, but i also intend to use this bike for very long distance stuff where i'll be doing long miles on roads of various sorts.

Cleaner
Posts: 213
Joined: Wed Oct 28, 2009 7:13 pm

by Cleaner

There are a myriad of resources for fitting advice on line.

Try one of these for general fit guidleines.

Watch this video
https://www.youtube.com/watch?v=clVyZQzTJ0Q

This web site will calculate some dimensions based on input anthropometric measurements of the rider. Use this as a guide and adjust based on how you feel on the bike.
https://www.wrenchscience.com/

zmjones
Posts: 182
Joined: Wed Oct 25, 2017 4:55 am
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by zmjones

Cleaner wrote:
Thu Nov 04, 2021 10:16 pm
There are a myriad of resources for fitting advice on line.

Try one of these for general fit guidleines.

Watch this video
https://www.youtube.com/watch?v=clVyZQzTJ0Q

This web site will calculate some dimensions based on input anthropometric measurements of the rider. Use this as a guide and adjust based on how you feel on the bike.
https://www.wrenchscience.com/
my question is not about bike fit in general. i am happy with my fit on road and gravel bikes already. thanks anyway.

ghostinthemachine
Posts: 780
Joined: Thu May 07, 2015 9:18 pm

by ghostinthemachine

I started with a position *almost* the same between MTB and road in the late 90s.
Seat tubes have got steeper, head angles have relaxed, reach has increased, wheelbase is longer, bars are wider, stems are shorter. (And, of course, 29er)
The last two or three mtbs i've bought, i have slowly moved to a more "rider forward" position wrt the bottom bracket/saddle relationship.
With all the other changes to geometry taken into account my skeletal biomechanics from somewhere mid spine to pedal are all but unchanged, just rotated forwards a little. So there is a little more weight on my hands (which is all changed anyway due to wide/straight bars) the rest is essentially unchanged.

So, have a play, keep an eye on the total relationship between spine, hips, knees etc. See how it goes. Don't get hung up on set back.

I've done everything from short course, MTB crits, XCO, XCM and multiday events, all with the same position (Bike dependant of course.)

Some of the bikes i've been given to ride have had some really out there positions (think Pole Evolink sort of thing) they take a bit more getting used to!

scant
Posts: 270
Joined: Fri Apr 30, 2004 2:05 pm
Location: S.Wales UK

by scant

its not a cheap solution, but there are a few dropper seatposts that do have a degree of offset compared to the rockshox reverb, which as you say is pretty inline. the extra leverage on the dropper internals are why inline dropper posts are more common. bikeyoke dropper posts allow a suprising amount of setback & so far after 2years of use theres no performance issues. bikeyoke is also a lot lighter than the reverb axs post.. yes I'm biased i'd vastly prefer reliable lighter over electrical anything on a bike :)

Hexsense
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Joined: Wed Dec 30, 2015 12:41 am
Location: USA

by Hexsense

zmjones wrote:
Thu Nov 04, 2021 10:02 pm

why would you not recommend matching position? and what would you suggest as a modification? it seems like the frame geometry is suggesting i should be more forward which i guess makes sense on steep single track and so on, but i also intend to use this bike for very long distance stuff where i'll be doing long miles on roads of various sorts.
When we think about it, TT use saddle more forward (steep seat tube). MTB use saddle more forward (steep seat tube).
Gravel is in fuzzy state and all over the place, so lets ignore it for now.

Only road put you far back. Why is it the case?
1) Tradition, old thoughts of KOPS. New school knows it doesn't matter.
2) Tradition, old thought of put cleats under ball of the feet. Again, we learned that cleats toward mid-foot is generally better.
3) Tradition, short top tube and long stem is pro. Bike design that way loss stability if you sit too far forward. We learned that longer top tube and shorter stem make the bike handle better-ish, if bike geometry adjust trail value and front center length accordingly.
4) Weight balance. On road bike, you lean forward a lot. Try standing and lean far far forward. The butt move back naturally to keep things balance, right? Yeah, so road need more set back too. This doesn't apply to TT because forearm rest on elbow pads so it doesn't have to be balanced. Nor MTB which sit more upright so you don't need to put butt that far back to feel balance.

Even on the road, you also see that once the tradition fitting is broken, people also use zero offset seatpost and seek for steeper seat tube angle as well. Only reason number 4 hold you back from setting it as far forward as MTB and TT.

Now, we know that saddle more forward is no longer needed on MTB vs road. But why is it more forward in the first place? You already write down one of the reason which is steep climbing.

Other reasons:
First, it open up hip angle and generally, allow harder down stroke. Open up hip angle is the biggest reason for TT position to set up even more aerodynamic position. But harder down stroke help the sudden surge which is needed on punchy MTB trail.
Another reason is mountain bike need longer wheelbase for stability. If you put all the extra length behind you (at chainstay), the bike won't feel good. So part of the extra length go to front of the bike too. If you sit far back, then all your weight will be on rear wheel. Front wheel get light and lose grip easily on steep climb. So there, sit more at the middle of the bike rather than far back please.

hannawald
Posts: 1706
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Location: Czech Republic

by hannawald

Things are so confusing for mtb:) I have just returned to mtb after 10 years of only road riding and looking for the position as well..geometries also differ a lot. While my Cannondale uses pretty normal 73.1 angle, Specialized has 74 degree seat tube angle and I have seen even steeper. I still put my saddle back to compensate for 0 offset seatpost (on road I have 15mm) but my hands were still in pain. I don't know what would I do with 74 degree angle.

So now I am going to put the saddle forward but change its angle more up and shorten the stem by 1cm, this will change my reach and maybe it helps. I have also found my old bike fits and to my surprise I was fitted with the saddle setback 1cm less on mtb compared to road but full 2.5 cm lower on mtb (xc race bike)!

zmjones
Posts: 182
Joined: Wed Oct 25, 2017 4:55 am
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by zmjones

Hexsense wrote:
Fri Nov 05, 2021 3:15 am
zmjones wrote:
Thu Nov 04, 2021 10:02 pm

why would you not recommend matching position? and what would you suggest as a modification? it seems like the frame geometry is suggesting i should be more forward which i guess makes sense on steep single track and so on, but i also intend to use this bike for very long distance stuff where i'll be doing long miles on roads of various sorts.
When we think about it, TT use saddle more forward (steep seat tube). MTB use saddle more forward (steep seat tube).
Gravel is in fuzzy state and all over the place, so lets ignore it for now.

Only road put you far back. Why is it the case?
1) Tradition, old thoughts of KOPS. New school knows it doesn't matter.
2) Tradition, old thought of put cleats under ball of the feet. Again, we learned that cleats toward mid-foot is generally better.
3) Tradition, short top tube and long stem is pro. Bike design that way loss stability if you sit too far forward. We learned that longer top tube and shorter stem make the bike handle better-ish, if bike geometry adjust trail value and front center length accordingly.
4) Weight balance. On road bike, you lean forward a lot. Try standing and lean far far forward. The butt move back naturally to keep things balance, right? Yeah, so road need more set back too. This doesn't apply to TT because forearm rest on elbow pads so it doesn't have to be balanced. Nor MTB which sit more upright so you don't need to put butt that far back to feel balance.

Even on the road, you also see that once the tradition fitting is broken, people also use zero offset seatpost and seek for steeper seat tube angle as well. Only reason number 4 hold you back from setting it as far forward as MTB and TT.

Now, we know that saddle more forward is no longer needed on MTB vs road. But why is it more forward in the first place? You already write down one of the reason which is steep climbing.

Other reasons:
First, it open up hip angle and generally, allow harder down stroke. Open up hip angle is the biggest reason for TT position to set up even more aerodynamic position. But harder down stroke help the sudden surge which is needed on punchy MTB trail.
Another reason is mountain bike need longer wheelbase for stability. If you put all the extra length behind you (at chainstay), the bike won't feel good. So part of the extra length go to front of the bike too. If you sit far back, then all your weight will be on rear wheel. Front wheel get light and lose grip easily on steep climb. So there, sit more at the middle of the bike rather than far back please.
my setback on road/gravel is not really large. position was decided on for balance reasons. i do lots of long stuff and any more forward and the hand pressure is pretty intolerable. i also have a lot of upper body mass (from climbing/lifting/genetics) and that also contributes to the problem. i'm worried an even more forward position will be worse but haven't ridden the mtb for more than 2ish hours at a time yet. i guess like you say the drop is a lot less so maybe it will be less of an issue. also for long distance stuff i'll add some clip ons so will have an option for alleviating hand pressure that way.

thanks for feedback all!

rothwem
Posts: 211
Joined: Wed Jul 09, 2014 4:45 pm
Location: Asheville, NC

by rothwem

I'd mention that droppers make a big difference too. A forward saddle help keep the front end in contact with the ground when climbing, but the weight shift forward puts a lot of weight on the front wheel and makes it tricky to pick the front wheel up over obstacles. However, a dropper allows for more freedom of movement during times when you aren't climbing so you can more easily weight the front when needed and shift back when needed.

Hexsense
Posts: 3270
Joined: Wed Dec 30, 2015 12:41 am
Location: USA

by Hexsense

If you transit from road and worry about hand/wrist issue.
Do yourself a favour and see video below about handlebar sweep then make sure your handlebar has the correct sweep for your body please.
https://youtu.be/HSD7AkY4Ycc
I suffer finger grip problem off the bike for a week on my first ride with steep descend because I had low sweep bar come stock with my XC bike while my body demand high sweep angle (16degree). Handlebar change eliminate that issue.

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boots2000
Posts: 1393
Joined: Mon Oct 15, 2007 9:28 pm

by boots2000

It depends.
1st point- You can't go by measured setback from bike to bike road vs. full sus. With suspension squish, you really need to get on the bike and determine the correct position. Not just measure the setback.
2nd point- You may or may not need to sit as far back on the full sus bike. It is a different animal and you are more dynamic on the mtb, moving around and in and out of the saddle more. That said, the pedaling and climbing position must feel good to you.
3rd point- many modern full suspension bikes- especially with zero offset head dropper posts can prevent a rider who needs setback from achieving their ideal position on the bike.
This was the case for me- I rode 2 different mountain bikes with zero offset posts. A 120mm travel Orbea Oiz and also a Specialized Epic HT 29er hardtail. Both had the saddle shoved back all the way on the post. Neither was ideal. I was totally uncomfortable after 1 hour of riding.
On my new bike I am using a 25mm offset rigid post. I have a 9point8 dropper with 25mm setback on the way so that I will have both a dropper and my ideal seat position.

Some are fine with a forward position. Some even better with it. Some worse!

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