29er MTB Geo

[MarinRider]

I am interested in getting a 29er MTB this year and looking for advice on proper sizing. I usually ride a 57cm tt road bike with a saddle drop of 9-10 cm with a 120 stem. I am 6', 160 lbs and rides competitively on road. Would like to do some long XC races for fun this year.

I am confused on the proper sizing for a 29er. The 29er that our host listed for auction has a 57.5 cm tt. Compare to other 29er on the market (Moots for example), however, this is a "small".

Two questions:

1) What is a proper guideline for picking a right size frame?

2) Would the NAHBS Serotta 29er fit someone my size?

Thank you.

[Peter P.]

Mountain bikes allow a lot more leeway in top tube length to get a proper fit, due to the fact you're moving around on the bike in rough terrain and you're sitting more upright. You can vary stem length by 2cm or even more and you'll still fit fine in the reach to the bars. You also must consider seat tube length on a mountain bike for crotch clearance in rocky areas. This should not need further explanation ;-)

Anyway, I've got a friend riding a 20.5" Gunnar Rockhound and he's your height. He rides a 58cm road frame with a 58.5cm top tube. That should give you a good idea that the 20.5" frame's top tube length is in your range. Here's their geometry for 26" wheels:
Gunnar Rockhound Geometry (http://www.gunnarbikes.com/rockhoundspecs.php)

Here's their geometry for 29er's:
Gunnar Rockhound 29er Geometry (http://www.gunnarbikes.com/rockhound29specs.php)

As you can see from the similar top tube lengths for the 20.5" sizes, changing from 26-29" wheels does NOT change the fit of the frame to the rider. It merely changes the design to accommodate 29" wheels.

So I don't think you need to look for anything different if you're seeking a 29 vs. a 26" mountain bike.

[gdw]

It's too small. A 19 or 20in. frame will have a longer top tube and fit you better. You most likely would want a frame with a 23.5in or longer top tube.
A don't know of any set rules on sizing and would recommend that you test ride a few bikes at the local shops to see what works for you.

[MarinRider]

Thank you guys. That was really helpful.

[scrooge]

A couple of things to keep in mind with TTs on MTBs:
1. MTBs are often designed to be ridden with shorter stems.
2. While you may keep your reach from seat to bars about the same (maybe a bit shorter, depending what kind of riding you want to do), if you usually ride on the hoods of your road bike, you will need to extend your MTB out more because of the flat bar.
At least that's what I was told...

[gearguywb]

I am 5'11" and ride a couple fo different 'niners. a lot depends on the brand and how they set the bikes up. Many full squish makers design the bikes to put more of the riders weight between the axles. A good exampleof this is my Niner that has a 24.5 TT and I run a 90mm stem. The other thought, for a faster hadling, race oriented bike, is my MootoX. It is a large but has a shorter TT that I run a 110 stem on.

The nice thing about mtn bikes, as previoudly stated, is that you can play with fit quite a bit more than with a typical road frame. At your height you would be looking at most companies "Large" which typically equates to a 19 or 20" frame.

[markie]

At your height you would be looking at most companies "Large" which typically equates to a 19 or 20" frame.

Ding ding DING.

I am 5'10.5" and I like medium 29ers, but I only just fit on them... If I were taller I would need the large.

[Mikej]

I'm 72", 160# and went custom with a 24.0 tt, 18.5 st 120 stem, 63mm bbd. That serotta nahbs bike is super small for a 29er, 22.6" tt is more for a 5'8" person. But that other cat was right in recomending just about any L size.

[DfCas]

For true mtb'ing I disagree about mtb's offering more flexibility in sizing. On steep ups, you need to be forward enough to keep the front wheel down, and for steep downs, you need to be able to get off the back of the bike.

Just as in road bikes, front center is the key. I size the bike so I can ride a stem between 10-12cm, with an 11 being ideal.

A longer stem will increase endo's, and a shorter stem will cause the front end to wander in slick turns and off camber situations.

A 29 is sized the same as a 26 or a 650B.