Frame geometry translation/transfer?

For discussions about bikes and equipment.
Post Reply
grazie
Posts: 38
Joined: 7 Jul 2014, 1:06pm

Frame geometry translation/transfer?

Post by grazie »

I have what I believe to be my near-perfect road bike frame. I usually go for medium size, but they're usually too large and small is usually too small. Is it possible to take a road bike geometry and deduce an XC MTB frame geometry that would fit well?

I'm happy to give the specific frame details if needed, but I thought it best to ask a generalised question first.
User avatar
531colin
Posts: 16083
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Frame geometry translation/transfer?

Post by 531colin »

Will you want the saddle in the same position relative to the bottom bracket on both bikes? Thats fairly easy.
I imagine you would want a different handlebar position, different steering geometry and higher bottom bracket?
rogerzilla
Posts: 2887
Joined: 9 Jun 2008, 8:06pm

Re: Frame geometry translation/transfer?

Post by rogerzilla »

MTB frames are quite long, as the trend is for very short stems. Road frames were usually shorter anyway to allow for dropped bars, which stick out more to the front (at least on the hoods or in the drops). So you're probably looking at a virtual top tube length 50-100mm shorter (depends how racy you want it), compared to a modern MTB.
TheBomber
Posts: 525
Joined: 16 Feb 2020, 8:18pm

Re: Frame geometry translation/transfer?

Post by TheBomber »

grazie wrote: 15 May 2021, 5:35pm Is it possible to take a road bike geometry and deduce an XC MTB frame geometry that would fit well?
IME - no, not really. Obviously a tall rider will need a large MTB just like they would for a road bike, but the more subtle elements of sizing don’t translate so well. Much of that comes down to fitting the bike to the terrain it will be used on. The good news though is that the exact fit of the bike to you is less important than on the road - as you move around so much more off road to balance your weight over the bike, the minutiae we worry about on the road just doesn’t seem to matter.
grazie
Posts: 38
Joined: 7 Jul 2014, 1:06pm

Re: Frame geometry translation/transfer?

Post by grazie »

Thanks for the info and pointers. Much appreciated.
User avatar
RickH
Posts: 5833
Joined: 5 Mar 2012, 6:39pm
Location: Horwich, Lancs.

Re: Frame geometry translation/transfer?

Post by RickH »

Translating road bike position onto a modern MTB may be challenging.

I've was just looking at a review of a new version of a Marin bike (Alpine Trail Carbon 1 to be precise), in the latest MBUK, & the frame geometry is enough to make a "72° parallel" traditionalist wince - 78° seat angle & 63.5° head angle! :D

The long frame, short stem design of modern MTBs may make things "interesting" too.
Former member of the Cult of the Polystyrene Head Carbuncle.
TheBomber
Posts: 525
Joined: 16 Feb 2020, 8:18pm

Re: Frame geometry translation/transfer?

Post by TheBomber »

I should also have said - does your favourite road frame manufacturer also make a XC MTB? There can be family traits between the models. Worked for me when I had an MTB that fitted me great; I subsequently bought all road and regular road frames from them.
grazie
Posts: 38
Joined: 7 Jul 2014, 1:06pm

Re: Frame geometry translation/transfer?

Post by grazie »

My favourite road frame is from Planet X, so On One did seem like the obvious starting point, especially as I want steel. However, I couldn't see any pattern in the numbers, for which I use to be very good at.
Post Reply