Stem length - go 10 or 20mm shorter? How to tell?

dubcat

Hi, my mountain bike is definitely too big for me but I can not afford to change it right now so it is case of adjusting what I have. If only I had known more about the subject before buying it

I have moved the seat as far forward as possible so my knee position is correct above the peddles. This has had the effect of making me feel MUCH more stable on the bike as well as peddling easier. I can ride down stuff I was scared of before. However, I still feel really stretched out on it so I would like to shorten the stem. It is currently a 90mm stem and I don't know whether to go for 70mm or 80mm. I was told by a chap in the shop that shortening by more than 10mm could compromise stability significantly but I notice on here many people change by much more than that.

My riding is primarily XC with some trails (i do want to do more trails over winter). What would you go for? How do i suss out what the best stem length is for me?

cooldad

Only by trying them out - buying cheapies off Ebay is an option. I doubt 20mm would be disastrous though, so I'd try that first.

mrmonkfinger

Dubcat wrote:

I can ride down stuff I was scared of before.

1 remove saddle & seatpost, place on ground/in car boot/dining room/fridge
2 stand on pedals holding bars
3 you now have the correct seating position for riding down stuff you might be scared of... which does not involve parking your arse on a saddle

just saying

.blitz

Dubcat wrote:

It is currently a 90mm stem and I don't know whether to go for 70mm or 80mm. I was told by a chap in the shop that shortening by more than 10mm could compromise stability significantly

imho 10mm on a stem is noticable but only for the first 30 seconds after you've fitted it. Stability will be reduced but not all the time, everywhere you will just notice it when the bars kick over some rubble or roots it's not like you will be scrubbing the front wheel sideways on the first corner.

90 to 70 is a reasonable change it will make you sit more upright and sharpen up the steering without making it too sensitive. As above get a cheapy from Chain Reaction/Superstar/lbs and see how it feels before spending ££££

FWIW have been from 90 to 70 to 40 and back to 50 on my Cannondale you will either prefer the barge-like lazy steering and no-hands stability that comes with a long stem or the jet fighter twitchiness of a short stem.

paul.skibum

I went from 100 to 70 and noticed the difference but only in a good way. Front end is a wee bit light on steep loose climbs but not too bad. I'd try the 20mm change first and go back up a bit if it doesnt work. I bought a Club Roost stem cheap on CRC to try out the new position witht he intention of replacing it witha more high end stem if I liked the position. That was 8 years ago.

dubcat

mrmonkfinger wrote:

Dubcat wrote:

I can ride down stuff I was scared of before.

1 remove saddle & seatpost, place on ground/in car boot/dining room/fridge
2 stand on pedals holding bars
3 you now have the correct seating position for riding down stuff you might be scared of... which does not involve parking your ars* on a saddle

just saying

Yeah problem was that I could not get my weight low and BACK as the seat was getting in the way! It was too far back for me to get around. Now with it shoved forward it is much easier to avoid.

dubcat

In the end I was advised to lower my seat a little (i had it too high) and move the stem above the last spacer that I had on the headset. Having done this i feel much more like I am sitting in the bike rather than on top of it. Also turns out my seat was tipped down a little at the front so having levelled that out I now no longer feel like I am constantly sliding off it.

All in all I think the bike is a better fit now without changing the stem so I will see how I get on over a few rides before making any changes.

Thanks for all the tips.