RM Instinct sizing 19" or 20.5" for 6'2"
I've just laid down a deposit on a cheap 03 19" Rocky Mountain Instinct, but wanted to get some feedback on sizing - the bike I could sit on was on layby to someone else and I couldn't test ride it. I'm 6'2" and the 19" is on the smaller side, but a 20.5" seemed huge. Ok sitting on it in the store (again a sold bike so no test ride), but had a very high BB. My inseam length is around 35" and it still felt big. I'm hoping a longer stem and offset post will make the 19" the right choice - it's being built up now, but there are no 20.5" bikes left... If all else fails there are other bikes in the store I guess.
Well I used to ride a 19" instinct with a 130mm 5 degree stem, and I'm 6' 0" with a 32" inseam. Since you're 6' 2" with a 35" inseam sounds like the issue for you would be standover height, which means you probably need a long seatpost and perhaps a 15 degree stem if you went with a 19". Its a tough call as you could probably ride either size but I would definitely try to compare 19" and 20.5" side by side to be sure. Also check out the geometry on Rocky's website. http://www.bikes.com/bikes/2003/fsxc/instinct.aspx
Originally Posted by telebond
yeah, I think I could probably go either way too. I like the idea of getting on a smaller frame, but I think it might be tight, and I don't want to go putting to long and high a stem on it. I'll head back into the shop today and see what I can do.
I'm just over 6'-1" with a 34" inseam and long arms. I ride a 19.5" Vertex but preferred a 19" Instinct. On the full suspension bike I preferred being on a smaller frame because it was easier to manage weight transfer and positioning. I had the bike setup with a 120mm 5deg stem and flat bars, and a Race Face zero layback seatpost.
I eventually sold the Instinct to a friend who was the same height but had shorter arms, and he switched to a layback seatpost and a 100mm stem and he was quite happy with the fit.
chips & bier
I think a lot will depend on riding style...
I prefer a small bike w/ long stem and setback post. The shorter wheelbase makes for a more agile bike, while a long stem (120-130 mm) keeps the bike from wandering on ultra-steep, technical climbs. Turning a corner is a little more work with a long stem, but I've been riding that way for almost 10 years. :P
That said, if you spend more time out on wide-open trails, a longer bike w/ a long wheelbase is probably a better bet. I think both frames would fit you:
> 20,5" with a 100-110 mm stem, zero-setback seatpost
> 19" with a 110-120 mm stem, possibly a setback post.
As a comparison, I'm 6'1" and ride an 18", with a 120 mm stem and flatbar, and serious setback on the seatpost. Effectively the bike sits 'longer' than any sotck 19", so even though my frame is on the 'too' side of 'small', I'm happy with it. I actually used a zero-setback post for a while, but for all-day rides the bike was just too short, then. Just so you know...next time I will buy a 19", though.
Another comparison: two friends of mine have 20,5" frames. One is 6'3" and has a 110 mm stem and zero-setback post; the other is 6'6" and has a 120 mm stem and setback post. His saddle-bar drop is huge, though, as this bike is on the small side for him!
West Coast Racing
cross post from general discussion
How come only Santa Cruz and Rocky Mtn have smartened up on frame geometry?
As forks get longer, top tubes have to get shorter to maintain proper handling. If anything as a fork gets longer, the head angle gets slacker and necessity for shorter top tube is even more important. As well, you can't cure a too small frame with a setback seat post (so if you are complaining that a top tube is too short - maybe it is meant to be that way).
I note that Turner and Titus, among others, have updated their frames for 100mm forks (vs. shorter travel forks) and if anything have made their top tubes longer (the amount of rear travel has not changed as significantly, so they are not maintaining the same relationship).
With a longer fork, the front centre becomes longer and the bike has slacker head and seat angles. Genisis geometry made sense back in the totally rigid days, but as a 100mm fork compresses, the head angle becomes radically steeper.
It seems that with the exception of Rocky and Santa Cruz that the bike manufacturers are designing for obselete California based magazine reviews, not from the feedback of the best test pilots. Even Specialized has built longer top tubes for their longer forked XC bikes (but somehow the california mags report that Santc Cruz's are the best handling but they still complain about the short top tube - they should give their heads a shake).
It is easy to counteract for a bike's handling when it is going slower and steep uphill (bend your elbows more), but as you go faster you can not react fast enough for non-optimal frame geometry. The bias on bike set up and geometry should for be when the rider is most challenged.
As far as thinking that a set back seat post can cure a too short rider cockpit, set back seat posts or sliding the rails back on the saddle, cures seat angle problems - not frame size problems. You need to think first - how the knees line up over the pedals (the old plumb bob over the knee when cranks are level classic setup). If you go down a frame size and have more seat post exposed to fit inseam length, the relationship between your knees and the pedals or BB has not changed. Road bikes have steep seat tube angles, therefore, it makes sense to have a set back seat post. XC bikes with 100mm forks should have slacker head angles (a steep head angle before compression will be impossible steep when compressed - so avoid XC bikes with 100mm forks and 1980s frame angles). Typically putting a 100mm fork on an XC frame will slacken the seat angle and you would require the seat to moved forward to maintain knee to pedal/BB relationship. The coach that sets up many of the top BC pro riders even turned a set back seat post backwards for my friend with a Specialized Epic and Talas fork to obtain the classic knee to pedal/BB relationship.
Just wanted to say thanks to everyone for responding to this request. I happily ended up with the 20.5" frame and have absolutely no doubt it was the right decision for me. In the end I combined the results from an online fit-kit style assessment with measurements from my singlespeed (an old 90s frame with slack angles) which I've spent a lot of time on and feel very comfortable with the setup, and just looked at trying to emulate those with the 19" and 20.5".
As suggested above, the 'setting up' was first based around the proper saddle position with respect to height and correct knee position over the pedals. This process quickly dispatched the 19" from contention...and I had no problem getting the 20.5" right. I've had to play with seat height a bit to compensate for changes in saddle height as the suspension sags... is this common??, but no probs there....
For what it's worth, while I was keen to try and get on as small a frame as possible, I can't stress enough how easy the decision was when I took an objective approach and went through the fitting process properly... obvious perhaps but easily forgotten when you lay eyes on a bargain... thankfully though I got what I wanted.. A spankin' new (well 03 maybe) Instinct with the RP3 shock as an upgrade. NICE!!
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