Ive posted this over on BikeRadar but thought Id spread the net 🙂
Sorry for the ridiculously long post.

Ive just bought some Oversize Ritchey carbon low rise bars to replace my Easton bars, partly due to saving weight and partly to go oversize.

I have a Thomson 90mm 5° 25.4mm Stem

and Easton Monkey Bars EA70 685mm

I fitted a new Thomson stem 90mm 0° 31.8mm to take the new carbon bars which are Ritchey Superlogic low rise 660mm (Im pretty sure that all the sweep, bend sizes are the same). I put a 5mm spacer under the stem to compensate for the rise in the old one.

After fitting the new stem and bars, took it for a little spin. The front end was very skittish, very neutral in a straight line but at the slightest lean to either side and the bars turned quickly and heavily on their own it seemed. A really unnerveing feeling.
Needless to say, as I have a big ride tomorrow, I took them off immediately as I felt so unstable, and knew I wouldnt be able to ride it.

The old set up was very neutral in both straight lines and in turning, very confidence inspiring.

Is it the fact that I didnt get the correct rise in the Stem to match the old one? (a 31.8 Thomson stem only comes in 10° rise, how that compares to a 25.4mm)
Should I have not put a spacer under the stem to compensate?
Or is the fact that the narrower carbon bars made a real difference to way it felt?

Right Ive done some measuring and plotted out how far off the bars actually are from my originals, not as far I first thought by the feel of them.

I thought the bars were the same but the Monkey Bars are a Mid-Rise bar (think they are 30mm rise) and the Carbon ones are a low rise bar (15mm).

I like the low rise look but need it to be higher really to match my old ones.

Could I just raise the angle of the stem to 10° to compensate or will this affect the steering in another way again??
If I lifted the stem by swapping the spacers over, that would help, but will the pivot point matter?

Should I just look for a mid-rise carbon bar?? or change the stem?

Wow. Just keep on throwing money at it, you’ll get it right in the end.

well lets hope I get it soon. A little knowledge is proving dangerous and expensive 🙁

If your hands end up in the same place then it’ll feel the same, regardless of the stem length and angle, spacers, bar width, rise and sweep you use to get there. Adding ~18mm of spacers would make the new match the old but it doesn’t look like your steerer tube is long enough…

give it a couple more rides on your locals before you make any more expensive decisions, new stuff takes time to get used to.

you never know you may prefare the new set up eventualy.

being used to a (680mmx80mm) i didnt like a new 50mm stem with 711mm bars set up on the carpark but they worked so much better on my locals and after a few runs i was really happy i made the investment.

chiefgrooveguru – thanks for that, I wasnt sure it worked like that. Thats really good to know. Dont think I have 18mm to play with, like you say.

oreetmon – you might be right. I used copter tape under the shifters and brake levers so if I have to sell the bars they’ll be in pristine condition. Took ages to swap em over. Think I should give em another go maybe.

There seems to be very limited Mid-Rise carbon bars out there, loads of lo or high rise.

Managed to try the spacers and I can just get a 20mm spacer underneath.
Didnt think it would work as simply as just lifting up the stem, thought it would affect steering pivot point etc.

Yet to swap the controls and give it a whirl but the height and position of the bars is now very similar, if not looking a little odd.