# A quick stem question

Lee, I have 90mm 6 degree stem and want to convert to a 70mm. What rise do I
need for the height to be the same? I was thinking 10 degrees. thanks

Yes, 10 mm.

A 90mm x 6 degree stem has about 7 mm of rise. A 70mm x 10 degree stem would have about the same.

But:

As you shorten your stem, you usually want to increase the rise. Imagine an arc that sweeps down and away from you; you want your bars along that arc.

Rock,

— Lee

3 replies
1. Jonas says:

I can’t see the point in this going round an arc. Early freeride bikes had like 100mm stems and 2″ riser bars. According to this going round an arc theory we should now ride 4″ riser bars with 50mm stems? I think, low and short is good. This brings the position more towards what BMX riders ride, and they know a lot about pumping, jumping and pedaling. Also, if you look around in the world cup circuit, everyone seems to go for low bars.

2. James says:

Regarding arch theory, if the 70 mm is purchased with a 10 degree rise, if you need more rise, would spacers be suffice to make up the subtle difference. Yet I understand Jonas’ comment. Interesting point.

3. leelikesbikes says:

Spacers should suffice.

This arc theory is all new. As far as I know, I’m the first to try to document this stuff. I’m in Orange County working with a bunch of BMXers, and I’m starting to see commonalities among all “handling” bikes (as opposed to “pedaling” bikes). I’ve looked at BMX, DJ, XC, all mountain, freeride, downhill and even motocross bikes, and they all seem to follow a pattern.

If you start with a neutral position, bikes that are made to be handled (MX motos, DH bikes) tend to be a bit higher than the average. Bikes that are made to be sprinted (BMX, pro 4X bikes, XC race bikes) tend to be a bit lower than the average.

I think. I’m still working on the Grand Unifying Theory of Braaap!