Saddle Height

walkingbootweather

When the saddle of my 7 year old's bike (24 inch wheels) is set at a height where they can comfortably put at least the toes of both feet on the ground there looks like too much bend in the knee on the down stroke. When the saddle is set at a height where legs are extended to the sort of angle that I'd expect (not straight, just a bit straighter) he can't reach the floor properly when sat on the saddle. How do you determine the optimum saddle height for your child?

karlth

It's a bit of a pain isn't it? It's down to the bottom bracket being higher (proportionally) than it would be on an adult bike. If it wasn't, then the bike would risk grounding the chainwheel. It's also partially because the bb height is influenced by the height of the axles so that the top of the chain runs reasonably horizontally, and child wheels while smaller than adult bike wheels are not as much smaller as the children are, if you see what I mean. Even adult MTBs have this problem to an extent.

Boy #1 is 8; he's about 4' tall - 2/3 my height. If his bike were in proportion with my MTB, the wheels would be 28 * 2/3 = 17". They're not; they're 20" and have the same sort of size tyres. Hence he's about 2-3" higher at the BB than he would be if everything was in proportion - hence the problem. All you can do is find a compromise position, or teach the child how to come forward off the saddle when they stop, but having the saddle that high can make them a bit unstable IME.

walkingbootweather

Good explanation karith - thanks.

The problem certainly seems worse now that he has migrated from a 20" wheel to a 24" wheel. I think you are right in that we need to find a compromise position and review it frequently. He can happily ride 40 miles and more in a weekend so I hope he doesn't wreck his knees before he grows up.

karlth

walkingbootweather wrote:

Good explanation karith - thanks.

The problem certainly seems worse now that he has migrated from a 20" wheel to a 24" wheel. I think you are right in that we need to find a compromise position and review it frequently. He can happily ride 40 miles and more in a weekend so I hope he doesn't wreck his knees before he grows up.

My lad's 8 and still on 20", with lots of room for upward growth still there. Are you sure he's big enough for 24"?

walkingbootweather

Well he's 7 and a half and about 1.40m tall which is the same as his sister who is 10. The 20" wheel bike he had earlier was looking too small even with the saddle at the maximum height. The saddle on the 24" wheel bike is a couple of inches above the minimum setting and 'looks' like a better fit, so I assume this is what he should be riding.

karlth

walkingbootweather wrote:

Well he's 7 and a half and about 1.40m tall which is the same as his sister who is 10. The 20" wheel bike he had earlier was looking too small even with the saddle at the maximum height. The saddle on the 24" wheel bike is a couple of inches above the minimum setting and 'looks' like a better fit, so I assume this is what he should be riding.

Fair enough. Must be very long legged. He's very tall for his age as well.

baudman

Yeah - bad geo. Vast majority of kid's bike have them.

Can sometimes be fixed with shorter cranks. Trek make kid's bikes that have multiple holes - VERY good idea and I wish other manufacturers would do it too.

You can get crank shorteners (bolt on - look in the tandem marketplaces, as having a younger/smaller one on the back is pretty common). Seems and OK solution, and something I'm considering for thing1.

walkingbootweather

Shorter cranks - wouldn't that make matters worse?

I want him to be able to get at least the front of both feet on the ground when he stops (which I can do) and his legs properly extended at the bottom of the down stroke (which I can't do unless I raise his saddle to the point where he can no longer touch the floor when stopped).

With shorter cranks his legs would be even more bent at the bottom of the down stroke.

baudman

Thinking about it that way... maybe.

Often, the issue is not so much full extension at the base, but the knee going well above the 90 degree (well, that's actually less than 90 degree but the knee going higher if you know what I mean) where the legs will get tired. (Why it's old for the BMXers to ride longer distances).

Near full extension is the optimum. But, if given the option of less extension with lower knee hight, or more extension but higher knee, I know which one I'd go for.

Plenty of adults ride bikes that don't allow both feet to touch - or at least only barely. Look at the numbers out of the saddle at traffic lights. I seem to be putting the saddle up on my 6yo's bike every few weeks.

walkingbootweather

Ah, I see what you mean now Baudman. We will have to experiment a bit more over the weekend. We do still have a couple of smaller bikes so I may have to consider transplanting some parts.

baudman

Thing1 now actually prefers it so that she's on her tippy-toes in the saddle, as she realises it makes pedalling more comfortable. However, she's not one for bumps/jumps etc most of the time, so she can afford to not have her feet closer to the ground.

In fact, she's actually practicing "Starting off like Mummy" (her words), where the saddle can be a tad higher, and she'll scoot on one pedal to start rolling and then sit up on the saddle. I'm not pushing/encouraging it at all - she's naturally doing it through watching her mother start her ride to work each morning.

But yeah... it is frustrating that there's often no 'correct' height. Always a compromise. And that's exacerbated by them continually growing!

Daz555

Not ideal with kids bike geom but remember that kids are super durable and flexible and growing all the time so there is no need to worry so much about the perfect riding position. Not like us old uns where 5mm one way or the other results in 3 weeks of physio.

baudman

Daz555 wrote:

... there is no need to worry so much about the perfect riding position...

The better the riding position, the longer the distances, and the easier the hills without complaint. (In my experience).

Daz555

baudman wrote:

Daz555 wrote:

... there is no need to worry so much about the perfect riding position...

The better the riding position, the longer the distances, and the easier the hills without complaint. (In my experience).

Agreed.