bottom bracket and tyre choice

[biking_fox]

I've been looking for a new frame and one I happen to like has a low bottom bracket height which the builder claims means it shouldn't be used with thin tyres.

"frames are designed for a 1.75 tyre, as the tyre gets
smaller the bottom bracket gets nearer the ground, when cornering with too
low a b/b the pedals can touch down on the road.
"

Is there really that much difference between a 1.75" tyre and 23mm in terms of wheel depth? I've only ever ridden on road tyres and have no idea how deep a 1.75" tyre is.

Considering I normally corner with the low peddle up anyway to prevent this, can I ignore a reputable frame builders advice - they really should know more than I do - and put a 23mm tyre on anyway.

 

[hubgearfreak]

Is there really that much difference between a 1.75" tyre and 23mm in terms of wheel depth?

the difference is 21 mm. ie. the bottom bracket will be 7/8ths of an inch closer to the ground if you go for the small tyres.

can I ignore a reputable frame builders advice - they really should know more than I do - and put a 23mm tyre on anyway.

of course you can ignore him, it's your money, your bike, your loss. but he hasn't become a framebuilder without knowing a lot, and you should listen to him.

there's something more specific about the ideal BB clearance within the article below.
http://www.rivbike.com/article/misc/650b_from_700c_conversions

 

[Steve Austin]

I would try it.

My MTB commuter has low profile tyres on it, and it don't ride like it did with high volume high profile tyres, but it is fine for me. It will make a difference, but not enough to worry about ime

 

[hubgearfreak]

having gone away and thought about it, you or i are getting confused? i guess that the 1.75 you refer to is a 26x1.75, 559mm. what's the 23? do you now get 26x23 tyres for a mtb size rim? or are you suggesting putting a 622x23 wheel and tyre on it?

 

[RedBike]

MTB tyres are normally measured in inches and road tyres are measured in mm.

A 23mm tyre might be too narrow for a rim designed for wider 1.75" (45mm) tyres.

 

[summerdays]

Considering I normally corner with the low peddle up anyway to prevent this, can I ignore a reputable frame builders advice - they really should know more than I do - and put a 23mm tyre on anyway.

If the low pedal is up then it isn't the low pedal... but the inside pedal up. I read somewhere that having the outside pedal down helped with the forces when going around the corner. Is that correct?

 

[longers]

Is that correct?

Yes, I couldn't explain why, but it is. Possibly something to do with physics.

 

[Te Bheag]

If the low pedal is up then it isn't the low pedal... but the inside pedal up. I read somewhere that having the outside pedal down helped with the forces when going around the corner. Is that correct?

That is indeed correct. Pressure on your outside pedal 'plants' the bike on the road, as well as lifting the inside pedal out of harms way.

 

[biking_fox]

Away from keyboard fro a few days - thanks for the responses so far.

Clarification:
I've pretty much only ever ridden a 700c road bike style wheels. And the bike I'm looking at is a Rohloff one - which comes with 26" wheels. About which I know very little.

The builder (Thorn) recommends a 1.75" width tyre, which sounds to me like an awful lot of rubber to be dragging around, considering that I previously rode a tyre 23mm width. I don't know what sizes are available in 26", but I hope there will be some thinner than that, and my question then reduces to what vertical height difference does this leave?

And considering that one tries to cycle with the inside pedal up, does it make a difference anyway?

So far the impression seems to be that it shouldn't matter much.

 

[4F]

OK so what you need to be looking at is mtb types and the smaller width's come in road versions. The Vittoria Rubino Pro Slick Tyre come in 26 x 1.00 however you will have to check the width of the wheel on your Thorn to see if they are acceptable.