Anybody try a 650b Ram with Hetres?

[Toshi Takeuchi]

I'm thinking about a potential 650b Ram with 42mm Hetres.  Apparently the 42 mm 650b would be equivalent in height to a 28 mm 700c tire, so perhaps the BB drop would not be an issue. I'd love to hear if anyone has successfully done this.

Thanks,

Toshi

[Steve Palincsar]

On Wed, 2012-10-31 at 08:33 -0700, IanA wrote:
> 650b rim diameter is 584mm. 700 is 622mm. Not sure that you'd get
> even 1cm extra height from the difference in tires. You might be
> dropping the BB the best part of 2cm. That's probably pedal strike
> territory.

People have done 650B conversions on 700C bikes for years. It often
turns out very well.



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[franklyn]

I am afraid that Ian is right. I have measured the circumference of my wife's 700cx28mm wheel and my 650bx42mm (hetre) wheel using the rolling test diagramed in user manual of every cyclometer, and here are the results:

1. 700c wheel with 28mm Clement 28mm tire: 2110mm

2. 650b wheel with 42mm GB Hetres tire: 2094mm

The difference is around 1.5cm. If you currently use 170mm or longer crank arms, you can switch to a 165mm crankset and mitigate the drop by 5mm (or a whole 1cm if you use 175mm), but the drop is significant.

I hope that's helpful,

Franklyn

On Wednesday, October 31, 2012 8:33:25 AM UTC-7, IanA wrote:

650b rim diameter is 584mm.  700 is 622mm. Not sure that you'd get even 1cm extra height from the difference in tires.  You might be dropping the BB the best part of 2cm.  That's probably pedal strike territory.  .

On Tuesday, October 30, 2012 3:48:33 PM UTC-6, ttoshi wrote:

[Steve Palincsar]

On Wed, 2012-10-31 at 08:47 -0700, franklyn wrote:
> I am afraid that Ian is right. I have measured the circumference of my
> wife's 700cx28mm wheel and my 650bx42mm (hetre) wheel using the
> rolling test diagramed in user manual of every cyclometer, and here
> are the results:
>
>
> 1. 700c wheel with 28mm Clement 28mm tire: 2110mm
> 2. 650b wheel with 42mm GB Hetres tire: 2094mm
>
>
> The difference is around 1.5cm. If you currently use 170mm or longer
> crank arms, you can switch to a 165mm crankset and mitigate the drop
> by 5mm (or a whole 1cm if you use 175mm), but the drop is significant.

So if the circumference is 16mm smaller, the difference in diameter will
be 2.55 mm less (dividing the difference by pi); but diameter is not
what's significant here, it's radius, i.e., half the diameter, and the
difference in radius is 1.2mm -- hardly 'significant'.

[J. Burkhalter]

Hi Toshi,

I just tested the fit of my Bleriot's Hetres on my Ram and they fit just fine, with room for fenders.  The resulting bottom bracket height is ~260mm.  My Hetres on Synergy rims measure ~670mm in diameter.  The new brake reach for 650b wheels is ~72mm-74mm on the Ram, so I think Paul Racers would be out (max reach is 67mm), but I think the Diacompe Mod 750 brakes would work. 

hope this helps some,

-Jay B. 

[Steve Palincsar]

On Wed, 2012-10-31 at 09:27 -0700, IanA wrote:
> The other issue, even if pedal strike is not exacerbated, is going to
> be if the Hertes fit in the frame/fork anyway, as there could be
> clearance issues due to width.

That is indeed a legitimate concern. Of course, if Hetres won't fit
there are several excellent tires that are 37-38mm wide that probably
would (although they would also have slightly less ground clearance).

[PATRICK MOORE]

The effective decrease in bb height per the figures below would be insignificant:

2110/3.14=672 diam

2094/3.14=667 diam

672-667=5 mm difference in diam

3 mm/2 = 2.5 mm diff in radius

When I ran 60 mm 559 Big Apples on 23 mm rims they measured about 26.25" in diameter (tho' my measuring method was quick and dirty). 

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[iamkeith]

Toshi,

Please keep us updated if you do this. I'd love to see how it turns
out.

[franklyn]

Steve,

Thanks for catching my brain fart. Of course, the 16mm circumference difference becomes 2.5mm delta in radius. I think this is about right.

best,
Franklyn

[franklyn]

260mm of BB height is pretty good. My wife had a Serotta 650b conversion that had 255mm BB height. With 165mm cranks she rode it for thousands of miles without ever a pedal strike.

best,
Franklyn

[Leslie]

Somewhere, Grant mentioned that he didn't think of the Ram as a good candidate for doing a 650b (don't remember if it was in an email to me or in a Reader), but it was due to its BB drop; however, I think that was more around assuming a MaxyFasty or maybe a Col de la Vie....   I've also pondered the Hetres thing, too...

I do agree, I think crank-length is something to keep in mind...

( I'm guessing you've pondered over this page by now:  http://www.rivbike.com/kb_results.asp?ID=64 )


Anywho, would be curious to hear how it goes... 

[Toshi Takeuchi]

Thanks Jay, Franklyn, Arthur and many others for all the advice and feedback.  I bought my Hetres today (Jitensha studio in Berkeley) and should be able to get it together for a test spin this weekend. I'll post an update.

Thanks,

Toshi

[Steve Palincsar]

On Wed, 2012-10-31 at 11:23 -0700, franklyn wrote:
> Steve,
>
> Thanks for catching my brain fart. Of course, the 16mm circumference
> difference becomes 2.5mm delta in radius. I think this is about right.

It's beginning to look a lot like this conversion will work!

[Leslie]

On Sunday, November 4, 2012 4:09:13 AM UTC-5, IanA wrote:

I'm wondering now if there is a way to convert a canti frame/fork designed for 700c? Without moving canti studs or creating a method of mounting the canti's lower with some sort of Frankenstein's bolt on arrangement I guess it's not feasible?  Probably not necessary as most 700c canti frames offer enough clearance for reasonably wide tires, but this thread got me wondering.

I'd pondered something similar awhile back, regarding Atlanti...   the 26" ones can be upped to a 650b w/ Hetres, since they have clearance, if you use an adjustable v-brake like the Paul Motolites.     For any 26" cantilever-braked bicycle, if it has clearance, such should work.

Going the other way, from a 700c to a 650b, works for caliper-braked bikes, with longer calipers (ala Tektro).  

And there's where the simple ways end:  to go the other way, to from a 700c to a 650b on cantis, is going to be moving posts.  Conversely, if you had a 26" bike that used calipers, I doubt there'd be room to go up to a 650b, either.  

So, summary:   700c calipers to 650b, drop-dependent; or, 26" cantis to 650b, clearance-dependent. 

[Leslie]

Oh!  PS:  I know you asked about 700c canti bikes, but, for those interested in 650b-ishness on a 26" wheeled bike w/o changing wheels, could look at http://janheine.wordpress.com/2011/08/09/compass-tires-in-26-x-1-75/

FWIW...

 

[Daniel]

On paper, the Sins brake post extender should work:

http://www.sinz-racing.com/product/SBPE-01.html

They're even MUSA, but as long as I've pondered them, I never pulled the trigger.

Daniel

[Toshi Takeuchi]

Although a frame can handle a larger tire, the larger tire will raise the bottom bracket height, and that may or may not affect the handling. If you want the same bottom bracket height with wider tire, then you'll have to do a conversion.

For example, the Rambouillet might have been designed for 700x28, and the 650bx42 gives the same BB height within a couple of mm. 

I recently rode the Ram with 700x35mm tires, and the bike felt a bit less stable than the Ram with 700x32mm, maybe because the wider tires put me higher off the ground...

Best,

Toshi