Distance of widest point of 650bx42 tire from axle
 

Hey everyone,
looking for the diameter of a 650b wheel with 42mm tire at its widest point (ie distance of widest point from axle).
Going to prep a steel frame that came with 27" wheels for a 650b conversion and don't want the BB to drop super far and know a 42 won't clear now, so going to add a couple small dimples to the chainstays. Need to know where exactly to make the dimples. I don't have a wheel/tire setup handy, otherwise this part would be easy. Also, gonna get it sandblasted and powdercoated before I start buying parts up.

Can anyone point me to a thread where this is covered if you know one, or anyone with this wheel/tire combo take this measurement real quick?

Thanks!

Beadseat diameter is 584. So 584/2 is 292 + half of the tire size, 21mm gives you 313mm. This is a pretty fair estimate I think.

In my opinion, you're asking for trouble by dimpling the stays before you have your wheelset/tire combo.

What frame is it?

I agree!

+1. If you know you're going to do the 650B conversion, it would behoove you to just wait until you have the wheels in hand.

Rene Herse sells a tool for this job, but unfortunately it's out of stock: https://www.renehersecycles.com/shop...ire-fit-gauge/

Alright, fair enough. Maybe I'll take it to the LBS and see if he has what I'm looking for laying around...

Also, it's a 1984 Schwinn Tempo. My idea for the build came from this bike here:

https://cimg4.ibsrv.net/gimg/bikefor...563f10dce5.jpg
Except mine's gonna be silver :D

I'm in Portland, Oregon, and have done a few dozen 650b conversions. I've had people come over to do a wheel fit, if you were close enough I'd offer the same. There are several BF C&V posters here that have that particular tire size on their bikes. Where are you located?

Read this:

650B Conversion Guidlines

A pretty good approximation for the wide spot on a 650B wheel/tire set is the outer rim edge on a 700C wheel, which is only 4mm inboard from a 27” rim edge.

If you’re converting 27” to 650B, watch out for brake reach issues.

Hey, that could be awesome! I'm in Foster-Powell. I'll PM you.

Thanks for the info! I've been through that document a few times. I think these guys are right though, I'd be best off having a real set of wheels/tires on there to have a look. Also, not that I obsessively went over the photos of that built-up Tempo, but I definitely found out those are "dural forge" MAFACS on it, which take a 650b with Hetre with some over-extended reach. I'll likely go with R559s for my project -- they have more reach than Racers, if i recall. Think they should do the trick.

Me I would just not do a 650 conversion on a Tempo it is a great bike as is with 700's and not well suited for this conversion. If your looking to do a 650 conversion you may actually be better off value price wise starting with a different bike.

Zukahn, what else would you suggest and why?

For a conversion I would look for a sports or touring framset with slightly more laid back geomtry which tends to work better when chaning things up. Road bikes with fairly aggresive geomtry just don't work as good for conversions major changes in setup. On sports touring stuff you have close to 10mm wiggle room.setup wise to work with while on a road you only have 5mm or so doesn't seem like a lot but it can make a world of difference.