Techspertise required.

For discussions about bikes and equipment.
Post Reply
Thehairs1970
Posts: 381
Joined: 11 Aug 2018, 9:30am

Techspertise required.

Post by Thehairs1970 »

Just acquired a 1990(ish) Dawes Galaxy frame that I want to update into a flat bar tourer for my son. This would ideally be running some kind of thumbshifter set up with a triple ring and v-brakes. At the mo it has bosses for down tube shifters.

1) can I convert to thumbshifters easily?
2) what speed cassettes can I run? Distance between internal walls of dropouts is approx 130mm.
3) I know what chain line is but have no idea where you would start knowing the BB axle length to get best shifting. There is no BB in at the mo but exterior shell length is appears to be 68mm.
4) Any recommendations for headset?

All help gratefully received.
rogerzilla
Posts: 2052
Joined: 9 Jun 2008, 8:06pm

Re: Techspertise required.

Post by rogerzilla »

1. How many speeds at the back? Shimano thumbshifters only really go to 7 speed, and good used ones are expensive. They can be made to work with 8 speed but it's suboptimal (cog spacing is slightly wrong). You can buy aftermarket mounts to use bar-end shifters, available in all speeds, as thumbshifters but they're a bit ugly.

2. Anything you like. 6 or 7 speed will need 4mm of extra spacers under the locknuts.

3.If you know the crank model, there is a database on Sheldon Brown's website giving the recommended BB length.

4. Assuming 1" steerer, Tange FL250C.
rjb
Posts: 4738
Joined: 11 Jan 2007, 10:25am
Location: Somerset (originally 60/70's Plymouth)

Re: Techspertise required.

Post by rjb »

Dawes of that era used Jis sized headsets. The crown race was 27.0 mm internal diameter. Check this out before purchasing a 1" headset which is more likely to be an ISO standard and won't fit. :wink:
Here's a link to crib sheet of headset dimensions. Yours is most likely to be 1" Jis but could be iso. You will need to get the forks off and the crown race removed to check. https://www.sheldonbrown.com/cribsheet-headsets.html

If your forks have narrow spaced bosses, 60mm springs to mind, it's possible V brakes won't be a good fit and you would be best to stick with your existing brakes, but this then becomes difficult to obtain flat bar levers which are compatible. V brake levers would pull too much cable requiring the brake blocks to be set extremely close to the rim and risk the levers hitting the bars before the brakes bite.
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin, Raleigh 20, Falcon K2 MTB dropped bar tourer, Longstaff trike conversion on a Falcon corsa. :D
mattsccm
Posts: 4064
Joined: 28 Nov 2009, 9:44pm

Re: Techspertise required.

Post by mattsccm »

130mm is normal road width so really anything will go in the back if it is a road hub. 135mm is MTB.*** That will go as well if you spring things. Either way you can go to 11 speed to match whatever shifters you choose.
*** Well except all the modern stuff but if you go for quick release wheels you'll be fine.
Get a couple of the down tube cable stops with adjusters in to go on those down tube bosses.
slowster
Posts: 2561
Joined: 7 Jul 2017, 10:37am

Re: Techspertise required.

Post by slowster »

Further to rjb's comments about the headset standards, if the current/original headset had a low stack measurement, you would need to choose a headset with a similarly low stack. You might be able to fit a headset with a very slightly larger stack by removing the cable hanger and instead mounting a cable hanger on the fork crown boss, i.e. this type: https://www.sjscycles.co.uk/brakes/rale ... le-hanger/, but that would probably give you no more than 1mm-2mm leeway.

I don't think you would have any difficulty finding suitable flat bar brake levers for cantilevers, e.g. these should do:

https://www.spacycles.co.uk/m7b0s103p10 ... ake-Levers

You just need to make sure you don't buy levers for V brake cable pull, nor levers designed for Shimano's modern NSSLR brakes which have a different cable pull, such as these for example:

https://www.spacycles.co.uk/m7b0s103p36 ... ake-Levers
Jamesh
Posts: 2317
Joined: 2 Jan 2017, 5:56pm

Re: Techspertise required.

Post by Jamesh »

You could use sti or gripshifts?

9 SPD is a hood balance of performance to economy.

Cheers James
Thehairs1970
Posts: 381
Joined: 11 Aug 2018, 9:30am

Re: Techspertise required.

Post by Thehairs1970 »

Sorry guys. When I said thumb shifters, I meant some kind of trigger shifters - MTB style.
Jamesh
Posts: 2317
Joined: 2 Jan 2017, 5:56pm

Re: Techspertise required.

Post by Jamesh »

Sounds more achievable.

Beware of fake shifters with poor quality shifting.

Cheers James
dondelion
Posts: 55
Joined: 13 Sep 2014, 10:48am

Re: Techspertise required.

Post by dondelion »

But if you did want thumbies, Microshift do them for 9-12 speed. I love mine. Mmm friction front shift.
Thehairs1970
Posts: 381
Joined: 11 Aug 2018, 9:30am

Re: Techspertise required.

Post by Thehairs1970 »

rjb wrote: 19 Sep 2021, 7:09pm If your forks have narrow spaced bosses, 60mm springs to mind, it's possible V brakes won't be a good fit and you would be best to stick with your existing brakes, but this then becomes difficult to obtain flat bar levers which are compatible. V brake levers would pull too much cable requiring the brake blocks to be set extremely close to the rim and risk the levers hitting the bars before the brakes bite.
Measured the brake bosses. They appear to be about 75mm apart. Will this give room for V-brakes?
rogerzilla
Posts: 2052
Joined: 9 Jun 2008, 8:06pm

Re: Techspertise required.

Post by rogerzilla »

Any decent bike shop can recut the frame and fork from JIS to ISO. I do it all the time.
djnotts
Posts: 2114
Joined: 26 May 2008, 12:51pm
Location: Nottingham

Re: Techspertise required.

Post by djnotts »

"Measured the brake bosses. They appear to be about 75mm apart. Will this give room for V-brakes?"

Maybe - for some! Stx-rc seem to be best suited to narrow spacing.

Lots of discussion on here and elsewhere on this issue, search on "boss spacing and v-brakes" as a starter!
colin54
Posts: 1914
Joined: 24 Sep 2013, 4:34pm

Re: Techspertise required.

Post by colin54 »

I've just measured the front fork brake bosses on a couple of V brake bikes, one measured 75mm c-c (centre to centre of the bosses; that's important), the other 80mm c-c. , so I think you should be OK if yours are 75mm c-c, it's worth double-checking though.
The reason I say to check is I found a Galaxy in the sold listings on ebay, very close in age to yours I would say.
Someone has fitted this with V brakes and they look extremely splayed out to me, it might just be the camera angle though. Here's a link to the ad and a picture I took of it, as the ad will eventually disappear.

https://www.ebay.co.uk/itm/Dawes-Galaxy ... 7675.l2557
P1150152.JPG
....and scroll down.
Good luck.
Nu-Fogey.
Post Reply