old 26inch to 700cc conversion

[lycra of the lane]

Hi I am stupidly trying to convert an Dawes discovery mtb into a 700cc hybrid for commuting and general hack I have the wheels as spare and they fit OK but need to sort brakes and rear mech for tiagra is this do able? I seem to remember reading about it in a mag once and am sure its been covered before any help or advice.

 

[RecordAceFromNew]

What you are looking into is by no means stupid, lots of people have tried it, some successfully.

The challenge is the brakes, in particular the brakes' reach to the larger 700c rims.

For some bikes, it is possible because the fork and rear stay bridge have mounting points (holes) suitably located for commonly available caliper brakes. Others use disc brake if the fork and rear stay have disc brake mounting brackets. Others use adaptors to make the existing V brakes reach. Further, some are converted to fixies, and "solve" the problem by having no brake at all!

A recent discussion on CC is <a href="https://www.cyclechat.net/">here</a>.<br><br><br><br>ps something funny about the site editor at the moment, the last link is wonky as a result...<br>

 

[lycra of the lane]

What you are looking into is by no means stupid, lots of people have tried it, some successfully.

The challenge is the brakes, in particular the brakes' reach to the larger 700c rims.

For some bikes, it is possible because the fork and rear stay bridge have mounting points (holes) suitably located for commonly available caliper brakes. Others use disc brake if the fork and rear stay have disc brake mounting brackets. Others use adaptors to make the existing V brakes reach. Further, some are converted to fixies, and "solve" the problem by having no brake at all!

A recent discussion on CC is <a href="https://www.cyclechat.net/">here</a>.<br><br><br><br>ps something funny about the site editor at the moment, the last link is wonky as a result...<br>

well thanks I will look at post but site keeps clocking me out! I do have holes and think cantis will fit but really wanted to put V brakes on but reach would be 45cm which I dont think will work although there are some expensive converters around.

 

[lycra of the lane]

well thanks I will look at post but site keeps clocking me out! I do have holes and think cantis will fit but really wanted to put V brakes on but reach would be 45mm which I dont think will work although there are some expensive converters around.

I have a tiagra compatable rear cassette on the 700c wheels and a triple mtb chainwheel on the front the old changer on the mb fits on the axle although there is a fitting on the frame which looks ok and the threads work so what should I look for as a changer? any help would be appreciated I have seen acera changers and 105 calipers on ebay will they work and what chain should I look for ?

 

[RecordAceFromNew]

If you are not changing shifters, to ensure gear compatibility, you only need to ensure the (Shimano compatible) cassette on your 700c wheel has the same number of cogs ("speed") as that of the mtb one (i.e. same as the existing rear shifter is designed for).

If the largest cog of the new cassette has less teeth than the old one, you may have to shorten your chain. If it has more teeth, you may have to buy a new, longer chain and possibly a new rear mech (depending on the number of teeth and existing mech spec).

If the cassettes are not of the same "speed", life would be simplest if the old cassette (or a new cassette of the same "speed") can be used on the new wheel - this is likely possible if they are either both freehub based or both screw-on freewheel based. Otherwise, you will have to change the rear shifter to match the "speed" of the rear cassette. If you are planning to change the left (front) shifter, you should be aware that a front road shifter will not be compatible with your triple mtb chainset.

If I were you I would get some clarity on the choice of brakes at the same time as designing the drive train. There is a chance that the choice of brakes may influence what brake levers to use, and therefore potentially what brifters to have.

More info on the spec of old and new equipment will help to confirm possibilities.

 

[lycra of the lane]

Hi Ace thanks for your help eh.
Mmm lots to think about, the cassette on the old wheel is 8 speed screw on and the 700c is 9 speed free hub, I am trying to change as little as possible so would like to keep changers and brake levers rapid fire( I think ) sooo could I change cassette to 8 speed free and run that ?

 

[RecordAceFromNew]

Just in case there is any mistake, 8 speed screw-on freewheels are rarer than hen's teeth. Could you check by reviewing this? I would expect the 8 speed on your mtb wheel is a cassette, not freewheel.

You can buy a new 8 speed cassette for the 700c freehub (provided the freehub is Shimano compatible) and run that. To keep things simple, if you can't use the old one (which I expect you can), you can buy one with the same number of teeth on the largest cog. Then you don't even need to touch the chain unless it is worn and should be replaced. You will likely have to make minor adjustments to the rear mech's limit screws.

Just for the avoidance of doubt, I know you said it fit OK earlier, but have you carefully checked that the rear wheels have the same OLN distance? I am asking because most 700c wheels are 130mm or less while most 26" are 135mm. If not, is the frame steel or aluminium?

 

[Ivan Ardon]

Weren't Dawes Discoverys 700c anyway?