WHEEL SIZES - HELP! (RE. 1993 Kona Hahanna *Project*)

[DMZ]

As a typical noob I am flummoxed by bike wheel sizes and reaching frustration point.

I am in the process of overhauling and customising a brilliant 1993 Joe Murray Project 2 Kona Hahanna mountain bike for fast road use (project introduction here http://www.retrobike.co.uk/forum/viewtopic.php?t=178633), doing a bit of engineering design to fit larger wheels with lower profile tires into the forks. But try as I might, I cannot make head nor tail of the wheel/tire measurement guides in the context of the measurements I have!

The current huge Joe Murray off-road tyres are described as 26"x 2.5(?). This I gather is the outer external diameter of the inflated tyre. I measured this and it checks out.
My forks, from centre of the hub to the absolute top of the arch is close enough 710mm (27.9"). I want the biggest tire outer diameter to fit this space as possible, for the lowest profile depth (height) of tire.

I realised that a 700mm outer tyre diameter corresponds to 27.6", just clear of my forks' arches. More comfortably clear would be 27" but that equates to an awkward 686mm. And by the 700mm outer diameter, I mean the very outside crown of the curvature of the tire, where it would touch the arch of my forks if it was too big - possibly not to be confused with the '700c' which I still, after hours of research, have no idea what the hell is referring to!

I want this to achieve a total of 700mm complete outer diameter (or approx) with the biggest diameter possible wheel rim (and narrowest), and can find no way of interpreting from the guides what is the biggest diameter/narrowest rim and lowest profile (height) tyre that would go together to achieve a 700mm total outer diameter. Or at least within a complete diameter of 710mm. The I can work out hub width (130/135mm? sigh!)

I'll be redesigning the brakes to reach the rims via a conversion kit, or more likely manufacturing my own custom pieces.

Does that make sense? And can anyone advise me as to sizing as I am incredibly frustrated....! I have a technical brian but this is stumping me.


...and please don't refer me to http://sheldonbrown.com/tire-sizing.html, as this site explains a lot but still doesn't make it make sense for the dummy!

Eddie

 

[Jussa]

Can i ask a question?

Why?, its a great bike and whilst most MTB's do go through a period of Road use, this is usally done with 26" wheels with Road, or Hybrid tyres. To go for a total config to Road dimensions would it not be easier to build around a road frame? dont get me wrong i am curious and will be watching this build, please post some pics and let us follow this Hybrid/Road/MTB you are creating

Good luck with the re-design sorry cant help on the size issue.

Jussa

 

[sylus]

Sell it and buy one of the hybrids

 

[stauqmuk]

I agree with Jussa, interesting idea to modify a mountain bike for the road but the bike manufacturers already did all the leg work for you in making their hybrids.

However, if your set on the mod you could probably use a set of 27" wheels. They were an early version of the 700c road wheel and can still get they pretty cheap at most bike shops. They come in skinny rim sizes and the tires made for 27" are almost all road worthy. The issue isn't going to be your fork it'll be the rear end. The area behind the bottom bracket between the chainstays is usually the section of frame with the least clearance so I'd start poking and measuring there before you go buy or make too many parts. Good luck.

 

[one-eyed_jim]

While I agree with the other responses, if you really want to do this, 700c rims are the way to go.

A 700c rim measures 622mm in diameter, bead seat to bead seat. You'll be able to fit a tyre up to 40mm in width. 700c tyres are widely available from 18mm slicks right up to 2.5" knobblies (usually referred to as 29").

The larger rim sizes that would work (630mm and 635mm) are effectively obsolete.

 

[raymondluxuryyacht]

I'm puzzled why you would want to do this.
You will struggle to get a total 700mm diameter without wide tyres.
680mm might be a more sensible goal.

A 27" rim with a 25mm tyre maybe be a good option for you. See->http://www.bikecalc.com/wheel_size_math
Or perhaps a 700c rim with a wider tyre (e.g. 28 or 32mm) ?

Regarding hub width, you'd be unlucky to have a frame designed for 130mm hubs as they were becoming uncommon by 1993. I seem to remember 135mm hubs became the norm when 7 speed gears appeared on the market (although I think there may have been some short-lived solutions for 7-speed on 130mm).

 

[bduc61]

see two builds with 26 frames

one with 700c wheels and 23 tyres -
I tried road brakes but impossible to tune properly so had to go mavic adapters

the other one with big 26 tires !

 

[unkleGsif]

Why not just get disc tab welded on for easier brake conversion?

G

 

[DMZ]

Thanks everyone for great responses.

A 27" rim with a 25mm tyre maybe be a good option for you. See->http://www.bikecalc.com/wheel_size_math
Or perhaps a 700c rim with a wider tyre (e.g. 28 or 32mm) ?

Finally a wheel size guide I can understand! In addition to everyone elses posts, I finally understand the sizes better. Whether I go for 700c or 27" is purely probably going to depend on what is available and at what price....I'm happy to go for a decent quality second hand race set to fit my budget..which is fairly conservative while there is uncertainty over the venture...

The issue isn't going to be your fork it'll be the rear end. The area behind the bottom bracket between the chainstays is usually the section of frame with the least clearance so I'd start poking and measuring there before you go buy

I have measured that, the clearances are all pretty much identical.

bduc61:

see two builds with 26 frames ..one with 700c wheels and 23 tyres - I tried road brakes but impossible to tune properly so had to go mavic adapters ..the other one with big 26 tires !

Yes! Thats the idea! I am aware of those brake adapters and I could probably make something similar if necessary.

Sell it and buy one of the hybrids

Never! If I fail I shall simply continue to ride across my college's grass at midnight laughing manically..

Will def. post pics. Starting with it as it is before I start trying things. Am doing it in bits of spare time so won't be instantaneous.

And why do I want to do it? I'm...a bit mad. I like doing things a bit differently. Its fairly normal that my projects meet a resonse of 'wtf why' until I've completed them...!! The other aspect of the project is the asethetic design, which shall be distinctive...as yet to decide...

 

[saint.vince]

Re:

So, where are the photos of the finished bike?