Singlespeed & Fixed Gear - Just a little question

I have a feeling the answer is no, but i couldn't find it by searching so i gotta ask.
I have an IRO Mark V and was wondering if its posible to run a 650c front wheel in the 700c fork. I don't need anyone telling me im dumb. I feel bad enough even asking.

sure, as long as...

1. you're not going to run a front brake
2. you can find a brake caliper with reach long enough. unlikely.

sure, as long as...

1. you're not going to run a front brake
2. you can find a brake caliper with reach long enough. unlikely.

and as long as you're only going straight without worrying about pedal strikes.

think about it, it will lower the front roughly 25mm, and probably bb height by 10~15mm.
it will also change frame angles quite a lot.

and as long as you're only going straight without worrying about pedal strikes.

think about it, it will lower the front roughly 25mm, and probably bb height by 10~15mm.
it will also change frame angles quite a lot.

All true, but remember the Mark V has an extremely high BB with a drop of only 50mm. The added 10-15mm drop would bring it into the range of most 'street track' bikes. I think you're right to point out the frame angle changes. For one thing the smaller wheel will reduce the trail which may make the bike less stable (steering-wise) at higher speeds.

Personally, I think the lowered BB would be an improvement, but the reduced trail, probably not. You might just have to try it and report back to us.

Jim

I have a feeling the answer is no, but i couldn't find it by searching so i gotta ask.
I have an IRO Mark V and was wondering if its posible to run a 650c front wheel in the 700c fork. I don't need anyone telling me im dumb. I feel bad enough even asking.

Here is what happens to your geometry:

Say the distance between the front and rear axles is 100cm and you replace the front 700c wheel with a 650c wheel, then the head tube angle increases by 1.4 degrees (divide 25mm (half or 700-650mm dia) by 100x10mm and take the inverse of sine or tangent - both being same for small angles). Mark-V has shallow head tube angle in small sizes. For 56cm size, the head tube angle is 73d with 700c wheels, which means with 650c it is 74.4d. Not bad, since bianchi pistas have 74.5d in most sizes. Steeper angles result in smaller trail.

Let us look at the trail with 700c wheel. My 700c wheel with 25cm tire has a radius of 34cm. With a head angle of 73d, the distance between the imaginary point on the ground where a line drawn through the center of the head tube will meet an imaginary point on the ground that is vertically below the front axle is 10.4cm (tangent of 17d (90 - head tube angle) multiplied by 34cm). Subtract 4cm (rake of fork) to get the trail. So the trail on the stock frame/fork is 6.4cm with 700c wheels.

The more the trail the more the tendency of the front wheel to align itself in the straight direction. Trail is also called caster. Effect of caster is similar to the offset on the wheels of grocery store shopping carts. As you drag the cart, the wheels align themselves in one direction. The more the offset, the more the tendency of the wheels to align and stay straight. Coming back to the 650c wheel and assuming you have 25c tire which iyields 31.5cm wheel radius with 650c rim, 40mm fork rake and 74.4d head angle, the trail works out to be 4.8cm. For comparison, a bianchi pista in 57cm with stock fork (2.8cm rake) has a trail of 6.6cm. It is quite easy to increase the trail, just get a fork with smaller rake. But smaller rake (like 2.8cm) result in quick steering which is uncomfortable for some folks (not me). If you get a bianchi fork (or soma fork) with 2.8cm rake, then your trail increses to 6.0cm.

As far a bottom bracket is concerned the numbers are quite good. The BB drop with 700c wheels is 5cm on a mark-v. With 650c wheels it increases to 6cm (sine of 1.4 degrees multiplied by chainstay length which is 39.1mm, and add the result to 5cm). 6cm is better than surly steamroller which has 7cm drop.

In summary it is not as bad as I initially thought. Go for it.

I think im gonna do it. Right now because of the way the fork was made i can only run 23c tires. Anything else rubs. Also because of that or something else on the fork i cant run brakes on it either (they rub too). I think it would be fun to try out, So if i find a 650 wheel for cheap, i'll do it and take pictures. Thanks

Right now because of the way the fork was made i can only run 23c tires. Anything else rubs. Thanks

Your statement/post does not make sense.

Were you trying to fit larger tires? Or were you looking at fitting larger tires on a 650 rim??????

I think im gonna do it. Right now because of the way the fork was made i can only run 23c tires. Anything else rubs. Also because of that or something else on the fork i cant run brakes on it either (they rub too). I think it would be fun to try out, So if i find a 650 wheel for cheap, i'll do it and take pictures. Thanks


why not just get a new fork?

I wanted to run larger tires but i also like the look of the smaller front wheel. Asking if it would work with a 650 up front was just a kinda out there question. I know i could get a new fork, but its hard to find a decent looking fork with a 1 1/8 steerer that isn't carbon and doesn't cost alot.