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26" Wheels Change Geo. of 700c frame?

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26" Wheels Change Geo. of 700c frame?

Old 04-17-10, 01:44 PM
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26" Wheels Change Geo. of 700c frame?

I picked up a (very cheap) Redline R530 frame to replace the bent frame from this thread. I'd like to build it up as a winter commuter, and light (I repeat light) trail bike. My plan is to build it up with a coaster brake, either single or 3spd internal hub. The frame is intended for use with 700c wheels, I was wondering if using 26 inch MTB wheels, and fork would be possible or if that would make the geometry too weird to use? Rear brake reach wouldn't be an issue because of the coaster, and I figured using a 26" MTB fork would solve the front brake reach issue. Maybe make sure to get short cranks to make up for the BB being closer to the ground?

I'd like use 26" wheels because they seem to be cheaper, and more readily available w/coaster brakes & 3spd hubs then 700c wheels. I also have an extra 26" front wheel & tire in my parts bin.

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Old 04-17-10, 02:49 PM
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As you noted, the bottom bracket height would be reduced and pedal strike could become an issue. The smaller wheels will reduce the height by 25-30 mm depending on the tires you use and even short cranks only compensate for 5 to 10 mm of that change. Be sure the 26" wheels will fit in the rear stays with the tires you plan to use.

If the replacement fork is the right length, the geometry shouldn't change much.
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Old 04-17-10, 07:19 PM
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As long as you're replacing BOTH wheels with 26", the geometry won't change; it'll just be the aforementioned BB height. Keep your inside pedal UP in the turns.

Hub spacing can also be an issue; I've had to really get 'creative' with some old frames to fit rear wheels into them.
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Old 04-17-10, 07:32 PM
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Originally Posted by DX-MAN
As long as you're replacing BOTH wheels with 26", the geometry won't change; it'll just be the aforementioned BB height. Keep your inside pedal UP in the turns.

Hub spacing can also be an issue; I've had to really get 'creative' with some old frames to fit rear wheels into them.
The frame geometry will not change, but there are wheel-size-dependent dimensions that will change...

1. Bottom bracket height (as mentioned above)
2. Trail - the derived measurement of how far the contact point of the front wheel is behind the point where the steering axis intersects the ground. More trail makes a more stable bike, less trail makes a less stable bike... A smaller wheel will reduce the trail and make a less stable bike.

However!!! What will the actual difference in wheel radius be? The difference in radius between a 700c rim and a 26" rim is 31.5mm... but the difference between a 700c wheel with a 23mm tire and a 26" wheel with a 2.35" tire is much less.

Anyhoo, it will change the handling of the bike, but you would probably get used to it within a couple of rides. It is unlikely to make the bike unridable or anything.

You could also choose a longer fork (maybe a 29er or hybrid fork) to push the front end up and slacken the head angle to increase trail and lift the bb a little.

edit: I just looked at the bike.. I assumed it was a road bike but it actually a hybrid. Why change the wheel size at all? Put some 700C wheels and medium width tires (like 700 X 35c... possibly available in studded winter versions if you are interested) and ride like a fiend.

Last edited by LarDasse74; 04-17-10 at 07:36 PM.
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Old 04-17-10, 07:57 PM
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I've done this many times and it works just fine. Mounted and pumped-up 700x25c and 26x2.00" tyres are both approximately 66.5cm tall, so there shouldn't be much change in geometry or handing. The fork-length is the major variable that's not known; you'll want to get a MTB fork with roughly the same length when loaded as the R530. Even if the MTB 26" fork+wheel combo is lower and results in less trail, the heavier tyre along with larger cross-section curvature on the ground will result in more stability than the stock 700c wheels.

Only issue is fitting rear brakes and I just brazed cantilever posts onto the seat-stays at the proper location. From the looks of it, you might not be able to get a tyre larger than 26x1.75" into the rear-end though.

Last edited by DannoXYZ; 04-17-10 at 08:01 PM.
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