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Old 06-14-09, 01:34 PM   #1
David Newton
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Look at the geometry on my project

Hi, new here.
These are 27 1/4" wheels on this specialized hard rock (meant for 26" wheels). I'll be riding this till I lose weight and can go on something better.
This feels twitchy, if I put on the stock wheels (which I'll have to rebuild, trying to go cheap till I get better) will it be longer? I want to ride hands off.
Any suggestions?
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Old 06-14-09, 01:41 PM   #2
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It probably won't be twitchy - I bet it will be very stable and slow handling. The quickness or slowness of steering on a bicycle is greatly impacted by a derived measurement called "trail," and generally speaking, more trail makes a bike more stable/slower handling, and less trail makes a bike less stable/quicker handling. Using larger diameter wheels gives you more trail. However, since the wheels fit into the same space as the stock wheels, it is probably not going to be a huge difference (I am guessing).

I am curious, though, why you used 27" wheels instead of just using the stock wheels with road tires. 26" road tires are available in dozens of sizes and styles, while 27" tire choices are limited.

Cool looking bike though! Ride the hell out of it!
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Old 06-14-09, 01:59 PM   #3
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I would also add to LarDasse's statement that a stock tire would be wider and inherently more stable. Larger low pressure tires put more tread in contact with the road and are less likely to be knocked offline by surface irregularities than narrow high-pressure tires...they're just not as fast. This is why mountain bikes require them: trails are entirely irregular and maintaining traction and stability is more important than low rolling resistance.

My Pugsley demonstrates this beautifully. When ridden on the pavement it takes a noticeable effort to force the tire to change lines. It's also accompanied by an audible ripping sound.

Other suggestions: If that wheelset is a vintage item, rear spacing is likely to be 120mm. Your MTB will have a 135mm spacing which may cause chainline issues. Running singlespeed on a multiple gear cluster also has its own issues. Again, if it's a vintage rear hub, it is likely a freewheel and may be replaced with a BMX single cog freewheel. I'm also wondering how you're planning to run a rear brake.
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Old 06-14-09, 02:10 PM   #4
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David in Beaumont, I have driven along I-10 and know that the gulf coast is generally flat. That would explain the lack of a rear brake. I see that you removed the original canti or V brakes because obviously those would not work with a much larger diameter rim. My only suggestion would be to figure out how to get a rear brake installed. I do 80+ percent of my braking using the front brake only, but it's nice to know the rear brake is there to help in a panic stop or if something went wrong with the front brake.
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Old 06-14-09, 06:51 PM   #5
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Thanks for the look guys.
Lar, those wheels were on the Miyata, and the tires were new. The stock wheels would have needed rebuilding and tires/tubes, strictly a financial decision. I was hot to get on a bike right away, and it was all I had, for now.
Word, yes the spacing issue raised it's head. I've pulled the frame in. The chain just happened to line up with the proper ratio, and I can get going pretty well. I'm hoping to get the stock wheels built up and tire'd soon.
I'm not planning to run a rear brake now, the front one pulls me up pretty well. As Zephyr mentioned, it's all flat around here.
Thanks guys, I'm hoping to take off a few pounds and get a decent ride in a year or so.
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Old 06-14-09, 08:35 PM   #6
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How in the bloody blazes do those fit?

As a side note, if you're using a loose-bearing bottom bracket you can remove the spindle and put it in backwards for a few more gearing options. The right pedal will stick out a centimeter or so, though.
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Old 06-14-09, 10:11 PM   #7
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I've been commuting on a modified '89 H'rock for the past few years (26" ,559, wheels), and have never felt comfortable riding hands free. I can do it, it just takes concentration. I can do a much better job on my road bike - funny thing, they seem to have very similar geometry (at least the seat tube and head tube angles seem to be about the same).
If your running a freewheel in the back, please run a rear brake. When the rims get wet, it's always nice to have a second brake to start slowing you down. If you run fixed gear, the rear brake can be eliminated, since you can slow the bike by simply resisting with your legs.
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Old 06-14-09, 11:15 PM   #8
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A 27x1-1/4" tyre is about 40mm taller in diameter than a 26x2.0" tyre. This 20mm extra increase in radius would result in less trail in the front-end geometry and result in twitchier steering.
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Old 06-15-09, 02:56 AM   #9
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Originally Posted by DannoXYZ View Post
A 27x1-1/4" tyre is about 40mm taller in diameter than a 26x2.0" tyre. This 20mm extra increase in radius would result in less trail in the front-end geometry and result in twitchier steering.
Danno - I think you may be looking at it backwards...

Larger wheel diameter gives more trail.

From http://www.phred.org/~josh/bike/trail.html (linked from Sheldon Brown's Bicycle Glossary entry "Trail")

T = (R X Cos H -F)/Sin H
Where 'T' is Trail and 'R' is the tire radius.

If tire radius increases in this formula, trail increases.
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Old 06-15-09, 03:15 AM   #10
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I put 26X1 3/8" wheels in a cheap MTB frame. I wanted to use the dyno hub, which was 40 spokes, so couldnt easily build into my 559 rims
Never noticed the steering being upset at all.
As the frame was evenly lifted up from the ground.
Being a cheap old MTB it had reasonable steering angles
The Hard rock will be more sporty. Those wide bars might give a bit to much leverage on the steering
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Old 06-15-09, 12:20 PM   #11
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Originally Posted by griftereck View Post
I put 26X1 3/8" wheels in a cheap MTB frame. I wanted to use the dyno hub, which was 40 spokes, so couldnt easily build into my 559 rims
Never noticed the steering being upset at all.
As the frame was evenly lifted up from the ground.
Being a cheap old MTB it had reasonable steering angles
The Hard rock will be more sporty. Those wide bars might give a bit to much leverage on the steering
26 X 1-3/8 overall diameter (including tire) is very close to the overall diameter of a 26 X 2.1 (including tire).

Bead seat diameter of 26X1-3/8 is 590mm, then add twice the height of the tire (roughly 35mm X 2) = 660mm

Bead seat diameter of 26X2.1 is 559, then add twice the height of the tire (say, 53mm X 2) = 665mm.

What I am getting at is replacing mtb wheels with 26X1-3/8 wheels is a very small change.

However, the difference between the diameter of 26 and 27 inch wheels (including tire) is roughly one inch and I would bet the OP's bike will still be perfectly rideable.
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Old 06-15-09, 10:38 PM   #12
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It's also very close to a 700c@23mm: 622+46mm=668.
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Old 06-16-09, 08:20 AM   #13
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So I've been riding this set-up for a week now, and I'm already thinking about changes. Maybe a little lighter wheel.
I have a set of hubs from a Dyno-GT with a freewheel, (which I haven't even counted spokes) What rims would be slightly smaller in Dia. than the 27-1/4" and would fit tires that will carry my 250 lbs. They can't be high-dollar rims.
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Old 06-25-09, 03:09 PM   #14
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This Specialized Hard Rock has a sealed bottom bracket, I think.
The take-off socket is some sort of splined fit that I'm not familiar with. Where are these sockets available?
Anyone know the threading of the BB and can it be replaced with any standard BB set?
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Old 06-25-09, 04:53 PM   #15
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Quote:
Originally Posted by LarDasse74 View Post
Danno - I think you may be looking at it backwards...

Larger wheel diameter gives more trail.

From http://www.phred.org/~josh/bike/trail.html (linked from Sheldon Brown's Bicycle Glossary entry "Trail")

T = (R X Cos H -F)/Sin H
Where 'T' is Trail and 'R' is the tire radius.

If tire radius increases in this formula, trail increases.
And more trail results in more stability, slower steering, better straight line tracking. So the stock wheel should be twitchier, except for the friction of the wider, softer tire.

I've not found the ability to no-hand a bike to be based on trail, though others may have. I find if I have a problem riding no-handed (and I'm going fast enough), there is a bias in the bike frame. Either a binding/notchy headset, a warped fork, or a frame not aligned.
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Old 06-26-09, 07:36 AM   #16
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David, if you want a slightly smaller wheel than 27", 700c is the way to go. As at the Clyde forum about tires, but my guess is that a 32mm tire would work fine. Continental makes some really nice, smooth ones.

BB tools can be gotten at any decent bike shop.
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