Did Miyata favor long top tubes?
03-01-08, 10:56 AM
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Did Miyata favor long top tubes?
This is admittedly based on only one bike, a badly neglected entry-level model Ninety 10 speed I got for $10 to see what I could salvage (frame is OK albeit rusty). And I'm still a noob.
It's a 49cm frame (measured) and the top tube is 54cm c/c - it even looked long before I measured it. By contrast my 49cm Schwinn World Sport conversion has a 51.5cm TT, which I find quite comfy.
Were longish top tubes a "thing" with Miyata?
It's a 49cm frame (measured) and the top tube is 54cm c/c - it even looked long before I measured it. By contrast my 49cm Schwinn World Sport conversion has a 51.5cm TT, which I find quite comfy.
Were longish top tubes a "thing" with Miyata?
03-01-08, 11:27 AM
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I don't think so, my 63cm has a 59cm top tube. If it had the proportions of your bike I'd be laid out like Superman.
03-01-08, 11:42 AM
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Death fork? Naaaah!!
The ones I've owned didn't run to longish top tubes, but Miyata did measure seat tubes C to T, so the frames tend to be a half size smaller than listed.
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03-01-08, 01:49 PM
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I have a 710; not sure of the year - late 1980s I'd guess. It's a 53 and the top tube is just barely longer than the seat tube.
03-01-08, 04:28 PM
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I've noticed on smaller frames, like the 49cm ones, some models will have longer top tubes or higher bottom bracket height. This has to do with fitting a 27" wheel on the bike. The frame needs to be either made longer so there is no toe overlap or they raise the bottom bracket to have clearance for the wheel, but then this causes the standover height taller. If you look at some models with a 49cm seat tube, you'll notice that the standover height is often the same or close to the 52cm frame.
This is fine with me, since I have short legs and a long torso, they often fit me nicely.
This is fine with me, since I have short legs and a long torso, they often fit me nicely.
03-01-08, 04:57 PM
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The mid-80's Miyata's tended toward the reverse measureents from yours, having tall seat tubes and remarkably short top tubes (like the 60 c2c seat vs 58 c2c top mentiond earlier, by memory comes that last bit). Just bought a friend a Scapin and it suffers from your measurement cannon; 51.75 c2c seat, 53.5 c2c top. I typically ride a 55/56 squared c2c and found that this frame is a better fit for me than for my friend, whom typically rides a 52 c2c. It's been a touch disconcerting to confirm that I might actually find good fit on a frame 3 full sizes smaller than my norm.
Danny
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03-01-08, 06:14 PM
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very typical of high volume 19-1/2"& 19-3/4"miyata-built bikes of the late 70's & 80's, including univegas,etc.
-the toptubes tended to have the same or similar dimensions & geometry to their 21" counterparts but seemingly with the seat and headtube lugs just slid down in the jig & cut shorter to produce a lower standover. It was usually "compensated for" by the manufacturer with a correspondingly ultra short stem in the 6.0-6.5 cm range in the small sizes.
-the toptubes tended to have the same or similar dimensions & geometry to their 21" counterparts but seemingly with the seat and headtube lugs just slid down in the jig & cut shorter to produce a lower standover. It was usually "compensated for" by the manufacturer with a correspondingly ultra short stem in the 6.0-6.5 cm range in the small sizes.
Last edited by caterham; 03-02-08 at 12:34 AM.
03-01-08, 06:37 PM
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goto miyatacatalogs.com and you can see all the measurements for bikes from 1981 to 1994. 49cm with 54cm top tube sounds strange...
03-01-08, 10:35 PM
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I've noticed on smaller frames, like the 49cm ones, some models will have longer top tubes or higher bottom bracket height. This has to do with fitting a 27" wheel on the bike. The frame needs to be either made longer so there is no toe overlap or they raise the bottom bracket to have clearance for the wheel, but then this causes the standover height taller. If you look at some models with a 49cm seat tube, you'll notice that the standover height is often the same or close to the 52cm frame.
This is fine with me, since I have short legs and a long torso, they often fit me nicely.
This is fine with me, since I have short legs and a long torso, they often fit me nicely.
Last edited by caterham; 03-02-08 at 12:35 AM.
03-01-08, 11:29 PM
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top tube on my 615 is pretty short.
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03-02-08, 12:44 AM
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actually for most of the entry to upper mid-level, sub-52 cm/21" japanese bikes of the time, toe-clip overlap probably wasn't the primary consideration, if at all, as most of the effected bikes would today be categorised as sport/recreational bikes with generous front/center dimensions. IMO, mass-production economies were the driving reasons for the excessive toptube lengths. In addition, the bottom bracket height issue was due to using a single "universal" btm bkt shell to cover the full range of sizes for a given model, again for production efficiency and cost containment esp in areas where the typical consumer would be least capable of discerning where cost cutting was done.
Originally Posted by Sheldon Brown (pbuh)
Let's say a given model comes in 25, 23, 21 and 19 inch frame sizes. A shop might have a 21 and a 23 on the floor. A small rider comes in, tries to stand over the 21, but it's too tall. She figures, well yeah, that's too tall, but the 19 ought to be two inches lower, and I'm sure I could fit a bike two inches lower, so I'll order one.
However, the 19 inch frame has a 3/4" higher bottom bracket, so the standover height is actually only 1 1/4" lower than the 21" model! Now, if the manufacturer really cared about customers who need the smaller frame size, they'd install shorter cranks on the 19". This would actually permit them to _lower_ the bottom bracket of the 19" size, since there's less of a pedal strike issue with the shorter cranks.
The problem turns out to be basically that the wheels are too large for the rider. However, there are marketing difficulties in selling a bike with smaller wheels, so that's an ignored option.
If you want to build a 19" frame with full-sized wheels _and_ a level top tube, you wind up with an itty-bitty head tube and steerer. This creates issues with the headset and handlebar stem, so they can't go below a certain minimum head-tube length.
That's where the cheating comes in...if you raise the bottom bracket, you can make a frame you can call a 19" and still have the level top tube and a reasonable head tube.
As I mentioned, this is no longer that common, since the sloping top tube eliminates the problem, but short riders looking at older used bikes should beware this scam.
However, the 19 inch frame has a 3/4" higher bottom bracket, so the standover height is actually only 1 1/4" lower than the 21" model! Now, if the manufacturer really cared about customers who need the smaller frame size, they'd install shorter cranks on the 19". This would actually permit them to _lower_ the bottom bracket of the 19" size, since there's less of a pedal strike issue with the shorter cranks.
The problem turns out to be basically that the wheels are too large for the rider. However, there are marketing difficulties in selling a bike with smaller wheels, so that's an ignored option.
If you want to build a 19" frame with full-sized wheels _and_ a level top tube, you wind up with an itty-bitty head tube and steerer. This creates issues with the headset and handlebar stem, so they can't go below a certain minimum head-tube length.
That's where the cheating comes in...if you raise the bottom bracket, you can make a frame you can call a 19" and still have the level top tube and a reasonable head tube.
As I mentioned, this is no longer that common, since the sloping top tube eliminates the problem, but short riders looking at older used bikes should beware this scam.
03-02-08, 02:06 AM
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Sure. I'll buy into your reasoning.
I hadn't fully considered that the 27" wheel clearances as being the principle factor for a disproportionate toptube length but rather had concentrated on the pricepointing/economics -in retrospect, the entry and mid-line bikes back then were invariably 27" models and, of course, the worst offenders.
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Last edited by caterham; 03-02-08 at 06:56 AM.
03-02-08, 09:40 AM
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Personally, I think the relatively long top tube is a combination of several factors, but the driving one seems to be the toe overlap. All the small Miyata road frames with 27" or 700C wheels have a front center of 590 +/- 5mm, which is a fairly narrow range. Pair this with a parallel angle frame and the minimum top tube length is defined by the front center distance less the fork rake. In the case of higher level frames, the seat tube geometry is generally steeper than the head tube, resulting in these tubes converging. The greater the difference between the two angles, the shorter the top can be for a specific frame size, while retaining the same front center. Factor in the smaller rake on the more performance oriented frames and the top tube can shrink even more.
Fudging the frame size by increasing the bottom bracket height certainly exaggerates the relative top tube length and there is no denying that ecomonics always comes into play, but it would appear that the minimum top tube length is primarily a function of maintaining an acceptable front center distance in conjunction with the head and seat tube angles and fork rake. So, the relatively long top tube will be restricted to the very small frame sizes with relaxed geometry such as the entry level sports models and maybe some grand touring models..
Fudging the frame size by increasing the bottom bracket height certainly exaggerates the relative top tube length and there is no denying that ecomonics always comes into play, but it would appear that the minimum top tube length is primarily a function of maintaining an acceptable front center distance in conjunction with the head and seat tube angles and fork rake. So, the relatively long top tube will be restricted to the very small frame sizes with relaxed geometry such as the entry level sports models and maybe some grand touring models..
03-04-08, 07:50 AM
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On vacation and mostly AFK for a week, but thanks for the replies! The small frame/long TT explanation makes sense. Unaquidon, I found your link really useful. Based on those scans, my frame seems to be an '84. The bike was one of a lot of three (one of which was bent and I refused after getting permission to strip useful parts) which had been neglected and abused, and were in a garage full of crap. This frame has a chrome fork and had a 5 speed freewheel which threw me, but I suspect these were later swaps. In particular, the Miyata's headset had a cracked cup - I bet the original fork got bent in a crash which cracked the cup and was replaced with the chrome one. Frame's OK though. If not for the long TT I'd build it up for myself.
