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#1
September 30th 03, 10:28 PM
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Small cyclocross frames and toe overlap?
I've never been one to get too deeply into the details of frame design
since I have a fairly average body and seem to adapt well to any reasonably designed bike. My wife is a different story though and I'm trying to understand the tradeoffs necessary to get a good fit for her with a small cyclocross bike. Her current frame is a 48 cm Redline Conquest that has been declared insufficient due to toe-wheel overlap. I've measured 4 cm of overlap with the current setup. I don't want to replace this frame only to have the same problem, so I've set about trying to calculate toe overlap based on the following published specifications and measurements: Frame Specifications: Wheelbase Chainstay length BB height Measurements: Wheel radius Crank Length Pedal offset from BB center Toe offset from pedal center I've created an Excel spreadsheet that calculates the dimensions of two triangles defined by the BB, dropouts, and the intersection of the wheelbase line and a line drawn vertically from the BB. It then calculates the toe clearance when the wheel is at an angle that intersects the toe. If I'm not mistaken, the only factor I'm neglecting is wheel flop due to head tube angle, but I assume that is negligible. My calculated value for the Redline is 1.6 cm of overlap compared to the actual value of 4 cm. For my wifes road bike, the measured and calculated values are within 1 cm. In any case, the calculation seems like a good basis for comparison of various geometrys. Plugging in some numbers from various vendor websites, I'm able to confirm that Redline has made some design tradeoffs that increase toe overlap. It has a short wheelbase and long chainstays compared to other makes. To make matters worse, my wifes Redline has a wheelbase that measures 1.5 cm under the spec, increasing the problem. I can't say for sure that this is build error because the bike has been loaned to juniors and crashed in ways that I can only speculate about. Looking at other designs, Kona's Jake the Snake (49)has 2.6 cm more toe clearance. They seem to have accomplished this by using a longer wheelbase and shortening the chainstay by using a steeper seat tube angle. The Gunnar Crosshair (48) also has better toe clearance. They have a shorter wheelbase than the Kona, but an even steeper seat tube allows for a shorter chainstay. It appears that the tradeoff is: Wheelbase vs. Seat Angle/Chainstay Length vs. Toe Clearance Comments? Is my methodology valid? Which tradeoff sounds better, Kona or Gunnar? Any recommendations for other well designed small cross frames? Is the Redline a pig or what? Should I have Mark Hickey do a custom frame? All opinions welcome, Bret P.S. If you'd like to have the spreadsheet, drop me an email. 
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#2
October 1st 03, 12:09 AM
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Small cyclocross frames and toe overlap?
"Bret Wade" wrote in message
om... I've never been one to get too deeply into the details of frame design since I have a fairly average body and seem to adapt well to any reasonably designed bike. My wife is a different story though and I'm trying to understand the tradeoffs necessary to get a good fit for her with a small cyclocross bike. Her current frame is a 48 cm Redline Conquest that has been declared insufficient due to toe-wheel overlap. I've measured 4 cm of overlap with the current setup. I don't want to replace this frame only to have the same problem, so I've set about trying to calculate toe overlap based on the following published specifications and measurements: Frame Specifications: Wheelbase Chainstay length BB height Measurements: Wheel radius Crank Length Pedal offset from BB center Toe offset from pedal center I've created an Excel spreadsheet that calculates the dimensions of two triangles defined by the BB, dropouts, and the intersection of the wheelbase line and a line drawn vertically from the BB. It then calculates the toe clearance when the wheel is at an angle that intersects the toe. If I'm not mistaken, the only factor I'm neglecting is wheel flop due to head tube angle, but I assume that is negligible. My calculated value for the Redline is 1.6 cm of overlap compared to the actual value of 4 cm. For my wifes road bike, the measured and calculated values are within 1 cm. In any case, the calculation seems like a good basis for comparison of various geometrys. Plugging in some numbers from various vendor websites, I'm able to confirm that Redline has made some design tradeoffs that increase toe overlap. It has a short wheelbase and long chainstays compared to other makes. To make matters worse, my wifes Redline has a wheelbase that measures 1.5 cm under the spec, increasing the problem. I can't say for sure that this is build error because the bike has been loaned to juniors and crashed in ways that I can only speculate about. Looking at other designs, Kona's Jake the Snake (49)has 2.6 cm more toe clearance. They seem to have accomplished this by using a longer wheelbase and shortening the chainstay by using a steeper seat tube angle. The Gunnar Crosshair (48) also has better toe clearance. They have a shorter wheelbase than the Kona, but an even steeper seat tube allows for a shorter chainstay. It appears that the tradeoff is: Wheelbase vs. Seat Angle/Chainstay Length vs. Toe Clearance Comments? Is my methodology valid? Which tradeoff sounds better, Kona or Gunnar? Any recommendations for other well designed small cross frames? Is the Redline a pig or what? Should I have Mark Hickey do a custom frame? All opinions welcome, Bret P.S. If you'd like to have the spreadsheet, drop me an email. I have a 54 cm conquest pro, my shoe size is a mens 7. I also have overlap with my front wheel . I've been racing cyclocross with it for three years with no problems. -- Pete Rissler http://web1.greatbasin.net/~rissler/
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#3
October 1st 03, 12:16 AM
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Small cyclocross frames and toe overlap?
"Bret Wade" wrote in message om... I've never been one to get too deeply into the details of frame design since I have a fairly average body and seem to adapt well to any reasonably designed bike. My wife is a different story though and I'm trying to understand the tradeoffs necessary to get a good fit for her with a small cyclocross bike. Her current frame is a 48 cm Redline Conquest that has been declared insufficient due to toe-wheel overlap. I've measured 4 cm of overlap with the current setup. I don't want to replace this frame only to have the same problem, so I've set about trying to calculate toe overlap based on the following published specifications and measurements: Frame Specifications: Wheelbase Chainstay length BB height Measurements: Wheel radius Crank Length Pedal offset from BB center Toe offset from pedal center I've created an Excel spreadsheet that calculates the dimensions of two triangles defined by the BB, dropouts, and the intersection of the wheelbase line and a line drawn vertically from the BB. It then calculates the toe clearance when the wheel is at an angle that intersects the toe. If I'm not mistaken, the only factor I'm neglecting is wheel flop due to head tube angle, but I assume that is negligible. My calculated value for the Redline is 1.6 cm of overlap compared to the actual value of 4 cm. For my wifes road bike, the measured and calculated values are within 1 cm. In any case, the calculation seems like a good basis for comparison of various geometrys. Plugging in some numbers from various vendor websites, I'm able to confirm that Redline has made some design tradeoffs that increase toe overlap. It has a short wheelbase and long chainstays compared to other makes. To make matters worse, my wifes Redline has a wheelbase that measures 1.5 cm under the spec, increasing the problem. I can't say for sure that this is build error because the bike has been loaned to juniors and crashed in ways that I can only speculate about. Looking at other designs, Kona's Jake the Snake (49)has 2.6 cm more toe clearance. They seem to have accomplished this by using a longer wheelbase and shortening the chainstay by using a steeper seat tube angle. The Gunnar Crosshair (48) also has better toe clearance. They have a shorter wheelbase than the Kona, but an even steeper seat tube allows for a shorter chainstay. It appears that the tradeoff is: Wheelbase vs. Seat Angle/Chainstay Length vs. Toe Clearance Comments? Is my methodology valid? Which tradeoff sounds better, Kona or Gunnar? Any recommendations for other well designed small cross frames? Is the Redline a pig or what? Should I have Mark Hickey do a custom frame? All opinions welcome, Bret P.S. If you'd like to have the spreadsheet, drop me an email. Now you know why Terry uses a 650 front wheel on their smaller bikes... Having said that, the only time you'll ever have a problem is when you're going slowly and trying to really turn sharply. Has there been some problem that your wife has had that is causing this email? Mike
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#4
October 1st 03, 03:54 AM
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Small cyclocross frames and toe overlap?
Mike S. wrote:
"Bret Wade" wrote in message om... I've never been one to get too deeply into the details of frame design since I have a fairly average body and seem to adapt well to any reasonably designed bike. My wife is a different story though and I'm trying to understand the tradeoffs necessary to get a good fit for her with a small cyclocross bike. Her current frame is a 48 cm Redline Conquest that has been declared insufficient due to toe-wheel overlap. I've measured 4 cm of overlap with the current setup. I don't want to replace this frame only to have the same problem, so I've set about trying to calculate toe overlap based on the following published specifications and measurements: Frame Specifications: Wheelbase Chainstay length BB height Measurements: Wheel radius Crank Length Pedal offset from BB center Toe offset from pedal center I've created an Excel spreadsheet that calculates the dimensions of two triangles defined by the BB, dropouts, and the intersection of the wheelbase line and a line drawn vertically from the BB. It then calculates the toe clearance when the wheel is at an angle that intersects the toe. If I'm not mistaken, the only factor I'm neglecting is wheel flop due to head tube angle, but I assume that is negligible. My calculated value for the Redline is 1.6 cm of overlap compared to the actual value of 4 cm. For my wifes road bike, the measured and calculated values are within 1 cm. In any case, the calculation seems like a good basis for comparison of various geometrys. Plugging in some numbers from various vendor websites, I'm able to confirm that Redline has made some design tradeoffs that increase toe overlap. It has a short wheelbase and long chainstays compared to other makes. To make matters worse, my wifes Redline has a wheelbase that measures 1.5 cm under the spec, increasing the problem. I can't say for sure that this is build error because the bike has been loaned to juniors and crashed in ways that I can only speculate about. Looking at other designs, Kona's Jake the Snake (49)has 2.6 cm more toe clearance. They seem to have accomplished this by using a longer wheelbase and shortening the chainstay by using a steeper seat tube angle. The Gunnar Crosshair (48) also has better toe clearance. They have a shorter wheelbase than the Kona, but an even steeper seat tube allows for a shorter chainstay. It appears that the tradeoff is: Wheelbase vs. Seat Angle/Chainstay Length vs. Toe Clearance Comments? Is my methodology valid? Which tradeoff sounds better, Kona or Gunnar? Any recommendations for other well designed small cross frames? Is the Redline a pig or what? Should I have Mark Hickey do a custom frame? All opinions welcome, Bret P.S. If you'd like to have the spreadsheet, drop me an email. Now you know why Terry uses a 650 front wheel on their smaller bikes... Having said that, the only time you'll ever have a problem is when you're going slowly and trying to really turn sharply. Has there been some problem that your wife has had that is causing this email? Mike Hi Mike, We spent the last weekend coaching juniors at a cyclocross camp and this did involve demonstrating some drills that accentuate the toe overlap problem. While I do agree that the frame is ridable, we've come to the conclusion that we want to make a change for this and other reasons. Why ride a bike that you don't enjoy? While shopping for a replacement, I want to choose a frame that minimizes toe overlap, while providing a similar fit, without causing other problems. So far, every other manufacturer I've looked at is an improvement. But what is the tradeoff adding 1-2 cm to the wheelbase? Thanks, Bret
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#6
October 1st 03, 05:59 AM
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Small cyclocross frames and toe overlap?
Mark Hickey wrote:
(Bret Wade) wrote: Looking at other designs, Kona's Jake the Snake (49)has 2.6 cm more toe clearance. They seem to have accomplished this by using a longer wheelbase and shortening the chainstay by using a steeper seat tube angle. The Gunnar Crosshair (48) also has better toe clearance. They have a shorter wheelbase than the Kona, but an even steeper seat tube allows for a shorter chainstay. It appears that the tradeoff is: Wheelbase vs. Seat Angle/Chainstay Length vs. Toe Clearance There's also fork rake to concider, and chainstay length really isn't part of the formula (unless you're subtracting it from wheelbase to get BB-front hub distance). That's what I was doing, subtracting the horizontal component of the chainstay length from wheelbase. The remainder of the wheelbase is then used as the horizontal component when calculating toe clearance. Comments? Is my methodology valid? Which tradeoff sounds better, Kona or Gunnar? Any recommendations for other well designed small cross frames? Is the Redline a pig or what? On a really small frame with 700c wheels, you have to compromise somewhere. You can steepen the seat tube, run a slightly longer top tube and maybe a little slacker head tube - but in the end you will probably find that the "real world effect" is that the compromises in handling that result are a bigger problem than a little toe overlap. I suggest to most people that are agonizing over TO to go ride around in tight little circles and get used to toe-tire contact - after just a few times, it becomes second nature to drop a heel or backpedal to clear it. Heck, I ride a stock 56x56cm road frame, have size 10 shoes (Euro 44), and because I ride my cleats far back on my shoes, I have toe overlap as well (and that's on about as "normal" a frame geometry as there is). The various manufacturers made different choices. Redline chose toe overlap while Kona and Gunnar shyed away from it. Does anyone think Kona and Gunnar have compromised handling in their smaller sizes? Should I have Mark Hickey do a custom frame? An excellent idea! ;-) Thanks, we'll consider it. Bret Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame All opinions welcome, Bret P.S. If you'd like to have the spreadsheet, drop me an email.
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#7
October 1st 03, 05:26 PM
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Small cyclocross frames and toe overlap?
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#8
October 2nd 03, 11:22 PM
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Small cyclocross frames and toe overlap?
This is similar to the thread "are short stems bad?" a while back. Long TT
for a given fit with a short stem is the best tradeoff for our petite comrades, For cross the reduced weight transfer while braking is very useful. Tom -- Bruni Bicycles "Where art meets science" brunibicycles.com 410.426.3420 David E. Belcher wrote in message om... (Bret Wade) wrote in message . com... Is the Redline a pig or what? Similar comments were made in UK review a few years ago re. toeclip overlap on Redlines - and the bike they tested wasn't a small one. Must be a general shortcoming of their design, and one that they seemingly haven't rectified in subsequent years' models. David E. Belcher
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