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650c front and 700c rear?
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 2009-09-11 1:31 PM |
 23 |  Subject: 650c front and 700c rear?I just switched to an entry level tri bike (scattante T-560) from an even more entry level road bike. On the proper seat height and lowest handlebar height settings, I still cannot maintain a near horizontal body position. Maybe my legs are too short, my arms are too long, or something, but I wanted to get optimal rider position for aerodynamics which is why I purchased this bike to begin with. I can either have the Fork/handlebar/stem region cut by ~1.5 inches and leave everything else the same but for training comfort leaving the handlebars slightly higher than optimal is actually more comfortable. If I could race with 650c wheels in the front and 700c wheels in the back that should tilt my head/shoulders down just enough for near optimal rider position, and I could still train with 700/700 setup and have that flexibility. I am about to purchase front racing wheels anyways so this would be a convenient time to do this switch if it is feasible. Are there aerodynamic or stability problems with running 650/700 combo because the bike is physically tilted to get my torso in horizontal position? The LBS said the 650c could easily be installed and would just have to adjust the brake calipers down a tad bit but they could not comment on performance/stability impacts for Tri racing. I'll be doing the Austin Longhorn HIM next month so plan on getting SRAM S60 clinchers for the front soon so need to decide whether to order 650c or 700c ASAP to have time to experiment and train on it. Thanks for any input. Lawrence |
| 2009-09-11 1:47 PM in reply to: #2401161 |
Giver 18427     | Subject: RE: 650c front and 700c rear? You could throw a 650c front wheel on your bike, but with a 700c fork, the brake pads would probably hit above th etire. To make it work, you'd have to swap the fork, too. Not sure what it would do for the handling, I dunno. COuldn't be good, though. |
| 2009-09-11 2:01 PM in reply to: #2401192 |
| 23 | Subject: RE: 650c front and 700c rear? run4yrlif - 2009-09-11 1:47 PM You could throw a 650c front wheel on your bike, but with a 700c fork, the brake pads would probably hit above th etire. To make it work, you'd have to swap the fork, too. Not sure what it would do for the handling, I dunno. COuldn't be good, though. thanks i'll stay away from the weird combo then. the LBS said I could keep the fork but just move the brakes down a tad bit and it would be fine but I was more concerned about the handling/performance issues. with 6 weeks left to train for my first HIM having just done my first Tri 4 days ago, now isn't the time to experiment with quirky stuff so I'll just have the handlebars lowered by cutting off 1.5 inches and keep the bike "guaranteed" stable. |
| 2009-09-11 2:13 PM in reply to: #2401161 |
Expert 792  Leicester | Subject: RE: 650c front and 700c rear? There is brake calipers that could accomodate the smaller wheel diameter. Don't forget that your front braking power (hopefully you will never need 100%) will be reduced by the change in mechanical advantage. you wheel diameter will go down by 6%, in reality it's going to drop the distance from your wheel axis to the ground by about 19mm... I think you could remove a spacer from your headset or buy a 'race day' stem that is 5degrees shallower and acheive similar drop. Considering the set up time I think a new stem with less rise or depending on where/what spacers you have between your head set and the stem, just a trainging vs race set up would be quicker and cheaper Check out Sheldon Brown's atricle on converting to 650b, It's not race/tri bike orinented but it's a good article and has a good pic of a 700c designed frame and forc with 650b's in it, you can see the long brake calipers. http://www.sheldonbrown.com/650b.html |
| 2009-09-11 2:21 PM in reply to: #2401241 |
Expert 792 Leicester | Subject: RE: 650c front and 700c rear? alex jb - 2009-09-11 2:13 PM ... you wheel diameter will go down by 6%, in reality it's going to drop the distance from your wheel axis to the ground by about 19mm... I think you could remove a spacer from your headset or buy a 'race day' stem that is 5degrees shallower and acheive similar drop. http://www.sheldonbrown.com/650b.html OOps, I misread the title, 700c to 650C will drop the axle by 25.5mm, not 19mm. I still think you can get 20mm drop from other components and not have to mess with your brakes.
What is your stem length and angle and what spacers do you have above and below it?
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| 2009-09-11 6:15 PM in reply to: #2401161 |
| Expert 1233 | Subject: RE: 650c front and 700c rear? There was a tri-bike fad, maybe 20 years ago, with the small front wheel set-up. The reasons were the same as yours, to get better aerodynamics. They were only around for a short while, so something let to their extinction (meaning nobody bought them). Have you had a bike fit? Aero position means nothing without a proper fit. |
| 2009-09-11 8:53 PM in reply to: #2401252 |
| 23 | Subject: RE: 650c front and 700c rear? alex jb - 2009-09-11 2:21 PM alex jb - 2009-09-11 2:13 PM ... you wheel diameter will go down by 6%, in reality it's going to drop the distance from your wheel axis to the ground by about 19mm... I think you could remove a spacer from your headset or buy a 'race day' stem that is 5degrees shallower and acheive similar drop. http://www.sheldonbrown.com/650b.html OOps, I misread the title, 700c to 650C will drop the axle by 25.5mm, not 19mm. I still think you can get 20mm drop from other components and not have to mess with your brakes. What is your stem length and angle and what spacers do you have above and below it? The stem is 65mm and angled down as much as it will go (not sure exact angle). I have three 1cm spacers above the headset. Should I remove all 3 spacers to drop 30mm and angle the stem up for comfortable training and angle it all the way down for racing? With the current spacers in place and stem angled down, the elbow pads are exactly the same height as the seat, so I think I need all 30mm. |
| 2009-09-11 9:02 PM in reply to: #2401612 |
| 23 | Subject: RE: 650c front and 700c rear? vonschnapps - 2009-09-11 6:15 PM There was a tri-bike fad, maybe 20 years ago, with the small front wheel set-up. The reasons were the same as yours, to get better aerodynamics. They were only around for a short while, so something let to their extinction (meaning nobody bought them). Have you had a bike fit? Aero position means nothing without a proper fit. I was fitted by the manager at Performance Bikes who is a veteran cyclist but has never done a triathlon. He told me immediately that the handlebar/elbow pads were very likely too high for optimal aero position but to try it out for a few rides before removing spacers. He also said I probably need a shorter stem because I'm extending my arms out too much. He just put my bike on a trainer, watched me spin for a bit while adjusting seat height and handlebar/stem positions. Not sure if this is a true fit or not but it wasn't done by a triathlon oriented person/store. |
| 2009-09-12 4:09 PM in reply to: #2401161 |
Expert 1379 Woodland, California | Subject: RE: 650c front and 700c rear? If you can't get enough of a drop between the proper seat height and the handlebars, and you are stretched out, it sounds like you might benefit from a smaller frame. If you bought the bike already this probably isn't what you want to hear. Have you removed all the spacers between your stem and head tube? Also, if you are only stretched out on the aerobars but ok on the bullhorns, you might benefit from shorter aerobars. I'm a small person and I had this very problem when I got my tri bike.
Edited by froglegs 2009-09-12 4:12 PM |
| 2009-09-12 10:57 PM in reply to: #2402444 |
| 23 | Subject: RE: 650c front and 700c rear? froglegs - 2009-09-12 4:09 PM If you can't get enough of a drop between the proper seat height and the handlebars, and you are stretched out, it sounds like you might benefit from a smaller frame. If you bought the bike already this probably isn't what you want to hear. Have you removed all the spacers between your stem and head tube? Also, if you are only stretched out on the aerobars but ok on the bullhorns, you might benefit from shorter aerobars. I'm a small person and I had this very problem when I got my tri bike. I think you're right. I removed 2 spacers today and moved the aerobars toward me 2cm and feels better now although still not perfect. I'm still a little off from full horizontal but barely so I'm gonna test it in the morning on a 50 miler. I have a feeling I'll have to remove the last spacer and also shorten the stem about 2cm but I want to try this new change for at least 100 miles before another modification. I only have 1 spacer left to remove so hopefully I'm almost there or else I'm screwed since the stem is already angled down maximally. I'm a stocky 150lb 5'6" with average length legs wearing 30" inseam pants (this is as scientific as I can estimate for now since I haven't done exact measurements, but it seems most 5'6" guys wear about 30" jeans) and I'm on a 48cm frame which in theory "should" be an OK fit. I still have 2 cheap modifcations available so hopefully it'll be almost perfect by the Longhorn HIM time  The bike is only 1 week old so I can still exchange it but unfortunately I don't think Performance has men's tri bikes smaller than 48cm and I got mine for a steal so I hope it works out. ( Scattante T-560 for $750 plus the 10% membership store credit for entry level Tri bike with 105 level components and Durace shifters.) Thanks for the input. Edited by lawrence131 2009-09-12 11:01 PM |
| 2009-09-13 2:24 PM in reply to: #2402847 |
Expert 1379 Woodland, California | Subject: RE: 650c front and 700c rear? 48cm frame shouldn't be too big for you. I'm 5'2 with a 28.5" inseam (I think) and that's what I ride. I also use a short stem (70mm) and adjustable (Profile Stryke) aerobars. I took out all the spacers and my bars are so low that I can't even use my aero drink bottle because it hits my tire. People laugh at my bike because it is so small, but I don't care because I feel great on it. I wouldn't worry too much about getting fully horizontal. Comfort should be your primary concern because if you're not comfortable, you won't spend enough time in aero for it to make a difference. You really should consider getting shorter and/or adjustable aerobars (rather than a shorter stem) if you're not stretched out on the bullhorns. |
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