single speed racing geometry- Mtbr.com
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  1. #1
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    single speed racing geometry

    What follows is a long story leading me to the following conclusion: a single speed bike races better than a geared bike with a more compact geometry than you are supposed to fit? A size below what manufacturers recommend in fact.

    Long version:
    I have just parted with my geared bike to go solely solo. The old bitsa GT single speed was getting most of the mileage and scoring first in fun, but the frame was cracked so I needed a replacement. Chris Jones is the maestro steel frame builder in Perth and if I sold my 27 gears I could afford 1.
    However, I race XC (only sport class at the moment - Masters next year) and wanted to still be competitive. Could a single gear do it? My Cannondale F400 had got me three 3rds out of three races. The 'dale was a big bike, about 40mm longer than the GT, very stable, railed corners, made up for my downhill nervousness and very comfy (size Large, I'm 6 foot). It didn't climb as quick as the shorter GT (same chainstay length but a 22" effective toptube compared to the Cannondales 24") but with gears it made it less taxing and capable of 12% grades. The SS GT stalls over 8% or rather I do. Previous geared bikes (Wheeler, Trek, KHS) had all been between these two sizes and all felt too short when I was going over the bars. 'Conventional wisdom' said the 'dale fit better.
    I will never know if the Cannondale had a 2nd or even 1st in it.
    I suppose I should have tried racing SS before I sold the gears but impatience won over. So I found myself on the broken GT (while the new frame was still being built), when the first XC race of the season rocked up. This race was a new format. We had a short course, hill climb time trial and mini XC with points for positions judging the eventual winner.
    I figured the shorter races might suit me but was surprised when I found myself leading the short course from the gun. Geared bikes, even $5000 ones take a while to get up to speed it seems. So first question answered. If I enter geared races on a SS the lead is mine if I want it. Could I keep it? Turned out there was another single speeder in Sport that day, an elite rider recovering from an injury and I didn't expect to beat him, so when he pulled alongside during the second lap I asked him to set the pace.
    Following I learned this: you need to spend even more time out of the saddle than I was used to and take the tightest lines available and that elite riders go downhill very fast. Our rigid forks and single gears even with a slipped rear wheel (the elite rider) and a dropped chain (me, curse the rear derailleur conversion) exceeded my expectations on the fast flowing short course terrain. I finished third, buzzing the wheel of second and if I hadn't dropped the chain I would have been second for sure. The absence of a big chain ring was no hindrance. But would the absence of a granny gear be the end of the single speeders bid for glory?
    20 minutes later I was struggling up the hill climb, but I was NOT walking. Going was hard but I was even reeling in a couple of riders. Switchbacks are easier on the GT's small wheel base (1065mm) but these were steep and I did have to jump off for one or two of them. Going down was steep and I ran out of pedalling power but I finished 2nd (20th overall) behind the elite single speeder who finished 5th overall. The geared playboys were no longer laughing.
    Mini XC followed after a much needed rest and even with some pretty bone jarring granite rockery single track I finished 2nd again and less than a minute behind the other single speeder. 2nd overall on the day. One better than I'd ever done with gears and AGAINST geared bikes. It felt good as did the surprised attention of the other riders.

    Next day I finalised my new frame's geometry. Basicaly the same as an 18" GT outpost 71 degree head angle but with a 72.8 degree seat tube so I can use a more in line seat post for the same positioning as the GT's 74 degrees. Same front centre (642mm) and effective top tube (590mm) but with Paul's horizontal dropouts and various racing gear combos (36/16, 34/16, or 32/16), a shorter wheelbase between 1060 and 1066 mm (chainstay between 418 and 424 mm).
    In a few weeks the new bike will be ready, just in time for the next XC race. This time its 3 laps, 24 k and I will lead from the start. Hopefully my elite competition will be back in elite and I will be reporting back with a First and an absolutely dialled XC racing single speed geometry. The course is fast, twisty, with short pitches, lots of downhill and a million log piles. Can't wait.

    flyingporkpies
    Last edited by flyingporkpies; 07-06-2006 at 01:55 AM. Reason: spelling

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