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short vs long wheelbase tri/TT bikes?
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Doodling on a piece of paper at the moment(obviously it's slow in the office at present) and began to think of the theoretical possibilities of short/long wheelbase tri/TT bikes. Maybe some of you bike designer or engineer types can help out with this.

It's a given that tri bikes generally don't handle as well as road bikes. But the wheelbase on your tri bike is usually fairly close to your road bike if they're the same frame size. So this is more of a function of the weight of the rider being placed forward. Slowman has a theory about improving a tri bike's handling characteristics by increasing the wheelbase in a tri bike. He suggests decreasing head tube angle and increasing fork rake thus increasing the center to front distance. This will give the bike an oversize wheelbase which he feels would give better rider weight distribution. However, it is to my understanding that the best way to increase a bike's handling is to increase the chainstay length, but in this case the chainstays are remaining the same. In fact they will even become proportionally shorter if only the center to front is increased. This in theory(as I understand it) should mean more twitchiness so would it not negate any advantages of the longer wheelbase.

Going the other way to a shorter than normal wheelbase would present problems of increased twitchy handling, decreased ride comfort and would be a pig for curvy descending. However there would be more frame stiffness and would be lighter so you should be able to better put the power to the road better without the longer frame flexiness. If you were racing a TT on a strait flat surface and not worried about hills or curves, would there not be advantages to making an extra short wheelbase bike?

I would imagine that a large part of bike design has been trial and error, so it's probably fair to assume that the shorter and longer than normal wheelbase designs have already been tried. Just wondering if anyone has any knowlege or thoughts about them.
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Re: short vs long wheelbase tri/TT bikes? [cerveloguy] [ In reply to ]
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However, it is to my understanding that the best way to increase a bike's handling is to increase the chainstay length


Not true -- well, not that simple. Every change to a frame changes some aspect of handling. Handling is very much a sum of the parts thing.

As with designing our training, we have to first ask what is it we want to accomplish. One person's fine handling bike is another's twitchy nightmare. Dan doesn't like a lot of trail; I happen to like an above-average amount of trail. A bike can be stable-riding with and without a lot of trail. As you mention, wheelbase is one of those considerations. For example, a tandem doesn't need as much trail as a regular bike.

I personally believe that the long front-center is the right answer in mid to large size tri frames ridden in the "forward" position. I also think that the longer front-center matches up quite nicely with shorter chainstays so that the overall wheelbase doesn't get too long. We can then have a bike that handles as sweetly as a stage-racing bike, yet allows us to ride forward and low. A caveat is that the longer front center cannot be accomplished merely by lengthening the top tube; it has to be a slacker head tube and more fork rake.

An important aspect of bike handling is the position of the bike's pivot point in relation to your center of mass when on the bike. Any bike, when moving forward and turning, rotates "around" a given point. Oddly enough, that point actually changes with bike speed and with the degree of turning. If that point at a given speed and turning radius is near to your center of mass, the bike handles nicely because everything feels in balance. If your COM is ahead of or behind that point, you'll be fighting adverse forces to stay on the bike and keep it under control. Leaning the bike and shifting fore and aft is our reflexive way of matching COM to the bikes changing pivot point.

So, to complicate things even further, one's favorite bike would depend on the typical speeds at which one will be riding the bike! Perhaps that's why criterium riders (fast, sharp high speed turning) favor different geometry than road racers (moderate, gentle high speed turning).
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Re: short vs long wheelbase tri/TT bikes? [cerveloguy] [ In reply to ]
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"Doodling on a piece of paper at the moment."

I do it all the time. Well, actually I've upgraded to doodling on the computer.

My theory on wheel base. Long wheel base equals good, so long as the chainstays are shorter to keep the rear-end from hopping. Though I could be wrong.

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I don't work here, I just live here
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