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I bought my first cx bike at the beginning of the summer and started watching a few races on YouTube and such, not because I plan to race but just because it was interesting to me. All summer I've been riding on paved trails until recently I took it off-road to a bike trail in the woods. Instantly I noticed how stiff my bike is (2015 Giant Revolt 3) and I started to feel each and every bump my wheels came in contact with.

So this made me question. Why are cx bikes so stiff if they are used to ride off-road a lot? Races are all off-road with bumps/hills/etc. as well. It makes sense for road bikes because they're riding on smooth paved road and don't need to worry about sudden bumps in the road.

My question is, why are cx bikes so stiff and what impact does it have on performance? I'm mainly interested in performance changes for off-road biking or cx racing.

Thanks.

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    Maybe you have your tire pressure too high, because that bike ships with decently big tires. And in race conditions, comfort isn't so important -- control and agility are. Your legs can absorb some of the shock. – Batman Aug 24 '15 at 14:14
  • 60psi is what I usually keep mine at. too high? – MB41 Aug 24 '15 at 14:20
  • Depends on how much you weigh and the amount of impacts you might sustain while riding. But tire pressure is something you have to play with -- its highly individual (up to of course, limits of the wheel and not being so low that you flat). – Batman Aug 24 '15 at 14:37
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    Try lowering the pressure. 4 bar is a lot for those 35mm tires. I also wouldn’t be too worried about breaking something. Get out of the saddle as soon as it gets rough or an obstace (e.g. stones, root) appears and try to keep your arms relaxed. Actively lifting shifting your weight to get over stuff helps too. Cyclocross feels rough, that’s why it’s so much fun! – Michael Aug 24 '15 at 15:25
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    You're losing 20-25 psi on a ride? Sounds like your tube/valve might be leaking. Also, note this is a commuter cross bike, rather than a race bike so this should be relatively comfortable. – Batman Aug 24 '15 at 15:57
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In general, cyclocross bikes are stiff because they are being used to race. A stiffer frame will transmit more energy from the pedal to the rear wheel. Cyclocross races are usually 45-60 minutes (less for lower levels, more for pros), so fatigue from bumps is not an issue. As noted by Frisbee, cyclocross race courses are not as bumpy as wooded trails. Race courses usually pass over grass fields, perhaps a little bit of trail, and often sand and/or mud. And racers usually run as low a tire pressure* as possible to increase traction, which also helps with smoothing the bumps.

In your specific instance, there are a few factors that might serve to smooth out your ride... 1. Check your tire size. Most cyclocross bikes can take a 40mm tire, though they are usually delivered with a 32mm tires (as 32mm is the UCI limit for races). Larger tires will provide more cushion. 2. Check your tire pressure. Most people run their road tires (21-25mm width) at 90-120psi. If you have wider tires, as commonly found on cyclocross bikes, try lowering the pressure to 60-80psi for long road rides. And even less for trail (though you'll have to balance your tolerance for flats vs comfort/traction).

  • With tubular tires (glue ups/sew ups) a lightweight pro can run below 20psi without flats. With standard clincher tires more pressure is required to avoid flats.
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  • You are mentioning between 90-120psi for a cx bike. I pump mine up to 60 psi with some effort and I can't imagine pumping mine up to 90psi. Frisbee mentions that the average is 40psi. So which one? Because that's a big difference. – MB41 Aug 24 '15 at 15:27
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    @MR04 He said 90-120 for a ROAD bike and I said it varies. There are lot of factors - there is not one number. – paparazzo Aug 24 '15 at 15:36
  • @Frisbee correct, I misread the "road tires" part. After doing a bit more research, I noticed that tire pressure is a common topic with many opinions. Either way you all satisfied my curiosity and answered my question. Some time in the future I plan to replace my cx bike with a road bike and get an inexpensive mountain bike for better experience. I guess riding the wooden trails around me is too rough for my cx bike to handle. Thanks! – MB41 Aug 24 '15 at 15:41
  • Tire pressure is definitely a personal choice. I tend to run mine at the low end of the advisable range (this is true on road, cyclocross, or mountain bike). But, I'm lightweight (145lbs) by American standards and fairly easy on equipment. I have friends that have to run at the high end, either because they are larger, or because they are harder on equipment. 60psi is fine for a 30-38mm tire. If you are running larger tires, you can try running 40-50psi (if the terrain isn't too rocky). It's an experiment to find the pressure that gives you the most comfort and traction without flats. – Alistair H Aug 24 '15 at 16:31
  • A laterally stiff frame will be more efficient under pedaling forces. However, a vertically stiff frame becomes increasingly inefficient the rougher terrain gets because the wheel will spend less time in contact with the ground. – Deleted User Aug 24 '15 at 21:34
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Race courses in city parks are not that bumpy. Most racers run closer to 40 psi (on a 34 mm) but it varies. Clincher tires to run low pressure with pinch flats is common. The bike is stiff for speed.

The Revolt 3 is not a true CX bike. It probably came with a 35 mm. That bike will take a 50 mm. You can safely run 50 mm at 40 psi (check the range on the tire) and get a pretty soft ride.

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  • I'm 170lbs riding on 60psi tires. I'll try lowering it a bit and see if it helps. To me it felt like I would break something on my bike going over bumps on the trail. – MB41 Aug 24 '15 at 15:16
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    Just because racers run at 40 psi does not mean you should. Racers will often run as low as they can and not get a pinch flat and have a spare wheel in the pit. Most race courses don't have rocks. I race at 35 but I train closer to 60. – paparazzo Aug 24 '15 at 15:32
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    FYI on alternate tires -- I've got a 2014 Revolt 1 and have been running a Clement X'Plor MSO 700x40 on the front and am trying a WTB Nano Raptor 29x2.1 on the back... – mike Aug 25 '15 at 21:32

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