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All,

I have a 2017 Scott Spark 720. It has 27.5 Plus Tires on it 2.8 maxis recon which I run at 16/18 psi (amazing traction).

I have been getting a lot of pedal strikes (In rocky/rooted turns, mild but annoying and throwing me off line) and have been considering purchasing a 29 inch wheel set to put 2.6 tires on it. I estimate that I would be running closer to 25 psi in them.

Approximately, how much would this increase my BB height by? I think if I could get 1-3 cm increase the pedal strikes would pretty much disappear.

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  • Do you ride with flat pedals? Might be worth exploring MTB cleats and shoes and clipless pedals. They're thinner and shorter, effectively harder to ground strike in the turns – Criggie♦ Jul 26 '18 at 19:53
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    I ride shimano spd cleats and small platform pedals. Its typically my shoe that contacts. – ak_slick Jul 26 '18 at 19:55
  • Your other option is to learn when to pedal and when to coast. For MTBs, turning with your outer-pedal down means the bars would strike the ground before the raised inner pedal. Sharper turns should be coasted with inside pedal raised. – Criggie♦ Jul 26 '18 at 19:55
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    How’s long are your cranks? I’m wondering if shorter cranks are an option. What about your 29er crank length? – Swifty Jul 26 '18 at 20:11
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    @Swifty thanks - there's nothing gained by being obnoxious. I didn't figure this out, someone told/taught me how to do it better. – Criggie♦ Jul 27 '18 at 3:40
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The difference between 622mm rims on 29” wheels and 584mm on 27.5” wheels is only 19mm - about 3/4 if an inch. If you run a narrower tire the rim plus tire diameter different is even less.

In general bike frames do not have clearance for larger wheels so this may not even be possible.

Note that larger wheels will also change your steering geometry.

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  • If I add the same height in the back and front steering geometry should be the same correct. – ak_slick Jul 26 '18 at 18:29
  • Steering angle will be kept the same but trail increases with larger wheels – Argenti Apparatus Jul 26 '18 at 18:34
  • Thats a good point but not much since 27plus tires are only about 1/4" shorter than my other 29er. I am really thinking I will get most benefit from less squat of the tire. – ak_slick Jul 26 '18 at 18:37
  • If you have a 29er then at least you can try the frame clearance before you buy new wheels! – Swifty Jul 26 '18 at 19:57
  • Great idea. My 29er is qr and the New bike is boost but just holding the 29" wheel in place and measuring my tire squat when seated on both bikes should give me a good idea of what benefits could be had. – ak_slick Jul 26 '18 at 20:26
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I have a 2017 Yeti SB5+. I too was running anywhere from 14-18 PSI when I first started riding it and I was getting a lot of pedal strikes, something I hadn't even thought of on other bikes. When I started riding on much faster downhill terrain the tire was wandering a lot and was very unstable. I swapped out my 2.8 Rekon on the front for a DHF and started running 20-23 PSI (front and rear, usually a bit less in the front). Not only did the ride become significantly more stable and planted at speed, but I noticed a huge reduction in pedal strikes with an almost negligible reduction in traction. The bike still feels great and provides all of the benefits of a plus sized platform, but is much more stable and rider friendly.

So long story short, try increasing your tire pressure.

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  • I will give this a try on my next ride – ak_slick Jul 26 '18 at 21:28

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