bikenh

I know this is a stupid question, and the answer is probably yes, but I'll ask it anyways.

Does the same size tire, mm wise, give the same size tire diameter-wise. Aka a 700x20 vs 700x32. Will both tires have the same external diameter, aka give you the same amount of height off the ground at the top of the tire?

Trying to figure out how to get more pedal clearance. Keep hitting the rocks with the pedals, the last thing I ever thought would be an issue with mountain biking.

I have never seen a true reference for the what a mountain bike tire would be, 700cc style reference. What are they.?

cyclic_eric

That is not a stupid question, but not a simple one to answer, either. And covered in countless tire size threads in this forum.
Very roughly, road bike tires are approximately circular in cross-section. So your 20mm size tire will be about 20mm in diameter. Likewise the 32mm tire.
These have a 12mm difference in diameter, almost 1/2 an inch. Completely different size tires
Many other factors contribute to pedal strike besides tire size. Crank length, pedal type, and bottom bracket drop also affect pedal strike.
Changing tire size and pedal type are relatively easy.

2old

Good answer above; sometimes it helps to think of extremes for answers, like small changes in head angle (think of large ones one way or the other and you'll have a perception of the direction of small ones). In this instance think of fat bike tires and how much they add to the height of a bike.

Kapusta

Your question is confusing. You are asking about tires of the same size, but then your example uses two different sizes.

In general, the height of the tires increases as the width increases. Of course, different tires have different profiles, so some 32mm wide tires may be a tad taller than others 32mm tires. This is even more the case with mtb tires where the tread may add height.

Yeah, pedal strikes are a thing with MTB, especially now that BB heights have gotten lower in recent years.

rumrunn6

no but the differences are so small I can't imagine it being a factor for pedal clearance. what is the issue with your current pedal clearance? hitting curbs? I think there are other factors that would help. for example I think hybrid bikes, in general, have higher pedal clearances. I forget what it's called but there's a word for it

bikenh

The pedal strike was something I would not have expected to see, especially on an upright bike, aka hybrid. The second day riding it I went around a corner and struck the pedal on the road. I was radically caught off guard as I have essentially never hit a pedal on the road while riding on a road bike, even while riding fixed gear.

Now when riding in the woods, three days straight, I seem to be hitting the pedals on roots and rocks all the time. I have one particular spot where I look at it and go how the heck do you get through there without hitting the pedals, pedaling through the rock wall is a requirement or you will lose too much momentum to make it up the climb that leads into the finish line of the race course. I knew the first second I saw it, going the opposite direction as the race course goes, that it would be an interesting location. From what I have seen it is one of the most technical spots of the entire race course and dab smack right before the finish line. It's not the only area where I hit the pedals, by a long shot. Between pedals strikes and not yet having gotten used to not letting the terrain steer the bike for me, LMAO, those are the two things which are kicking my butt the most. Occasionally leaf litter is making it hard to climb the steepest of the climbs due to using the road bike tires that came on the hybrid I'm riding.

As to the question, I didn't realize wider would even mean taller. I figured the tire width only meant the width of the tread changed. I thought the diameter would remain the same. Glad I asked the stupid question.

How much of a difference is there, diameter-wise, between a 700c and a 29er. From what I have seen I get the idea they are pretty much the same size.

Yes, I'm riding a hybrid off-road with 32mm road bike tires. You can flame me all you want but if I didn't feel comfortable doing, I wouldn't. The only problem thus far has been trying to figure out how to make the move at the rock wall. I'm a ***** and if I don't like something I see, I walk. I'm man enough to walk and I walk through mud/water all the time.

rumrunn6

https://asingletrackmind.com/avoid-p...l%20up%20ahead.

https://www.mtbr.com/threads/pedal-s...usion.1176487/

prj71

Tires are "U" shaped.

20 and 32 are the width of the tire. Not the diameter.

prj71

This happens because you had the wrong pedal down when going around a corner and probably should have been coasting around the corner. If turning right, the right pedal should be up and vice versa.

They are only the same size tire at the beads where they fit on the rim. The outside diameter will be all over the board depending on make and model.

You have the wrong tool for the job. This explains everything.

79pmooney

bikenh, look at your pedals and cranks. You may want different. Pedal have different depths below the pedal spindle. Some of the double sided MTB pedals are quite deep. Some of the one sided high performance road pedals barely project down below the spindle in an effort to be as aerodynamic as possible.

Also, look at how wide the pedal is along the bottom. Pedals that are, looking from behind, deep and square will hit on a turn very early. Pedals where they remove all the material at the outbourd bottom "corner" will have far more clearance pedaling through turns.

Crank length. Straight forward. Longer, more strikes.

In turns, crank width also matters. The "Q-factor". How far outboard the pedals sit from the center plane of the bike. (Now, the Q-factor doesn't tell you all because it is simply the width between the cranks where the pedals meet and doesn't take into account any asymmetry. Nevertheless, high Q cranks are pedal scrapers and low Qs considerably better.

Finally, look at the BB height. Pull out a tape measure and measure from the floor up to the center of the BB spindle. (Using BB height means the tire diameter has been accounted for.) I think in English here. !2" is very high. 11" on the road is about the max you will ever see. 10 5/8" to 10 3/4" is popular road race. 10 3/8" is about as low as you are going to see on a road bike.

All this stuff matters. Some - you have the frame and it's pretty hard to change. Cranks aren't hard to change but there are lots of things to consider. Pedals - there are a vast number of types and shapes.

And last - some real world examples from a guy who loves to pedal around corners, When I raced, I was slow. Being able to pedal deeper into a corner and sooner out of it was a saver of precious muscle. And I fell in love with fix gears my first season, 47 years ago and have been pedaling those things around the corners of 100,000 miles. So:

All these bikes have 175mm cranks. (My knees don't like change.)

My former race bike - 11" BB with narrow (1970s) cranks. Traditional racing rattrap pedals, fairly "square" but not all that wide. I could pedal that bike very deep into corners and hit pedals only twice despite being rather fearless.

My two Peugeots converted to fix gears. BB height around 10 3/8: Leotard "Berthet" platforms. Narrow and clean underneath. I called both of those bikes "slinkies". I hit the pedals on a regular basis and so early in turns that the strike wasn't scary. (On my fully laid over race bike, it was!) Every left pedal got it's left dustcap unscrewed with hits. (Right side screwed on tighter.)

My Raleigh Competition with the Peugeots' BB height using 35c tires. Triple crankset. Decent QA-factor. (My knees don't like wide.) Shimano double sided MTP SPD pedals; fairly narrow but deep. Pedals strike on everything. Early on turns, any speed bump.)

My current "good" bikes. 10 3/4" BBs. (10 7/8" on the fix gear.) Narrow old school racing cranksets. Shimano semi-platform and LOOK Delta-style pedals. (Both 1980s race narrow, shallow and with no "corners".) Gottat lay those bikes over pretty good to hit. Almost never hit on a speed bump, even the nastiest. For me, the sweet spot.+

I know, a lot of info here but maybe it will give you a little direction. (And notice - I did not say "coast through all your turns".)

Ben - who loves to keep those pedals spinning!

bikenh

It's not going around a corner its going over rocks, mostly when climbing hills.

Yes, it may be the wrong tool for the job but it's what I have to use. I had no intention of ever riding off road but the new bike someone gave me made me change my mind. I've decided to play with it and see what I can do, expand my way of thinking about things.

Yes, on the road I can understand what you said about hitting the pedal going around the corner. The real problem though is with hitting the pedals on the rocks while trying to go over them on the trail. Hitting them on the road is no problem and can easily be avoided while trying to uphill and getting stopped by the pedal hitting the rocks is another story altogether. Especially where the rocks happen to sit in such lovely locations where you have a choice of which rock you want to hit, rock 1, rock 2, rock 3, or take the steeper line covered with leaves. I finally managed to get to where I could get tires between the rocks yesterday but the pedal strike stopped me dead in my tracks.

bikenh

Gee, is someone else crazy like me. Was the Peugeots singlespeed to fix convert or multiple speed to fixed converts. I converted a Specialized Allez Comp to a fix gear, amazing what you can do with angle iron. Never had a problem with dropping chains, always came off the chain ring, not once has it dropped of the cog. Then someone gave me an old Raleigh fixed gear touring bike. The first time the chain dropped while riding it was the 'last'. Bent the dropout. I may be wrong but I think they need to make the openings on fixed/singlespeed bikes narrower. Not the hub, just the opening the hub goes into. I know the opening on my Allez Comp when converted had to be slightly tweaked open each time I went to mount the wheel as the wheel wouldn't just 'drop in' like it normally does on a regular bike. The angle iron I bolted on made the opening smaller than normal and I think that must add 'tightness' to the spinning wheel and as a result it doesn't allow the chain to drop off the cog.

I don't have a tape measure handy to measure the BB depth right now but I know on the Sirrus when I have the bike fully upright and the pedals all the way down the pedal does not sit very high off the ground. Until I got the Sirrus I have used clipless road pedals for 30 years. It was joke on the first ride with the Sirrus, I went to upclip when I stopped the bike, I LOLed over my preprogrammed notion that I was still riding clipless. Now since I'm riding off-road an also since I can't get the one pedal off my other bike(broken crank arm, pedal off, but the other I can't get it off with allen wrench or pedal wrench, the usual corrosion from riding year-round in NH especially in the salt/sand of winter.

Kapusta

It is just a matter of getting used to it and timing the pedal strokes. Some ratcheting or pedal re-orientation may be involved. Eventually, your brain gets used to it. Its just a skill that gets developed over time.

My newest MTB has a pretty low BB compared to previous ones, and at first I was getting pedal strikes. Over the first few months I adapted to it, and it is no longer an issue.

bikenh

Sorry, this may not come out right, don't get offended. But how do you do it when climbing. How do you keep the momentum when ratcheting? I agree, I've only been riding in the woods now for less than a week, so I should shut up, but I think you can see my point. There are only two places where I'm having massive trouble with it, and they are good spots. Both of them I keep riding riding back and forth trying it again and again, at least until the black flies force me to leave Is it Father's Day yet, at least then I'll only have mosquitoes to deal with and not these darn black flies

Kapusta

No offense taken. Depends on the situation, but whether you are ratcheting or just re-positioning, you want to give a good hard push just before you backpedal. There may also be some body English involved, moving your weight forward just before you back-pedal (or coast) and then pushing the bike forward when you lay off the gas. Sorry if this is clear as mud, I am not sure how to explain.

What also helps is pushing a higher gear than you think you should be. That slows the pedal stroke down and makes it easier to time the pedal position better.

mtnbud

bikenh - You're not going crazy. When I bought my new bike, I had the same issue. I believe it's due to differences in the geometry of newer bikes. I assume my bottom bracket is lower. I eventually adjusted my timing and pedal strokes by looking ahead and planing. I took me quite a few months to get the hang of timing my pedal strokes, but I rarely hit roots and rocks now. I had to be very conscious about my timing for awhile, but I do it now without even thinking about it.

bikenh

I see myself occasionally thinking about it now. Saw it last night once or twice while also seeing myself still hitting the rocks a few times as well.

I guess when you are not used to dealing with something, after being a roadie for so darn long, you just have a tendency to let it bother you more than you should, LOL

Took a couple of photos of one of the two areas last night. The first one shows a close up of the rock wall, while the second one shows a broader perspective of the lead in to get there. The other spot is almost the same kind of scenario. Gotta love it.

79pmooney

And of course there is the other approach. Armour the crank end. Use those indestructible double sided Shimano SPD pedals. And make it known to that wall if it tries to stop you, it will pay. Then just do it. Eventually you'll blast a path through. (You may eventually have to armour the entire bike but those paths will happen a lot faster when you hit with your 20 pounds of bike and 80 of case hardened steel.

(And you'll develop some real climbing legs.)

prj71

Nothing you posted in those pictures is difficult...if you have the right bike. I would have no problem pedaling up that and not striking the pedals. I wouldn't even have to ratchet. The risk of pedal strike increase when you try to ride in-between rocks instead of over them. In your pictures I would be riding over those rocks if they were of a height to cause a pedal strike by trying to ride in-between them.

Again...you have the wrong tool for the job. Purchase the right tool or rent one and try it to see for yourself.

bikenh

And sometimes there is another problem, lack of experience. The other spot I had been having trouble with(the one with loose rocks) I managed to make it up it twice this morning for the first time. It was lack of experience causing the problem. Yes, the right tool for the job could help but it can also provide bad technique which will bite you later on. Taking the easy way out isn't always the best thing to do for the long haul.

prj71

You are riding a hybrid bike on mountain bike trails. Its not the easy way out....It's picking the right tool for the job.

Kind of like if you were to jump on a mountain bike and try keep up with a pack of road bikers...it's not going to work.