Ken Cox

In another thread, someone kindly suggested I put a fork on my proposed Surly Steamroller Ice Bike that would accommodate cantilever brakes, and this in turn would give me the much-needed clearance for 35mm studded Nokians.

On Surly's site, I saw two forks with bosses for cantilever brakes: the Cross Check and the Long Haul Trucker.
I also noted these two forks had different amounts of rake, or offset, depending on the terminology of choice.

I wondered how the different rakes/offsets would affect the handling of the Steamroller, given that the Cross Check and the Long Haul Trucker frames have different head tube angles than that of the Steamroller frame.
I could have waited til Monday morning and telephoned Surly and asked, but I didn't see the fun in that.

Therefore, with much searching, I found an online program for figuring trail; given head tube angle, tire diameter and offset/rake.

As a general rule, as trail increases, or, as the distance between the point where the tire contacts the ground and the point where a line drawn through the head tube intercepts the ground increases, so does centering force increase.

To see a picture worth a thousand words, and the online steering geometry calculator, check out the following site:

https://www.kreuzotter.de/english/elenk.htm

At the above site, the distance "N" equals the trail, or centering force of the front wheel in motion.

So, I plugged in the numbers.
It took me awhile to find all numbers, but I have them and I'll share them below.

The Nokian 700X35 studded tire I want to use has a rolling diameter of 27.36"

The Surly Steamroller has a head tube angle of 74 degrees, and the Steamroller fork has an offset, or rake of 1.5".

With the Nokian tires, then, the Steamroller from the factory has a trail of 2.4".

I find this really interesting because my Bianchi Pista, with 700X23 Armadillos (26.3" diameter), has exactly the same trail of 2.4".

But, what would happen to the Steamroller frame if I put the Cross Check fork on it, with the Nokians?

We still have the the same head tube angle of 74 degrees, and the same rolling diameter of 27.36"; only the offset/rake changes, from 1.5" to 1.7", which gives us a trail of 2.7".

It follows, then, that putting the Cross Check fork on the Steamroller frame would increase the trail from 2.4" to 2.7" and, theoretically, increase the centering forces operating on the front wheel.
How much difference will I feel with .3" greater trail?
I don't know.
I feel better about that, though, than if the trail had decreased.

Head tube angle, offset, wheel diameter, wheelbase and many other factors influence the handling and turning radius of a bicycle, and calculating the trail doesn't begin to answer all my questions.
However, it does tell me that the fork swap falls within a range that intuitively doesn't seem too weird.
Assuming, of course, that .3" in trail does in fact represent a small number.

Well, I don't have any real questions for the forum beyond whether or not the Cross Check fork will work on the Steamroller frame.
I just thought folks might find the Steering Geometry Calculator interesting.
I'll also get back with a report on what the Surly folks tell me about the proposed change.

habitus

ken, your thoughtful posts are too complex for us simpletons. this is not your fault, ken. it's not your fault. you set your expectations high and we must learn to reach them. it might take time, though. it might take time.

yonderboy

I worked out that the Crosscheck frameset will have the same trail as the Steamroller/Crosscheck fork. But your wheelbase with the Steamroller will be about 2" shorter. I would think the steering will be similar between setups, with a little more stability than the stock Steamroller. You could end up with a lazy front end that likes to wander. I'm going to defer to the framebuilders, however.

Ken Cox

Yonderboy wrote:

"You could end up with a lazy front end that likes to wander."

My Bianchi Pista seems to go where I want it to go all by itself, without me really thinking about it.
By "lazy front end" does yonderboy mean I will have to do more because the Steamroller/CrossCheck will do less?

yonderboy

In my experience, more trail usually leads to a less responsive front wheel. Combine that with a slack head angle, and you have a bike that doesn't track very straight. If you take your hands off the bars, for example, the front wheel will tend to wander around, rather than keep pointing straight ahead.

What I gathered from https://www.velonews.com/media/Block40.pdf is that if the two bikes have the same trail, the turning characteristics should be the same. Other performance aspects will be different with the shorter/longer wheelbase.

So it's possible that you'll be fine, but I'm not a framebuilder, so my opinion should be taken with a grain of salt.

jimv

Hi Ken...

This subject comes up from time to time. There may be something in here for you.

https://www.bikeforums.net/singlespeed-fixed-gear/81106-forks-geometry.html

Take care...

Jim

Smorgasbord

Ken, as mentioned above, your posts are always great, and your contributions to the forum well appreciated.

Unless I've misunderstood something, you are considering increasing your fork rake. This will decrease trail (moves contact point closer to where the head tube points).

Using the numbers you provided, trail is 2.4 in (6 cm) with the steamroller fork and 2.2 in (5.5 cm) with the crosscheck.

Ken Cox

Yep.
I just redid the calculations this morning after reading Smorgasbord's recent post, and I get the same numbers as did Smorgasbord.
In my defense, I have a lot of drugs on board.
Well, in a couple of hours the Surly folks will get to work and I will greet them just about the time the fifth cup of coffee and the second percocet hits my bloodstream.
I had best take notes.

This makes three weeks on percocets.
In about four more days I will need to start weaning myself off of these puppies.
I have had a very unpleasant experience in the past quitting percocets.
I hope it goes more smoothly this time.

Smorgasbord

Any word from the Surly folks?
I hope everything's feeling as best as it can.

dabern

More trail would lead to a "less responsive" wheel (if you define less responsive as harder to turn) and the wheel would want to go straight rather than turn - so it certainly would not wander any worse than it does now. Folks always seem to think track bikes have quick steering but that's not really true when you have only 38mm of offset/rake as most pure track framesets have...stick a 43 or 45 on there and see how quick it gets! It's all a trade-off, though, and wheelbase would be slightly longer with the increased rake which would mitigate that somewhat...track bikes feel quick mostly because of the short wheelbase not because of the "stock" 38mm rake.

powers2b

Keep your standards low and you'll never be dissapointed.

Aim Low.

Enjoy

Ken Cox

Powers2b wrote:

"Keep your standards low and you'll never be dissapointed."

I like that.
Ironically, I tell friends, of all the forums in which I participate, I encounter the best thinking and writing on this forum, by far.
I wonder why.

Anyway, I've had several e-mail exchanges and phone calls with the Surly folks.
What great customer care, and I don't even own a Surly yet.
They've impressed me with their knowledge and patience.
I think these guy like what they do.

My question about clearance came from a review of the Nokian 35mm H-W106 studded tires on a Surly Steamroller.
On that bike, a brown bike, the studs just barely knicked the Shimano R-100 brake.
Nick, at Surly, has told me since the brown bike days they have added 7mm's of depth to the forks, and the Nokians will now clear.
Plus, he said a different brake, specifically the R-600, would probably buy me another millimeter or two.